Sequential Decoding with ARQ and Code Combining

In this paper we consider sequential decoding with ARQ and code combining under the time-out condition. That is whenever the decoding time of a given packet exceeds some predetermined duration, decoding is stopped and retransmission of the packet is requested. However the unsuccessfull packets are not discarded, but are combined with their retransmitted copies. We show that the use of code combining allows sequential decoding to operate efficiently even when the coding rate R exceeds the computational cut-off rate Rcomo. Furthermore, an analysis of the Ideal-Selective-Repeat ARQ scheme shows that the use of code combining yields a significant throughput even at very high channel error rates, thus making it a very robust hybrid FEC/ARQ system.