Power Control for an Asynchronous Multi-rate

Abstract

The varied Quality of Service (QoS) or bit error rate (BER) requirements of multimedia traffic require the use of power control for CDMA wireless systems employing multiuser detection. Using a decorrelator in an asynchronous multi-rate DS/CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multi-rate decorrelator that is suitable for a class of BER based link quality objectives. If the uplink channel gain of the desired user is known, then it is simple for each user to choose the transmitter power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple, distributed, iterative power control algorithm. In this algorithm, each mobile will use the output of its own decorrelator to update its transmitted power in order to achieve its QoS objective. We will show that when a user’s bits have nonzero asymptotic efficiencies, then the power control algorithm converges quickly in the mean square sense to an optimal power at which the desired user achieves its QoS objective.