Turbo Coded Modulation as an Alternative to Space-Time Codes: The Case of Large Number of Transmit and Receive Antennas

摘要

In a recent paper we have shown that a simple turbo coded modulation scheme provides significatn performance improvement with respect to the properly interleaved space-time trellis codes for block Rayleigh fading channels. The turbo coded modulation scheme for the multiple antenna system is based on a simple encoding procedure which uses the encoder for a binary turbo code and maps the encoded bits to a certain constellation, and a simple decoding procedure which is based on a log-likelihood computation of the transmitted bits and the use of these log-likelihoods in a sub-optimal iterative decoding algorithm. Although the computation of log-likelihoods is not a problem for small number of transmit antennas, the comptuational complexity at the receiver is too high for the case of large number of transmit antennas. In this paper we present a practical method for handling this problem. In particular, we present a new decoding algorithm which does not suffer from the same computational complexity. Our method is similar to the array processing/group interference suppresion scheme developed for space-time trellis coding. We present examples for the case of four transmit - four receive antennas and for the case of eight rate of 10~-5 over the multi-layered space-time trellis coding with symbole interleaving. We also observe that although the current approach is computationally efficient, it results in a considerable performance degradation compared to the original (more complex) approach.