Presenter: Dr. Dmitriy Garmatyuk, Department of Electrical & Computer Engineering, Miami University

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Ultra-Wideband Imaging Radar Based on OFDM:

Exploration of Its Potential

Presented on June 20, 2007 at Naval Research Lab, Washington D.C.

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Miami UniversityMiami University

• In Ohio, not Florida• Established in 1809• Named after Indian tribe• … the T-shirt says it all:

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Talk OverviewTalk Overview

• History of OFDM• OFDM waveform design • UWB-OFDM in Communications and Radar• UWB-OFDM SAR: First steps

• Range and cross-range imaging examples• Bigger picture: General scenario of interest• AFOSR project• Summary, Q/A

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Brief History of OFDMBrief History of OFDM

• Originated by Bell Labs researcher R. W. Chang in 1966-68*• Next 20 years: System architecture prototype design, adaptation for digital broadcasting, mostly, by Thomson-CSF (currently, part of Thales Group), French electronics/communications company – best achievement was 70 Mbit/s HDTV link at 8 MHz bandwidth• The 90’s: OFDM was adapted for wireless LAN applications (20 MHz bandwidth, max of 54 Mbit/s link capacity)• February 14, 2002: FCC opens up 3.1 – 10.6 GHz for commercial use at –41.3 dBm/MHz, triggering R&D efforts in UWB communications among industrial companies**; OFDM is a primary candidate for system architecture• Now: MB-OFDM is still a #1 choice for WPAN (short-range PC-to-peripherals high data rate communications technology) and is being tapped for 4G (next-generation cellular)

* “A Theoretical Study of Performance of an Orthogonal Multiplexing Data Transmission Scheme,” R. Chang and R. Gibby, IEEE Trans. on Communications, vol. 16, no. 4, April 1968.** “Design of Multiband OFDM System for Realistic UWB Channel Environments,” A. Batra, J. Balakrishnan, G. R. Aiello, et al., IEEE Trans. on Microwave Theory and Tech., vol. 52, no. 9, Sept. 2004.

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Fundamental Benefits and Reasons for Fundamental Benefits and Reasons for SurvivabilitySurvivability

•Dynamic spectrum allocation: User decides which sub-bands are to be occupied for each outgoing pulse

•Digital-friendly architecture – as digital technology becomes cheaper, so do OFDM systems

•Expandability: Bandwidth is determined solely by sampling speed

•Robust against narrowband interference: Turn on/off sub-bands adaptively

•Time synchronization is not a big issue: All processing is done in frequency domain

•Very good spectral efficiency: One pulse can contain many bits of information

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Simplest OFDM TransmitterSimplest OFDM Transmitter

Step 1: Decide how many sub-bands we want

Example: 32 sub-bands (usually – 128 or 256)

DC

. . . . . .

32 discrete sub-carriers

Mathematical spectrum representation

Frequency0

Fmax-Fmax Fk Fk+1-Fk-Fk+1

Step 2: Create signal by populating the frequency vector

DC point

Positive frequency half-axis

Negative frequency half-axis (flipped)*

* MATLAB-specific notation

Step 3: Feed this vector to IFFT processor

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Simplest OFDM Transmitter – Cont’dSimplest OFDM Transmitter – Cont’d

Step 4: Feed the time-domain vector to DAC

Quick calculation: If we assume 1 Gs/s speed of D/A conversion and 65 data points in the data vector, then there will be (65-1) samples at DAC’s output, each with 1 ns of duration output signal will be 64 ns long

Quick calculation 2: The signal is an RF pulse at 31.25 MHz carrier frequency and 64 ns duration theoretical spectrum is a sinc-function centered at 31.25 MHz and 31.25 MHz main-lobe bandwidth

fc

2/Tpulse

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Orthogonality IllustrationOrthogonality Illustration

Step 5: Compose the frequency vector anew and place ‘1’ in adjacent positions

Each sub-band has exactly zero interference from other sub-bands precisely at its carrier frequency (sub-carrier)

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How to Make OFDM Ultra-Wideband?How to Make OFDM Ultra-Wideband?

