Selective repeat type-II hybrid fec/arq systems using concatenated codes

Hybrid forward error correction/automatic-repeat request (FEC/ARQ) systems achieve greater throughput than ARQ systems by combining forward error correction with automatic-repeat requests. A type-II hybrid FEC/ARQ system is capable of adapting error-correction capacity according to varying channel conditions. Although a high throughput can be achieved in such systems by using conventional convolutional or rate compatible punctured convolutional (RCPC) codes, when the channel signal-to-noise ratio (SNR) Es/N0 is low, resulting throughput efficiency and mean block delay performances are unsatisfactory. In this paper, selective repeat type-II hybrid FEC/ARQ systems using concatenated codes are proposed to improve the throughput efficiency and mean block delay performances on channels with low SNRs. Systems using concatenated Reed-Solomon outer codes and either rate one-half convolutional or rate compatible convolutional (RCPC) inner codes are evaluated. The throughput efficiency and mean packet waiting and block delay times of these two types of concatenated coding systems are evaluated. A theoretical analysis and computer simulation of throughput efficiency of the proposed systems show increased performance for a wide range of Es/N0 over previous systems that use either stand-alone rate one-half convolutional or RCPC codes. It is also shown that the transmitter mean packet queueing delay and mean block delay times are reduced. In particular, by computer simulation, it is shown that when the traffic density is high, mean block delay times are greatly reduced by the use of RCPC inner codes.