Fast MAP decoding algorithm for variable length codes

Since MAP decoding algorithm for variable length codes (VLC) is computational impractical, a fast algorithm is proposed in this paper, which simplifies the trellis representation for VLC so that the number of states is bounded by a constant, thus the computational complexity of the MAP decoding algorithm is significantly reduced, asymptotically from O(n²) to O(n). In simulations, only a slight performance degradation of the fast algorithm relative to exact MAP decoding is observed, while it runs about 6 times faster than exact MAP decoding.