# ANTSpin: Efficient Absolute Localization Method of RFID Tags via Spinning Antenna
## 1 Introduction  
At present, Global Positioning System (GPS) has achieved fruitful results in outdoor positioning, which can achieve high localization accuracy and it is widely applied in map navigation [1]. However, GPS cannot capture accurate information in indoor environments, and it is difficult to meet the accuracy requirements of indoor positioning. In actual production life, there are many indoor positioning requirements in indoor navigation, building buildings, warehouse management, parking guidance, etc. Therefore, research regarding indoor positioning technology is very necessary. However, indoor positioning is more complicated than outdoor positioning with more influencing factors of the signal. Once the error is large, the whole localization system will lose its practical significance and application value, as the precision requirement is higher [2]. At present, technologies that are applied to indoor positioning mainly include Wi-Fi, Bluetooth, infrared, Radio Frequency Identification (RFID), ZigBee, and ultrasonic [3; 4; 5; 6; 7]. Commercial technologies basically adopt wireless communication base station schemes, such as RFID and Wi-Fi. RFID localization technology exchanges data through non-contact two-way communication for the purpose of mobile device identification and positioning. The current use of RFID technology to build indoor positioning systems also has great advantages. With the growing of RFID hardware and software technology, the production cost of RFID tags has been reduced to a few cents and the anti-collision algorithm for multi-tag identification is becoming more and more mature. The performance of RFID readers isalso superior. It can quickly read a large number of tags in a few milliseconds, which is extremely efficient [8]. RFID has a great development space in indoor positioning as an important key technology for implementing Internet of Things. RFID indoor positioning technology has experienced more than a decade of development, bringing about a variety of localization systems. However, there is still no universally recognized stable high-precision indoor positioning system in the current research process due to some problems in these localization systems. We summarize some of the disadvantages of current localization scheme, as follows [9; 10; 11; 12; 13; 14; 15; 16]. First, most of them collect data from a number of static antennas in fixed positions, which results in the high deployment cost in antennas. Second, when deploy the antenna in a static state, the antennas are in the edge of localization area with spatial limitation. Third, in the static identification environment, the relative positions of the antenna and tags are not changed. Due to the multipath effect and the mutual interference between tags, the tags of some specific dead angles fail to obtain enough signal energy to activate itself for feedback, which results in a \"tag missing\" phenomenon. Fourth, many schemes require a large number of reference tags. The cost and difficulty of deployment are simultaneously increased. Fifth, some schemes use the rotating table, place the antenna on the edge and collect data during the rotation process. Indeed, this saves antenna costs, but it requires a relatively large rotating table, which is inconvenient to deploy. In addition, localization accuracy and stability are still the most important. Although there are many methods that have achieved high accuracy, it is difficult to balance accuracy, stability, and deployment cost. In this paper, we proposed ANTspin: Efficient Absolute Localization Method of RFID Tags via the Spinning Antenna, which introduces a rotating table in the experiment. We place the antenna in the center of rotating table, and rotate the antenna by 360 degrees at a fixed point to collect dynamic data. When compared to static schemes, more information is collected for localization.