It is well known that CDMA systems are interference limited, which implies that the multiaccess interference (MAI) is a key parameter that governs system performance and capacity. Fading and the random activity of users are two fundamental ingredients of the MAI. In this chapter, we focus primarily on investigating the effect of traffic activity on the capacity of CDMA systems, based on ON/OFF traffic models.

In CDMA systems, the interference can be suppressed by monitoring the traffic activity of users, which corresponds to improving the system capacity because CDMA systems are interference limited. The simplest way to take into account the effect of traffic activity on system capacity is to consider the long-term average interference, which simplifies the random characteristics of traffic activity into the mean of traffic activity. A more practical way is to statistically consider the fluctuation of interference due to the traffic activity by modeling the traffic activity as a binomial random variable. In this chapter, the capacity of a CDMA system supporting multiclass services with ON/OFF activity is analyzed based on the latter way, and the corresponding capacity is compared with the capacity analyzed the former way. The influence of traffic activity on the system capacity is further investigated under the same transmission rate and under the same average rate. According to the traffic activity factor, the average rate changes under the same transmission rate, while the transmission rate changes under the same average rate. From the investigation under the same...