Design And System Implementation Of Time Division Multiple Access Mechanism For LoRaWan

The Internet has realized the connection between people.As an extension of the Internet,the Internet of Things solves the connection between people and things,things and things.Along with the widespread application of some mature wireless Internet of Things technologies,some new low-power WAN technologies such as LoRa have received more and more attention and are widely used in various fields.With the establishment of China's LoRa Application Alliance and the participation of various big Internet companis,LoRa has developed rapidly in China.Each terminal node of the standard LoRaWAN protocol uses ALOHA to transmit data,and the channel utilization is very low.This paper summarizes several improvements to the LoRaWAN system from the actual work,designs the time division multiple access mechanism,and implements the nodes,gateways and servers separately.The main work of the thesis includes the following points:1)Design and implement the improved LoRaWAN terminal node.First,selecting hardware of the terminal node,STM32L073RZT6 for the single-chip microcomputer,SX1278 module for the LoRa RF module,and CP2102 for the debugging of the UART to USB module.When the LoRaWAN network requires higher channel utilization,each LoRa terminal node cannot send data using the ALOHA protocol,otherwise the frequent transmission of the signal will result in a high packet loss rate.The terminal node of the system realizes time division multiple access after monitoring the multicast scheduling data,and each node in the network system transmits at different times and frequencies.The terminal node is classified into ClassB type and ClassC type.The multicast data listening window of ClassC type is continuously opened,and the multicast data listening window of ClassB type is opened periodically.In order to open the multicast data listening window at a precise time,time synchronization with the LoRa gateway is required,and time synchronization is performed using the LoRa gateway beacon.2)Designed and implemented the improved LoRaWAN gateway.First,selecting hardware of the gateway,the single-chip microcomputer using raspberry pi 3,the RF module using SX1301 and SX1278 module,the GPS module and the PPS signal module using u-blox 8 module and SKG09 A module respectively.LoRa Gateway is responsible for the transfer of data,to a certain extent,also affects the channel utilization of the network.When there are multicast scheduling data of ClassB type and ClassC type in the network,the LoRa gateway sends the multicast scheduling data of ClassC type immediately,using the SX1278 module;while the ClassB type multicast data needs accurate timing transmission,using SX1301 module.The LoRa gateway periodically sends LoRa beacons to perform time synchronization with each ClassB type of terminal node,and the LoRa beacon is accurately transmitted when the PPS signal arrives.3)Design and implement the improved LoRaWAN server.The LoRa server consists of four parts: LoRa bridge that handles UDP and MQTT data conversion,LoRa network server that handles the MAC layer,LoRa application server that handles the application layer,and a LoRa TDMA server that implements time-division multiple access.Firstly,the LoRa bridge,LoRa network server and LoRa application server involved in the original LoRaWAN protocol are designed and implemented.Then the implementation of LoRa TDMA server is explained in detail.The LoRa TDMA server stores the sequence number of the corresponding multicast address generated by server when each terminal node join the network.When the sending period of the node arrives,the multicast data is used for scheduling,so that the transmission of each terminal node does not interfere with each other.4)Test the improved LoRaWAN system.The packet loss rate of ALOHA transmission,ClassC TDMA transmission,and ClassB TDMA transmission is tested at different channel frequencies and different spreading factors,and the performance of the improved LoRaWAN system and the stability of the experimental results are demonstrated according to the experimental results.At the same time,an automated test system was designed and implemented,batch programming of device firmware,and automatic log collection and analysis.