Spatial Filtering and CDMA

Abstract

A number of smart antenna techniques will form an important part of the new Wideband Code Division Multiple Access (WCDMA) standard that will realize the Universal Mobile Telephone System (UMTS). One such technique is High Sensitivity Reception (HSR) which is implemented in the uplink of cellular systems. This chapter addresses a few issues of importance when HSR techniques are used in a cellular CDMA system. Firstly, a brief overview of smart antenna techniques is presented followed by a theoretical analysis of a HSR/CDMA system. The analysis is focused on both micro and macro multi cell, multipath Rayleigh fading scenario’s with imperfect power control. As a system performance measure, Bit Error Rate (BER) is used to investigate the influence of user location, number of antennas and power control error. An important parameter in the design of a HSR system is the antenna array element spacing. In the analysis a Uniform Linear Array (ULA) is considered and a measure is defined to determine the optimal antenna element spacing in a CDMA cellular environment. Normally, the mobile users in a cell are assumed to be uniformly distributed in cellular performance calculations. To reflect a more realistic situation, a novel probability density function is proposed to model the non-uniform distribution of the mobile users in a cell. It is shown that multipath and imperfect power control, even with antenna arrays, reduces the system performance substantially.