Talking about the four positioning modes based on RFID technology

　　Although RFID technology can be applied to indoor positioning, due to the complexity of indoor environment furnishings and high precision requirements, indoor positioning systems are very difficult in actual use, including signal strength collection, database establishment, positioning algorithms, and how to correct Obtain the signal data from each RFID reader, how the RFID reader and RFID tag should be placed to improve the accuracy of the system positioning, how to reduce the cost of establishing the positioning system through estimation, and what to do after receiving the relevant signal data Convert to location consultation, etc.

　　Currently, there are four positioning modes for positioning services in a wireless network environment: signal strength method, receiving angle method, receiving time, and receiving time difference.

　　3.1 Signal strength method positioning technology

　　The Received Signal Strength (RSS) method uses the channel propagation model to describe the attenuation of the path loss to the distance. If this information is used for positioning, a propagation loss model of the environment must be constructed in advance. Only in this way can the distance between the moving object and the fixed object be judged by the attenuation of the signal strength. The position of the moving object should be located on a circle with the fixed object as the center and the estimated distance as the radius. Therefore, there must be at least 3 fixed objects in order to be positioned. Because the radio propagation in the room will exhibit multi-path interference attenuation and shielding effects, these factors will cause a large difference between the received signal strength and the propagation result in a free vacuum, which will cause errors in the estimated propagation distance. In this case, moving objects The estimated position of will not intersect with the previous calculation, but will fall within an estimated area.

　　3.2 Receiving angle method positioning technology

　　The working principle of the Angle of Arrival (AOA) positioning system is to use a directional antenna or antenna array to determine the possible source direction of the active tag signal. This direction can determine a straight line starting from the RFID reader on the 2D plane. Use more than two RFID readers to measure the direction of the active tag. The intersection of two or more straight lines is the active tag’s Possible location.

　　AOA positioning technology is currently not the mainstream technology of most reader positioning systems, but in the future, if reader smart antenna devices are added, and the angle resolution of the system is improved, moreover, AOA can be used without adding reader devices. Combined with active tags, AOA may become the mainstream positioning technology.

　　3.3 Receiving time positioning technology

　　The TIme of Arrival (TOA) positioning technology uses geometric principles, which are the same as the geometric principles of the signal strength method. The only difference is that the parameter that determines the radius of the circle is not the signal strength, but the signal propagation time. According to the signal propagation time from the active tag to the reader, multiplying the signal propagation time by the propagation speed can obtain the distance between the active tag and the reader. TOA positioning can be applied to positioning at various distances. Unlike AOA, the positioning accuracy will decrease as the distance between the active tag and the reader increases. However, because the signal propagation speed is very fast, TOA is very sensitive to time. High, the actual propagation time of the signal must be measured very accurately. Even a slight time error can cause an error in the true distance, and the error may be large.

　　3.4 Receiving time difference positioning technology

　　The TIme Difference of Arrival (TDOA) positioning technology uses the principle of hyperbolic positioning to measure the time difference between the propagation of the signal from the base station to the user.

　　The method uses a mobile terminal to monitor the base station and measure the time difference between the signal reaching the two base stations, and obtain a measurement value for each two base stations, thereby forming a hyperbolic positioning area. In this way, the three base stations will get two hyperbolic positioning areas, and by solving their junction points and adding additional conditions, the exact location of the mobile terminal can be obtained. TDOA is an improvement to TOA. It does not directly use the signal arrival time and does not require precise time synchronization. Therefore, the positioning accuracy will be improved.

　　The formula of TDOA is to measure the time difference between the signals of the mobile terminal and multiple base stations, and then calculate the spatial coordinates X and Y of the mobile terminal through a matrix calculation.

　　4 Conclusion

　　With the continuous development of RFID technology and the widespread use of RFID technology, there will definitely be more RFID-based positioning applications in the future, and the application of RFID in positioning will also increase. Especially in short-distance indoor positioning, compared with other wireless technologies, RFID wireless positioning solutions have great advantages in positioning.

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