Iterative enhanced packet combining over hybrid-ARQ

Abstract

Many widely used wireless networking protocols, such as WiMAX, UMTS and 3GPP Long Term Evolution use Hybrid ARQ for error control. H-ARQ improves the bit error rate performance and reduces the number of retransmissions. If the packet is in error even after forward error correction, then a retransmission request is made by the receiver. In order to reduce the retransmissions, different methods to combine the retransmitted erroneous packet(s) with the previous copies have been proposed earlier. In this paper, an enhanced packet combining method is presented that corrects both the even and odd errors in an erroneous packet by combining the current erroneous copy with the previous one and thereafter performing iterative decoding. The combining method uses both soft and hard information for better performance. A performance comparison is given with certain existing packet combining methods. The proposed method not only reduces the number of retransmissions, but also detects all the errors, with a high probability as given, if the number of errors remains within a certain threshold. The probability of the success of packet recovery for the proposed method is presented. Finally, simulation results for bit error rate, packet acceptance rate and retransmission rates for different packet sizes are presented for comparison.