Investigating the Effects of Imperfect Digital Beamforming on Cell Capacity in a Cellular CDMA Communication System

Abstract

Cell capacity in a CDMA communication system can be increased through the use of base station antenna arrays and digital beamforming. It is necessary to estimate suitable beamforming weights from the received signal data which contains interference and noise. This imperfect beamforming produces corrupted weight values which affect the performance of the system. Due to the data coding methods used in IS95, it is necessary to utilize an enhanced beamforming weight estimation technique which we present here. This permits significantly more accurate estimates of the beamforming coefficients to be made. A simplified method for cell capacity estimation based on the power control information is also included. Sample simulation results indicate that approximately a 50% increase in capacity is obtained when beamforming with two antenna elements is used instead of one element. Results obtained from the proposed imperfect beamforming and the power control capacity estimation technique agree with those obtained for the situation where perfect beamforming weights are used