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11

PREPARED BY:

MULCHANDANI BHARTI D

JHALA AANAL D

IMPLEMENTATION OF RANGECOMPRESSION FOR SYNTHETIC

APERTURE RADAR USING VIRTEX-II

XC2V3000

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INTRODUCTION TO ISROINTRODUCTION TO ISRO

GovernmentGovernment of of IndiaIndia setset upup SpaceSpace CommissionCommission andand DepartmentDepartment of of SpaceSpace (DOS)(DOS)inin JuneJune 19721972.. IndianIndian SpaceSpace ResearchResearch OrganizationOrganization (ISRO)(ISRO) underunder DOSDOS executesexecutesSpaceSpace programmeprogramme throughthrough itsits establishmentsestablishments locatedlocated inin differentdifferent placesplaces inin IndiaIndia..DrDr.. VikramVikram SarabhaiSarabhai waswas thethe foundingfounding fatherfather of of thethe IndianIndian spacespace program,program, andand isisconsideredconsidered aa scientificscientific visionaryvisionary byby many,many, asas wellwell asas aa nationalnational herohero..

Main objective of ISRO: It includes development of satellites, launch vehicles,

Sounding Rockets, Crossed several major milestones and associated ground

systems.

Centres of ISRO

Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram

ISRO Satellite Centre (ISAC), Bangalore

Satish Dhawan Space Centre (SHAR), Sriharikota

Liquid Propulsion Systems Centre (LPSC), Thiruvananthapuram Space Applications Centre (SAC), Ahmedabad

Development and Educational Communication Unit (DECU), Ahmedabad

ISRO Telemetry, Tracking and Command Network (ISTRAC), Bangalore

INSAT Master Control Facility (MCF), Hassan

ISRO Inertial Systems Unit (IISU), Thiruvananthapuram

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Department of space

MSDPDMSCED

Indian Space Research Organization (ISRO)

Space Application Centre (SAC)

MSDG MSIGMSTG

MSSG MRSASIIPA SITAASPSA SPTA SEDA ESSG SRG PPG

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HISTORY OF RADARSHISTORY OF RADARS

InIn 19501950¶s,¶s, imagingimaging devicesdevices withwith sensitivitiessensitivities beyondbeyond thethe visiblevisible rangerange of of

wavelengthwavelength of of 00..44 toto 00..88 microns,microns, intointo thethe infraredinfrared regionregion of of 00..88 toto 1515 microns,microns,detecteddetected energyenergy thatthat waswas eithereither sunlightsunlight reflectedreflected fromfrom terrainterrain oror fromfrom manman--mademade structure,structure, oror waswas radiatedradiated byby themthem asas aa functionfunction of of theirtheir temperaturetemperature..

AtAt visiblevisible andand infraredinfrared wavelength,wavelength, however,however, thethe atmosphereatmosphere absorbsabsorbs aasignificantsignificant fractionfraction of of radiation,radiation, eveneven inin thethe clearclear environmentenvironment.. InIn cloudycloudy ororrainyrainy weather,weather, thethe performanceperformance of of visiblevisible andand infraredinfrared detectorsdetectors isis seriouslyseriously

impairedimpaired becausebecause of of thethe factfact thatthat aa greatgreat amountamount of of emittedemitted energyenergy isis absorbedabsorbedbyby thethe atmosphereatmosphere..

ToTo overcomeovercome thisthis dependencedependence onon weatherweather RadarRadar systemssystems werewere inventedinvented thatthatoperatesoperates atat aa wavelengthwavelength of of oneone toto 3030 centimeters,centimeters, fulfillfulfill bothboth of of thethe aboveaboverequirementsrequirements provideprovide anan allall--weatherweather operationoperation..

TheseThese systemssystems provideprovide theirtheir ownown sourcesource of of illuminationillumination byby transmissiontransmission of of electromagneticelectromagnetic energyenergy..

