Power Control Based On Stochastic Theory And Cost Founction In CDMA System

CDMA (Code Division Multiple Access) is one of the promising technology for future mobile conununication system because of its several features with which other multiple access technology can not compare: higher efficiency of frequency allocation, robust ani-multipath effect, macro diversity mitigating intefference, soft capacity, low power, soft handoff, simple frequency design, easy access, and so on. In CDMA system, it is interference limited. Any method to decrease transmits power control and interference to other users will increase the system capacity and communication quality. Power control is one of the most important approaches to effectively combat the near-far problem and corner problem, to suppress system interferences and to increase the system capacity.This thesis is concerned with power control algorithms in CDMA cystems. The work summarized as follows: Firstly, the most three competitive technique are introduced: WCDMA, CDMA2000 and TD-SCDMA, then the three technique are compared in these aspect: synchronization, switch, power control, and so on. Analyzing and sorting out their respective advantages and disadvantages. Secondly, based on introducing the basic tenets of the CDMA communication system, detailed analyzing the capacity of CDMA system and the method for calculating the capacity of TDMA system. Further discussions of the main parameters affecting the capacity of CDMA system, compared the capacity of TDMA and CDMA systems, and come a conclusion that CDMA system capacity is about four times of the capacity of TDMA system. Thirdly, researched and analyzed two power control algorithm based on the stochastic theory: 1) The power control algorithm based on stochastic differential equation; 2) The power control algorithm based on the cost function. In this thesis, based on traditional distributed power control algorithm, considering the non-negative cost function, and the existing of a minimum value, using transmitting power and SIR to define the cost function. A cost function is derived based on the power control algorithm. Finally, the algorithm is validated by using Matlab.