A BLIND SEQUENCE DETECTION AND ITS APPLICATION TO DIGITAL MOBILE COMMUNICATION

A method of sequence detection without the knowledge of the channel re sponse is proposed. The Viterbi algorithm is extended to a blind form by introducing a new branch-metric, defined as the minimum of the shor t time-average of the squared error (y(k) - y(k))(2), where y(k) and y (k) are the received signal and its replica, respectively. All possibl e candidate sequences contained in the short time squared error are de fined as trellis states, for which the short time squared error is min imized in respect to a variable of the unknown channel response. The p roposed Implicit Blind Sequence Detection need not keep each variable after the branch metric is calculated. The consistency of the algorith m is justified by proving that a unique sequence is detected in noise free case. The proof is accomplished under condition that the period o f the time-average is longer than the channel response. If the additiv e white Gaussian noise is assumed, the short time squared errors are m inimized beyond the desired minimum by the standard Viterbi algorithm using an apriori known channel response. In this paper, we call this p henomenon as over-minimization. The over-minimization is a major reaso n of the unavoidable error rate degradation in the blind receiver. An objective of this paper is to establish blind sequence detection for d igital mobile communication. Provided the channel response can be rega rded as time-invariant during the period of the short time-average of the squared error, the blind sequence detection keeps the same perform ance as in time-invariant case. In order to improve the error rate per formance, an algorithm based on the fractional sampling scheme is intr oduced. Several error rate performances and behaviors of error events are investigated by computer simulation.