Research On Resource Allocation Of Coordinated Transmission In Cloud Radio Access Network

The growing demand for broadband communication facilitates the rapid develop-ment of novel wireless communication technologies.The core feature of CoMP in C-RAN(Cloud Radio Access Network)is that the cooperation between the geographically dispersed antennas needs to exchange data and channel state information at the centralized baseband processing unit through fronthaul.This,however,lays a great burden to the data transmission of fronthaul transmission link.Meanwhile,in the areas where wired optical fronthaul link is unavailable,the microwave radio wireless link is usually deployed as the fronthaul.How to fully utilize the flexibility of the wireless fronthaul link to facilitate the base station coordinated transmission is critical to optimize the spectral and energy effi-ciency performance of C-RAN.In addition,the optimization of the system performance in C-RAN is affected by the transceiver hardware impairments,which will generate dis-tortion noise and needs to be compensated to achieve the robustness of coordinated trans-mission.Therefore,this thesis studies the optimization of coordinated multi-point transmis-sion in C-RAN,including the principle of pre-coding based beamforming,optimization of antenna clustering and fronthaul bandwidth allocation,etc.To sum up,the main work of this thesis are as follows:(1)C-RAN architecture and optimization model.The network architecture and the signal transmission process of the centralized multi-cell cooperation system and the tradi-tional cellular system are compared.The working mechanism of three kinds of multi-cell cooperative transmission modes,i.e,joint processing,cooperative beamforming and co-operative silence,are introduced.Then the principle of multi-cell joint processing is ana-lyzed,which is modeled as an optimization problem and solved by analyzing the structure of optimal solution and obtaining the optimal pre-coding strategy of the specific coverage scenarios.The above work provide the theoretical basis for the subsequent study.(2)When the system uses low-cost hardware,the transceiver hardware impairment will affect the performance of coordination.By establishing a hardware derivation model for transceivers in C-RAN,the transmitter and receiver distortions are obtained,and then the wireless transmission capacity and the impact of the hardware impairment on system performance are deduced.An KKT(Karush-Kuhn-Tucker)based optimization problem is then formulated to enhance the worst energy efficiency performance,which generates the robustness of C-RAN to the transceiver hardware impairments.(3)The concept of asymmetric cooperative transmission is proposed considering the multi-cell cooperative complexity and the demand for green communication with low energy consumption in the coverage scenario of fiber-optic fronthaulled C-RAN.Then,the energy efficiency enhancement of C-RAN is transformed into an optimization problem,whose objective function is transformed into its lower bound by using Jensen's inequality to satisfy convexity.Furthermore,an iterative convex optimization scheme is proposed to optimize the number of antennas participating in the cooperation and the corresponding transmission power,thus realizing energy efficient CoMP under fronthaul constraints.(4)For wireless fronthaulled C-RAN,the wireless fronthaul is regarded as an addi-tional resource that can be allocated among antennas.The models of wireless cooperative transmission and wireless fronthaul link are established with a coupling relationship be-tween the two.Then the degree of contribution is defined to measure the enhancement to system spectral efficiency,based on which the wireless fronthaul bandwidth allocation is formulated into a knapsack optimization problem.In the knapsack problem,the degree of contribution of each link through cooperation is defined as the benefit,and the occupied wireless fronthaul bandwidth is defined as the cost.Then,the concept of virtual antenna is proposed to further convert the knapsack problem into a 0-1 knapsack problem,which is then solved by a recursive and divide-and-conquer algorithm.Meanwhile,the concepts of optional and mandatory knapsack are utilized to maximize the degree of contribution while guaranteeing the quality of service of mobile terminals,thus enhancing the perfor-mance of wireless fronthaulled C-RAN.