Optimum transmitter power control in cellular systems with heterogeneous SIR thresholds

Power control is of great importance to increase the capacity of cellular mobile systems. In early papers, optimum transmitter power control theory has been fully investigated for cellular systems under the assumption of system-wide homogeneous signal-to-interference ratio (SIR) threshold, a minimum required SIR also known as the protection ratio. In reality, the minimum required SIR for each mobile is a function of that mobile's fading rate and other channel characteristics. Therefore it varies from mobile to mobile and can also change as a function of time as individual mobiles change their speeds. A homogeneous SIR threshold would have to be set according to the required SIR in the worst case, which would result in reduced system performance. In this paper, we explore the optimum transmitter power control theory under the assumption of heterogeneous SIR thresholds. Distributed power control algorithms are also investigated. The efficiency of these algorithms is demonstrated through simulation of CDMA cellular systems.