Parallel Viterbi decoding methods for uncontrollable and controllable sources

AbsrructThe fastest conventional Viterhi decoding method processes all states in parallel, but still decodes code symbols sequentially. In order to decode faster than this rate, parallel methods must be developed to break the processing into independent state-parallel decoding tasks. This paper discusses parallel Viterbi decoding for two different cases: uncontrollable sources and controllable sources. For general, uncontrollable Markov processes, we extend a previously known parallel method to a hierarchical parallel decoding approach, which achieves a lower latency. For controllable Markov sources in telecommunications applications, we propose new parallel decoding methods by controlling the source processes in appropriate ways. This paper focuses on the parallel decoding methods for controllable sources because these methods have zero processing overhead. Because the methods modify the coding process, they bring positive changes to framing and negative changes to latency and code performance. However, we can adjust the parameters of the methods to make the degradation negligible. Because of their low overhead, the methods are most attractive for high-speed decoders for convolutional and trellis codes, and also applicable to other sequential algorithms for suboptimal decoding and estimation of complex Markov sources.