Research ArticleExperimental Results of a Differential Angle-of-Arrival Based2D Localization Method Using Signals of Opportunity

M A Aziz 1 and C T Allen2

1Maury Microwave Corporation Ontario CA USA2Electrical and Computer Engineering University of Kansas Lawrence KS USA

Correspondence should be addressed to M A Aziz masudalazizoutlookcom

Received 29 October 2017 Revised 11 February 2018 Accepted 20 February 2018 Published 25 March 2018

Academic Editor Sandro M Radicella

Copyright copy 2018 M A Aziz and C T Allen This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This paper presents a study of differential AoA (Angle-of-Arrival) based 2D localization method utilizing FM radio signals(88MHzndash108MHz) as Signals of Opportunity (SOP) Given prior knowledge of the transmittersrsquo position and signal characteristicsthe proposed technique utilizes triangulation to localize receiverrsquos 2D position Dual antenna interferometry provides the receivedsignalsrsquo AoA required for triangulation Reliance on precise knowledge of antenna systemrsquos orientation is removed by utilizingdifferential Angle of Arrivals (dAoAs) The 2D localization accuracy is improved by utilizing colocated transmitters a conceptproposed in this paper as supertowers Analysis simulation and ground-based experiments have been presented results showedthat when the SNR (Signal-to-Noise Ratio) is higher than 45 dB the proposed method localizes the receiverrsquos 2D position with anerror of less than 15m

1 Introduction

Satellite based navigation system such as GNSS (GlobalNavigation Satellite System) suffers from poor availabilityin challenging environments such as indoor or urban areaand is subject to detrimental interferences such as jammingand spoofing [1] Due to a plethora of ambient RF signals anew paradigm termed asOpNav (Opportunistic Navigation)using SOP (Signal of Opportunity) has been proposed toovercome the limitation of satellite based navigation system[2] SOPs are signals that are transmitted for purposes otherthan navigation such as AMFM radio [3] cellular [4] digitaltelevision [5] iridium satellite [6] and Wi-Fi signals [7 8]

Current trends in OpNav are based on trilateration(where timing of the transmitted signal is known a priori)and triangulation (where the antenna systemrsquos orientationis known a priori) A dAoA (differential Angle-of-Arrival)based localization system eliminates the aforementionedrequirements where neither the timing of the transmittedsignals nor the antenna systemrsquos orientation needs to beknown a priori Moreover in AoA (Angle-of-Arrival) basedlocalization system the receiver needs to track an off-groundsource accurately to eliminate the spurious effect caused

by the phase difference in the plane defined by the lineof sight and the line of separation of the apertures [9]Therefore this paper proposes a dAoA based 2D localizationmethod utilizing FM radio signals as SOP The choice ofFM radio signals (88MHzndash108MHz) as SOP lies in the factthat the numbers of FM band transmitters are often higherin number than its SOP counterparts and FM transmittersfor different FM stations (operating at different frequencies)are often colocated on the same tower and thus providesan opportunity to improve the localization accuracy bypostprocessing AoAs of the colocated FM transmitters

The contribution of this paper is twofold First it demon-strates a dAoA based 2D localization method that eliminatesrequirement of knowledge about antenna systemrsquos orienta-tion Second it presents the experimental results supportingthe claim that the localization accuracy can be improved byexploiting supertowers In this paper supertowers are termedas towers that host two or more FM transmitters operating atdifferent frequencies

The proposed concept is appropriate for applicationssuch as indoor (eg arenas office spaces warehouses hos-pitals hangers and homes) and underground (eg caves

HindawiInternational Journal of Navigation and ObservationVolume 2018 Article ID 5470895 6 pageshttpsdoiorg10115520185470895

2 International Journal of Navigation and Observation

Rx

dAo13

dAo32

H

dAo21

TＲ1 TＲ2

TＲ3

Figure 1 dAoAs between transmitter pairs

mines bunkers and tunnels) 2D localization where signalsfrom satellite are unavailable or received signal strength fromsatellite is low for accurate localization

2 Model Description

The dAoA based triangulation is based on dAoAs betweenSOP transmitters (Tx) as shown in Figure 1

In Figure 1 Tx119909 is the state vector of the SOP transmitter119909with 2D position states (Tx119909 ≜ [119883119909 119884119909]119879) Rx is the receiverstate vector with 2D position states (Rx ≜ [119883 119884]119879) anddAoA119909119910 is the difference between AoA119909 and AoA119910 as shownin

dAoA119909119910 = AoA119909 minus AoA119910 (1)

where AoA119909 and AoA119910 are the AoAs from transmitters 119909 and119910 respectively The AoAs can be measured exploiting a twoantenna element interferometry as shown in

120579 = cosminus1 ( 1205822120587119889120593) (2)

where 120593 is the phase difference between the received signalsat two antenna elements 119889 is the separation between antennaelements (119889 le 1205822 where 120582 is the wavelength at the operatingfrequency) and 120579 is the AoA of the corresponding SOP Txrelative to the interferometry baseline With a set of at least 3SOP Tx a set of simultaneous equations can be constructedand the 2D localization of the receiver can be resolved

3 Higher Localization AccuracyUtilizing Supertowers

FM band signals spread from 88MHz to 108MHz with200 kHz channel spacing However during the FFT of thereceived signals a 10 kHz frequency bin was found to bethe optimum to maximize SNR and extract accurate phaseinformation This leads to a question of which frequencybin or bins are to be selected to measure accurate AoA andsupertowers provide the answer on which frequency bins tochoose

0

0005

001

0015

002

0025

003

Ｉ(∘)

500 1000 1500 20000

N４

SN２ = 40 dBSN２ = 45 dBSN２ = 50 dB

SN２ = 55 dBSN２ = 60 dB

Figure 2 AoA accuracy versus119873FFT versus SNR

The phase differences between the received signals thatare transmitted from two colocated FM transmitters (trans-mitting at different frequencies) should be related to eachother as shown in

cosminus1 ( 12058212120587119889120593) = cosminus1 ( 12058222120587119889120593

1015840) (3)

where 120593 and 1205931015840 are the phase differences between the samereceived signals at two different sensors from colocated FMtransmitters It can be seen in (3) that the product of phasedifference (120593) and 1205822120587119889 should be equal to each otherfor colocated FM transmitters This mathematical conditioncan then be applied to find the optimum frequency bin tocalculate AoA accurately

