A FPGA-Based Architecture for In-Flight Synthetic Aperture Radar (SAR) Motion

Compensation in Unmanned Aerial Vehicles

Fernando Ortiz

EM Photonics, Inc.Newark, DE

Ortiz 2 MAPLD 2005/1009

Outline

• Introduction & Motivation

• SAR Reconstruction Basics

• Motion Compensation

• The Hardware Platform

• Architecture for Real-time SAR Motion Compensation

• Conclusion and Future Work

Ortiz 3 MAPLD 2005/1009

SAR Concept

• Radar waves used to visualize objects because of their ability to penetrate a range of materials

Goal: gain the advantages of a large aperture radar by using a smaller, traveling aperture

• Resolution of image improves as aperture size increases

• Unfortunately, increasing aperture size (antenna length) may simply be impractical (antenna lengths in kilometers)

Ortiz 4 MAPLD 2005/1009

SAR Applications

Mining/Space Exploration

Ocean FloorTopography

Air TrafficControl

Target Detection

and Tracking

MedicalImaging

Buried ObjectDetection

Ortiz 5 MAPLD 2005/1009

Motion Compensation

• Problem: cannot guarantee perfect motion paths• Result: degraded images• Solution: motion compensation

• Options for aerial platforms:– Massive onboard computers– Slower processing (secs per frame)– Ground processing

Without Compensation

With Compensation

Complexity of motion compensation is limiting factor in deploying

SAR systems!

Ortiz 6 MAPLD 2005/1009

Motivation

Space-Based Airborne UAV• Simple motion

compensation

• Power/area available for calculations

• Disregard motion compensation (for stable orbits)

• Ground processing practical

How does this impact in-flight systems?

X

UAVs require fast, low area/power motion compensation solversSolution: reconfigurable platforms!

• Advanced motion compensation (erratic path, wind interaction)

• Minimal power/area for processing

Ortiz 7 MAPLD 2005/1009

SAR Geometry

x

y (cross-range domain)

z

xn

yn

ImagedRegion

Reflectivetargets

range

GoalDetermine x,y,for each target

How?•Range Imaging•Cross Range Imaging

Ortiz 8 MAPLD 2005/1009

SAR Basics: Range Imaging

Received signal n

nn c

xtpts )

2()(

Desired information n

nn xxxf )()(0

Combines Range and ReflectivityMatched Filter

x1 x2 x3 x4

1

2 3

4

1

p(t)

x1

2

x2

3

x3

4

x4

1p(t-2x1/c)Yc

2p(t-2x2/c) 3p(t-2x3/c) 4p(t-2x4/c)

Ortiz 9 MAPLD 2005/1009

SAR Basics: Cross-Range Imaging

• Use matched filtering (again) to determine cross-range information

• Put these two together and you have a 2D imaging system

Typical SAR problem

y3

y2

y1

Xc

Fourier Transform(t,u) (w,ku)

2D Matched Filter

Inverse Transform(kx,ky) (x,y)

FFTs are the bottleneck in traditional SAR

c

uYXtputs cc

22 )(2),(

ReceivedSignal

OutputImage

Ortiz 10 MAPLD 2005/1009

MC SAR Processing Flow

Motion Compensation

is the NEW Bottleneck

22

222222

22*

sinsin)(sin)(coscos)(

)()()()()(

)(exp),(

zxk

kyu

uzuyux

zuyxuzzuyuyuxxur

urkkjkkH

x

y

czececze

nnnenenenen

enyxyxexyz

Motion Compensation Filter

Reconfigurable platform permits massive parallelization and pipelining

FFT

ReceivedSignal

ReconstructedImage

IFFT

SARFilter

MCFilter

c

uYXtputs cc

22 )(2),(

SAR Filter

Ortiz 11 MAPLD 2005/1009

Hardware Platform

PLX 9656(External PCI Control)

16 GB DDR SDRAM

PCI 64/66 Interface

Xilinx Virtex-II8000 FPGA

Custom, FPGA-based PCI Card

36 MbDDR SRAM

Ortiz 12 MAPLD 2005/1009

Platform Success

Platform used to develop accelerated solvers for electromagnetic simulations.

Single PC

PC cluster, 30 nodes

EM Photonics Celerity Platform

0

5

10

15

20

25

30

35

0 50 100 150 200Nodes (Millions)

Performance vs. Problem Size

0

5

10

15

20

25

30

35

0 50 100 150 200Nodes (Millions)

Mil

lion

s of

nod

es/s

ec (

Mn

ps)

Key Statistics• 9.5 GB/s Main Memory Bandwidth• 150+ Floating-Point Units @ 133 MHz

Ortiz 13 MAPLD 2005/1009

SAR Motion Compensation Architecture

kx

ky

xy

Round

Cos c

Sin c

yn

xn

REG

U

BRAMxe LUTye LUT

Norm

Norm

Norm

Out

xk

kyu

uyuxuyxuyuyuxxur

urkkjkkH

x

y

cecennenenen

enyxyxexyz

sin)(cos)(-)()()()(

)(exp),(

2222

22*

Ortiz 14 MAPLD 2005/1009

Resource Utilization

26.3921.67% of XC2V8000

3820190

 

Total

8111288111281FPEXP

0171905733FPSQRT

057305731FPDIV

301890318910FPMUL

04880048810FPADD

MultsLUTs

Total

MultsLUTsQuantity 

Three parallel SAR MCUs are feasible within a single chip

Ortiz 15 MAPLD 2005/1009

Conclusion and Future Work

• SAR Motion Compensation requires significant computing power

• Demonstrated FPGA platform capable of in-flight SAR MC

• RC platforms ideal fit for UAV applications – Comm. Bandwidth savings– Airborne processing enables

further applications (e.g. ATR)– Low weight/power– Hardware reusable for other tasks

For the future:

• This solves only one piece– FFTs – Interface

• Form factor has to be converted– Less memory– No PCI– Interface with the rest of the

system– Integrate cooling into the airframe