Improved Radio-over-fiber-based Distributed Antenna System With Spatial Diversity For Passive UHF RFID

In recent years, the Internet of Things (IOT) , which integrates a variety of technologies including communications, radio frequency identification and sensors, is motivating the third wave of world information industry after the computer and the Internet. Without artificial interference, Radio Frequency Identification as the key technology of the perception level, could automatically identify the target and obtain data, which makes it much suitable for harsh environment, such as cold or high temperature.However,due to multipath fading in complex wireless environments, there is the "nulls"in the RFID system, where the electronic tags couldn't be detected. In addition, RFID system cannot be effectively applied to the scenes of large field and intensive tags because of the limit of read range and detection accuracy.In this paper, an improved radio-over-fiber-based distributed antenna system with spatial diversity for passive UHF RFID has been proposed, which integrated distributed radio over fiber technology and RFID technology. On the one hand, the system uses optical fiber as the transmission medium to eliminate the distance limit between the reader and the antenna, so that it could improve the read range and realize centralized management of multiple readers. On the other hand, by applying photonic lantern and microwave power divider to the proposed system for space diversity, it is possible to eliminate the inherent "nulls" to improve the detection accuracy. Photonic lantern combines multiple single-mode signals into one multimode signal with low loss. In this paper, we have further built a indoor experiment, not only conducted several tests, but also analyzed the experimental results in detail, which prodives a solid foundation for the application of photonic lantern in the distributed radio-over-fiber-based RFID system.In order to set up the system demonstration experiment, this paper first measures link performance index of the power-sensitive RoF uplink, so as to optimize the link structure. The performance of the RoF uplink is as follows:RF gain=0.29dB, noise figure =36.21dB, output third-order intercept point=15.5dBm, spurious-free dynamic range= 102.00 dB·Hz2/3; when input power is -42dBm to -20dBm , the system EVM is less than 4%All the values indicates that the performance of the link could fully meet the demands of RFID systems. Based on the RoF link optimization, this paper built a demonstration system. Compared with the radio-over-fiber-based distributed antenna system with RF switch for passive UHF RFID, the conclusion is drawn as follows:1? The proposed system can improve the single tag detection speed by almost 20% at each power.2?With denser electronic tags or smaller transmission power, the improved performance of the proposed system is much more obvious.3?For the same detection performance of the two system, the proposed system can offer many advantages such as spares extra transmission power of the reader, reduce extra reading time and reduce the number of used antennas.