A simplified BGT MAP algorithm and its dual

In this paper, the modified BCJR MAP algorithm derived in Berrou,C et al., (1996) is simplified, resulting in a new MAP algorithm for recursive systematic convolutional codes. This new MAP algorithm is called the SBGT MAP algorithm in order to distinguish it from its original formulation in Berrou,C et al., (1996) (called the BGT MAP algorithm) and other modified versions of the BCJR MAP algorithm. A dual version of the SBGT MAP algorithm, called the dual SBGT MAP algorithm, is then derived. These two mutually dual algorithms have the same signal processing requirements in terms of memory utilization and computational load and have demonstrated almost identical BER performance in computer simulations.