End-to-End Distortion Analysis of Nonorthogonal Layered Coding Over Relay-Assisted Networks

This article investigates cross-layer design of nonorthogonal layered (NOL) coding schemes over relay-assisted downlink of cellular networks that incorporates with successive refinement (SR) source code for transmission of adaptive multiresolution multimedia content. Two novel-layered relaying strategies, namely NOL compress-forward (NOL-CF) and NOL decode-forward (NOL-DF) coding, concatenated to the SR source coding scheme are outlined. The network parameters are jointly optimized, to derive optimal end-to-end system performance. Taking the expected distortion (ED) as the end-to-end system performance metric, the explicit analytical solution achieving optimal ED under the proposed NOL-CF scheme with two layers is derived. For the NOL-DF coding, the numerical analysis demonstrates the merits of the proposed scheme, which dynamically adapts the transmission to the instantaneous channel realization in the absence of channel knowledge at the source node. The superiority of the proposed layered coding over several available nonorthogonal multiple access relaying schemes is demonstrated for Gaussian channels. Also, simulation results confirm the effectiveness of the proposed relay-assisted NOL codes to improve the ED over Rayleigh fading channel.

I. Introduction

Multifold increase in spectral efficiency and throughput is envisioned in the fifth generation (5G) of cellular networks to meet the requirements of IMT-2020 on massive connectivity and tremendous data traffic [1]. This is achieved by evolution in three aspects of current networks. The first aspect is shrinking the cell sizes and deploying dense picocells and femtocells to boost the spectral reuse. The second is to allocate more spectrum resources including millimeter-wave bands. The third is deploying highly efficient communications techniques [2].