Research On Passive Backscatter Communication Technology For IoT

The rise of the Internet of Things(IoT)has empowered our world with intelligent connectivity,giving birth to scenarios such as smart homes,precision agriculture,and smart cities.In these intelligent interconnection scenarios,a large number of nodes are required to realize the perception and transmission of information.At present,most IoT nodes use battery-powered solutions,which have high maintenance costs and environmental costs.An alternative solution is wireless RF energy harvesting.At the same time,backscatter communication consumes only microwatts of energy to transmit information.Therefore,in the low-power IoT scenario,it is expected to realize an energy self-sustaining communication network by means of RF energy harvesting and backscatter communication technology,i.e.,passive backscatter communication technology.Passive backscatter communication technology can realize the tight coupling of wireless data transmission and wireless energy transmission,but its application scope is limited due to the low efficiency of wireless RF energy harvesting and the high loss of the communication link of the backscatter system.Therefore,this thesis first designs a backscatter modulation tag,and then designs and implements a backscatter communication system based on chirp spread spectrum modulation.Then,the RF energy harvesting technology is studied,and the feasibility of supplying power to the backscattering tag is verified through circuit design and testing.The key contributions of the thesis are three-fold described as follows:Firstly,on the basis of analyzing the basic principles of chirp spread spectrum modulation and backscatter modulation,a backscatter modulation algorithm based on chirp spread spectrum technology is proposed,and the correctness of the proposed algorithm is verified in the MATLAB simulation platform.Secondly,a backscatter tag based on chirp spread spectrum modulation,i.e.,backscatter transmitter,is designed.Then,the software radio platform based on AD9361 is configured to realize the backscatter receiver,and the backscatter modulation test system is built.The simulation results are compared with the actual circuit test results to verify the correctness of the designed algorithm and hardware circuit,and the power consumption of the backscatter tag is only 0.719 mw.At last,according to the requirements of the backscattering scenario in this thesis,the RF energy harvesting circuits of 470 MHz and 2.45 GHz are designed respectively.Because the high-frequency and low-frequency responses of the circuit are different,the lumped parameter theory and the distributed parameter theory are used in this thesis to complete the simulation design and processing of the matching circuit and rectifier circuit working at 470 MHz and 2.45 GHz respectively.Then,a boost circuit is designed using the BQ25504.Finally,a circuit performance test is performed.The test results show that the RF energy harvesting circuit can meet the requirements of low-power backscattering tags in terms of output voltage and power consumption.