Abstract
In this paper, a simple structure is proposed for accommodating reuse-within-cell in the downlink of a time-division multiple-access system using a transmit antenna array at the base station and joint detection of the cochannel signals at the single-antenna mobile receivers. The transmit array is used solely for system capacity increase; diversity is obtained in the traditional way through standard coding and interleaving. Due to the spatial formatting of the coded symbols prior to transmission, a single multiantenna channel usage spans several trellis transitions - an unconventional situation which is handled through a trellis. Using the merged trellis, a combined joint detector/soft-decision decoder is constructed, and an analytical expression is derived for the coded bit-error rate based on the exact computation of pairwise error probabilities. It is shown that while the system suffers a reduction in diversity order as the number of intracell cochannel users increases, the reduction may be countered by increasing the constraint length of the code. Although this increases complexity, it is shown that multiple users may be supported, all enjoying good performance at low signal-to-noise ratios, while keeping the complexity in check.
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