Monostatic Airborne Synthetic Aperture Radar Using Commercial WiMAX Transceivers In the

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Kai Liu, The University of Western Ontario
Supervisor: Dr. Xianbin Wang, The University of Western Ontario
Joint Supervisor: Dr. Jagath Samarabandu, The University of Western Ontario
A thesis submitted in partial fulfillment of the requirements for the Master of Engineering
Science degree in Electrical and Computer Engineering
© Kai Liu 2014
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Liu, Kai, "Monostatic Airborne Synthetic Aperture Radar Using Commercial WiMAX Transceivers In the
License-exempt Spectrum" (2014). Electronic Thesis and Dissertation Repository. 2611.
https://ir.lib.uwo.ca/etd/2611
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MONOSTATIC AIRBORNE SYNTHETIC APERTURE RADAR USING
COMMERCIAL WIMAX TRANSCEIVERS IN THE LICENSE-EXEMPT
SPECTRUM
(Thesis format: Monograph)
by
Kai Liu
Graduate Program in Engineering Science of Electrical and Computer
Engineering
A thesis submitted in partial fulfillment
of the requirements for the degree of
Masters of Science Engineering
The School of Graduate and Postdoctoral Studies
The University of Western Ontario
London, Ontario, Canada
⃝c Kai Liu 2014
Abstract
The past half-century witnessed an evolution of synthetic aperture radar (SAR). Boosted
bydigitalsignalprocessing(DSP),avarietyofSARimagingalgorithmshavebeendeveloped,
in which the wavenumber domain algorithm is mature for airborne SAR and independent of
signalwaveforms. Apartfromthealgorithmdevelopment,thereisagrowinginterestinhowto
acquiretherawdataoftargets’echoesbeforetheDSPforSARimaginginacost-effectiveway.
For the data acquisition, various studies over the past 15 years have shed light on utilizing the
signal generated from the ubiquitous broadband wireless technology – orthogonal frequency
division multiplexing (OFDM). However, the purpose of this thesis is to enable commercial
OFDM-basedwirelesssystemstoworkasanairborneSARsensor.
The unlicensed devices of Worldwide interoperability for Microwave Access (WiMAX)
are the first option, owing to their accessibility, similarity and economy. This dissertation first
demonstrates the feasibility of applying WiMAX to SAR by discussing their similar features.
Despitethesimilaritiestheyshare,thecompatibilityof thetwotechnologiesisunderminedby
a series of problems resulted from WiMAX transceiver mechanisms and industrial rules for
radiated power. In order to directly apply commercial WiMAX base station transceivers in
unlicensed band to airborne SAR application, we propose a radio-frequency (RF) front design
together with a signal processing means. To be specific, a double-pole, double-throw (DPDT)
switch is inserted between an antenna and two WiMAX transceivers for generating pulsed
signal. By simulations, the transmitted power of the SAR sensor is lower than 0dBm, while
its imaging range can be over 10km for targets with relatively large radar cross section (RCS),
such as a ship. Its range resolution is 9.6m whereas its cross-range resolution is finer than 1m.
Equippedwiththemulti-mode,thisSARsensorisfurtherenhancedtosatisfytherequirements
of diversified SAR applications. For example, the width of the scan-mode SAR’s range swath
is 2.1km, over five times the width of other modes. Vital developed Matlab code is given in
AppendixD,anditscorrectnessisshownbycomparingwiththeimageofchirpedSAR.
Tosummarize,thesignificanceofthisdissertationistopropose,forthefirsttime,adesign
ofdirectlyleveragingcommercialOFDM-basedsystemsforairborneSARimaging. Compared
withexistingdesignsofairborneSAR,itisapromisinglow-costsolution.
Keywords: SAR,WiMAX,OFDM,DPDT,low-cost,multi-mode.
ii
You never grow old
you become old by not continuing to grow.
This thesis is dedicated
To my beloved Parents, Wife and Baby.
iii
Acknowlegements
First,Iwouldliketooffermyoverwhelminggratitudetomysupervisor,Dr. XianbinWang
for his guidance, support and encouragement. His enlightening supervisions inspired me with
confidencetoundertakethisresearch,broadenedmyoutlookandhelpedmeorganizemyideas.
Itwasaproductiveandjoyfuljourneytolearnfromhim.
Second,Iwouldliketothankmyco-supervisor,Dr. JagathSamarabanduforhismentoring,
for shaping my scattered ideas and for pointing out the primary problems in my research. It
wasmypleasuretoworkwithhim.
