Optimal distributed power control in cellular wireless systems

In this paper, an optimal closed-loop SIR-based power control scheme is proposed for CDMA systems. The amount of power change is proportional to the SIR error, and the optimal gain is chosen to achieve the minimum SIR error at the next time instant. The proposed controller is an estimator based controller. Assuming perfect estimation and prediction of the channel quality, the SIR error goes to zero in one step. In practical situations, where the estimator need several steps to make accurate estimation and prediction, the SIR error goes to zero in less than ten steps. In order to adapt to frequent channel changes, an H_∞ filter is applied in the proposed scheme to facilitate the system filtering regardless of the nature of the system and measurement disturbances. The simulation results of a multi-cell CDMA system in all cases fit the theoretical analysis very well. These results indicate that the proposed optimal power control scheme is a very promissing solution to the distributed power control problem in wireless systems, both theoretically and practically.