4 Simulation

The dAoA based 2D localization accuracy depends on theAoA accuracy of each SOP transmitter The measured AoAof a Tx is a function of the number of samples during FFT(119873FFT) SNR (Signal-to-Noise Ratio) of the received signal atthe receiver and the spacing between Rx antenna elementsThe received signal is assumed to have a thermal noisespectrum that is modelled by Gaussian Random sequenceThe received signals at two antenna elements are thenmodelled by signal + noise contribution with a set of SNRand 119873FFT The AoAs are then averaged over 1000 trials andthe corresponding standard deviation of AoA error (120590AoA) isshown in Figure 2

It can be seen in Figure 2 that theAoAaccuracy reaches itsoptimum value after 1024 samples In order to find the impactof AoA error (120590AoA) on 2D localization a Gaussian Randomsequence of 1024 samples has been modelled as 120590AoA and

International Journal of Navigation and Observation 3

SN２ = 45 dB N４ = 1024

025 045005Spacing between Rx antennas (d)

0

0005

001

0015

002

0025

003

0035

Ｉ(∘)

Figure 3 AoA accuracy versus spacing between Rx antennaelements

0

1

2

3

4

5

AoA

2

minus

2

minus

Figure 4 A uniformly spaced 5 elements (identical) Rx antennaarray for measuring AoA

Table 1 Impact of AoA accuracy over Rx localization

(120590AoA1 120590AoA2 120590AoA3) (degree) Localization error (m)(005 minus005 005) 1195(0025 minus0025 0025) 718(001 minus001 001) 239(0005 minus0005 0005) 119

added to true AoAThe resulting AoAs are then triangulatedto find the localization error and the result is shown in Table 1

In this paper the localization accuracy is targeted to beless than 15m and thus a minimum SNR of 45 dB has beenchosen based on Figure 2 and Table 1

The effect of spacing between antenna elements wasinvestigated while keeping119873FFT fixed to 1024 and SNR fixedto 45 dB as shown in Figure 3

In this paper the spacing between the Rx antennas waschosen to be 1205822 where 120582 is the free-space wavelength Theassumed values of all the parameters are shown in Table 2

The effect of number of Rx antenna elements on the AoAaccuracy has also been studied Consider 5 uniformly spacedantenna arrays with identical antenna elements as shown inFigure 4

In Figure 4 the spacing between the antenna elements arechosen to be 1205822 and Tx transmitters are considered to be in

Table 2 Assumed values of the parameters that affectAoA accuracy

Parameter Value119873FFT 1024SNR 45 dB

Separation between Rx antenna elements 1205822

Table 3 120590AoA (∘) values for different Rx antenna combinations

Antenna pair 120590AoA (∘)1 2 000332 3 000283 4 000354 5 00032Average 00032

the far field of the Rx antennas and thus the receiving wavesare plane waves The AoAs are then calculated for each Rxpair with a separation of 1205822 between them Finally all theAoAs from all the pairs are averaged to find out the effect ofnumber of antenna elements as shown in Table 3

It can be seen in Table 3 that the AoA accuracy from the5 elements antenna array is similar to that obtained from a 2-elements antenna array interferometry However a 2-elementantenna array introduces an AoA ambiguity between (minus120587 0)and (0120587)Therefore a third element is necessary to eliminatethe AoA ambiguity Thus a 3-elements antenna array is theoptimum size for accurate and ambiguity free interferometry

5 Minimum Clearance Conditionbetween Tx and Rx

It is shown in [10] that the LoS (Line of Sight) calculation isbased on earthrsquos radius as well as the altitudes of the Tx andRx as shown in

119877 = radic2119870119877earth (radicℎ1 + radicℎ2) (4)

where 119877 is the total LoS 119877earth is the radius of the earth ℎ1and ℎ2 are the Tx and the Rx antenna heights respectivelyand 119896 is the 119896-factor of the earth bulge Under normal weathercondition 119896 = 43 whereas it becomes less than 1 in stormyweather to cause fading in transmission Therefore (4) canbe expressed as in (5) to calculate LoS under normal weathercondition

119877 = 141 (radicℎ1 + radicℎ2) (5)

where 119877 is the total LoS in miles and ℎ1 and ℎ2 are infeet For example with a Tx antenna altitude of 600 feet(typical of an FM tower) and a Rx antenna altitude of 400 feet(representative of the altitude ceiling for a small UAV undercurrent FAA rules) the maximum range can be estimatedfrom (5) to be 6273 miles or 100 km On the other handwith the same Tx antenna height but with a 6 feet Rxantenna height (typical of a ground-based measurement)

4 International Journal of Navigation and Observation

Filter Stream to vectorUSRP FFT

Vector to stream Database

Figure 5 A generic GRC flow graph

Options

Variable

Variable

Variable

in

in

inin

in in

in

in

in

in

in

in

in

in

in

out

out

out

out

out out

outout

out

out

out0

out1Complex to Mag

Complex to Arg

Complex to Mag

Complex to Arg

Freq Set Varname None

WX GUI FFT SinkTitle FFT PlotSample Rate 2048MBaseband Freq 87MY per Div 10 dBY Divs 10Ref Level (dB) 0Ref Scale (p2p) 2FFT Size 2048kRefresh Rate 15

Ch0 Center Freq (Hz) 87MCh0 Gain (dB) 0Ch0 Antenna TXRXCh1 Center Freq (Hz) 87MCh1 Gain (dB) 0Ch1 Antenna TXRX

UHD USRP SourceSamp Rate (Sps) 2048M

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_2_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_2_cStream to Vector

