WO2007012893A1 - Transceiver apparatus - Google Patents

Transceiver apparatus Download PDF

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Publication number
WO2007012893A1
WO2007012893A1 PCT/GB2006/050208 GB2006050208W WO2007012893A1 WO 2007012893 A1 WO2007012893 A1 WO 2007012893A1 GB 2006050208 W GB2006050208 W GB 2006050208W WO 2007012893 A1 WO2007012893 A1 WO 2007012893A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
antenna
phase
leakage
carrier
Prior art date
Application number
PCT/GB2006/050208
Other languages
French (fr)
Inventor
John Domokos
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB0515110A external-priority patent/GB0515110D0/en
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO2007012893A1 publication Critical patent/WO2007012893A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
    • H04B1/40—Circuits
    • H04B1/50—Circuits using different frequencies for the two directions of communication
    • H04B1/52—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
    • H04B1/525—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa with means for reducing leakage of transmitter signal into the receiver

Definitions

  • This invention relates to a transceiver apparatus and a method of carrier leakage cancellation therein, in particular a cancellation loop for RFID interrogators.
  • Radio Frequency Identification Devices play an increasingly important role in the supply chain management sector.
  • An RFID system typically consists of a reader (transmitter and receiver), one or more antennas, and a population of tags.
  • the tag In passive RFID systems, the tag is energized by a continuous wave (CW) radio frequency (RF) field which is transmitted via the antenna of the reader.
  • CW continuous wave
  • RF radio frequency
  • the reader to tag communication is arranged by modulating the CW signal.
  • the tag decodes this signal and responds by back-scattering the transmitted CW.
  • the back-scattered signal is received by the antenna and is then decoded in the receiver.
  • the power of the transmitted CW signal is in the order of 10OmW to 2W and the back-scattered signal is recovered with a homodyne receiver.
  • the received signal is very weak, in the order of InW to 10OnW depending on the distance between the reader and the tag.
  • RFID readers are homodyne, i.e. they have zero IF frequency.
  • the reader has a transmitter, a receiver and at least one antenna which sends an RF signal to a tag and the tag sends a backscattered signal to the receiver.
  • Installation costs make a two antenna solution less desirable , so one can have a circulator with a single antenna for both transmitting and receiving, i.e. to send and receive from the tag.
  • a problem with using a circulator is that there is parasitic coupling between the transmitter and the receiver, because the circulator is not perfect.
  • One known solution to this problem is to use a switching matrix, where all spare antennas in a multiple antenna system are used as receive antennas, but only one antenna is used to transmit. However, this is less attractive for a handheld device, so it is desirable to make the circulator work better
  • a transceiver apparatus comprises at least one antenna, selectively connectable to a receiver portion and a transmitter portion of the apparatus; wherein the apparatus further comprises a carrier cancellation loop comprising a vector phase modulator, whereby magnitude and phase of an output continuous wave (CW) signal are scaled and inverted and added to an input signal to cancel CW leakage.
  • the apparatus further comprising a memory to store predicted values of CW leakage magnitude and phase.
  • the apparatus comprises a plurality of antennas.
  • the apparatus further comprises a circulator to couple the transmit and receive portions to their respective antennas.
  • a method of carrier leakage cancellation in a transceiver apparatus comprises outputting a continuous wave (CW) carrier signal from a transmitter portion to an antenna; sampling the carrier signal in the apparatus; scaling the magnitude of the sample and inverting the phase of the carrier signal; receiving an input signal at the receiver portion; and applying the scaled and inverted signal to the input signal to cancel CW carrier leakage.
  • CW continuous wave
  • values of residual CW leakage magnitude and phase at predetermined frequencies are stored in a memory.
  • antenna allocations for the predetermined frequencies are also stored.
  • variations in signal path are monitored and stored in the memory for the predetermined frequency and antenna combinations.
  • Figure 1 is a block diagram of a typical tag reader, with four common transmit/receiver antennas;
  • FIG. 2 is a block diagram of a reader having four separate transmit and receiver antennas
  • Figure 3 shows the reader of Fig. 2, incorporating a switching matrix
  • Figure 4 illustrates an example of apparatus according to the present invention.
  • Figure 5 shows an alternative cancellation loop for use in the apparatus of Fig.4.
  • FIG. 1 shows a block diagram of a typical reader having a transmitter 1, receiver 2, circulator 3 and switch 4.
  • Four antennas A, B, C, D are used for interrogating a tag (not shown) . If a path from antenna A to the tag is obstructed, or impaired by multipath propagation, the switch 4 selects antenna B. The switch cycles through all antennas until communication between the reader and the tag has been successfully completed.
