A Discrete Queue-Based Model for Capturing Memory and Soft-Decision Information in Correlated Fading Channels

A discrete (binary-input 2^q-ary output) communication channel with memory is introduced to judiciously capture both the statistical memory and the soft-decision information of a time-correlated discrete fading channel (DFC) used with antipodal signaling and soft output quantization of resolution q. The discrete channel, which can be explicitly described via its binary input process and a 2^q-ary noise process, is shown to be symmetric, thus admitting a simple expression for its capacity when its noise is stationary ergodic. It is observed that considerable capacity gains can be achieved due to the channel´s memory and the use of as few as 2 bits for soft-decision over interleaving the channel (to render it memoryless) and hard-decision demodulation (q=1). The 2^q-ary noise process is next modeled via a queue-based (QB) ball-sampling mechanism to produce a mathematically tractable stationary ergodic Markovian noise source. The DFC is fitted by the QB noise model via an iterative procedure that minimizes the Kullback-Leibler divergence rate between the DFC and QB noise sources. Modeling results, measured in terms of channel noise correlation function and capacity reveal a good agreement between the two channels for a broad range of fading conditions.