Num Items 2048k

Stream to VectorNum Items 2048k

Vector to StreamNum Items 2048k

Vector to StreamNum Items 2048k

Value 2048k

Value 87M

ID samp_rate

Generate Options WX GUIID top_block

ID F

ID N

Value 2048M

Figure 6 GRC flow graph for SDR card to receive two signals at two ports

the maximum range shrinks to 60 km Since the proposedlocalization method is demonstrated based on FM transmit-ters and ground-based measurement the maximum range isestimated to be 60 km for this paper

6 Measurement Setup

The proposed method has been validated by performingmeasurement utilizing a dual channel receiver using SDR(Software Defined Radio model B210) [11] The B210 SDRcard contains 2Tx and 2Rx ports with fully coherent 2 times 2MIMO (Multiple Input Multiple Output) capabilities Thecoherency between the Rx ports is an essential feature forextracting accurate phase difference between the receivedsignals Moreover the SDR card covers RF frequencies from70MHz to 6GHz with a bandwidth of maximum 3072MHzin 2 times 2 MIMOmodes Thus the B210 SDR card was an idealcandidate for this project Besides the B210 board comeswithan AD9361 chip that performs the function of ADC and DSP

The receiver utilizes 2-element antenna array interferom-etry to extract the phase difference between its 2 channelsThe measured phase difference is then utilized to calculatethe AoAs dAoAs and 2D position estimate The SDR cardwas configured with the GNU Radio Companion (GRC)interface GRC is a graphical user interface to build GNU

radio flow graphs or the software circuits The GNU radioflow graph enables the SDR card to receive signals from thetwo antennas spectrally isolate them and then calculate thephase difference between the received signals A generic blockdiagram of GRC flow graph is shown in Figure 5

A description of all the blocks can be found in [12] Asample implementation of each block in Figure 5 is shownin Figure 6

A picture of the complete measurement setup is shown inFigure 7

7 Experimental Results

Ground-based experiment was conducted at Blue ValleyPark in Kansas City MO in USA The serving FM bandTx locations were found in FCC database [13] as shown inTable 4

The SNR of all the frequency bins for all the Tx frequen-cies at tower 2 is shown in Figure 8(a)Moreover the productsof phase differences and 1205822120587119889 are shown in Figure 8(b)

The selection of the appropriate frequency bin dependson two factors such as the SNR gt 45 dB (Figure 8(a)) and theproduct terms being close to each other Based onFigures 8(a)and 8(b) the optimum frequency bins for tower 2 are foundas shown in Table 5

International Journal of Navigation and Observation 5

SDR card

Antennas

Figure 7 A picture of the complete measurement setup

Table 4 The colocated FM transmitters

Tower index Tx frequency (MHz)1 885 - - -2 933 1033 941 -3 893 1043 - -4 949 1021 1051 9735 901 - - -

Table 5 Calculated AoAs from optimum frequency bins for tower2

Tx freq (MHz) Calc AoA (∘) Optimum bin Highest SNR bin933 minus28137 11 111033 minus2842 12 12941 minus2848 15 14

The AoA of tower 2 is then calculated to be the averageof all 3 AoAs It should be noted here that the optimumfrequency bin is not the frequency bin with the highest SNRA similar algorithmwas applied to towers 3 and 4 to calculatethe corresponding AoAs

The calculated AoAs are then triangulated to localize thereceiver and the Rx position error is calculated as shown in

120576pos= radic(Rx119909 (true) minus Rx119909 (calc))2 + (Rx119910 (true) minus Rx119910 (calc))2

(6)

where (Rx119909(true) Rx119910(true)) are the true Rx positions(Rx119909(calc) Rx119910(calc)) are the calculated Rx positions and120576pos is the localization error in meters The resultant local-ization error for with and without supertowers are shown inTable 6

It can be seen from Table 6 that the localization accuracyis finest when utilizing all 3 supertowers

0 2 4 6 8 10 12 14 16 18Frequency bin index

0

10

20

30

40

50

60

70

80

90

100

SNR

(dB)

941 MHz1033 MHz933 MHz SN２ = 45 dB

(a)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Frequency bin index

941 MHz1033 MHz933 MHz

0

01

02

03

04

05

06

07

08

09minusΔ

(2

d

)

(b)

Figure 8 (a) Phase difference between received signals from tower2 (b) Product of 120593 and 1205822120587119889 for all transmitted signals from tower2

8 Conclusion

In this paper a dAoA based 2D localization method hasbeen demonstrated using FM radio signals as SOP A pathto utilize colocated FM transmitters to obtain further local-ization accuracy has been proposed and validated throughexperimental results It has been shown that the utilizationof all supertowers provides the least error of 13m in 2Dlocalization

6 International Journal of Navigation and Observation

Table 6 A comparison of localization with and without supertowers

Number of used supertowers Indices of the used supertowers Localization error 120576pos (m)3 2 3 and 4 12572 1 2 and 3 32552 1 2 and 4 22432 1 3 and 4 46372 2 3 and 5 33432 2 4 and 5 30372 3 4 and 5 48281 1 2 and 5 26351 1 3 and 5 63311 1 4 and 5 3048

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] S DrsquoAddio and M Martin-Neira ldquoComparison of processingtechniques for remote sensing of earth-exploiting reflectedradio-navigation signalsrdquo IEEE Electronics Letters vol 49 no4 pp 297-298 2013

[2] L A Merry R M Faragher and S Scheding ldquoComparison ofOpportunistic Signals for Localisationrdquo in Proceedings of the 7thIFAC Symposium on Intelligent Autonomous Vehicles vol 43 pp109ndash114 2010

[3] V Moghtadaiee and A G Dempster ldquoIndoor location fin-gerprinting using FM radio signalsrdquo IEEE Transactions onBroadcasting vol 60 no 2 pp 336ndash346 2014

[4] C Yang T Nguyen and E Blasch ldquoMobile positioning viafusion of mixed signals of opportunityrdquo IEEE Aerospace andElectronic Systems Magazine vol 29 no 4 pp 34ndash46 2014

[5] M Rabinowitz and J J Spilker Jr ldquoA new positioning systemusing television synchronization signalsrdquo IEEE Transactions onBroadcasting vol 51 no 1 pp 51ndash61 2005

