Parameter estimation in a space time bit-interleaved coded modulation scheme for DS-CDMA

This paper deals with space-time detection and channel parameter estimation in a bit-interleaved coded modulation (BICM) scheme for asynchronous direct-sequence code division multiple access (DS-CDMA) transmission over frequency selective channels. Using a pilot sequence to obtain sufficiently accurate channel estimates for this system requires an unacceptably large number of pilot symbols. In this contribution, we consider several code-aided estimation schemes which can be incorporated in an iterative space-time (ST) turbo detection scheme. We point out that the EM algorithm, which has recently been addressed as a convenient tool for code-aided estimation, has some serious drawbacks because of the large number of parameters to be estimated. These can be resolved using the space alternating generalized expectation maximization (SAGE) algorithm. We show through computer simulations that the proposed low complexity ST receiver with SAGE estimation considerably outperforms conventional estimation schemes.