Design methodology for high-speed iterative decoder architectures

We propose a novel approach to the design and analysis of VLSI architectures for the soft-input soft-output a posteriori probability (SISO-APP) decoding algorithm used in iterative decoders such as turbo decoders. The approach is based on a tile-graph composed of recursion patterns that model the resource-time scheduling of the forward-backward recursion equations of the algorithm. The problem of constructing a SISO-APP architecture is formulated as a three-step process of constructing and counting the patterns needed and then tiling them. The problem of optimizing the architecture for high speed and low power reduces to optimizing the individual patterns and the tiling scheme for minimal delay and storage overhead. The various forms of the sliding and parallel-window (PW) architectures in the literature are instances of the proposed tile-graph. Using the tile-graph approach, a new PW architecture controlled by the window width r is proposed that achieves for r = 10 a 45%, a 71%, a 51%, and a 25% reduction in decoding delay, state, input, and output metrics storage respectively, compared to a conventional architecture with a 10% increase in resources.