[6] M Joerger L Gratton B Pervan and C E Cohen ldquoAnalysis ofIridium-augmented GPS for floating carrier phase positioningrdquoNAVIGATION Journal of the Institute of Navigation vol 57 no2 pp 137ndash160 2010

[7] I Bisio M Cerruti F Lavagetto et al ldquoA trainingless WiFifingerprint positioning approach over mobile devicesrdquo IEEEAntennas and Wireless Propagation Letters vol 13 pp 832ndash8352014

[8] Z M Kassas and T E Humphreys ldquoReceding horizon trajec-tory optimization in opportunistic navigation environmentsrdquoIEEE Transactions on Aerospace and Electronic Systems vol 51no 2 pp 866ndash877 2015

[9] D L Fried ldquoDifferential angle of arrivalTheory evaluation andmeasurement feasibilityrdquo Radio Science vol 10 no 1 pp 71ndash761975

[10] C Haslett Essentials of Radio Wave Propagation CambridgeUniversity Press 2008

[11] Ettus Research USRP B210 (Board Only) httpwwwettuscomcontentfilesb200-b210specsheetpdf

[12] M A Aziz Navigation for UAVs using Signals of Opportunity[PhD thesis] Dept of Electrical Engineering University ofKansas USA 2015

[13] httpwwwzipsignalv-softcom 2015

International Journal of Navigation and Observation 3

SN２ = 45 dB N４ = 1024

025 045005Spacing between Rx antennas (d)

0

0005

001

0015

002

0025

003

0035

Ｉ(∘)

Figure 3 AoA accuracy versus spacing between Rx antennaelements

0

1

2

3

4

5

AoA

2

minus

2

minus

Figure 4 A uniformly spaced 5 elements (identical) Rx antennaarray for measuring AoA

Table 1 Impact of AoA accuracy over Rx localization

(120590AoA1 120590AoA2 120590AoA3) (degree) Localization error (m)(005 minus005 005) 1195(0025 minus0025 0025) 718(001 minus001 001) 239(0005 minus0005 0005) 119

added to true AoAThe resulting AoAs are then triangulatedto find the localization error and the result is shown in Table 1

In this paper the localization accuracy is targeted to beless than 15m and thus a minimum SNR of 45 dB has beenchosen based on Figure 2 and Table 1

The effect of spacing between antenna elements wasinvestigated while keeping119873FFT fixed to 1024 and SNR fixedto 45 dB as shown in Figure 3

In this paper the spacing between the Rx antennas waschosen to be 1205822 where 120582 is the free-space wavelength Theassumed values of all the parameters are shown in Table 2

The effect of number of Rx antenna elements on the AoAaccuracy has also been studied Consider 5 uniformly spacedantenna arrays with identical antenna elements as shown inFigure 4

In Figure 4 the spacing between the antenna elements arechosen to be 1205822 and Tx transmitters are considered to be in

Table 2 Assumed values of the parameters that affectAoA accuracy

Parameter Value119873FFT 1024SNR 45 dB

Separation between Rx antenna elements 1205822

Table 3 120590AoA (∘) values for different Rx antenna combinations

Antenna pair 120590AoA (∘)1 2 000332 3 000283 4 000354 5 00032Average 00032

the far field of the Rx antennas and thus the receiving wavesare plane waves The AoAs are then calculated for each Rxpair with a separation of 1205822 between them Finally all theAoAs from all the pairs are averaged to find out the effect ofnumber of antenna elements as shown in Table 3

It can be seen in Table 3 that the AoA accuracy from the5 elements antenna array is similar to that obtained from a 2-elements antenna array interferometry However a 2-elementantenna array introduces an AoA ambiguity between (minus120587 0)and (0120587)Therefore a third element is necessary to eliminatethe AoA ambiguity Thus a 3-elements antenna array is theoptimum size for accurate and ambiguity free interferometry

5 Minimum Clearance Conditionbetween Tx and Rx

It is shown in [10] that the LoS (Line of Sight) calculation isbased on earthrsquos radius as well as the altitudes of the Tx andRx as shown in

119877 = radic2119870119877earth (radicℎ1 + radicℎ2) (4)

where 119877 is the total LoS 119877earth is the radius of the earth ℎ1and ℎ2 are the Tx and the Rx antenna heights respectivelyand 119896 is the 119896-factor of the earth bulge Under normal weathercondition 119896 = 43 whereas it becomes less than 1 in stormyweather to cause fading in transmission Therefore (4) canbe expressed as in (5) to calculate LoS under normal weathercondition

119877 = 141 (radicℎ1 + radicℎ2) (5)

where 119877 is the total LoS in miles and ℎ1 and ℎ2 are infeet For example with a Tx antenna altitude of 600 feet(typical of an FM tower) and a Rx antenna altitude of 400 feet(representative of the altitude ceiling for a small UAV undercurrent FAA rules) the maximum range can be estimatedfrom (5) to be 6273 miles or 100 km On the other handwith the same Tx antenna height but with a 6 feet Rxantenna height (typical of a ground-based measurement)

4 International Journal of Navigation and Observation

Filter Stream to vectorUSRP FFT

Vector to stream Database

Figure 5 A generic GRC flow graph

Options

Variable

Variable

Variable

in

in

inin

in in

in

in

in

in

in

in

in

in

in

out

out

out

out

out out

outout

out

out

out0

out1Complex to Mag

Complex to Arg

Complex to Mag

Complex to Arg

Freq Set Varname None

WX GUI FFT SinkTitle FFT PlotSample Rate 2048MBaseband Freq 87MY per Div 10 dBY Divs 10Ref Level (dB) 0Ref Scale (p2p) 2FFT Size 2048kRefresh Rate 15

Ch0 Center Freq (Hz) 87MCh0 Gain (dB) 0Ch0 Antenna TXRXCh1 Center Freq (Hz) 87MCh1 Gain (dB) 0Ch1 Antenna TXRX

UHD USRP SourceSamp Rate (Sps) 2048M

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_2_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_2_cStream to Vector

