Publications
By Research Topic
Reinforcement Learning
Wireless Communications
Detection and Estimation
Reinforcement Learning
Wireless Communications
Detection and Estimation
Deep Reinforcement Learning
Jeonghye Kim, Yongjae Shin, Whiyoung Jung, Sunghoon Hong, Deunsol Yoon, Youngchul Sung, Kanghoon Lee, and Woohyung Lim*, "Penalizing infeasible actions and reward scaling in reinforcement learning with offline data," accepted to International Conference on Machine Learning (ICML), 2025 (Spotlight Paper)
Yongjae Shin, Jeonghye Kim, Whiyoung Jung, Sunghoon Hong, Deunsol Yoon, Youngsoo Jang, Geonhyeong Kim, Jongseong Chae, Youngchul Sung, Kanghoon Lee, and Woohyung Lim*, "Online pre-training for offline-to-online reinforcement learning," accepted to International Conference on Machine Learning (ICML), 2025
Giseung Park, Whiyoung Jung, Seungyul Han, Sungho Choi and Youngchul Sung*, "Adaptive multi-model fusion learning for sparse-reward reinforcement learning," Neurocomputing, vol. 633, Jun. 2025
Jeonghye Kim, Suyoung Lee, Woojun Kim, and Youngchul Sung*, "Adaptive Q-aid for conditional supervised learning in offline reinforcement learning," Conference on Neural Information Processing Systems (NeurIPS ), 2024
G. Kim, J. Kim, S. Lee, J. Baek, H. Moon, S. Shin and Y. Sung*, "Robust reinforcement learning under dimension-wise state information drop," IEEE Access, 2024
Jeonghyee Kim, Suyoung Lee, Woojun Kim*, and Youngchul Sung*, “Decision convformer: Local filtering in metaformer is sufficient for decision making,” International Conference on Learning Representations (ICLR) , May 2024
Woojun Kim+, Yongjae Shin+, Jongeui Park, and Youngchul Sung*, "Sample-efficient and safe deep reinforcement learning via reset deep ensemble agents," Conference on Neural Information Processing Systems (NeurIPS ), New Orleans, LA, Dec. 2023 (+Equal contribution)
Woojun Kim+, Jeonghye Kim+ and Youngchul Sung*, "LESSON: Learning to integrate exploration strategies for reinforcement learning via an option framework," International Conference on Machine Learning (ICML), Hawaii, HI, Jul. 2023 (+Equal contribution)
W. Jung, M. Cho, J. Park and Y. Sung*, "Quantile constrained reinforcement learning: A reinforcement learning framework constraining outage probability," Conference on Neural Information Processing Systems (NeurIPS), Dec. 2022
Giseung Park, Sungho Choi and Youngchul Sung*, "Blockwise sequential model learning for partially observable reinforcement learning," the 36rd AAAI Conference on Artificial Intelligence (AAAI ), Feb. 2022 (Selected as oral presentation)
Seungyul Han and Youngchul Sung*, "A max-min entropy framework for reinforcement learning," Conference on Neural Information Processing Systems (NeurIPS) , Dec. 2021.
