Design Of Backscatter Communication System Based On Chirp Spread Spectrum Modulation

The development of the Internet of Things has had a profound impact on people’s work,life,and production.Through Io T technology,we can achieve communication between various intelligent devices.Wireless communication technology is an important foundation for the implementation of the Internet of Things.Traditional active wireless communication technology has exposed many shortcomings in the application scenarios of the Internet of Things,such as high power consumption,high equipment costs,and the need to occupy additional spectrum resources.The backscatter communication based on environmental signal is a new wireless communication technology,which can use the existing electromagnetic wave signal in the environment to achieve wireless communication.It has the advantages of low cost,low power consumption and low complexity.In this thesis,a new type of backscatter device using chirp spread spectrum modulation(CSS)is designed,and an environmental backscatter communication system based on CSS modulation is realized.The main work includes the following three aspects.Firstly,the key technologies of CSS modulation reflection equipment were studied.The chirp modulation method for backscatter equipment is designed,and the frequency offset method for harmonic suppression using multiple reflection states is proposed.The frame structure for frequency shifted chirp backscatter communication is designed.Specifically,in the linear frequency modulation method,a radio frequency switch control algorithm was designed to generate linear frequency modulation reflection waves.By controlling the switching time of the radio frequency switch,high-precision frequency offset was achieved.In the harmonic elimination frequency offset technology,the relationship between the number of reflection states and the highest frequency of harmonic suppression by frequency offset was quantitatively studied.In the design of the frame structure,a linear frequency modulation symbol without cyclic shift is used as the synchronization head to achieve time synchronization.Secondly,the key technologies of backscatter communication receiver in CSS modulation environment are studied.A corresponding time synchronization algorithm was designed based on the characteristic that the time shift of linear frequency modulation symbols in the synchronization head of CSS frame structure is equivalent to frequency shift.The demodulation algorithm of FSCM symbols was studied,and the software development and testing of frame synchronization and symbol demodulation were completed.The simulation model of frequency shifted chirp backscatter communication receiver is established,and the influence of the bandwidth of environmental RF signal source on the communication performance of backscatter communication system is studied.Furthermore,the implementation technology of backscatter communication system in CSS modulation environment is studied.The circuit design of CSS backscatter device is completed,including backscatter controller,frequency conversion clock generator,RF switch and impedance network.The influence of hardware parameters such as resolution,sampling rate of digital to analog converter in CSS backscatter device circuit and slope of voltage frequency transfer function of voltage controlled oscillator on backscatter communication is revealed,including bandwidth,frequency offset step size,symbol transmission rate and other indicators.Use software radio platform to build CSS backscatter receiver.Finally,the CSS backscatter communication system was tested for data transmission,and 800 bit/s reliable communication was achieved when the environment signal source transmitting power was 20 d Bm,the backscatter device was14.3m away from the environment signal source,and 4.8m away from the receiver.