Performance evaluation of DS/CDMA systems employing adaptive transmission rate under imperfect power control

Power control is essential for CDMA systems to increase the capacity. Power control based on equalizing the received power levels from different users was proposed. Perfect power control is hard to achieve for high mobility users. The error in the received signal is usually modeled as a lognormal variable with a standard deviation that is a function of the mobile's velocity. In a previous work, we have shown that this standard deviation is also a function of whether or not the mobile is communicating with the base station where the power is measured. In this work, we use the error statistics to model the intercell interference. We also employ adaptive rate transmission where the data transmission rate is a function of the number of users in the system and the errors in the power of the received signals. We show that the adaptive rate scheme helps to reduce the blocking probability and the average service time for light traffic conditions. However, for heavy traffic, users reduce their transmission rate and start to accumulate in the system making its performance similar to the constant rate system. Finally, we investigate the effect of imperfect power control on such an adaptive rate scheme.