International Journal

105.	P. Kim, H. Park Performance Assessment for LDM Transmission Based on DVB Satellite Standard Journal Article IEEE Transactions on Broadcasting, 2024. Links \| BibTeX @article{Kim2024, title = {Performance Assessment for LDM Transmission Based on DVB Satellite Standard}, author = {P. Kim, H. Park}, doi = {10.1109/TBC.2024.3349789}, year = {2024}, date = {2024-02-29}, journal = {IEEE Transactions on Broadcasting}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TBC.2024.3349789 Close
104.	A. Ahmadian, W. Shin, H.Park Long-Term Throughput Maximization in Wireless Powered Communication Networks: A Multi-Task DRL Approach Journal Article IEEE Internet of Things Journal, 2024. Links \| BibTeX @article{Ahmadian2024, title = {Long-Term Throughput Maximization in Wireless Powered Communication Networks: A Multi-Task DRL Approach}, author = {A. Ahmadian, W. Shin, H.Park}, doi = {10.1109/JIOT.2024.3370192}, year = {2024}, date = {2024-02-26}, journal = {IEEE Internet of Things Journal}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JIOT.2024.3370192 Close
103.	J. Jee, B. Tamiru, H. Park Channel Estimation and Pilot Reduction for mmWave Massive MIMO Systems Using Deep Neural Networks Journal Article ICT Express, 2024. Links \| BibTeX @article{Jee2024b, title = {Channel Estimation and Pilot Reduction for mmWave Massive MIMO Systems Using Deep Neural Networks }, author = {J. Jee, B. Tamiru, H. Park}, doi = {https://doi.org/10.1016/j.icte.2024.02.003}, year = {2024}, date = {2024-02-09}, journal = {ICT Express}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:https://doi.org/10.1016/j.icte.2024.02.003 Close
102.	H. Son, G. Kwon, H. Park, J. Park, Signal Model and Linear Combining Design for Multi-Numerology Massive MIMO Systems Journal Article IEEE Transactions on Vehicular Technology, 2024. Links \| BibTeX @article{Son2024, title = {Signal Model and Linear Combining Design for Multi-Numerology Massive MIMO Systems}, author = {H. Son, G. Kwon, H. Park, J. Park, }, doi = {10.1109/TVT.2024.3362330}, year = {2024}, date = {2024-02-06}, journal = {IEEE Transactions on Vehicular Technology}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2024.3362330 Close
101.	G. Kwon, Z. Liu, A. Conti, H. Park, M. Win Integrated Localization and Communication for Efficient Millimeter Wave Networks Journal Article IEEE Journal on Selected Areas in Communications, pp. 3925 - 3941, 2023. Links \| BibTeX @article{Kwon2023, title = {Integrated Localization and Communication for Efficient Millimeter Wave Networks}, author = {G. Kwon, Z. Liu, A. Conti, H. Park, M. Win}, doi = {10.1109/JSAC.2023.3322760}, year = {2023}, date = {2023-11-29}, journal = {IEEE Journal on Selected Areas in Communications}, pages = {3925 - 3941}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JSAC.2023.3322760 Close
100.	J. Jee, H. Park Deep Learning-based Joint Optimization of Closed-Loop FDD MmWave Massive MIMO: Pilot Adaptation, CSI Feedback, and Beamforming Journal Article IEEE Transactions on Vehicular Technology, 73 (3), pp. 4019 - 4034, 2023. Links \| BibTeX @article{Jee2023, title = {Deep Learning-based Joint Optimization of Closed-Loop FDD MmWave Massive MIMO: Pilot Adaptation, CSI Feedback, and Beamforming}, author = {J. Jee, H. Park}, doi = {10.1109/TVT.2023.3327276}, year = {2023}, date = {2023-10-24}, journal = {IEEE Transactions on Vehicular Technology}, volume = {73}, number = {3}, pages = {4019 - 4034}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2023.3327276 Close
99.	H.S Park, J. Jee, H Park Outage Probability Analysis and Joint Optimization for UAV-aided FSO/RF Systems with Nonlinear Power Amplifiers Journal Article IEEE Photonics Journal, (7304913), 2023. Links \| BibTeX @article{Park2023, title = {Outage Probability Analysis and Joint Optimization for UAV-aided FSO/RF Systems with Nonlinear Power Amplifiers}, author = {H.S Park, J. Jee, H Park}, doi = {10.1109/JPHOT.2023.3321144}, year = {2023}, date = {2023-10-02}, journal = {IEEE Photonics Journal}, number = {7304913}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JPHOT.2023.3321144 Close
98.	J. Jee, G. Kwon, H. Park Cooperative Beamforming with Nonlinear Power Amplifiers: A Deep Learning Approach for Distributed Networks Journal Article IEEE Transactions on Vehicular Technology, 72 (5), pp. 5973-5988, 2023. Links \| BibTeX @article{Jee2022, title = {Cooperative Beamforming with Nonlinear Power Amplifiers: A Deep Learning Approach for Distributed Networks}, author = {J. Jee, G. Kwon, H. Park}, doi = {10.1109/TVT.2022.3226799}, year = {2023}, date = {2023-05-18}, journal = {IEEE Transactions on Vehicular Technology}, volume = {72}, number = {5}, pages = {5973-5988}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2022.3226799 Close
97.	M. Hwang, J.Jee, J.Kang, H.Park, S.Lee, J.Kim Dynamic Error Recovery Flow Prediction Based on Reusable Machine Learning for Low Latency NAND Flash Memory under Process Variation Journal Article IEEE Access, 10 , pp. 117715 - 117731, 2022. Links \| BibTeX @article{Hwang2022bb, title = {Dynamic Error Recovery Flow Prediction Based on Reusable Machine Learning for Low Latency NAND Flash Memory under Process Variation}, author = {M. Hwang, J.Jee, J.Kang, H.Park, S.Lee, J.Kim}, doi = {10.1109/ACCESS.2022.3220337}, year = {2022}, date = {2022-11-07}, journal = {IEEE Access}, volume = {10}, pages = {117715 - 117731}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/ACCESS.2022.3220337 Close
96.	S. Jun, G. Kwon, H. Park Energy-Efficient Multi-Tap Single Carrier Hybrid Beamforming in Uplink Wideband Millimeter Wave Systems Journal Article IEEE Transactions on Vehicular Technology, 71 (10), pp. 10782 - 10795, 2022. Links \| BibTeX @article{Jun2022b, title = {Energy-Efficient Multi-Tap Single Carrier Hybrid Beamforming in Uplink Wideband Millimeter Wave Systems}, author = {S. Jun, G. Kwon, H. Park}, doi = {10.1109/TVT.2022.3187841}, year = {2022}, date = {2022-10-17}, journal = {IEEE Transactions on Vehicular Technology}, volume = {71}, number = {10}, pages = {10782 - 10795}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2022.3187841 Close
95.	H. Son, G. Kwon, H. Park, J. Park Massive MIMO Precoding for Interference-Free Multi-numerology Systems Journal Article IEEE Transactions on Vehicular Technology, 71 (9), pp. 9765 - 9780, 2022. Links \| BibTeX @article{Son2022b, title = {Massive MIMO Precoding for Interference-Free Multi-numerology Systems}, author = {H. Son, G. Kwon, H. Park, J. Park}, doi = {10.1109/TVT.2022.3182408}, year = {2022}, date = {2022-09-19}, journal = {IEEE Transactions on Vehicular Technology}, volume = {71}, number = {9}, pages = {9765 - 9780}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2022.3182408 Close
94.	H. An, H. Park Energy Balancing Resource Allocation for Wireless Cooperative IoT Networks with SWIPT Journal Article IEEE Internet of Things Journal, 9 (14), pp. 12258 - 12271, 2022. Links \| BibTeX @article{An2021b, title = {Energy Balancing Resource Allocation for Wireless Cooperative IoT Networks with SWIPT}, author = {H. An, H. Park}, doi = {10.1109/JIOT.2021.3135282}, year = {2022}, date = {2022-07-15}, journal = {IEEE Internet of Things Journal}, volume = {9}, number = {14}, pages = {12258 - 12271}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JIOT.2021.3135282 Close
93.	G. Kwon, A. Conti, H. Park, M.Z. Win Joint Communication and Localization in Millimeter Wave Networks Journal Article IEEE Journal of Selected Topics in Signal Processing, 15 (6), pp. 1439 - 1454, 2021. Links \| BibTeX @article{Kwon2021b, title = {Joint Communication and Localization in Millimeter Wave Networks}, author = {G. Kwon, A. Conti, H. Park, M.Z. Win}, doi = {10.1109/JSTSP.2021.3113115}, year = {2021}, date = {2021-12-02}, journal = {IEEE Journal of Selected Topics in Signal Processing}, volume = {15}, number = {6}, pages = {1439 - 1454}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JSTSP.2021.3113115 Close
92.	G. Kwon, H. Park, M.Z. Win Joint Beamforming and Power Splitting for Wideband Millimeter Wave SWIPT Systems Journal Article IEEE Journal of Selected Topics in Signal Processing, 15 (5), pp. 1211 - 1227, 2021. Links \| BibTeX @article{Kwon2021, title = {Joint Beamforming and Power Splitting for Wideband Millimeter Wave SWIPT Systems}, author = {G. Kwon, H. Park, M.Z. Win}, doi = {10.1109/JSTSP.2021.3089026}, year = {2021}, date = {2021-10-04}, journal = {IEEE Journal of Selected Topics in Signal Processing}, volume = {15}, number = {5}, pages = {1211 - 1227}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JSTSP.2021.3089026 Close
91.	J. Jee, G. Kwon, H. Park Joint Precoding and Power Allocation for Multiuser MIMO System with Nonlinear Power Amplifiers Journal Article IEEE Transactions on Vehicular Technology, 70 (9), pp. 8883 - 8897, 2021. Links \| BibTeX @article{Jee2021b, title = {Joint Precoding and Power Allocation for Multiuser MIMO System with Nonlinear Power Amplifiers}, author = {J. Jee, G. Kwon, H. Park}, doi = {10.1109/TVT.2021.3097775}, year = {2021}, date = {2021-09-17}, journal = {IEEE Transactions on Vehicular Technology}, volume = {70}, number = {9}, pages = {8883 - 8897}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2021.3097775 Close
90.	H. An, M. Hwang, H. Park Phase Aligned Time-reversal for Multi-user Wireless Power Transfer Systems with Non-linear Energy Harvesting Journal Article IEEE Access, 9 , pp. 109976 - 109985, 2021. Links \| BibTeX @article{An2021, title = {Phase Aligned Time-reversal for Multi-user Wireless Power Transfer Systems with Non-linear Energy Harvesting}, author = {H. An, M. Hwang, H. Park}, doi = {10.1109/ACCESS.2021.3102864}, year = {2021}, date = {2021-08-11}, journal = {IEEE Access}, volume = {9}, pages = {109976 - 109985}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/ACCESS.2021.3102864 Close
89.	J. Choi, G. Kwon, H.Park Multiple Intelligent Reflecting Surfaces for Capacity Maximization in LOS MIMO Systems Journal Article IEEE Wireless Communications Letters, 10 (8), pp. 1727-1731, 2021. Links \| BibTeX @article{Choi2021, title = {Multiple Intelligent Reflecting Surfaces for Capacity Maximization in LOS MIMO Systems}, author = {J. Choi, G. Kwon, H.Park}, doi = {10.1109/LWC.2021.3078151}, year = {2021}, date = {2021-08-09}, journal = {IEEE Wireless Communications Letters}, volume = {10}, number = {8}, pages = {1727-1731}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/LWC.2021.3078151 Close
88.	S. Kim, G. Kwon, H. Park High-Resolution Multi-Beam Tracking With Low Overhead for mmWave Beamforming System Journal Article ICT Express, 2021, 7 (1), pp. 28 - 35, 2021. Links \| BibTeX @article{Kim2021, title = {High-Resolution Multi-Beam Tracking With Low Overhead for mmWave Beamforming System}, author = {S. Kim, G. Kwon, H. Park}, doi = {10.1016/j.icte.2021.01.014}, year = {2021}, date = {2021-03-10}, journal = {ICT Express, 2021}, volume = {7}, number = {1}, pages = {28 - 35}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1016/j.icte.2021.01.014 Close
87.	Y. Shim, H. Park, W. Shin Joint Time Allocation for Wireless Energy Harvesting Decode-and-Forward Relay Based IoT Networks with Rechargeable and Non-Rechargeable Batteries Journal Article IEEE Internet of Things Journal, 8 (4), pp. 2792 - 2801, 2021. Links \| BibTeX @article{Shin2020, title = {Joint Time Allocation for Wireless Energy Harvesting Decode-and-Forward Relay Based IoT Networks with Rechargeable and Non-Rechargeable Batteries}, author = {Y. Shim, H. Park, W. Shin}, doi = {10.1109/JIOT.2020.3020960}, year = {2021}, date = {2021-02-15}, journal = {IEEE Internet of Things Journal}, volume = {8}, number = {4}, pages = {2792 - 2801}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JIOT.2020.3020960 Close
86.	T. H. Jang, D. M. Kang, S. H. Kim, C. J. Lee, S. Jun, H. Park, J. H. Kim, C. S. Park 120 GHz Wideband I/Q Receiver Based on Baseband Equalizing Technique Journal Article IEEE Journal of Solid State Circuits, pp. 1-1, 2020. Links \| BibTeX @article{Jang2020, title = {120 GHz Wideband I/Q Receiver Based on Baseband Equalizing Technique}, author = {T. H. Jang, D. M. Kang, S. H. Kim, C. J. Lee, S. Jun, H. Park, J. H. Kim, C. S. Park}, doi = {10.1109/JSSC.2020.3032022}, year = {2020}, date = {2020-11-26}, journal = {IEEE Journal of Solid State Circuits}, pages = {1-1}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JSSC.2020.3032022 Close
85.	A. Ahmadian, W. Shin, H. Park Max-min Throughput Optimization in FDD Multi-Antenna Wirelessly-Powered IoT Networks Journal Article IEEE Internet of Things Journal, 8 (7), pp. 5866-5880, 2020. Links \| BibTeX @article{Ahmadian2020, title = {Max-min Throughput Optimization in FDD Multi-Antenna Wirelessly-Powered IoT Networks}, author = {A. Ahmadian, W. Shin, H. Park}, doi = {10.1109/JIOT.2020.3033227}, year = {2020}, date = {2020-10-22}, journal = {IEEE Internet of Things Journal}, volume = {8}, number = {7}, pages = {5866-5880}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JIOT.2020.3033227 Close
84.	J. Jee, G. Kwon, H. Park Precoding Design and Power Control for SINR Maximization of MISO System with Nonlinear Power Amplifiers Journal Article IEEE Transactions on Vehicular Technology, 69 (11), pp. 14019 - 14024, 2020. Links \| BibTeX @article{Jee2020, title = {Precoding Design and Power Control for SINR Maximization of MISO System with Nonlinear Power Amplifiers}, author = {J. Jee, G. Kwon, H. Park}, doi = {10.1109/TVT.2020.3026752}, year = {2020}, date = {2020-09-25}, journal = {IEEE Transactions on Vehicular Technology}, volume = {69}, number = {11}, pages = {14019 - 14024}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TVT.2020.3026752 Close
83.	H. Choe, J. Jee, S.-C. Lim, S. Joe, I. Park, H. Park Machine-Learning-Based Read Reference Voltage Estimation for NAND Flash Memory Systems Without Knowledge of Retention Time Journal Article IEEE Access, 8 , pp. 176416-176429, 2020. Links \| BibTeX @article{Choe2020, title = {Machine-Learning-Based Read Reference Voltage Estimation for NAND Flash Memory Systems Without Knowledge of Retention Time}, author = {H. Choe, J. Jee, S.-C. Lim, S. Joe, I. Park, H. Park}, doi = {10.1109/ACCESS.2020.3026232}, year = {2020}, date = {2020-09-24}, journal = {IEEE Access}, volume = {8}, pages = {176416-176429}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/ACCESS.2020.3026232 Close
82.	H. Han, G. Kwon, H. Park MMSE-Interference Canceling Receiver for QAM-FBMC Systems Journal Article IEEE Communications Letters, 24 (11), pp. 2589 - 2593, 2020. Links \| BibTeX @article{Han2020, title = {MMSE-Interference Canceling Receiver for QAM-FBMC Systems}, author = {H. Han, G. Kwon, H. Park}, doi = {10.1109/LCOMM.2020.3007895}, year = {2020}, date = {2020-07-08}, journal = {IEEE Communications Letters}, volume = {24}, number = {11}, pages = {2589 - 2593}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/LCOMM.2020.3007895 Close
81.	W. Wang, H. Park CFO Estimation Based on Auto-correlation with Flexible Intervals for OFDM Systems with 1-bit ADCs Journal Article IEEE Access, 8 , pp. 108474-108481, 2020. Links \| BibTeX @article{wang2020cfo, title = {CFO Estimation Based on Auto-correlation with Flexible Intervals for OFDM Systems with 1-bit ADCs}, author = {W. Wang, H. Park}, doi = {10.1109/ACCESS.2020.3001226}, year = {2020}, date = {2020-06-09}, journal = {IEEE Access}, volume = {8}, pages = {108474-108481}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/ACCESS.2020.3001226 Close
80.	S.-C. Lim, N. Kim, H. Park Polar Coding-Based Selective Mapping for PAPR Reduction Without Redundant Information Transmission Journal Article IEEE Communications Letters, 24 (8), pp. 1621-1625, 2020. Links \| BibTeX @article{Lim2020, title = {Polar Coding-Based Selective Mapping for PAPR Reduction Without Redundant Information Transmission}, author = {S.-C. Lim, N. Kim, H. Park}, doi = {10.1109/LCOMM.2020.2989205}, year = {2020}, date = {2020-04-21}, journal = {IEEE Communications Letters}, volume = {24}, number = {8}, pages = {1621-1625}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/LCOMM.2020.2989205 Close
79.	G. Kwon, H. Park Limited Feedback Hybrid Beamforming for Multi-Mode Transmission in Wideband Millimeter Wave Channel Journal Article IEEE Transactions on Wireless Communications, 19 (6), pp. 4008-4022, 2020. Links \| BibTeX @article{Kwon2020, title = {Limited Feedback Hybrid Beamforming for Multi-Mode Transmission in Wideband Millimeter Wave Channel}, author = {G. Kwon, H. Park}, doi = {10.1109/TWC.2020.2979184}, year = {2020}, date = {2020-03-13}, journal = {IEEE Transactions on Wireless Communications}, volume = {19}, number = {6}, pages = {4008-4022}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/TWC.2020.2979184 Close
78.	H. Han, N. Kim, H. Park Design of QAM-FBMC Waveforms Considering MMSE Receiver Journal Article IEEE Communications Letters, 24 (1), pp. 131-135, 2020. Links \| BibTeX @article{Han2019b, title = {Design of QAM-FBMC Waveforms Considering MMSE Receiver}, author = {H. Han, N. Kim, H. Park}, doi = {10.1109/LCOMM.2019.2952375}, year = {2020}, date = {2020-01-01}, journal = {IEEE Communications Letters}, volume = {24}, number = {1}, pages = {131-135}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/LCOMM.2019.2952375 Close
77.	G. Kwon, H. Park Joint User Association and Beamforming Design for Millimeter Wave UDN With Wireless Backhaul Journal Article IEEE Journal on Selected Areas in Communications, 37 (12), pp. 2653-2668, 2019. Links \| BibTeX @article{Kwon2019b, title = {Joint User Association and Beamforming Design for Millimeter Wave UDN With Wireless Backhaul}, author = {G. Kwon, H. Park}, doi = {10.1109/JSAC.2019.2947926}, year = {2019}, date = {2019-10-25}, journal = {IEEE Journal on Selected Areas in Communications}, volume = {37}, number = {12}, pages = {2653-2668}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close doi:10.1109/JSAC.2019.2947926 Close
76.	H. Han, N. Kim, H. Park Analysis of CFO Estimation for QAM-FBMC Systems Considering Non-Orthogonal Prototype Filters Journal Article IEEE Transactions on Vehicular Technology, 68 (7), pp. 6761-6774, 2019. BibTeX @article{Han2019a, title = {Analysis of CFO Estimation for QAM-FBMC Systems Considering Non-Orthogonal Prototype Filters}, author = {H. Han, N. Kim, H. Park}, year = {2019}, date = {2019-09-16}, journal = {IEEE Transactions on Vehicular Technology}, volume = {68}, number = {7}, pages = {6761-6774}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close
75.	J. Jee, G. Kwon, H. Park Regularized Zero-forcing Precoder for Massive MIMO System with Transceiver I/Q Imbalances Journal Article IEEE Wireless Communications Letters, 8 (4), pp. 1028-1031, 2019, ISBN: 2162-2345. BibTeX @article{Jee2019a, title = {Regularized Zero-forcing Precoder for Massive MIMO System with Transceiver I/Q Imbalances}, author = {J. Jee, G. Kwon, H. Park}, isbn = {2162-2345}, year = {2019}, date = {2019-08-04}, journal = {IEEE Wireless Communications Letters}, volume = {8}, number = {4}, pages = {1028-1031}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close
74.	G. Kwon, H. Park Beamforming Design for Low-Power In-Band Wireless Backhaul Systems: Centralized and Distributed Approaches Journal Article IEEE Transactions on Vehicular Technology, 68 (2), pp. 1549 - 1563, 2019. Links \| BibTeX @article{Kwon2019a, title = {Beamforming Design for Low-Power In-Band Wireless Backhaul Systems: Centralized and Distributed Approaches }, author = {G. Kwon, H. Park}, url = {https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8580398}, year = {2019}, date = {2019-02-13}, journal = {IEEE Transactions on Vehicular Technology}, volume = {68}, number = {2}, pages = {1549 - 1563}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8580398 Close
73.	G. Kwon, N. Kim, H. Park Millimeter Wave SDMA with Limited Feedback: RF-only Beamforming Can Outperform Hybrid Beamforming Journal Article IEEE Transactions on Vehicular Technology, 68 (2), pp. 1534 - 1548, 2019. Links \| BibTeX @article{Kwon2019a, title = {Millimeter Wave SDMA with Limited Feedback: RF-only Beamforming Can Outperform Hybrid Beamforming }, author = {G. Kwon, N. Kim, H. Park}, url = {https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8580400}, year = {2019}, date = {2019-02-13}, journal = {IEEE Transactions on Vehicular Technology}, volume = {68}, number = {2}, pages = {1534 - 1548}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8580400 Close
72.	S.-C. Lim, H. Park Gaussian approximation based belief propagation receiver for uplink SCMA systems with imperfect CSIR Journal Article IEEE Communications Letters, 22 (12), pp. 2611-2614, 2018. Links \| BibTeX @article{Lim2018b, title = {Gaussian approximation based belief propagation receiver for uplink SCMA systems with imperfect CSIR}, author = {S.-C. Lim, H. Park}, url = {URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8485389&isnumber=8570950}, year = {2018}, date = {2018-12-11}, journal = {IEEE Communications Letters}, volume = {22}, number = {12}, pages = {2611-2614}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8485389&isn[...] Close
