Transmitter Power Control with Adaptive Safety Margins Based on Duration Outage

Abstract

Transmitter power control in cellular networks is principally used to maintaina stable voice quality and to improve bandwidth utilization. There are twomain types of quality based power control algorithms that have been extensivelystudiedin the literature and implemented in practice. One is the Signal toInterferenceRatio (SIR) based algorithms, and the other is the Bit Error Rate(BER) basedalgorithms. Several practical issues however, were left open in the algorithms that havebeen proposed in the literature. The most critical issue in the SIR-basedalgorithms is how to determine the SIR target parameter; and the most critical one in theBER-basedalgorithms is how to derive good BER estimators in light of the rareoccurrences of erroneous bits. Another issue that is shared by both algorithm types is thefunctional relation between the BER and the SIR. This relationship is required as one mayserve as a control valve and the other as a control objective. Determining the SIR target control parameter (in SIR or BER based algorithms) involves more than just a static transformation between the BER and the SIR.Sincethe actual SIR values is a stochastic process in nature, its variation andtimecorrelation must be accounted for. This paper addresses the problems described above by evaluating a durationoutage probability of the underlying time process of the SIR values. Weshow that this probability can reasonably be approximated by a simple expressionthat relates between the duration outage probability and the SIR targetcontrolparameter. The distributed algorithm that is implied by this method is adurationoutage based power control that uses an estimator for the most likelyevent (incontrast to BER-based algorithms).