Trellis transition-probability calculation with threshold normalization

摘要

A circuit performs threshold normalization of accumulated transition probabilities for a given state of a state transition trellis in a maximum likelihood detector. Threshold normalization may be accomplished by comparison and setting of a single bit in stored transition probabilities. Threshold value comparison may be accomplished by comparing the bbit of the stored transition probabilities if the threshold value is 2b. When all transition probabilities exceed the threshold value at a stage of the trellis, the transition probabilities are scaled, such as by subtracting the threshold value. Scaling may be implemented by setting the compared bbits to zero before storage. In general, since accumulated transition probabilities are monotonically increasing for transition probabilities of paths through the trellis in both forward and reverse directions, the present invention may be employed for both threshold normalization of both the forward (alpha) and reverse (beta) transition probabilities.