Physical-Layer Network Coding Based on Residual Field of Algebraic Integers in OFDM-VLC Two-Way Relay Networks

We propose a novel physical-layer network coding (PNC) scheme based on residual field of algebraic integers (RFAI) for orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) two-way relay networks (TWRNs). The proposed scheme employs operations in the RFAI and many-to-one mapping to encode the superposed signal of users at the relay so that the constellation size of the superposed signal is reduced, thereby significantly improving the performance. Systematic analyses on the construction of the RFAI and the codebook of the transmitted signals from users, the encoding at the relay and the rules of parameter optimization to maximize the minimal Euclidean distance, are carried out. Experiments of OFDM-VLC TWRN with up to 1.47-Gbit/s throughput under both symmetric and asymmetric uplink channel conditions are conducted to verify the proposed theory. In both scenarios, uniform 8QAM/16QAM and adaptively-loaded OFDM are investigated. It is shown that in both scenarios, the proposed scheme exhibits much better performance than the conventional amplify-and-forward PNC, and the results can be well explained by the theory. It is also shown that in the asymmetric scenario, proper adjustment of transmitted power at users can improve the performance of TWRN while reducing the power consumption.