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Rfid reader

Rfid reader description/claims

This application claims priority of United Kingdom Patent Office application No. 0709313.1 GB filed May 15, 2007 and of United Kingdom Patent Office application No. 0802055.4 GB filed Feb. 05, 2008, which are incorporated by reference herein in their entirety.

The mass application of passive ultra high frequency (UHF) radio frequency identification (RFID) systems is becoming widespread in the retail industry, logistics and commerce. In most applications, it is very important that all tags are interrogated successfully during an inventory round, and no tags are missed. Despite efforts in improving the performance of the current RFID systems, 100% success rate has not yet been reached in some applications.

In passive RFID systems the tags receive their power from the RF field transmitted by the reader. The efficiency of the power transfer from the reader to the tags is essential for reliable operation.

It is well know in the art, that radio wave propagation suffers from multipath effects. In the presence of reflections, the power received by the tags varies over location and frequency. If the received power at the tag falls below the sensitivity threshold of the tag, the tag will be missed from the inventory. Typical sensitivity of the tags today is −15 dBm to −20 dBm.

There are two commonly used methods to minimize the effect of multipath propagation in RFID systems, space diversity and frequency hopping.

A typical gate reader employs several antennas that provide space diversity. First, the tags are interrogated from a first antenna. The majority of the tags, which receive adequate power, will respond. However, the tags which are in the nulls of the interference pattern are missed from the first reading cycle. Next, the tags are interrogated from a second antenna, which is located in a different position. From the second antenna, the multipath pattern is different and those tags which were in a null previously are now likely to be energized adequately. The interrogation is repeated, switching all antennas in a sequential fashion and therefore maximising the read probability.

In addition to space diversity, in some systems, frequency hopping is also used to mitigate the multipath effects even further. In this case the tag population is interrogated at a certain frequency F1 first. After a pre-set time, when the interrogation is completed at F1, the reader is switched to a different frequency F2. At F2, the multipath pattern is different from that of F1 and those tags which were missed during the first reading cycle are now likely to be read. The interrogation is repeated, switching the reader to different frequencies in a sequential fashion and therefore maximising the success rate.

In the frequency hopping system, the tags are illuminated one frequency at a time. The consecutive reading cycles at different frequencies are performed sequentially. This means that if there are N frequencies, and the time taken for a reading cycle is R, the total inventory time is Tinv=N*R.

Reading speed and success rate is a major competitive parameter for RFID systems. This is particularly the case in fast moving applications, or in cases where the tags are buried in the shadow of conductive items and therefore the illumination time is relatively short.

In accordance with a first aspect of the present invention an RFID reader comprises a receiver section for receiving an RF signal and a transmitter section for transmitting an RF signal; wherein the reader is a multicarrier RFID reader and both the transmitted RF signal and the received RF signal comprise at least two frequencies.

In the present invention, unlike in the frequency hopping systems, the tags are now illuminated at several frequencies simultaneously. This shortens the inventory time substantially, because the reading is performed at the several frequencies parallel. The total inventory time for a multicarrier reader is therefore Tinv=R.

Preferably, the receiver section comprises an input to receive an RF signal; a down converter stage to downconvert the RF signal to baseband; and a processor.

Preferably, the downconverter stage further comprises a splitter to split the received RF signal into its component frequency signals; and wherein each component signal is downconverted.

Alternatively, in a digital implementation, the RF signal undergoes a first downconversion stage using an RF carrier local oscillator, then a second downconversion stage for each individual carrier frequency.

Preferably, a down converter is provided for each of the split RF signals.

Preferably, the reader further comprises a baseband filter to filter out beat frequencies of the received, downconverted signal.

Preferably, the transmitter section comprises a baseband signal generator, an upconverter stage and an RF output.

Preferably, the upconverter stage further comprises a splitter to split a signal from the baseband signal generator into at least two frequencies; and wherein upconversion of each baseband signal is performed.

Alternatively, in a digital implementation, a first upconversion stage is carried out using a local oscillator at each individual carrier frequency, then a further upconversion stage is carried out using an RF carrier frequency local oscillator.

• Provisional Patent
• Utility Patent

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