An improved SOVA algorithm for turbo codes over AWGN and fading channel

We present a modified soft-output Viterbi algorithm (MSOVA) that performs as good as the a posteriori probability (APP) algorithm with a complexity similar to that of the conventional SOVA algorithm. The idea behind the MSOVA centers around reducing the inherent correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA), where the latter is typically much higher than its APP counterpart. The proposed algorithm employs two attenuators, one applied directly to the output of the SOVA and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). We examine the MSOVA on additive white Gaussian noise (AWGN) and fading channels. We show that the MSOVA provides improvements of about 0.8 to 1.0 dB at P/sub b/ = 10/sup -5/ in AWGN over the conventional SOVA, and is only about 0.1 dB away from the APP. It also provides improvements of 1.4 to 2.0 dB at P/sub b/ = /sup -5/ on fading channels.

[1]  Joachim Hagenauer,et al.  Source-controlled channel decoding , 1994, Proceedings of 1994 IEEE International Symposium on Information Theory.

[2]  Roger S. Cheng,et al.  Improvements in SOVA-based decoding for turbo codes , 1997, Proceedings of ICC'97 - International Conference on Communications.

[3]  John G. Proakis,et al.  Digital Communications , 1983 .

[4]  Alain Glavieux,et al.  Reflections on the Prize Paper : "Near optimum error-correcting coding and decoding: turbo codes" , 1998 .

[5]  Joachim Hagenauer,et al.  Iterative decoding of binary block and convolutional codes , 1996, IEEE Trans. Inf. Theory.

[6]  Joachim Hagenauer,et al.  A Viterbi algorithm with soft-decision outputs and its applications , 1989, IEEE Global Telecommunications Conference, 1989, and Exhibition. 'Communications Technology for the 1990s and Beyond.

[7]  William E. Ryan,et al.  Concatenated Convolutional Codes and Iterative Decoding , 2003 .

[8]  A. Robert Calderbank,et al.  Space-Time block codes from orthogonal designs , 1999, IEEE Trans. Inf. Theory.

[9]  Jr. G. Forney,et al.  The viterbi algorithm , 1973 .

[10]  Patrick Robertson,et al.  Improved decoding with the SOVA in a parallel concatenated (Turbo-code) scheme , 1996, Proceedings of ICC/SUPERCOMM '96 - International Conference on Communications.

[11]  Patrick Robertson,et al.  A comparison of optimal and sub-optimal MAP decoding algorithms operating in the log domain , 1995, Proceedings IEEE International Conference on Communications ICC '95.

[12]  A. Glavieux,et al.  Near Shannon limit error-correcting coding and decoding: Turbo-codes. 1 , 1993, Proceedings of ICC '93 - IEEE International Conference on Communications.

[13]  A. Ghrayeb,et al.  Performance of high rate turbo codes employing the soft-output Viterbi algorithm (SOVA) , 1999, Conference Record of the Thirty-Third Asilomar Conference on Signals, Systems, and Computers (Cat. No.CH37020).