Performance analysis of PLNC using hierarchical modulation

In this paper, we propose and analyze the performance of a two-way relay network (TWRN) using physical layer network coding (PLNC) with hierarchical modulation (HM). The performance is evaluated for additive white Gaussian noise (AWGN) channels. The TWRN consists of two end nodes and a relay, where each node has a single antenna and operates in a half-duplex mode. Using an analytical approach, we derive the end-to-end symbol error rate (SER) performance expression of the 4/16-QAM HM for the high priority (HP) and the low priority (LP) streams, respectively, as a function of signal-to-noise ratio (SNR). It has been found the analytical and simulation results are in close agreement. The utilization of the proposed HM-PLNC system minimizes the computational complexity of the denoise and forward (DNF) operations at the relay by reducing the number of Euclidean distance computations required to 18 compared to the 49 required in an equivalent 16-QAM based PLNC system.

I. Introduction

The first concept of the two-way relay network (TWRN) based on the principle of physical layer network coding (PLNC) was discussed in [1] as a novel method in order to raise spectral efficiency. The TWRN system consists of two end nodes, A and B, that exchange their information via a relay node, R, simultaneously. PLNC can potentially elevate the throughput of a traditional TWRN by 100 % [2], [3]. To relay information, PLNC can utilize various strategies at the relay, such as amplify-and-forward (AF) and denoise-and-forward (DNF) [4]. This paper focuses on the DNF scheme which has attracted much interest in recent research because it avoids noise amplification and can improve the achievable throughput [5].