AtAt wavelengthwavelength of of greatergreater thanthan oneone centimetercentimeter thethe atmosphericatmospheric absorptionabsorptionof of transmittedtransmitted andand reflectedreflected energyenergy isis minimalminimal..

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RADAR PRINCIPLE

The acronym RADAR stands for Radio Detection And Ranging. RADAR is

essentially a ranging or distance measuring device. It consists fundamentally of atransmitter, a receiver, an antenna, and an electronics system to process and

record the data.

Radar transmits a pulse and measures reflected echo (backscatter)

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Flight Track of spacecraft

The measurement of the time delay between the transmission of a pulse and the

reception of the backscattered "echo" from different targets, their distance from the

radar and thus their location can be determined. As the sensor platform moves forward,

recording and processing of the backscattered signals builds up a two-dimensional imageof the surface.

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CLASSIFICATION OF RADARSCLASSIFICATION OF RADARS

Radars

Non-Imaging RadarsImaging Radars

Synthetic Aperture RadarReal Aperture Radars

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SYNTHETIC APERTURE RADAR

Synthetic Aperture Radar (SAR) refers to a technique used to synthesize a very

long antenna by combining signals (echoes) received by the radar as it moves

along its flight track.

Synthetic Aperture Radar Imaging Concept

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As the radar moves, a pulse is transmitted at each position; the return echoes passthrough the receiver and are recorded in an 'echo store.' Because the radar is

moving relative to the ground, the returned echoes are Doppler-shifted (negatively

as the radar approaches a target; positively as it moves away).

Constructing a Synthetic Aperture

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Comparing the Doppler-shifted frequencies to a reference frequency allows many

returned signals to be "focused" on a single point, effectively increasing the length of

the antenna that is imaging that particular point. This focusing operation is

commonly known as SAR processing. The SAR processing requires correct matching

of the variation in Doppler frequency for each point in the image.

Doppler¶s Principle of shifted frequencies

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SAR IMAGE GENERATION PROCESS

The SAR image generation process can be broken up into three basic stages, as

shown in figure. The stages are: (i) sensing of the area target using the imaging

radar, (ii) digitalization and compression of the reflected SAR signal for

downlink to a ground station, and (iii) processing of the reconstructed SAR

signal into image data.

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APPLICATIONS OF SYNTHETIC APERTURE RADARSAPPLICATIONS OF SYNTHETIC APERTURE RADARS

ApplicationApplication PhenomenonPhenomenon

Water ResourcesWater Resources Surface water, Flood and Wetland MappingSurface water, Flood and Wetland Mapping

Drainage Basin MappingDrainage Basin Mapping

Lake Ice MappingLake Ice Mapping

VegetationVegetation Vegetation Type DeterminationVegetation Type Determination

GeologyGeology Surface Structural MappingSurface Structural Mapping

GeomorphologyGeomorphology

OceanologyOceanology Directional Wave Spectrum DeterminationDirectional Wave Spectrum Determination

Currents Boundary detectionCurrents Boundary detection

Ice Extent, Motion, Ridge and Lead DeterminationIce Extent, Motion, Ridge and Lead Determination

OthersOthers Land Use MappingLand Use Mapping

Ship DetectionShip Detection

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MERITS AND DEMERITS OF SYNTHETIC APERTUREMERITS AND DEMERITS OF SYNTHETIC APERTURE

RADAR RADAR

MeritsMerits

It images a surface with very fine resolution of a few meters to severalIt images a surface with very fine resolution of a few meters to severalkilometers.kilometers.

It can provide imagery to a given resolution independently of altitude, limitedIt can provide imagery to a given resolution independently of altitude, limitedonly by transmitted power available.only by transmitted power available.

A number of fundamental parameters such as polarization and look angle canA number of fundamental parameters such as polarization and look angle canbe varied to optimize the system for a specific application.be varied to optimize the system for a specific application.

Imaging is independent of solar illumination because the system provides itsImaging is independent of solar illumination because the system provides itsown source of illumination.own source of illumination.

It can operate independently of weather conditions if sufficiently longIt can operate independently of weather conditions if sufficiently longwavelengths are chosen.wavelengths are chosen.

