| As an Low-Power Wide-Area Network(LPWAN)technology,Long Range(LoRa)has rapidly developed into one of the most mature and commercialized Internet of Things technology in the world due to its characteristics of Low Power,Long distance and Low cost.However,its Medium Access Control(MAC)layer adopts ALOHA random access protocol,and serious collisions will occur in the future scenario of massive access to the Internet of Things,resulting in serious degradation of network quality.Therefore,how to improve LoRa’s multiple access ability and avoid collisions has become a key bottleneck for LoRa to successfully cope with challenges of the future Internet of Things.Therefore,this paper mainly studies how to improve LoRa’s multiple access capability,so that it can meet the development needs of the Internet of Things in the future.Firstly,the expression of LoRa in time domain is given and analyzed.The expression and physical meaning of fractional Fourier transform are given.The principle of LoRa optimal receiver demodulation algorithm and fractional Fourier transform based demodulation algorithm are deduced,and the optimal receiver demodulation algorithm is taken as the demodulation algorithm in the following section The specific content of LoRa Wide Area Network(LoRa WAN)that is relevant to this article is introduced.This chapter lays the foundation for the research of LoRa multiple access algorithm.Secondly,by dividing LoRa transmission bit into address code and information code,Orthogonal LoRa Multiple Access(OLMA)Algorithm is proposed to distinguish users by address code.The implementation method and representation of OLMA multiple access algorithm in time domain and fraction domain are analyzed,and the orthogonality between different user signals is deduced and proved.The collision probability calculation and simulation experiments verify that OLMA algorithm can greatly reduce the impact of collision and increase the number of access users,and the longer the address code length,the better the performance of multiple access.Then,in order to further improve the multiple access capability of OLMA and improve the demodulation efficiency of OLMA,S-ALOHA is used as LoRa’s multiple access protocol,and OLMA algorithm based on S-ALOHA was proposed.The implementation method of S-ALOHA in class A working state is studied,and A synchronization algorithm with simple implementation and low cost is designed by using uplink timestamp and Acknowledgement(ACK)information.The LoRa network model was established by using random geometry theory,and the collision intensity was defined.The collision intensity of the proposed algorithm and several existing access algorithms was analyzed,and the proposed algorithm was proved to have lower collision intensity.The LoRa network model was established by using random geometry theory,and the collision intensity was defined.The collision intensity of the proposed algorithm and several existing access algorithms was analyzed,and the proposed algorithm was proved to have lower collision intensity.Finally,an adaptive collision suppression algorithm based on collision probability is proposed to prevent serious collisions or bit waste in the face of rapidly changing access number.The algorithm adaptively adjusts the length of OLMA address code according to the collision probability to meet different access requirements,and uses Successive Interference Cancellation(SIC)algorithm to assist demodulation when the length of OLMA address code is too long.Simulation verifies that the length of address code can change with the change of user access number in real time,avoiding bit waste and reducing collision,enabling LoRa to show superior performance in the face of dynamically changing user number. |
