Fundamental limits and joint design of wireless systems with vector antennas

Multiple-antenna systems have generated tremendous research interest in the recent past mainly because of their promise of significant gains in capacity and performance as compared to single-antenna systems. Most work on multiple antennas has focused on the design of coding and modulation schemes, channel estimation algorithms and decoding architectures. Information is sent by the transmitter as electromagnetic waves which subsequently undergo multipath fading before they reach the receiver. The electromagnetic properties of the antennas and the nature of the scattering environment jointly impact the performance of communication algorithms. However, there are relatively few works in the literature that consider this interrelation in the design of transmitter-receiver architectures. In this dissertation we study three such problems: the dependence of capacity on the electromagnetic properties of antennas and the scattering environment, the limits on performance of parameter estimation algorithms at the receiver and finally, the fundamental limits on the capacity that volume-limited multiple-antenna systems can achieve.; We first consider the joint design of multi-element antennas and capacity-optimal signalling for a multiple-input multiple-output (MIMO) wireless channel. We propose a signal propagation model and then use it derive criteria for capacity-optimal signalling and antenna design. We show that antennas that have orthogonal and equal norm electric-field patterns maximize the ergodic capacity. Polarimetrically sensitive antennas known as the vector antennas satisfy this criteria, but a uniform linear array does not.; We next consider the problem of positioning and direction-of-arrival (DOA) estimation with ultrawideband (UWB) vector antennas. We first derive a frequency-domain Cramer-Rao Bound formula in the asymptotic case of a large number of observation samples in stationary noise. Criteria based on the Cramer-Rao Bound are used to design signal pulses that give uniform resolving capability to the antennas for any DOA.; Finally, we consider the fundamental capacity limits that a multi-element antenna system that is restricted to occupy a fixed volume can achieve. The system is first described as a linear operator, and the exact singular values of the system are derived in closed form. We calculate the capacity of such a system, and provide capacity formulas that are accurate at high signal-to-noise ratio.