The Research Of Closed Loop Power Control In 3G Mobile System

Firstly, this paper introduces the history of 3G mobile system, the standard of radio interface, the structure of system and correlative key technologies. After that, it expounds the concept of power control in 3G, the principle of power control, power control guidelines, the factors which affect the performance of power control. And then, this paper introduces a problem which influences the system capacity of CDMA greatly: multiple access interference and near-far effect, according to this problem, the paper explains in Mathematics why CDMA system needs power control technology. Then, power control is discussed in detail, including classification and present status of research; especially introduces several main power control technology, including uplink or downlink power control, centralized or distributed power control, fixed or variable step power control, loop power control, and analyse their method of realization,scope of application and advantages or disadvantages.Afterwards, according to the loop power control, this paper researches the closed loop power control algorithm deeply: on the one hand, it gives the clear mathematical definitions to the propagation model, the loss model, the distributed power control algorithm, the limit to power transmitted and the outage probability, particularly it gives the strict mathematical justifications to the loss model, the framework of constructing distributed power control algorithm and its iterative convergence; on the other hand, it puts forward a new algorithm which can predict the loss of channels based on SIR measurement. Finally, it simulates this algorithm with OPNET and compares with the distributed -unpredictable power control algorithm, the result shows that: the distributed-predictable power control algorithm not only can raise the convergence speed and stability, but also can low the outage probability and increase the capacity.