Bit-by-Bit Iterative Decoding Expedites the Convergence of Repeat Accumulate Decoders

In this paper, we propose bit-by-bit iterative decoding for expediting the convergence of Repeat Accumulate (RA) decoders. In a conventional RA decoder, the repeat and accumulate component decoders are operated iteratively, to facilitate near-capacity communication. However, whenever one decoder is activated, the other is kept idle. The outputs of the active component decoder are stored until its operation is completed, whereupon the outputs are forwarded to the other decoder all at once and the activation of the decoders is swapped. The proposed bit-by-bit RA decoder expedites this process by allowing both component decoders to operate simultaneously, continuously exchanging outputs without buffering. We present both EXtrinsic Information Transfer (EXIT) charts and Bit Error Ratio (BER) results, which demonstrate that the proposed bit-by-bit RA decoder requires fewer decoding iterations to converge, at the cost of a slightly increased complexity per decoding iteration. Overall, we demonstrate that in a range of practical scenarios, the proposed bit-by-bit RA offers gains of up to 0.86 dB, without imposing any additional decoding complexity and without requiring any additional transmission-energy, -bandwidth or -duration.