It operates in a band of electromagnetic spectrum different from the bandsIt operates in a band of electromagnetic spectrum different from the bandsused by visible and infrared imagers.used by visible and infrared imagers.

Rapid updates.Rapid updates.

DemeritsDemerits

Complexity of deployment.Complexity of deployment.

It provides only 2It provides only 2--D operation.D operation.

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RANGE COMPRESSIONRANGE COMPRESSION

RangeRange resolutionresolution ¨R ¨R isis determineddetermined byby pulsepulse widthwidth of of thethe transmittedtransmitted pulsepulse asas

¨R ¨R == cc//22

where,where, ¨R ¨R isis thethe rangerange resolution,resolution, isis thethe pulsepulse width,width, andand cc isis thethe velocityvelocity of of propagationpropagation of of electromagneticelectromagnetic energyenergy..

InIn orderorder toto achieveachieve betterbetter rangerange resolution,resolution, pulsepulse compressioncompression techniquetechnique isisusedused inin whichwhich sensitivitysensitivity of of radarradar dependsdepends onon thethe energyenergy transmittedtransmitted inin thetheradarradar pulsespulses.. ThisThis cancan bebe expressedexpressed inin termsterms of of thethe averageaverage transmittedtransmitted powerpower--thatthat is,is, thethe peak peak powerpower multipliedmultiplied byby thethe transmittertransmitter dutyduty cyclecycle..

PPavgavg == PPpeak peak **/T/T == PPpeak peak ***B*B

where,where, PPavgavg=average=average transmittedtransmitted powerpower

PPpeak peak =peak =peak transmittedtransmitted powerpower

=pulse=pulse widthwidth

T=pulseT=pulse durationduration

/T=duty/T=duty cyclecycle

B=bandwidthB=bandwidth

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ADVANTAGES AND DISADVANTAGES OF PULSEADVANTAGES AND DISADVANTAGES OF PULSE

COMPRESSIONCOMPRESSION

AdvantagesAdvantages

Lower pulse power is requiredLower pulse power is required

Higher maximum rangeHigher maximum range

Good range resolutionGood range resolution

Better jamming immunityBetter jamming immunity

DisadvantagesDisadvantages

Poor minimum rangePoor minimum range

Appearance of sideAppearance of side--lobeslobes

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INTRODUCTION TO CHIRPINTRODUCTION TO CHIRP

AA chirpchirp isis aa signalsignal inin whichwhich thethe frequencyfrequency increasesincreases ('up('up--chirp')chirp') oror decreasesdecreases('down('down--chirp')chirp') withwith timetime.. ItIt isis commonlycommonly usedused inin sonarsonar andand radarradar..

Advantages of Chirp SignalAdvantages of Chirp Signal

HighHigh RangeResolutionRangeResolution

HighHigh SNR SNR PerformancePerformance

MinimumMinimum SideSide lobeslobes

Figure shows the Chirp

Characteristics.

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BLOCK DIAGRAM OF SAR PROCESSOR BLOCK DIAGRAM OF SAR PROCESSOR

Range AzimuthRange Azimuth

Compression CompressionCompression Compression

IFFT

Samplingand A/DConversion

RangeLine Buffer

IFFT

FFT

RangeReference

Corner turnMemory

FFT

MultilockProcessing

Detection

Formatter

Azimuth

Reference

Image

QuadratureDetected EchoSignal

Synthetic aperture radar processing algorithms are divided into steps.Synthetic aperture radar processing algorithms are divided into steps.

Range compressionRange compression

Azimuth compression.Azimuth compression.

