On reducing the rate of retransmission in time-varying channels

For data communications in time-varying channels such as wireless channels, the dynamic channel fluctuations often cause high frame-error rates. When the link layer detects that a frame is in error, conventionally, the frame is dropped and retransmission of the frame is requested. Based on the fact that the erroneous frames still contain useful information, several schemes have been proposed, such as packet combining and incremental redundancy, which retain and utilize the erroneous frames to improve retransmission performance. In this paper, we address two questions: 1) how much information is still useful in the erroneous frame; and 2) how to design a retransmission scheme to make efficient use of such information. We model this scenario (retransmission with an erroneous frame available at the receiver) as communication with side information at the receiver, and for a class of time-varying channels, the compound block interference channels, we derive with information-theoretic arguments the minimum information rate sufficient for retransmission to recover the erroneous frame. Motivated by the theoretical results, we propose an embedded channel coding/modulation structure together with a rate-adaptive retransmission scheme. Performance results indicate significant improvements over existing retransmission schemes in both additive white Gaussian noise and quasi-static Rayleigh fading channels.