This Report was presented to the Faculty of the Graduate School of the University of Texas at Austin in partial fulfillment of the requirements for the degree of

Master of Science in Engineering


Space-Time Processing for Wireless Base Stations 


Srikanth K. Gummadi, M.S.E.

The University of Texas at Austin, December 1998


Supervisor: Brian L. Evans

Reader: Gustavo de Veciana


The explosive growth in the demand for cellular communications services has driven research into improving spectrum efficiency, battery life, and link quality in wireless systems. Using space-time diversity in antenna arrays for transmission and reception is an emerging solution to all three problems. A space-time system operates simultaneously on all of the antennas by processing signal samples both in space and time. This extra dimension enables interference cancellation in a way that is not possible single antenna systems.

At the base station, received signals suffer from cochannel signal interference from other users and degradation from the channel. This report discusses a Constant Modulus (CM) array for separating cochannel users and 2-D unitary ESPRIT for estimating channel parameters. Each stage in a CM array consists of a CM beamformer and an adaptive signal canceler that recovers one cochannel signal. The 2-D unitar ESPRIT algorithm jointly estimates the direction-of-arrival (DOA) and time-of-arrival (TOA) of each path impinging on an antenna array. By knowing the DOA and TOA, we can locate the mobile user, and transmit the signal in a narrow beam towards the mobile, which improves spectral efficiency, link quality, and battery life. The key contributions are (i) a modified error criterion for CM array, which makes the CM array phase sensitive, and (ii) a closed-form solution for joint angle and delay estimation, which significantly reduces computational complexity.


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