Performance Enhancement of Modified SOVA Decoding Algorithm for Turbo Codes
Turbo coding (TC) has been adopted as a channel coding scheme for several 3G mobile systems, in particular GPP(third Generation Partnership Project) and 4G standards for high data rates. Turbo decoder uses any one of the decoding algorithms, Maximum A posteriori Probability (MAP), or Soft Output Viterbi Algorithm (SOVA) because it produces error correction near to Shannon’s limit. SOVA is an extension of classical Viterbi algorithm which is incorporated with a-priori information. The performance of SOVA algorithm is improved by scaling the extrinsic information exchanged between two decoders. Modified SOVA (MSOVA) algorithm is achieved by fixing an arbitrary value for inner decoder (S2) and an optimized value for the outer decoder (S1). A simple but effective technique to enhance the performance of MSOVA, called Enhanced SOVA (ESOVA) is proposed. In ESOVA, the arbitrary scaling factor S2 is optimized and is made to adapt with received Eb/N0. The use of an emphatically determined optimal scaling factor improved the performance of the decoding algorithm in terms of Bit Error Rate (BER). A comprehensive analysis of the proposed algorithm, by considering different channel conditions and code rates are presented. Appropriate mathematical relationship between scaling factor and Eb/N0 is also proposed.
C.Berrou, A.Glaviex, and P.Thitimajshima, “Near Shannon limit error-correction coding. Turbo codes,” in Proc. International Conf.Communication, May 1993, pp. 1064-1070.
CCSDS, Recommendation for space data system standards. TM synchronization and channel coding, 131.0-B-1, Blue Book, Sep 2003.
DVB, Interaction channel for satellite distribution systems, ETSI EN 301 790, v. 1.2.2, 2000.
Third Generation Partnership Project (3GPP), Technical Specification 25.212: Multiplexing and Channel Coding (Frequency Division Duplex Mode), ver. 3.0.0, Oct 1999.
Hagenauer, J. and Papke, L., “Decoding “Turbo” Codes with the Soft Output Viterbi Algorithm (SOVA),” Proceedings of International Symposium on Information Theory, Trondheim, Norway, June 1994, pp.164-168.
Hagenauer, J., Robertson, P., and Papke, L., “Iterative (“Turbo”) Decoding of Systematic Convolutional Codes with the MAP and SOVA Algorithms,” Proceedings of ITG, Oct. 1994, pp. 21-29.
Papke L., Robertson P., Villebrun E., “Improved decoding with SOVA in parallel concatenated (Turbo-code) scheme”, Proc. IEEE International Conf. on Communication (ICC), Dallas, USA, July 1996, pp. 102-106.
Jonson P.Woodard and Lajos Hanzo, “Comparative Study of Turbo Decoding Techniques: An Overview” IEEE Transactions on vehicular technology, Vol.49, No.6, Nov 2000, pp. 2208-2233.
P Robertson, E Villebrun, and P Hoher, “A comparison of optimal and sub-optimal MAP decoding algorithms operating in the log domain”,Proc. IEEE ICC ’95, Seattle, USA, June 1995, pp. 1009-1013.
T.Gnanasekaran and K. Duraiswamy, “Modified Soft Output Viterbi Error Correcting Algorithm” International Journal of Computer Science and Network Security Vol.8, No.9, Sep 2008, pp. 161-165.
Shannon C E, “A Mathematical Theory of Communication”, The Bell System Technical Journal, Vol. 27, July 1948, pp. 379–423.
Hagenauer, J. Hoeher, German Aerosp. Res. Establ., “A Viterbi Algorithm with Soft-Decision Outputs and its Applications”. Global Publication, Vol.3, 1989, pp. 1680-1686.
Colavolpe G., Ferrari G., Raheli R., “Extrinsic information in iterative decoding: a unified view”, IEEE Transactions on Communication, Vol.49, 2001, pp. 2088–2094.
Gnanasekaran T. and Duraiswamy K., “Application of Scaling factors for MAP and SOVA for Robust Performance in Forward Error Correction”,International Journal of Recent Trends in Engineering, Vol. 1, No. 3, Nov 2009, pp. 47-51.
C Chaikalis, M Salimi-Khaligh, N Panayotopoulos, J M Noras, “Reconfiguration between soft output viterbi and log maximum a posteriori decoding algorithms”, Proc. IEE 3G2002, London, UK, March 2000, pp. 316-320.
Barbulescu, A. S. and Pietrobon, S. S., “Interleaver Design for Turbo Codes,” Electronics Letters, Vol. 30, No. 25, Dec. 8, 1994, pp.2107-2108.
Gnanasekaran T., Duraiswamy K., Aarthi V. and Brindha C.,“Performance of Turbo Codes Using Code Generator [15, 13] and [31,17] in AWGN and Fading Channel”, International Journal of Recent Trends in Engineering (Electrical & Electronics), Vol. 2, No. 6, Nov 2009, pp. 20-23.
- There are currently no refbacks.
This work is licensed under a Creative Commons Attribution 3.0 License.