71.	Y. Shim; H. Park Beamforming Design for Multi-Hop Amplify-and-Forward MIMO Relay Journal Article IEEE Transactions on Vehicular Technology, 67 (9), pp. 8144-8153, 2018, ISSN: 1939-9359. Abstract \| Links \| BibTeX @article{Shim2018, title = {Beamforming Design for Multi-Hop Amplify-and-Forward MIMO Relay}, author = {Y. Shim; H. Park}, doi = {10.1109/TVT.2017.2690300}, issn = {1939-9359}, year = {2018}, date = {2018-09-19}, journal = {IEEE Transactions on Vehicular Technology}, volume = {67}, number = {9}, pages = {8144-8153}, abstract = {This paper considers multi-hop amplify-andforward (AF) multiple-input multiple-output (MIMO) relay networks. In the multi-hop AF MIMO relay networks, the performance deteriorates as the number of hops increases because the effect of noise is enhanced. This paper proposes the two beamforming schemes using channel state information (CSI) for transmit beamforming at source, relay beamforming at relay, and receive beamforming at destination. The forward-and-backward-CSI and all-CSI based beamforming schemes are designed at each relay based on the minimum mean square error criterion under the source and relay transmit power constraint. The forwardand-backward-CSI based beamforming scheme is designed using the two matrices, both forward and backward channels. The two matrices are designed by the beamforming matrices and channels from previous relays. Unlike the forward-and-backward-CSI based beamforming scheme, the all-CSI based beamforming scheme is designed by using all channels and iterative algorithm. In terms of complexity, the forward-and-backward-CSI based scheme is superior to the all-CSI based scheme. However, the all-CSI based scheme has advantage over the forward-andbackward-CSI based scheme in terms of performance.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers multi-hop amplify-andforward (AF) multiple-input multiple-output (MIMO) relay networks. In the multi-hop AF MIMO relay networks, the performance deteriorates as the number of hops increases because the effect of noise is enhanced. This paper proposes the two beamforming schemes using channel state information (CSI) for transmit beamforming at source, relay beamforming at relay, and receive beamforming at destination. The forward-and-backward-CSI and all-CSI based beamforming schemes are designed at each relay based on the minimum mean square error criterion under the source and relay transmit power constraint. The forwardand-backward-CSI based beamforming scheme is designed using the two matrices, both forward and backward channels. The two matrices are designed by the beamforming matrices and channels from previous relays. Unlike the forward-and-backward-CSI based beamforming scheme, the all-CSI based beamforming scheme is designed by using all channels and iterative algorithm. In terms of complexity, the forward-and-backward-CSI based scheme is superior to the all-CSI based scheme. However, the all-CSI based scheme has advantage over the forward-andbackward-CSI based scheme in terms of performance. Close doi:10.1109/TVT.2017.2690300 Close
70.	S.-C. Lim, H. Park Codebook optimization for the superposition transmission of uplink SCMA systems Journal Article IEEE Transactions on Vehicular Technology, 67 (10), pp. 10112-10117, 2018. BibTeX @article{Lim2018, title = {Codebook optimization for the superposition transmission of uplink SCMA systems}, author = {S.-C. Lim, H. Park}, year = {2018}, date = {2018-08-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {67}, number = {10}, pages = {10112-10117}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close
69.	G. Kim; H. Park; W. Choi MDS Coded Caching with MRT and Its Optimization Journal Article ICT Express, 2018. Abstract \| BibTeX @article{Choi2018, title = {MDS Coded Caching with MRT and Its Optimization}, author = {G. Kim; H. Park; W. Choi}, year = {2018}, date = {2018-05-08}, journal = {ICT Express}, abstract = {In conventional maximum distance separable (MDS) coded caching systems, storage-ecient caching strategy which minimizes unnecessarily redundant data is believed to be optimal. However, the conventional storage ecient caching strategy may not be optimal because redundantly stored data can be utilized as diversity sources to combat wireless channel impairments due to channel fading. This paper explores how MDS coded caching facilitates coordinated maxi- mum ratio transmission (MRT) in cache enabled wireless networks. Optimizing the length of MDS coded sequence and the amount of redundant cached data, we}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In conventional maximum distance separable (MDS) coded caching systems, storage-ecient caching strategy which minimizes unnecessarily redundant data is believed to be optimal. However, the conventional storage ecient caching strategy may not be optimal because redundantly stored data can be utilized as diversity sources to combat wireless channel impairments due to channel fading. This paper explores how MDS coded caching facilitates coordinated maxi- mum ratio transmission (MRT) in cache enabled wireless networks. Optimizing the length of MDS coded sequence and the amount of redundant cached data, we Close
68.	J. Jeon, Y. Shim, H. Park The Optimal Power Allocation with Hybrid Relaying Based on Channel Condition Journal Article Applied Science, 8 (5), pp. 1-18, 2018, ISSN: 2076-3417. Abstract \| BibTeX @article{Jeon2018, title = {The Optimal Power Allocation with Hybrid Relaying Based on Channel Condition}, author = {J. Jeon, Y. Shim, H. Park}, issn = {2076-3417}, year = {2018}, date = {2018-04-19}, journal = {Applied Science}, volume = {8}, number = {5}, pages = {1-18}, abstract = {This paper considers a hybrid relay network consisting of the source, the amplify-and-forward (AF) relay, the decode-and-forward (DF) relay, and the destination. We propose the optimal power allocation schemes between two different relays which maximize the achievable rate under a sum relay power constraint for given channel gains and transmit power from source. 5 By solving the optimization problem to maximize the achievable rate for each relay network, the transmit power values in closed-form are derived. When the channel gains are the same, the optimal power allocation scheme for AF-DF relay network proves that a more power should be allocated at the first relay to maximize the achievable rate. In case of the DF-AF relay network, we derive the optimal power allocation scheme for the possible four cases. Under the same SNR condition at the 10 first hop, we show that the achievable rate of AF-DF relay network is greater than that of DF-AF relay network when the channel gain between two relays is higher than that between the second relay and destination. Simulation results show that the proposed power allocation schemes provide a higher achievable rate than the equal power allocation schemes. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers a hybrid relay network consisting of the source, the amplify-and-forward (AF) relay, the decode-and-forward (DF) relay, and the destination. We propose the optimal power allocation schemes between two different relays which maximize the achievable rate under a sum relay power constraint for given channel gains and transmit power from source. 5 By solving the optimization problem to maximize the achievable rate for each relay network, the transmit power values in closed-form are derived. When the channel gains are the same, the optimal power allocation scheme for AF-DF relay network proves that a more power should be allocated at the first relay to maximize the achievable rate. In case of the DF-AF relay network, we derive the optimal power allocation scheme for the possible four cases. Under the same SNR condition at the 10 first hop, we show that the achievable rate of AF-DF relay network is greater than that of DF-AF relay network when the channel gain between two relays is higher than that between the second relay and destination. Simulation results show that the proposed power allocation schemes provide a higher achievable rate than the equal power allocation schemes. Close
67.	G. Kim; B. Hong; W. Choi; H. Park MDS Coded Caching Leveraged by Coordinated Multi-point Transmission Journal Article IEEE Communications Letters, 22 (6), pp. 1220-1223, 2018, ISSN: 1089-7798. Abstract \| BibTeX @article{Kim2018, title = {MDS Coded Caching Leveraged by Coordinated Multi-point Transmission }, author = {G. Kim; B. Hong; W. Choi; H. Park}, issn = {1089-7798}, year = {2018}, date = {2018-03-19}, journal = {IEEE Communications Letters}, volume = {22}, number = {6}, pages = {1220-1223}, abstract = {In conventional maximum distance separable (MDS) coded caching systems, the storage-efficient caching strategy which minimizes redundant data was believed to be optimal. However, redundantly stored data can rather be utilized to combat wireless channel impairments due to channel fading or interference. This paper explores how MDS coded caching facilitates coordinated multi-point (CoMP) transmission in cache enabled wireless networks. Optimizing the length of MDS coded sequence and the amount of redundant cached data, we demonstrate the gain of MDS coded caching leveraged by CoMP.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In conventional maximum distance separable (MDS) coded caching systems, the storage-efficient caching strategy which minimizes redundant data was believed to be optimal. However, redundantly stored data can rather be utilized to combat wireless channel impairments due to channel fading or interference. This paper explores how MDS coded caching facilitates coordinated multi-point (CoMP) transmission in cache enabled wireless networks. Optimizing the length of MDS coded sequence and the amount of redundant cached data, we demonstrate the gain of MDS coded caching leveraged by CoMP. Close
66.	E. Heo; N. Kim; H. Park Sparse Structure-Based Channel Estimation for Uplink SCMA System Journal Article IEEE Transactions on Vehicular Technology, 66 (9), pp. 8037-8046, 2017, ISSN: 1939-9359. Abstract \| Links \| BibTeX @article{heo2017sparseb, title = {Sparse Structure-Based Channel Estimation for Uplink SCMA System}, author = {E. Heo; N. Kim; H. Park}, url = {http://ieeexplore.ieee.org/document/7873353/}, doi = {10.1109/TVT.2017.2679020}, issn = {1939-9359}, year = {2017}, date = {2017-09-22}, journal = {IEEE Transactions on Vehicular Technology}, volume = {66}, number = {9}, pages = {8037-8046}, publisher = {IEEE}, abstract = {To fully utilize the performance gain of sparse code multiple access (SCMA) system, the channel state information of multi-users must be obtained at the base station (BS). However, conventional channel estimation approach causes significant training overhead as the number of active users becomes large. In this paper, we propose a channel estimation scheme for the uplink SCMA system to reduce the training overhead, which is based on the unstructured channel estimator (UCE). However, it is ineffective in terms of the resource usage to apply the UCE scheme to SCMA system directly since the data detection requires only channel information on the nonzero subcarriers of the SCMA codeword. Thus, we introduce a sparse pilot structure where the location of non-zero pilot symbols correspond to the location of non-zero symbols in the SCMA codeword and provide an optimal pilot allocation scheme for the sparse pilot structure, which can achieve the mean square error (MSE) lower bound. In addition, we consider the codebook reuse scenario to support more users with the existing SCMA codebooks. While the codebook reuse can help realize the massive connectivity, it has a problem that interference on each resource grows irregularly, which in turn leads to overwhelming training overhead. To solve this problem, we propose a channel estimation approach to reduce interference per subcarrier uniformly by the weight-regularization (WR) algorithm, and apply the optimal pilot allocation and least-squares (LS) algorithm. The puncturing channel information by the WR algorithm can be obtained by a minimum mean square error (MMSE) interpolator or a combined interpolator. Analytical results and simulations shows effectiveness of the proposed channel estimators.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close To fully utilize the performance gain of sparse code multiple access (SCMA) system, the channel state information of multi-users must be obtained at the base station (BS). However, conventional channel estimation approach causes significant training overhead as the number of active users becomes large. In this paper, we propose a channel estimation scheme for the uplink SCMA system to reduce the training overhead, which is based on the unstructured channel estimator (UCE). However, it is ineffective in terms of the resource usage to apply the UCE scheme to SCMA system directly since the data detection requires only channel information on the nonzero subcarriers of the SCMA codeword. Thus, we introduce a sparse pilot structure where the location of non-zero pilot symbols correspond to the location of non-zero symbols in the SCMA codeword and provide an optimal pilot allocation scheme for the sparse pilot structure, which can achieve the mean square error (MSE) lower bound. In addition, we consider the codebook reuse scenario to support more users with the existing SCMA codebooks. While the codebook reuse can help realize the massive connectivity, it has a problem that interference on each resource grows irregularly, which in turn leads to overwhelming training overhead. To solve this problem, we propose a channel estimation approach to reduce interference per subcarrier uniformly by the weight-regularization (WR) algorithm, and apply the optimal pilot allocation and least-squares (LS) algorithm. The puncturing channel information by the WR algorithm can be obtained by a minimum mean square error (MMSE) interpolator or a combined interpolator. Analytical results and simulations shows effectiveness of the proposed channel estimators. Close http://ieeexplore.ieee.org/document/7873353/ doi:10.1109/TVT.2017.2679020 Close
65.	W. Lim; G. Kwon; H. Park Interference mitigation using random antenna selection in millimeter wave beamforming system Journal Article EURASIP Journal on Wireless Communications and Networking, 2017 (1), pp. 87, 2017. Abstract \| Links \| BibTeX @article{lim2017interference, title = {Interference mitigation using random antenna selection in millimeter wave beamforming system}, author = {W. Lim; G. Kwon and H. Park}, url = {http://jwcn-eurasipjournals.springeropen.com/articles/10.1186/s13638-017-0868-5}, doi = {10.1186/s13638-017-0868-5}, year = {2017}, date = {2017-05-12}, journal = {EURASIP Journal on Wireless Communications and Networking}, volume = {2017}, number = {1}, pages = {87}, publisher = {Springer}, abstract = {In multi-user beamforming systems, the inter-user interference are controlled by spatial filtering. Since the implementation of digital beamforming is difficult due to high hardware cost of large array system, the analog beamforming system with one phase shifter at each antenna element is considered with antenna selection scheme. However, the beamwidth is not sufficiently narrow to perfectly remove the interference due to limited size of antenna arrays. To mitigate the interference, we propose the random antenna selection system in millimeter wave channel. The random antenna selection expands the effective array size so that the beamwidth becomes narrow. We compare the beamwidth of conventional fixed antenna selection with random antenna selection and analyze the amount of interference for each selection scheme. Theoretical analysis and bit error rate simulation results indicate that the beamforming with random antenna selection can take advantage of large array.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In multi-user beamforming systems, the inter-user interference are controlled by spatial filtering. Since the implementation of digital beamforming is difficult due to high hardware cost of large array system, the analog beamforming system with one phase shifter at each antenna element is considered with antenna selection scheme. However, the beamwidth is not sufficiently narrow to perfectly remove the interference due to limited size of antenna arrays. To mitigate the interference, we propose the random antenna selection system in millimeter wave channel. The random antenna selection expands the effective array size so that the beamwidth becomes narrow. We compare the beamwidth of conventional fixed antenna selection with random antenna selection and analyze the amount of interference for each selection scheme. Theoretical analysis and bit error rate simulation results indicate that the beamforming with random antenna selection can take advantage of large array. Close http://jwcn-eurasipjournals.springeropen.com/articles/10.1186/s13638-017-0868-5 doi:10.1186/s13638-017-0868-5 Close
64.	J. Kim; W. Choi; H. Park Beamforming for Full-Duplex Multiuser MIMO Systems Journal Article IEEE Transactions on Vehicular Technology, 66 (3), pp. 2423-2432, 2017, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN70, title = {Beamforming for Full-Duplex Multiuser MIMO Systems}, author = {J. Kim and W. Choi and H. Park}, doi = {10.1109/TVT.2016.2581213}, issn = {0018-9545}, year = {2017}, date = {2017-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {66}, number = {3}, pages = {2423-2432}, abstract = {We solve a sum rate maximization problem of full-duplex (FD) multiuser multiple-input-multiple-output (MU-MIMO) systems. Since additional self-interference (SI) in the uplink channel and cochannel interference (CCI) in the downlink channel are coupled in FD communication, the downlink and uplink multiuser beamforming vectors are required to be jointly designed. However, the joint optimization problem is nonconvex and difficult to solve due to the coupled effect. To properly address the coupled design issue, we reformulate the problem into an equivalent uplink channel problem by using the uplink and downlink channel duality known as multiple-access channel-broadcast channel duality (MAC-BC duality). Then, using a minorization-maximization (MM) algorithm based on an affine approximation, we obtain a solution for the reformulated problem. In addition, without any approximation and thus performance degradation, we develop an alternative algorithm based on iterative water filling (IWF) to solve the nonconvex problem. The proposed algorithms warrant fast convergence and low computational complexity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We solve a sum rate maximization problem of full-duplex (FD) multiuser multiple-input-multiple-output (MU-MIMO) systems. Since additional self-interference (SI) in the uplink channel and cochannel interference (CCI) in the downlink channel are coupled in FD communication, the downlink and uplink multiuser beamforming vectors are required to be jointly designed. However, the joint optimization problem is nonconvex and difficult to solve due to the coupled effect. To properly address the coupled design issue, we reformulate the problem into an equivalent uplink channel problem by using the uplink and downlink channel duality known as multiple-access channel-broadcast channel duality (MAC-BC duality). Then, using a minorization-maximization (MM) algorithm based on an affine approximation, we obtain a solution for the reformulated problem. In addition, without any approximation and thus performance degradation, we develop an alternative algorithm based on iterative water filling (IWF) to solve the nonconvex problem. The proposed algorithms warrant fast convergence and low computational complexity. Close doi:10.1109/TVT.2016.2581213 Close
63.	N. Kim; J. Kim; S.-C. Lim; H. Park BER of MIMO-BICM System at Current Detection/Decoding Cycle Journal Article IEEE Wireless Communications Letters, 6 (1), pp. 78-81, 2017, ISSN: 2162-2337. Abstract \| Links \| BibTeX @article{RN72, title = {BER of MIMO-BICM System at Current Detection/Decoding Cycle}, author = {N. Kim and J. Kim and S.-C. Lim and H. Park}, doi = {10.1109/LWC.2016.2632714}, issn = {2162-2337}, year = {2017}, date = {2017-01-01}, journal = {IEEE Wireless Communications Letters}, volume = {6}, number = {1}, pages = {78-81}, abstract = {In this letter, we analyze the bit error rate (BER) of a multiple-input multiple-output bit-interleaved coded modulation (MIMO-BICM) system with an iterative receiver that consists of a soft-in soft-out (SISO) minimum mean square error detector and an SISO channel decoder. At a current detection/decoding cycle, an upper bound on a BER is derived based on the moment generating function of signal-to-interference-and-noise ratio at the detector output. We utilize the analytical BER derived from the current cycle to update the upper bound at the next cycle in an iterative manner. By an asymptotic approach, we also show that the BER of the MIMO-BICM system with an iterative receiver converges to that of the maximal ratio combining system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we analyze the bit error rate (BER) of a multiple-input multiple-output bit-interleaved coded modulation (MIMO-BICM) system with an iterative receiver that consists of a soft-in soft-out (SISO) minimum mean square error detector and an SISO channel decoder. At a current detection/decoding cycle, an upper bound on a BER is derived based on the moment generating function of signal-to-interference-and-noise ratio at the detector output. We utilize the analytical BER derived from the current cycle to update the upper bound at the next cycle in an iterative manner. By an asymptotic approach, we also show that the BER of the MIMO-BICM system with an iterative receiver converges to that of the maximal ratio combining system. Close doi:10.1109/LWC.2016.2632714 Close
