Research On Random Access Method Based On Cooperative Beamforming Technology For Satellite Internet Of Things

The Internet of Things(IoT)is one of the main directions in the application of 5G wireless networks.Mass deployment of low-cost terminals requires the construction of a large number of ground base stations to form a communication network.However,the construction of base stations on the ground is restricted by the geographical environment.For example,it is impossible to construct base stations in extreme environmental areas such as oceans and deserts,in remote,sparsely populated areas,it is expensive to construct and maintain base stations,and the ground network is vulnerable to damage when natural disasters occur.Therefore,the terrestrial Io T exhibits a serious shortage of service capabilities in the above application scenarios.Satellite communication systems have become a research hotspot in the the Io T due to their global coverage capabilities that are not affected by geographic environments.The problem of concurrent access to a large number of terminals under limited time-frequency resources within the coverage of resource-constrained loworbit satellites requires reference to the Massive MIMO technology in the 5G terrestrial Io T to increase the number of concurrent access terminals under the same time-frequency resources.However,different from the ground-rich reflection environment channel,the satellite channel is an under-scattered channel where the direct component is the main component.The space-time coding technology based on multi-antenna transmission and reception in the ground 5G network cannot achieve ideal diversity gain.Beam Division Multiple Access(BDMA)technology based on Massive MIMO arrays has certain application potential in low-orbit satellite Io T,but it is limited by the spatial resolution capability of phased arrays and the height of low-orbit satellites.Phased arrays of the same caliber cannot achieve accurate spatial clustering of Io T terminals on low-orbit satellites.In addition,compared to the terrestrial Io T with a coverage of tens of kilometers,the signal propagation distance of satellite Io T terminals is usually thousands of kilometers.The electromagnetic wave signal has the characteristics of large attenuation due to the long-distance transmission of the satellite communication link,and the power of the Io T terminal and the gain of the transmitting antenna are limited,which causes the transmission performance of the node to be greatly restricted.In response to the above-mentioned problem of limited spatial resolution of single-satellite phased arrays,we apply multi-satellite cooperative beamforming technology to the low-orbit satellite Io T,and fully tap the space domain resources covered by multi-satellites in the common-view zone of multi-satellite coverage.A collision-tolerant asynchronous random access scheme based on multisatellite cooperative beamforming is proposed.Through the joint processing method of the multisatellite forwarding signal at the gateway station,the signal to interference and noise ratio of the collision data packet is improved,the multi-access interference in the multi-satellite coverage area is converted into the space domain resources that can be used by the system,thereby increasing the number of concurrently connected terminals under the same time-frequency resource.The simulation results show that the random access scheme we proposed has good throughput and packet loss rate performance.Under high load conditions,it alleviates the loop phenomenon in traditional random access systems.In addition,in order to solve the contradiction between the weak capability of the Io T terminal and the long-distance transmission of satellite communication,we propose an uplink access method based on node selection cooperative beamforming for a class of terminals with communication capabilities in the Io T application scenario.Under the condition of error in node location information,the average power pattern function of node transmission is derived and designed a region grouping node selection algorithm,the selection of high-quality nodes is narrowed through satellite link budget analysis and area selection.Simulation results show that compared with the traditional distributed cooperative beamforming node selection algorithm,the algorithm we proposed has better performance in sidelobe suppression and null generation in the error model.