MAP Decoding Methods Derived from SOVA

Different from MAP, the soft output of SOVA is not the exact a posteriori probability, and few literatures describe SOVA in mathematical form. This paper gives a new comprehensive mathematical expression of SOVA, and deduces two MAP-equivalent SISO decoding methods in the form of SOVA. The first method is just OSA algorithm given by Li et al, (1995)which is suitable for continuous decoding. The other one is the improved version of OSA，whose output is equivalent to that of OSA with the decrease of complexity.