ARQ and Interleaving Techniques

Abstract

Modern communication systems usually need some form of error control to achieve a low bit-error rate and to guarantee a stipulated constant quality of service. All of the error-control systems discussed in the preceding eight chapters can be used on channels in which the message flow is in only one direction. Such error-control systems are called forward error-correcting (FEC) systems. However, in many applications data flow is bi-directional. In such cases messages are sent over the “forward” channel and acknowledgment signals are sent back from the “return” channel. The simplest error control for channels with feedback is the technique, called automatic repeat-request (ARQ) protocol[2]. In these protocols the transmitted data are encoded for error detection; detected errors at the receiver result in the generation of a retransmission request. ARQ provides the best performance on pure-burst channels with memory while most FEC schemes work efficiently only on memoryless channels.