Research On Zero-Forcing Precoding For Massive MIMO

Massive MIMO system is an emerging wireless communication technology.It can serve more users at the same time mainly by deploying hundreds of antenna arrays on the base station side,which can significantly increase capacity of the system and enhance the reliability of the channel without increasing the bandwidth of system.But with increase of the number of base station antennas and users,the interference among the users becomes more and more serious.In the downlink channel of the system,the precoding technology used by the transmitter can not only effectively reduce the interference between users and improve the spectral efficiency of the system,but also reduce the complexity of the client receiver,which makes the hardware implementation simply and reduces its power consumption.Therefore,the precoding technique has a high research significance and application prospects.First of all,spatial multiplexing is adopted in the thesis in the case of network topology,which can improve the energy efficiency of the cell under the premise of satisfying user’s QoS(Quality of Service).At the same time,the massive MIMO system and heterogeneous network are combined,and the non-coherent information beam sended by a plurality of transmitters is formed and synthesized into the information which is received by the user.And the total power of the base station is minimized while meeting the satisfaction of the user’s QoS as the constraint condition,improving the energy utilization ratio.Meanwhile,existing RZF precoding is improved so that improved RZF precoding can be effectively used in the massive MIMO system and the heterogeneous networks of Small Cells,making the system and rate achieve optimal performance.Secondly,the implementation of precoding algorithm for massive MIMO is researched in this thesis,a precoding algorithm is proposed based on truncation polynomial expansion,aiming at the problem that the realization complexity of precoding in massive MIMO systems increases with the increase of system dimension.and then analyze.The simulation results indicated the superiority of the proposed algorithm compared with the traditional RZF precoding.Meanwhile researched precoding optimal precoding matrix of the algorithm based on the spectrum efficiency of the system and the complexity.Finally,in the case of a multi-cell massive MIMO system,It can be concluded the main reason for pilot contamination which limit system performance is depended on the large scale fading coefficient.Therefore,the large scale fading coefficient is estimated by utilizing the mode of cooperation among base stations,precoding is calculated the simulation results testified the precoding can reduce the influence of pilot contamination and increase the spectrum efficiency of the system.