Characteristics of closed loop power control algorithms for a cellular DS/CDMA system

Abstract

The authors consider the performance of a reverse link DS/CDMA system with fast closed loop power control algorithms. For power control purposes, the received signal-to-interference ratio (SIR) must be measured. A simple procedure is proposed for estimating received SIR which does not need much calibration. The result shows that the BER performance is sensitive to the feedback delay or the inverse of the power control updating frequency. The power control mechanism is effective provided that the power control command updating frequency is ten times higher than the Doppler frequency. A step-size of 2 dB for the single step-size power control algorithm is found to be optimal for the mobile unit's velocity, which is uniformly distributed in the range 0–100 km/h. It was also found that the BER performance is very sensitive to the power control command channel error rate in the range 10-1–10-2. This suggests that the system designer should concentrate on minimising this error to improve the overall performance. Lastly, if a multiple step-size power control algorithm is to be implemented, two power control command bits would perform better than one, three, or more bits in a mobile channel environment.