Num Items 2048k

Stream to VectorNum Items 2048k

Vector to StreamNum Items 2048k

Vector to StreamNum Items 2048k

Value 2048k

Value 87M

ID samp_rate

Generate Options WX GUIID top_block

ID F

ID N

Value 2048M

Figure 6 GRC flow graph for SDR card to receive two signals at two ports

the maximum range shrinks to 60 km Since the proposedlocalization method is demonstrated based on FM transmit-ters and ground-based measurement the maximum range isestimated to be 60 km for this paper

6 Measurement Setup

The proposed method has been validated by performingmeasurement utilizing a dual channel receiver using SDR(Software Defined Radio model B210) [11] The B210 SDRcard contains 2Tx and 2Rx ports with fully coherent 2 times 2MIMO (Multiple Input Multiple Output) capabilities Thecoherency between the Rx ports is an essential feature forextracting accurate phase difference between the receivedsignals Moreover the SDR card covers RF frequencies from70MHz to 6GHz with a bandwidth of maximum 3072MHzin 2 times 2 MIMOmodes Thus the B210 SDR card was an idealcandidate for this project Besides the B210 board comeswithan AD9361 chip that performs the function of ADC and DSP

The receiver utilizes 2-element antenna array interferom-etry to extract the phase difference between its 2 channelsThe measured phase difference is then utilized to calculatethe AoAs dAoAs and 2D position estimate The SDR cardwas configured with the GNU Radio Companion (GRC)interface GRC is a graphical user interface to build GNU

radio flow graphs or the software circuits The GNU radioflow graph enables the SDR card to receive signals from thetwo antennas spectrally isolate them and then calculate thephase difference between the received signals A generic blockdiagram of GRC flow graph is shown in Figure 5

A description of all the blocks can be found in [12] Asample implementation of each block in Figure 5 is shownin Figure 6

A picture of the complete measurement setup is shown inFigure 7

7 Experimental Results

Ground-based experiment was conducted at Blue ValleyPark in Kansas City MO in USA The serving FM bandTx locations were found in FCC database [13] as shown inTable 4

The SNR of all the frequency bins for all the Tx frequen-cies at tower 2 is shown in Figure 8(a)Moreover the productsof phase differences and 1205822120587119889 are shown in Figure 8(b)

The selection of the appropriate frequency bin dependson two factors such as the SNR gt 45 dB (Figure 8(a)) and theproduct terms being close to each other Based onFigures 8(a)and 8(b) the optimum frequency bins for tower 2 are foundas shown in Table 5

International Journal of Navigation and Observation 5

SDR card

Antennas

Figure 7 A picture of the complete measurement setup

Table 4 The colocated FM transmitters

Tower index Tx frequency (MHz)1 885 - - -2 933 1033 941 -3 893 1043 - -4 949 1021 1051 9735 901 - - -

Table 5 Calculated AoAs from optimum frequency bins for tower2

Tx freq (MHz) Calc AoA (∘) Optimum bin Highest SNR bin933 minus28137 11 111033 minus2842 12 12941 minus2848 15 14

The AoA of tower 2 is then calculated to be the averageof all 3 AoAs It should be noted here that the optimumfrequency bin is not the frequency bin with the highest SNRA similar algorithmwas applied to towers 3 and 4 to calculatethe corresponding AoAs

The calculated AoAs are then triangulated to localize thereceiver and the Rx position error is calculated as shown in

120576pos= radic(Rx119909 (true) minus Rx119909 (calc))2 + (Rx119910 (true) minus Rx119910 (calc))2

(6)

where (Rx119909(true) Rx119910(true)) are the true Rx positions(Rx119909(calc) Rx119910(calc)) are the calculated Rx positions and120576pos is the localization error in meters The resultant local-ization error for with and without supertowers are shown inTable 6

It can be seen from Table 6 that the localization accuracyis finest when utilizing all 3 supertowers

0 2 4 6 8 10 12 14 16 18Frequency bin index

0

10

20

30

40

50

60

70

80

90

100

SNR

(dB)

941 MHz1033 MHz933 MHz SN２ = 45 dB

(a)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Frequency bin index

941 MHz1033 MHz933 MHz

0

01

02

03

04

05

06

07

08

09minusΔ

(2

d

)

(b)

Figure 8 (a) Phase difference between received signals from tower2 (b) Product of 120593 and 1205822120587119889 for all transmitted signals from tower2

8 Conclusion

In this paper a dAoA based 2D localization method hasbeen demonstrated using FM radio signals as SOP A pathto utilize colocated FM transmitters to obtain further local-ization accuracy has been proposed and validated throughexperimental results It has been shown that the utilizationof all supertowers provides the least error of 13m in 2Dlocalization

6 International Journal of Navigation and Observation

Table 6 A comparison of localization with and without supertowers

Number of used supertowers Indices of the used supertowers Localization error 120576pos (m)3 2 3 and 4 12572 1 2 and 3 32552 1 2 and 4 22432 1 3 and 4 46372 2 3 and 5 33432 2 4 and 5 30372 3 4 and 5 48281 1 2 and 5 26351 1 3 and 5 63311 1 4 and 5 3048

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] S DrsquoAddio and M Martin-Neira ldquoComparison of processingtechniques for remote sensing of earth-exploiting reflectedradio-navigation signalsrdquo IEEE Electronics Letters vol 49 no4 pp 297-298 2013

[2] L A Merry R M Faragher and S Scheding ldquoComparison ofOpportunistic Signals for Localisationrdquo in Proceedings of the 7thIFAC Symposium on Intelligent Autonomous Vehicles vol 43 pp109ndash114 2010

[3] V Moghtadaiee and A G Dempster ldquoIndoor location fin-gerprinting using FM radio signalsrdquo IEEE Transactions onBroadcasting vol 60 no 2 pp 336ndash346 2014

[4] C Yang T Nguyen and E Blasch ldquoMobile positioning viafusion of mixed signals of opportunityrdquo IEEE Aerospace andElectronic Systems Magazine vol 29 no 4 pp 34ndash46 2014

