Patent ID: 8711988

Claim:
A method of generating soft bit values for a sequence of transmitted symbols using a demodulator, the method comprising: updating an M-state trellis managed by the demodulator responsive to a transition from symbol time n−1 to symbol time n, where M is a function of the number of bits per symbol in the sequence of transmitted symbols; saving survivor metrics associated with the M states of the trellis each symbol time so that the demodulator can calculate soft bit values with regard to transitions from symbol time n+D−1 to symbol time n+D, the survivor metrics indicating the probability that each respective state represents the transmitted symbol associated with symbol time n+D−1 , where D is a decision depth of the demodulator; and tracing back through the trellis to calculate soft bit values for only a particular symbol detected at symbol time n−D based on survivor metrics saved for the M states at symbol time n−D.