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Accuracy of RFID Position Estimation using SAW Compressive Receivers
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 120 (2015) 320 – 323
EUROSENSORS 2015
Accuracy of RFID Position Estimation using SAW Compressive Receivers Martin Brandl* Center for Integrated Sensor Systems, Danube University Krems, Krems 3500, Austria
Abstract Nowadays, RFID tags are under use in numerous applications. The communication distance and therefore the ranging distance between base station and RFID tags is strongly limited by the maximum transmission power and the receiver sensitivity. A method based on passive SAW compressive receivers is presented to enhance the transmission distance for RFID tag ranging. The position estimation was done by active transmission of chirp pulses by the RFID tag and ToA and PoA measurements at the receivers. ©2015 2015The The Authors. Published by Elsevier Ltd. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROSENSORS 2015.
Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
Keywords: Radio frequency identification (RFID); position estimation, surface acoustic wave device
1. Introduction Localization technologies for position estimation or tracking of RFID devices will be an important feature in modern devices [1-3]. The communication of an active (self-powered) RFID with its base station is clear limited by the transmission power, the distance and the receiver sensitivity. For self-powered (battery powered) RFID’s the device life time is strongly dependent on the energy management. Therefore the RFID is not continuously in the active mode but will be set normally in the low power sleep state and powered up only to scheduled time points or on request by a received wake-up signal. In the sleep mode the RFID receiver is powered down and no active amplification of the wake-up signal can be achieved. To trigger the RFID comparator input for wake-up, high power signals or a passive compressive receiver can be used. For RFID wake-up we are using a chirp signal centered at
* Corresponding author. E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
doi:10.1016/j.proeng.2015.08.625
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323
321
250 0 MHz with bbandwidth of Bc=80 MHz and a a chirp duuration of Tc=1 = μs which is sent from thhe base station to a passsive surface aacoustic wave (SAW) comp pressive receivver (matched filter) located d at the RFID board (Fig. 1)). The SAW W compressivve receiver haas a compression gain Tc*B Bc of 19 dB an nd delivers a short pulse off high amplitu ude to the comparator innput of the RF FID for wake-u up. Compres ssed chirp signal for localizatiion
Basestation #1
RFID
RFID wake-up
Basestation #2
Chirp
Fig.. 1: Principle of th he RFID-tag locaation estimation by b chirp ToA and PoA.
The T SAW chirrp filter placed on the RFID D board can bbe also used fo or RFID localiization purposses. By excitin ng the chirrp SAW filterr with a time signal s matcheed to the filterr impulse resp ponse (e.g. forr an up-chirp filter with a downd chirrp time signall) a short pulsse with duratio on Tc=1/Bc=112.5 ns at the filter output is i generated aand transmitted to a set of o receiving bbase stations (F Fig. 2). 1.2 1
Ampl. [arb. units]
0.8 0.6 0.4 0.2 0 -0.2 0.96
0.97 7
0.98
0.99
1 t [s]
1.01
1.02 2
1.03
1.04 -6
x 10
F Fig. 2: Compresseed chirp signal with duration Tc affter incoherent deemodulation in the base station (BSS).
After wake-uup the RFID tag starts a periodic trannsmission of compressed chirp signals . The tag po osition estim mation can bee done by ToA A (time of arrrival) togetherr with PoA (ph hase of arrival) measuremeents at the receeiving basee stations andd subsequent triangulation [4]. The locaalization accurracy of the prroposed methood was determ mined und der the assum mption of an AWGN (add ditive white G Gaussian noise) transmission channel. Fig. 3a show w the sim mulation resultts for a RFID D located at x= =y=1.5m andd the estimated d positions caalculated by T ToA under AWGN con nditions.
