Cross-Layer Chase Combining With Selective Retransmission, Analysis, and Throughput Optimization for OFDM Systems

In this paper, we present a bandwidth efficient retransmission method employing selective retransmission approach at a modulation layer under orthogonal frequency division multiplexing (OFDM) signaling. The proposed cross-layer design embeds a selective retransmission sub-layer in physical layer (PHY) that targets the retransmission of information symbols transmitted over poor quality OFDM sub-carriers. Most of the times, a few errors in decoded bit stream result in packet failure at medium access control (MAC) layer. The unnecessary retransmission of good quality information symbols of a failed packet has detrimental effect on the overall throughput of transceiver. We propose a cross-layer Chase combining with selective retransmission (CCSR) method by blending Chase combining approach at MAC layer and selective retransmission in PHY. The selective retransmission in PHY targets the poor quality information symbols prior to decoding, which results in lower hybrid automatic repeat reQuest retransmissions at MAC layer. We also present bit-error rate upper bound and throughput lower bound for the CCSR method. In order to maximize the throughput, we formulate optimization problem with respect to the amount of information to be retransmitted in selective retransmission. We also present an impact of selective retransmission on latency. The proposed CCSR method achieves a significant throughput gain as compared with the conventional Chase combining method.