62.	S.-C. Lim; N. Kim; H. Park Uplink SCMA System with Multiple Antennas Journal Article IEEE Transactions on Vehicular Technology, 66 (8), pp. 6982-6992, 2017, ISSN: 1939-9359. Abstract \| Links \| BibTeX @article{RN74, title = {Uplink SCMA System with Multiple Antennas}, author = {S.-C. Lim and N. Kim and H. Park}, doi = {10.1109/TVT.2017.2664894}, issn = {1939-9359}, year = {2017}, date = {2017-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {66}, number = {8}, pages = {6982-6992}, abstract = {Sparse code multiple access (SCMA) is a codebookbased non-orthogonal multiple access which exploits the coding gain of designed codebooks and the near-optimum performance of belief-propagation (BP) detection. In this paper, we study an uplink SCMA system equipped with multiple receive antennas utilized to get a diversity gain. Assuming that the maximum likelihood detection is applied to the system, we derive the upper bound on the average bit error rate (ABER) and analyze the diversity order which is shown to be the product of the number of receive antennas and the spreading gain. Exploiting the multiple received signals, we also propose a simplified detection method called Gaussian approximation based BP (GA-BP) detection with linear pre-filtering. As the first step of the proposed detection, a conventional linear filter is applied to mitigate the multiuser interferences. Then, the GA-BP iteratively removes the residual interferences which may be approximated to a Gaussian random variable for the massive number of user equipments (UEs). Numerical results show that for moderate and high signal to noise ratio region the analyzed upper bounds on ABER of SCMA system tightly coincide with the simulation results. Also, for the moderate numbers of antennas, the ABER of GA-BP with matched filter closely approaches to that of the conventional BP detection with much lower computational costs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Sparse code multiple access (SCMA) is a codebookbased non-orthogonal multiple access which exploits the coding gain of designed codebooks and the near-optimum performance of belief-propagation (BP) detection. In this paper, we study an uplink SCMA system equipped with multiple receive antennas utilized to get a diversity gain. Assuming that the maximum likelihood detection is applied to the system, we derive the upper bound on the average bit error rate (ABER) and analyze the diversity order which is shown to be the product of the number of receive antennas and the spreading gain. Exploiting the multiple received signals, we also propose a simplified detection method called Gaussian approximation based BP (GA-BP) detection with linear pre-filtering. As the first step of the proposed detection, a conventional linear filter is applied to mitigate the multiuser interferences. Then, the GA-BP iteratively removes the residual interferences which may be approximated to a Gaussian random variable for the massive number of user equipments (UEs). Numerical results show that for moderate and high signal to noise ratio region the analyzed upper bounds on ABER of SCMA system tightly coincide with the simulation results. Also, for the moderate numbers of antennas, the ABER of GA-BP with matched filter closely approaches to that of the conventional BP detection with much lower computational costs. Close doi:10.1109/TVT.2017.2664894 Close
61.	E. Heo; O. Simeone; H.Park Optimal fronthaul compression for synchronization in the uplink of cloud radio access networks Journal Article EURASIP Journal on Wireless Communications and Networking, 2017 (1), pp. 22, 2017, ISSN: 1687-1499. Abstract \| Links \| BibTeX @article{RN75, title = {Optimal fronthaul compression for synchronization in the uplink of cloud radio access networks}, author = {E. Heo; O. Simeone; H.Park}, url = {http://dx.doi.org/10.1186/s13638-017-0804-8}, doi = {10.1186/s13638-017-0804-8}, issn = {1687-1499}, year = {2017}, date = {2017-01-01}, journal = {EURASIP Journal on Wireless Communications and Networking}, volume = {2017}, number = {1}, pages = {22}, abstract = {A key problem in the design of cloud radio access networks (CRANs) is to devise effective baseband compression strategies for transmission on the fronthaul links connecting a remote radio head (RRH) to the managing central unit (CU). Most theoretical works on the subject implicitly assume that the RRHs, and hence the CU, are able to perfectly recover time synchronization from the baseband signals received in the uplink, and focus on the compression of the data fields. This paper instead does not assume a priori synchronization of RRHs and CU, and considers the problem of fronthaul compression design at the RRHs with the aim of enhancing the performance of time and phase synchronization at the CU. The problem is tackled by analyzing the impact of the synchronization error on the performance of the link and by adopting information and estimation-theoretic performance metrics such as the rate-distortion function and the Cramer-Rao bound (CRB). The proposed algorithm is based on the Charnes-Cooper transformation and on the Difference of Convex (DC) approach, and is shown via numerical results to outperform conventional solutions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A key problem in the design of cloud radio access networks (CRANs) is to devise effective baseband compression strategies for transmission on the fronthaul links connecting a remote radio head (RRH) to the managing central unit (CU). Most theoretical works on the subject implicitly assume that the RRHs, and hence the CU, are able to perfectly recover time synchronization from the baseband signals received in the uplink, and focus on the compression of the data fields. This paper instead does not assume a priori synchronization of RRHs and CU, and considers the problem of fronthaul compression design at the RRHs with the aim of enhancing the performance of time and phase synchronization at the CU. The problem is tackled by analyzing the impact of the synchronization error on the performance of the link and by adopting information and estimation-theoretic performance metrics such as the rate-distortion function and the Cramer-Rao bound (CRB). The proposed algorithm is based on the Charnes-Cooper transformation and on the Difference of Convex (DC) approach, and is shown via numerical results to outperform conventional solutions. Close http://dx.doi.org/10.1186/s13638-017-0804-8 doi:10.1186/s13638-017-0804-8 Close
60.	H. Han; H. Kim; N. Kim; H. Park An Enhanced QAM-FBMC Scheme With Interference Mitigation Journal Article IEEE Communications Letters, 20 (11), pp. 2237-2240, 2016, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN69, title = {An Enhanced QAM-FBMC Scheme With Interference Mitigation}, author = {H. Han and H. Kim and N. Kim and H. Park}, doi = {10.1109/LCOMM.2016.2604250}, issn = {1089-7798}, year = {2016}, date = {2016-01-01}, journal = {IEEE Communications Letters}, volume = {20}, number = {11}, pages = {2237-2240}, abstract = {Cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) has been used as a waveform for mobile communications, but CP-OFDM has weaknesses in an asynchronous heterogeneous network scenario. To overcome the disadvantage of CP-OFDM, a quadrature amplitude modulation (QAM)-filter-bank-based multi-carrier (FBMC) system is proposed to achieve superior spectrum confinement and better spectral efficiency. However, QAM-FBMC has inevitable performance degradation because of interferences from non-orthogonal filters. In this letter, we propose a decision feedback equalization (DFE)-based interference mitigation scheme for the QAM-FBMC system to cancel a residual interference. The interference from the filters of QAM-FBMC influences to other subcarriers and symbols, and it is modeled as an end-to-end system transfer function with para-Hermitian poly-nomial matrix form, equivalently. By spectral factorization of the system transfer function, the system response is transformed into causal, and the receiver detects the symbols successively. This letter describes the spectral factorization method and formulates the feed-forward and feedback filter of the DFE structure with the spectral factor of transfer function. Simulation results show the superiority of the proposed scheme to the conventional QAM-FBMC receiver scheme.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) has been used as a waveform for mobile communications, but CP-OFDM has weaknesses in an asynchronous heterogeneous network scenario. To overcome the disadvantage of CP-OFDM, a quadrature amplitude modulation (QAM)-filter-bank-based multi-carrier (FBMC) system is proposed to achieve superior spectrum confinement and better spectral efficiency. However, QAM-FBMC has inevitable performance degradation because of interferences from non-orthogonal filters. In this letter, we propose a decision feedback equalization (DFE)-based interference mitigation scheme for the QAM-FBMC system to cancel a residual interference. The interference from the filters of QAM-FBMC influences to other subcarriers and symbols, and it is modeled as an end-to-end system transfer function with para-Hermitian poly-nomial matrix form, equivalently. By spectral factorization of the system transfer function, the system response is transformed into causal, and the receiver detects the symbols successively. This letter describes the spectral factorization method and formulates the feed-forward and feedback filter of the DFE structure with the spectral factor of transfer function. Simulation results show the superiority of the proposed scheme to the conventional QAM-FBMC receiver scheme. Close doi:10.1109/LCOMM.2016.2604250 Close
59.	Y. Shim; W. Choi; H. Park Beamforming Design for Full-Duplex Two-Way Amplify-and-Forward MIMO Relay Journal Article IEEE Transactions on Wireless Communications, 15 (10), pp. 6705-6715, 2016, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN68, title = {Beamforming Design for Full-Duplex Two-Way Amplify-and-Forward MIMO Relay}, author = {Y. Shim and W. Choi and H. Park}, doi = {10.1109/TWC.2016.2587768}, issn = {1536-1276}, year = {2016}, date = {2016-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {15}, number = {10}, pages = {6705-6715}, abstract = {We consider the full-duplex (FD) two-way amplify-and-forward relay system with imperfect cancellation of loopback self-interference (SI) and investigate joint design of relay and receive beamforming for minimizing the mean square error (MSE) under a relay transmit power constraint. Due to loopback channel estimation error and limitation of analog-to-digital converter, the loopback SI cannot be completely canceled. Multiple antennas at the relay can help loopback SI suppression, but beamforming is required to balance between the residual SI suppression and the desired signal transmission. Moreover, the relay beamforming matrix should be updated every time slot, because the residual SI in the previous time slot is amplified by the current beamforming matrix and added to the received signals from the two sources in the current time slot. We derive the optimally balanced relay beamforming and receive beamforming matrices in closed form based on minimum MSE, taking into account the propagation of the residual loopback SI from the first to the current time slot. We also propose beamforming design using only the channels of the $m$ latest time slots, not from the first time slot. Based on our numerical results, we also identify when FD is beneficial and propose selection between FD and half-duplex according to signal-to-noise ratio and interference-to-noise ratio.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We consider the full-duplex (FD) two-way amplify-and-forward relay system with imperfect cancellation of loopback self-interference (SI) and investigate joint design of relay and receive beamforming for minimizing the mean square error (MSE) under a relay transmit power constraint. Due to loopback channel estimation error and limitation of analog-to-digital converter, the loopback SI cannot be completely canceled. Multiple antennas at the relay can help loopback SI suppression, but beamforming is required to balance between the residual SI suppression and the desired signal transmission. Moreover, the relay beamforming matrix should be updated every time slot, because the residual SI in the previous time slot is amplified by the current beamforming matrix and added to the received signals from the two sources in the current time slot. We derive the optimally balanced relay beamforming and receive beamforming matrices in closed form based on minimum MSE, taking into account the propagation of the residual loopback SI from the first to the current time slot. We also propose beamforming design using only the channels of the $m$ latest time slots, not from the first time slot. Based on our numerical results, we also identify when FD is beneficial and propose selection between FD and half-duplex according to signal-to-noise ratio and interference-to-noise ratio. Close doi:10.1109/TWC.2016.2587768 Close
58.	Y. Shim; K. Lee; H. Park Joint Relay Beamforming Design for Multilevel Nondistributed and Distributed Amplify-and-Forward Relay Networks Journal Article IEEE Transactions on Vehicular Technology, PP (99), pp. 1-1, 2016, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN71, title = {Joint Relay Beamforming Design for Multilevel Nondistributed and Distributed Amplify-and-Forward Relay Networks}, author = {Y. Shim and K. Lee and H. Park}, doi = {10.1109/TVT.2016.2598178}, issn = {0018-9545}, year = {2016}, date = {2016-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {PP}, number = {99}, pages = {1-1}, abstract = {This paper considers both nondistributed and distributed multilevel amplify-and-forward (AF) wireless relay networks. For a fair comparison, the nondistributed multilevel AF relay network consists of a one-source-one-destination pair and a relay at each level with multiple antennas, whereas the distributed network consists of a one-source-one-destination pair and multiple distributed relays at each level with a single antenna at each relay. In this paper, relay beamforming matrices are determined for both networks based on the minimum mean square error criterion. During data transmission, power is independently and individually constrained at the relays at each level. Finally, an iterative algorithm is proposed to solve the desired optimization problem.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers both nondistributed and distributed multilevel amplify-and-forward (AF) wireless relay networks. For a fair comparison, the nondistributed multilevel AF relay network consists of a one-source-one-destination pair and a relay at each level with multiple antennas, whereas the distributed network consists of a one-source-one-destination pair and multiple distributed relays at each level with a single antenna at each relay. In this paper, relay beamforming matrices are determined for both networks based on the minimum mean square error criterion. During data transmission, power is independently and individually constrained at the relays at each level. Finally, an iterative algorithm is proposed to solve the desired optimization problem. Close doi:10.1109/TVT.2016.2598178 Close
57.	Mi‐Hyun Son; Sooho Bae; Hyuncheol Park; Hyuck M Kwon The effect of void on characteristics of LDMOS power amplifier Journal Article Microwave and Optical Technology Letters, 58 (3), pp. 691-694, 2016, ISSN: 1098-2760. Abstract \| BibTeX @article{RN67, title = {The effect of void on characteristics of LDMOS power amplifier}, author = {Mi‐Hyun Son and Sooho Bae and Hyuncheol Park and Hyuck M Kwon}, issn = {1098-2760}, year = {2016}, date = {2016-01-01}, journal = {Microwave and Optical Technology Letters}, volume = {58}, number = {3}, pages = {691-694}, abstract = {The effect of void on characteristics of the laterally diffused metal oxide semiconductor (LDMOS) power amplifier (PA) is analyzed using the thermal and circuit analysis together. Thermal analysis is performed for finding the junction temperature of LDMOS PA as void area changes. Circuit analysis is performed from these results and LDMOS PA libraries. The analysis results show the linearity, gain, and efficiency degradation in the LDMOS PA as a result of the increase in void area. And this simulation methodology can be used for the design of the PA. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:691–694, 2016}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The effect of void on characteristics of the laterally diffused metal oxide semiconductor (LDMOS) power amplifier (PA) is analyzed using the thermal and circuit analysis together. Thermal analysis is performed for finding the junction temperature of LDMOS PA as void area changes. Circuit analysis is performed from these results and LDMOS PA libraries. The analysis results show the linearity, gain, and efficiency degradation in the LDMOS PA as a result of the increase in void area. And this simulation methodology can be used for the design of the PA. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:691–694, 2016 Close
56.	H. Kim; G. Kim; W. Choi; H. Park Asymptotic Sum Rate in Spatially Correlated Two-Cell Channel With User Scheduling Journal Article IEEE Transactions on Vehicular Technology, 64 (3), pp. 1235-1243, 2015, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN65, title = {Asymptotic Sum Rate in Spatially Correlated Two-Cell Channel With User Scheduling}, author = {H. Kim and G. Kim and W. Choi and H. Park}, doi = {10.1109/TVT.2014.2329477}, issn = {0018-9545}, year = {2015}, date = {2015-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {64}, number = {3}, pages = {1235-1243}, abstract = {Coordinated beamforming (CBF) provides improved sum rate with less overhead and computational complexity, and its theoretical performance analysis is mostly finished in a spatially uncorrelated environment. In this paper, we investigate the effect of spatial correlation on the sum rate of a two-cell multiuser downlink channel. We analyze the scaling laws of the sum rate with a large number of users. To improve the performance, different roles are assigned to the two cells: One is a master cell, and the other is a slave cell. The base station (BS) of the master cell requests the interference cancellation to the slave cell, and the BS of the slave cell performs precoding to cancel the interference influencing over the master cell, although the achievable rate of the slave cell is decreased. The decision of the master and slave cells can be affected by the number of users and the degree of spatial correlations. From computer-based simulations, we show that our proposed algorithm can achieve a higher sum rate than other previous approaches with lower overhead.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Coordinated beamforming (CBF) provides improved sum rate with less overhead and computational complexity, and its theoretical performance analysis is mostly finished in a spatially uncorrelated environment. In this paper, we investigate the effect of spatial correlation on the sum rate of a two-cell multiuser downlink channel. We analyze the scaling laws of the sum rate with a large number of users. To improve the performance, different roles are assigned to the two cells: One is a master cell, and the other is a slave cell. The base station (BS) of the master cell requests the interference cancellation to the slave cell, and the BS of the slave cell performs precoding to cancel the interference influencing over the master cell, although the achievable rate of the slave cell is decreased. The decision of the master and slave cells can be affected by the number of users and the degree of spatial correlations. From computer-based simulations, we show that our proposed algorithm can achieve a higher sum rate than other previous approaches with lower overhead. Close doi:10.1109/TVT.2014.2329477 Close
55.	K. Lee; J. Yang; H. M. Kwon; H. Park; Y. H. Lee Centralized Two-Way AF MIMO Multiple Dispersed Relay Network Journal Article IEEE Transactions on Vehicular Technology, 64 (5), pp. 2133-2138, 2015, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN66, title = {Centralized Two-Way AF MIMO Multiple Dispersed Relay Network}, author = {K. Lee and J. Yang and H. M. Kwon and H. Park and Y. H. Lee}, doi = {10.1109/TVT.2014.2338075}, issn = {0018-9545}, year = {2015}, date = {2015-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {64}, number = {5}, pages = {2133-2138}, abstract = {This paper considers a two-way amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network consisting of two sources (each with multiple antennas) and multiple physically dispersed single-antenna relays. A central station finds the optimum relay amplifying matrices and transmit/receive beamforming vectors explicitly and iteratively under the transmit power constraints at the sources and the relays. The minimum-mean-square-error criterion is used. Numerical results show that the proposed scheme outperforms the existing two-way AF MIMO network schemes proposed by Arti et al. and Wang et al.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers a two-way amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network consisting of two sources (each with multiple antennas) and multiple physically dispersed single-antenna relays. A central station finds the optimum relay amplifying matrices and transmit/receive beamforming vectors explicitly and iteratively under the transmit power constraints at the sources and the relays. The minimum-mean-square-error criterion is used. Numerical results show that the proposed scheme outperforms the existing two-way AF MIMO network schemes proposed by Arti et al. and Wang et al. Close doi:10.1109/TVT.2014.2338075 Close
