A reduced-state soft input soft output algorithm based on state partitioning

SISO (soft input soft output) algorithms are present in several decoding schemes, particularly in concatenated ones that admit an efficient iterative detection, e.g. turbo codes. These algorithms have been an interesting research subject, especially for the aspects related to complexity reduction. This paper presents the idea of partitioning the set of original states in a channel or a code, generating a scaled (or reduced) trellis. Merging two or more states produces a new super-state and a standard SISO algorithm can follow the system evolution in terms of the new description.