I am also grateful for Dr. Xianbin Wang and Dr. Jagath Samarabandu’s understanding and
leniencyforthedelayedresearchprogressduetomybaby’sbirthinthemiddleofmygraduate
studies.
Genuine thanks to Dr. Luiz Fernando Capretz, Dr. Abdallah Shami and Dr. Lucian Ilie
for sparing their valuable time in reviewing my dissertation and serving as my examination
committee. True thank also to Dr. Hanif Ladak for his gateway course of Matlab and serving
asthechairofmythesisexaminationboard.
IwouldliketoexpressmysincerethankstoDr. AuonMuhammadAkhtar,forhispatience
andprecisenessinhelpingmerevisemyacademicpaper. Also,earnestthankstogroupfellows,
Dr. Aydin Behnad, Dr. Arash Khabbazibasmenj and Jiazi Liu for their instructive suggestions
about paper-writing skills. Many thanks also to other group members, and it was gratifying to
workwithyou.
Heartfelt thanks to the patient administrative staff in our department and to the warm-
heartedlibrariansintheD.B.WeldonLibrary.
Iamindebtedtomybelovedparentsandwife. Withouttheirunselfishhelpandendlesslove
for me, I would not have completed the challenging research, which was a brand-new field of
knowledgeforme. I amgratefulfortheirsupport,understandingandforgiveness.
Finally, I want to express appreciation for all the friends I have made in Canada and for
theircordialassistanceinmylife.
iv
Contents
Abstract ii
Acknowlegements iv
ListofFigures viii
ListofTables xii
ListofAppendices xiii
ListofAbbreviations xiii
1 Introduction 1
1.1 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 DissertationOutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Radar,SARandWiMAX 6
2.1 ChapterIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 RadarFundamentalsandImagingRadar . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Radarfundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Imagingradar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 SARparametersspecifications . . . . . . . . . . . . . . . . . . . . . . 15
2.3 SAROperatingModesandItsImagingAlgorithms . . . . . . . . . . . . . . . 19
v
2.3.1 PrimarySARoperatingmodes . . . . . . . . . . . . . . . . . . . . . . 20
2.3.2 Wavenumberdomainalgorithm . . . . . . . . . . . . . . . . . . . . . 25
2.4 AirborneSARandBroadbandWirelessTechnologies . . . . . . . . . . . . . . 31
2.4.1 CurrentairborneSARapplications . . . . . . . . . . . . . . . . . . . . 31
2.4.2 WiMAXandotherOFDM-basedwirelesssystems . . . . . . . . . . . 32
2.4.3 SimilaritiesbetweenSARandWiMAX . . . . . . . . . . . . . . . . . 37
2.5 ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3 ProblemsofUtilizingWiMAXforSAR 46
3.1 ChapterIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2 WiMAXTransceiverMechanism . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2.1 Transmittersignalform . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2.2 Receiverstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3 PowerRestrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3.1 Transmittedpowerrestrictionfromindustrialregulations . . . . . . . . 49
3.3.2 PracticalconsiderationfortheprocessinggainofSAR . . . . . . . . . 50
3.4 ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4 AirborneStripmapSARUsingLicenseExemptWiMAXTransceivers 57
4.1 ChapterIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 SystemModelofWiMAXSAR . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3 RangeMatchedFilteringbyWiMAXReceiver . . . . . . . . . . . . . . . . . . 59
4.4 RFDesignforWiMAXSAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.4.1 Systemrangelevel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.4.2 Designtoincreasesignalprocessinggain . . . . . . . . . . . . . . . . 67
4.5 SystemParametersandSimulationResults . . . . . . . . . . . . . . . . . . . . 72
4.5.1 ImagequalityimprovementbyincreasingPRF . . . . . . . . . . . . . 73
4.5.2 IdealandrealWiMAXSARimage . . . . . . . . . . . . . . . . . . . . 76
4.5.3 Codecorrectnessverification . . . . . . . . . . . . . . . . . . . . . . . 77
4.6 ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
vi
5 EnhancedWiMAXSARSystemEquippedwithMultipleModes 81
5.1 ChapterIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2 SystemModelofMulti-modeWiMAXSAR . . . . . . . . . . . . . . . . . . . 82
5.3 Scan-modeWiMAXSAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.3.1 Operatingrange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.3.2 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.4 SimulationResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
