Research On Ambient Backscatter Communication Detection Algorithm And Performance Analysis Based On New Frequency Diverse Array

Ambient Backscatter Communication(AmBC)provides a new solution to the energy efficiency problem of the Internet of Things.Backscatter sensors do not require additional radio frequency(RF)sources to provide dedicated carrier frequency signals.While they use RF signals that already exist in the air to power themselves and communicate with the readers.However,since the device of the backscatter sensor is simple,the signal energy backscattered to the reader is weak,which limits the communication distance and data transmission rate.Besides,the interference signals energy is strong,which brings great challenges to the signal detection from backscatter sensors.To improve the signal detection performance,the research on the backscattered signal detection method by suppressing strong interferences has great significance in AmBC.The main work and innovations of this master's thesis are as follows:(1)The mathematical model of frequency diverse array(FDA)and its working principle are firstly introduced.Based on the angle-range-time dependent characteristics of its transmitted signal,we propose a FDA-based AmBC system model.To test detection performance of the system,we then propose a differential demodulation-based minimum bit error rate(BER)detection.We construct the detection statistics by the principle of differential modulation and demodulation,and derive the closed theoretical expressions of detection threshold and BER,we also plot curves of the BER.Compared to the traditional phase array(PA)-based AmBC system,the FDA-AmBC system has improved bit-error performance.Besides,we also analyze the impact of the frequency offset of the FDA on the AmBC system's BER.(2)To separate the direct link signal from the backscatter link signal in the time domain,by using time-variant FDA signal and assuming that the RF source is far from the backscatter tag,we propose a double-threshold-based adaptive detection algorithm,according to the time-variant characteristic of the signal received by the reader,we design the frequency offset and tag' boundary,and determine the limit detection angle,and then two detection variables are calculated based on the energy detection method,the expressions of two theoretical detection thresholds and BER are derived.(3)To detect the transmitted signals of backscatter tags located at different directions,this thesis also proposes a multi-antenna-based beamforming detection method,the proposed approach can suppress the strong interference from direct link and enhance the backscatter signals energy from other directions;the algorithm can detect target signals from multiple directions without the need to set additional boundary tags.Disadvantage is that it increases the complexity of the receiver and hardware requirements.