322
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323
a)
b) Dist. STD= 0.022892m SNR= S 10.0227dB 2.2
BS S1
2
y [m] [ ]
1.8 1.6 1.4 1.2
BS S2
BS 3
1 0.8 0.8
1
1.2
1.4
x [m]
1.6
1.8
2
2.2
Fig. 3. aa) Estimated posittion of the RFID tag and b) distribbution of the estim mated RFID posittion. N=100, SNR R=10dB.
The T distributioon of the localization error is i depicted in Fig. 3b from which the meean position esstimation accu uracy was calculated (F Fig. 4). For SN NR values abo ove 10dB thee relative mean n position esttimation errorr is below 1.5%. If neceessary, higher accuracies caan be gained by b additional P PoA evaluatio on of the bandp pass signal, buut with the neeed of much higher signaal processing efforts in the BS.
Fig. 4.Meaan accuracy of thee RFID position eestimation under AWGN A condition ns. N=100.
Ack knowledgemen nts The T authors thaank the governnment of Low wer Austria forr funding this work and thee European Coommission (EF FRE) for supporting s ourr activities witthin the projecct ID No. WS T3-T-91/026--2012. Refeerences [1] J. S. Choi, H. Lee,, R. Elmasri, andd D.W. Engels, Localization system ms using passivee UHF RFID, in Proc. P 5th Int. Joinnt Conf. INC, IM MS and ID DC, (2009) 1727––1732. [2] M. M Bouet, A.L. Doos Santos, RFID tags: Positioning g principles and llocalization techn niques. In Wireless Days, 2008. W WD'08. 1st IFIP, (2008) 1--5.
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323 [3] C. Hausleitner, R. Steindl, A. Pohl, M. Brandl, F. Seifert, State of the art radio interrogation system for passive surface acoustic wave sensors. In EUROCOMM 2000. Information Systems for Enhanced Public Safety and Security. IEEE/AFCEA, (2000) 158-161. [4] A. Povalac, J. Sebesta, Phase of arrival ranging method for UHF RFID tags using instantaneous frequency measurement, ICECom 2010, Conference Proceedings, (2010) 1-4.
323
ScienceDirect Procedia Engineering 120 (2015) 320 – 323
EUROSENSORS 2015
Accuracy of RFID Position Estimation using SAW Compressive Receivers Martin Brandl* Center for Integrated Sensor Systems, Danube University Krems, Krems 3500, Austria
Abstract Nowadays, RFID tags are under use in numerous applications. The communication distance and therefore the ranging distance between base station and RFID tags is strongly limited by the maximum transmission power and the receiver sensitivity. A method based on passive SAW compressive receivers is presented to enhance the transmission distance for RFID tag ranging. The position estimation was done by active transmission of chirp pulses by the RFID tag and ToA and PoA measurements at the receivers. ©2015 2015The The Authors. Published by Elsevier Ltd. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROSENSORS 2015.
Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
Keywords: Radio frequency identification (RFID); position estimation, surface acoustic wave device
1. Introduction Localization technologies for position estimation or tracking of RFID devices will be an important feature in modern devices [1-3]. The communication of an active (self-powered) RFID with its base station is clear limited by the transmission power, the distance and the receiver sensitivity. For self-powered (battery powered) RFID’s the device life time is strongly dependent on the energy management. Therefore the RFID is not continuously in the active mode but will be set normally in the low power sleep state and powered up only to scheduled time points or on request by a received wake-up signal. In the sleep mode the RFID receiver is powered down and no active amplification of the wake-up signal can be achieved. To trigger the RFID comparator input for wake-up, high power signals or a passive compressive receiver can be used. For RFID wake-up we are using a chirp signal centered at
* Corresponding author. E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
doi:10.1016/j.proeng.2015.08.625
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323
321
250 0 MHz with bbandwidth of Bc=80 MHz and a a chirp duuration of Tc=1 = μs which is sent from thhe base station to a passsive surface aacoustic wave (SAW) comp pressive receivver (matched filter) located d at the RFID board (Fig. 1)). The SAW W compressivve receiver haas a compression gain Tc*B Bc of 19 dB an nd delivers a short pulse off high amplitu ude to the comparator innput of the RF FID for wake-u up. Compres ssed chirp signal for localizatiion
Basestation #1
RFID
RFID wake-up
Basestation #2
Chirp
Fig.. 1: Principle of th he RFID-tag locaation estimation by b chirp ToA and PoA.
