Irregular Variable Length Coding for Near-capacity Joint Source and Channel Coding

In this paper we propose a novel Irregular Variable Length Coding (IrVLC) scheme for near-capacity joint source and channel coding. We employ a number of component Variable Length Coding (VLC) codebooks having different coding rates for encoding particular fractions of the input source symbol stream. With the aid of EXtrinsic Information Transfer (EXIT) charts, these fractions may be chosen such that the EXIT curve of the IrVLC codec may be matched to that of a serially concatenated channel codec as closely as possible. In this way, an open EXIT chart tunnel may be created even at low Eb/N0 values that are close to the channel capacity. We demonstrate iteratively decoded schemes in which we opt to serially concatenate the proposed IrVLC designs with Trellis Coded Modulation (TCM). These schemes are shown to be capable of operating within 0.6 dB of the uncorrelated narrowband Rayleigh fading channel’s capacity at an effective bandwidth efficiency of 1.56 bit/s/Hz, assuming ideal Nyquist filtering. By contrast, the equivalent-rate VLC-based benchmarker schemes were found to be capable of operating at 1.1 dB from capacity, which is nearly double the discrepancy of the proposed IrVLC-TCM schemes.