[5] M Rabinowitz and J J Spilker Jr ldquoA new positioning systemusing television synchronization signalsrdquo IEEE Transactions onBroadcasting vol 51 no 1 pp 51ndash61 2005

[6] M Joerger L Gratton B Pervan and C E Cohen ldquoAnalysis ofIridium-augmented GPS for floating carrier phase positioningrdquoNAVIGATION Journal of the Institute of Navigation vol 57 no2 pp 137ndash160 2010

[7] I Bisio M Cerruti F Lavagetto et al ldquoA trainingless WiFifingerprint positioning approach over mobile devicesrdquo IEEEAntennas and Wireless Propagation Letters vol 13 pp 832ndash8352014

[8] Z M Kassas and T E Humphreys ldquoReceding horizon trajec-tory optimization in opportunistic navigation environmentsrdquoIEEE Transactions on Aerospace and Electronic Systems vol 51no 2 pp 866ndash877 2015

[9] D L Fried ldquoDifferential angle of arrivalTheory evaluation andmeasurement feasibilityrdquo Radio Science vol 10 no 1 pp 71ndash761975

[10] C Haslett Essentials of Radio Wave Propagation CambridgeUniversity Press 2008

[11] Ettus Research USRP B210 (Board Only) httpwwwettuscomcontentfilesb200-b210specsheetpdf

[12] M A Aziz Navigation for UAVs using Signals of Opportunity[PhD thesis] Dept of Electrical Engineering University ofKansas USA 2015

[13] httpwwwzipsignalv-softcom 2015

4 International Journal of Navigation and Observation

Filter Stream to vectorUSRP FFT

Vector to stream Database

Figure 5 A generic GRC flow graph

Options

Variable

Variable

Variable

in

in

inin

in in

in

in

in

in

in

in

in

in

in

out

out

out

out

out out

outout

out

out

out0

out1Complex to Mag

Complex to Arg

Complex to Mag

Complex to Arg

Freq Set Varname None

WX GUI FFT SinkTitle FFT PlotSample Rate 2048MBaseband Freq 87MY per Div 10 dBY Divs 10Ref Level (dB) 0Ref Scale (p2p) 2FFT Size 2048kRefresh Rate 15

Ch0 Center Freq (Hz) 87MCh0 Gain (dB) 0Ch0 Antenna TXRXCh1 Center Freq (Hz) 87MCh1 Gain (dB) 0Ch1 Antenna TXRX

UHD USRP SourceSamp Rate (Sps) 2048M

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

FFTFFT Size 2048kForwardReverse ForwardWindow windowblackmanhar Shift YesNum Threads 1

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_1_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_mag_2_c

File Sink

Unbuffered OffAppend file Overwrite

File formanceFFT_phi_2_cStream to Vector

Num Items 2048k

Stream to VectorNum Items 2048k

Vector to StreamNum Items 2048k

Vector to StreamNum Items 2048k

Value 2048k

Value 87M

ID samp_rate

Generate Options WX GUIID top_block

ID F

ID N

Value 2048M

Figure 6 GRC flow graph for SDR card to receive two signals at two ports

the maximum range shrinks to 60 km Since the proposedlocalization method is demonstrated based on FM transmit-ters and ground-based measurement the maximum range isestimated to be 60 km for this paper

6 Measurement Setup

The proposed method has been validated by performingmeasurement utilizing a dual channel receiver using SDR(Software Defined Radio model B210) [11] The B210 SDRcard contains 2Tx and 2Rx ports with fully coherent 2 times 2MIMO (Multiple Input Multiple Output) capabilities Thecoherency between the Rx ports is an essential feature forextracting accurate phase difference between the receivedsignals Moreover the SDR card covers RF frequencies from70MHz to 6GHz with a bandwidth of maximum 3072MHzin 2 times 2 MIMOmodes Thus the B210 SDR card was an idealcandidate for this project Besides the B210 board comeswithan AD9361 chip that performs the function of ADC and DSP

The receiver utilizes 2-element antenna array interferom-etry to extract the phase difference between its 2 channelsThe measured phase difference is then utilized to calculatethe AoAs dAoAs and 2D position estimate The SDR cardwas configured with the GNU Radio Companion (GRC)interface GRC is a graphical user interface to build GNU

radio flow graphs or the software circuits The GNU radioflow graph enables the SDR card to receive signals from thetwo antennas spectrally isolate them and then calculate thephase difference between the received signals A generic blockdiagram of GRC flow graph is shown in Figure 5

A description of all the blocks can be found in [12] Asample implementation of each block in Figure 5 is shownin Figure 6

A picture of the complete measurement setup is shown inFigure 7

7 Experimental Results

Ground-based experiment was conducted at Blue ValleyPark in Kansas City MO in USA The serving FM bandTx locations were found in FCC database [13] as shown inTable 4

The SNR of all the frequency bins for all the Tx frequen-cies at tower 2 is shown in Figure 8(a)Moreover the productsof phase differences and 1205822120587119889 are shown in Figure 8(b)

The selection of the appropriate frequency bin dependson two factors such as the SNR gt 45 dB (Figure 8(a)) and theproduct terms being close to each other Based onFigures 8(a)and 8(b) the optimum frequency bins for tower 2 are foundas shown in Table 5

International Journal of Navigation and Observation 5

SDR card

Antennas

Figure 7 A picture of the complete measurement setup

Table 4 The colocated FM transmitters

Tower index Tx frequency (MHz)1 885 - - -2 933 1033 941 -3 893 1043 - -4 949 1021 1051 9735 901 - - -

Table 5 Calculated AoAs from optimum frequency bins for tower2

Tx freq (MHz) Calc AoA (∘) Optimum bin Highest SNR bin933 minus28137 11 111033 minus2842 12 12941 minus2848 15 14

The AoA of tower 2 is then calculated to be the averageof all 3 AoAs It should be noted here that the optimumfrequency bin is not the frequency bin with the highest SNRA similar algorithmwas applied to towers 3 and 4 to calculatethe corresponding AoAs

The calculated AoAs are then triangulated to localize thereceiver and the Rx position error is calculated as shown in

