Research On Several Key Technologies For Heterogeneous Cognitive Radio Networks Convergence

Currently, along with the continuous development of wireless communication technologies and the increasing demands of mobile users, heterogeneous wireless networks with different bands, modes, access methods and coverages have been becoming the mainstream paradigm of wireless communication systems. However, the traditional static resource management mode results in serious problem, including independent information process, independent resource management and low spectrum efficiency, turning into the bottlenecks of the wireless networks development. The heterogeneous cognitive radio networks (HCRNs), which are based on the cognitive technology, can realize the information and resource sharing among heterogenesous networks through the cognition of heterogeneous enviorments and intelligent decision-making within networks. Therefore, to improve the spectrum efficiency and promote the development of wireless communication systems, it is meaningful to research the key technologies for HCRNs convergence.This dissertation firstly summarizes the development tendency of HCRNs through a detailed description of the current research status in the literature. The challenges of the key technologies such as:access control, transmission control and the HCRNs convergence with the limited backhaul resource are deeply analyzed. The research idea of this dissertation is addressed as:firstly, aiming to maximize the system capacity, the access control technologies are researched for the multi-homed/single-network users on the link-layer. Secondly, the researches on the cross-layer end-to-end transmission control for multi-path sessions are carried out on the link-layer and transport-layer to improve the end-to-end efficiency in HCRNs. Finally, this dissertation analyses the impact of the limited backhaul resource on the convergence of HCRNs, and focuses on the research of the HCRNs convergence technologies with the limited backhaul resource.With respect to the access control for HCRNs, concentrating on the hybrid scene that multi-homed users coexisting with single-network users, the optimization model of joint network selection, spectrum and power allocation is formulated to maximize the system capacity. To solve the model efficiently, a near-optimal solution is proposed to decompose the original problem into several sub-problems by exploiting the dual decomposition method. Simulation results show that the proposed algorithm is able to approximate the optimal method very well and is of good compatibility, hence greatly improving the system capacity. Based on the above researches, the model is extended to the Orthogonal Frequency Division Multiplexing (OFDM) scene. A multi-dimension optimization model with joint network selection, subcarrier assignment and power allocation is formulated. To settle this multi-dimension optimization model, the original problem is relaxed into a linear programming problem. Based on the optimal solution for the relaxed problem, a step-by-step algorithm is proposed to perform network selection, subcarrier assignment and power allocation separately. Simulation results show that using the proposed access control method, the system capacity is improved, and the interference for primary users is well controled.With respect to the transmission control for HCRNs, aiming at improving the end-to-end efficiency of multi-path sessions, the cross-layer optimization model is formuluted to jointly carry out the power/spectrum allocation and traffic splitting. To address the model efficiently, the problem is decomposed into two independent sub-problems, and exploting the iterative optimization algorithm, a good solution of the power/spectrum allocation and traffic splitting is achieved. Simulation results show that the proposed algorithm is able to fast converge to a stable solution, result in a reduced end-to-end delay and an improved user experience, especially when the traffic is high.With respect to the convergence of HCRNs with the limited backhaul resource, the impact of the limited backhaul resource on the HCRNs convergence is analysed. Considering the multi-tiered HCRNs with the limited backhaul resource, a novel macrocell/femtocell Coordinated Multiple Points (CoMP) transmission scheme is formulated. After analysing the available CoMP transmission capacity with the limited backhaul resource, a universal dual bisection methoed is designed to obtain the optimal spectrum and power allocation. Simulation results indicate that the CoMP gain can be improved by the proposed algorithm. Moreover, when macrocell users move close to the femtocell, the capacity of the femtocell is enhanced while the data communications of macrocell users are well protected.In summary, to realize the convergence of the HCRNs, this dissertation investigates the following key problems:access control, transmission control and the HCRNs convergence with the limited transmission resource. Through the mathematical modeling and theoretical analysis of the above key problems, efficient solutions are proposed and verified by simulations respectively. The proposed solutions can promote the convergence of HCRNs effectively and improve the spectrum efficiency. The research results can serve as a preliminary research for the programing and deployment of the next generation heterogeneous wireless networks, and have great significance to promoting the convergence of the heterogeneous wireless networks in the future.