The Research Of Power Control Algorithm In WCDMA Communication Systems

In this thesis, I mainly have an in-depth study on power control in radio resource management for 3G WCDMA network, particularly, on downlink closed-loop power control technology.In CDMA system," multi-address interference"," near-far problem " and " shading effect" deteriorate the quality of communication, which leading to the system capacity decrease. Power control is introduced to solve these problems effectively. Power control technology is introduced to weak the influence of interference, and to make the transmit power maintain the lowest level satisfying SIR requirement. Power control technology both help the transmit and reduce the interference to other users. Thus system capacity can be improved.Recently, large amount of data services are required in downlink direction, which makes more load of downlink. Downlink capacity becomes bottle neck, so, as key technology of WCDMA system, downlink power control is very important. Because bottle neck problem of downlink capacity is more and more prominent, the requirement to downlink power control is more and more strict, the study of downlink power control has good practical purport.Link level power control algorithm based on SIR is used in this thesis. With matlab, the closed loop power control is modeled and programmed. Through analyzing result after simulation, it is proved that system performance using power control is superior to that without using power control. The SIR is computed with the conventional Maximal Likelihood Estimation Algorithm. That is, each path of despreaded DPCCH signal is combined by RAKE receiver, then instantaneous power MAI and background noise power of the combined signal are obtained. Combined MAI and background noise power can obtained by a filter. Following that, SIR of each slot is finally obtained by using definition of SIR=S/N. In every step of WCDMA power control, it is always very important to precisely compute SIR of received signal of each channel.This thesis introduced the downlink traditional power control model and two kinds of power control models based on cost function (new power control algorithm and joint power control algorithm based on cost function respectively) in WCDMA mobile communication system. Through the system simulation, it had been proved that the latter two kinds of power control algorithms had the good performance enhancement compared to the traditional algorithm, moreover, the system capacity also enhanced greatly.