| The rapid growth in demand for cellular communications services has encouraged research into the design of wireless systems to improve spectrum efficiency, increase portable battery life and link quality. A promising approach to achieve these goals is the use of antenna arrays in transmit and receive at the base station. In order to take full advantage of these multiple antennas, advanced space-time signal processing techniques need to be developed. A key aspect of these is the estimation of the channel and channel parameters. Wireless signal propagation often exhibits specular multipath. In this case, the channel has an underlying structure which can be exploited to improve channel estimation and tracking, and to determine the direction or time of arrival of signals. Improved channel estimation can result in improved signal to noise ratios, channel equalization, co-channel interference rejection and mobile localization. These in turn yield improved network performance.; This dissertation focuses on the estimation of channel parameters for a specular propagation model. The channel parameters of interest are the direction-of-arrival (DOA) and time-of-arrival (or delay) of each impinging path at an antenna array. We assume that (a) the signals employ linear digital modulation, (b) training signals are available to estimate the channel, and (c) there are only a few dominant specular multipath arrivals. After presenting multipath propagation and signal models, we describe maximum likelihood and subspace algorithms for jointly estimating the DOAs and delays. Next, by assuming a special array geometry, we present a low complexity approach to parameter estimation that exploits underlying shift invariances in the channel. This is followed by derivation of the deterministic and stochastic Cramer-Rao lower bounds for the DOA/delay estimates. We then investigate the resolvability of the signal parameters addressed. We then describe a blind channel and channel parameter estimation algorithm that uses second-order statistics. Finally, we conclude with a summary of contributions and directions for future research. |
