Delay-constrained joint source-channel coding using incremental redundancy with feedback

We present a joint source-channel coding scheme based on incremental redundancy and feedback for transmission of real-time sources over wireless channels under strict delay constraints. The proposed scheme operates at constant bit rate and delay so as to capture the benefits of a feedback channel, while keeping the synchronous nature of pure forward error correction systems. We formulate the underlying Markov chain by introducing the notion of codetype and present a design algorithm for channel and source rate allocation. We present simulation results for speech transmission and show gains of up to 1 dB over pure FEC systems. We also present an application to CDMA networks and show increases of up to 28 % in the number of calls that can be simultaneously supported.