Research On Key Technologies For Enhancement Of Link Capacity Of Aerial Base Station System

In the future network,it is necessary to build an integrated space-airground network to achieve truly seamless and continuous coverage for the whole areas.The future integrated space-air-ground network will be highly integrated.And a typical integrated network usually consists of the following major components:satellite communication network composed of high,medium and low orbiting satellites,air platform communication network composed of flying platforms,and ground mobile network that has evolved over a long period of time.Among them,the aerial base station network composed of various flying platforms will become an important part of the future 6G network.Aerial base station system usually refers to the communication system in which wireless base stations,transponders,passive relays and other communication equipment is placed on a flying platform that stays in the air for a long time to provide communication services.As an important node of aerial base station network,the research on link capacity enhancement key technology of aerial base station system will be an important direction.At this stage,the research on aerial base station system has the following problems:(1)the scientific and systematic aerial base station network model and performance evaluation methods are not yet perfect;(2)the research on the combination of aerial base station system and artificial intelligence algorithm for system performance improvement has not been thoroughly studied;(3)the research on the combination of aerial base station system and reconfigurable intelligent surface(RIS)for system performance improvement is still in the initial stage;(4)the research on the aerial base station system for other wireless services such as broadcasting system and sensor network system performance improvement is not yet perfect.For improving the performance evaluation of the air-port in aerial base station system,this paper proposes an air base station system model and a solution to better evaluate the performance.The solution innovatively combines ITU-R related recommendations and 3GPP link-level simulation methods,which provides an evaluation basis for the impact of subsequent key technologies on system performance.The method was adopted to evaluate the air-port performance indicators of the HAPS IMT Base Station(HIBS)defined in ITU-R Resolution 247(WRC-19).Meanwhile,the evaluation conclusions are contributed to the ITU-R WP5D working document,by which the validity of the method is proved.For overcoming the insufficient network coverage capacity in mobile IoT scenarios,an AI-assisted airborne RIS beam forming method is proposed in this paper for mobile scenarios.The innovative RIS is combined with low and medium altitude UAVs and cooperated with ground network to enhance the system capacity.Since the relative position relationship between UAV nodes and ground mobile IoT terminals changes in real time,an A-LSTM prediction-based RIS beam forming is introduced.The proposal uses recurrent neural networks(RNN)and its variants exhibiting powerful modeling prediction capability for timing sequences to predict the relative position relationship between RIS antenna arrays on UAV nodes and ground mobile IoT terminals.And based on the position relationship,beam direction gets optimized.The proposal enhances the link capacity with the improvement of signal-to-noise ratio of IoT terminals in mobile IoT scenarios.For increasing coverage of the angle range for the common RIS combination with low-altitude and medium-altitude UAVs in wide-area IoT scenarios,a performance optimization method for 5G/6G IoT systems based on aerial shaped RIS assistance is introduced.Considering the characteristics of the aerial base station system,the shaped RIS and utilization of the shaped RIS in the aerial base station system are proposed and studied for the first time in this paper.The air shaped RIS assisted 5G/6G system is modeled with mathematical system and analyzed the impact of the shaped RIS of the system.The simulation results show that the over-the-air shaped RIS assisted 5G/6G system can effectively improve the signal strength in the weak coverage area and enhance the system throughput compared with the traditional aerial base station system and the common RIS-assisted 5G/6G system.For mitigating the limitation of system throughput due to the impact of the worst user’s SINR in the broadcasting service scenario of 5G system,this paper proposes a performance optimization method for 5G broadcasting system based on the assistance of over-the-air shape adaptive RIS.The use of RIS in 5G multicast TV applications is investigated.The shape adaptive RIS deployed over the air is designed to relay 5G multicast TV signals and achieve additional RIS gain.To optimize the shape bending of the shape adaptive RIS,the Deep Deterministic Policy Gradient(DDPG)algorithm is applied to determine the optimal angle.The result shows that the SINR of the worst user is significantly improved.At the same time,the overall system modulation and coding scheme(MCS)and system throughput for 5G mobile broadcast services are increased when combining with the DDPG algorithm with shape adaptive capability.