120576pos= radic(Rx119909 (true) minus Rx119909 (calc))2 + (Rx119910 (true) minus Rx119910 (calc))2

(6)

where (Rx119909(true) Rx119910(true)) are the true Rx positions(Rx119909(calc) Rx119910(calc)) are the calculated Rx positions and120576pos is the localization error in meters The resultant local-ization error for with and without supertowers are shown inTable 6

It can be seen from Table 6 that the localization accuracyis finest when utilizing all 3 supertowers

0 2 4 6 8 10 12 14 16 18Frequency bin index

0

10

20

30

40

50

60

70

80

90

100

SNR

(dB)

941 MHz1033 MHz933 MHz SN２ = 45 dB

(a)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Frequency bin index

941 MHz1033 MHz933 MHz

0

01

02

03

04

05

06

07

08

09minusΔ

(2

d

)

(b)

Figure 8 (a) Phase difference between received signals from tower2 (b) Product of 120593 and 1205822120587119889 for all transmitted signals from tower2

8 Conclusion

In this paper a dAoA based 2D localization method hasbeen demonstrated using FM radio signals as SOP A pathto utilize colocated FM transmitters to obtain further local-ization accuracy has been proposed and validated throughexperimental results It has been shown that the utilizationof all supertowers provides the least error of 13m in 2Dlocalization

6 International Journal of Navigation and Observation

Table 6 A comparison of localization with and without supertowers

Number of used supertowers Indices of the used supertowers Localization error 120576pos (m)3 2 3 and 4 12572 1 2 and 3 32552 1 2 and 4 22432 1 3 and 4 46372 2 3 and 5 33432 2 4 and 5 30372 3 4 and 5 48281 1 2 and 5 26351 1 3 and 5 63311 1 4 and 5 3048

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] S DrsquoAddio and M Martin-Neira ldquoComparison of processingtechniques for remote sensing of earth-exploiting reflectedradio-navigation signalsrdquo IEEE Electronics Letters vol 49 no4 pp 297-298 2013

[2] L A Merry R M Faragher and S Scheding ldquoComparison ofOpportunistic Signals for Localisationrdquo in Proceedings of the 7thIFAC Symposium on Intelligent Autonomous Vehicles vol 43 pp109ndash114 2010

[3] V Moghtadaiee and A G Dempster ldquoIndoor location fin-gerprinting using FM radio signalsrdquo IEEE Transactions onBroadcasting vol 60 no 2 pp 336ndash346 2014

[4] C Yang T Nguyen and E Blasch ldquoMobile positioning viafusion of mixed signals of opportunityrdquo IEEE Aerospace andElectronic Systems Magazine vol 29 no 4 pp 34ndash46 2014

[5] M Rabinowitz and J J Spilker Jr ldquoA new positioning systemusing television synchronization signalsrdquo IEEE Transactions onBroadcasting vol 51 no 1 pp 51ndash61 2005

[6] M Joerger L Gratton B Pervan and C E Cohen ldquoAnalysis ofIridium-augmented GPS for floating carrier phase positioningrdquoNAVIGATION Journal of the Institute of Navigation vol 57 no2 pp 137ndash160 2010

[7] I Bisio M Cerruti F Lavagetto et al ldquoA trainingless WiFifingerprint positioning approach over mobile devicesrdquo IEEEAntennas and Wireless Propagation Letters vol 13 pp 832ndash8352014

[8] Z M Kassas and T E Humphreys ldquoReceding horizon trajec-tory optimization in opportunistic navigation environmentsrdquoIEEE Transactions on Aerospace and Electronic Systems vol 51no 2 pp 866ndash877 2015

[9] D L Fried ldquoDifferential angle of arrivalTheory evaluation andmeasurement feasibilityrdquo Radio Science vol 10 no 1 pp 71ndash761975

[10] C Haslett Essentials of Radio Wave Propagation CambridgeUniversity Press 2008

[11] Ettus Research USRP B210 (Board Only) httpwwwettuscomcontentfilesb200-b210specsheetpdf

[12] M A Aziz Navigation for UAVs using Signals of Opportunity[PhD thesis] Dept of Electrical Engineering University ofKansas USA 2015

[13] httpwwwzipsignalv-softcom 2015

International Journal of Navigation and Observation 5

SDR card

Antennas

Figure 7 A picture of the complete measurement setup

Table 4 The colocated FM transmitters

Tower index Tx frequency (MHz)1 885 - - -2 933 1033 941 -3 893 1043 - -4 949 1021 1051 9735 901 - - -

Table 5 Calculated AoAs from optimum frequency bins for tower2

Tx freq (MHz) Calc AoA (∘) Optimum bin Highest SNR bin933 minus28137 11 111033 minus2842 12 12941 minus2848 15 14

The AoA of tower 2 is then calculated to be the averageof all 3 AoAs It should be noted here that the optimumfrequency bin is not the frequency bin with the highest SNRA similar algorithmwas applied to towers 3 and 4 to calculatethe corresponding AoAs

The calculated AoAs are then triangulated to localize thereceiver and the Rx position error is calculated as shown in

120576pos= radic(Rx119909 (true) minus Rx119909 (calc))2 + (Rx119910 (true) minus Rx119910 (calc))2

(6)

where (Rx119909(true) Rx119910(true)) are the true Rx positions(Rx119909(calc) Rx119910(calc)) are the calculated Rx positions and120576pos is the localization error in meters The resultant local-ization error for with and without supertowers are shown inTable 6

It can be seen from Table 6 that the localization accuracyis finest when utilizing all 3 supertowers

0 2 4 6 8 10 12 14 16 18Frequency bin index

0

10

20

30

40

50

60

70

80

90

100

SNR

(dB)

941 MHz1033 MHz933 MHz SN２ = 45 dB

(a)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Frequency bin index

941 MHz1033 MHz933 MHz

0

01

02

03

04

05

06

07

08

09minusΔ

(2

d

)

(b)

Figure 8 (a) Phase difference between received signals from tower2 (b) Product of 120593 and 1205822120587119889 for all transmitted signals from tower2