Quick calculation: If all sub-bands are ON, then the entire occupied spectrum is 0.5 GHz – or half the sampling rate. This holds for any number of sub-bands, or other system parameters – total potential bandwidth of an OFDM signal is always half the DAC speed, hence the non-existence of UWB-OFDM systems in the past.

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UWB-OFDM in CommunicationsUWB-OFDM in Communications

• Can apply QPSK before feeding the frequency-domain vector to the DAC: Each sub-band will then represent a 4-bit symbol• Make use of fast integrated FFT/IFFT processors and D/A and A/D converters• With 128 sub-bands we can squeeze 128x4=512 bits into 128 ns pulse (theoretically) translates to 4 Gb/s!• Practically, of course, some bits in the sequence will be needed for synchronization, etc, plus low power requirement will result in losses at the receiver and the necessity to re-transmit data several times, thus realistically 100-500 Mb/s are currently achievable• Pros: Fading/multi-path resistance, excellent spectral efficiency, good potential for interference mitigation, relatively cheap implementation in integrated CMOS technology, good scalability/spectrum flexibility potential

• Cons: Doppler sensitivity, issue of high peak-to-average power ratio

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UWB-OFDM Benefits for Radar UWB-OFDM Benefits for Radar High waveform diversity potential Dual-use architecture (radar/communications)Noise-like waveforms for increased LPI/LPD Ease of narrowband jamming and interference

mitigationHigh potential for coexistence with other

services/radars High resolution and multi-path potential Modern technology allows for inexpensive

implementation

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Stripmap SAR topology was assumed

Radar TX/RX antenna

15 m24 m

160 range delays150

Radar antenna

movementAntenna beamCross-range

swath: 16 m Range

Cro

ss-r

ange

Backprojection algorithm in fast- and slow-time domains was chosen as a basis for image formation†

Standard SAR setup and analysis

† - REFERENCE: M. Soumekh, “Synthetic aperture radar signal processing with MATLAB algorithms,” John Wiley & Sons, 1999

First Step: UWB-OFDM SARFirst Step: UWB-OFDM SAR

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First UWB-OFDM Radar Simulation Test-First UWB-OFDM Radar Simulation Test-BenchBench

Single range profile

response

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Range Profile Recovery: Standard SARRange Profile Recovery: Standard SAR

Focusing via

matched filtering

D. Garmatyuk, “Simulated imaging performance of UWB radar based on OFDM,” Proceedings of The 2006 IEEE International Conference on Ultra-Wideband, pp. 237-242, Waltham, MA, September 2006.

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Cross-Range Profile Recovery: OFDM Cross-Range Profile Recovery: OFDM Benefits from Easy Sub-Carrier Benefits from Easy Sub-Carrier

ExtractionExtraction

nnnnRX uyx

cjTFus 220

0 2exp),(

22000 2exp),( uX

cjus c

In cross-range signals are represented in phase domain before computing their cross-correlation

where sRX(0,u) represents radar signal at frequency 0 received when

the radar platform was at the cross-range coordinate u; TFn is a

reflectivity constant of nth target within the radar beamwidth; xn and yn

are range and cross-range coordinates of the nth point target; and s0(0,u) is defined as an ideal return from a unit reflector located at the

centre of the radar-scanned target area – i.e. (xn, yn) = (Xc, 0), where Xc

is the range distance to the centre of target’s area.

In OFDM single-frequency

components in frequency domain are

already available after FFT in the

receiver*!

* Receiver:

Ref Phase Function Generation: An Ref Phase Function Generation: An IllustrationIllustration

-3 -2 -1 0 1 2 3-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Cross-Range (meters)

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- Beamwidth Coverage

yo = 0

Target

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Cross-Range Imaging ResultCross-Range Imaging Result

Span of 16 meters was assumed and various PRFs were simulated

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Full ImageFull Image

Successful target recovery for SNRs down to –20dB

with resolution 0.1…1 meter

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General Scenario of Interest General Scenario of Interest

Scenario feasibility study will be presented at EuRAD’07 (October 11, Munich) and published in the proceedings (“Feasibility study of a multi-carrier dual-use imaging radar and communication system”, Dmitriy Garmatyuk, Jon Schuerger, Jade Morton, Kyle Binns, Michael Durbin, John Kimani; all – Miami University)

