Tilt Optimization Of Large-Scale Multi-Antenna System

With the development of several decades,mobile communication has a large impact on every aspects of people's production and life.Nowadays,with the increasing number of mobile users and terminal equipment,the Internet has become our necessity.The traditional technology is obviously unable to meet the needs.Therefore,the research of the fifth generation(5G)mobile communication system is an inevitable trend of the development of the times.Adding a large number of antennas on the basis of traditional multiple-input multiple-output(MIMO)can optimize the system performance and break the technical bottleneck.As a result,massive MIMO technology has rapidly become the core technology of the new generation communication system.The base station(BS)antenna,as the transceiver terminal of the communication system,is used to transmit signals,and it can realize the bidirectional function of receiving and transmitting signals,and is an important part of the cellular network system.Multi-antenna technology brings more challenges due to the continuous increase in the number of antennas.The antenna tilt is used as a main parameter to represent the BS antenna,which has great potential in eliminating interference and improving system performance.There are two types of tilt,i.e.,the mechanical tilt and the electrical tilt.How to set the antenna tilt will have an important impact on the coverage of the antenna,and will also have an impact on inter-cell interference.Therefore,it is necessary to fully understand the working principle of the antenna tilt,and design a correct and reasonable antenna tilt,which will help the design of the base station of the wireless system and make it play a better role.In this context,this paper mainly studies the tilt of the BS antenna.The main work and research results are as follows:(1)For the mechanical tilt,an antenna tilt optimization method for multi-cell massive MIMO systems is studied.The BS is equipped with two linear arrarys parallel to the ground in the system,which correspond to two mechanical tilts,respectively.Because the mechanical tilt is not adjustable after being fixed,it needs to be statistically optimized according to the user's distribution.Discussed in the two cases where the system has perfect channel state information(CSI)and imperfect CSI.In the limit of the number of the BS antennas,the channel orthogonality is employed to derive the limit and the lower bound of the sum rates.By maximizing the lower bound or the limit sum rate,the two antenna tilt angles are optimized.Simulation results show that the system sum rate can be optimized with the designed tilts.(2)For the electrical tilt,an electrical tilt optimization method for single-cell massive MIMO systems is studied.There are multiple users with single antenna in the cell.And the BS has a large planar antenna array.The BS can adjust the electronic tilt in real-time based on the location information of the users.When the number of BS antennas is very large,the orthogonality of the channel is used to derive the asymptotic sum rate in the uplink and downlink,respectively.Based on the correlation property of the array steering vectors,the users are grouped based on the elevation direction-of-arrivals.Then,the tilt is optimized by finding the maximum sum rate among all groups.Simulation analysis show that the method of optimizing the tilt can increase the cell sum rates.In a word,the optimization methods of multi-cell mechanical tilt and single-cell electronic tilt can improve the performance of communication system.