The Research of RFID Localization Technology Based on Bi-directional RSSI

Improvements are presented for the radio frequency identification (RFID) location technology based on received signal strength indication (RSSI) in this paper. A semi-active tag with RSSI is designed, which increases the circuit of measuring the signal strength between the rectifier modules and digital modules, thus tags can measure the signal strength. This paper theoretically analyzes the method of signal received by tags to reduce the reflection interference. The method of bi-directional RSSI is proposed, which gets signal by tags and readers, and the spatial diversity technique is introduced, which can be utilized to compensate channel uncertainties such as multipath fading. The method of bi-directional RSSI is that tags and the reader can locate each other, and is a special spatial diversity technique. In this paper, spatial diversity is exploited for locating stationary and mobile objects in the indoor environment. Space diversity technique is introduced for small scale motion and temporal variation compensation of received signal strength and it is demonstrated analytically that it enhances location accuracy. The three common linear combining approaches are selection combining (SC), maximal ratio combining (MRC) and equal gain combining (EGC). Taking into account the ease of implementation, SC is adopted in the paper. It is theoretically analyzed that the method of bi-directional RSSI can be effectively against multipath fading, improve signal reception gain, and enhance the communication quality.