54.	D. s. Cho; Y. Shim; H. Park Optimal time allocation for two-way relay channel using physical-layer network coding Journal Article IET Communications, 8 (14), pp. 2469-2475, 2014, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN61, title = {Optimal time allocation for two-way relay channel using physical-layer network coding}, author = {D. s. Cho and Y. Shim and H. Park}, doi = {10.1049/iet-com.2014.0253}, issn = {1751-8628}, year = {2014}, date = {2014-01-01}, journal = {IET Communications}, volume = {8}, number = {14}, pages = {2469-2475}, abstract = {This study proposes an optimal time allocation scheme for two-way relay channel (TWRC) using the physical-layer network coding (PNC). In other words, this study analytically determines the optimal transmit time durations for the first and the second time slot, which maximise the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate for the proposed optimal time allocation is greater than or equal to that for equal time allocation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This study proposes an optimal time allocation scheme for two-way relay channel (TWRC) using the physical-layer network coding (PNC). In other words, this study analytically determines the optimal transmit time durations for the first and the second time slot, which maximise the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate for the proposed optimal time allocation is greater than or equal to that for equal time allocation. Close doi:10.1049/iet-com.2014.0253 Close
53.	Hyun Seok Choi; Sun Yool Kang; Seong Jun Cho; Inn-Yeal Oh; Mincheol Shin; Hyuncheol Park; Chaun Jang; Byoung-Chul Min; Sang-Il Kim; Seung-Young Park; Chul Soon Park Spin nano–oscillator–based wireless communication Journal Article Scientific Reports, 4 , pp. 5486, 2014, ISSN: 2045-2322. Abstract \| Links \| BibTeX @article{RN60, title = {Spin nano–oscillator–based wireless communication}, author = {Hyun Seok Choi and Sun Yool Kang and Seong Jun Cho and Inn-Yeal Oh and Mincheol Shin and Hyuncheol Park and Chaun Jang and Byoung-Chul Min and Sang-Il Kim and Seung-Young Park and Chul Soon Park}, url = {http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4074786/}, doi = {10.1038/srep05486}, issn = {2045-2322}, year = {2014}, date = {2014-01-01}, journal = {Scientific Reports}, volume = {4}, pages = {5486}, abstract = {Spin–torque nano–oscillators (STNOs) have outstanding advantages of a high degree of compactness, high–frequency tunability, and good compatibility with the standard complementary metal–oxide–semiconductor process, which offer prospects for future wireless communication. There have as yet been no reports on wireless communication using STNOs, since the STNOs also have notable disadvantages such as lower output power and poorer spectral purity in comparison with those of LC voltage–controlled oscillators. Here we show that wireless communication is achieved by a proper choice of modulation scheme despite these drawbacks of STNOs. By adopting direct binary amplitude shift keying modulation and non–coherent demodulation, we demonstrate STNO–based wireless communication with 200–kbps data rate at a distance of 1 m between transmitter and receiver. It is shown, from the analysis of STNO noise, that the maximum data rate can be extended up to 1.48 Gbps with 1–ns turn–on time. For the fabricated STNO, the maximum data rate is 5 Mbps which is limited by the rise time measured in the total system. The result will provide a viable route to real microwave application of STNOs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Spin–torque nano–oscillators (STNOs) have outstanding advantages of a high degree of compactness, high–frequency tunability, and good compatibility with the standard complementary metal–oxide–semiconductor process, which offer prospects for future wireless communication. There have as yet been no reports on wireless communication using STNOs, since the STNOs also have notable disadvantages such as lower output power and poorer spectral purity in comparison with those of LC voltage–controlled oscillators. Here we show that wireless communication is achieved by a proper choice of modulation scheme despite these drawbacks of STNOs. By adopting direct binary amplitude shift keying modulation and non–coherent demodulation, we demonstrate STNO–based wireless communication with 200–kbps data rate at a distance of 1 m between transmitter and receiver. It is shown, from the analysis of STNO noise, that the maximum data rate can be extended up to 1.48 Gbps with 1–ns turn–on time. For the fabricated STNO, the maximum data rate is 5 Mbps which is limited by the rise time measured in the total system. The result will provide a viable route to real microwave application of STNOs. Close http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4074786/ doi:10.1038/srep05486 Close
52.	Junpyo Jeon; Hyoung-Muk Lim; Hyuncheol Park; Hyoung-Kyu Song An Improved Cooperative Technique Sharing the Channel in OFDMA-Based System Journal Article IEICE Transactions on Information and Systems, E97.D (12), pp. 3222-3225, 2014. Abstract \| Links \| BibTeX @article{RN64, title = {An Improved Cooperative Technique Sharing the Channel in OFDMA-Based System}, author = {Junpyo Jeon and Hyoung-Muk Lim and Hyuncheol Park and Hyoung-Kyu Song}, doi = {10.1587/transinf.2014EDL8024}, year = {2014}, date = {2014-01-01}, journal = {IEICE Transactions on Information and Systems}, volume = {E97.D}, number = {12}, pages = {3222-3225}, abstract = {Cooperative communication has been proposed to improve the disadvantages of the multiple-input multiple-output (MIMO) technique without using extra multiple antennas. In an orthogonal frequency division multiple access (OFDMA) system, a cooperative communication that each user shares their allocated sub-channels instead of the MIMO system has been proposed to improve the throughput. But the cooperative communication has a problem as the decreased throughput because it is necessary that users send and receive the information to each other to improve reliability. In this letter, the modified cooperative transmission scheme is proposed to improve reliability in the fading channel, and it can solve the problem for BER performance that is dependent on the errors in the first phase that exchanges the information between both users during the first time.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Cooperative communication has been proposed to improve the disadvantages of the multiple-input multiple-output (MIMO) technique without using extra multiple antennas. In an orthogonal frequency division multiple access (OFDMA) system, a cooperative communication that each user shares their allocated sub-channels instead of the MIMO system has been proposed to improve the throughput. But the cooperative communication has a problem as the decreased throughput because it is necessary that users send and receive the information to each other to improve reliability. In this letter, the modified cooperative transmission scheme is proposed to improve reliability in the fading channel, and it can solve the problem for BER performance that is dependent on the errors in the first phase that exchanges the information between both users during the first time. Close doi:10.1587/transinf.2014EDL8024 Close
51.	J. Kim; H. Park A Coding Scheme for Visible Light Communication With Wide Dimming Range Journal Article IEEE Photonics Technology Letters, 26 (5), pp. 465-468, 2014, ISSN: 1041-1135. Abstract \| Links \| BibTeX @article{RN57, title = {A Coding Scheme for Visible Light Communication With Wide Dimming Range}, author = {J. Kim and H. Park}, doi = {10.1109/LPT.2013.2296934}, issn = {1041-1135}, year = {2014}, date = {2014-01-01}, journal = {IEEE Photonics Technology Letters}, volume = {26}, number = {5}, pages = {465-468}, abstract = {For visible light communications (VLCs), dimming support is desirable to provide variable levels of lighting brightness. When error correction coding schemes are used for VLC systems, different code rates should be employed according to target dimming levels. In this letter, we propose a coding scheme, which can provide a wide range of brightness and a simple encoding/decoding structure for all different rates by using a rate-compatible punctured code. Puncturing patterns having the minimum bit error rate are provided by computer search. The results show that the VLC system with the proposed coding scheme can achieve optimum performances as well as a precise dimming support.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close For visible light communications (VLCs), dimming support is desirable to provide variable levels of lighting brightness. When error correction coding schemes are used for VLC systems, different code rates should be employed according to target dimming levels. In this letter, we propose a coding scheme, which can provide a wide range of brightness and a simple encoding/decoding structure for all different rates by using a rate-compatible punctured code. Puncturing patterns having the minimum bit error rate are provided by computer search. The results show that the VLC system with the proposed coding scheme can achieve optimum performances as well as a precise dimming support. Close doi:10.1109/LPT.2013.2296934 Close
50.	K. Lee; J. Yang; H. M. Kwon; H. Park; Y. H. Lee Closed Form of Optimum Cooperative Distributed Relay Amplifying Matrix Journal Article IEEE Transactions on Wireless Communications, 13 (5), pp. 2741-2755, 2014, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN58, title = {Closed Form of Optimum Cooperative Distributed Relay Amplifying Matrix}, author = {K. Lee and J. Yang and H. M. Kwon and H. Park and Y. H. Lee}, doi = {10.1109/TWC.2013.033114.131350}, issn = {1536-1276}, year = {2014}, date = {2014-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {13}, number = {5}, pages = {2741-2755}, abstract = {This paper presents a closed form of an optimal cooperative amplify-and-forward (AF) relay amplifying matrix for a distributed relay network of M-source-M-destination pairs and N relays, called a cooperative distributed AF relay network. The objective of this paper is to derive closed forms of minimum mean square error (MMSE)-based and zero-forcing (ZF)-based optimal AF relay amplifying matrices for the cooperative distributed AF relay network under the transmitter power constraint (TPC) at the relays, the receiver power constraint (RPC) at the destinations, and the no-power constraint (NPC) condition. Additionally, by substituting the derived optimum AF relay amplifying matrices into the original cost functions (CFs), the behavior of the optimum CFs and the total optimum signal component power (SCP) at the destinations are compared to each other for different cases. Finally, using the MMSE criterion, a novel relay selection scheme is proposed for the cooperative distributed AF relay network.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper presents a closed form of an optimal cooperative amplify-and-forward (AF) relay amplifying matrix for a distributed relay network of M-source-M-destination pairs and N relays, called a cooperative distributed AF relay network. The objective of this paper is to derive closed forms of minimum mean square error (MMSE)-based and zero-forcing (ZF)-based optimal AF relay amplifying matrices for the cooperative distributed AF relay network under the transmitter power constraint (TPC) at the relays, the receiver power constraint (RPC) at the destinations, and the no-power constraint (NPC) condition. Additionally, by substituting the derived optimum AF relay amplifying matrices into the original cost functions (CFs), the behavior of the optimum CFs and the total optimum signal component power (SCP) at the destinations are compared to each other for different cases. Finally, using the MMSE criterion, a novel relay selection scheme is proposed for the cooperative distributed AF relay network. Close doi:10.1109/TWC.2013.033114.131350 Close
49.	Y. Shim; H. Park A Closed-Form Expression of Optimal Time for Two-Way Relay Using DF MABC Protocol Journal Article IEEE Communications Letters, 18 (5), pp. 721-724, 2014, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN59, title = {A Closed-Form Expression of Optimal Time for Two-Way Relay Using DF MABC Protocol}, author = {Y. Shim and H. Park}, doi = {10.1109/LCOMM.2014.022514.132755}, issn = {1089-7798}, year = {2014}, date = {2014-01-01}, journal = {IEEE Communications Letters}, volume = {18}, number = {5}, pages = {721-724}, abstract = {In this paper, we propose the optimal time allocation for two-way relay using decode-and-forward (DF) multiple access broadcast (MABC) protocol. We analytically determine the optimal transmit time durations for the first and the second time slots, which maximize the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate of the optimal time allocation is greater than or equal to that of the equal time allocation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we propose the optimal time allocation for two-way relay using decode-and-forward (DF) multiple access broadcast (MABC) protocol. We analytically determine the optimal transmit time durations for the first and the second time slots, which maximize the achievable sum rate under a sum time constraint for a given squared magnitude of the channel coefficients and transmit power values. Numerical results show that the achievable sum rate of the optimal time allocation is greater than or equal to that of the equal time allocation. Close doi:10.1109/LCOMM.2014.022514.132755 Close
48.	C. Shin; H. Park; H. M. Kwon PHY-Supported Frame Aggregation for Wireless Local Area Networks Journal Article IEEE Transactions on Mobile Computing, 13 (10), pp. 2369-2381, 2014, ISSN: 1536-1233. Abstract \| Links \| BibTeX @article{RN63, title = {PHY-Supported Frame Aggregation for Wireless Local Area Networks}, author = {C. Shin and H. Park and H. M. Kwon}, doi = {10.1109/TMC.2014.2304393}, issn = {1536-1233}, year = {2014}, date = {2014-01-01}, journal = {IEEE Transactions on Mobile Computing}, volume = {13}, number = {10}, pages = {2369-2381}, abstract = {An aggregate medium access control (MAC) service data unit (A-MSDU) contains multiple subframes with a single sequence number. Hence, it has a major drawback in environments with high error rates because if any subframes are corrupted, then the entire A-MSDU will be lost. In addition, performance of the A-MSDU depends strongly on the choice of parameters, such as frame size, modulation level, coding rate, and spatial mode. In this paper, a novel link-adaptation mechanism, dubbed physical (PHY)supported frame aggregation (PSFA), is proposed over IEEE 802.11 networks, and its performance is analyzed. The proposed PSFA technique is based on a cross-layer interaction that enables joint optimization of various parameters between the PHY and MAC layers. This paper derives a new packet error rate (PER) expression for convolutionally coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems as an example. Then, this PER expression is used to efficiently estimate the link quality, given the channel conditions and system parameters, and most importantly, it is able to facilitate a parametric study of the cross-layer interaction. In the proposed PSFA algorithm, we present a rule for selecting the parameters so that MAC throughput is maximized. It is shown analytically and verified using Monte Carlo simulations that this choice of parameters can improve throughput performance significantly and also ensure quality of service (QoS) requirements compared to existing conventional algorithms.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close An aggregate medium access control (MAC) service data unit (A-MSDU) contains multiple subframes with a single sequence number. Hence, it has a major drawback in environments with high error rates because if any subframes are corrupted, then the entire A-MSDU will be lost. In addition, performance of the A-MSDU depends strongly on the choice of parameters, such as frame size, modulation level, coding rate, and spatial mode. In this paper, a novel link-adaptation mechanism, dubbed physical (PHY)supported frame aggregation (PSFA), is proposed over IEEE 802.11 networks, and its performance is analyzed. The proposed PSFA technique is based on a cross-layer interaction that enables joint optimization of various parameters between the PHY and MAC layers. This paper derives a new packet error rate (PER) expression for convolutionally coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems as an example. Then, this PER expression is used to efficiently estimate the link quality, given the channel conditions and system parameters, and most importantly, it is able to facilitate a parametric study of the cross-layer interaction. In the proposed PSFA algorithm, we present a rule for selecting the parameters so that MAC throughput is maximized. It is shown analytically and verified using Monte Carlo simulations that this choice of parameters can improve throughput performance significantly and also ensure quality of service (QoS) requirements compared to existing conventional algorithms. Close doi:10.1109/TMC.2014.2304393 Close
47.	K. Kim; H. Park; H. M. Kwon New Subcarrier Allocation for Uplink-OFDMA under Time-Varying Channels Journal Article IEEE Transactions on Communications, 61 (1), pp. 7-12, 2013, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN55, title = {New Subcarrier Allocation for Uplink-OFDMA under Time-Varying Channels}, author = {K. Kim and H. Park and H. M. Kwon}, doi = {10.1109/TCOMM.2012.100512.110011}, issn = {0090-6778}, year = {2013}, date = {2013-01-01}, journal = {IEEE Transactions on Communications}, volume = {61}, number = {1}, pages = {7-12}, abstract = {Inter-carrier interference (ICI) and multiuser interference (MUI) occur in an uplink orthogonal frequency division multiple access system if a channel between a mobile user and a base station is rapidly time-varying. To reduce the ICI and MUI, this letter proposes a subcarrier allocation method. The key idea is to allocate a high-speed user's subcarrier near a low-speed user's one. Then, a wide Doppler spread of a high-speed user can be spilled over a low-speed user's subcarrier band with insignificant influence, and the signal-to-interference-plus-noise ratio (SINR) at each high-speed user's subcarrier can be maximized. This can provide a significant performance improvement of multiuser detection in an uplink-OFDMA.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Inter-carrier interference (ICI) and multiuser interference (MUI) occur in an uplink orthogonal frequency division multiple access system if a channel between a mobile user and a base station is rapidly time-varying. To reduce the ICI and MUI, this letter proposes a subcarrier allocation method. The key idea is to allocate a high-speed user's subcarrier near a low-speed user's one. Then, a wide Doppler spread of a high-speed user can be spilled over a low-speed user's subcarrier band with insignificant influence, and the signal-to-interference-plus-noise ratio (SINR) at each high-speed user's subcarrier can be maximized. This can provide a significant performance improvement of multiuser detection in an uplink-OFDMA. Close doi:10.1109/TCOMM.2012.100512.110011 Close
46.	B. Song; H. Park A Binary Space-Time Code for Additional Diversity Gains Journal Article IEEE Transactions on Wireless Communications, 12 (11), pp. 5780-5787, 2013, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN56, title = {A Binary Space-Time Code for Additional Diversity Gains}, author = {B. Song and H. Park}, doi = {10.1109/TWC.2013.093013.130107}, issn = {1536-1276}, year = {2013}, date = {2013-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {12}, number = {11}, pages = {5780-5787}, abstract = {In this paper, we introduce a bit-interleaved binary space-time code (B-STC) for a coded multiple-input multiple-output (MIMO) system to obtain an additional diversity gain over the full-rate spatial multiplexing (SM) transmission. By applying the B-STC scheme, codeword bits from each stream are transmitted effectively through N_t or (N_t - 1) layers in N_r x N_t MIMO systems. At the receiver, the iterative decoding is performed. The extrinsic information provided by the soft-in/soft-out (SISO) decoder is applied as an improved priori information after the B-STC decoding at the next iteration. Since a priori information can be extracted from multiple layers independently by the B-STC scheme, codeword bits have an improved diversity gain of (N_t - 1). In order to verify the proposed scheme, we derive the asymptotic bit error probability, which can be achieved after convergence of the iterative decoder. Because the proposed B-STC scheme is a binary code for coded MIMO systems, different types of channel codes and various space-time codes can be also concatenated.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we introduce a bit-interleaved binary space-time code (B-STC) for a coded multiple-input multiple-output (MIMO) system to obtain an additional diversity gain over the full-rate spatial multiplexing (SM) transmission. By applying the B-STC scheme, codeword bits from each stream are transmitted effectively through N_t or (N_t - 1) layers in N_r x N_t MIMO systems. At the receiver, the iterative decoding is performed. The extrinsic information provided by the soft-in/soft-out (SISO) decoder is applied as an improved priori information after the B-STC decoding at the next iteration. Since a priori information can be extracted from multiple layers independently by the B-STC scheme, codeword bits have an improved diversity gain of (N_t - 1). In order to verify the proposed scheme, we derive the asymptotic bit error probability, which can be achieved after convergence of the iterative decoder. Because the proposed B-STC scheme is a binary code for coded MIMO systems, different types of channel codes and various space-time codes can be also concatenated. Close doi:10.1109/TWC.2013.093013.130107 Close