8 Conclusion

In this paper a dAoA based 2D localization method hasbeen demonstrated using FM radio signals as SOP A pathto utilize colocated FM transmitters to obtain further local-ization accuracy has been proposed and validated throughexperimental results It has been shown that the utilizationof all supertowers provides the least error of 13m in 2Dlocalization

6 International Journal of Navigation and Observation

Table 6 A comparison of localization with and without supertowers

Number of used supertowers Indices of the used supertowers Localization error 120576pos (m)3 2 3 and 4 12572 1 2 and 3 32552 1 2 and 4 22432 1 3 and 4 46372 2 3 and 5 33432 2 4 and 5 30372 3 4 and 5 48281 1 2 and 5 26351 1 3 and 5 63311 1 4 and 5 3048

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] S DrsquoAddio and M Martin-Neira ldquoComparison of processingtechniques for remote sensing of earth-exploiting reflectedradio-navigation signalsrdquo IEEE Electronics Letters vol 49 no4 pp 297-298 2013

[2] L A Merry R M Faragher and S Scheding ldquoComparison ofOpportunistic Signals for Localisationrdquo in Proceedings of the 7thIFAC Symposium on Intelligent Autonomous Vehicles vol 43 pp109ndash114 2010

[3] V Moghtadaiee and A G Dempster ldquoIndoor location fin-gerprinting using FM radio signalsrdquo IEEE Transactions onBroadcasting vol 60 no 2 pp 336ndash346 2014

[4] C Yang T Nguyen and E Blasch ldquoMobile positioning viafusion of mixed signals of opportunityrdquo IEEE Aerospace andElectronic Systems Magazine vol 29 no 4 pp 34ndash46 2014

[5] M Rabinowitz and J J Spilker Jr ldquoA new positioning systemusing television synchronization signalsrdquo IEEE Transactions onBroadcasting vol 51 no 1 pp 51ndash61 2005

[6] M Joerger L Gratton B Pervan and C E Cohen ldquoAnalysis ofIridium-augmented GPS for floating carrier phase positioningrdquoNAVIGATION Journal of the Institute of Navigation vol 57 no2 pp 137ndash160 2010

[7] I Bisio M Cerruti F Lavagetto et al ldquoA trainingless WiFifingerprint positioning approach over mobile devicesrdquo IEEEAntennas and Wireless Propagation Letters vol 13 pp 832ndash8352014

[8] Z M Kassas and T E Humphreys ldquoReceding horizon trajec-tory optimization in opportunistic navigation environmentsrdquoIEEE Transactions on Aerospace and Electronic Systems vol 51no 2 pp 866ndash877 2015

[9] D L Fried ldquoDifferential angle of arrivalTheory evaluation andmeasurement feasibilityrdquo Radio Science vol 10 no 1 pp 71ndash761975

[10] C Haslett Essentials of Radio Wave Propagation CambridgeUniversity Press 2008

[11] Ettus Research USRP B210 (Board Only) httpwwwettuscomcontentfilesb200-b210specsheetpdf

[12] M A Aziz Navigation for UAVs using Signals of Opportunity[PhD thesis] Dept of Electrical Engineering University ofKansas USA 2015

[13] httpwwwzipsignalv-softcom 2015

6 International Journal of Navigation and Observation

Table 6 A comparison of localization with and without supertowers

Number of used supertowers Indices of the used supertowers Localization error 120576pos (m)3 2 3 and 4 12572 1 2 and 3 32552 1 2 and 4 22432 1 3 and 4 46372 2 3 and 5 33432 2 4 and 5 30372 3 4 and 5 48281 1 2 and 5 26351 1 3 and 5 63311 1 4 and 5 3048

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

References

[1] S DrsquoAddio and M Martin-Neira ldquoComparison of processingtechniques for remote sensing of earth-exploiting reflectedradio-navigation signalsrdquo IEEE Electronics Letters vol 49 no4 pp 297-298 2013

[2] L A Merry R M Faragher and S Scheding ldquoComparison ofOpportunistic Signals for Localisationrdquo in Proceedings of the 7thIFAC Symposium on Intelligent Autonomous Vehicles vol 43 pp109ndash114 2010

[3] V Moghtadaiee and A G Dempster ldquoIndoor location fin-gerprinting using FM radio signalsrdquo IEEE Transactions onBroadcasting vol 60 no 2 pp 336ndash346 2014

[4] C Yang T Nguyen and E Blasch ldquoMobile positioning viafusion of mixed signals of opportunityrdquo IEEE Aerospace andElectronic Systems Magazine vol 29 no 4 pp 34ndash46 2014

[5] M Rabinowitz and J J Spilker Jr ldquoA new positioning systemusing television synchronization signalsrdquo IEEE Transactions onBroadcasting vol 51 no 1 pp 51ndash61 2005

[6] M Joerger L Gratton B Pervan and C E Cohen ldquoAnalysis ofIridium-augmented GPS for floating carrier phase positioningrdquoNAVIGATION Journal of the Institute of Navigation vol 57 no2 pp 137ndash160 2010

[7] I Bisio M Cerruti F Lavagetto et al ldquoA trainingless WiFifingerprint positioning approach over mobile devicesrdquo IEEEAntennas and Wireless Propagation Letters vol 13 pp 832ndash8352014

[8] Z M Kassas and T E Humphreys ldquoReceding horizon trajec-tory optimization in opportunistic navigation environmentsrdquoIEEE Transactions on Aerospace and Electronic Systems vol 51no 2 pp 866ndash877 2015

[9] D L Fried ldquoDifferential angle of arrivalTheory evaluation andmeasurement feasibilityrdquo Radio Science vol 10 no 1 pp 71ndash761975

[10] C Haslett Essentials of Radio Wave Propagation CambridgeUniversity Press 2008

[11] Ettus Research USRP B210 (Board Only) httpwwwettuscomcontentfilesb200-b210specsheetpdf

[12] M A Aziz Navigation for UAVs using Signals of Opportunity[PhD thesis] Dept of Electrical Engineering University ofKansas USA 2015

[13] httpwwwzipsignalv-softcom 2015

International Journal of

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VLSI Design

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