Performance of Cdma Systems Using Digital Beamforming with Mutual Coupling and Scattering Effects

The mobile communications market has seen an explosion of growth over the past several years. Moreover, trends indicate that this growth will continue uninterrupted into the next decade. To meet this increasing demand, the use of base station antenna arrays implementing digital beamforming is being proposed as a method to enhance both the performance and capacity of cellular systems. In this work, we will examine the effects of mutual coupling occurring within the base station antenna arrays of code division multiple access (CDMA) cellular systems. First, we examine three different methods of incorporating mutual coupling effects within the base station antenna array. These methods are then applied to several antenna array models for comparison with the ideal case and with each other. Following this, we then improve a method for determining CDMA system uplink capacity, given by Earnshaw, by including the effects of mutual coupling. Next, we derive a generalized model for the cross-correlation statistics between elements of an antenna array in a scattering environment to include mutual coupling effects and arbitrary distributions of angle-of-arrival (AOA) statistics. Using this model, we further improve the above method for determining CDMA system uplink capacity by including the effects of both scattering and mutual coupling. Finally, we investigate an improved system capacity prediction where imperfect power control is assumed. In this derivation, the signal-to-noise ratio is a random ii variable with a log-normal distribution, rather than a fixed value, as in the case of perfect power control. Furthermore, the outage probability associated with the imperfect power control case is derived.