Reliability-based hybrid-ARQ using convolutional codes

In this work we develop selective-retransmission hybrid-ARQ protocols for communication systems that use soft-input soft-output (SISO) decoders. The schemes that we propose are based on reliability-based hybrid-ARQ that use the estimated a posteriori probabilities at the output of the SISO decoder to adaptively determine the set of bits to be retransmitted in response to error detection.;First we show the performance of the proposed scheme for nonfading additive white Gaussian noise channels without any interference. We begin by evaluating the performance of a simple reliability-based hybrid ARQ scheme that uses fixed rate convolutional codes in the forward channel and exploits their time-correlation properties to achieve smaller retransmission requests. Then we extend our work where rate-compatible punctured convolutional (RCPC) codes are used in the forward channel and arithmetic coding is used in the feedback channel. We compare the performance of the proposed scheme with the common approach to hybrid-ARQ that uses punctured convolutional codes. The results show that the proposed RB-HARQ scheme achieves better performance than a hybrid-ARQ scheme that uses only RCPC codes.;Next we extend our work to improve communication performance on partial-time jamming channels. For channels with partial-time jamming, we can extend our measure of reliability to incorporate not only a posteriori probability information but also estimates of the probability that a bit was jammed. We compare the performance of the proposed scheme with that of a conventional approach in which a predetermined set of bits is retransmitted in response to a packet failure. The results show that RB-HARQ schemes can achieve better performance than the conventional approach.;Next we extend our work to wireless networks that use carrier sense multiple access with collision avoidance (CSMA-CA). We first propose a new channel model that considers the packet errors due to channel noise as well as those due to interference from simultaneous transmission by other nodes. The proposed channel model takes into account the fact that collisions may result in parts of a packet being corrupted while other parts are received without corruption. Therefore, the proposed channel model is more realistic than an AWGN channel model and can be used in a cross-layer design approach which considers combining ARQ at the data link layer and channel coding at the physical layer. We also investigate the performance of a RB-HARQ technique for CSMA-CA-based wireless networks.