Research On Power Control Algorithm In CDMA Mobile Communication System

CDMA is a wireless spread spectrum communication technology with the development of digital mobile communication in recent years. CDMA system has good secrecy, good communication quality, high usage of frequency and is strongly anti-jamming. But CDMA mobile communication system is a interference limited system. As the number of users increases, the interference will be more and more big, thus make CDMA mobile communication system have three important problems: "near-far "effect, community edge problems and multi-access interference. In order to effectively reduce the system interference, the research should compensate the channel fading and solve the above three problems, to ensure the service quality of communication link. Power control is especially important for CDMA system, it becomes one of the key technology in the third generation (3G) mobile communication system. Power control technology in CDMA communication system is studied in this paper and the main work and contribution are summed up as follows:Firstly, this paper probed into the theory of power control. The classification of power control, formula of power control, influence factors of power control, basic method and the mathematical model of power control are summarized. The basic content of power control technology in CDMA system provides theoretical basis for more in-depth research.Secondly, the function of power control on the system capacity in CDMA communication system is introduced, and the factors that influence the system capacity are summarized. Then the propagation features and the mathematical model of mobile communication channel are introduced, these basic knowledge of mobile communication channel is the theoretical basis of the simulation.Finally, this part is the key research content of this paper about power control technology. Firstly several typical distributed power control algorithms are studied, like DBA, DPC, FDPC and BDPC algorithm. DBA and DPC algorithm are early proposed distributed algorithms, but these two algorithms require the whole link information of the communication system to determine unknown parameter, other wise, it will affect the correctness of power control algorithm, so the DBA and DPC algorithm are not completely distributed power control algorithm. FDPC algorithm was put forward to solve the problem of those two algorithms. But the transmitting power worked out by FDPC algorithm is gradually decreasing infinitely, that might make the transmitting power of users decrease towards zero. Although the problem can be solved by the addition of protection power as a restriction, it will affect the convergence of FDPC algorithm. This problem can be solved by the BDPC algorithm that not only assures transmitting power remaining in an appropriate dynamic range, but also avoid destroying convergence. But the formula of BDPC algorithm is complex and it needs to compare the power first in the interaction processing, which will increase the power control delay. The proposed algorithm in this paper is on the basis of FDPC algorithm, and it combines the concept of second-order power control, the generally thought of second-order power control algorithm is that the algorithm determine the next transmitting power according to the transmitting power in the present moment and former moment and the SIR of the communication link.It can be proved by theoretical analysis and simulation that the new algorithm has faster convergence speed than traditional FDPC and BDPC algorithm, the signal-to-noise ratio of users increase more quickly, it won't cause power control delay, and the transmitting power of new algorithm is no less than the minimum protection power system in the actual communication system. We know that the communication channel environment and the locations of mobile users are randomly changing and only efficient and rapid power control can maintain the normal work of practical communication systems. The proposed new algorithm has good convergence, and this advantage meets the requirements of practical communication system.