An Approximated Soft Decoding Algorithm of 16-APSK Signal for DVB-S2

In this paper, we propose a pragmatic soft decoding algorithm for 16-APSK (amplitude phase shift keying) signal of DVB-S2 (digital video broadcasting-satellite, second generation). Because the 16-APSK is one of non-constant envelope modulation schemes with two rings (inner and outer) in the constellation mapped with imperfect Gray code, we use a pragmatic and statistical approach to obtain bitwise metrics of a symbol codeword. The proposed algorithm can be used for binary iterative decoder with LDPC (low density parity check) or turbo code. We also show the proposed algorithm has better performance comparing to the well-known max-log-MAP algorithm through computer simulation with iterative turbo decoder.