Universal coding for quasi-stationary processes

A quasi-stationary, or composite, source model arises in a variety of practical and theoretical situations: time-division multiplex environments, speech modeling, and in the study of stationary, nonergodic random processes. This paper considers the problem of coding (with respect to a fidelity criterion) for such processes when the collection of modes is fixed but the switch is unknown. Universal-type codes are sought and it is shown that, for any rate R, there exists a sequence of codes with increasing blocklength whose rates approach R and whose distortions (for any switch process) approach the lowest theoretically obtainable. This result is shown to provide theoretical justification for some current findings in speech compression and in template generation for speaker-independent word recognition.