Sithamparanathan Sabesan

Demonstration of improved passive UHF RFID coverage using optically-fed distributed multi-antenna system

Optically-fed distributed antenna system (DAS) technology is combined with passive ultra high frequency (UHF) radio frequency identification (RFID). It is shown that RFID signals can be carried on directly modulated radio over fiber links without impacting their performance. It is also shown that a multi-antenna DAS can greatly reduce the number of nulls experienced by RFID in a complex radio environment, increasing the likelihood of successful tag detection. Consequently, optimization of the DAS reduces nulls further. We demonstrate RFID tag reading using a three antenna DAS system over a 20m×6m area, limited by building constraints, where 100% of the test points can be successfully read. The detected signal strength from the tag is also observed to increase by an average of approximately 10dB compared with a conventional switched multi-antenna RFID system. This improvement is achieved at +31dBm equivalent isotropically radiated power (EIRP) from all three antenna units (AUs).

Wide Area Passive UHF RFID System Using Antenna Diversity Combined With Phase and Frequency Hopping

This paper presents a long range and effectively error-free ultra high frequency (UHF) radio frequency identification (RFID) interrogation system. The system is based on a novel technique whereby two or more spatially separated transmit and receive antennas are used to enable greatly enhanced tag detection performance over longer distances using antenna diversity combined with frequency and phase hopping. The novel technique is first theoretically modelled using a Rician fading channel. It is shown that conventional RFID systems suffer from multi-path fading resulting in nulls in radio environments. We, for the first time, demonstrate that the nulls can be moved around by varying the phase and frequency of the interrogation signals in a multi-antenna system. As a result, much enhanced coverage can be achieved. A prototype RFID system is built based on an Impinj R2000 transceiver. The demonstrator system shows that the new approach improves the tag detection accuracy from to 100% over a 20 m ×15 m area, compared with a conventional switched multi-antenna RFID system.

An error free passive UHF RFID system using a new form of wireless signal distribution

A wide area and error free ultra high frequency (UHF) radio frequency identification (RFID) interrogation system based on the use of multiple antennas used in cooperation to provide high quality ubiquitous coverage, is presented. The system uses an intelligent distributed antenna system (DAS) whereby two or more spatially separated transmit and receive antenna pairs are used to allow greatly improved multiple tag identification performance over wide areas. The system is shown to increase the read accuracy of 115 passive UHF RFID tags to 100% from <;60% over a 10m × 8m open plan office area. The returned signal strength of the tag backscatter signals is also increased by an average of 10dB and 17dB over an area of 10m × 8m and 10m × 4m respectively. Furthermore, it is shown that the DAS RFID system has improved immunity to tag orientation. Finally, the new system is also shown to increase the tag read speed/rate of a population of tags compared with a conventional RFID system.

Passive UHF RFID interrogation system using wireless RFID repeater nodes

This paper presents a new wireless radio frequency identification (RFID) repeater system, facilitating remote interrogation without the need for arrays of wired antennas, despite using entirely passive, low-cost ultra high frequency (UHF) RFID tags. The proposed system comprises a master RFID reader with both transmit and receive functions, and multiple RFID repeaters to receive, amplify and retransmit tag-to-reader and reader-to-tag communications. This expands the area over which the master RFID reader may provide coverage for a given maximum transmit power at each antenna. We first demonstrate a single hop wireless repeater system to allow similar read performance to a standard commercial passive UHF RFID reader. Finally, a proof of principle system demonstrates that a single wireless repeater node can allow an extension in range.

Tag read enhancement using unsynchronized signal from adjacent readers in multi-cell RFID system

This paper addresses the interference issue in a passive multi-cell radio frequency identification (RFID) system. Instead of considering the negative effect of interfering RF signals from adjacent readers, we investigate its constructive effect in providing extra RF power to tags in the cell of the desired reader system. Through detailed simulation and experimental analysis, it is found that the unsynchronised signal from neighbouring readers can be utilized to activate marginal tags through enhancing power delivery. This results in improved tag received signal strength indicator (RSSI). In addition, it is found that the overlap zone between two RFID cells is not as vulnerable to interference as one might think. In fact, the adjacent reader may facilitate the desired reader to read more tags in the overlapping zone, although a longer inventory period may be required. We believe these findings might provide a new insight into the interference effect on multi-cell RFID system and be applied to future medium access control (MAC) protocols.

An optimization model for antenna selection and deployment in single and multi-cell RFID systems

This paper presents an optimization model for antenna selection and deployment in ceiling mounted, single and multi-cell RFID systems. The proposed model utilises a three-dimensional (3D) antenna radiation pattern, taking into consideration of both antenna half power beam width and downtilt angle. Specifically, we have analysed the effects of cell structures on detection probability in single-cell operation and signal-to-interference ratio (SIR) in multi-cell scenario. Four cell structures have been studied, namely, triangular cells, conventional rectangular cells, offset rectangular cells and hexagonal cells. Several design examples are also presented to show how to use this model to find the optimal configuration to cover the maximum area with a minimum number of antennas for a single cell scenario, as well as the trade-offs that have to be made to achieve a reasonable SIR in multi-cell operation. We believe this optimization model provides new insights into the optimal deployment of single and multi-cell RFID systems.