  • the drawback of this arrangement is that the receiver 2 is desensitized by a signaltransmitted from the transmitter 1. This signal leaks Pl through the circulator 3 because of the finite isolation of a practical device.
  • some of the transmitted signal is reflected back P2 from the antenna A, B, C, D because of return loss limitations of the antenna and its cabling.
  • the receiver transmitter isolation i.e. the sum of Pl and P2, is in the order of 15 to 25 dB. This limits the reading range of this type of reader to about Im to 3 m.
  • a transmitters and a receiver 6 are coupled via switches 7, 8 to their antennas.
  • the isolation P 3 in this case is typically 30 to 4OdB which means that the reading range is now increased to between 3m and 10m.
  • the disadvantage of the system in Fig. 2 is that twice as many antennas are required for the reader, as in Fig. 1, so the hardware and the installation costs of this system are higher.
  • FIG. 3 A block diagram of such a switching matrix is shown in Fig. 3, in which a transmitter 9 and multi-channel receiver 10 are connected via switches 11, 12 to the same antennas A, B, C, D .
  • the main disadvantage of the switching matrix solution is that it always requires more than one antenna and therefore it is not a good choice for a hand- held reader.
  • Another drawback of the switching arrangement is due to the separate transmit and receive paths. Once the system identifies an acceptable path for the transmit operation, the same path cannot be used for reception. This means that there is a chance that the receiver path is blocked even though the tag has been successfully energized and is transmitting back-scatter.
  • the carrier cancellation loop of the present invention is able to achieve similar isolation and therefore similar read range to that of the switching matrix. However, it has the advantages that it can be used with one antenna, making it suitable for portable applications and that the receiver and the transmitter paths are the same at any given read cycle , so that both the receiver and the transmitter can operate through the optimum channel simultaneously
  • An example of apparatus according to the present invention is shown in the block diagram of Fig. 4.
  • the reader comprises a transmitter 13, a receiver 14 and a circulator 15 which connects the transmitter and receiver to an antenna 16.
  • reader to tag data 17 is modulated onto a continuous wave (CW) signal from a signal generator 18, in a multiplier 19 and output through an amplifier 20 and coupler 21 to the circulator 15 and one of the antennas 16.
  • CW continuous wave
  • the coupler also provides an input to a vector modulator 22 and forms part of a cancellation loop.
  • the cancellation loop also includes a summing device 23, a memory 24 and digital to analogue converters 25.
  • the cancellation loop operates as follows.
  • the coupler 21 couples a small sample of the output CW signal from the transmitter amplifier 20 to the vector modulator 22.
  • the vector modulator scales magnitude and rotates phase of the output CW signal so that it is equal in magnitude, but opposite in phase to any incoming CW leakage from the circulator. When the scaled, rotated signal is added to an input signal, received at the antennas, the unwanted CW leakage component is cancelled out.
  • the vector modulator 22 is controlled by the homodyne receiver 14.
  • the receiver receives an input signal and the output of the vector modulator via the summer
  • phase and quadrature components of the CW signal are produced in a local oscillator 27 and multiplied 28 with the output of the summer 23, then separately A to D converted in ADCs 29 and input to a demodulator 26. Residual CW is demodulated in the demodulator 26 and magnitude and phase information are stored in the memory
  • the magnitude and phase of the residual CW depend upon the frequency of the signal, the particular antenna selection made and the signal path.
  • the frequency and the antenna selection parameters are used to address the memory 24. Slow variations in the signal paths are tracked with the cancellation loop and the corresponding magnitude and phase (or I /Q values) are continuously updated in the memory. The loop applies these complex values to the vector modulator 22 via the D/A converters 25 in the opposite polarity to achieve signal cancellation.
  • the loop further comprises an integrator - not shown in Fig. 4.
  • the integrator or an appropriate loop filter, determines the transfer function of the tracking loop.
  • This integrator can be implemented either digitally or by analogue RC elements.
  • the cancellation loop may also be implemented without a circulator 15.
  • Fig. 5 shows an example in which a 3dB coupler 30 is used between the receiver 14 and the transmitter 13, in place of the circulator. This arrangement operates in an identical fashion to that of Fig. 4. Should the two antennas 31, 32 be cross-polarized, they would produce circularly polarized RF waves.
  • the arrangement of Fig. 5 offers an ideal solution for a hand -held reader using co- located antenna elements.
  • the present invention has the advantages that it has a large reading range due to the elimination of the self blocking, the same transmit and receive paths are used simultaneously and it is suitable for integration and for hand-held applications.
  • the parasitic path is also dependant on the antenna properties and its inefficient reflection coefficient, so the memory can also include a reference to the relevant antenna to be used for the best result For readers with frequency hopping, the memory also needs to update when the frequency changes.

