PRI and RF Prediction
Enabling Technology
ByKen McRitchie, Rémi Gauvin & Scott McDonald
Ottawa, Ontario, Canada
Visit us at http://www.mc-cm.com
MC Countermeasures Inc.
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Overview
• Introduction• Electronic Attack Problem: Pulse to Pulse
Agility• What is PRI & RF Prediction?• Prediction in a Corrupt or Multi- Emitter
Environment• Prediction Applications• Summary
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Good Radar Design
• PRI changes help eliminate blind speeds and ambiguous ranges in MPRF and MTI radar modes
• RF changes help de-correlate and hence reduce sea clutter
• Both are effective ECCM/EPM
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The EA Task
• Provide effective jamming in a typical radar environment:
– Many emitters: interleaved pulse trains
– Radar TX misfire: missing pulses
– Scanning modes: short illumination time
– PRI and/or RF agility: stagger, sliding, sine, jitter
– RF jitter may be sinusoidal, but generally random, non-coherent radars
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Noise - SOJ
• Bandwidth tailored to radar’s RF agility bandwidth: 10’s to 100’s MHz
• Complete range masking so PRI agility not a factor
• Need lots of power, dedicated aircraft
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Deception - SPJ
• Frequency Memory Loop– Limited delay due to noise build-up after few
times around loop, generally 10 us max– Restricted to down-range false targets only– Negated by leading edge track, guard gates
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Deception - DRFM
• DRFM– Indefinite delay, enables full PRI delay so up-
range false targets are possible– Initially developed for pulsed Doppler radar– Ok for high PRF constant PRI modes– Rendered ineffective by pulse-pulse agility
common in low or medium PRF modes
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Problem - Agility
• PRI Agility:– Limits deception based system to down range
capability
• RF Agility:– Limits deception based system to down range
capability– Noise jamming requires high power / wide
bandwidth
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Staggered PRI
Two Frames of a 5 - Element, 25 - Position Staggered Pattern
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40 45 50
PRI Stagger Level
PR
I Ele
me
nts
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Without Prediction Only Down-Range FT Are Possible
Staggered PRI
PRI A FT
PRI B FT
PRI C FT
False Target Delay Range 1
False Target Delay
False Target Delay
Range 2
Range 3
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PRI Prediction
• To take full advantage of DRFM, TOA of next pulse is required
• Even with prediction, need to adjust DRFM delay for each pulse
• Hence, need to closely integrate techniques generator with Predictor
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Up-Range Targets
Variable Delay Creates Up-Range FT
PRI A FT
PRI B FT
PRI C FT
False Target Delay 2
False Target Delay 3
Range 1
Range 1
False Target Delay 1 Range 1
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Benefits of PRI Prediction
• Compensate for jammer throughput delay
• Fade + Fast re-acquisition on scanning radars
• Improve low isolation performance
• Improved ECM– RGPI– CRBM – RGPI/O >>PRI
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Achieving PRI Prediction
Multiple Parallel Processes
Process 2
Process N
Process Configuration
PRI DataAcquisition
...
PredictionArbitrator
Process 1
Predicted PRIPRI
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RF Agile Sources
From: Radar Technology Encyclopedia, D.K. Barton & S.A. Leonov editors, 1997
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Sine RF, Staggered PRI
8800
8850
8900
8950
9000
9050
9100
9150
9200
0 2000 4000 6000 8000 10000
Time (µs)
RF
(M
Hz)
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Sine RF, Staggered PRI
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RF Agility
• With RF prediction in addition to PRI prediction:– Fast tuning VCO can be used to generate
consistent false targets– Switch frequency at halfway point in PRI
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Why RF Prediction?
