Relay Network

In this paper network coding based relay for multi-access channel is studied. In the system, two nodes send messages to a common access point (AP). A relay assists the two nodes by forwarding a network coded version of the messages. The AP performs joint channel and network decoding to recover the two original messages from three received signals. Two schemes, soft network coding (SoftNC) and turbo network coding (TurboNC), both focusing on bitwise exclusive or (XOR) based network coding, are proposed to salvage messages from erroneous signals. SoftNC is simple and backward compatible with existing protocol stack of wireless networks, and reduces packet errors by maximal ratio combining (MRC). TurboNC improves channel efficiency by letting the relay node transmit only parity check bits of the interleaved XORed message, where reliability is retained by iterative decoding. Simulation results show that compared with the network-layer path diversity scheme [8], both SoftNC and TurboNC greatly improve the reliability, and Tur-boNC also achieves a much higher throughput. The proposed schemes are suitable for improving the performance of wireless local area networks (WLAN).

Background: Visible Light Communication (VLC) has emerged as a promising alternative to radio frequency (RF) communication, providing high data rates, enhanced security, and cost-efficient deployment using existing lighting infrastructure. However, VLC is vulnerable under low-light and line-of-sight (LOS) blockage scenarios, which expose the system to performance degradation and security threats. In this paper, we propose a RIS-assisted adaptive optimization framework for enhancing physical layer security in low-light VLC environments. By dynamically reconfiguring RIS elements, the system maximizes the secrecy capacity, maintains high signal-to-noise ratio (SNR), and suppresses the information leakage to potential eavesdroppers. To achieve this, we develop an enhanced feedback-controlled adaptive particle swarm optimization (FC-APSO) scheme with a security-driven cost function, balancing SNR, bit error rate (BER), and secrecy capacity. Simulation results demonstrate that our proposed RIS-assisted secure VLC framework outperforms static RIS placement, traditional PSO, and genetic algorithms (GA), achieving up to 35% secrecy capacity improvement and consistently maintaining BER below 10 in the presence of eavesdroppers under dim-light scenarios. This work highlights the potential of RIS-assisted optimization as a foundation for secure VLC-based IoT and indoor wireless systems.