Soft-input soft-output modules for the construction and distributed iterative decoding of code networks

Soft-input soft-output building blocks (modules) are presented to construct and iteratively decode in a distributed fashion code networks, a new concept that includes, and generalizes, various forms of concatenated coding schemes. Among the modules, a central role is played by the SISO module (and the underlying algorithm): it consists of a four-port device performing a processing of the sequences of two input probability distributions by constraining them to the code trellis structure. The SISO and other soft-input soft-output modules are employed to construct and decode a variety of code networks, including "turbo codes" and serially concatenated codes with interleavers.