Abstract

A transceiver apparatus comprises at least one antenna (16), selectively connectable (15) to a receiver portion (14) and a transmitter portion (13) of the apparatus. The apparatus further comprises a carrier cancellation loop comprising a vector phase modulator (22), whereby magnitude and phase of an output continuous wave (CW) signal are scaled and inverted and added to an input signal to cancel CW leakage.

Description

TRANSCEIVER APPARATUS
This invention relates to a transceiver apparatus and a method of carrier leakage cancellation therein, in particular a cancellation loop for RFID interrogators. Radio Frequency Identification Devices (RFID) play an increasingly important role in the supply chain management sector. An RFID system typically consists of a reader (transmitter and receiver), one or more antennas, and a population of tags.
In passive RFID systems, the tag is energized by a continuous wave (CW) radio frequency (RF) field which is transmitted via the antenna of the reader. The reader to tag communication is arranged by modulating the CW signal. The tag decodes this signal and responds by back-scattering the transmitted CW. The back-scattered signal is received by the antenna and is then decoded in the receiver.
In a typical system, the power of the transmitted CW signal is in the order of 10OmW to 2W and the back-scattered signal is recovered with a homodyne receiver. The received signal is very weak, in the order of InW to 10OnW depending on the distance between the reader and the tag.
RFID readers are homodyne, i.e. they have zero IF frequency. The reader has a transmitter, a receiver and at least one antenna which sends an RF signal to a tag and the tag sends a backscattered signal to the receiver. Installation costs make a two antenna solution less desirable , so one can have a circulator with a single antenna for both transmitting and receiving, i.e. to send and receive from the tag.
A problem with using a circulator is that there is parasitic coupling between the transmitter and the receiver, because the circulator is not perfect. One known solution to this problem is to use a switching matrix, where all spare antennas in a multiple antenna system are used as receive antennas, but only one antenna is used to transmit. However, this is less attractive for a handheld device, so it is desirable to make the circulator work better
In accordance with a first aspect of the present invention, a transceiver apparatus comprises at least one antenna, selectively connectable to a receiver portion and a transmitter portion of the apparatus; wherein the apparatus further comprises a carrier cancellation loop comprising a vector phase modulator, whereby magnitude and phase of an output continuous wave (CW) signal are scaled and inverted and added to an input signal to cancel CW leakage. Preferably, the apparatus further comprising a memory to store predicted values of CW leakage magnitude and phase.
Preferably, the apparatus comprises a plurality of antennas. Preferably, the apparatus further comprises a circulator to couple the transmit and receive portions to their respective antennas.
In accordance with a second aspect of the present invention, a method of carrier leakage cancellation in a transceiver apparatus comprises outputting a continuous wave (CW) carrier signal from a transmitter portion to an antenna; sampling the carrier signal in the apparatus; scaling the magnitude of the sample and inverting the phase of the carrier signal; receiving an input signal at the receiver portion; and applying the scaled and inverted signal to the input signal to cancel CW carrier leakage.
Preferably, values of residual CW leakage magnitude and phase at predetermined frequencies are stored in a memory.
Preferably, antenna allocations for the predetermined frequencies are also stored.
Preferably, variations in signal path are monitored and stored in the memory for the predetermined frequency and antenna combinations.
An example of apparatus for and a method of carrier leakage cancellation will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram of a typical tag reader, with four common transmit/receiver antennas;
Figure 2 is a block diagram of a reader having four separate transmit and receiver antennas;
Figure 3 shows the reader of Fig. 2, incorporating a switching matrix; Figure 4 illustrates an example of apparatus according to the present invention; and,
Figure 5 shows an alternative cancellation loop for use in the apparatus of Fig.4.
Figure 1 shows a block diagram of a typical reader having a transmitter 1, receiver 2, circulator 3 and switch 4. Four antennas A, B, C, D are used for interrogating a tag (not shown) . If a path from antenna A to the tag is obstructed, or impaired by multipath propagation, the switch 4 selects antenna B. The switch cycles through all antennas until communication between the reader and the tag has been successfully completed. The drawback of this arrangement is that the receiver 2 is desensitized by a signaltransmitted from the transmitter 1. This signal leaks Pl through the circulator 3 because of the finite isolation of a practical device. Furthermore, some of the transmitted signal is reflected back P2 from the antenna A, B, C, D because of return loss limitations of the antenna and its cabling. The receiver transmitter isolation, i.e. the sum of Pl and P2, is in the order of 15 to 25 dB. This limits the reading range of this type of reader to about Im to 3 m.
