Non-memoryless Analog Network Coding in Two-Way Relay Channel

TL;DR

This paper introduces a non-memoryless Analog Network Coding scheme for two-way relay channels, utilizing a soft-input soft-output decoder that exploits channel coding redundancy to significantly improve performance over traditional symbol-by-symbol ANC methods.

Contribution

It proposes a novel non-memoryless ANC scheme with a decoder that leverages symbol correlation, providing notable SNR improvements and practical insights into LDPC code selection.

Findings

SNR improvement lower bounded by 1/R with repeat code

Decoder exploits correlation among symbols for better MSE

LDPC codes of different degrees are optimal in different SNR regions

Abstract

Physical-layer Network Coding (PNC) can significantly improve the throughput of two-way relay channels. An interesting variant of PNC is Analog Network Coding (ANC). Almost all ANC schemes proposed to date, however, operate in a symbol by symbol manner (memoryless) and cannot exploit the redundant information in channel-coded packets to enhance performance. This paper proposes a non-memoryless ANC scheme. In particular, we design a soft-input soft-output decoder for the relay node to process the superimposed packets from the two end nodes to yield an estimated MMSE packet for forwarding back to the end nodes. Our decoder takes into account the correlation among different symbols in the packets due to channel coding, and provides significantly improved MSE performance. Our analysis shows that the SNR improvement at the relay node is lower bounded by 1/R (R is the code rate) with the simplest LDPC code (repeat code). The SNR improvement is also verified by numerical simulation with LDPC code. Our results indicate that LDPC codes of different degrees are preferred in different SNR regions. Generally speaking, smaller degrees are preferred for lower SNRs.