Research And Implementation Of Hybrid Multiple Access In Satellite Network

As a relay node with wide coverage and unaffected by geographical and meteorological factors,low earth orbit satellites can overcome the weaknesses of the ground network on long-distance transmission.Compared with satellites on other orbits,they have higher flexibility,higher reliability,lower costs,and are easier to satisfy the service quality demands of ground mobile users.Hence,it has received huge attentions from the academia and industry.With the rapid development of communication technology,the number of user terminals continues to increase,and the scope of business also continues to expand.all of them put forward higher requirements for the access and other performance of future satellite network.In current satellite network environment,the user distribution range is very large,and the carrier sense based conflict avoidance mechanism in the ground networks cannot be adopted.Besides,the data packets are always emerging suddenly with different lengths.In the current research on the multiple access of satellite network,the on-demand multiple access is only suitable for long packets,and cannot effectively deal with short-burst packets.While the existing random multiple access can be adopted for the short-bursts packets,the simultaneous access for a large number of users will cause serious data conflicts due to limited uplink channel resource in high-load communication network scenarios,and will result in the decrease of resource utilization rate.Therefore,for the low earth orbit satellite network with high-load mixed service scenario,designing an efficient and feasible multiple access scheme under limited communication link resources is a problem to be solved urgently.Focusing on the above challenges,this thesis mainly conducts the following research:Aiming at the high-load low earth orbit satellite network scenario with long delay and hybrid service types,a contention resolution based hybrid multiple access scheme is proposed with the combination of non-slot synchronous random multiple access technology and on-demand allocation mechanism.The physical frame structure suitable for this technique is also given.In the proposed scheme,the uplink frame is divided into a random access area and an ondemand allocation area.In the random access area,data packets are sent in the manner of contention resolution ALOHA.On the other hand,data transmission is implemented at an allocated resource block in the on-demand allocation area.With the improved physical frame structure,resource allocation strategy for the on-demand allocation area is proposed.The users with allocated resources will implement its data transmission at the on-demand allocation area in the next frame.Besides,a maximum access threshold is set to ensure the fairness of user access.Then the performance index of the proposed contention resolution based hybrid multiple access is analyzed.By simulating the satellite-to-ground network communication process under this protocol,the influence of various protocol parameters on its performance is compared and analyzed.Simulation results show that the proposed protocol has better latency and throughput performance in high-load scenarios compared with the competitive contention resolution ALOHA.In order to further verify the actual performance of the proposed contention resolution based hybrid multiple access in this paper,a demonstration and verification platform of the contention resolution based hybrid multiple access is established.First,the design of the demonstration platform is given,including the design of the processor system and key functional modules on the programmable logic side.Secondly,a new data frame structure for the protocol is designed.Finally,the demonstration platform was realized in the Zedboard development board based Xilinx Zynq chip,which verified the feasibility of the proposed contention resolution based hybrid multiple access protocol in this article in actual application scenarios.