An improved arrangement is shown in Fig. 2. In this case, a transmitters and a receiver 6 are coupled via switches 7, 8 to their antennas. There are four antennas Aτ, Bτ, Cτ, DT for the transmitter and four separate antennas AR, BR, CR, DR for the receiver, so the desensitization is greatly improved. The isolation P 3 in this case is typically 30 to 4OdB which means that the reading range is now increased to between 3m and 10m. However, the disadvantage of the system in Fig. 2 is that twice as many antennas are required for the reader, as in Fig. 1, so the hardware and the installation costs of this system are higher.
One solution to this is to use a switching matrix as described in our co- pending UK pateil application no.GB 0510208.2, which reduces the cost of the arrangement in Fig. 2. A block diagram of such a switching matrix is shown in Fig. 3, in which a transmitter 9 and multi-channel receiver 10 are connected via switches 11, 12 to the same antennas A, B, C, D . The main disadvantage of the switching matrix solution is that it always requires more than one antenna and therefore it is not a good choice for a hand- held reader. Another drawback of the switching arrangement is due to the separate transmit and receive paths. Once the system identifies an acceptable path for the transmit operation, the same path cannot be used for reception. This means that there is a chance that the receiver path is blocked even though the tag has been successfully energized and is transmitting back-scatter.
The carrier cancellation loop of the present invention is able to achieve similar isolation and therefore similar read range to that of the switching matrix. However, it has the advantages that it can be used with one antenna, making it suitable for portable applications and that the receiver and the transmitter paths are the same at any given read cycle , so that both the receiver and the transmitter can operate through the optimum channel simultaneously An example of apparatus according to the present invention is shown in the block diagram of Fig. 4. The reader comprises a transmitter 13, a receiver 14 and a circulator 15 which connects the transmitter and receiver to an antenna 16. In the transmitter 13, reader to tag data 17 is modulated onto a continuous wave (CW) signal from a signal generator 18, in a multiplier 19 and output through an amplifier 20 and coupler 21 to the circulator 15 and one of the antennas 16. The coupler also provides an input to a vector modulator 22 and forms part of a cancellation loop. The cancellation loop also includes a summing device 23, a memory 24 and digital to analogue converters 25. The cancellation loop operates as follows. The coupler 21 couples a small sample of the output CW signal from the transmitter amplifier 20 to the vector modulator 22. The vector modulator scales magnitude and rotates phase of the output CW signal so that it is equal in magnitude, but opposite in phase to any incoming CW leakage from the circulator. When the scaled, rotated signal is added to an input signal, received at the antennas, the unwanted CW leakage component is cancelled out.
The vector modulator 22 is controlled by the homodyne receiver 14. The receiver receives an input signal and the output of the vector modulator via the summer
23. In phase and quadrature components of the CW signal are produced in a local oscillator 27 and multiplied 28 with the output of the summer 23, then separately A to D converted in ADCs 29 and input to a demodulator 26. Residual CW is demodulated in the demodulator 26 and magnitude and phase information are stored in the memory
24. The magnitude and phase of the residual CW depend upon the frequency of the signal, the particular antenna selection made and the signal path.
The frequency and the antenna selection parameters are used to address the memory 24. Slow variations in the signal paths are tracked with the cancellation loop and the corresponding magnitude and phase (or I /Q values) are continuously updated in the memory. The loop applies these complex values to the vector modulator 22 via the D/A converters 25 in the opposite polarity to achieve signal cancellation.
The loop further comprises an integrator - not shown in Fig. 4. The integrator, or an appropriate loop filter, determines the transfer function of the tracking loop. This integrator can be implemented either digitally or by analogue RC elements.
The cancellation loop may also be implemented without a circulator 15. Fig. 5 shows an example in which a 3dB coupler 30 is used between the receiver 14 and the transmitter 13, in place of the circulator. This arrangement operates in an identical fashion to that of Fig. 4. Should the two antennas 31, 32 be cross-polarized, they would produce circularly polarized RF waves. The arrangement of Fig. 5 offers an ideal solution for a hand -held reader using co- located antenna elements. The present invention has the advantages that it has a large reading range due to the elimination of the self blocking, the same transmit and receive paths are used simultaneously and it is suitable for integration and for hand-held applications.
The parasitic path is also dependant on the antenna properties and its inefficient reflection coefficient, so the memory can also include a reference to the relevant antenna to be used for the best result For readers with frequency hopping, the memory also needs to update when the frequency changes.