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Senior Design Project (Spring’07): UWB-Senior Design Project (Spring’07): UWB-OFDM Image Communication System OFDM Image Communication System

Simulator in MATLABSimulator in MATLAB

To be presented in October at EuRAD’07

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AFOSR-Sponsored ProjectAFOSR-Sponsored Project Objectives:

• Design workable UWB-OFDM transceiver• Test imaging performance of UWB-OFDM radar• Test data communication performance of UWB-OFDM• Lay foundation for subsequent research of UWB-OFDM imaging radar networks

Plans and personnel:• 1st year: System component acquisition and theoretical analysis of realistic 256 sub-band (0.5 GHz BW) SAR• 2nd year: Imaging radar assembly and test• 3rd year: Image communication test and imaging radar network analysis (theory)• 1 faculty member (me) and 1 M.S. student (who is much interested in working for NRL or AFRL after graduation)

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UWB-OFDM System Prototype PlanUWB-OFDM System Prototype Plan

Component Price per unit TX or RX Units totalFM480 20,000.00$ TX/RX 2DRO-1000 950.00$ TX 1PD2-4000/8000-30S 315.00$ TX 1DM0412LW2 435.00$ TX/RX 2DBP-0208N533 2,000.00$ TX 1Antenna+adaptor 550.00$ TX/RX 2Antenna cables 250.00$ TX/RX 2AFS3-02000800-18ULN 945.00$ RX 2PBA30F-15-N Pwr Sup. 50.00$ TX/RX 5Misc. (cables, conn., etc) 500.00$ TX/RX 1

Total : 48,375.00$

PCI interface

FM480 board: TX

Virtex-4IFFT core DAC281

1Gs/sSampling card(1 Vpk-pk out)

256-point IFFT3.68 ms

AC-coupled OUT

64-bit66 MHz

256 MBDDR2 SDRAM

PC w/MATLAB PCI interface

64-bit66 MHz

SMA

Microwave Dynamics DRO-1000

Free-running oscillator (7.5 GHz, 13 dBm)

Miteq PD2-4000/8000-30S

Power dividerLO

RF (out)

IF

Miteq DM0412LW2Mixer

Advanced Technical Materials Low-loss cable (N(m)-SMA(m)) CF-300-3M-NM-SM (3 meters)

Miteq AFS3-02000800-18ULN

Ultra-Low Noise Amplifier (24 dB)

Narda Microwave

DBP-0208N533 Power Amplifier

(33 dBm)

Advanced Technical Materials Standard horn antenna (137-441-2, 15 dB) and coax N-type adaptor flange (137-253B-2)

LO

RF

IF (out)

Miteq DM0412LW2Mixer

FM480 board: RX

Virtex-4IFFT coreADC291

1Gs/sSampling card(0.5 Vpk-pk in)

256-point FFT3.68 ms

AC-coupled OUT

256 MBDDR2 SDRAM

SMA

TRC ElectronicsPower Supply PBA30F-15-N:

85-264V IN, 15 V/2 Amps OUT

PCI interface

SMA(f)

SMA(f)Advanced Technical Materials Low-loss cable (N(m)-SMA(m)) CF-300-3M-NM-SM (3 meters)

N(f)

N(f)

Advanced Technical Materials Low-loss

cable (N(m)-SMA(m)) CF-300-3M-NM-SM

(0.5 meters)

Rev 3.0

Miteq AFS3-02000800-18ULN

Ultra-Low Noise Amplifier (24 dB)

• Summer’07: FPGA-based digital transceiver design and assembly;• Fall-Winter’07: Digital testing and antenna system acquisition and test;• Spring’08: RF assembly and test• Summer’08: Complete system test and implementation

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Topics NOT Covered So FarTopics NOT Covered So Far

• RF detriments in the transceiver and how they will affect system performance• Doppler effect*• Clutter effects on various frequencies in UWB-OFDM bands• Custom design (e.g. high transmit power, integrated ASIC-based digital part)• Weight/power/complexity trade-offs for practical usage models• Intelligent signal design (e.g. to reduce PAPR)• Actual effects of jamming on performance

* But TU-Delft (The Netherlands) researchers have concluded that it is possible to perform Doppler estimation using OFDM: G. E. A. Franken, H. Nikookar and P. van Genderen, “Doppler tolerance of OFDM-coded radar signals,” in Proc. 3rd European Radar Conf., 2006, pp. 108-111.

