Research On Power Control For Successive Interference Cancellation In Wireless Networks

High bandwidth and multiple user capacity is the development of next generation in wireless communication system, but with the increase of bandwidth and users, the inherent characteristic of wireless channel with limited resources and channel fading is bound to lead to increased interference between users, thus the capacity of wireless communication system is limited, so the effective way to solve this problem is multiple user detection technology. In recent years, research is focused on nonlinear implementation method for multiple user detection; it includes successive interference cancellation, parallel interference cancellation and zero-forcing decision feedback. Among many nonlinear multiple user detection algorithms of wireless communication system, successive interference cancellation is the key technology because of its easy realization and low complexity. The algorithm uses an loop way to subtract the received multiple channel mixed signals, in each loop process, the strongest signal is subtracted from the mixed signals, which contains multiple signals and noises, and then the second strongest signal is selected from the remaining signals to be detected, until the signal to interference and noise ratio is less than or equal to a given threshold, detection process ends. Under the condition of limited spectrum resource, research results show that successive interference cancellation can effectively increase the network throughput and user capacity. The premise to implement successive interference cancellation is that signal intensity ratio between signals of mobile terminals from multiple channels meet proper values in base station, which thus needs transmitting power control for mobile terminals. In this dissertation, for uplink CDMA system with single base station with multiple mobile terminals, based on the target that signal to interference and noise ratio for power control criterion is optimal in base station, three power control methods are proposed, which are iterative power control method, fuzzy logic power control method and game theory power control method.Simulation results show that the proposed power control algorithms for successive interference cancellation can effectively improve the throughput of wireless networks and user capacity. The main work are as follows:(1) Based on signal to interference and noise ratio, power control model is established, which builds the foundation for further study on power control of successive interference cancellation. In this model, it is considered that the situation which signals are not completely eliminated in loop detection application for successive interference cancellation, an incomplete eliminated parameter is introduced, and also it is studied that the relationship between transmitting power reduction and this parameter in this power control model, finally power control error margin for successive interference cancellation is defined and the effect of power control error on signal decoding is analyzed. The simulation results show that total transmit power can be greatly reduced, with the minimum value compared with the maximum value for incomplete eliminated parameter and with desired gradient decoding order for singal intensity of mobile terminals in base station.(2) Iterative power control for successive interference cancellation is proposed. First, considering the situation that signal is not completely eliminated, the mathematical expression of iterative power control is established. Second, the feasible solutions for iterative power control are verified. Third, the convergence of iterative power control is analyzed with the relationship with imperfect cancellation parameter. In addition, the effect on convergence between variable steps in iterative power control is studied. Finally, network performance of iterative power control for successive interference cancellation is studied in static channel. Simulation results show that the system throughput of iterative power control method for successive interference cancellation is much better than that of network throughput of other three classical power control methods.(3) Fuzzy logic power control for successive interference cancellation is proposed. First, the range of transmit power selection for mobile terminals is derived. Second, input parameters are designed for fuzzy logic power control. Third, time complexity of fuzzy logic power control is analyzed. Forth, the algorithm flow of the power control is proposed. Moreover, comparisons between proposed method and existing classical power control for successive interference cancellation are analyzed. Simulation results show that fuzzy logic power control method of successive interference cancellation have better network performance than other three classical power control methods, which have low computation and good performance, can improve network throughput.(4) Game theory power control method for successive interference cancellation is proposed. First, mathematical expression of transmitted power is established for each mobile terminal. Second, based on the game theory, the utility function for successive interference cancellation is proposed, third, the existence and uniqueness of Nash Equilibrium is proved. Fouth, the flow of the game theory power control algorithm is given. Finally, making comparisons that power control based on game theory is better than other power control method, simulation results show that the proposed power control method can increase network throughput than other three classical power control methods, for successive interference cancellation.(5) Analysis and comparison for three kinds of power control methods. In this dissertation, for the value of research work, three kinds of power control methods for successive interference cancellation not only are compared with classical literature of power control methods, but also are compared with themselves. According to the difference between calculation complexity, difficulty of implementation and effect of power control for three power control methods, they can be applied to different application environments.