Hybrid Precoding Based On Dynamic Subarrays In Millimeter Wave MIMO System

In recent years,with the rapid development of wireless communication technologies,the everchanging communication services and application scenarios,the demand for wireless smart mobile terminals represented by mobile phones has been increasing,and the communication service dominated by streaming media has gradually replaced.The traditional communication service represented by voice message service.At the same time,the rapid development of the Internet of Things and the Internet of Vehicles has become increasingly demanding on the quality of wireless communication networks.At this stage,the increasingly scarce spectrum resources are no longer able to satisfy people's demand of high-quality communication services.Although the efficiency of limited spectrum resources can be improved by techniques such as frequency division multiplexing,multiple input multiple output,beamforming,and cooperative communication,the existing frequency band resources have been met by the arrival of the 5G(fifth generation mobile communication)era.There is no need for ultra-high transmission peak rates such as 10 Gbit/s.At this time,the study of high-frequency millimeter waves is particularly important.The short wavelength of millimeter-waves makes it possible to package many antennas on smaller-sized components.At the same time,large-scale MIMO technology can use antennas brought by large-scale antenna arrays.The gain further improves the performance of the communication system,so the combination of millimeter-wave and massive MIMO will become the trend of 5G development.In millimeter-wave massive MIMO systems,hybrid precoding has two types of fully connected structures and partially connected structures.In the fully connected structure,each RF link is connected to all the antennas,and a large-scale antenna array gain can be obtained,but the hardware implementation complexity is high;In the partially-connected structure,each RF link is connected to one antenna sub-array,which can greatly reduce the hardware implementation complexity,but performance has dropped a lot.Therefore,the problem of balance between energy consumption and performance in millimeter-wave massive MIMO systems has become the main direction of research.In this paper,a low-complexity antenna combination algorithm is proposed for a millimeterwave MIMO system with partially-connected structure,which lays a foundation for the practical application of dynamic connection in millimeter-wave MIMO systems.In order to improve the spectral efficiency of the millimeter-wave MIMO system under the partially-connected structure,a switch network can be inserted between the RF link and the analog precoder,so that the array elements(antennas)in the antenna array of the transmitter can be freely combined.Each sub-array is implemented to achieve the best match with the channel.However,optimal grouping of antennas requires an exhaustive search of all possible antenna combinations according to certain criteria,which is difficult to achieve for millimeter-wave massive MIMO systems where the antenna size of the transmitting antenna is often over one hundred.Therefore,this paper proposes a low complexity antenna combination method.By introducing certain combination constraints,the number of candidate combinations in the array can be significantly reduced,and the complexity of the dynamic connection structure in the millimeter wave MIMO system is further reduced.Simulation results show that the proposed method can achieve a good compromise between performance and complexity.Subsequently,this paper optimizes and improves on the basis of single-user dynamic sub-array,making it more suitable for multi-user massive MIMO systems.Different from the multi-user processing method commonly used at the present stage,first,the antenna sub-array with the highest transmission efficiency is selected according to the channel state information of each user.Secondly,according to the order of the antenna sub-array,the connection between the RF link and the antenna is dynamically adjusted by means of the switching network,thereby constructing a multi-user multistate connected millimeter-wave massive MIMO system.Finally,the simulation results show that the proposed method has a certain performance reduction compared with the fully connected structure millimeter wave MIMO system,but it has a great improvement in performance compared with the partial connection structure millimeter wave MIMO system.The research in this paper shows that the application of dynamic sub-array structure in millimeter-wave massive MIMO system can achieve better balance between performance and hardware complexity.