Robust Adaptive Power Control Algorithms For CDMA Systems

Code Division Multiple Access (CDMA) technology has been selected as the access technique for the third generation wireless communication system. Consequently, it has received a significant amount of attention in provision of advanced algorithms for improved performance in kinds of key technologies. Accurate power control is one of the most important technologies of the CDMA systems. There is a great advantage in system capacity when accurate power control technology is adopted in CDMA system.Firstly, 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 analyses their method of realization, scope of application and advantages or disadvantages. Then it expounds the concept of robust adaptive control and the stability. Finally, we proposed the system model and design the robust adaptive controller.The major contributions of this dissertation are as follows:(1) We use a nonlinear model with boundary disturbance to characterize the system. At the same time, we consider the user's transmission power as the input of the nonlinear model and signal-to-interference power ratio (SIR) as the output of the nonlinear model.(2) We get the tracking error through output track the optimal value. (3) A kind of fuzzy logic system is used to approximate the unknown nonlinearities. At the same time, this paper considers the existence of the approximation error and the system's external disturbance. Provide the approximation error and the system's external disturbance has an unknown boundary, an adaptive estimation boundary is designed.(4) Based on the above mentioned nonlinear model and adaptive estimation boundary, we design the robust adaptive controller based on SIR measurement.(5) Certify the final controller can guarantees that the closed-loop system is robust stable and tracking error converges to a neighborhood of zero.(6) The rationality and the superiority of the final controller are demonstrated through the simulation.