Power Control Algorithm Based On Game Theory For Uplink In CDMA System

In order to transmit and receive multi-media information, The Third Generation Mobile Communication System should support high bit-rate services. In theory, FDMA, TDM A and CDMA all can be used in 3G Because CDMA communication system with power control has some merits such as high capacity, anti interference, low transmitting power and anti multi-path effect etc., the 3G composed mainly of W-CDMA, CDMA2000 and TD-SCDMA takes CDMA as its multi-access scheme.In CDMA communication system, the users are identified by their different spread spectrum codes. If the correlation between different two spread spectrum codes is not zero, there would be multi-access interference. Additionally, CDMA communication system is an interference-limited system, that is to say that the interference directly influences the capacity of the system and the QoS of the users in the system.Traditional power control algorithm in CDMA is oriented to voice service. It can be divided into two kinds -distributed and centralized power control algorithm. The centralized power control algorithm points out the theoretical upper bound of the power control performance. In practice, the distributed algorithm by iteration is utilized. Owing to some traits in multi-media service, it is difficult to attain better performance, if traditional power control method is employed in 3GGame theory used to be thought as the optimal controlling theory. The power control in CDMA can be regarded as a game. All users in the game can obtain maximal utilities by adjusting their signal power. The game ends at the Nash equilibrium. The power control based on game theory is classified into two kinds according to two different utility functions. One utility function is formulated as correctly received information bit number per unit power consumed by anticipated user. This function not only depends on sir, also on system parameters, such as coding, decoding etc. Thus, this power control method is complicated. Another one takes channel capacity as utility. The capacity depends only on the sir of user's signal as well as the bandwidth of the channel.Traditional power control based on game theory takes simultaneous-decisionmechanism. It is an imperfect information game. All users in the game don't know the others' strategies to be selected, they only to select strategies simultaneously. However, in fact, the power control in CDMA can be treated as a perfect information game. It takes alternate-decision mechanism, that is to say, all users select strategies in turn. So, some users could regard the strategies selected formerly by others as new information when they move. Simulation results show that the rate of convergence using this method is obviously higher than that using simultaneous-decision mechanism. Thus, the performance of the system could be improved.Because the unitary power control method could not further advance the performance of CDMA system, combined power control is becoming a hot topic in research area. Multi-rate transmission is also the key technology in 3G Using multi-rate transmission, multi-media service can be accomplished conveniently. Multi-rate transmission includes multi-code as well as multi-carrier techniques. Combined power and rate control can improve the performance to a great extent in 3G. In this paper, a combined power and rate control method is presented. Simulation results show that all users in the system can work at a higher rate when the system is idle, or slow down the rate to secure the system capacity when it is busy. Therefore, the spectrum resource in mobile communication system can be effectively utilized by this means.