Optimizing the search of finite-state joint source-channel codes based on arithmetic coding

Joint source-channel (JSC) coding is an important alternative to classic separate coding in wireless applications that require robustness without feedback or under stringent delay constraints. JSC schemes based on arithmetic coding can be implemented with finite-state encoders (FSE) generating finite-state codes (FSC). The performance of an FSC is primarily characterized by its free distance, which can be computed with efficient algorithms. This work shows how all FSEs corresponding to a set of initial parameters (source probabilities, arithmetic precision, design rate) can be ordered in a tree data structure. Since an exhaustive search of the code with the largest free distance is very difficult in most cases, a criterion for optimized exploration of the tree of FSEs is provided. Three methods for exploring the tree are proposed and compared with respect to the speed of finding a code with the largest free distance.