Implementation of Physical-layer Network Coding

TL;DR

This paper demonstrates the first practical implementation of physical-layer network coding (PNC) using OFDM on USRP hardware, addressing synchronization and channel estimation challenges to improve relay network performance.

Contribution

It introduces a frequency domain PNC (FPNC) implementation based on OFDM, with experimental validation showing comparable performance in synchronized and asynchronous conditions.

Findings

FPNC achieves similar BER performance in both synchronous and asynchronous scenarios.

Implementation on USRP requires moderate modifications to existing 802.11a/g OFDM PHY.

FPNC effectively handles symbol asynchrony and multi-path effects using OFDM cyclic prefix.

Abstract

This paper presents the first implementation of a two-way relay network based on the principle of physical-layer network coding. To date, only a simplified version of physical-layer network coding (PNC) method, called analog network coding (ANC), has been successfully implemented. The advantage of ANC is that it is simple to implement; the disadvantage, on the other hand, is that the relay amplifies the noise along with the signal before forwarding the signal. PNC systems in which the relay performs XOR or other denoising PNC mappings of the received signal have the potential for significantly better performance. However, the implementation of such PNC systems poses many challenges. For example, the relay must be able to deal with symbol and carrier-phase asynchronies of the simultaneous signals received from the two end nodes, and the relay must perform channel estimation before detecting the signals. We investigate a PNC implementation in the frequency domain, referred to as FPNC, to tackle these challenges. FPNC is based on OFDM. In FPNC, XOR mapping is performed on the OFDM samples in each subcarrier rather than on the samples in the time domain. We implement FPNC on the universal soft radio peripheral (USRP) platform. Our implementation requires only moderate modifications of the packet preamble design of 802.11a/g OFDM PHY. With the help of the cyclic prefix (CP) in OFDM, symbol asynchrony and the multi-path fading effects can be dealt with in a similar fashion. Our experimental results show that symbol-synchronous and symbol-asynchronous FPNC have essentially the same BER performance, for both channel-coded and unchannel-coded FPNC.