Research On Key Technologies Of NOSA System In Satellite Internet Of Things

Satellite communication network is expected to play an important role in future Io T communication networks,which is an enhanced and complementary part of terrestrial communication infrastructure.As the main communication scenario of the 5G Io T,massive machinetype communication puts forward higher requirements for the device access capability of the wireless network.In order to cope with the simultaneous access of a large number of devices,several efficient random access protocols based on time division multiple access have been proposed.The typical representative is the Contention Resolution Diversity Slotted Aloha(CRDSA)protocol.Through inter-tile packet repetition and interference cancellation,the CRDSA protocol improve the access capability and throughput of satellite Internet of Things.To reduce the multiple access interference of packets and the complexity of detection,the CRDSA protocol and its derived protocols generally adopt Orthogonal Multiple Access,such as Orthogonal Frequency Division Multiple Access(OFDMA).The orthogonal access technology limits the increase in the number of access users.Therefore,to further improve the throughput performance of the system,a Non-Orthogonal Slotted Aloha(NOSA)protocol is proposed.The NOSA protocol combines the CRDSA protacol and the Sparse Code Multiple Access(SCMA)technology,which introduce intra-tile packet-level sparse mapping and the inter-tile packet repetitions.At the receiver,superimposed packets are joint multi-packet detected,thereby improving the system access capability and throughput performance.In this paper,the researches on the fast evaluation model of throughput and packet loss rate performance in NOSA system and the low-complexity detection algorithm at the receiver are mainly carried out.The paper first introduces the random access protocol of satellite Internet of Things based on time division multiple access,and focuses on the NOSA system based on SCMA multiple access technology.The basic parameters of the NOSA system and the basic work flow of the modem are introduced.Secondly,the research on the high complexity of the multi-user detection algorithm at the receiving of the NOSA system is carried out,and a low-complexity detection algorithm based on the combination of tabu search and local maximum likelihood algorithm is proposed.By studying the improved low-complexity detection algorithm,the detection complexity is polynomial complexity,and the detection performance can approach the optimal maximum likelihood detection performance.Finally,through the simulation experiment,the verification of the detection performance and complexity of the algorithm is given.Finally,the quickly evaluation model of NOSA system is studied,and a simplified physical layer model and a theoretical analysis model are proposed.Since the non-orthogonal multiple access technology of SCMA is introduced into the NOSA system,the detection performance of the physical layer of the NOSA system has a great relationship with the collision situation of the SCMA codebook.In this paper,the codebook collision situation of terminals under different powers is analyzed through simulation,and the key factors that determine the physical layer performance of NOSA system are obtained.Then,the fitting polynomial is obtained by simulation to replace the packet loss rate performance of the physical layer,which avoids a lot of time waste caused by the simulation of the physical layer.On this basis,the simplified physical layer model and theoretical analysis model are obtained,and the accuracy of the model evaluation is verified by experiments.