Research On Key Technologies Of LPWAN Physical Layer Based On CSS And FPGA Implementation

In the field of LPWAN,Lo Ra is widely deployed in various industries because of its low power consumption,long transmission distance,flexible networking and other characteristics that meet the needs of the Internet of Things.However,the security of Lo Ra cannot be guaranteed due to the privacy of its physical layer protocol,which also limits its application field.Therefore,it is particularly important to develop alternative technologies for Lo Ra bottom layer.This paper designs a set of physical layer protocol based on THE modulation of CSS(Chirp Spread Spectrum),including the design and implementation of modulation and demodulation,channel coding and decoding,and uses the excellent transmission performance of CSS technology to realize the long-distance transmission of communication network.The specific research content is as follows:Firstly,the theoretical basis of CSS communication and channel codec is introduced.It includes the expression and principle of modulation signal,analyzes the amplitude spectrum of CSS signal,then focuses on the demodulation method of CSS signal based on DFT,analyzes the bit error rate of CSS communication under the additive Gaussian white noise channel,and analyzes the inter-device interference of CSS communication.In addition,convolutional code,CRC check,whitening and interleaving are introduced.Secondly,a set of CSS communication system design scheme is proposed,including modulation signal generation,modulation frame structure,design and implementation of modulator and demodulation scheme design,analysis and understanding of the modulation frame synchronization algorithm,carrier frequency offset CFO,symbol timing offset STO and sampling frequency offset SFO influence on demodulation.The design and implementation structure of frame synchronization algorithm for these three kinds of offset are proposed,and the simulation results and performance analysis are given.Then,the channel coding and decoding scheme is determined,and the scheme design of the frame structure,CRC check code,error correction code,whitening and interleaved modules after coding is carried out,focusing on the selection of error correction code,convolutional code coding and Viterbi decoding scheme.Finally,the hardware implementation scheme of CSS communication system was designed,and the FPGA verification hardware platform of the system was built.The program of each module of transmitter and receiver was realized by using Verilog hardware description language,and all the design functions were realized.The system transceiver test was conducted.When the receiver has a bandwidth of 500 KHz and SF=7,the frame error rate is less than 5% under the condition of-6d B SIGNal-to-noise ratio,which verifies the feasibility and effectiveness of the CSS communication system scheme from the point of view of hardware.