Research On Real-time Precise Positioning Technology Based On RFID

With the continuous advancement of Industry 4.0 and the continuous development of information technology,people's lives have gradually become intelligent and networked.Among them,service scenarios based on location information have also attracted more and more attention.Although the current satellite positioning technology has achieved accurate results in open outdoor scenes,it is difficult for satellite positioning technology to achieve the ideal positioning accuracy in shadow areas,such as tunnels,lower layers of multi-layer bridges,streets beside high buildings and densely vegetated places.In response to the positioning problems in these scenarios,radio frequency identification(RFID)-based positioning technology stands out among many technologies due to its advantages of low cost,non-contact,low latency,easy deployment,and multi-target recognition.This dissertation will study the radio frequency identification positioning algorithm based on phase information,and mainly study the ambiguity in the process of positioning based on phase signal.The specific content is as follows:(1)This paper proposes a positioning method based on the phase difference of multi-frequency signals.First of all,this article introduces the principle of the reader to obtain the phase signal from the perspective of hardware implementation,that is,the received signal is divided into two orthogonal signals through orthogonal demodulation,and then the phase of the received signal is determined according to the trigonometric function relationship.Secondly,this paper studies the variation of the phase of the single-frequency signal with the distance and the phase ambiguity in the ranging process based on the phase of the single-frequency signal.Finally,a distance measurement method based on the phase difference of multi-frequency signals is proposed according to the variation law of the phase of the single-frequency signal with distance,that is,the problem of phase ambiguity caused by the single-frequency signal for ranging is solved by transmitting multi-frequency signals.(2)This paper studies the positioning method based on the Chinese remainder theorem according to the changing law of the phase difference of the multi-frequency signal with the distance.First,the reader transmits signals of multiple frequencies,and then the phase information of the corresponding frequency signals can be obtained at the receiving end.According to the obtained phase information,a ranging equation set based on the phase difference of the multi-frequency signal can be established.This system of equations can be solved using the Chinese remainder theorem(CRT).However,due to the influence of measurement errors,the traditional Chinese remainder theorem will produce larger errors when solving distances.Therefore,this paper studies two more robust Chinese remainder theorems(the Chinese remainder theorem with closed-form solutions and the Chinese remainder theorem based on the maximum likelihood estimation),and compared the performance of two Chinese remainder theorems.Simulation experiments prove that the Chinese remainder theorem based on maximum likelihood estimation has higher accuracy in solving.Secondly,this paper uses the Levenberg-Marquardt(Lvenberg-Marquardt,LM)algorithm to optimize the target position coordinates.Using this algorithm to optimize the target position coordinates,the number of iterations is small,the convergence speed is fast,and it can avoid the matrix irreversibility when using the Gauss Newton(GN)algorithm to solve the problem.The simulation results prove that,under the system parameters given in this article,the probability that the positioning error is less than 30 cm is 90%.(3)This article designs a hardware circuit for phase measurement of the received signal and introduces the main parts of the circuit in detail.First,a phase-locked loop circuit that can be configured through a software program is designed,which can generate a local oscillator signal.After that,the received signal is sent to the FPGA for processing through filtering and sampling circuits.The FPGA program has designed a numerically controlled oscillator(NCO).The NCO can generate two orthogonal signals for quadrature demodulation.Finally,a serial communication circuit is designed,which can send the processed data back to the computer for checking.Through the analysis of the data returned by the circuit board,the circuit designed in this article can basically complete the function of measuring the phase of the received signal,but some circuits need to be further improved.