45.	B. Chun; H. Park A Spatial-Domain Joint-Nulling Method of Self-Interference in Full-Duplex Relays Journal Article IEEE Communications Letters, 16 (4), pp. 436-438, 2012, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN53, title = {A Spatial-Domain Joint-Nulling Method of Self-Interference in Full-Duplex Relays}, author = {B. Chun and H. Park}, doi = {10.1109/LCOMM.2012.020712.111733}, issn = {1089-7798}, year = {2012}, date = {2012-01-01}, journal = {IEEE Communications Letters}, volume = {16}, number = {4}, pages = {436-438}, abstract = {In this letter, a spatial-domain joint-nulling method is proposed as a new means of suppressing the self-interference (or echo) occurring in full-duplex relays. Both amplify-and-forward (AF) and decode-and-forward (DF) type relays are considered. While the conventional method searches for the relay processing matrix from a discrete set of basis vectors obtained from the singular value decomposition (SVD) of the echo channel, the proposed method directly solves the optimal relay processing matrix over a continuous domain. As a result, it is shown that the proposed approach gives better performance than the conventional one in terms of the achievable rate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, a spatial-domain joint-nulling method is proposed as a new means of suppressing the self-interference (or echo) occurring in full-duplex relays. Both amplify-and-forward (AF) and decode-and-forward (DF) type relays are considered. While the conventional method searches for the relay processing matrix from a discrete set of basis vectors obtained from the singular value decomposition (SVD) of the echo channel, the proposed method directly solves the optimal relay processing matrix over a continuous domain. As a result, it is shown that the proposed approach gives better performance than the conventional one in terms of the achievable rate. Close doi:10.1109/LCOMM.2012.020712.111733 Close
44.	K. Kim; H. Park; H. M. Kwon Optimum Clustered Pilot Sequence for OFDM Systems under Rapidly Time-Varying Channel Journal Article IEEE Transactions on Communications, 60 (5), pp. 1357-1370, 2012, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN54, title = {Optimum Clustered Pilot Sequence for OFDM Systems under Rapidly Time-Varying Channel}, author = {K. Kim and H. Park and H. M. Kwon}, doi = {10.1109/TCOMM.2012.032012.100508}, issn = {0090-6778}, year = {2012}, date = {2012-01-01}, journal = {IEEE Transactions on Communications}, volume = {60}, number = {5}, pages = {1357-1370}, abstract = {As channel time-variation increases, orthogonality among subcarriers in an orthogonal frequency division multiplexing (OFDM) symbol can be destroyed because of the relatively long symbol period, whereupon intercarrier interference (ICI) appears, and hence an irreducible error floor occurs. It was shown recently that grouping pilot tones into a number of equally spaced clusters can yield better channel estimation against the doubly selective channel than placing each pilot tone in an equally spaced manner. However, a random pilot sequence was used in the literature, and an optimal sequence has not yet been studied. This paper presents how to optimize the clustered pilot sequence. First, this paper (a) proves the existence of an optimum pilot sequence and (b) suggests a guideline for finding an optimum sequence. Second, this paper shows that an optimum sequence is independent of the signal-to-noise ratio and Doppler rate, and the sequence is generally optimum for any channels. Third, this paper verifies through analysis and simulation that the coded-OFDM system with an optimized cluster pilot sequence can yield a smaller mean square channel estimation error and lower bit error rate than the system with an equidistance pilot or a random cluster pilot under a rapidly time-varying channel.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close As channel time-variation increases, orthogonality among subcarriers in an orthogonal frequency division multiplexing (OFDM) symbol can be destroyed because of the relatively long symbol period, whereupon intercarrier interference (ICI) appears, and hence an irreducible error floor occurs. It was shown recently that grouping pilot tones into a number of equally spaced clusters can yield better channel estimation against the doubly selective channel than placing each pilot tone in an equally spaced manner. However, a random pilot sequence was used in the literature, and an optimal sequence has not yet been studied. This paper presents how to optimize the clustered pilot sequence. First, this paper (a) proves the existence of an optimum pilot sequence and (b) suggests a guideline for finding an optimum sequence. Second, this paper shows that an optimum sequence is independent of the signal-to-noise ratio and Doppler rate, and the sequence is generally optimum for any channels. Third, this paper verifies through analysis and simulation that the coded-OFDM system with an optimized cluster pilot sequence can yield a smaller mean square channel estimation error and lower bit error rate than the system with an equidistance pilot or a random cluster pilot under a rapidly time-varying channel. Close doi:10.1109/TCOMM.2012.032012.100508 Close
43.	B. Song; N. Kim; H. Park A Binary Space-Time Code for MIMO Systems Journal Article IEEE Transactions on Wireless Communications, 11 (4), pp. 1350-1357, 2012, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN52, title = {A Binary Space-Time Code for MIMO Systems}, author = {B. Song and N. Kim and H. Park}, doi = {10.1109/TWC.2012.021412.101510}, issn = {1536-1276}, year = {2012}, date = {2012-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {11}, number = {4}, pages = {1350-1357}, abstract = {In this paper, we introduce a simple bit-interleaved binary space-time code (B-STC) for a coded multi-input multi-output (MIMO) system to obtain an increase in information rate, where two transmit and two receive antennas are used. We derive a probability density function (pdf) of log-likelihood ratio (LLR) for the B-STC decoder output and approximate it with the pdf of MIMO detector output having the degraded SNR. The average bit error probability at the i-th iteration is represented in terms of moment generating function with differently distributed SNRs. Although the iterative decoder in the B-STC structure increases the computational complexity, the number of iterations i is not large (i≤3). Because the proposed B-STC scheme is a binary code for MIMO systems, different types of channel codes and various space-time codes can be concatenated. To achieve near-capacity performance on MIMO channels, an iterative receiver structure with a soft interference cancellation scheme can be also adopted as an outer iteration. And the proposed scheme can be extended to arbitrary number of transmit and receive antennas.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we introduce a simple bit-interleaved binary space-time code (B-STC) for a coded multi-input multi-output (MIMO) system to obtain an increase in information rate, where two transmit and two receive antennas are used. We derive a probability density function (pdf) of log-likelihood ratio (LLR) for the B-STC decoder output and approximate it with the pdf of MIMO detector output having the degraded SNR. The average bit error probability at the i-th iteration is represented in terms of moment generating function with differently distributed SNRs. Although the iterative decoder in the B-STC structure increases the computational complexity, the number of iterations i is not large (i≤3). Because the proposed B-STC scheme is a binary code for MIMO systems, different types of channel codes and various space-time codes can be concatenated. To achieve near-capacity performance on MIMO channels, an iterative receiver structure with a soft interference cancellation scheme can be also adopted as an outer iteration. And the proposed scheme can be extended to arbitrary number of transmit and receive antennas. Close doi:10.1109/TWC.2012.021412.101510 Close
42.	Haelyong Kim; Wan Choi; Hyuncheol Park The Effects of Spatial Correlation on Multiple Antenna Techniques with Multiuser Scheduling Journal Article IEICE Transactions on Communications, E94.B (2), pp. 591-594, 2011. Abstract \| Links \| BibTeX @article{RN47, title = {The Effects of Spatial Correlation on Multiple Antenna Techniques with Multiuser Scheduling}, author = {Haelyong Kim and Wan Choi and Hyuncheol Park}, doi = {10.1587/transcom.E94.B.591}, year = {2011}, date = {2011-01-01}, journal = {IEICE Transactions on Communications}, volume = {E94.B}, number = {2}, pages = {591-594}, abstract = {This letter investigates the effects of spatial correlation on several multiple antenna schemes in multiuser environments. Using an order statistics upper bound on achievable capacity, we quantify the interaction among spatial correlation, spatial diversity, spatial multiplexing and multiuser diversity. Also, it is verified that the upper bound is tighter than asymptotic capacity when the number of users is relatively small.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This letter investigates the effects of spatial correlation on several multiple antenna schemes in multiuser environments. Using an order statistics upper bound on achievable capacity, we quantify the interaction among spatial correlation, spatial diversity, spatial multiplexing and multiuser diversity. Also, it is verified that the upper bound is tighter than asymptotic capacity when the number of users is relatively small. Close doi:10.1587/transcom.E94.B.591 Close
41.	K. Kim; H. Park; H. M. Kwon Rate-Compatible SFBC-OFDM under Rapidly Time-Varying Channels Journal Article IEEE Transactions on Communications, 59 (8), pp. 2070-2077, 2011, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN51, title = {Rate-Compatible SFBC-OFDM under Rapidly Time-Varying Channels}, author = {K. Kim and H. Park and H. M. Kwon}, doi = {10.1109/TCOMM.2011.053111.090181}, issn = {0090-6778}, year = {2011}, date = {2011-01-01}, journal = {IEEE Transactions on Communications}, volume = {59}, number = {8}, pages = {2070-2077}, abstract = {An inter-carrier interference (ICI) occurs in an orthogonal frequency division multiplexing (OFDM) system when a channel is rapidly time-varying. The proposed scheme employs a polynomial cancellation code (PCC) to suppress this ICI, and uses a linear complex field (LCF) code as a transmit-diversity technique to make the transmission rate compatible up to n_{T} / (n_{T}+1), where n_{T} is the number of transmit antennas used. The conventional orthogonal code (OC), such as the Alamouti code, with accompanying PCC cannot achieve this rate. Both analysis and simulation results verify that the proposed scheme can achieve higher channel capacity as well as lower bit error rate (BER) than the other schemes in rapidly time-varying channels, even with a linear receiver and inaccurate channel estimation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close An inter-carrier interference (ICI) occurs in an orthogonal frequency division multiplexing (OFDM) system when a channel is rapidly time-varying. The proposed scheme employs a polynomial cancellation code (PCC) to suppress this ICI, and uses a linear complex field (LCF) code as a transmit-diversity technique to make the transmission rate compatible up to n_T / (n_T+1), where n_T is the number of transmit antennas used. The conventional orthogonal code (OC), such as the Alamouti code, with accompanying PCC cannot achieve this rate. Both analysis and simulation results verify that the proposed scheme can achieve higher channel capacity as well as lower bit error rate (BER) than the other schemes in rapidly time-varying channels, even with a linear receiver and inaccurate channel estimation. Close doi:10.1109/TCOMM.2011.053111.090181 Close
40.	S. Kim; J. Heo; H. Park Improved Stopping Set Elimination by Parity-Check Matrix Extension of LDPC Codes Journal Article IEEE Communications Letters, 15 (5), pp. 557-559, 2011, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN49, title = {Improved Stopping Set Elimination by Parity-Check Matrix Extension of LDPC Codes}, author = {S. Kim and J. Heo and H. Park}, doi = {10.1109/LCOMM.2011.032811.102095}, issn = {1089-7798}, year = {2011}, date = {2011-01-01}, journal = {IEEE Communications Letters}, volume = {15}, number = {5}, pages = {557-559}, abstract = {Stopping sets associated with a parity-check matrix of low-density parity-check codes limit the performance of iterative decoding over the binary erasure channel. In this letter, we propose a parity-check matrix extension scheme that eliminates stopping sets of small sizes. The results show that our proposed scheme provides significant performance improvement compared to previously known parity-check matrix extension schemes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Stopping sets associated with a parity-check matrix of low-density parity-check codes limit the performance of iterative decoding over the binary erasure channel. In this letter, we propose a parity-check matrix extension scheme that eliminates stopping sets of small sizes. The results show that our proposed scheme provides significant performance improvement compared to previously known parity-check matrix extension schemes. Close doi:10.1109/LCOMM.2011.032811.102095 Close
39.	K. Lee; H. Park Modulations for Visible Light Communications With Dimming Control Journal Article IEEE Photonics Technology Letters, 23 (16), pp. 1136-1138, 2011, ISSN: 1041-1135. Abstract \| Links \| BibTeX @article{RN50, title = {Modulations for Visible Light Communications With Dimming Control}, author = {K. Lee and H. Park}, doi = {10.1109/LPT.2011.2157676}, issn = {1041-1135}, year = {2011}, date = {2011-01-01}, journal = {IEEE Photonics Technology Letters}, volume = {23}, number = {16}, pages = {1136-1138}, abstract = {Visible light communication (VLC) uses solid-state lightings to transmit information; therefore, it is necessary that modulation schemes for VLC provide dimming control. In this letter, we propose a multiple pulse position modulation (MPPM) to offer both functions of modulating data-stream and controlling the brightness at the same time. According to the dimming level, we control the number of pulses of MPPM in one symbol duration. We analyze communication performance in terms of the normalized power requirement and spectral efficiency. From our studies, we show that MPPM is superior to variable on-off keying (VOOK) and variable pulse position modulation (VPPM) proposed in the IEEE 802.15 VLC task group.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Visible light communication (VLC) uses solid-state lightings to transmit information; therefore, it is necessary that modulation schemes for VLC provide dimming control. In this letter, we propose a multiple pulse position modulation (MPPM) to offer both functions of modulating data-stream and controlling the brightness at the same time. According to the dimming level, we control the number of pulses of MPPM in one symbol duration. We analyze communication performance in terms of the normalized power requirement and spectral efficiency. From our studies, we show that MPPM is superior to variable on-off keying (VOOK) and variable pulse position modulation (VPPM) proposed in the IEEE 802.15 VLC task group. Close doi:10.1109/LPT.2011.2157676 Close
38.	K. Lee; H. Park; J. R. Barry Indoor Channel Characteristics for Visible Light Communications Journal Article IEEE Communications Letters, 15 (2), pp. 217-219, 2011, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN46, title = {Indoor Channel Characteristics for Visible Light Communications}, author = {K. Lee and H. Park and J. R. Barry}, doi = {10.1109/LCOMM.2011.010411.101945}, issn = {1089-7798}, year = {2011}, date = {2011-01-01}, journal = {IEEE Communications Letters}, volume = {15}, number = {2}, pages = {217-219}, abstract = {In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectance of indoor reflectors. We perform a computer simulation to compare the power delay profile of the VLC with that of infrared communications. From our studies, we show that the VLC provides a larger transmission bandwidth than infrared communications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectance of indoor reflectors. We perform a computer simulation to compare the power delay profile of the VLC with that of infrared communications. From our studies, we show that the VLC provides a larger transmission bandwidth than infrared communications. Close doi:10.1109/LCOMM.2011.010411.101945 Close
37.	C. Shin; H. Kim; K. J. Kim; H. Park High-Throughput Low-Complexity Link Adaptation for MIMO BIC-OFDM Systems Journal Article IEEE Transactions on Communications, 59 (4), pp. 1078-1088, 2011, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN48, title = {High-Throughput Low-Complexity Link Adaptation for MIMO BIC-OFDM Systems}, author = {C. Shin and H. Kim and K. J. Kim and H. Park}, doi = {10.1109/TCOMM.2011.012711.100141}, issn = {0090-6778}, year = {2011}, date = {2011-01-01}, journal = {IEEE Transactions on Communications}, volume = {59}, number = {4}, pages = {1078-1088}, abstract = {This paper introduces a new link adaptation (LA) approach called the adaptive modulation, coding, and spatial mode (AMCS) scheme for multiple-input multiple-output bit-interleaved coded orthogonal frequency division multiplexing (MIMO BIC-OFDM) systems. The AMCS technique can provide both minimal performance degradation and significant throughput gain by controlling the spatial streams. With this technique, we can derive a simple and accurate closed-form expression of an instantaneous bit error rate (I-BER). Based on the I-BER, the proposed AMCS scheme chooses an appropriate modulation, coding, and spatial mode (MCS) type that improves the system performance while satisfying the quality of service (QoS) requirement. A simplified MCS type search method is also proposed, which allows the receiver to effectively select a MCS type and then send it back to the transmitter by using only a small amount of information bits. The simulation results confirm the superiority of the proposed AMCS approach over conventional LA schemes in trading high-throughput for reduced complexity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper introduces a new link adaptation (LA) approach called the adaptive modulation, coding, and spatial mode (AMCS) scheme for multiple-input multiple-output bit-interleaved coded orthogonal frequency division multiplexing (MIMO BIC-OFDM) systems. The AMCS technique can provide both minimal performance degradation and significant throughput gain by controlling the spatial streams. With this technique, we can derive a simple and accurate closed-form expression of an instantaneous bit error rate (I-BER). Based on the I-BER, the proposed AMCS scheme chooses an appropriate modulation, coding, and spatial mode (MCS) type that improves the system performance while satisfying the quality of service (QoS) requirement. A simplified MCS type search method is also proposed, which allows the receiver to effectively select a MCS type and then send it back to the transmitter by using only a small amount of information bits. The simulation results confirm the superiority of the proposed AMCS approach over conventional LA schemes in trading high-throughput for reduced complexity. Close doi:10.1109/TCOMM.2011.012711.100141 Close
36.	H. Kim; N. Kim; W. Choi; H. Park Performance of Multiuser Transmit Diversity in Spatially Correlated Channels Journal Article IEEE Communications Letters, 14 (9), pp. 824-826, 2010, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN45, title = {Performance of Multiuser Transmit Diversity in Spatially Correlated Channels}, author = {H. Kim and N. Kim and W. Choi and H. Park}, doi = {10.1109/LCOMM.2010.080410.100909}, issn = {1089-7798}, year = {2010}, date = {2010-01-01}, journal = {IEEE Communications Letters}, volume = {14}, number = {9}, pages = {824-826}, abstract = {This paper investigates the performance of an Alamouti coding based transmit diversity scheme with multiuser max-scheduling in spatially correlated channels. An exact closed form of ergodic capacity is derived, and bit error rate (BER) analysis is performed with a log likelihood radio (LLR) approach for two transmit antennas case. Our analytical and numerical results verify a positive effect of spatial correlation on multiuser diversity in terms of ergodic capacity. We show, however, that spatial correlation is beneficial in terms of BER until a certain signal-to-noise ratio (SNR) level while it hurts BER as SNR increases compared with ergodic capacity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper investigates the performance of an Alamouti coding based transmit diversity scheme with multiuser max-scheduling in spatially correlated channels. An exact closed form of ergodic capacity is derived, and bit error rate (BER) analysis is performed with a log likelihood radio (LLR) approach for two transmit antennas case. Our analytical and numerical results verify a positive effect of spatial correlation on multiuser diversity in terms of ergodic capacity. We show, however, that spatial correlation is beneficial in terms of BER until a certain signal-to-noise ratio (SNR) level while it hurts BER as SNR increases compared with ergodic capacity. Close doi:10.1109/LCOMM.2010.080410.100909 Close
