Research On The Load Balancing In Cooperative Communication Networks

As cooperative communication can enhance the wireless communication link quality between user and base station and the system reliability because of the diversity gain and coverage gain, and it has been considered as the future development direction of wireless communication. The fluctuation of user distribution will lead to unbalanced load distribution in the wireless network, and consequently the load balancing techology is required. Therefore, the research of load balancing has certain practical meaning in cooperative communication networks. In this thesis, load balancing technology in cooperative communication networks is studied through the following two aspects.Firstly, the existing balancing technologies either ignore the user cooperation in target cell or assume that the uer cooperation in target cell must be able to achieve, which leads to the lower handover decision accuracy. Focus on the above problem, the cooperation probability is introduced in the load balancing process of cooperation network.Firstly, gets the number of calling users by making use of the target cell's load, and then furtherly predicts the probability distribution of the total number of user in target cell. The probability of users in cooperation area can be derived based on the probability distribution of the total number of user in target cell and the ratio of cooperation area size to the cell coverage size. Combing with the receiver signal strength of users in target cell, the cooperation probability of user in the target cell can be getten, and then the traditional handoff decision function based on the received signal strength of user and the load in target cell is modified by linearly adding the cooperation probability. Furthermore, according to the above theory, a load balancing mechanism based on cooperation probability is proposed for the cooperative communication networks. Simulation results show that the proposed scheme can achieve a balanced distribution of network load, improve user satisfaction and network fairness, and enhance the system capacity and resource utilization.Secondly, aiming at the problem that the existing load balancing technology based on channel borrowing is achieved by the frequent information interaction among base stations, and consequently will greatly increase the network signaling overhead and energy consumption, and then the spectrum sensing technology which can adaptively detect the idle spectrum is proposed to be applied to the load balancing mechanism based on spectrum borrowing in cooperative networks. In the designed mechanism, the base station utilizes the spectrum sensing technology to detect the spectrum holes of the network, and then generates the available spectrum set. Once the spectrum resource of base station is exhausted, the base station will invoke the available spectrum set, and choose the target borrowing user. Then borrowing the spectrum from the available spectrum set according to the conditions that whether the target borrowing user has cooperation in the base station. If the target borrowing user does not have cooperation in the serving cell, the spectrum borrowing problem is turned to select the optimal spectrum, which can maximize the utility function which jointly considers the idle rate and the spectrum quality for the direct communication link. If the user has cooperative communication in the cell, based on the spectrum selection of direct communication link, the objective of the spectrum borrowing is to maximize the utility by choosing the optimal available spectrum and cooperative partner. The simulation results show that the mechanism not only can improve the network fairness and resource utilization rate, but also can reduce the degree of unsatisfied user.