Iterative Decoding withM -ary Orthogonal Walsh Modulation in OFDM-CDMA Systems

Iterative decoding of a serial concatenated coding scheme consisting of an outer convolutional code and M -ary orthogonal Walsh modulation as inner Walsh-Hadamard block code in an OFDM-CDMA system is applied. New aspects arise because OFDM enables the iterative decoding structure to exploit time as well as frequency diversity of a mobile channel. Moreover, the paper points out the low complex symbol-by-symbol maximum a posteriori (SS-MAP) decoding of Walsh-Hadamard block codes. Besides the derivation of the log-likelihood-ratio used for SSMAP Walsh-Hadamard decoding, simulation results are shown for a differently interleaved indoor channel. They confirm the iterative decoding property to benefit from selectivity in time as well as frequency direction.