35.	H. Lee; Y. Lee; H. Park An efficient CP compensation for SC-FDE with insufficient CP symbols Journal Article IEEE Communications Letters, 14 (6), pp. 548-550, 2010, ISSN: 1089-7798. Abstract \| Links \| BibTeX @article{RN43, title = {An efficient CP compensation for SC-FDE with insufficient CP symbols}, author = {H. Lee and Y. Lee and H. Park}, doi = {10.1109/LCOMM.2010.06.092435}, issn = {1089-7798}, year = {2010}, date = {2010-01-01}, journal = {IEEE Communications Letters}, volume = {14}, number = {6}, pages = {548-550}, abstract = {In this letter, we propose a method to mitigate interferences for single carrier frequency domain equalization (SC-FDE) with insufficient cyclic prefix (CP) symbols. The resultant channel matrices are not circulant due to some missing symbols. Unlike OFDM, however, the reconstruction of missing symbols using the estimated symbols is not effective. We propose that these missing symbols may be filled with the symbols in the following received block when the channel is static over the consecutive blocks. Since this method does not require estimation of symbols, the precision of detection can be enhanced. The improvement in the performance of this method is still limited since interferences are not completely removed. An iterative interference cancellation method is used to remove the residual interferences. The performance of proposed method is verified by simulations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we propose a method to mitigate interferences for single carrier frequency domain equalization (SC-FDE) with insufficient cyclic prefix (CP) symbols. The resultant channel matrices are not circulant due to some missing symbols. Unlike OFDM, however, the reconstruction of missing symbols using the estimated symbols is not effective. We propose that these missing symbols may be filled with the symbols in the following received block when the channel is static over the consecutive blocks. Since this method does not require estimation of symbols, the precision of detection can be enhanced. The improvement in the performance of this method is still limited since interferences are not completely removed. An iterative interference cancellation method is used to remove the residual interferences. The performance of proposed method is verified by simulations. Close doi:10.1109/LCOMM.2010.06.092435 Close
34.	Y. Lee; N. Kim; H. Park Performance of MC-CDM Systems With MMSEC Over Rayleigh Fading Channels Journal Article IEEE Transactions on Vehicular Technology, 59 (6), pp. 3126-3130, 2010, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN44, title = {Performance of MC-CDM Systems With MMSEC Over Rayleigh Fading Channels}, author = {Y. Lee and N. Kim and H. Park}, doi = {10.1109/TVT.2010.2046506}, issn = {0018-9545}, year = {2010}, date = {2010-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {59}, number = {6}, pages = {3126-3130}, abstract = {In this paper, we investigate the performance of multicarrier code-division multiplexing (MC-CDM) systems with minimum mean square error combining (MMSEC) over a Rayleigh fading channel. An approximated expression on the symbol error rate (SER) for MMSEC is derived. The approximated expression provides an accurate approximation of the true SER, particularly for systems with higher modulation and a small spreading factor. Through the derived error performances, we also calculate the achievable diversity order. MC-CDM systems with MMSEC achieve the same asymptotical diversity order of 1, regardless of the spreading factor. Within practical signal-to-noise ratio (SNR) ranges, the effective diversity order is further increased as a larger spreading factor is used. The derived analytical expressions are verified by numerical and simulation results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we investigate the performance of multicarrier code-division multiplexing (MC-CDM) systems with minimum mean square error combining (MMSEC) over a Rayleigh fading channel. An approximated expression on the symbol error rate (SER) for MMSEC is derived. The approximated expression provides an accurate approximation of the true SER, particularly for systems with higher modulation and a small spreading factor. Through the derived error performances, we also calculate the achievable diversity order. MC-CDM systems with MMSEC achieve the same asymptotical diversity order of 1, regardless of the spreading factor. Within practical signal-to-noise ratio (SNR) ranges, the effective diversity order is further increased as a larger spreading factor is used. The derived analytical expressions are verified by numerical and simulation results. Close doi:10.1109/TVT.2010.2046506 Close
33.	N. Kim; H. Park Bit error performance of convolutional coded MIMO system with linear MMSE receiver Journal Article IEEE Transactions on Wireless Communications, 8 (7), pp. 3420-3424, 2009, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN42, title = {Bit error performance of convolutional coded MIMO system with linear MMSE receiver}, author = {N. Kim and H. Park}, doi = {10.1109/TWC.2009.080938}, issn = {1536-1276}, year = {2009}, date = {2009-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {8}, number = {7}, pages = {3420-3424}, abstract = {In this letter, we introduce an analytical expression to the coded bit error rate (BER) of a MIMO system with a linear minimum mean square error (MMSE) receiver. We derive the moment generating function (MGF) of the SINR for arbitrary antenna configurations from the cumulative density function of SINR.We show that the moment generating function of the SINR at the MMSE detector output can be used to estimate the BER performance of a coded MIMO system. The analysis is simple and gives an accurate BER estimation at a high SNR. Based on the analytical and simulated results, the diversity order is dependent on the antenna configuration and the free distance of the convolutional code. Finally, we compare the analytical expression with simulated results for validation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we introduce an analytical expression to the coded bit error rate (BER) of a MIMO system with a linear minimum mean square error (MMSE) receiver. We derive the moment generating function (MGF) of the SINR for arbitrary antenna configurations from the cumulative density function of SINR.We show that the moment generating function of the SINR at the MMSE detector output can be used to estimate the BER performance of a coded MIMO system. The analysis is simple and gives an accurate BER estimation at a high SNR. Based on the analytical and simulated results, the diversity order is dependent on the antenna configuration and the free distance of the convolutional code. Finally, we compare the analytical expression with simulated results for validation. Close doi:10.1109/TWC.2009.080938 Close
32.	Yusung Lee; Namshik Kim; Hyuncheol Park BER Performance of Downlink MC-CDMA with ORC in Nakagami-m Fading Channel Journal Article IEICE Transactions on Communications, E92.B (4), pp. 1349-1352, 2009. Abstract \| Links \| BibTeX @article{RN41, title = {BER Performance of Downlink MC-CDMA with ORC in Nakagami-\textit{m} Fading Channel}, author = {Yusung Lee and Namshik Kim and Hyuncheol Park}, doi = {10.1587/transcom.E92.B.1349}, year = {2009}, date = {2009-01-01}, journal = {IEICE Transactions on Communications}, volume = {E92.B}, number = {4}, pages = {1349-1352}, abstract = {In this letter, we derive an exact bit error rate (BER) expression for downlink multi-carrier code division multiple access (MC-CDMA) systems with orthogonal restoring combining (ORC) in Nakagami-m fading channel. A simple approximated expression is also provided. For uncoded and coded MC-CDMA systems, the BER expressions are calculated based on the moment generating function (MGF) of the combined fading random variable. The derived analytic expressions are verified by simulation results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we derive an exact bit error rate (BER) expression for downlink multi-carrier code division multiple access (MC-CDMA) systems with orthogonal restoring combining (ORC) in Nakagami-m fading channel. A simple approximated expression is also provided. For uncoded and coded MC-CDMA systems, the BER expressions are calculated based on the moment generating function (MGF) of the combined fading random variable. The derived analytic expressions are verified by simulation results. Close doi:10.1587/transcom.E92.B.1349 Close
31.	Y. Lee; H. Park A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem Journal Article IEEE Transactions on Vehicular Technology, 58 (1), pp. 198-206, 2009, ISSN: 0018-9545. Abstract \| Links \| BibTeX @article{RN39, title = {A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem}, author = {Y. Lee and H. Park}, doi = {10.1109/TVT.2008.925001}, issn = {0018-9545}, year = {2009}, date = {2009-01-01}, journal = {IEEE Transactions on Vehicular Technology}, volume = {58}, number = {1}, pages = {198-206}, abstract = {In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword. Close doi:10.1109/TVT.2008.925001 Close
30.	J. Park; Y. Lee; H. Park Preamble design for joint estimation of CFO and I/Q imbalance for direct conversion OFDM system Journal Article IET Communications, 3 (4), pp. 597-602, 2009, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN40, title = {Preamble design for joint estimation of CFO and I/Q imbalance for direct conversion OFDM system}, author = {J. Park and Y. Lee and H. Park}, doi = {10.1049/iet-com.2008.0249}, issn = {1751-8628}, year = {2009}, date = {2009-01-01}, journal = {IET Communications}, volume = {3}, number = {4}, pages = {597-602}, abstract = {This paper proposes a preamble structure for joint estimation of carrier frequency offset (CFO) and I/Q imbalance. Because existing methods cannot guarantee correct solutions within all range of CFOs, we derive two constraints of phase rotations applied to repetition patterns. By using the preamble based on the presented constraints, CFO is optimally estimated, and I/Q imbalance estimation is possible in all ranges of CFO with low complexity. Numerical results verify the importance and necessity of these constraints for joint estimation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper proposes a preamble structure for joint estimation of carrier frequency offset (CFO) and I/Q imbalance. Because existing methods cannot guarantee correct solutions within all range of CFOs, we derive two constraints of phase rotations applied to repetition patterns. By using the preamble based on the presented constraints, CFO is optimally estimated, and I/Q imbalance estimation is possible in all ranges of CFO with low complexity. Numerical results verify the importance and necessity of these constraints for joint estimation. Close doi:10.1049/iet-com.2008.0249 Close
29.	Jongsub Cha; Kyungho Park; Joonhyuk Kang; Hyuncheol Park Low Complexity Tree Searching-Based Iterative Precoding Techniques for Multiuser MIMO Broadcast Channel Journal Article IEICE Transactions on Communications, E91.B (6), pp. 2045-2048, 2008. Abstract \| Links \| BibTeX @article{RN35, title = {Low Complexity Tree Searching-Based Iterative Precoding Techniques for Multiuser MIMO Broadcast Channel}, author = {Jongsub Cha and Kyungho Park and Joonhyuk Kang and Hyuncheol Park}, doi = {10.1093/ietcom/e91-b.6.2045}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {6}, pages = {2045-2048}, abstract = {In this letter, we propose two computationally efficient precoding algorithms that achieve near-ML performance for multiuser MIMO downlink. The proposed algorithms perform tree expansion after lattice reduction. The first full expansion is tried by selecting the first level node with a minimum metric, constituting a reference metric. To find an optimal sequence, they iteratively visit each node and terminate the expansion by comparing node metrics with the calculated reference metric. By doing this, they significantly reduce the number of undesirable node visit. Monte-Carlo simulations show that both proposed algorithms yield near-ML performance with considerable reduction in complexity compared with that of the conventional schemes such as sphere encoding.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this letter, we propose two computationally efficient precoding algorithms that achieve near-ML performance for multiuser MIMO downlink. The proposed algorithms perform tree expansion after lattice reduction. The first full expansion is tried by selecting the first level node with a minimum metric, constituting a reference metric. To find an optimal sequence, they iteratively visit each node and terminate the expansion by comparing node metrics with the calculated reference metric. By doing this, they significantly reduce the number of undesirable node visit. Monte-Carlo simulations show that both proposed algorithms yield near-ML performance with considerable reduction in complexity compared with that of the conventional schemes such as sphere encoding. Close doi:10.1093/ietcom/e91-b.6.2045 Close
28.	Sooyoung Hur; Namshik Kim; Hyuncheol Park; Joonhyuk Kang Enhanced Lattice-Reduction Precoding Using List Quantizer for Multi-Antenna Multi-User Communication Journal Article IEICE Transactions on Communications, E91.B (1), pp. 351-354, 2008. Abstract \| Links \| BibTeX @article{RN30, title = {Enhanced Lattice-Reduction Precoding Using List Quantizer for Multi-Antenna Multi-User Communication}, author = {Sooyoung Hur and Namshik Kim and Hyuncheol Park and Joonhyuk Kang}, doi = {10.1093/ietcom/e91-b.1.351}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {1}, pages = {351-354}, abstract = {Based on an analysis of the error patterns in lattice-reduction (LR) precoding in a multiple-antenna broadcast channel, this paper proposes a simple precoding technique that can reduce the quantization error. The proposed scheme establishes a lattice list to provide more can-didates for transmission power reduction based on the analysis of the patterns of the error in the LR precoding method [9]. Simulation results show that the proposed scheme matches the BER performance of more complex precedents (such as the vector perturbation using sphere encoding) with significant saving in complexity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Based on an analysis of the error patterns in lattice-reduction (LR) precoding in a multiple-antenna broadcast channel, this paper proposes a simple precoding technique that can reduce the quantization error. The proposed scheme establishes a lattice list to provide more can-didates for transmission power reduction based on the analysis of the patterns of the error in the LR precoding method [9]. Simulation results show that the proposed scheme matches the BER performance of more complex precedents (such as the vector perturbation using sphere encoding) with significant saving in complexity. Close doi:10.1093/ietcom/e91-b.1.351 Close
27.	H. Kim; H. Park Approaching maximum-likelihood performance with reduced complexity for a double space-time transmit diversity system Journal Article IET Communications, 2 (5), pp. 682-689, 2008, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN34, title = {Approaching maximum-likelihood performance with reduced complexity for a double space-time transmit diversity system}, author = {H. Kim and H. Park}, doi = {10.1049/iet-com:20070305}, issn = {1751-8628}, year = {2008}, date = {2008-01-01}, journal = {IET Communications}, volume = {2}, number = {5}, pages = {682-689}, abstract = {A reduced-complexity detector approaching maximum-likelihood (ML) detection performance is presented for the double space-time transmit diversity system. The proposed scheme exploits both the special structure of equivalent channel matrix and decision-feedback detection. This accounts for accomplishing near-ML or ML performance with significantly relieved computational loads. Moreover, to moderate the average complexity, several distance metric selection criteria are proposed. We can control performance and computational savings according to different distance metric selection rules. Numerical results show that the proposed detector requires significantly fewer computations than that of the Schnorr-Euchner sphere-decoding algorithm in terms of both the worst-case and the average complexity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A reduced-complexity detector approaching maximum-likelihood (ML) detection performance is presented for the double space-time transmit diversity system. The proposed scheme exploits both the special structure of equivalent channel matrix and decision-feedback detection. This accounts for accomplishing near-ML or ML performance with significantly relieved computational loads. Moreover, to moderate the average complexity, several distance metric selection criteria are proposed. We can control performance and computational savings according to different distance metric selection rules. Numerical results show that the proposed detector requires significantly fewer computations than that of the Schnorr-Euchner sphere-decoding algorithm in terms of both the worst-case and the average complexity. Close doi:10.1049/iet-com:20070305 Close
26.	Hyounkuk Kim; Hyuncheol Park An Efficient Maximum-Likelihood Detector for Four-Transmit-Antenna Quasi-Orthogonal Space-Time Block Code Journal Article IEICE Transactions on Communications, E91.B (2), pp. 666-668, 2008. Abstract \| Links \| BibTeX @article{RN32, title = {An Efficient Maximum-Likelihood Detector for Four-Transmit-Antenna Quasi-Orthogonal Space-Time Block Code}, author = {Hyounkuk Kim and Hyuncheol Park}, doi = {10.1093/ietcom/e91-b.2.666}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {2}, pages = {666-668}, abstract = {This letter deals with computationally efficient maximumlikelihood (ML) detection for the quasi-orthogonal space-time block code (QOSTBC) with four transmit antennas. The proposed ML detector uses a permutation based real-valued equivalent channel matrix representation. As a result, the complexity of ML detection problem is moderated from O(2\|A\|2) to O(4\|A\|), where \|A\| is modulation order. Numerical results show that the proposed ML detector provides ML performance and achieves greatly high computational savings.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This letter deals with computationally efficient maximumlikelihood (ML) detection for the quasi-orthogonal space-time block code (QOSTBC) with four transmit antennas. The proposed ML detector uses a permutation based real-valued equivalent channel matrix representation. As a result, the complexity of ML detection problem is moderated from O(2\|A\|2) to O(4\|A\|), where \|A\| is modulation order. Numerical results show that the proposed ML detector provides ML performance and achieves greatly high computational savings. Close doi:10.1093/ietcom/e91-b.2.666 Close
25.	Hyounkuk Kim; Hyuncheol Park Reduced-Complexity Near-ML Detector for a Coded DSTTD-OFDM System Journal Article IEICE Transactions on Communications, E91.B (11), pp. 3749-3752, 2008. Abstract \| Links \| BibTeX @article{RN37, title = {Reduced-Complexity Near-ML Detector for a Coded DSTTD-OFDM System}, author = {Hyounkuk Kim and Hyuncheol Park}, doi = {10.1093/ietcom/e91-b.11.3749}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {11}, pages = {3749-3752}, abstract = {This letter introduces an efficient near-maximum likelihood (ML) detector for a coded double space-time transmit diversity-orthogonal frequency division multiplexing (DSTTD-OFDM) system. The proposed near-ML detector constructs a candidate vector set through a relaxed minimization method. It reduces computational loads from $mathcalO(2\|mathcalA\|^2)$ to $mathcalO(\|mathcalA\|^2)$, where $\|mathcalA\|$ is the modulation order. Numerical results indicate that the proposed near-ML detector provides both almost ML performance and considerable complexity savings.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This letter introduces an efficient near-maximum likelihood (ML) detector for a coded double space-time transmit diversity-orthogonal frequency division multiplexing (DSTTD-OFDM) system. The proposed near-ML detector constructs a candidate vector set through a relaxed minimization method. It reduces computational loads from $mathcalO(2\|mathcalA\|^2)$ to $mathcalO(\|mathcalA\|^2)$, where $\|mathcalA\|$ is the modulation order. Numerical results indicate that the proposed near-ML detector provides both almost ML performance and considerable complexity savings. Close doi:10.1093/ietcom/e91-b.11.3749 Close
24.	Hyounkuk Kim; Hyuncheol Park Simplified Maximum-Likelihood Detection for a Coded DSTTD-OFDM System Journal Article IEICE Transactions on Communications, E91.B (3), pp. 959-962, 2008. Abstract \| Links \| BibTeX @article{RN33, title = {Simplified Maximum-Likelihood Detection for a Coded DSTTD-OFDM System}, author = {Hyounkuk Kim and Hyuncheol Park}, doi = {10.1093/ietcom/e91-b.3.959}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {3}, pages = {959-962}, abstract = {We present a low-complexity maximum likelihood (ML) detector for a coded double space-time transmit diversity-orthogonal frequency division multiplexing (DSTTD-OFDM) system. The proposed ML detector exploits properties of two permuted equivalent channel matrices and multiple decision-feedback (DF) detections. This can reduce computational efforts from O(\|A\|4) to O(2\|A\|2) with maintaining ML performance, where \|A\| is the modulation order. Numerical results shows that the proposed ML detector obtains ML performance and requires remarkably lower computational loads compared with the conventional ML detector.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We present a low-complexity maximum likelihood (ML) detector for a coded double space-time transmit diversity-orthogonal frequency division multiplexing (DSTTD-OFDM) system. The proposed ML detector exploits properties of two permuted equivalent channel matrices and multiple decision-feedback (DF) detections. This can reduce computational efforts from O(\|A\|4) to O(2\|A\|2) with maintaining ML performance, where \|A\| is the modulation order. Numerical results shows that the proposed ML detector obtains ML performance and requires remarkably lower computational loads compared with the conventional ML detector. Close doi:10.1093/ietcom/e91-b.3.959 Close
