Backscatter Communication System And Application Based On Two-bit On-off Keying

Backscatter communication is regarded as one of the advanced technologies for IoT applications due to its ultra-low power consumption.However,due to its short communication distance and low communication rate,it is difficult to be widely promoted in practical applications.In order to avoid the self-interference of the excitation source signal in the backscatter communication,the spectrum shifting technique is usually used.The double-sideband problem will occur in the spectrum transfer,which causes the wastage of backscatter signal energy.In order to solve the energy wastage problem,single-sideband(SSB)backscatter communication is introduced and carefully crafted.In SSB backscatter communication,the backscatter signal on one side is completely discarded,resulting in the waste of spectrum.In order to use the spectrum of the backscatter system efficiently,a spectrum-efficient on-off keying modulation technique is proposed,which is based on two-bit On-Off Keying(OOK)technique.It can effectively improve the spectrum utilization of the backscatter signal,thereby improving the performance of the backscatter communication system.On realizing two-bit on-off keying modulation,it is necessary to use the SSB technique to eliminate one side of the two generated backscatter signals that are mirror images of each other.After derivation,we found that delaying the incident signal of the passive tag by 1/4 cycle,and delaying the spectrum shifting square wave by 1/4 and 3/4 cycles can realize the left and right single sidebands,respectively.In the system design of this paper,a phase-locked loop is used to realize the square wave delay,and a phase shifter is used to generate the delay of the incident signal.We have simulated the system,and the obvious SSB effect can be seen from the simulation results.In addition,it was observed that the signal energy representing bit "1" is different between the backscatter signals "10" and "11".We propose a demodulation method based on the sum and difference of two backscatter signals,which makes full use of the energy of the backscatter signals and improves the decoding accuracy.After simulation,we can get that when the bit error rate is guaranteed to be lower than 1%,the rate of our two-bit on-off keying modulation is about 1.7 times of the single-sideband enhanced OOK modulation,and about 3.86 times of the OOK modulation without any single-sideband processing.In order to realize multi-tag communication,this dissertation uses frequency division multiple access technology.It has been tested that the two backscatter signals do not interfere with each other when their spectral interval is 500K.Finally,we leverage on-off keying modulation to improve the performance of shelf monitoring an IoT application.In order to reduce the amount of data transmitted,in the low-bandwidth solution,the CNN running locally on the camera is used for image recognition,but limited by power consumption,the image resolution recognized by CNN is only 32*32.In order to improve the recognition effectively,we use two-bit on-off keying modulation to transmit image data.It increases the resolution of the recognized image from 32*32 to 314*314.After testing,the two-bit on-off keying can increase the horizontal recognition range by about 11%compared with common on-off keying,and by about 20%compared with the low-bandwidth solution.For different shapes of goods,the two-bit on-off keying modulation can improve the longitudinal identification range by 5.4cm.