Research On Radio Resource Management And Load Balancing Strategy In Next Generation Wireless Networks

Cellular, WLAN, WiMAX are given increasing attentation as the main candidates of broadband technologies to access the Internet. All of these wireless networks have an interactive relationship of not only competition but cooperation as useful supplementary to the others for their advantages and disadvantages. In order to provide more voice, data, multimedia services with bettet QoS guarantees and lower price, the next generation wireless networks need to support the convergence of heterogeneous networks, adopt orthogonal frequency-division multiplexing (OFDM) as one of the key techniques, have the capability of reconfiguration for cognitive radio, and support distributed network architecture, ad hoc network, multihop relaying, etc. In this dissertation, we research the radio resource management and load balancing strategy of next generation wireless networks.Firstly, the orthogonal frequency division multiplexing (OFDM) technique, as the key technique of next generation network, is researched. Because subcarrier and power allocation algorithms based on the channel status information (CSI) feedback have high complexity and great overhead of control channel, and the channel independent scheduling algorithms in OFDM system have poor performance, a novel wireless resources allocation algorithm is proposed based on statistical tap correlation information, in which the channel status statistical information is utilized so as to reduce the channel feedback. The proposed algorithm is converted into discrete method to achieve a lower algorithm complexity. And in multiuser orthogonal frequency division multiple access (OFDMA) system, from the viewpoint of service differentiation, we develop an adaptive cross-layer scheduling scheme combined with dynamic subcarrier allocation algorithm according to instantaneous traffic load condition. The algorithm is designed to grant higher priority to realtime traffic packet of voice and multimedia than data packet, and dynamically allocate subcarriers for data service according to the packet number of each user in the buffer queue with fairness guarantee. Simulation results show that the proposed algorithm has very little reduction in overall system capacity, but much lower complexity and small channel feedback comparing to the traditional scheduling algorithm based on CSI, and it outperforms greatly channel independent scheduling algorithm based on pathloss in fast Rayleigh fading channel under any conditions. Moreover, our proposed adaptive cross-layer scheduling and dynamic subcarrier allocation algorithm improves delay performance for realtime traffic and spectrum efficiency in OFDMA system.In OFDM-based multi-hop cognitive radio networks, the color-sensitive graph coloring (CSGC) model is viewed as an efficient solution to the spectrum assignment problem. We extend the model by taking into account the power control strategy to avoid interference among secondary users and adapt dynamic topology. We formulate the optimization problem encompassing the channel allocation, power control with the interference constrained below a tolerable limit, the optimization objective focuses on the routes according to two different optimization strategies, but not the links as traditional approaches. A heuristic solution to this NP-hard problem is presented, it performs iteratively channel allocation according to the lowest transmission power that guarantees the link connection and make channel reuse as possibly as it can, and then the transmission power of each link is maximized to improve channel capacity by adding gradually power level from the lowest transmission power until all co-channel links can not satisfy the interference constraints. Numerical results show that our proposed strategies outperform the existing spectrum assignment algorithms on the performance of both the total network bandwidth and minimum route bandwidth of all routes.A major challenge of the heterogeneous wireless networks is how to jointly utilize the resources of different radio access technologies in an efficient manner. Because of the different system capacities of BS/AP and ununiformity of traffic distribution in different cells, quantities of new calls may be blocked in the overloaded cell in some hot spots; whereas its neighboring under-loaded BS/AP have superfluous bandwidth. In order to raise resource utilization of heterogeneous networks, several novel load balancing strategies are proposed, which combine the call admission control and multi-hop routing protocol of ad-hoc network. These load balancing algorithms firstly make a decision whether to admit a new call or not, and then transfer the denied users into neighboring under-loaded cell with surplus channel according to certain load balancing strategy. The simulation results show that the proposed load balancing strategies can distribute the services to the whole heterogeneous wireless networks, improve the load balance index, and avoid the call block phenomenon almost absolutely.In order to improve the system performance of the block probability and throughput in communication hot spots overlapped by heterogeneous networks such as cellular, WLAN, WiMAX networks, etc., two cooperative load balancing strategies based on hops-limited routing algorithm of ad hoc network are proposed to raise the resource utilization of the whole overlapping heterogeneous networks. They both firstly make a decision whether to admit a new call or not based on common radio resource management strategies, and in overloaded condition select certain traffic to transfer into targeted BS/AP according to minimum price strategy or minimum load BS/AP and nearest traffic strategy, which take into account these factors such as load index, number of hops, traffic prediction, cost, etc. An analytical model is used to compute the call block probability and throughput performance for two different traffic models. Simulation results show that the proposed load balancing strategies can distribute traffics to the whole heterogeneous wireless networks, decrease the call block probability, improve system throughputs efficiently, and obviously outperform HM-MACA and HS-TC load balancing strategies.Radio resource management and network selection algorithm based on network utility is a hotspot of research in heterogeneous wireless networks. We propose an economic model to allocate radio resources and select networks with QoS guarantees. In the CDMA uplink, the resources usage constraint is deduced with the consideration of multi-cell interference power, then radio resources are allocated with the objective of maximizing the social welfare of CDMA network under the resources constraint. On the other hand, we also get the closed-form expression of net benefits in WLAN network when it achieves the maximum throughput by controlling the optimum collision probability. Finally, we design the access control mechanisms and load balancing strategy under different load conditions. Numerical results show that approximately more than 20% number of users can be achieved according to our radio resources allocation algorithms compared with traditional ones in single network environment such as CDMA or WLAN network, meanwhile providing effective signal quality guarantees for each mobile user. Moreover, our proposed network selection and load balancing strategy based on economic model can achieve more 10% network benefits than UFAS mechanism, even more gain of social welfare than single network access mechanism in heterogeneous networks environment.Finally, the works of this dissertation are summarized briefly, and we also figure out the research programme in the future period, including the novel research ideas.