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Summary: UWB-OFDM system at Miami U Summary: UWB-OFDM system at Miami U Platform collecting target image data

Platform receiving target image data Image data transmission

High-resolution airborne radar imaging (SAR, 0.3…1 meter resolution theoretical bounds)

Broadband image data communication between airborne platforms

Potential for image-based navigation in GPS-denied environments (future topic)

-10.07dBSNR

Component Price per unit TX or RX Units totalFM480 20,000.00$ TX/RX 2DRO-1000 950.00$ TX 1PD2-4000/8000-30S 315.00$ TX 1DM0412LW2 435.00$ TX/RX 2DBP-0208N533 2,000.00$ TX 1Antenna+adaptor 550.00$ TX/RX 2Antenna cables 250.00$ TX/RX 2AFS3-02000800-18ULN 945.00$ RX 2PBA30F-15-N Pwr Sup. 50.00$ TX/RX 5Misc. (cables, conn., etc) 500.00$ TX/RX 1

Total : 48,375.00$

PCI interface

FM480 board: TX

Virtex-4IFFT core DAC281

1Gs/sSampling card(1 Vpk-pk out)

256-point IFFT3.68 ms

AC-coupled OUT

64-bit66 MHz

256 MBDDR2 SDRAM

PC w/MATLAB PCI interface

64-bit66 MHz

SMA

Microwave Dynamics DRO-1000

Free-running oscillator (7.5 GHz, 13 dBm)

Miteq PD2-4000/8000-30S

Power dividerLO

RF (out)

IF

Miteq DM0412LW2Mixer

Advanced Technical Materials Low-loss cable (N(m)-SMA(m)) CF-300-3M-NM-SM (3 meters)

Miteq AFS3-02000800-18ULNUltra-Low Noise Amplifier

(24 dB)

Narda Microwave

DBP-0208N533 Power Amplifier

(33 dBm)

Advanced Technical Materials Standard horn antenna (137-441-2, 15 dB) and coax N-type adaptor flange (137-253B-2)

LO

RF

IF (out)

Miteq DM0412LW2Mixer

FM480 board: RX

Virtex-4IFFT coreADC291

1Gs/sSampling card(0.5 Vpk-pk in)

256-point FFT3.68 ms

AC-coupled OUT

256 MBDDR2 SDRAM

SMA

TRC ElectronicsPower Supply PBA30F-15-N:

85-264V IN, 15 V/2 Amps OUT

PCI interface

SMA(f)

SMA(f)Advanced Technical Materials Low-loss cable (N(m)-SMA(m)) CF-300-3M-NM-SM (3 meters)

N(f)

N(f)

Advanced Technical Materials Low-loss

cable (N(m)-SMA(m)) CF-300-3M-NM-SM

(0.5 meters)

Rev 3.0

Miteq AFS3-02000800-18ULN

Ultra-Low Noise Amplifier (24 dB)

Complete simulation-based feasibility study is ~80% done and hardware assembly plan commenced in April’07

1. D. Garmatyuk, “Ultrawideband imaging radar based on OFDM: System simulation analysis,” Proceedings of SPIE, Radar Technology X, Vol. 6210, pp. 66-76, Orlando, FL, May 2006.

2. D. Garmatyuk, “Simulated imaging performance of UWB radar based on OFDM,” Proceedings of The 2006 IEEE International Conference on Ultra-Wideband, pp. 237-242, Waltham, MA, September 2006.

3. D. Garmatyuk, Y. Jade Morton, “On co-existence of in-band UWB-OFDM and GPS signals,” Proceedings of The 2007 Institute of Navigation National Technical Meeting, San Diego, CA, January 2007.

Questions, discussion…Questions, discussion…