Research On Concurrent Transmissioncontrol Technology In LoRa Network

In recent years,the traditional Internet of things is difficult to deploy in a large scale because of its high power consumption and short communication distance.As one of the most mature technologies in low power wide area network,LoRa has become a research hotspot in the field of IOT because of its ultra-low power consumption and ultra-long transmission distance.At present,LoRa has been widely used in large-scale scenarios such as logistics tracking,intelligent city,wildlife monitoring and so on.This thesis studied the data transmission performance of LoRa network under the existing lorawan protocol.Through theoretical and experimental analysis,it is found that LoRa gateway supports multi-channel and concurrent uplink transmission with different orthogonal spreading factor,and can effectively improve network throughput through concurrent transmission.However,the continuous concurrent transmission of the uplink will hinder the transmission of downlink,and rashly downlink transmission will also interrupts the ongoing uplink transmission.This problem is referred to as the asymmetry between uplink and downlink in the concurrent transmission of LoRa network,which mainly includes the priority asymmetry and load capacity asymmetry between the uplink and downlink.Asymmetric between the uplink and downlink will seriously reduce the effective throughput of the network,which is experimentally verified that the effective throughput only accounts for half of the total throughput,resulting in the waste of LoRa node resources and network bandwidth resources.Aiming at this problem,this thesis proposed a concurrent transmission system named BLoRa according to backscatter technology.The proposed BLoRa system can start up the downlink transmission without affecting the uplink transmission,which effectively solves the problem of load capacity asymmetry between the uplink and downlink.By the way,due to the principle of backscatter scattering signal,BLoRa has the problem of asymmetric transmission distance between the uplink and downlink,which makes the downlink scattered data cannot be successfully received by the source node.To solve this problem,this thesis proposed the method of extending backscatter tag matrix and the selection strategy of excitation signal,and verified the overall performance of the improved BLoRa by experiments.The innovations and researches of this thesis are as follows:1.To solve the priority asymmetry and load capacity asymmetry between the uplink and downlink in the concurrent transmission of LoRa network,this thesis proposed a new concurrent transmission system named BLoRa.BLoRa based on the Backscatter technology,uses the uplink data as the excitation signal,and uses backscatter tag matrix to transmit downlink data.The performance optimization of BLoRa compared with the original LoRa network in the case of concurrent transmission is verified by experiments.2.To solve the problem of asymmetric transmission distance between uplink and downlink in BLoRa concurrent transmission system caused by too short backscatter communication distance,this thesis proposed a tag matrix and a selection mechanism of excitation signal to improve the communication distance of backscatter tags,which effectively solved the problem of asymmetric transmission distance.Experiments show that the downlink transmission distance of the improved BLoRa system can reach 600 m.