A FPGA-Based Architecture for In-Flight Synthetic Aperture Radar (SAR) Motion Compensation in Unmanned Aerial Vehicles

1
A FPGA-Based Architecture for In-Flight Synthetic
Aperture Radar (SAR) Motion Compensation in
Unmanned Aerial Vehicles

• Fernando Ortiz
• EM Photonics, Inc.Newark, DE

2
Outline

• Introduction Motivation
• SAR Reconstruction Basics
• Motion Compensation
• The Hardware Platform
• Architecture for Real-time SAR Motion
  Compensation
• Conclusion and Future Work

3
SAR Concept

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

• Resolution of image improves as aperture size
  increases

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

Goal gain the advantages of a large aperture
radar by using a smaller, traveling aperture
4
SAR Applications
Target Detectionand Tracking
Buried ObjectDetection
Ocean FloorTopography
Air TrafficControl
Mining/Space Exploration
MedicalImaging
5
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

Complexity of motion compensation is limiting
factor in deploying SAR systems!
6
Motivation
How does this impact in-flight systems?
X
Space-Based
Airborne
UAV

• Simple motion compensation
• Power/area available for calculations

• Disregard motion compensation (for stable orbits)
• Ground processing practical

• Advanced motion compensation (erratic path, wind
  interaction)
• Minimal power/area for processing

UAVs require fast, low area/power motion
compensation solvers
Solution reconfigurable platforms!
7
SAR Geometry
z
Goal Determine x,y,s for each target
range

• How?
• Range Imaging
• Cross Range Imaging

yn
y (cross-range domain)
Imaged Region
xn
x
Reflective targets
8
SAR Basics Range Imaging
Combines Range and Reflectivity
Matched Filter
Desired information
9
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
Received Signal
Output Image
2D Matched Filter
FFTs are the bottleneck in traditional SAR
10
MC SAR Processing Flow
Motion Compensationis the NEW Bottleneck
SAR Filter
Motion Compensation Filter
Reconfigurable platform permits massive
parallelization and pipelining
11
Hardware Platform
Custom, FPGA-based PCI Card
Xilinx Virtex-II 8000 FPGA
36 Mb DDR SRAM
PCI 64/66 Interface
16 GB DDR SDRAM
PLX 9656 (External PCI Control)
12
Platform Success
Platform used to develop accelerated solvers for
electromagnetic simulations.
Performance vs. Problem Size
)
35
35
Mnps
30
30
EM Photonics Celerity Platform
25
25
20
20
Millions of nodes/sec (
15
15
PC cluster, 30 nodes
10
10
5
5
Single PC

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

0
0
0
50
100
150
200
0
50
100
150
200
Nodes (Millions)
Nodes (Millions)
13
SAR Motion Compensation Architecture
14
Resource Utilization
Total
Mults
LUTs
Quantity
 
Mults
LUTs
0
4880
0
488
10
FPADD
30
1890
3
189
10
FPMUL
0
573
0
573
1
FPDIV
0
1719
0
573
3
FPSQRT
8
11128
8
11128
1
FPEXP
38
20190
 
Total
26.39
21.67
of XC2V8000
Three parallel SAR MCUs are feasible within a
single chip
15
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