End-to-end distortion analysis of multicasting over orthogonal receive component decode-forward cooperative broadcast channels

This paper studies the end to end distortion of transmission of a layered encoded source over a cooperative relay broadcast channel. A jointly optimised source-channel code is proposed to multicast a two-layered encoded source to two destinations. A degraded discrete memoryless broadcast channel is assumed, where the first destination with better channel conditions decodes both layers consisting of the common base layer and the refining layer for source reconstruction at a higher quality. Meanwhile, the second destination only decodes the base layer for a lower quality reconstruction of the source. The first destination cooperates in transmitting the common base layer to the second destination using a decode-forward (DF) relaying protocol over an orthogonal receive component (ORC) relay channel. An inner bound on the capacity region of the ORC-DF cooperative broadcast channel with a degraded message set is derived and the end to end distortion of reconstructing the source at both of the destinations is characterized. The achievable rate region and distortion performance of such network are demonstrated to outperform another variant of a DF-based cooperative broadcast channel, as well as with the non-cooperative broadcast channel.

I. Introduction

Layered source code has been deployed widely, to enable the adaptation of transmission of a source to several destinations with different channel conditions, in the absence of channel state information (CSI) of destinations' links at the transmitter side [1] and [2]. Each destination, based on the quality of its link can decode some of the layers, and decode the source sequence within a certain level of distortion. The destinations with better links can decode more layers, which results in a lower distortion and better quality reconstruction of the source. By mapping the layered source code to different multi user transmission schemes at the channel, a jointly optimised source-channel coding framework can be formed, which has been proved to outperform separate source and channel codes in multi-user network architectures [3].