US Patent 7649952 Low complexity soft demapping

A method of analyzing soft symbol information in a communication system that transmits multiple independent data streams is disclosed. The method includes setting a trellis structure using a fixed spatial delay constraint, calculating a joint probability between a targeted symbol and a set of observation samples either recursively or nonrecursively, and approximating a likelihood function for a given branch by a single probability density function with mean and variance computed based on available soft information on past symbols relative to the branch that is being currently considered.