Downlink Transmission And Interference Coordination For FD-MIMO Systems Exploiting Statistical Channel State Information

Massive multiple-input multiple-output(MIMO),where base station(BS)is equipped with large numbers of antennas,has been widely recognized as one of the key techniques to meet such demand due to its ability to greatly improve the spectral and power efficiency.There remains several challenges for massive MIMO.One of the main challenges for massive MIMO is that the number of antennas can be deployed is limited by BS factor.This has motivated full-dimension MIMO(FD-MIMO)systems.By placing antennas in two-dimensional(2D)grid,more antennas can be adopted and vertical dimension can be exploited in FD-MIMO systems.The large overhead of the channel state information(CSI)feedback in system is another challenge for massive MIMO,especially for mobile communication and frequency-division-duplex(FDD)system.Therefore,in this thesis,the downlink transmission and interference coordination exploiting statistical CSI are investigated for FD-MIMO systems with 2D unitary planar antenna array at BS.Firstly,with only statistical CSI,the downlink transmission and user scheduling algorithm is introduced for single cell FD-MIMO systems with 2D unitary planar antenna array at BS.Based on the maximization of the derived lower bound of each user's average signal-to-leakage-and-noise ratio(SLNR),a low complexity three-dimensional(3D)beamforming downlink transmission algorithm exploiting only statistical CSI is implemented.Simulation results show that the achievable sum rate performance of the 3D beamforming transmission algorithm with only statistical CSI at BS is comparable to or even better than the traditional matched filter(MF)and zero-forcing(ZF)algorithm when the instantaneous CSI obtained at BS is imperfect.Next,the downlink transmission and interference coordination strategy is investigated for downlink FD-MIMO systems with D2 D communications underlaying.To reduce the CSI feedback and data exchange,only each user's statistical CSI and the effective CSI of a small fraction of users are available at the BS.With 3D beamforming downlink transmission applied for cellular users,an approximation of the interference-to-signal ratio for cellular users is derived,and a coordination strategy exploiting only statistical CSI to mitigate the interference from D2 D pairs to cellular users is proposed.Based on the lower bound of the interference-to-signal ratio for D2 D pairs,interference coordination strategies exploiting statistical CSI and some effective CSI are proposed to mitigate the interference caused by cellular users(CUE)to D2 D pairs and the interference between D2 D pairs.Simulation results show that the proposed coordination strategy performs well in terms of achieving good tradeoff between the achievable rate of CUEs and D2 D pairs.Finally,the downlink transmission and interference coordination exploiting the benefits of both fractional-frequency-reuse(FFR)and cooperative transmission is investigated for multi-cell FD-MIMO systems.To reduce the amount of CSI required at each BS and the CSI exchange overhead,we assume that only statistical CSI can be obtained at each BS.We propose a FFR scheme for multi-cell FD-MIMO systems,which classifies the users in whole system into cell-center and cell-edge users,so that all the center users share the same frequency resources and all the edge users share the rest frequency resources.Based on the proposed FFR scheme,two joint 3D beamforming transmission and interference coordination strategies based on SIR(Signal-to-Interference Ratio,SIR)are proposed to mitigate the inter-cell interference for the cell-edge users,which are the fully-cooperative interference coordination and partial-cooperative interference coordination.In fully-cooperative interference coordination,all BSs provide cooperative transmission for scheduled edge-users,while in partial-cooperative coordination,only BSs that meet some certain constraints can provide coordinated transmission.The simulation results show that the proposed interference coordination strategy performs well in terms of the cell-edge rate,as well as the achievable sum rate.