9.1 Introduction

With the advent of mobile high-speed data applications, it is expected that the downlink of 3G CDMA systems will be the limiting link as far as capacity is concerned. Hence, it is important to investigate methods that can increase the downlink capacity to cope with increasing demand. Performance enhancements that are possible with diversity reception in wireless systems are well known and have been employed in cellular systems for decades on base station receivers [1, 2]. Commercial implementation of some form of diversity in wireless devices has also been reported [3 11]. Widespread implementation of diversity-equipped wireless devices has not been achieved yet for several reasons. The most important hurdle is that the implementation of diversity reception increases the complexity and cost of mobile stations. The second reason, the lack of widespread commercialization of diversity handsets for cellular systems, relates to the fact that the benefits that could be obtained from such devices are technology dependent. CDMA-based networks are well suited to benefit from any reduction in the interference levels in the system even if only a portion of the mobiles are equipped with diversity receivers. The capacity improvement in the downlink is simply proportional to the percentage of the advanced handsets (i.e., those equipped with receiver diversity). This is the case because a dual receiver unit requires a smaller amount of base station transmit power, thus allowing more simultaneous connections for an equivalent amount of spectrum and average power constraint. The downlink capacity of a CDMA system is...