Study On LoRa Multipoint Communication Protocol For Industrial IOT Environment

With the rise of industrial Internet of things(IoT),the traditional manufacturing industry is often confronted with the problems of upgrading and transformation.In the process of building information factories,digital factories and intelligent factories,the first thing to be solved is to break the isolation of equipments,that is,to solve the networking problem of machines.Machine networking can be wired or wireless.In the large-scale Internet of things application scenarios,when the number of machines is too large or it has mobile devices,compared with the huge deployment and modification cost of wired mode,the wireless mode is more flexible and convenient.Therefore,it has been widely concerned by the industrial Internet field and has been widely applied.On the one hand,traditional IOT wireless technology has problems such as big power consumption,small coverage and unstable connection,on the other hand,industrial IOT has characteristics such as small amount of data,long transmission distance,and strong multipath interference.This paper selects the emerging LoRa communication technology with low power consumption,long distance,strong anti-interference ability and other characteristics,and this paper also proposes a LoRa wireless application protocol based on LoRa technology,which is applicable to the industrial Internet of things application scenarios and the protocol has high data reliability and strong anti-interference ability.LoRaWAN,a standard protocol proposed for LoRa communication technology,and other MAC protocols based on competitive mode are studied.And the emerging LoRa communication technology is also analysized.The protocol proposed in this paper mainly combines LoRa technology with IEEE802.11DCF mechanism,and adopts RTS/CTS handshake and CSMA/CA mechanism.The main contents of this agreement include:(1)Determination of time slot,inter-frame interval and frame model.Combined with LoRa's transceiver conversion time,CAD preamble detection time and protocol processing time,this protocol redefines the time slot in the DCF mechanism.According to the four idle channels in the handshake stage and data interaction stage,this protocol formulates the frame intervals of DIFS and SIFS to distinguish the channel idle in the data interaction stage from the channel idle after data interaction.The protocol also establishes frame models of handshake frame RTS,CTS,DATA frame and ACK frame.(2)Channel access mode.In the channel access mode of this protocol,CAD preamble detection is used as the virtual carrier interception.The nodes need to interception before each channel access.When the channel is truly idle,that is,the number of channel idle slots reaches DIFS,the nodes can access the channel and enter the handshake stage.And only after a successful handshake can nodes enter the data interaction stage.This ensures that conflicts can only occur during the handshake phase and that the data interaction process is not broken.(3)Withdrawal mechanism.This paper makes a more fair improvement on the avoidance algorithm.The binary exponential regression algorithm and the improved algorithm based on this algorithm are studied and analyzed in this paper.The basic idea is that if communication conflicts,the competition window will be expanded,and if successful,the competition window will be reduced.In this way,there is a greater chance to cause unfairness,and nodes that have competed to the channel have a greater priority in the next competition,because their competition windows are smaller.In this protocol,the design of the avoidance algorithm is more in line with the principle of fairness.The main idea is:in case of communication conflicts,the competition window should be appropriately reduced to make nodes more likely to compete to the channel next time.If the communication succeeds for a certain number of times continuously,the competition window will be expanded to give way to other nodes actively and other nodes will take the initiative.Competition windows have upper and lower bounds.In this paper,the design process,basic parameters and key technologies of the protocol are discussed in detail.Then,markov model analysis is established and MATLAB platform is used to conduct network simulation analysis of the protocol from two aspects of network throughput and fairness.Simulation results show that compared with binary exponential algorithm,this protocol has slightly lower throughput,but obviously higher fairness.Finally,this paper implements the hardware platform based on STM32 and LoRa,realizes LoRa communication,and completes protocol migration.It mainly includes low-level driver migration,LoRa point-to-point and point-to-multipoint transmission communication test,LoRa communication parameter setting,communication rate and anti-interference test,many-to-one polling communication and many-to-one random communication test.Finally,the simulation protocol is transplanted to the hardware platform to realize the wireless communication protocol of industrial equipments.The protocol was verified and evaluated in the industrial field environment and the simulated strong interference environment.The results showed that the protocol transplantation was successful,the terminal nodes could fairly report data,and it had a good ability to resist multi-path interference.