Weijun Hong

A Novel Fast Tag Estimate Method for Dynamic Frame Length Aloha Anti-Collision Algorithms in RFID System

In an Radio Frequency Identification (RFID) system, Dynamic Frame Length Aloha (DFSA) has been widely used in anti-collision protocol due to its high efficiency. A fast and accurate estimate of tag population is critical to the performance of DFSA. In this paper, we propose a closed-form tag estimator which reduces greatly the computational complexity while maintains high accuracy. Also we propose a two-step estimate method which can further improve the estimate performance. Simulations show that the error of proposed tag estimator is less than 4%. Furthermore, the proposed tag estimator has significant advantage in lower complexity over existing estimate methods.

Tag Identifiable Probability Study While Reader Collision Occurs

Present studies on reader collision problem of RFID are commonly based on an assumption that if intersection areas exist between interrogation range of different readers, reader collision problem will confuse the tags within the intersection area and make them unable to communicate with any reader. On the contrary, the reader-to-tag collision phenomenon is detailedly analyzed in this paper, a new probability model based on the communication protocol of RFID is proposed, the probabilities that tags involved in reader-to-tag collision can be identified by both readers or only can be recognized by one of them, or even can not be identified by any reader are exactly calculated. According to this model even two readers interrogate the tag in the intersection area simultaneously, tags still can be identified by both readers with a relative high probability, and the probability that the tag can not be identified by any reader is quite low.

A novel antenna with a feed networks for RFID reader at ultra high frequency

The antenna and feed networks are presented for reader applications of radio frequency identification at ultra high frequency of 840 MHz - 845 MHz and 920 MHz - 925 MHz that is allocated for RFID use in China. The antenna is composed of two dual-L antennas orthogonally placed on a ground plane. The feed networks which are used to attain circular polarization characteristics of the antenna are introduced to control horizontal and vertical radiation current flows for each dual-L antenna respectively. The antenna can also be applied to ultra high frequency of 860 MHz - 960 MHz that is proposed for RFID use by ISO/IEC. The simulation and measurement were performed and the desired frequency bands with a return loss less than -10 dB were achieved.

Compatibility between RFID and STL

China has issued document to assign the frequency band 840~845 MHz and 920~925 MHz for RFID application on April 23, 2007. However, as the frequency 920~925MHz was originally used by stereo transmit link (STL) service, the power emitted by RFID system will probably cause interference to STL system. This paper presents the methods of conduct measurement and field test to exhibit in what condition a RFID system will not cause performance degradation on STL system.