Given the limit on spectrum resources, efficient optimization techniques are needed for realizing cost-efficient ways to maximize the capacity in a W–CDMA network. The capacity is essentially interference limited by the overall interference level in the coverage area of each site. A computer simulation for investigating the system capacity was performed that modeled the radio channel in an urban environment. The simulator included many of the CDMA characteristics such as power control and different parameter setting in the hand over algorithm. Given this simulation, antenna characteristics such as sector orientation, number of sectors per site, horizontal beamwidth, and front-to-back ratio were studied. Also studied was the influence of the radio environment, giving rise to different orthogonality factors.

The signal-to-interference ratio typically limits the probability of having service in a dense cell site. As we can see from Figure 1, the roll off of service probability for voice traffic is quite quick—from 160 to 180 users per cell site in a typical three-sector configuration compared to about 90 users for omni site configurations. The error bars in the following figures annotate plus or minus one standard deviation about the mean value obtained from the numerical simulations. The numerically obtained results using a set of network statistics for a typical urban setting are shown in Figure 1.

Figure 1. Cell Site Loading in a Three-Sector Network Configuration