This work investigates sum-rate maximization in a space-air-ground integrated network (SAGIN), where a terrestrial base station and an IRS-equipped high-altitude platform jointly serve ground and satellite users. The study develops a Lagrange-dual-based optimization framework and an unsupervised deep neural network to jointly optimize transmit power and IRS phase shifts. The proposed approach achieves near-optimal sum-rate performance with significantly lower computational complexity than conventional optimization methods, enabling efficient resource allocation for SAGIN environments.

This work proposes a context-aware embedding masking scheme for multi-user semantic multiplexing, in which the masking policy dynamically adapts according to the signal-to-noise ratio (SNR) and number of users. A low-rank actor trained using proximal policy optimization (PPO) is employed to learn the masking strategy while considering semantic similarity and mask orthogonality. Evaluations using real BERT embeddings demonstrate improved semantic recovery across different SNR conditions, showing the effectiveness of context-aware adaptation for multi-user semantic communication systems.

The study addresses sum-rate maximization in space–air–ground integrated networks (SAGIN) by considering a high-altitude platform (HAP) equipped with an intelligent reflecting surface (IRS). It develops an unsupervised deep neural network (DNN) with a Lagrange dual approach to efficiently optimize the network and improve communication performance.

The paper titled "Contrastive Embedding Multiplexing for Multi-User Semantic Communication Systems", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, is now accepted for publication in IEEE Signal Processing Letters (IF: 3.6, Q1).

The paper titled "O-NIIS: Open and Intelligent IRS-SWIPT for Wireless Energy-Efficiency Enhancement", authored by Dara Ron and Jung-Ryun Lee, is now accepted for publication in IEEE Transactions on Vehicular Technology (IF: 7.1, Q1).

The paper titled "Context-Aware Embedding Masking Based on Reinforcement Learning for Semantic Multiplexing", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, is now accepted for publication in IEEE Wireless Communications Letters (IF: 5.1, Q1).

The paper titled "Multi-UAV-aided Power-up and Data Collection: Multi-agent DQL with Genetic Algorithm Approach", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 297, Part B, Feb. 2026.

The paper titled "Multiple Quality-of-Services Optimization in Space–Air–Ground Integrated Network: Centralized and Decentralized Deep Reinforcement Learning Approaches", authored by Sengly Muy, Vitou That, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 297, Part B, Feb. 2026.

The paper titled "Federated Learning-Based Spectrum and Energy Efficiency Enhancement in HAP-Assisted LEO Satellite Communication", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 296, Part A, on 15 Jan. 2026.

The paper titled "Joint Optimization of Secrecy Rate and Energy Consumption for RSMA in SAGIN via MADRL", authored by Kimchheang Chhea and Jung-Ryun Lee, was published in IEEE Transactions on Vehicular Technology (IF: 7.1, Q1), vol. 75, no. 2, Feb. 2026.

The paper titled "Transformer-Based Shared Embedding for Multiple Access in Semantic Communications", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, was published in IEEE Journal on Selected Areas in Communications (IF: 17.2, Q1), vol. 44, on 20 Feb. 2026.

The paper titled "Beamforming Center Control in LEO Satellite Communications for Maximizing Minimum Throughput of Ground Users", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Aerospace Science and Technology (IF: 5.8, Q1), vol. 170, March 2026.

The paper titled "Attention-Driven Semantic Transmission Scheme for AI-Native Wireless Communications", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, was published in IEEE Communications Letters (IF: 4.4, Q2), vol. 30, March 2026.

The paper titled "Intelligent Energy Efficiency and Service Reliability Optimization for UAV-Aided Terrestrial Networks", authored by Dara Ron and Jung-Ryun Lee, was published in IEEE Transactions on Green Communications and Networking (IF: 6.7, Q1), vol. 10, 2026.

The paper titled "Deep Reinforcement Learning-Based Active Sensing on a Bicycle for Vehicle Tracking", authored by Woongsun Jeon, Dara Ron, and Jung-Ryun Lee, was published in IEEE Transactions on Instrumentation & Measurement (IF: 5.9, Q1), vol. 75, 2026.

The paper titled "Maximizing SAGIN Coverage with Joint HAP/UAV Placement, Power, Bandwidth, and Beamforming via Deep Actor-Critic with a Temperature Function-based Policy", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, is now accepted for publication as of 14 Jan. 2026, in Journal of King Saud University Computer and Information Sciences (IF: 6.1, Q1). 

The paper titled "Multi-UAV-aided Power-up and Data Collection: Multi-agent DQL with Genetic Algorithm Approach", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 297, Part B, Feb. 2026.

The paper titled "Multiple Quality-of-Services Optimization in Space–Air–Ground Integrated Network: Centralized and Decentralized Deep Reinforcement Learning Approaches", authored by Sengly Muy, Vitou That, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 297, Part B, Feb. 2026.

The paper titled "Federated Learning-Based Spectrum and Energy Efficiency Enhancement in HAP-Assisted LEO Satellite Communication", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Expert Systems with Applications (IF: 7.5, Q1), vol. 296, Part A, on 15 Jan. 2026.

The paper titled "Joint Optimization of Secrecy Rate and Energy Consumption for RSMA in SAGIN via MADRL", authored by Kimchheang Chhea and Jung-Ryun Lee, was published in IEEE Transactions on Vehicular Technology (IF: 7.1, Q1), vol. 75, no. 2, Feb. 2026.

The paper titled "Transformer-Based Shared Embedding for Multiple Access in Semantic Communications", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, was published in IEEE Journal on Selected Areas in Communications (IF: 17.2, Q1), vol. 44, on 20 Feb. 2026.

The paper titled "Beamforming Center Control in LEO Satellite Communications for Maximizing Minimum Throughput of Ground Users", authored by Vitou That, Sengly Muy, and Jung-Ryun Lee, was published in Aerospace Science and Technology (IF: 5.8, Q1), vol. 170, March 2026.

The paper titled "Attention-Driven Semantic Transmission Scheme for AI-Native Wireless Communications", authored by Ki-Ho Lee, Hyun-Ho Choi, and Jung-Ryun Lee, was published in IEEE Communications Letters (IF: 4.4, Q2), vol. 30, March 2026.

The paper titled "Intelligent Energy Efficiency and Service Reliability Optimization for UAV-Aided Terrestrial Networks", authored by Dara Ron and Jung-Ryun Lee, was published in IEEE Transactions on Green Communications and Networking (IF: 6.7, Q1), vol. 10, 2026.

The paper titled "Deep Reinforcement Learning-Based Active Sensing on a Bicycle for Vehicle Tracking", authored by Woongsun Jeon, Dara Ron, and Jung-Ryun Lee, was published in IEEE Transactions on Instrumentation & Measurement (IF: 5.9, Q1), vol. 75, 2026.