5.5 EvaluationofWiMAXSAR . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
5.6 ChapterSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
6 ConclusionandFutureWork 99
6.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.2 FutureResearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
A DerivationofEq. (2.30)usingMSP 102
B Target’scross-rangeresolutionofsquintspotlightSAR 104
C Areaexpansionduetosquintangle 106
D KeydevelopedMatlabcode 108
Bibliography 110
CurriculumVitae 114
vii
List of Figures
2.1 Flowchartofsignalprocessingforhighrangeresolution . . . . . . . . . . . . 9
2.2 Schematicofenvelopedetectionforradarsignalbyamatchedfilter . . . . . . 10
2.3 Crossrangeresolutionofrealapertureradar. . . . . . . . . . . . . . . . . . . . 13
2.4 CrossrangeresolutioncomparisonbetweenSARandRAR. . . . . . . . . . . . 14
2.5 Three dimensional geometry of an airborne stripmap SAR. gr, x and y are
groundrange,crossrangeandaltitude,respectively,whilerrepresentstheslant
range. Red area is actual SAR imaging plane, and blue shadow area is slant-
rangeplane. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.6 TwofundamentalmodesofairborneSAR. . . . . . . . . . . . . . . . . . . . . 20
2.7 SchematicofastripmapSAR,whereL isthelengthofflightpathtoensurethe
x
uniformcross-rangeresolution∆CRforwholetargetarea,while L isaperture
a
sizeforonetargetwithrangeofr ,and a isthewidthofazimuthimagingunit. 21
c w
2.8 Schematic of a broadside spotlight SAR, where (cid:26) is rotational angle of the
whole flight path of SAR platform from the perspective of the target at the
centeroftherectangulartargetarea. . . . . . . . . . . . . . . . . . . . . . . . 22
2.9 Schematicofascan-modeSAR,inwhichtheflightlengthL isbiggerthanL
x2 x1
due to larger azimuth width a of imaging area, corresponding to the farther
w2
rangeswathr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
sw2
2.10 Schematic of a squint stripmap SAR. Its target area requires to be enlarged to
cover the counterpart area of broadside stripmap SAR, causing flight length
increasedby∆L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
x
viii
2.11 Two major steps for all SAR receivers: First is two dimensional compression
for targets at reference range, while the second is algorithm-dependent correc-
tionforfocusingallothertargetsintheimagingarea. . . . . . . . . . . . . . . 26
2.12 FlowchartofSARimagingprocessedby ΩKAalgorithm. . . . . . . . . . . . 28
2.13 Basicdiagramofangenerally-acceptedOFDMsystem. . . . . . . . . . . . . . 33
2.14 DownlinksubframestructureofWirelessMANOFDMPHYforWiMAXbase
stationinTDDmode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.15 Rangeandcross-rangeimagingwithresolutionof7.5mand0.5m,respectively. 39
2.16 Channelscomparisonbetweenradarandwirelesscommunications . . . . . . . 41
2.17 Radiofrequency(RF)blockdiagramofaWiMAXreceiver . . . . . . . . . . . 43
3.1 Envelopedetectionandthresholdjudgeofaradarreceiverforthesingle-carrier
sinusoidalwaveform. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.2 Comparison between simulation results and theoretical equation for obtaining
thedetectableprobabilityofanOFDMsymbolbyenvelopedetection. . . . . . 53
3.3 ReconstructedSARimageby ΩKAalgorithm . . . . . . . . . . . . . . . . . . 55
3.4 Envelopedetectionjudgedbyathresholdof167.6 . . . . . . . . . . . . . . . . 55
4.1 Block diagram of WiMAX SAR system. The memory device is needed to
collected the frequency-domain echo data for the following software-based 2-
Dimaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2 TheoperationofcirculantconvolutionbetweenanOFDMsymbolandchannel,
whichisestablishedthroughtheinsertedcyclicprefix(CP). . . . . . . . . . . . 60
4.3 Thepulse,withthelengthofanOFDMsymbol,istransmittedandreceivedby
WiMAXSAR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.4 Schematic diagram of WiMAX SAR RF design. When the black switches
are working, WiMAX SAR is transmitting. When a whole symbol is already
transmitted,theredswitchesworkforechoreceivingasshowninFigure4.3. . 68
4.5 The reasons why two WiMAX base stations are required to be used include:
forcingthelengthofpulsestobeonlyonesymbolduration;obtainingconstant
PRF;increasingthePRFtosatisfytherequirementofDopplerbandwidth. . . . 70
ix