Design And Performance Study Of Transmission Protocol For LoRa Terminals To Autonomously Allocate SF And Time-slots

The current large-scale deployment is the wave of IoT development.Network scalability,coverage,and lifetime become increasingly crucial in various IoT application scenarios.In order to meet the demand for low-cost,large-scale deployment,and energy-efficient IoT development,a branch of IoT technology—Low Power Wide Area Network（LPWAN）—has been widely discussed in recent years.LoRaWAN is one of the dominant wireless communication technology standards in LPWAN.But because of the pseudo-orthogonality between the Spread Factor（SF）and the fact that LoRaWAN doesn’t have a Listen-Before-Transmit（LBT）mechanism,the ALOHA-based transmission scheduling method will cause serious channel conflicts that will drastically reduce the scalability of LoRa networks.This means that LoRaWAN won’t be able to meet the development demand for massive machine-type communication（m MTC）.Therefore,to solve the problem of signal co-channel suppression in LoRa networks,this paper conducted a detailed study on the application of NP-CSMA to LoRa networks based on the Carrier Sense Multiple Access（CSMA）mechanism.Then,to further solve the problem of co-SF interference and inter-SF interference in LoRa networks,a time slot transmission protocol applicable to LoRa terminals for autonomous SF allocation was designed based on the communication idea of Time Division Multiple Access（TDMA）.Given this,the main contributions of this paper are as follows:Firstly,this paper explains the LoRa modulation technique and looks at the imperfect orthogonality between the performance of the LoRa modulation technique and SFs using MATLAB.This is done while taking into account how the LoRa physical layer coding affects the correct demodulation of the receiver.Then,the signal-to-noise ratio（SNR）threshold required for demodulation of the receiver under the Bit Error Rate（BER）of 10^-4and the signal-to-Interference Ratio（SIR）threshold to ensure that the signal between SFs is not affected by interference were given,respectively.Secondly,based on the nature of LoRa networks,this paper selected NP-CSMA from many CSMA variants for relevant research and fully illustrated the scheduling mechanism of NP-CSMA in LoRa networks.Based on the scheduling process of NP-CSMA in LoRa networks and the ratio occupied by hidden terminals,this paper analyzed the fragile period of the transmission process of NP-CSMA in LoRa networks to derive the theoretical packet delivery rate and channel utilization performance of NP-CSMA.Then,to ensure a conflict-free transmission process in LoRa networks,this paper proposed a time slot transmission protocol（AA-SF&TS）combining SF allocation mechanism,and detailed the implementation process from six aspects:frame structure,autonomous SF allocation mechanism,autonomous time-slot allocation algorithm,frame period length,parallel transmission scheduling process and key parameters.Finally,in order to analyze the performance of the proposed protocol AA-SF&TS,this paper compared several network performance indexes of LoRaWAN,NP-CSMA,and AA-SF&TS under single-channel and multi-channel based on NS3 simulation system and theoretical values.Experimental results show that the time-slot exclusivity feature enabled AA-SF&TS to maintain an almost 100%packet delivery rate;in terms of channel utilization,compared to 18.8%for LoRaWAN and 59.2%for NP-CSMA,AA-SF&TS can provided about 73%saturated channel utilization even at the maximum data rate,and accommodated more nodes than LoRaWAN and NP-CSMA.Although,the additional energy consumption caused by global time synchronization of AA-SF&TS is consumed about 2.77 m J～24.02 m J due to the beacon length and transmission rate;however,the additional energy consumption of AA-SF&TS was still in a reasonable range compared with the energy consumption caused by LoRaWAN and CSMA retransmission and the signal loss caused by collision.