Research On RFID Signal Station Positioning Technology Based On OFDM Signal Excitation

Given the deepening industrial informatization,many kinds of smart home devices can be seen everywhere,and people's requirements for accurate location services are getting higher and higher.It is difficult for a satellite positioning system to provide accurate positioning information when indoors,so there are more and more researches on indoor positioning.Among various technologies,Radio Frequency Identification(RFID)has gradually become the focus of research in recent years due to its low cost,strong antiinterference ability,and simple tag layout.At present,the multi-base station scheme is mainly applied to the common indoor positioning technology.However,in some situations,the multi-base station environment is unavailable due to the small space.Therefore,this thesis studies the RFID single-base station positioning.The content of this thesis is as follows.First of all,in view of the difficulty in parameter estimation of a single based station,the Orthogonal Frequency Division Multiplexing(OFDM)signals is used to replace traditional DC excitation signals in this thesis.The content of the method mainly includes:the optimized design of excitation signal,detection of RFID echo signal and channel estimation of RFID tag.The excitation signal is designed and verified on the Software Defined Radio platform,and the signal is optimized to improve the system robustness.Considering that the complex waveform of echo signal is difficult to distinguish,the method of time-frequency domain correlation detection based on the characteristics of RFID preamble is carried out without recovering the RFID signal.Then the channel difference method is used to estimate the RFID channel according to the difference and relation of the channel state between the two RFID working modes.In addition,in order to avoid the fast channel fading caused by RFID level switching,the data is preprocessed to make the channel estimation more accurate.Secondly,in view of the characteristics of single base station positioning,combining angle and distance information to position is adopted.The content of the method mainly includes: Multiple Signal Classification algorithm to estimate the signal angle of arrival,dual-frequency carrier phase ranging algorithm and construction of a single-station positioning model.Antenna and subcarrier information are combined for spatial smoothing so as to eliminate the indoor coherent signal interference.As for the carrier phase period ambiguity,the Chinese Remainder Theorem is used to perform a cluster search on the basis of dual-band excitation signals,and the Phase Difference of Arrival is used to calculate the initial estimation of distance to optimize the efficiency of the algorithm.After that,the angle and distance information are combined to complete singlestation positioning.Finally,a large number of simulation tests and analysis have been carried out.The results show that the RFID indoor single-station positioning system proposed in this thesis has a positioning accuracy of decimeters,which has the potential to be widely applied in the future.