Research On Synchronous Networking Method Of Multi-Channel LoRa Wireless Monitoring System

With the development of Internet of Things technology,LoRa,as an emerging wireless modulation technology,can realize low-power long-distance transmission,and is widely used in wireless monitoring systems that require energy consumption and monitoring range.Networking of wireless communication devices can effectively expand the range of information perception and improve the performance of the monitoring system.Aiming at the problems of insufficient single-channel network capacity in existing LoRa networking applications,low network robustness in the face of interference,and low channel utilization in random competition,this paper proposes a multi-channel synchronous networking method.Time synchronization includes firstlevel gateway synchronization and second-level subnet synchronization,as well as research on networking methods,so that the wireless monitoring system can realize large-scale sensor node access and stable and reliable communication.The main research work includes:(1)8-channel independent channel gateway based on SX1276 module and its network system architecture design.Aiming at the problems of insufficient independent physical channels and limited parallel access capability in the LoRa WAN network,a multi-channel gateway with a private networking protocol is designed,and multiple SX1276 RF chips are used to form 8 independent physical channels that do not interfere with each other,including a control channel and seven It provides more options for parallel access of large-scale sensor nodes,and improves network capacity and data transmission efficiency.On this basis,a multi-channel synchronous networking protocol is designed,and the architecture is easy to expand based on the SX1276 module multi-channel LoRa gateway and its tree network topology.(2)Research on multi-level time synchronization method.Aiming at the requirement of device synchronization in the network,a multi-level time synchronization method is proposed,including the first-level gateway synchronization and the second-level subnet synchronization.In the first-level gateway synchronization,the external high-precision GPS time is introduced through the GPS receiver,the serial port output and PPS second pulse are used to complete the GPS timing,and the backup network time-based synchronization scheme is started when the GPS signal is not received.In the secondary subnet synchronization,the node completes the adjustment of the local clock through the message interaction with the gateway;the correction parameter of the clock frequency deviation is obtained by the least squares linear fitting,and is substituted into the relevant register of the real time clock(RTC).Perform frequency fine-tuning to achieve correction of node clock frequency deviation.Through comparative experiments with other LoRa network time synchronization methods,the feasibility and practicability of this method are proved.(3)Research on multi-channel synchronous networking method.Aiming at the problems of low channel utilization in random competition and insufficient robustness of the network in the face of interference,a multi-channel CSMA and TDMA hybrid access mechanism and an Adaptive Data Rate(Adaptive Data)based on Packet Loss Rate(PLR)are proposed.Rate,ADR)regulation mechanism.The node accesses the control channel by means of CSMA,obtains the channel resource allocation and time synchronization information of the gateway,and then accesses the corresponding service channel by means of TDMA to periodically report service data to avoid data conflict.In this paper,the packet loss rate,signal-to-noise ratio and received signal strength of wireless communication are used as the evaluation indicators of LoRa network link quality.Corresponding adjustments are made according to the periodic link budget estimation to improve the robustness of the network,thereby achieving stable and reliable communication.Using MATLAB software simulation,the network throughput and average communication delay of the multi-channel CSMA and TDMA hybrid access mechanism in this paper are analyzed,and then the effectiveness of multichannel synchronous networking is proved by comparative experiments.