Capacity and linear precoding for packet retransmissions

This paper presents a method for enhancing wireless ARQ system performance by combining packet retransmissions through frequency-selective channels. As a measure of system performance, we derive the total mutual information (or channel capacity) provided by multiple transmissions of a packet through different channels. Retransmissions are uniquely linear precoded and/or truncated in relation to the original transmission. With the objective of maximizing total throughput, optimal linear precoders are developed for zero-padded packet transmissions. These precoders effectively implement power loading with the right singular vectors of the original transmission channel serving as basis vectors. Simulation results validate the increase the overall mutual information and throughput from optimized precoding.