Cross-layer Chase Combining with Selective Retransmission, Analysis and Throughput Optimization for OFDM Systems

TL;DR

This paper introduces a cross-layer retransmission method for OFDM systems that selectively retransmits poor quality symbols, significantly improving throughput by reducing unnecessary retransmissions and optimizing the retransmission process.

Contribution

It proposes a novel cross-layer Chase combining with selective retransmission (CCSR) method that targets poor quality symbols at the physical layer to enhance throughput.

Findings

Significant throughput gains over conventional Chase combining.

Derived tight BER upper bound for the CCSR method.

Formulated an optimization problem to maximize throughput.

Abstract

In this paper, we present bandwidth efficient retransmission method employong selective retransmission approach at modulation layer under orthogonal frequency division multiplexing (OFDM) signaling. Our proposed cross-layer design embeds a selective retransmission sublayer in physical layer (PHY) that targets retransmission of information symbols transmitted over poor quality OFDM sub-carriers. Most of the times, 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 overall throughput of transceiver. We propose a cross-layer Chase combining with selective retransmission (CCSR) method by blending Chase combining at MAC layer and selective retransmission in PHY. The selective retransmission in PHY targets the poor quality information symbols prior to decoding, which results into lower hybrid automatic repeat reQuest (HARQ) retransmissions at MAC layer. We also present tight bit-error rate (BER) upper bound and tight throughput lower bound for CCSR method. In order to maximize throughput of the proposed method, we formulate optimization problem with respect to the amount of information to be retransmitted in selective retransmission. The simulation results demonstrate significant throughput gain of the proposed CCSR method as compared to conventional Chase combining method.