Claims

1. A transceiver apparatus comprising at least one antenna, selectively connectable to a receiver portion and a transmitter portion of the apparatus; wherein the apparatus further comprises a carrier cancellation loop comprising a vector phase modulator, whereby magnitude and phase of an output continuous wave (CW) signal are scaled and inverted and added to an input signal to cancel CW leakage.
2. Apparatus according to claim 1, the apparatus further comprising a memory to store predicted values of CW leakage magnitude and phase.
3. Apparatus according to claim 1 or claim 2, wherein the apparatus comprises a plurality of antennas.
4. Apparatus according to claim 3, further comprising a circulator to couple the transmit and receive portions to their respective antennas.
5. A method of carrier leakage cancellation in a transceiver apparatus, the method comprising outputting a continuous wave (CW) carrier signal from a transmitter portion to an antenna; sampling the carrier signal in the apparatus; scaling the magnitude of the sample and inverting the phase of the carrier signal; receiving an input signal at the receiver portion; and applying the scaled and inverted signal to the input signal to cancel CW carrier leakage.
6. A method according to claim 5, whereh values of residual CW leakage magnitude and phase at predetermined frequencies are stored in a memory.
7. A method according to claim 6, wherein antenna allocation for the predetermined frequencies is also stored.
8. A method according to claim 7, wherein variations in signal path are monitored and stored in the memory for the predetermined frequency and antenna combinations.
PCT/GB2006/050208 2005-07-25 2006-07-17 Transceiver apparatus WO2007012893A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB0515110.5 2005-07-25
GB0515110A GB0515110D0 (en) 2005-07-25 2005-07-25 Interrogation system
GB0603968A GB2428940A (en) 2005-07-25 2006-02-28 Carrier leakage cancellation in an RFID reader
GB0603968.9 2006-02-28

Publications (1)

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WO2007012893A1 true WO2007012893A1 (en) 2007-02-01

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PCT/GB2006/050208 WO2007012893A1 (en) 2005-07-25 2006-07-17 Transceiver apparatus

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110181397A1 (en) * 2009-03-27 2011-07-28 Kang Yanggi Backscattering type rfid communication system
US8175535B2 (en) 2008-02-27 2012-05-08 Telefonaktiebolaget Lm Ericsson (Publ) Active cancellation of transmitter leakage in a wireless transceiver

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5574978A (en) * 1994-05-12 1996-11-12 American Nucleonics Corporation Interference cancellation system and radio system for multiple radios on a small platform
EP0831594A2 (en) * 1996-09-18 1998-03-25 Kipp, Ludwig Frequency cancelling system and method
US6340932B1 (en) * 1998-06-02 2002-01-22 Rf Code, Inc. Carrier with antenna for radio frequency identification
WO2002017506A1 (en) * 2000-08-22 2002-02-28 Novatel Wireless, Inc. Method and apparatus for transmitter noise cancellation in an rf communications system
US6507728B1 (en) * 1998-07-27 2003-01-14 Nec Corporation Radio transceiver and a method of preventing transmission spurious response
WO2005089427A2 (en) * 2004-03-19 2005-09-29 Samsys Techologies, Inc. A method and apparatus for canceling the transmitted signal

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5574978A (en) * 1994-05-12 1996-11-12 American Nucleonics Corporation Interference cancellation system and radio system for multiple radios on a small platform
EP0831594A2 (en) * 1996-09-18 1998-03-25 Kipp, Ludwig Frequency cancelling system and method
US6340932B1 (en) * 1998-06-02 2002-01-22 Rf Code, Inc. Carrier with antenna for radio frequency identification
US6507728B1 (en) * 1998-07-27 2003-01-14 Nec Corporation Radio transceiver and a method of preventing transmission spurious response
WO2002017506A1 (en) * 2000-08-22 2002-02-28 Novatel Wireless, Inc. Method and apparatus for transmitter noise cancellation in an rf communications system
WO2005089427A2 (en) * 2004-03-19 2005-09-29 Samsys Techologies, Inc. A method and apparatus for canceling the transmitted signal

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8175535B2 (en) 2008-02-27 2012-05-08 Telefonaktiebolaget Lm Ericsson (Publ) Active cancellation of transmitter leakage in a wireless transceiver
US20110181397A1 (en) * 2009-03-27 2011-07-28 Kang Yanggi Backscattering type rfid communication system
US9479229B2 (en) * 2009-03-27 2016-10-25 Idro Co., Ltd. Backscattering type RFID communication system

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