Seungyul Han and Youngchul Sung*, "Diversity actor-critic: Sample-aware entropy regularization for sample-efficient exploration," International Conference on Machine Learning (ICML) , Jul. 2021
Whiyoung Jung, Giseung Park, and Youngchul Sung*, "Population-Guided Parallel Policy Search for Reinforcement Learning," International Conference on Learning Representations (ICLR) , Vienna, Austria, May 2020
Seungyul Han and Youngchul Sung*, "Dimension-Wise Importance Sampling Weight Clipping for Sample-Efficient Reinforcement Learning," International Conference on Machine Learning (ICML) , Long Beach, CA, USA, Jun. 2019
Meta RL, Multi-Task RL, and Multi-Objective RL
Myungsik Cho, Jongeui Park, Jeonghye Kim and Youngchul Sung*, "ARS: Adaptive reward scaling for multi-task reinforcement learning," accepted to International Conference on Machine Learning (ICML), 2025
Giseung Park and Youngchul Sung*, "Reward dimension reduction for scalable multi-objective reinforcement learning," International Conference on Learning Representations (ICLR) , Singapore, Apr. 2025
Myungsik Cho, Jongeui Park, Suyoung Lee and Youngchul Sung*, "Hard task first: Multi-task reinforcement learning through task scheduling," International Conference on Machine Learning (ICML) 2024
Giseung Park, Woohyeon Byeon, Seongmin Kim, Elad Habakuk, Amir Leshem and Youngchul Sung*, "The max-min formulation of multi-objective reinforcement learning: From theory to a model-free algorithm," International Conference on Machine Learning (ICML) 2024
Suyoung Lee, Myungsik Cho, and Youngchul Sung*, "Parameterizing Non-Parametric Meta-Reinforcement Learning Tasks via Subtask Decomposition, Conference on Neural Information Processing Systems (NeurIPS ), New Orleans, LA, Dec. 2023
Myungsik Cho, Whiyoung Jung, and Youngchul Sung*, "Multi-task reinforcement learning with task representation method," ICLR Workshop on Generalizable Policy Learning in Physical World (GPL), Apr. 2022
Imitation Learning
Sungho Choi, Seungyul Han*, Woojun Kim, Jongseong Chae, Whiyoung Jung, and Youngchul Sung, "Domain adaptive imitation learning with visual observation," Conference on Neural Information Processing Systems (NeurIPS ), New Orleans, LA, Dec. 2023
Jongseong Chae, Seungyul Han*, Whiyoung Jung, Myungsik Cho, Sungho Choi, and Youngchul Sung, “Robust imitation learning against variations in environment dynamics,” International Conference on Machine Learning (ICML) 2022 , Baltimore, MD, USA, Jul. 2022
Multi-Agent Reinforcement Learning
Woojun Kim and Youngchul Sung*, "An adaptive entropy regularization framework for multi-agent reinforcement learning," International Conference on Machine Learning (ICML), Hawaii, HI, Jul. 2023
Woojun Kim, Whiyoung Jung, Myungsik Cho, and Youngchul Sung*, “A variational approach to mutual information-based coordination for multi-agent reinforcement learning,” International Conference on Autonomous Agents and Multiagent Systems (AAMAS), May 2023
Woojun Kim and Youngchul Sung, “Network pruning for scalable multi-agent deep reinforcement learning,” International Conference on Autonomous Agents and Multiagent Systems (AAMAS), May 2023
Jeewon Jeon, Woojun Kim*, Whiyoung Jung and Youngchul Sung, “MASER: Multi-Agent reinforcementlearning with Subgoals generated from Experience Replay buffer,” International Conference on Machine Learning (ICML) 2022 , Baltimore, MD, USA, Jul. 2022
Woonjun Kim, Jongeui Park, and Youngchul Sung*, "Communication in multi-agent reinforcement learning: Intention sharing," International Conference on Learning Representations (ICLR) 2021, May 2021
Woojun Kim, Myungsik Cho, and Youngchul Sung*, "Message-dropout: An efficient training method for multi-agent deep reinforcement learning," the 33rd AAAI Conference on Artificial Intelligence (AAAI ) 2019, Honolulu, HW, USA, Jan. 2019
Applications
Sohee Bae, Seungyul Han, and Youngchul Sung*, "A reinforcement learning formulation of the Lyapunov optimization: Application to edge computing systems with queue stability," available at arXiv, Dec. 2020
Training Signal Design and Channel Estimation for MIMO and Related Systems
Song Noh, Kyungsik Seo, Youngchul Sung, David Love, Junse Lee* and Heejung Yu*, "Joint direct and indirect channel estimation for RIS-assisted millimeter-wave systems based on array signal processing," IEEE Transactions on Wireless Communications, vol. 22, no. 11, pp. 8378 - 8391, Nov. 2023
Song Noh, Junse Lee, Gilwon Lee, Kyungsik Seo, Youngchul Sung and Heejung Yu*, "Channel Estimation Techniques for RIS-Assisted Communication: Millimeter-Wave and Sub-THz Systems ," IEEE Vehicular Technology Magazine, vol. 17, no. 2, pp. 64 - 73, Jun. 2022
Song Noh, Heejung Yu, and Youngchul Sung*, "Training signal design for sparse channel estimation in intelligent reflecting surface-assisted millimeter-wave communication," IEEE Transactions on Wireless Communications, vol. 21, no. 4, pp. 2399 - 2413, Apr. 2022
Song Noh, Jiho Song, and Youngchul Sung*, "Fast beam search and refinement for millimeter-wave massive MIMO based on two-level phased arrays," IEEE Transactions on Wireless Communications, vol. 19, no. 10, pp. 6737 - 6751, Oct. 2020
Junyeong Seo, Youngchul Sung*, Gilwon Lee, and Donggun Kim, "Training beam sequence design for millimeter-wave MIMO systems: A POMDP framework," IEEE Transactions on Signal Processing, vol. 64, no. 5, pp. 1228 - 1242, Mar. 2016.