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RANGE COMPRESSION DESCRIPTION

Received echoFF

T

IF

F

T

Reference

memory

Memory

RangeRange compressioncompression isis carriedcarried outout usingusing pulsepulse compressioncompression techniquetechnique.. AsAs shownshown ininfigure,figure, pulsepulse compressioncompression isis obtainedobtained byby crosscross--correlatingcorrelating thethe receivedreceived signalsignal withwiththethe transmittedtransmitted signalsignal.. ItIt isis computationallycomputationally moremore efficientefficient toto implementimplement thisthiscorrelationcorrelation processprocess byby FastFast convolution,convolution, whichwhich consistsconsists of of anan FFTFFT (of (of thethe receivedreceiveddata),data), aa vectorvector complexcomplex multiplicationmultiplication (with(with thethe FFTFFT of of reference),reference), andand anan inverseinverseFFTFFT.. TheThe referencereference signalsignal isis thethe complexcomplex conjugateconjugate of of thethe transmittedtransmitted signalsignal.. AAlinearlinear frequencyfrequency modulatedmodulated signalsignal calledcalled chirpchirp signalsignal isis usedused asas transmittedtransmitted signalsignal..

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DESIGN AND DEVELOPEMENT TOOLSDESIGN AND DEVELOPEMENT TOOLS

SoftwareSoftware ToolTool:: XILINXXILINX

ItIt isis thethe world'sworld's largestlargest developerdeveloper andand manufacturermanufacturer of of aaclassclass of of reconfigurablereconfigurable hardwarehardware chips,chips, fieldfield --programmableprogrammable gategate arraysarrays (FPGAs)(FPGAs) devicesdevices..

DeviceDevice FamilyFamily:: VirtexVirtex--IIII

DeviceDevice TypeType:: XCXC22VV30003000

TargetTarget FPGAFPGA:: VIRTEXVIRTEX--IIII

LanguageLanguage usedused:: VHSICVHSIC HardwareHardware DescriptionDescription LanguageLanguage

SimulationSimulation ToolTool:: MATLABMATLABTheThe namename MATLABMATLAB standsstands forfor MATrixMATrix LABoratoryLABoratory..MatlabMatlab isis aa softwaresoftware packagepackage forfor highhigh--performanceperformance numericalnumericalcomputationcomputation andand visualizationvisualization..

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FPGA IMPLEMENTATION OF RANGE COMPRESSION

FFT

CoreIFFT

Core

Complex

Multiplication

Reference

Memory

O

ut

p

ut

I

n

p

ut

XC2V3000

Project Design

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FFT ARCHITECTURESFFT ARCHITECTURES

FFT core provides three architectures to compute FFT/IFFT.FFT core provides three architectures to compute FFT/IFFT.

Pipelined ArchitecturePipelined Architecture

RadixRadix--4 Architecture4 Architecture

RadixRadix--2 Architecture2 Architecture

Resource Utilization Comparison of FFT architectures

Number of samples = 32768

Input width = 16 bits

Output width = 16 bits

Architecture Latency

(in clock

cycles)

Resource utilization Total Memory

(BRAMs+Slic

es)

(in Kbits)

MULTs Block

RAMs

Slices Look-up

table

Flip-

flops

Available 96 96 14336 28672 28672 2187

Pipelined, Bit-

reversed output

32640 Used 21

(21 %)

43

(44 %)

3643

(44 %)

5761

(20 %)

5292

(18 %)

891

(40%)

Radix-4,

Natural order

output

76128 Used 9

(9 %)

84

(87 %)

1876

(13 %)

2670

(9 %)

2130

(7 %)

1572

(71%)

Radix-2,

Natural order

output

200576 Used 3

(3 %)

66

(68 %)

1032

(7 %)

1870

(6 %)

1330

(4%)

1221

(55%)

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DESIGN APPROACHESDESIGN APPROACHES

Approach 1:Approach 1: 32k point FFT using pipelined architecture32k point FFT using pipelined architecture

TheThe pipelinedpipelined architecturearchitecture withwith bitbit--reversedreversed outputoutput orderingordering cancan bebe usedused totoimplementimplement thethe rangerange compressioncompression techniquetechnique.. TheThe outputoutput of of thethe FFTFFT isis inin bitbit--reversedreversed order,order, soso thethe multiplicationmultiplication isis alsoalso inin bitbit--reversedreversed formform.. SinceSince thethemultiplicationmultiplication resultresult isis inin bitbit--reversedreversed order,order, additionaladditional memorymemory isis requiredrequired totostorestore thethe resultresult andand convertconvert intointo naturalnatural orderorder forfor IFFTIFFT computationcomputation asas thethecorecore requiresrequires thethe inputinput toto bebe inin naturalnatural orderorder.. ThisThis increasesincreases thethe memorymemory

utilizationutilization andand alsoalso thethe latencylatency of of outputoutput.. HenceHence thisthis approachapproach cannotcannot bebe usedused..

