Analysis of a class of distributed asynchronous power control algorithms for cellular wireless systems

In cellular wireless communication systems, uplink power control is needed to provide each mobile user with an acceptable signal to interference ratio (SIR) while simultaneously minimizing transmit power levels. We consider a class of distributed asynchronous power control algorithms based on the schemes used in IS-95 inner loop power control. Each user's received SIR is measured (using possibly outdated information) and compared to a threshold, and a single control bit is then sent to the user, indicating whether its power level should be increased or decreased. The SIR measurements and power updates do not require synchronization. We show that under certain conditions, this class of algorithms is stable and converges to a region around the optimal power assignment. We characterize this region and show that it can be made as small as desired by choosing the algorithm parameters appropriately. For an appropriate choice of algorithm parameters, we show that convergence occurs in a finite number of iterations and derive an upper bound. To illustrate our general results, we apply them to systems with fixed base station assignment, dynamic base station assignment, and macrodiversity. Finally, we give an example to illustrate the algorithm's robustness to errors in the power control commands.