Cooperative Transmission Methods For Non-ideal Fronthaul In Cloud-radio Access Networks

In the face of the growing demand for mobile Internet business,it is imperative to find a way to provide users with low cost wireless business.The traditional Radio Access Network is gradually losing its competitiveness by its high capital expenditure and maintenance expenses,though the Cloud-Radio Access Network(C-RAN)can effectively reduce energy consumption,save operation and maintenance costs,improve the network capacity,achieve the flexible allocation of resources.However,based on the actual situation,in the Cloud-Radio Access Network architecture,the fronthaul between the Base Band Unit Pool(BBU Pool)and the remote radio heads(RRH)is often not ideal.In the face of this problem,it is very important to design a cooperative transmission method for the RRHs in order to improve the performance of the system.In this thesis,we study the cooperative transmission method of the non-ideal fronthaul link of the Cloud-Radio Access Network in several aspects as follows:For the uplink transmission scenario of wired fronthaul,in order to achieve the improving of user’s information transmission rate,the optimization problem of the maximum the RRHs’ computation rate upper bound is built up.Aiming at the dilemma that the optimization problem is generally non convex in the practical situation,a low complexity method based on Dijkstra algorithm is proposed.The simulation results show that when the number of users and RRHs are both 3,the proposed algorithm can improve the sum rate by 50%compared with the traditional compute-and-forward algorithm.For the downlink transmission scenario of wired fronthaul,a fixed intro-cluster cooperation strategy is studied,and the utility function of the system is designed based on the derived successful access probability.Based on the designed utility function,we formulate the problem of grouping remote radio heads as a coalitional formation game,and purpose a cluster formatting algorithm under limited cluster size circumstances.We also proves the stability of the algorithm.The simulation results show that when the energy efficiency exponent is small enough,the proposed algorithm can exceed the average rate of the centralized cooperative algorithm,while it can also guarantee the reasonable utilization of the link resources and avoid the high power consumption.For the downlink transmission scenario of wireless fronthaul,the remote radio head selection scheme is designed,and based on the proposed channel mark,the expression of coverage probability is derived by applying stochastic geometry.The correctness of the performance analysis results can be verified by the comparison of the results of numerical simulation and Monte Carlo simulation.