Space-time processing for multiple-antenna wireless systems

The demand for wireless systems that can support high data rates and a better link quality has been increasing constantly. Recently, it has been shown that the use of multiple antennas at both the transmitter and the receiver can provide a many-fold increase in channel capacity. This thesis investigates receiver algorithms for these multiple antenna systems.; The performance of the decoding algorithm in the Bell Labs Layered Space-Time (BLAST) system is analyzed. The analysis shows that the overall performance is limited by the first subchannel the receiver decodes. To reduce the error propagation effect, we propose to combine a partial Maximum-Likelihood (ML) decoding with Decision-Feedback Equalization (DFE). A suboptimal ordering scheme that gives the best performance for the worst subchannel is derived. For the case in which the receiver does not have enough computing power, a power allocation scheme based on the statistics of the subchannel gains is also proposed.; An iterative soft Interference-Cancellation (IC) scheme that takes into account of the discrete nature of the inputs is proposed. The basic idea of the iterative soft IC is to consider the multiple antenna system as a parallel concatenation of inputs from different transmit antennas so that Turbo (iterative) decoding can be applied. For multiple antenna systems with channel coding, an iterative receiver based on the principle of “turbo equalization” is proposed. Since the maximum a posteriori (MAP) decoder for the channel is often complex especially when the channel has a large delay spread, we propose to replace the full MAP decoder with the proposed soft interference-cancellation scheme.; For the use of space-time coding over frequency-selective channels, we propose to apply the multiple-input multiple-output equalization to mitigate the temporal intersymbol interference, so that the ML decoding can be implemented by a simple processing. A receiver architecture for an Orthogonal Frequency Division Multiplexing (OFDM) system with multiple antennas is also discussed.; Finally, maximizing spectral efficiency for fading channels by adaptive modulation is investigated. The adaptive modulation scheme that takes the peak power constraint into account is proposed.