Transmitter Power Control with Adaptive Safety Margins Based on Duration Outage

Abstract

Transmitter power control in cellular networks is principally used to maintain a stable voice quality and to improve bandwidth utilization. There are two main types of quality based power control algorithms that have been extensively studied in the literature and implemented in practice. One is the Signal to Interference Ratio (SIR) based algorithms, and the other is the Bit Error Rate (BER) based algorithms. Several practical issues however, were left open in the algorithms that have been proposed in the literature. The most critical issue in the SIR-based algorithms is how to determine the SIR target parameter; and the most critical one in the BER-based algorithms is how to derive good BER estimators in light of the rare occurrences of erroneous bits. Another issue that is shared by both algorithm types is the functional relation between the BER and the SIR. This relationship is required as one may serve 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. Since the actual SIR values is a stochastic process in nature, its variation and time correlation must be accounted for. This paper addresses the problems described above by evaluating a duration outage probability of the underlying time process of the SIR values. We show that this probability can reasonably be approximated by a simple expression that relates between the duration outage probability and the SIR target control parameter. The distributed algorithm that is implied by this method is a duration outage based power control that uses an estimator for the most likely event (in contrast to BER-based algorithms).