23.	N. Kim; Y. Lee; H. Park Performance Analysis of MIMO System with Linear MMSE Receiver Journal Article IEEE Transactions on Wireless Communications, 7 (11), pp. 4474-4478, 2008, ISSN: 1536-1276. Abstract \| Links \| BibTeX @article{RN38, title = {Performance Analysis of MIMO System with Linear MMSE Receiver}, author = {N. Kim and Y. Lee and H. Park}, doi = {10.1109/T-WC.2008.070785}, issn = {1536-1276}, year = {2008}, date = {2008-01-01}, journal = {IEEE Transactions on Wireless Communications}, volume = {7}, number = {11}, pages = {4474-4478}, abstract = {This paper considers the uncoded multiple-input multiple-output (MIMO) system with linear minimum mean square error (MMSE) detection under ideal fast fading. The distribution of SINR at the output of the MMSE detection is derived for a small number of transmit and receive antennas. We present new approximation for the Gaussian Q-function driven by numerical simulation. Based on the SINR distribution and new approximation for Q-function, we analyze the performance of linear MMSE detection under ideal fast fading environment. By comparing the analytical results and Monte Carlo simulated results, we validate the analytical results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers the uncoded multiple-input multiple-output (MIMO) system with linear minimum mean square error (MMSE) detection under ideal fast fading. The distribution of SINR at the output of the MMSE detection is derived for a small number of transmit and receive antennas. We present new approximation for the Gaussian Q-function driven by numerical simulation. Based on the SINR distribution and new approximation for Q-function, we analyze the performance of linear MMSE detection under ideal fast fading environment. By comparing the analytical results and Monte Carlo simulated results, we validate the analytical results. Close doi:10.1109/T-WC.2008.070785 Close
22.	N. Kim; H. Park Low-complexity iterative equalisation and decoding for wireless optical communications [optical wireless communications] Journal Article IET Communications, 2 (1), pp. 61-65, 2008, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN31, title = {Low-complexity iterative equalisation and decoding for wireless optical communications [optical wireless communications]}, author = {N. Kim and H. Park}, doi = {10.1049/iet-com:20060388}, issn = {1751-8628}, year = {2008}, date = {2008-01-01}, journal = {IET Communications}, volume = {2}, number = {1}, pages = {61-65}, abstract = {A low-complexity scheme of iterative equalisation and decoding by combining a recursive systematic convolutional code and a pulse-position modulation is proposed here. A graph- based equalisation for intersymbol interference (ISI) known at both transmitter and receiver is considered. By representing the memory channel with ISI as the factor graph and applying sum-product (SP) algorithm to this graph, a posteriori probability (APP) of the desired symbol necessary to implement iterative equalisation and decoding is derived. A partial response precoding is used to reduce the span of ISI from a possible infinite number of two baud periods. This precoding scheme makes the factor graph of memory channel cycle-free, and SP algorithm for combating ISI converges to an optimum detection. Numerical results show that the proposed low-complexity strategy has almost the same performance as the optimum turbo equalisation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A low-complexity scheme of iterative equalisation and decoding by combining a recursive systematic convolutional code and a pulse-position modulation is proposed here. A graph- based equalisation for intersymbol interference (ISI) known at both transmitter and receiver is considered. By representing the memory channel with ISI as the factor graph and applying sum-product (SP) algorithm to this graph, a posteriori probability (APP) of the desired symbol necessary to implement iterative equalisation and decoding is derived. A partial response precoding is used to reduce the span of ISI from a possible infinite number of two baud periods. This precoding scheme makes the factor graph of memory channel cycle-free, and SP algorithm for combating ISI converges to an optimum detection. Numerical results show that the proposed low-complexity strategy has almost the same performance as the optimum turbo equalisation. Close doi:10.1049/iet-com:20060388 Close
21.	Cheolkyu Shin; Hyounkuk Kim; Hyuncheol Park Improved Decision-Feedback Detection Schemes for STBC over Time-Selective Fading Channels Journal Article IEICE Transactions on Communications, E91.B (9), pp. 3013-3016, 2008. Abstract \| Links \| BibTeX @article{RN36, title = {Improved Decision-Feedback Detection Schemes for STBC over Time-Selective Fading Channels}, author = {Cheolkyu Shin and Hyounkuk Kim and Hyuncheol Park}, doi = {10.1093/ietcom/e91-b.9.3013}, year = {2008}, date = {2008-01-01}, journal = {IEICE Transactions on Communications}, volume = {E91.B}, number = {9}, pages = {3013-3016}, abstract = {This letter proposes two efficient decision-feedback (DF) detection schemes for space-time block code (STBC) over time-selective fading channels. The existing DF detection causes error propagation when the first symbol is not detected correctly. However, the proposed detection schemes provide two candidates according to a channel gain or an average log-likelihood ratio (LLR) based selection rule and choose a better candidate for the first symbol. Simulation results show that the proposed detection schemes reduce error propagation and yield significant signal-to-noise ratio (SNR) gain with moderate complexity, compared to the existing DF detection scheme.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This letter proposes two efficient decision-feedback (DF) detection schemes for space-time block code (STBC) over time-selective fading channels. The existing DF detection causes error propagation when the first symbol is not detected correctly. However, the proposed detection schemes provide two candidates according to a channel gain or an average log-likelihood ratio (LLR) based selection rule and choose a better candidate for the first symbol. Simulation results show that the proposed detection schemes reduce error propagation and yield significant signal-to-noise ratio (SNR) gain with moderate complexity, compared to the existing DF detection scheme. Close doi:10.1093/ietcom/e91-b.9.3013 Close
20.	KIM Hyounkuk; JEON Kihwan; KANG Joonhyuk A V-BLAST system using modulation set selection for reduced-complexity tree searching in the QRD-M algorithm Journal Article IEICE transactions on communications, 90 (12), pp. 3665-3669, 2007, ISSN: 1745-1345. Abstract \| BibTeX @article{RN29, title = {A V-BLAST system using modulation set selection for reduced-complexity tree searching in the QRD-M algorithm}, author = {KIM Hyounkuk and JEON Kihwan and KANG Joonhyuk}, issn = {1745-1345}, year = {2007}, date = {2007-01-01}, journal = {IEICE transactions on communications}, volume = {90}, number = {12}, pages = {3665-3669}, abstract = {This letter presents a new vertical Bell Labs layered space-time (V-BLAST) transmission scheme for developing low-complexity tree searching in the QRD-M algorithm. In the new V-BLAST system, we assign modulation scheme in ascending order from top to bottom tree branches. The modulation set to be assigned is decided by two criteria: minimum performance loss and maximum complexity reduction. We also propose an open-loop power allocation algorithm to surmount the performance loss. Numerical results show that the proposed V-BLAST transmission approach can significantly reduce the computational loads of the QRD-M algorithm with a slight performance degradation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This letter presents a new vertical Bell Labs layered space-time (V-BLAST) transmission scheme for developing low-complexity tree searching in the QRD-M algorithm. In the new V-BLAST system, we assign modulation scheme in ascending order from top to bottom tree branches. The modulation set to be assigned is decided by two criteria: minimum performance loss and maximum complexity reduction. We also propose an open-loop power allocation algorithm to surmount the performance loss. Numerical results show that the proposed V-BLAST transmission approach can significantly reduce the computational loads of the QRD-M algorithm with a slight performance degradation. Close
19.	Y. Kang; K. Kim; H. Park Efficient DFT-based channel estimation for OFDM systems on multipath channels Journal Article IET Communications, 1 (2), pp. 197-202, 2007, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN27, title = {Efficient DFT-based channel estimation for OFDM systems on multipath channels}, author = {Y. Kang and K. Kim and H. Park}, doi = {10.1049/iet-com:20050337}, issn = {1751-8628}, year = {2007}, date = {2007-01-01}, journal = {IET Communications}, volume = {1}, number = {2}, pages = {197-202}, abstract = {An improved discrete Fourier transform (DFT)-based channel estimation for orthogonal frequency division multiplexing systems is proposed. Conventional DFT-based channel estimations improve the performance by suppressing time domain noise. However, they potentially require information on channel impulse responses and may also result in mean-square error (MSE) floor due to incorrect channel information such as channel delay spread. In contrast, our purposed channel estimation can improve the performance by deciding significant channel taps adaptively without requiring any channel statistical information. Significant channel taps are detected on the basis of a predetermined threshold. The optimal threshold to reduce the MSE of the estimation is also derived, and it is confirmed by computer simulation. Simulation results demonstrate that the proposed algorithm can improve the MSE performance ~6.5 dB compared with the conventional DFT-based estimation, and the MSE floor is not observed in any channels.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close An improved discrete Fourier transform (DFT)-based channel estimation for orthogonal frequency division multiplexing systems is proposed. Conventional DFT-based channel estimations improve the performance by suppressing time domain noise. However, they potentially require information on channel impulse responses and may also result in mean-square error (MSE) floor due to incorrect channel information such as channel delay spread. In contrast, our purposed channel estimation can improve the performance by deciding significant channel taps adaptively without requiring any channel statistical information. Significant channel taps are detected on the basis of a predetermined threshold. The optimal threshold to reduce the MSE of the estimation is also derived, and it is confirmed by computer simulation. Simulation results demonstrate that the proposed algorithm can improve the MSE performance ~6.5 dB compared with the conventional DFT-based estimation, and the MSE floor is not observed in any channels. Close doi:10.1049/iet-com:20050337 Close
18.	J. Kim; J. Kim; H. Park; B. Kim; S. Park Modified enhanced max-log-maximum a posteriori algorithm using variable scaling factor Journal Article IET Communications, 1 (5), pp. 1061-1066, 2007, ISSN: 1751-8628. Abstract \| Links \| BibTeX @article{RN28, title = {Modified enhanced max-log-maximum a posteriori algorithm using variable scaling factor}, author = {J. Kim and J. Kim and H. Park and B. Kim and S. Park}, doi = {10.1049/iet-com:20060632}, issn = {1751-8628}, year = {2007}, date = {2007-01-01}, journal = {IET Communications}, volume = {1}, number = {5}, pages = {1061-1066}, abstract = {Using a variable scaling factor (VSF), a modified enhanced max-log-maximum a posteriori (EMLMAP) algorithm is proposed to improve the performance of the conventional EMLMAP algorithm which uses a fixed SF. The VSF, maximising the mutual information exchanged between component decoders in a turbo decoder, is adaptively varied with a priori information of each component decoder. For a large size of interleaver, it is shown that the proposed algorithm improves the bit error rate performance and speed of decoding convergence of the conventional EMLMAP algorithm. The improved speed of the decoding convergence reduces the average number of iterations and results in low-power implementations of a turbo decoder.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Using a variable scaling factor (VSF), a modified enhanced max-log-maximum a posteriori (EMLMAP) algorithm is proposed to improve the performance of the conventional EMLMAP algorithm which uses a fixed SF. The VSF, maximising the mutual information exchanged between component decoders in a turbo decoder, is adaptively varied with a priori information of each component decoder. For a large size of interleaver, it is shown that the proposed algorithm improves the bit error rate performance and speed of decoding convergence of the conventional EMLMAP algorithm. The improved speed of the decoding convergence reduces the average number of iterations and results in low-power implementations of a turbo decoder. Close doi:10.1049/iet-com:20060632 Close
17.	K. Kim; J. Lee; Y. Lee; J. Kang; H. Park High speed transmission for a coaxial cable based in-home network Journal Article IEEE Transactions on Consumer Electronics, 52 (2), pp. 430-435, 2006, ISSN: 0098-3063. Abstract \| Links \| BibTeX @article{RN25, title = {High speed transmission for a coaxial cable based in-home network}, author = {K. Kim and J. Lee and Y. Lee and J. Kang and H. Park}, doi = {10.1109/TCE.2006.1649660}, issn = {0098-3063}, year = {2006}, date = {2006-01-01}, journal = {IEEE Transactions on Consumer Electronics}, volume = {52}, number = {2}, pages = {430-435}, abstract = {The in-home network is a crucial system for ubiquitous multimedia environments, in order to provide economical and effective high data rate transmission, we propose a transmission scheme based on the multi-carrier technique. We employ a coaxial cable channel as the transmission medium deployed for cable television (CATV). Through experiments, we show that it is possible to transmit a signal centered at 1.2 GHz with 528 MHz bandwidth without giving severe interference to the CATV system. With this observation, we propose an orthogonal frequency division multiplexing (OFDM)-based transmission scheme motivated by successful implementation of multiband OFDM (MB-OFDM) as the short range wireless transmission medium. The proposed OFDM-based system with several elementary techniques specialized in the coaxial cable for home network (CoHoNet) can achieve robust transmission over several experimental channel realizations with low power consumption.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The in-home network is a crucial system for ubiquitous multimedia environments, in order to provide economical and effective high data rate transmission, we propose a transmission scheme based on the multi-carrier technique. We employ a coaxial cable channel as the transmission medium deployed for cable television (CATV). Through experiments, we show that it is possible to transmit a signal centered at 1.2 GHz with 528 MHz bandwidth without giving severe interference to the CATV system. With this observation, we propose an orthogonal frequency division multiplexing (OFDM)-based transmission scheme motivated by successful implementation of multiband OFDM (MB-OFDM) as the short range wireless transmission medium. The proposed OFDM-based system with several elementary techniques specialized in the coaxial cable for home network (CoHoNet) can achieve robust transmission over several experimental channel realizations with low power consumption. Close doi:10.1109/TCE.2006.1649660 Close
16.	M. Noh; Y. Lee; H. Park Low complexity LMMSE channel estimation for OFDM Journal Article IEE Proceedings - Communications, 153 (5), pp. 645-650, 2006, ISSN: 1350-2425. Abstract \| Links \| BibTeX @article{RN26, title = {Low complexity LMMSE channel estimation for OFDM}, author = {M. Noh and Y. Lee and H. Park}, doi = {10.1049/ip-com:20050026}, issn = {1350-2425}, year = {2006}, date = {2006-01-01}, journal = {IEE Proceedings - Communications}, volume = {153}, number = {5}, pages = {645-650}, abstract = {The authors propose low complexity versions of a linear minimum mean square error (LMMSE) channel estimator for orthogonal frequency division multiplexing (OFDM) systems. They partition the channel autocorrelation matrix in the LMMSE estimator into small sub-matrices. The size of sub-matrix is determined by channel coherence bandwidth, a range of highly correlated channel frequency responses. Since the proposed estimator uses small sub-matrices instead of the whole channel auto-correlation matrix, the complexity is significantly reduced in spite of slight performance degradation. The performance of mean square error (MSE) has been evaluated in an exponential decay channel model through computer simulation to verify the validities of proposed schemes}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The authors propose low complexity versions of a linear minimum mean square error (LMMSE) channel estimator for orthogonal frequency division multiplexing (OFDM) systems. They partition the channel autocorrelation matrix in the LMMSE estimator into small sub-matrices. The size of sub-matrix is determined by channel coherence bandwidth, a range of highly correlated channel frequency responses. Since the proposed estimator uses small sub-matrices instead of the whole channel auto-correlation matrix, the complexity is significantly reduced in spite of slight performance degradation. The performance of mean square error (MSE) has been evaluated in an exponential decay channel model through computer simulation to verify the validities of proposed schemes Close doi:10.1049/ip-com:20050026 Close
15.	Kim Jaebum; Kim Namshik; Ji Kumran; Kim Seungwon; Park Hyuncheol A new enhanced coding scheme for robust bit-stream of ATSC DTV Journal Article IEEE Transactions on Consumer Electronics, 51 (2), pp. 457-462, 2005, ISSN: 0098-3063. Abstract \| Links \| BibTeX @article{RN23, title = {A new enhanced coding scheme for robust bit-stream of ATSC DTV}, author = {Kim Jaebum and Kim Namshik and Ji Kumran and Kim Seungwon and Park Hyuncheol}, doi = {10.1109/TCE.2005.1467987}, issn = {0098-3063}, year = {2005}, date = {2005-01-01}, journal = {IEEE Transactions on Consumer Electronics}, volume = {51}, number = {2}, pages = {457-462}, abstract = {In this paper a new enhanced coding scheme of ATSC DTV standard is presented. The proposed coding scheme is a modified trellis codes of enhanced 8-VSB for robust bit-stream mode. By computing the distance spectrum, we derive the theoretical upper bound on the first event error probability of the proposed trellis codes. Based on the derivation, the proposed coding scheme has slightly better performance on AWGN channel than the conventional enhanced S-VSB coding scheme at high signal-to-noise ratio (SNR). We also show that the proposed coding scheme has better performance than any existing coding schemes of ATSC DTV standard by using the Monte Carlo simulations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper a new enhanced coding scheme of ATSC DTV standard is presented. The proposed coding scheme is a modified trellis codes of enhanced 8-VSB for robust bit-stream mode. By computing the distance spectrum, we derive the theoretical upper bound on the first event error probability of the proposed trellis codes. Based on the derivation, the proposed coding scheme has slightly better performance on AWGN channel than the conventional enhanced S-VSB coding scheme at high signal-to-noise ratio (SNR). We also show that the proposed coding scheme has better performance than any existing coding schemes of ATSC DTV standard by using the Monte Carlo simulations. Close doi:10.1109/TCE.2005.1467987 Close
14.	Kwanghoon Kim; Haelyong Kim; Hyuncheol Park An Efficient Channel Tracking Method for OFDM Based High Mobility Wireless Multimedia System Book Chapter Ho, Yo-Sung; Kim, Hyoung-Joong (Ed.): Advances in Multimedia Information Processing - PCM 2005: 6th Pacific Rim Conference on Multimedia, Jeju Island, Korea, November 13-16, 2005, Proceedings, Part II, pp. 235-245, Springer Berlin Heidelberg, Berlin, Heidelberg, 2005, ISBN: 978-3-540-32131-6. Links \| BibTeX @inbook{RN24, title = {An Efficient Channel Tracking Method for OFDM Based High Mobility Wireless Multimedia System}, author = {Kwanghoon Kim and Haelyong Kim and Hyuncheol Park}, editor = {Ho, Yo-Sung and Kim, Hyoung-Joong}, url = {http://dx.doi.org/10.1007/11582267_21}, doi = {10.1007/11582267_21}, isbn = {978-3-540-32131-6}, year = {2005}, date = {2005-01-01}, booktitle = {Advances in Multimedia Information Processing - PCM 2005: 6th Pacific Rim Conference on Multimedia, Jeju Island, Korea, November 13-16, 2005, Proceedings, Part II}, pages = {235-245}, publisher = {Springer Berlin Heidelberg}, address = {Berlin, Heidelberg}, keywords = {}, pubstate = {published}, tppubtype = {inbook} } Close http://dx.doi.org/10.1007/11582267_21 doi:10.1007/11582267_21 Close
13.	Park Hyuncheol; J. R. Barry Trellis-coded multiple-pulse-position modulation for wireless infrared communications Journal Article IEEE Transactions on Communications, 52 (4), pp. 643-651, 2004, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN20, title = {Trellis-coded multiple-pulse-position modulation for wireless infrared communications}, author = {Park Hyuncheol and J. R. Barry}, doi = {10.1109/TCOMM.2004.826382}, issn = {0090-6778}, year = {2004}, date = {2004-01-01}, journal = {IEEE Transactions on Communications}, volume = {52}, number = {4}, pages = {643-651}, abstract = {We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length. Close doi:10.1109/TCOMM.2004.826382 Close