Jungho So, Donggun Kim, Yuni Lee, and Youngchul Sung*, "Pilot signal design for massive MIMO systems: A received signal-to-noise-ratio-based approach," IEEE Signal Processing Letters, vol. 52, no. 5, pp. 549 - 553, May 2015.
Song Noh, Youngchul Sung*, and Michael Zoltowski, "A new precoder design for blind channel estimation for MIMO-OFDM systems," IEEE Transactions on Wireless Communications, vol. 13, no. 12, pp. 7011 - 7024, Dec. 2014
Song Noh, Michael Zoltowski, Youngchul Sung*, and David Love, "Pilot beam pattern design for channel estimation in massive MIMO systems," IEEE Journal of Selected Topics in Signal Processing, vol. 8, no. 5, pp. 787 - 801, Oct. 2014.
Youngchul Sung, Tae Sung, Brian M. Sadler, and Lang Tong, "Training for MIMO communications," in Space-Time Wireless Systems: From Array Processing to MIMO Communications, edited by H. Bolcskei, D. Gesbert, C. Papadias, and A. J. van der Veen, Cambridge University Press, 2006.
Beamformer Design for Massive MIMO
Junyeong Seo, Youngchul Sung*, and Hamid Jafarkhani, "A high-diversity transceiver design for MISO broadcast channels," IEEE Transactions on Wireless Communications, vol. 18, no. 5, pp. 2591 - 2606, May 2019
Jungho So, Youngchul Sung*, and Yong H. Lee, "Tomlinson-Harashima precoding-aided multi-antenna non-orthogonal multiple access," arXiv, Aug. 2018
Junyeong Seo and Youngchul Sung*, "Beam design and user scheduling for non-orthogonal multiple access with multiple antennas based on Pareto-optimality" IEEE Transactions on Signal Processing, vol. 66, no. 11, pp. 2876 - 2891, Jun. 2018
Junyeong Seo and Youngchul Sung*, "A new transceiver architecture for multi-user MIMO communication based on mixture of linear and non-linear reception,” SPAWC 2017, Sapporo, Japan, Jul. 2017
Yongjin Kwon, Jihoon Chung, and Youngchul Sung*, "Hybrid beamformer design for mmWave wideband multi-user MIMO-OFDM systems," Invited Paper to The Special Session of Signal Processing for Millimeter Wave Communication Systems in SPAWC 2017, Sapporo, Japan, Jul. 2017
Jungho So and Youngchul Sung*, "Improving non-orthogonal multiple access by forming relaying broadcast channels," IEEE Communications Letters, vol. 20, no. 9, pp. 1816 - 1819, Sep. 2016. An extended version is available at arXiv.
