Energy efficient multiple antenna communication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 111-115).We consider a multiple-input, multiple-output (MIMO) wideband Rayleigh block fading channel where the channel state is unknown at the transmitter and receiver and there is only an average input power constraint. We compute the capacity and analyze its dependence on coherence length, number of antennas and receive signal-to-noise ratio (SNR) per degree of freedom. We establish conditions on the coherence length and number of antennas for the non-coherent channel to have a "near coherent" performance in the wideband regime. We also propose a signaling scheme that is near-capacity achieving in this regime. We compute the decoding error probability and study its dependence on SNR, number of antennas and coherence length. We show that error probability decays inversely with coherence length and exponentially with the product of the number of transmit and receive antennas. Moreover, in the wideband regime, channel outage dominates error probability and the critical and cut-off rates are much smaller than channel capacity. In the second part of this thesis, we introduce the concept of a fiber aided wireless network architecture (FAWNA), which allows high-speed mobile connectivity by leveraging the speed of optical networks.(cont.) Specifically, we consider a single-input, multiple-output (SIMO) FAWNA, which consists of a SIMO wireless channel interfaced with an optical fiber channel through wireless-optical interfaces. We propose a design where the received wireless signal at each interface is sampled and quantized before being sent over the fiber. The capacity of our scheme approaches the capacity of the architecture, exponentially with fiber capacity. We also show that for a given fiber capacity, there is an optimal operating wireless bandwidth and number of interfaces. We show that the optimal way to divide the fiber capacity among the interfaces is to ensure that each interface gets enough rate so that its noise is dominated by front end noise rather than by quantizer distortion. We also show that rather than dynamically change rate allocation based on channel state, a less complex, fixed rate allocation scheme can be adopted with very small loss in performance.by Siddharth Ray.Ph.D

On Jamming in the Wideband Regime

Abstract — We consider the problem of jamming in noncoherent wideband fading channels. While the problem is well understood for coherent channels, the results for the coherent case do not generalize in the non-coherent regime. We show that energy-limited jammers do not affect capacity in the wideband regime. We also propose a training based transmission scheme that is able to achieve the wideband limit in the presence of a jammer. I