12.	Namshik Kim; Jaebum Kim; Hyuncheol Park; Seung-Bum Suh An Improvement of UMP-BP Decoding Algorithm Using the Minimum Mean Square Error Linear Estimator Journal Article ETRI Journal, 26 (5), pp. 432-436, 2004, ISSN: 1225-6463. Abstract \| Links \| BibTeX @article{RN22, title = {An Improvement of UMP-BP Decoding Algorithm Using the Minimum Mean Square Error Linear Estimator}, author = {Namshik Kim and Jaebum Kim and Hyuncheol Park and Seung-Bum Suh}, doi = {http://dx.doi.org/10.4218/etrij.04.0703.0019}, issn = {1225-6463}, year = {2004}, date = {2004-01-01}, journal = {ETRI Journal}, volume = {26}, number = {5}, pages = {432-436}, abstract = {In this paper, we propose the modified uniformly most powerful (UMP) belief-propagation (BP)-based decoding algorithm which utilizes multiplicative and additive factors to diminish the errors introduced by the approximation of the soft values given by a previously proposed UMP BP-based algorithm. This modified UMP}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we propose the modified uniformly most powerful (UMP) belief-propagation (BP)-based decoding algorithm which utilizes multiplicative and additive factors to diminish the errors introduced by the approximation of the soft values given by a previously proposed UMP BP-based algorithm. This modified UMP Close doi:http://dx.doi.org/10.4218/etrij.04.0703.0019 Close
11.	N. Kim; H. Park Modified UMP-BP decoding algorithm based on mean square error Journal Article Electronics Letters, 40 (13), pp. 816-817, 2004, ISSN: 0013-5194. Abstract \| Links \| BibTeX @article{RN21, title = {Modified UMP-BP decoding algorithm based on mean square error}, author = {N. Kim and H. Park}, doi = {10.1049/el:20040551}, issn = {0013-5194}, year = {2004}, date = {2004-01-01}, journal = {Electronics Letters}, volume = {40}, number = {13}, pages = {816-817}, abstract = {The modified uniformly most powerful belief-propagation (UMP-BP) decoding algorithm is proposed. This utilises a new normalisation factor to diminish the error introduced by approximation of the soft values. The proposed algorithm shows better performance than the normalisation UMP-BP algorithm, and has the same complexity of implementation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The modified uniformly most powerful belief-propagation (UMP-BP) decoding algorithm is proposed. This utilises a new normalisation factor to diminish the error introduced by approximation of the soft values. The proposed algorithm shows better performance than the normalisation UMP-BP algorithm, and has the same complexity of implementation. Close doi:10.1049/el:20040551 Close
10.	Hyuncheol Park Performance Bound on Multiple-Pulse Position Modulation Journal Article Optical Review, 10 (3), pp. 131-132, 2003, ISSN: 1349-9432. Abstract \| Links \| BibTeX @article{RN18, title = {Performance Bound on Multiple-Pulse Position Modulation}, author = {Hyuncheol Park}, url = {http://dx.doi.org/10.1007/s10043-003-0131-7}, doi = {10.1007/s10043-003-0131-7}, issn = {1349-9432}, year = {2003}, date = {2003-01-01}, journal = {Optical Review}, volume = {10}, number = {3}, pages = {131-132}, abstract = {In this paper we derive the performance bound on multiple-pulse position modulation (MPPM). We compare this bound with power and bandwidth efficiency of MPPM derived from the error probability, cutoff rate, and inverse pulse width approximation expressions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper we derive the performance bound on multiple-pulse position modulation (MPPM). We compare this bound with power and bandwidth efficiency of MPPM derived from the error probability, cutoff rate, and inverse pulse width approximation expressions. Close http://dx.doi.org/10.1007/s10043-003-0131-7 doi:10.1007/s10043-003-0131-7 Close
9.	H. Park; J. R. Barry Partial-response precoding scheme for multiple pulse-position modulation Journal Article IEE Proceedings - Optoelectronics, 150 (2), pp. 133-137, 2003, ISSN: 1350-2433. Abstract \| Links \| BibTeX @article{RN17, title = {Partial-response precoding scheme for multiple pulse-position modulation}, author = {H. Park and J. R. Barry}, doi = {10.1049/ip-opt:20030209}, issn = {1350-2433}, year = {2003}, date = {2003-01-01}, journal = {IEE Proceedings - Optoelectronics}, volume = {150}, number = {2}, pages = {133-137}, abstract = {The authors propose a partial-response precoding scheme for combating intersymbol interference that is compatible with trellis codes based on multiple pulse-position modulation. The scheme reduces the span of intersymbol interference from a possibly infinite number to two baud periods, significantly reducing the complexity of the receiver equaliser. Numerical results show that, in terms of performance and complexity, the proposed scheme compares favourably to conventional linear equalisation, block decision-feedback equalisation and superstate maximum-likelihood sequence detection.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The authors propose a partial-response precoding scheme for combating intersymbol interference that is compatible with trellis codes based on multiple pulse-position modulation. The scheme reduces the span of intersymbol interference from a possibly infinite number to two baud periods, significantly reducing the complexity of the receiver equaliser. Numerical results show that, in terms of performance and complexity, the proposed scheme compares favourably to conventional linear equalisation, block decision-feedback equalisation and superstate maximum-likelihood sequence detection. Close doi:10.1049/ip-opt:20030209 Close
8.	Jeong Wonjeong; Park Hyuncheol; Lee Hyuckjae; Hwang Sunghyun Performance improvement techniques for CCK-OFDM WLAN modem Journal Article IEEE Transactions on Consumer Electronics, 49 (3), pp. 602-605, 2003, ISSN: 0098-3063. Abstract \| Links \| BibTeX @article{RN19, title = {Performance improvement techniques for CCK-OFDM WLAN modem}, author = {Jeong Wonjeong and Park Hyuncheol and Lee Hyuckjae and Hwang Sunghyun}, doi = {10.1109/TCE.2003.1233781}, issn = {0098-3063}, year = {2003}, date = {2003-01-01}, journal = {IEEE Transactions on Consumer Electronics}, volume = {49}, number = {3}, pages = {602-605}, abstract = {In this paper, we show the equivalence between complementary code keying (CCK) codeword and coset of the first order Reed-Muller (RM) code with variables of three. The CCK codewords are Golay sequences which have peak-to-average power ratio (PAPR) of two at most and can correct one error. We propose a CCK-orthogonal frequency division multiplexing (OFDM) modem to reduce PAPR. Also, we present the performance improvement techniques by increasing the variables of four to correct three errors and reduce PAPR at least 9dB with this system. Although, two Fast Hadamard Transform (FHT) blocks of size 8 × 64 are required at the receiver, we reduce the complexity by using FHT blocks of size 8 × 64 and 2 × 4 without deteriorating the performance. We generalize our results that we may increase the variables of RM code to enhance the error correcting and PAPR reduction capabilities without increasing receiver's complexity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we show the equivalence between complementary code keying (CCK) codeword and coset of the first order Reed-Muller (RM) code with variables of three. The CCK codewords are Golay sequences which have peak-to-average power ratio (PAPR) of two at most and can correct one error. We propose a CCK-orthogonal frequency division multiplexing (OFDM) modem to reduce PAPR. Also, we present the performance improvement techniques by increasing the variables of four to correct three errors and reduce PAPR at least 9dB with this system. Although, two Fast Hadamard Transform (FHT) blocks of size 8 × 64 are required at the receiver, we reduce the complexity by using FHT blocks of size 8 × 64 and 2 × 4 without deteriorating the performance. We generalize our results that we may increase the variables of RM code to enhance the error correcting and PAPR reduction capabilities without increasing receiver's complexity. Close doi:10.1109/TCE.2003.1233781 Close
7.	Park Hyuncheol Convolutional coded pulse-position modulation on wireless infrared link Journal Article IEE Proceedings - Optoelectronics, 148 (4), pp. 199-203, 2001, ISSN: 1350-2433. Abstract \| Links \| BibTeX @article{RN16, title = {Convolutional coded pulse-position modulation on wireless infrared link}, author = {Park Hyuncheol}, doi = {10.1049/ip-opt:20010697}, issn = {1350-2433}, year = {2001}, date = {2001-01-01}, journal = {IEE Proceedings - Optoelectronics}, volume = {148}, number = {4}, pages = {199-203}, abstract = {The performance of convolutional codes based on pulse-position modulation (PPM) for wireless infrared communication is reported. It is assumed that the receiver uses maximum-likelihood sequence detection (MLSD) to mitigate the effects of channel dispersion, which are modelled using a first-order low-pass filter. The upper bounds are derived for the minimum distance of convolutional coded PPM and compared with the Simplex bound. The performance of convolutional coded PPM is compared with the cutoff rate}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The performance of convolutional codes based on pulse-position modulation (PPM) for wireless infrared communication is reported. It is assumed that the receiver uses maximum-likelihood sequence detection (MLSD) to mitigate the effects of channel dispersion, which are modelled using a first-order low-pass filter. The upper bounds are derived for the minimum distance of convolutional coded PPM and compared with the Simplex bound. The performance of convolutional coded PPM is compared with the cutoff rate Close doi:10.1049/ip-opt:20010697 Close
6.	Cho Jaehee; Cho Namshin; Bang Keukjoon; Park Myunghee; Jun Heeyoung; Park Hyuncheol; Hong Daesik PC-based receiver for Eureka-147 digital audio broadcasting Journal Article IEEE Transactions on Broadcasting, 47 (2), pp. 95-102, 2001, ISSN: 0018-9316. Abstract \| Links \| BibTeX @article{RN14, title = {PC-based receiver for Eureka-147 digital audio broadcasting}, author = {Cho Jaehee and Cho Namshin and Bang Keukjoon and Park Myunghee and Jun Heeyoung and Park Hyuncheol and Hong Daesik}, doi = {10.1109/11.948262}, issn = {0018-9316}, year = {2001}, date = {2001-01-01}, journal = {IEEE Transactions on Broadcasting}, volume = {47}, number = {2}, pages = {95-102}, abstract = {We present the design and implementation for a Eureka-147 digital audio broadcasting (DAB) receiver. We establish the specifications for the receiver and design the blocks required for DAB reception. Due to the fact that orthogonal frequency division multiplexing (OFDM) is the transmission technique used in the DAB system, the synchronization block plays a key role in the overall system performance among the receiving blocks in the DAB receiver, and for this reason we describe it in detail here. We also include descriptions of several implementation techniques that enable the receiver to run in real-time on a PC. Our findings show that the receiver implemented as described here satisfactorily meets our predetermined specifications}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We present the design and implementation for a Eureka-147 digital audio broadcasting (DAB) receiver. We establish the specifications for the receiver and design the blocks required for DAB reception. Due to the fact that orthogonal frequency division multiplexing (OFDM) is the transmission technique used in the DAB system, the synchronization block plays a key role in the overall system performance among the receiving blocks in the DAB receiver, and for this reason we describe it in detail here. We also include descriptions of several implementation techniques that enable the receiver to run in real-time on a PC. Our findings show that the receiver implemented as described here satisfactorily meets our predetermined specifications Close doi:10.1109/11.948262 Close
5.	Bang Keukjoon; Cho Namshin; Cho Jaehee; Jun Heeyoung; Kim Kwangchul; Park Hyuncheol; Hong Daesik A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth Journal Article IEEE Transactions on Communications, 49 (8), pp. 1320-1324, 2001, ISSN: 0090-6778. Abstract \| Links \| BibTeX @article{RN15, title = {A coarse frequency offset estimation in an OFDM system using the concept of the coherence phase bandwidth}, author = {Bang Keukjoon and Cho Namshin and Cho Jaehee and Jun Heeyoung and Kim Kwangchul and Park Hyuncheol and Hong Daesik}, doi = {10.1109/26.939841}, issn = {0090-6778}, year = {2001}, date = {2001-01-01}, journal = {IEEE Transactions on Communications}, volume = {49}, number = {8}, pages = {1320-1324}, abstract = {We propose a new coarse frequency offset estimation algorithm in orthogonal frequency-division multiplexing systems, which performs robust operation in the presence of a symbol timing offset within an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed, and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. The proposed algorithm adapts the concept of the coherence phase bandwidth for the purpose of weakening the effect of the symbol timing offset}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We propose a new coarse frequency offset estimation algorithm in orthogonal frequency-division multiplexing systems, which performs robust operation in the presence of a symbol timing offset within an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed, and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. The proposed algorithm adapts the concept of the coherence phase bandwidth for the purpose of weakening the effect of the symbol timing offset Close doi:10.1109/26.939841 Close
4.	H. Park Upper bounds on error probability of equalisation schemes in wireless infrared link Journal Article Electronics Letters, 37 (5), pp. 319-321, 2001, ISSN: 0013-5194. Abstract \| Links \| BibTeX @article{RN13, title = {Upper bounds on error probability of equalisation schemes in wireless infrared link}, author = {H. Park}, doi = {10.1049/el:20010117}, issn = {0013-5194}, year = {2001}, date = {2001-01-01}, journal = {Electronics Letters}, volume = {37}, number = {5}, pages = {319-321}, abstract = {The performance of equalisation schemes in the presence of multipath distortion in a diffuse infrared link is examined. The upper bounds of error probability are derived for two types of symbol-by-symbol equalisation schemes, such as decision feedback equalisation (DFE) and linear equalisation (LE)}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The performance of equalisation schemes in the presence of multipath distortion in a diffuse infrared link is examined. The upper bounds of error probability are derived for two types of symbol-by-symbol equalisation schemes, such as decision feedback equalisation (DFE) and linear equalisation (LE) Close doi:10.1049/el:20010117 Close
3.	G. Sonu; N. Nadershahi; S. Radzewicz; Kim Young-Mook; Lee Jae-Wook; Shim Daeyun; K. O. Cho; Park Hyucheol; Lee Kiwon; Park Hyun-Soo; Shim Jae-Seong Partial-response maximum-likelihood core development for a CD/DVD controller integrated circuit Journal Article IEEE Transactions on Magnetics, 37 (2), pp. 663-669, 2001, ISSN: 0018-9464. Abstract \| Links \| BibTeX @article{RN12, title = {Partial-response maximum-likelihood core development for a CD/DVD controller integrated circuit}, author = {G. Sonu and N. Nadershahi and S. Radzewicz and Kim Young-Mook and Lee Jae-Wook and Shim Daeyun and K. O. Cho and Park Hyucheol and Lee Kiwon and Park Hyun-Soo and Shim Jae-Seong}, doi = {10.1109/20.917598}, issn = {0018-9464}, year = {2001}, date = {2001-01-01}, journal = {IEEE Transactions on Magnetics}, volume = {37}, number = {2}, pages = {663-669}, abstract = {A new PRML architecture is presented to demonstrate its superiority over the conventional analog channel in a DVD system. In this new architecture, the robustness to the baseline disturbance in the readback signal is emphasized in developing the algorithms for the PLL, digital gain control, asymmetry control, adaptive FIR filter, and Viterbi detector and post processor. In addition, a method of modeling the asymmetrical readback signal is discussed. A new algorithm for the digital PLL is described which does not require the oversampling. A simple method is presented to reduce the asymmetry in the ADC samples. To further improve the sensitivity to the baseline wandering, a Viterbi detector is designed using the difference metric approach and followed by a post processor, which corrects the baseline related errors from the VD. A test chip is fabricated using 0.35 μm CMOS technology to demonstrate the performance of the proposed architecture}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A new PRML architecture is presented to demonstrate its superiority over the conventional analog channel in a DVD system. In this new architecture, the robustness to the baseline disturbance in the readback signal is emphasized in developing the algorithms for the PLL, digital gain control, asymmetry control, adaptive FIR filter, and Viterbi detector and post processor. In addition, a method of modeling the asymmetrical readback signal is discussed. A new algorithm for the digital PLL is described which does not require the oversampling. A simple method is presented to reduce the asymmetry in the ADC samples. To further improve the sensitivity to the baseline wandering, a Viterbi detector is designed using the difference metric approach and followed by a post processor, which corrects the baseline related errors from the VD. A test chip is fabricated using 0.35 μm CMOS technology to demonstrate the performance of the proposed architecture Close doi:10.1109/20.917598 Close
2.	H. Park Information and cut-off rates for multiple-pulse position modulation on multi-path channels Journal Article IEE Proceedings - Optoelectronics, 147 (4), pp. 229-233, 2000, ISSN: 1350-2433. Abstract \| Links \| BibTeX @article{RN11, title = {Information and cut-off rates for multiple-pulse position modulation on multi-path channels}, author = {H. Park}, doi = {10.1049/ip-opt:20000494}, issn = {1350-2433}, year = {2000}, date = {2000-01-01}, journal = {IEE Proceedings - Optoelectronics}, volume = {147}, number = {4}, pages = {229-233}, abstract = {The effect is examined of multipath dispersion on the information and cut-off rates of multiple-pulse position modulation. Over multipath channels, intersymbol interference (ISI) can reduce the information rate significantly. When the input codewords are independent and identically distributed with a uniform distribution, lower and upper bounds are presented for the information rate on a moderate ISI channel in terms of the average mutual information of a memoryless Gaussian vector channel with scaled input codewords. The cut-off rate of each modulation scheme is also examined in the presence of ISI, and the power required to achieve the cut-off rate is calculated for various bit rates over the channel 3 dB bandwidth}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The effect is examined of multipath dispersion on the information and cut-off rates of multiple-pulse position modulation. Over multipath channels, intersymbol interference (ISI) can reduce the information rate significantly. When the input codewords are independent and identically distributed with a uniform distribution, lower and upper bounds are presented for the information rate on a moderate ISI channel in terms of the average mutual information of a memoryless Gaussian vector channel with scaled input codewords. The cut-off rate of each modulation scheme is also examined in the presence of ISI, and the power required to achieve the cut-off rate is calculated for various bit rates over the channel 3 dB bandwidth Close doi:10.1049/ip-opt:20000494 Close
1.	H. Park; J. R. Barry Performance of multiple pulse position modulation on multipath channels Journal Article IEE Proceedings - Optoelectronics, 143 (6), pp. 360-364, 1996, ISSN: 1350-2433. Abstract \| Links \| BibTeX @article{RN10, title = {Performance of multiple pulse position modulation on multipath channels}, author = {H. Park and J. R. Barry}, doi = {10.1049/ip-opt:19960698}, issn = {1350-2433}, year = {1996}, date = {1996-01-01}, journal = {IEE Proceedings - Optoelectronics}, volume = {143}, number = {6}, pages = {360-364}, abstract = {The effect of multipath dispersion on multiple pulse position modulation (MPPM) and its variants PPM and overlapping PPM are examined. Upper bounds for the error probability of each modulation scheme in the presence of intersymbol interference are presented, considering both an unequalised receiver and the optimal maximum-likelihood sequence detection receiver. Numerical results show that all the PPM-based schemes are approximately equally sensitive to multipath dispersion, and significantly more sensitive to multipath dispersion than on-off keying when maximum-likelihood sequence detection is used}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The effect of multipath dispersion on multiple pulse position modulation (MPPM) and its variants PPM and overlapping PPM are examined. Upper bounds for the error probability of each modulation scheme in the presence of intersymbol interference are presented, considering both an unequalised receiver and the optimal maximum-likelihood sequence detection receiver. Numerical results show that all the PPM-based schemes are approximately equally sensitive to multipath dispersion, and significantly more sensitive to multipath dispersion than on-off keying when maximum-likelihood sequence detection is used Close doi:10.1049/ip-opt:19960698 Close