The Modified Max-Log-MAP Turbo Decoding Algorithm by Extrinsic Information Scaling for Wireless Applications

Abstract

Turbo codes have found use in various wireless communication applications and have been incorporated into important standards like 3GPP and DVB. The iterative nature of turbo decoding algorithms increases their complexity compare to the conventional FEC decoding algorithms. A simple but effective technique to improve the performance of the Max-Log-MAP turbo decoding algorithm is to scale the extrinsic information exchanged between two MAP decoders. A comprehensive analysis of the selection of the scaling factors according to channel conditions and decoding iterations is presented in this chapter. Choosing a constant scaling factor for all SNRs and iterations is compared with the best scaling factor selection for changing channel conditions and decoding iterations. It is observed that a constant scaling factor for all channel conditions and decoding iterations is the best solution and provides a 0.2–0.4 dB gain over the standard Max-Log-MAP algorithm. Therefore, a constant scaling factor should be chosen for the best compromise.