Research On Joint Processing Based On Multi-Cell Cooper Ation In Lte-Advanced Networks

The explosive increasing number in mobile internet users and mobile applications requires higher and higher capacity and coverage of mobile communication systems, which also brings us a big challenge. As one of the key technologies of LTE-Advanced systems, joint processing(JP) is characterized by the same data transmitted from multi-cell using the same time-frequency resources, which mitigates the inter-cell interference(ICI) and increase the desired signal power, so as to increase system’s capacity and coverage. The purpose of this thesis is to enhance the capacity and coverage of LTE-Advanced systems by using joint processing.Firstly, system model of joint processing based on multi-cell cooperation in LTE-Advanced systems is presented, based on which the optimization goal to prompt the system’s capacity and coverage is given. Then we use heuristic algorithm to solve the problem since it’s is of great difficult to solve by mathematic way. We do the optimization of joint processing by designing schemes from three aspects including network topology, MIMO array gain and3D MIMO.Since the same frequency resources of multi-cell are required to send the same data to the same user at the same time in joint processing, the frequency reuse factor is reduced if only single user MIMO(SU-MIMO) transmission mode is used. The overall spectral efficiency would decrease if the capacity gain achieved by joint processing cannot offset the declined spectral efficiency caused by the reduced frequency reuse factor. So we design a use selection algorithm and cooperation set configuration algorithm from the perspective of network topology. The cooperation set configuration algorithm proposed can achieved good balance between the gain of joint processing and the complexity of system’s scheduling. The user selection algorithm proposed can guarantee system capacity while improving system coverage in SU-MIMO transmission mode. User selection algorithm for MU-MIMO transmission mode is also proposed based on the one for SU-MIMO transmission mode. In fact, joint processing can be seen as network MIMO. As is known to all, MIMO can achieve diversity gain and array gain by using spatial diversity and multiplexing gain by using spatial multiplexing. The array gain of MIMO means the gain achieved by coherent combining of received signals, which requires co-phasing among the signals. To achieve the array gain in multi-cell joint processing, we design a scheme which is transparent to the user to feedback the inter-cell phase information. Coherent combing of multi-cell’s signal is then made possible, which enables coherent joint transmission and enhances the performance in terms of capacity and coverage.With3D MIMO enabled by Active Antenna System(AAS), we proposed a scheme combining multi-cell joint processing with3D beamforming. The proposed scheme is based on the following two observations:1) The performance of multi-cell joint processing is highly dependent on the received signal strength from the coordinated cells,2) Interference may become more severe at the cell boundary due to the extremely flat beams serving the cell edge users with3D beamforming. In the proposed scheme, users at the cell boundary are served with JP and3D beamforming simultaneously, and those at the cell center are served with3D beamforming. Simulation results based on LTE-Advanced systems show that significant gains can be achieved by the scheme compared to joint processing and3D beamforming.