Performance of Turbo Codes Using Code Generator [13, 15] and [31, 17] in AWGN and Fading Channel

Turbo coding is a very powerful error correction technique that has made a tremendous impact on channel coding in the last few years. They are recommended for increased capacity at higher transmission rates due to their superior performance over conventional codes. Turbo codes use any one of the decoding algorithms, Maximum a posteriori Probability (log MAP), Soft Output Viterbi Algorithm (SOVA), modified log MAP (MMAP) and modified SOVA (MSOVA) for decoders in Forward Error Correction (FEC), because it produces error correction near to Shannon’s limit. This paper presents the performance analysis of turbo codes using code generator (13, 15), (31, 17), rate 1/3. The results are compared to turbo codes (7, 5) and rate 1/2. An emphatically determined optimal scaling factor is used for MAP and SOVA to derive MMAP and MSOVA, which improve the performance in terms of bit error rate (BER) at turbo decoder. A typical BER is in the order of 10-2 for Additive White Gaussian Noise Channel (AWGN). Similar analysis is done for the fading channel and performance improvement in BER is found to be 10.