Study On Power Control Algorithms Of Stochastic Uncertain Mobile Communication Systems

Transmitter power control has been proven to be an important means in suppressing co-channel interference, combating near-far problem, lowering power consumption and increasing systems capacity. It has been one of the key technologies in 3G mobile communication systems. Power control methods mainly include Signal-Interference Ratio balancing and Quality of Service tracing. Many scholars have done a great deal investigations for the power control problems in the mobile communication systems and have obtained some power control algorithms. Most of these power control algorithms assume that link gain, signal-interference ratio and interfemce power are some fixed quantities. However, estimating these quantities perfectly is impossble in practice, Some power control algorithms obtained in case of certain conditions can not be applied in practice. The stochastic and time-varying characteristics of mobile communication systems are considered in this dissertation, the power control problems are studieded with stochastic approximation theory and matrix analysis theory. The main work of this dissertation is as follows.The stochastic power control problems of mobile communication system are studied in this dissertation, the three power control algorithms are presented for user with the certain matched filter output, link gains with the stochastic estimation error and SIR with multiplicative noise. The convergence of algorithms is proved by the classical stochastic approximation theory.The interference power is a stochastic process and it is a formidable task to measure it in practice. A power control algorithm based on the interference estimation is presented in this dissertation, it is shown that power control problems can be converted to a zero point problem of a specific founction and the convergence of algorithms is proved by the mathematics induction.A distributed fixed-step power control algorithm is presented for a large CDMA cellular system and is a feedback-modulating algorithm. It is shown that transmitter power of each user converges to a fixed point and the received SIR of each user falls within a certain target region that is determined by a power control step-size and an SIR target.Most of power control algorithms need several bits to be used for sending the power control command back to each user. In this dissertation, a binary feedback power control is presented when link gains are assumed to be time varying and only one bit is sent back to each transmitter. The convergence of proposed algorithm is proved and the proposed scheme can be adopted in practical mobile communication systems.