Donggun Kim, Gilwon Lee, and Youngchul Sung*, "Two-stage beamformer design for massive MIMO downlink by trace quotient formulation," IEEE Transactions on Communications, vol. 63, no. 6, pp. 2200 - 2211, Jun. 2015
Masahiro Yukawa*, Youngchul Sung and Gilwon Lee, "Dual-domain adaptive beamformer under linearly and quadratically constrained minimum variance," IEEE Transactions on Signal Processing, vol. 61, no. 11, pp. 2874 - 2886, Jun. 2013
Gilwon Lee, Juho Park, Youngchul Sung* and Junyeong Seo, "A new approach to beamformer design for massive MIMO systems based on k-regularity," International Workshop on Emerging Technologies for LTE-Advanced and Beyond 4G in conjunction with IEEE Globecom 2012, Anaheim, CA, Dec. 2012
User Scheduling for mmWave Massive Multi-User MIMO
Junyeong Seo and Youngchul Sung*, "Beam design and user scheduling for non-orthogonal multiple access with multiple antennas based on Pareto-optimality," IEEE Transactions on Signal Processing, vol. 66, no. 11, pp. 2876 - 2891, Jun. 2018
Gilwon Lee and Youngchul Sung*, "A new approach to user scheduling in massive multi-user MIMO broadcast channels," IEEE Transactions on Communications, vol. 66, no. 4, pp. 1481 – 1495, Apr. 2018
Gilwon Lee and Youngchul Sung, "MAC scheduler for mmWave massive MIMO," in MmWave Massive MIMO: A Paradigm for 5G, edited by Shahid Mumtaz and Jonathan Rodriquez, Elsevier, Longdon, UK, Nov. 2016
Gilwon Lee, Youngchul Sung*, and Marios Kountouris, "On the performance of random beamforming in sparse millimeter wave channels," IEEE Journal of Selected Topics in Signal Processing, vol. 10, no. 3, pp. 560 - 575, Apr. 2016
Gilwon Lee, Youngchul Sung*, and Junyeong Seo, "Randomly-directional beamforming in mm-wave multi-user MISO downlink," IEEE Transactions on Wireless Communications, vol. 15, no. 2, pp. 1086 - 1100, Feb. 2016
Gilwon Lee, Youngchul Sung*, Jungho So, and Junyeong Seo, "Research trends in realizing massive MIMO for 5G (in Korean),” Special Issue on 5G and Beyond, The Magazine of the IEIE, Oct. 2015
Gilwon Lee, Youngchul Sung*, and Marios Kountouris, "On the performance of randomly directional beamforming between line-of-sight and rich scattering channels,” Invited Paper to The Special Session of Signal Processing for Millimeter Wave Communication Systems in SPAWC 2015, Stockholm, Sweden, Jun. 2015
Gilwon Lee and Youngchul Sung*, "Asymptotically optimal simple user scheduling for massive MIMO downlink with two-stage beamforming," Proc. of SPAWC 2014, Toronto, CA, Jun. 2014
MIMO Interference Channels
Heejung Yu, Juho Park, Youngchul Sung*, and Y. H. Lee "Research trend in interference alignment in multi-user interference channels (a survey article in Korean)," The Magazine of the IEEK, vol. 40, pp. 348 - 360, Apr. 2013.
Juho Park and Youngchul Sung*, "On the Pareto-optimal beam structure and design for multi-user MIMO interference channels," IEEE Transactions on Signal Processing, vol. 61, no. 23, pp. 5932 - 5946, Dec. 2013.
Juho Park, Gilwon Lee, Youngchul Sung*, and Masahiro Yukawa, "Coordinate beamforming with relaxed zero forcing: The sequential orthogonal projection combining method and rate control," IEEE Transactions on Signal Processing, vol. 61, no. 12, pp. 3100 - 3112, Jun. 2013.
Juho Park, Youngchul Sung*, Donggun Kim and H. Vincent Poor, "Outage probability and outage-based robust beamforming for MIMO interference channels with imperfect channel state information," IEEE Transactions on Wireless Communications, vol. 11, no. 10, pp. 3561 - 3573, Oct. 2012. A technical report related to the paper regarding series expansion of Gaussian quadratic forms is also available.
Youngchul Sung*, Juho Park, and Donggun Kim, "Trends and advances in MISO/MIMO technologies (in Korean)," KICS Information and Communications Magazine, Aug. 2012.
Yeongseok Oh, Heejung Yu, Yong H. Lee* and Youngchul Sung, "A nonlinear transceiver architecture for overloaded MIMO interference channels," IEEE Transactions on Communications, vol. 60, no. 4, pp. 946 - 951, Apr. 2012.
Junse Lee, Heejung Yu and Youngchul Sung*, "Beam tracking for interference alignment in time-varying MIMO interference channels: A conjugate gradient based approach," IEEE Transactions on Vehicular Technology, vol. 63, no. 6, pp. 958 - 964, Feb. 2014.
