Research On Ambient Backscatter Localization Technology Based On Array Antenna

With the arrival of the 5G era,the traffic and the number of connections in the communication network is increasing rapidly.In the field of the Internet-of-Things(Io T),the "Internet-of-Everything" is becoming the reality,but the scarcity of spectrum resources has gradually emerged.Am BC technology is one of the solutions for the Io T.It has the advantages of high spectrum efficiency,low cost and low power consumption,and it has attracted wide attention once it has been proposed.There is a great demand for the localization of the Io T devices in reality,such as find Io T devices and logistics management.The use of Am BC technology for the localization of Io T devices has huge application potential.The Direction of Arrival(DOA)information of the signal is an accurate localization parameter,and it can distinguish the signal and interference in the space.To obtain the DOA information of the signal,the array antenna is required.Therefore,this paper studies the Am BC localization technology based on array antennas.For the localization scenario where single tag is accessed,this thesis selects appropriate parameters and methods of localization,and proposes two localization schemes.The first localization scheme proposed in this thesis needs to use two receivers to estimate the DOA of the received signal separately,and use the geometric method to estimate the coordinates of the tag.In this thesis,the path loss is taken into account in the channel model,and the path loss is estimated by estimating the energy of the received signal,and then the signal propagation distance is estimated,so as to propose the second localization scheme.When the backscatter signal has experienced double path loss and the tag distance cannot be directly estimated,this thesis proposes a method to estimate the tag distance after cancelling the interference by using DOA information and energy information.This scheme requires only one receiver,but it is more susceptible to noise than the first scheme.The simulation results show that the two localization schemes can achieve the required accuracy.For the localization scenario where multiple tags are accessed,a spatial filtering algorithm is proposed,which can suppress the energy of signals from other directions,and this algorithm is better than the traditional Minimum Variance Distortionless Response(MVDR)algorithm in the Am BC localization system.After spatial filtering,the multiple tags localization problem is transformed into a single tag localization problem,and we can localization multiple tags at the same time.The simulation results show that the localization performance of multi-tag access is equivalent to that of single-tag access.For multiple backscattered signals and their localization results,it is necessary to discuss how to identify them to different tags.For the general ambient radio frequency source,a spread-spectrum based tag signal demodulation scheme is proposed using the idea of Code Division Multiple Access(CDMA).By assigning different orthogonal code chips for different transmission symbols of different tags,the receiver uses the known code to despreading the signal then determine the tag corresponding to the signal.This thesis designs the waveform of the tag signal for Orthogonal Frequency Division Multiplexing(OFDM)radio frequency source,and realizes the direct demodulation of the tag signal by using the cyclic structure of the OFDM symbol.We can transmit the pilot symbol to identify the signal to the tag.The information transmission rate and bit error rate performance of the OFDM radio frequency source scheme is better than the spreadspectrum based scheme,but the ambient radio frequency source needs to be limited to the OFDM radio frequency source.The simulation results show that the recognition rate is satisfactory,and the bit error rate performance of the proposed recognition algorithm for communication can also meet the requirements of Io T machine communication.This paper focuses on the localization scenario where the number of tags is greater than or equal to the number of array antennas in Io T applications,and uses nested arrays and MVDR algorithms to deal with the localization of tags in this scenario.The simulation results show that,compared with the location scenario where the number of tags is less than the number of array antennas,there is a bound on the localization performance in this scenario,but the performance can meet the requirements of Io T device localization.