The T SAW chirrp filter placed on the RFID D board can bbe also used fo or RFID localiization purposses. By excitin ng the chirrp SAW filterr with a time signal s matcheed to the filterr impulse resp ponse (e.g. forr an up-chirp filter with a downd chirrp time signall) a short pulsse with duratio on Tc=1/Bc=112.5 ns at the filter output is i generated aand transmitted to a set of o receiving bbase stations (F Fig. 2). 1.2 1
Ampl. [arb. units]
0.8 0.6 0.4 0.2 0 -0.2 0.96
0.97 7
0.98
0.99
1 t [s]
1.01
1.02 2
1.03
1.04 -6
x 10
F Fig. 2: Compresseed chirp signal with duration Tc affter incoherent deemodulation in the base station (BSS).
After wake-uup the RFID tag starts a periodic trannsmission of compressed chirp signals . The tag po osition estim mation can bee done by ToA A (time of arrrival) togetherr with PoA (ph hase of arrival) measuremeents at the receeiving basee stations andd subsequent triangulation [4]. The locaalization accurracy of the prroposed methood was determ mined und der the assum mption of an AWGN (add ditive white G Gaussian noise) transmission channel. Fig. 3a show w the sim mulation resultts for a RFID D located at x= =y=1.5m andd the estimated d positions caalculated by T ToA under AWGN con nditions.
322
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323
a)
b) Dist. STD= 0.022892m SNR= S 10.0227dB 2.2
BS S1
2
y [m] [ ]
1.8 1.6 1.4 1.2
BS S2
BS 3
1 0.8 0.8
1
1.2
1.4
x [m]
1.6
1.8
2
2.2
Fig. 3. aa) Estimated posittion of the RFID tag and b) distribbution of the estim mated RFID posittion. N=100, SNR R=10dB.
The T distributioon of the localization error is i depicted in Fig. 3b from which the meean position esstimation accu uracy was calculated (F Fig. 4). For SN NR values abo ove 10dB thee relative mean n position esttimation errorr is below 1.5%. If neceessary, higher accuracies caan be gained by b additional P PoA evaluatio on of the bandp pass signal, buut with the neeed of much higher signaal processing efforts in the BS.
Fig. 4.Meaan accuracy of thee RFID position eestimation under AWGN A condition ns. N=100.
Ack knowledgemen nts The T authors thaank the governnment of Low wer Austria forr funding this work and thee European Coommission (EF FRE) for supporting s ourr activities witthin the projecct ID No. WS T3-T-91/026--2012. Refeerences [1] J. S. Choi, H. Lee,, R. Elmasri, andd D.W. Engels, Localization system ms using passivee UHF RFID, in Proc. P 5th Int. Joinnt Conf. INC, IM MS and ID DC, (2009) 1727––1732. [2] M. M Bouet, A.L. Doos Santos, RFID tags: Positioning g principles and llocalization techn niques. In Wireless Days, 2008. W WD'08. 1st IFIP, (2008) 1--5.
Martin Brandl / Procedia Engineering 120 (2015) 320 – 323 [3] C. Hausleitner, R. Steindl, A. Pohl, M. Brandl, F. Seifert, State of the art radio interrogation system for passive surface acoustic wave sensors. In EUROCOMM 2000. Information Systems for Enhanced Public Safety and Security. IEEE/AFCEA, (2000) 158-161. [4] A. Povalac, J. Sebesta, Phase of arrival ranging method for UHF RFID tags using instantaneous frequency measurement, ICECom 2010, Conference Proceedings, (2010) 1-4.
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