Heejung Yu, Youngchul Sung*, Haksoo Kim and Yong H. Lee, "Beam tracking for interference alignment in slowly-fading MIMO interference channels: A perturbations approach under a linear framework," IEEE Transactions on Signal Processing, vol. 60, no. 4, pp. 1910 - 1926, Apr. 2012.
Gilown Lee, Juho Park, Youngchul Sung* and Masahiro Yukawa, "Coordinated beamforming with relaxed zero forcing," in Proc. of the 2011 International Conference on Wireless Communications and Signal Processing (WCSP), an invited paper to the special session "Interference Management Techniques in Wireless Networks," Nov. 2011.
Heejung Yu and Youngchul Sung*, "Least squares approach to joint beam design for interference alignment in multiuser multi-input multi-output interference channels," IEEE Transactions on Signal Processing, vol. 58, no. 9, pp. 4960 - 4966, Sep. 2010.
Donggun Kim, Youngchul Sung*, and Jihoon Chung, "Filter-and-forward relay design for MIMO-OFDM systems," IEEE Transactions on Communications, vol. 62, no. 7, pp. 2329 - 2339, Jul. 2014.
Donggun Kim, Junyeong Seo and Youngchul Sung*, "Filter-and-forward transparent relay design for OFDM systems," IEEE Transactions on Vehicular Technology, vol. 62, no. 9, pp. 4392-4407, Nov. 2013.
Yingbo Yua*, Daniel W. Bliss, Saeed Gazor, Yue Rong, and Youngchul Sung, "Guest Editorial: Theories and methods for advanced wireless relays - Issue II" IEEE Journal on Selected Areas in Communications, vol. 31, no. 8, pp. 1361 - 1367, Aug. 2013
Yingbo Yua*, Daniel W. Bliss, Saeed Gazor, Yue Rong, and Youngchul Sung, "Guest Editorial: Theories and methods for advanced wireless relays - Issue I," IEEE Journal on Selected Areas in Communications, vol. 30, no. 8, pp. 1297 - 1303, Sep. 2012
Cheolsoon Kim, Youngchul Sung* and Yong H. Lee, "A joint time-invariant filtering approach to the linear Gaussian relay problem," IEEE Transactions on Signal Processing , vol. 60, no. 8, pp. 4360 - 4375, Aug. 2012. Matlab code.
Youngchul Sung* and Cheolsoon Kim, "The capacity for the linear time-invariant Gaussian relay channel," Sep. 2011. Available at ArXiv. (This paper presents the capacity of a noncausal LTI Gaussian relay channel.) An improved version which provides causal achievability of the rate in the previous paper in arXiv.
Youngchul Sung*, Yirang Lim, Lang Tong and Alle-Jan van der Veen, "Signal processing advances for 3G CDMA: From rake receivers to blind techniques," IEEE Communications Magazine, vol. 47, no. 1, pp. 48 - 54, Jan. 2009
Youngchul Sung, participation in 3G WCDMA Basestation Modem Design and System Optimization, at the Corporate R & D Center, Qualcomm, Inc., San Diego, CA, USA, 2005 - 2007
Youngchul Sung, Lang Tong* and Ananthram Swami, "Blind channel estimation for space-time coded WCDMA," EURASIP Journal on Wireless Communications and Networking, vol. 2004, no. 2, pp. 322 - 334, Dec. 2004
Youngchul Sung and Lang Tong*, "Tracking of fast-fading channels in long code WCDMA," IEEE Transactions on Signal Processing, vol. 52, no. 3, pp. 786 - 795, Mar. 2004
Lang Tong*, Alle-Jan van der Veen, Patrick Dewilde and Youngchul Sung, "Blind decorrelating rake receiver for long code WCDMA," IEEE Transactions on Signal Processing, vol. 51, no. 6, pp. 1642 - 1655, Jun. 2003
Youngchul Sung and Juyul Lee, "System simulation of wireless communication systems using HP-ADS," 1999 Hewlett-Packard Workshop, Seould, Korea, 1999.
Youngchul Sung, participation in Wireless Local Loop (WLL) Project based on Wideband CDMA (WCDMA), Dept. of Digital Communications, LG Information and Communications, ltd., 1997 - 1999
Signal Detection
Yuni Lee and Youngchul Sung*, "Generalized Chernoff information for mismatched Bayesian detection and its application to energy detection," IEEE Signal Processing Letters, vol. 19, no. 11, pp. 753 - 756, Nov. 2012.
