At present, GPS and base station positioning technologies basically meet the needs of users for location services in outdoor scenarios. However, people spend 80% of their lives indoors, and it is difficult to achieve the ideal positioning effect with satellite positioning technology in some heavily obscured indoor areas, such as tunnels, low bridges, streets with many tall buildings and dense vegetation.

To address the localization problem in these scenarios, Associate Professor Chen Rui's team from Xi'an University of Electronic Science and Technology published a paper entitled "UHF-RFID-Based Real-Time Vehicle Localization in GPS-Less Environments" in IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS. Localization in GPS-Less Environments", proposing a new real-time vehicle localization scheme based on UHF-RFID, proposing a localization method based on phase difference of multi-frequency signals, solving the problem of phase ambiguity caused by using single-frequency signals for localization, and proposing for the first time a localization algorithm based on maximum likelihood estimation The first localization algorithm based on the Chinese remainder theorem is proposed, and the Levenberg-Marquardt (LM) algorithm is used to optimize the target position coordinates. Experimental results show that the proposed scheme is able to track the position of the vehicle with an error of less than 27 cm with 90% probability.

It is reported that the vehicle location system consists of a UHF-RFID tag placed on the roadside, an RFID reader with antenna mounted on top of the vehicle, and an on-board computer. When the vehicle is traveling on such a road, the RFID reader can obtain the phase of the backscattered signals from multiple tags and the location information stored in each tag in real time. Since the reader transmits a multi-frequency signal, the RFID reader can obtain multiple phases corresponding to the different frequencies of each tag. This phase and position information will be used by the on-board computer to calculate the distance from the antenna to each RFID tag and then determine the coordinates of the vehicle.

In the future, the shape of the city will be changed when the network is ubiquitous and location technology can be embedded in any device. The continuous innovation in the field of indoor location services through the application of a series of technologies will bring more surprises and possibilities for the whole IoT era.