Research On Power Control And Vertical Handoff Algorithms In Wireless Networks

With the fast development and increasing inosculation of mobile communications, data communications and Internet network, not only the high-quality voice service, but also the wideband multimedia services analogous to Table-PC are expected by the users in communication systems. In addition, the users hope to access the network anytime and anywhere. Therefore, next generation communication system will be the network with tight combination of mobile communication and information processing. CDMA technique based modern mobile communication systems, which can provide wideband multimedia services and connect with Internet, have attracted more and more attentionFrom the development of mobile communication, mobile communication technology faces some problems, such as the rapid increase of user number, the diversification of mobile services and the improvement of QoS (Quality of Service) from users. Different businesses need different QoS (such as time delay, throughput and bit error rate) and different transmission data rate, and hence the communication system needs to provide more radio resources and more complicated control mechanisms. However, the radio resources (i.e. spectrum, power, data rate, time slot and code word) in the communication system are limited, so it looks very important to control and optimize the radio resources. The aspects such as deploying the complicated radio physical channels and network resources with all kinds of method of RRM (Radio Resource Management), improving the compatibility of the heterogeneous network and protecting the transmission quality of services with different characteristic have become important research issues. According to the fundamental characteristics of radio resources management, based on systematic analysis and demonstration of existing RRM algorithms, this paper analyzes the following several key technologies and theoretical problems in detail.Firstly, optimal distributing power control algorithm based on predictor is introduced. After systematic research on power control in mobile communication systems, an optimal distributed closed loop power control algorithm concerning SIR error and transmitted power is introduced and verified. The proposed algorithm uses the sum of the square of SIR error and the square of transmitted power as its optimizing parameters, and chooses the optimal ratio of gain in order to minimize the SIR error and transmitted power at the next time-step. This scheme adopts H∞filter as the system filter. Simulation shows that the proposed algorithm with a fast converging speed, is a power control scheme which can adapt to link interference and variation of the channel, reduce the'party'effect of the system and achieve the tradeoff between the required QoS and power consumption.Secondly, we propose a new non-cooperative power control algorithm based on Game Theory. Since conventional scheme of power control focused on voice service instead of multimedia services in different data rate, we propose an algorithm suitable to wireless data network and design a new target function based on pricing. The function, which has Pareto efficiency, consists of subtraction of utility function and cost function. We prove the existence and uniqueness of Nash Equilibrium point in this game algorithm. Mobile user can reach a rational level of SIR using lower transmission power with this algorithm, which could be applicable in environments with various data rate. Finally we complete simulations to compare the proposed algorithm with existing algorithm, and prove its better practicability.Thirdly, a joint transmitting power and transmission rate optimal control algorithm is put forward. In wireless channel, SIR is strongly related to transmission rate, which can be effectively regulated by power control. According to those reasons, a control method that combines power and rate is designed based on the Game Theory, which consists of two game layers. Each game layer has a target function. The first game is a non-cooperative rate control algorithm with pricing, which sets rules for the users in order to make them reach the unique rate operating point of Nash equilibrium. The non-cooperative power control algorithm in the second game supports the transmission data rate obtained in the first game layer, through calculating transmitted power, and hence the problem of utilization of radio resources can be solved using this two layer game. Simulations show that users were able to attain transmission rates that are higher than their minimum required transmission rates at low transmit power levels.Fourthly, a vertical handoff method used in heterogeneous wireless networks is given, which maps the vertical handoff to a multi-standard process of decision-making. Considering various parameters of the system and different service type of users, a multi-object vertical handoff decision algorithm is brought up. This method contains the pre-handoff decision process and the handoff decision process. The quality of service function is used to choose proper access system for users in the pre-handoff decision process, and then the maximal system utility function is used to make decision for the vertical handoff. The proposed algorithm is compared with the existing algorithm using simulations, and the result shows that the proposed algorithm has better performance.