Maximum likelihood decoding through trellis search
Trellis: Each state represents shift register contents. Branches show state transitions for input 0 or 1.
Branch Metrics: Hamming distance between received bits and expected output for each branch.
Path Metrics: Cumulative distance along each path. Lower = more likely path.
Survivor Selection: At each state, keep only the path with minimum metric. Prune others.
Traceback: After all symbols processed, trace back from minimum-metric state to find decoded bits.
Complexity: O(n × 2^K) where n = message length, K = constraint length.