Bauwelinck, Johan

DANNEELS, J

DEBACKER, P

Demuytere, Pieter

OLBRECHTS, J

SPIESSENS, P

STUBBE, F

Torfs, Guy

TUBBAX, H

Vandewege, Jan

WOUTERS, J

Yin, Xin

Ghent University Academic Bibliography

Embedded ranging system in ISM bandX. Yin, J. Bauwelinck, G. Torfs, P. Demuytere,J. Vandewege, H. Tubbax, J. Wouters, P. Debacker,J. Olbrechts, P. Spiessens, F. Stubbe and J. DanneelsA new embedded ranging system in the ISM band is described. Theproposed indoor ranging system combines the advantages of bothbroadband and narrowband signals to achieve high ranging accuracyin the presence of strong multipath reﬂections to achieve a good linkbudget and to be compliant with spectral regulations. The system isbased on a WLAN transceiver (with embedded ranging speciﬁc cir-cuits) and uses the same frequency band for both communica-tion and ranging purposes so that no separate dedicated rangingtransceiver is needed. A prototype has been implemented to evaluatethe performance of the proposed technique in a realistic environment.Experimental results show ranging accuracies of less than 20 cm.Introduction: Well-established technologies for position determinationmostly address outdoor scenarios, e.g. the Global Positioning System(GPS). While these techniques have adequate performance outdoorsand when a sufﬁciently strong line-of-sight signal is available, theysuffer from low accuracy in indoor environments. The key reason forthis performance degradation is that the received signals consist of mul-tiple superimposed attenuated, delayed and phase rotated copies of thissignal [1]. Especially owing to the narrowband nature of the transmittedsignals, these copies have a wide span in the time-domain and hencetend to overlap, as shown in Fig. 1. As a result, copies having travelledseveral metres more can typically not be separated from the line-of-sightpath by the receiver, and it induces errors in the position estimate of thesame order of magnitude.direct path reflectionswidebandsignalnarrorwbandsignaltime timea bFig. 1 Transmission over fading multipath channels, and received widebandand narrowband signal in dense multipath environmentsa Transmission over fading multipath channelsb Received wideband and narrowband signal in dense multipath environmentsTo enable accurate position determination in indoor environments,techniques based on received-signal strength (RSS) [2] and propa-gation-time of signalling [1, 3] have been proposed. RSS systems arebased on sophisticated pathloss models for indoor environments. Butthere is no strong correlation between RSS and distance and its distri-bution depends on hardware implementations [2]. Reference [3] pro-posed to measure the propagation delay of WLAN packets, but theachieved accuracy (8 m) is not good enough for most indoor locationapplications. The propagation time based UWB system providessuperior distance estimation accuracy because the transmitted signalsfeature a very short span in the time-domain and hence provide improvedresolution for separating the line-of-sight propagated copy from thereﬂected copies [1]. However, UWB signalling has serious disadvan-tages with respect to narrowband communication in terms of the linkbudget. Because of this, and also the high frequency at which ultra-wide-band communication usually takes place, the operational range of suchsystems tend to be signiﬁcantly shorter than that of classical narrowbandsystems. In [4], technologies combining the advantages of narrowbandand wideband signals are proposed. In these systems, a narrowbandtransceiver is used for low-rate data communication, again typicallyfor discovery purposes, whereas a wideband transceiver is used forranging. The separate ranging transceiver increases system costs and fre-quency usage is not efﬁcient because the signalling happens in distinctfrequency bands.In this Letter, an indoor ranging scheme is proposed, combining theadvantages of both wideband and narrowband signals, whichinvolves a single radio transceiver (with the addition of a few rangingspeciﬁc circuits) and a single frequency band for both communicationand ranging purposes (patented [5]). The fundamental idea is that alsoELECTRONICS LETTERS 14th August 2008 Vol. 44relatively narrowband radios such as those used in WLAN productsexhibit and/or can be stimulated to generate wideband transientsignals, which can then be leveraged for improved positioning accuracyat the receiver, by processing these wideband transient signals ratherthan just the narrowband communication signal. A proof-of-conceptprototype ranging system (2.4 GHz ISM band) has been developedusing commercial off-the-shelf components in order to evaluate the per-formance of the proposed technique.Transceiver architecture: Fig. 2 shows the architecture of the WLANtransceiver with embedded ranging. The transceiver is designed forusing the existing WLAN infrastructure with minor modiﬁcations.While signals with standard channel bandwidth (e.g. 20 MHz) areused for data communication and nodes discovery, ranging signalshaving a bandwidth encompassing the whole WLAN band (ISM orU-NII band) can be generated for increasing ranging accuracy. In thetransmit path, an RF switch has been inserted between the WLAN trans-mitter and