Yirang Lim, Juho Park and Youngchul Sung*, "Upper bound for the loss of energy detection of signals in multipath fading channels," IEEE Signal Processing Letters, vol. 16, no. 11, pp. 949 - 952, Nov. 2009.
Youngchul Sung*, H. Vincent Poor and Heejung Yu, "How much information can one get from a wireless ad hoc sensor network over a correlated random field?," IEEE Transactions on Information Theory, vol. 55, no. 6, pp. 2827 - 2847, Jun. 2009. Simple Condition for Theorem 2.
Youngchul Sung*, "Large deviations principle and its applications," in Proceedings of Korean Information and Communications Society (KICS), Coding and Information Theory Workshop, Jan. 2009.
Youngchul Sung*, Xin Zhang, Lang Tong and H. Vincent Poor, "Sensor configuration and activation for field detection in large sensor arrays," IEEE Transactions on Signal Processing, vol. 56, no. 2, pp. 447 - 463, Feb. 2008.
Youngchul Sung, Saswat Misra, Lang Tong, and Anthony Ephremides, "Cooperative routing for signal detection in large sensor networks," IEEE Journal on Selected Areas in Communications, Vol. 25, no. 2, pp. 471 - 483, Feb. 2007.
Youngchul Sung, Saswat Misra, Lang Tong*, and Anthony Ephremides, "Signal processing for application-specific ad-hoc networks," IEEE Signal Processing Magazine, vol. 23, no. 5, pp. 74 - 83, Sep. 2006.
Youngchul Sung, Lang Tong*, and H. Vincent Poor, "Neyman-Pearson detection of Gauss-Markov signals in noise: Closed-form error exponent and properties," IEEE Transactions on Information Theory, vol. 52, no. 4, pp. 1354-1365, Apr. 2006.
Youngchul Sung, Lang Tong*, and H. Vincent Poor, "Optimal and suboptimal detection of Gaussian signals in noise: Asymptotic relative efficiency," in the proceeding of the Conference on Advanced Signal Processing Algorithms, Architectures, and Implementations XV, part of SPIE International Symposium, San Diego, CA, Jul. 2005.
Youngchul Sung, Lang Tong*, and Ananthram Swami, "Asymptotic locally optimal detector for large scale sensor networks under the Poisson regime," IEEE Transactions on Signal Processing, vol. 53, no. 6, pp. 2005 - 2017, Jun. 2005.
Youngchul Sung, Lang Tong*, and H. Vincent Poor, "A large deviations approach to sensor scheduling for detection of correlated random fields," in Proc. of ICASSP 2005, Philadelphia, PA, Mar. 2005. (ICASSP 2005 Best Student Paper Award)
Blind Estimation
Song Noh, Youngchul Sung*, and Michael Zoltowski, "A new precoder design for blind channel estimation in MIMO-OFDM systems," IEEE Transactions on Wireless Communications, vol. 13, no. 12, pp. 7011-7024, Dec. 2014
Youngchul Sung*, Yirang Lim, Lang Tong and Alle-Jan van der Veen, "Signal processing advances for 3G CDMA: From rake receivers to blind techniques," IEEE Communications Magazine, vol. 47, no. 1, pp. 48 - 54, Jan. 2009
Youngchul Sung, Lang Tong* and Ananthram Swami, "Blind channel estimation for space-time coded WCDMA," EURASIP Journal on Wireless Communications and Networking, vol. 2004, no. 2, pp. 322 - 334, Dec. 2004
Youngchul Sung and Lang Tong*, "Tracking of fast-fading channels in long code WCDMA," IEEE Transactions on Signal Processing, vol. 52, no. 3, pp. 786 - 795, Mar. 2004
Lang Tong*, Alle-Jan van der Veen, Patrick Dewilde and Youngchul Sung, "Blind decorrelating rake receiver for long code WCDMA," IEEE Transactions on Signal Processing, vol. 51, no. 6, pp. 1642 - 1655, Jun. 2003
(Asterisks denote corresponding authors.)