Performance comparison of layered coding and multiple description coding in packet networks

We examine the performance of multiple descriptions coding (MDC) with and without the use of automatic retransmission request (ARQ) protocols for packet network communication. The rate-distortion lower bound of MDC and layered coding (LC) are incorporated into a performance measure that accounts for the additional costs of excess rates and delay incurred from using ARQ. Results show that unaided MDC is the best for large packet loss rates and large delay, and LC is the best for small loss and moderate delay. In between these two extremes, MDC aided by ARQ provides the best performance

I. Introduction

Layered coding (LC) and multiple description coding (MDC) have been proposed as source coding schemes that can offer robust communication over packet loss channels. In contrast to traditional coding schemes that generate a single bitstream, LC and MDC generate two or more bitstreams. In LC, one bitstream is sent as a base layer and the other bitstreams are successive enhancement layers. The base layer has higher priority than the enhancement layers as the loss of the base layer makes the information received from the enhancement layers useless. An enhancement layer can be decoded only if the base layer and all previous enhancement layers have been correctly received. Automatic repeat request (ARQ) or forward error correction (FEC) is generally employed for error control in the base layer. In the rest of this paper, unless otherwise noted, the base layer of LC is transmitted using ARQ (and requisite error detection coding). The multiple bitstreams (descriptions) of MDC, however, are equally important. Any subset of the bitstreams is decodable, and reconstruction quality improves with the size of the subset. One means of realizing MDC is using FEC codes [1].