| Recent years have witnessed an explosive growth of mobile data services with ultrahigh bandwidth requirements.Those services are bringing higher requirements for network capacity.Multiple-in Multiple-out(MIMO)technology has the potential to improve the system performance.Ultra-Dense Cloud-Radio Access Network(UDC-RAN)improves the energy efficiency of the system through dense deployment of access nodes and centralization of baseband processing.Full-Duplex Relay Network has also received widespread attention since it can significantly increase the system's spectral efficiency.The application of MIMO technology in these two network architectures can better play their own advantages and provide users with better services.However,with the introduction of multiple antenna nodes,interference in the system has become more complex and more difficult to handle.So,in this paper,we study the interference coordination problems in the multi-user MIMO system: UDC-RAN and Full-Duplex Relay Network are studied in depth.Firstly,we consider a downlink UDC-RAN system.To deal with the severe interference,we formulate the problem to maximize the total system throughput,subject to the minimum data rate requirement of each user,as well as the limited power budget of each transmit node.Due to the nonconvex and combinatorial nature of the problem,a three-step sub-optimal solution is designed to solve the optimization problem efficiently.Specifically,we first devise a user-centric clustering scheme meeting the serving capability of each RRH.Then,the allocation of sub-channels for each user is performed in priority order,based on users' channel states and the capacity of the serving clusters.Finally,the non-convex beamforming problem is solved by the weighted sum meansquare-error method.The simulation through MATLAB and comparison with the comparison algorithm show that the algorithm proposed in this paper can effectively deal with interference in this MIMO network and improve system throughput and energy efficiency performance.Moreover,we discuss the problem of channel interference situation in a full-duplex network where each relay serves only one uplink/downlink user.An interference coordination model is established with the objective of minimizing the total power of the transmit nodes in the system and the constraints of the uplink and downlink users' data rate requirements.By constructing the model as a quadratically constrained quadratic program problem,the transmission power allocation and beamforming vectors of multiantenna nodes are solved.Simulation results show that the algorithm proposed in this paper can improve the energy efficiency of the system and the data transmission rate of users,and at the same time better guarantee the fairness of the uplink and downlink users in the system.Then,we studied the interference situation of a MIMO full-duplex network with multiple uplink/downlink users serviced by one relay node.We formulate a joint optimization problem model of transmit and receive beamforming with the goal of minimizing the total power usage of the system and considering the user data rate requirements.We propose a receive beamforming algorithm based on self-interference cancellation.Furthermore,a global transmit beamforming algorithm based on semipositive definite relaxation method and a sub-optimal beamforming algorithm based on interference cancellation are designed.Simulation results show that the algorithm proposed in this paper can improve the energy utilization rate of the system and the data transmission rate of users. |
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