Joint detection and estimation in space-time communications

A way to improve performance in wireless communications is to exploit spatial diversity by deploying multiple antennas at the transmitter and/or receiver. In recent years, coding and modulation techniques designed for multiple transmit antennas—called space-time coding or transmit diversity—have been shown to be very effective in mitigating the effects of fading and can also dramatically increase spectral efficiency on multipath channels.; Most work on space-time coding has assumed that accurate channel estimates are available at the receiver, which may be problematic in certain situations. The severity of the problem increases with the number of transmit antennas, since more path gains must be estimated and each is reduced in signal-to-noise ratio. One approach to cope with this problem is to use joint estimation and detection methods.; This dissertation focuses on suboptimal receivers for multiple-antenna systems. Our interest is to explore whether suboptimal receivers can approximate the performance of the optimal coherent receiver with reduced complexity and minimum bandwidth consumption due to the insertion of pilot symbols in the transmitted sequence.; We propose an iterative receiver for space-time communication systems based on the Expectation-Maximization (EM) algorithm. The receiver performs iterative joint channel estimation and data sequence detection in alternating steps. Under different fading conditions, the receiver may achieve near-coherent performance with modest complexity and very few pilot symbols.; Then an adaptive receiver based on per-survivor processing is considered for detecting space-time trellis codes transmitted over time-varying flat-fading channels, and its performance is examined for several examples. Simulations suggest that, when pilot symbols alone give poor channel estimates, the new receiver can significantly outperform iterative approaches based on Kalman filtering and the expectation-maximization algorithm, at the cost of increased receiver complexity.; Finally, we consider a multipath channel in which the signal propagates from the transmitter to the receiver through few significant multipath components. We study how the error probability and outage capacity of space diversity systems vary with the number of multipath components and antenna array size.