Study On Energy-Efficient Hybrid Precoding Algorithm For Multi-User Millimeter Wave Massive MIMO System

Millimeter wave(mm Wave)technology can use the undeveloped millimeter wave band to solve the problem of insufficient communication spectrum resources in the future.Massive multi-input multi-output(MIMO)technology can provide significant array gain and a high degree of freedom space,can ease the huge millimeter wave Free-space path loss.Combining millimeter-wave and massive MIMO technology to form millimeter-wave massive MIMO system,the channel capacity of the communication system can be greatly enhanced.The huge antenna array in millimeter-wave massive MIMO system will bring huge hardware cost and power consumption,and hybrid precoding technology is expected to solve this problem.Most hybrid precoding studies are based on fixed subarray structures in fullyconnected and partially-connected structures.In a fully connected structure,each radio frequency(RF)chain needs to be connected to an antenna.With the increase of the number of antennas,the number of phase shifters and adders connected to the RF chain increases,which leads to the increase of hardware power consumption and hardware cost.Although the fixed subarray structure can alleviate the problem of excessive power consumption in hardware,its cost is the loss of some spectrum efficiency.In this paper,a high energy efficiency hybrid precoding scheme based on dynamic subarray structure is proposed,which considers the energy efficiency of the system,the reach rate of the system and the fairness of users.In this scheme,cyclic antenna partitioning algorithm is used to design the antenna subarray,and the fairness of users is considered,so that each RF chain can dynamically connect nearly equal number of antennas.The dynamic subarray structure obtained by this algorithm is optimized by hybrid precoding,and the simulated precoding is designed to maximize the user channel gain,and then the equivalent channel is simulated by multiple users,a baseband digital precoding based on the Minimum mean square error criterion is designed to eliminate user interference and reduce the impact of low SNR on the system.Simulation results show that the proposed scheme can achieve better energy efficiency,system reachability rate and user fairness than the existing schemes.On the other hand,the research of multi-user mixed precoding is usually limited to the fact that the number of RF chains is no less than the total number of data streams and generally assumed that they are equal.In addition,when the number of users increases,the complexity of hybrid precoding will increase.Most researches consider using user group to reduce the complexity of hybrid precoding,however,the existing user schemes often set the number of users or the number of user cluster centers,but in a real scenario,the number of user groups is a priori unknown.In this paper,a multi-user hybrid precoding scheme based on user group strategy is proposed,which considers the optimization of radio frequency and the computational complexity in the hybrid precoding.In the design of multi-user hybrid precoding,the user grouping algorithm in this paper can obtain the number of user groups first and then group users based on the similar departure angle information of users.Moreover,considering the hybrid precoding structure of cluster controller,this scheme can not only effectively reduce the number of RF chains,but also improve the energy efficiency of the system.Simulation results demonstrate that the spectrum efficiency of this article proposed scheme is slightly better than the existing schemes,and improve the energy efficiency of the proposed methods,clearly.