the power ampliﬁer, which are usually two separate chips. Inthis way, broadband signals with short rise/fall times can be generated.As typical for WLAN receivers, the receiver implements a direct conver-sion architecture, but the baseband paths need sufﬁcient bandwidth (e.g.200 MHz) to pass the fast rising edges of the RF ranging signals. Whena ranging event occurs, the transmitter ranging engine will generate aranging pulse with short rise/fall time to the RF switch and save thecurrent ranging event timestamp. The received ranging RF pulse willbe converted to baseband by using quadrature mixing. Then sampled Iand Q signals are fed into the receiver ranging engine for distance esti-mation, where the baseband ranging pulse is recovered and the time ofarrival (TOA) of the direct path is extracted from the rising edge of therecovered pulse.wideband rangingoutput / WLANpacketBPFdeplexerPAranging eventTX–enableTXrangingenginegenericWLAN TXWLANbasebandtimestampsRXrangingengineADCLPFLPFLNAADC090Fig. 2 Conceptual block diagram of proposed ISM band ranging transceiver20500 m V/div. vertical2.5 n/div. horizontal 0–20–40–60–100frequency, MHz240r 241r 242r 243r 244r 245r 246r 247r 248r–80dBmWLAN spectral mask (IEEE 802.11g)Fig. 3 Transmitter output ranging waveform and spectruma Waveformb SpectrumExperimental results: The output RF waveform and spectrum areshown in Fig. 3. The output signal spectrum is fully compliant withthe WLAN spectral mask (IEEE 802.11 g) as long as the rangingevents occur at a reasonable rate, e.g. every 40 ms (corresponding to25 000 ranging measurements per second). The received signal isshown in Fig. 4, illustrating the relatively strong multipath reﬂectionsin the measurement room. In these experiments, the synchronisationbetween the ranging transmitter and receiver is realised with a coaxialcable of known delay which transfers a trigger signal from transmitterNo. 17to receiver. However, in a practical application, the synchronisation ofthe different nodes is avoided by performing round-trip time (RTT)measurements.03000 3200 3400 3600 3800 4000 4200 4400 4600 4800 50000.010.020.030.040.050.060.070.08samplesabsolute amplitude, Vmultipath reflectionsdirect pathFig. 4 Received baseband ranging pulseSeveral distance measurements are performed out at real distancesfrom 0 to 14.4 m at intervals of 1.8 m. For each distance, 500 waveformswere statistically analysed. In Fig. 5, the results at 7.2 m are shown as anexample. Both empirical histogram and normal ﬁt illustrate very smallabsolute error and variance, showing good accuracy of our rangingsystem. The ranging results are shown in Table 1 and the average ofmeasured data is selected as the statistical estimator for real distance.For all cases a very high accuracy with an error of less than 20 cm isachieved and the statistical variation is also very small (3s , 0.5 m).150100500measurements at 7.2 mnormal fit7.10 7.15 7.20 7.25 7.30 7.35 7.40 7.45 7.50Fig. 5 Histogram and normal ﬁt of measured data at real distance of 7.2 mELECTRONITable 1: Ranging resultsDistance(m)Estimateddistance (m)Standarddeviation (m)Absoluteerror (m)1.8 1.937 0.029 0.143.6 3.793 0.042 0.195.4 5.511 0.064 0.117.2 7.324 0.045 0.129.0 8.956 0.127 20.0410.8 10.687 0.147 20.1112.6 12.656 0.079 0.0614.4 14.411 0.115 0.01Conclusion: A new embedded ranging system in the ISM band is pro-posed. The concept does not require a separate dedicated transceiver andis fully compliant with the spectral requirements, even though it usesboth broadband and narrowband signals. Experimental results in a multi-path environment show that a very high accuracy can be achieved.Acknowledgment: The authors thank the IWT Vlaanderen for ﬁnancialsupport under the scope of the project ELOCA.# The Institution of Engineering and Technology 200823 April 2008Electronics Letters online no: 20081157doi: 10.1049/el:20081157X. Yin, J. Bauwelinck, G. Torfs, P. Demuytere and J. Vandewege(INTEC/IMEC, Ghent University, Sint-Pietersnieuwstraat 41, GhentB-9000, Belgium)E-mail: xin.yin@intec.ugent.beH. Tubbax, J. Wouters, P. Debacker, J. Olbrechts, P. Spiessens,F. Stubbe and J. Danneels (Essensium, Gaston Geenslaan 9, LeuvenB-3001, Belgium)References1 Gezici, S., Tian, Z., Giannakis, G., Kobayashi, H., Molisch, A., Poor, V.,and Sahinoglu, Z.: ‘Localization via ultra-wideband radios’, IEEE SignalProcess. Mag., 2005, 22, (4), pp. 70–842 Kaemarungsi, K.: ‘Distribution of WLAN received signal strengthindication for indoor location determination’. 2006 1st Int. Symp. onWireless Pervasive Computing, Phuket, Thailand, January 20063 Gu¨nther, A., and Hoene, C.: ‘Measuring round trip times to determine thedistance between WLAN nodes’, Networking, 2005, pp. 768–7794 Werb, J.P.: ‘Hybrid real time locating system and methodology’,International Patent Application, WO 02/088776 A2, May 20025 Vandenameele, P.: ‘Method for estimating distance between transmitterand receiver, and transmitter and receiver implementing same’,International Patent no. WO2007071748 A1, June 2007CS LETTERS 14th August 2008 Vol. 44 No. 17

Embedded ranging system in ISM band

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Embedded ranging system in ISM band

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