ApproachApproach 22:: 3232k k pointpoint FFTFFT usingusing twotwo FPGAsFPGAs

InIn thisthis approach,approach, twotwo FPGAsFPGAs cancan bebe used,used, oneone toto performperform thethe forwardforward FFTFFTandand otherother toto performperform inverseinverse FFTFFT.. ThisThis increasesincreases thethe overalloverall memorymemoryutilizationutilization andand isis thusthus notnot efficientefficient toto implementimplement..

ApproachApproach 33:: 3232k k pointpoint FFTFFT usingusing overlapoverlap savesave approachapproach

ToTo overcomeovercome thethe limitationslimitations of of aboveabove architectures,architectures, thethe overlapoverlap savesave methodmethod isisusedused..

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Input sequence, x(n) segmented into blocks of L samples

x(2L ± M + 1)«x(3L - 1)

x(L ± M + 1)«x(2L - 1)

Block 3 Output, y3(n)


Block 1 Output, y1(n) Block 1 Output, y2(n) Block 1 Output, y3(n)


Discard

Discard

Discard

x(0)«x(L - 1)0,«,0

M ± 1

zeros

M ± 1

M ± 1

M ± 1

M ± 1

M ± 1

Block 1

Block 2

Block 3

x2(n)

x1(n)

L LL

Final

output

y(n)

In our case, L = 4096 and M ± 1 = 4096. Hence, L + M ± 1 = 8192.

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Design

Approach

Latency

(in clock

cycles)

Resource utilization Memory (in

Kbits)MULTs Block

RAMs

Slices Look-up

table

Flip-

flops

Approach 1 32640 Used 32(33%)

147*

(153%)5457(38%)

8401(29%)

8122(28%)

2820*

(128%)

Available 96 96 14336 28672 28672 2187

Approach 2 65280 Used 62 (32%) 182

(94%)

10914

(38%)

16802

(29%)

16244

(28%)

3625

(82%)

Available 192 192 28672 57344 57344 4374

Approach 3 32600 Used 54(54%)

81(84%)

12747(88%)

23351(81%)

15966(55%)

1865(85%)

Available 96 96 14336 28672 28672 2187

* Over-utilization of memory

Resource Utilization Comparison based on design approachComparison based on design approachNumber of samples = 32768Number of samples = 32768

Input width = 16 bitsInput width = 16 bits

Output width = 16 bitsOutput width = 16 bits

Reference data width = 8 bitsReference data width = 8 bits

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CONCLUSION AND FUTURE SCOPE

Conclusion

The real-time range compressor signal processor module is designed andimplemented using Xilinx development system. Target FPGA selected for

implementation of range compression for Synthetic Aperture Radar processor is

Xilinx XC2V3000 Virtex-II FPGA. The language used to create the design is

VHSIC Hardware Description Language (VHDL). Functionality of top-level

module and all the sub-modules is verified by writing testbenches in VHDL and

carrying out functional simulation using ModelSim. Maximum supportingfrequency for the design is 50.4 MHz. FPGA resource utilization of complete

design is about 85%. The total signal processing time is approximately 18 ms,

which meets necessary timing requirements for system pulse repetition frequency

(PRF) of 2050 Hz.

Future Scope

Xilinx coregenerator can be modified for optimum utilization of available

memory.

Development of FFT architecture optimized in resource utilization can be

considered for future work.

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&

ANY QUERIES??!!

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