• Because DRFM generates false targets by delaying a copy of the previous radar pulse, any RF agility is fatal
• Even with prediction, up-range false targets are at the wrong frequency
• Wide Bandwidth / High Power needed for noise jamming
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Benefits of RF Prediction
• Smarter noise jamming
• Generate up-range false targets that integrate non-coherently
• Greatly reduce power required for effective ECM, possibly by 10-20 dB
• Provide training for RF agile radar modes
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Achieving RF Prediction
• Isolate agile emitter first
• Stagger RF:– Track PRI & RF
independently in parallel
• Sine RF:– RF requires PRI
prediction input
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System Integration
Predictor TG
DRFM
VIDEO&
RF TAG
Write
Trigger
Predicted RF
Modulated Output
Output Control
RF IN
Output Control
Blanking / Look ThruControl
ReadRead
RF OUT
VCO
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Test Setup• Can Generate Complex
Video Environment– 6 independent emitters
• Predictor Control• Predictor Performance
Assessment• Pre-trial Parameter
Adjustment & Optimization
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Video Generation Features
• 6 Emitters, each with :– Illumination and scan control– Multiple bursts of complex staggered or sine
PRI– RF and PW Control
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RF Prediction Accuracy
• Preliminary results for sine RF prediction
• Main sources of error are:– DFD measurement error– Prediction error– VCO tuning error
• Prediction error almost totally dependent on DFD error: 90% of predictions within DFD error limits
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Sine RF Prediction• PRI: 2.333 ms• RF mean: 9100 MHz• RF dev: 200 MHz• RF period: 100 ms• DFD res: 1 MHz• DFD error: 0
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-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10+
Error (MHz)
% o
f P
red
icti
on
99% < 1MHz
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Sine RF Prediction• PRI: 2.333 ms• RF mean: 9100 MHz• RF dev: 200 MHz• RF period: 100 ms• DFD res: 1 MHz• DFD error: 1.5 MHz
0
5
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30
35
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10+
Error (MHz)
% o
f P
red
icti
on
97% < 3MHz
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Sine RF Prediction• PRI: 2.333 ms• RF mean: 9100 MHz• RF dev: 200 MHz• RF period: 100 ms• DFD res: 1 MHz• DFD error: 3 MHz
0
5
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15
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-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10+
Error (MHz)
% o
f P
red
icti
on
91% < 5MHz
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RF Agility Demonstration
Sinusoidal RF Agile Emitter with:
Mean RF of 9.1 GHz
Deviation of 150 MHz
Cycle Time of 1.667 ms
Mean PRI of 400 us
Lock time = 46 PRI
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Lock Time = 18.4 ms
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RF Agility Demonstration
Sinusoidal RF Agile Emitter with:
Mean RF of 9.1 GHz
Deviation of 200 MHz
Cycle Time of 50 ms
Mean PRI of 2.333 ms
Input Error Versus Output Error
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± 10 MHz
DFD (Input) Error VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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± 10 MHz
DFD (Input) Error VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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± 10 MHz
DFD (Input) Error VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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± 10 MHz
DFD (Input) Error VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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± 10 MHz
DFD (Input) Error VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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RF Agility Demonstration
Sinusoidal RF Agile Emitter with:
Mean RF of 9.1 GHz
Deviation of 200 MHz
Cycle Time of 50 ms
Mean PRI of 2.333 ms
Lock Versus Output Error
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Lock
Acq / Lock VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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Lock
Acq / Lock VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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Lock
Acq / Lock VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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Lock
Acq / Lock VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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Lock
Acq / Lock VCO Tuning (Output) Error Visit us at http://www.mc-cm.com
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Implementation Challenges
• Multi-Signal Environment
• Dropped Pulses – By the Radar or Receiver
• System Limitations– Non-Simultaneous Transmit / Receive
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Example Signal Environment
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Example Signal Environment (2)
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Prediction Challenge
• Accounting for Dropped and Interfering Pulses– Interference can be removed using:
• RF, AOA, PW or Expected Time of Arrival
– Missing Pulses can be Added using:• Expected Time of Arrival
• Filtering by Expected TOA Makes SenseVideo Signal X Y
Expected TOA
False Target
X denotes dropped pulse and Y denotes interfering pulse
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Pulse Train De-interleaving
• Multiple parallel PRI prediction channels permit real time de-interleaving
• Signals present on their own at least part of the time for pattern acquisition
• Multiple scanning emitters, even with 1 or 2 non-scanning emitters
• Can select single emitter to jam based on PRI, PW and pattern length
• Or timeshare, first come first served
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Acquisiton(MAP) CPU’s
TrackCh5
TrackCh4
TrackCh3
TrackCh2
TrackCh1
TrackCh0
Video PulsePre-Processor
Track Channel Selection Logic
AndPre-trigger Generator
Lookthru Generator
User SelectCriteria
Timeshare
User Configuration
Video_In
DRFM_WDRFM_RLockFadeLook_ThruExpctd_VideoStagger_PositionEM_ID
Constant - Dwell Shift Channel
Adaptive Acquisition
TDDTime Domain De-interleaving
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TDD ResultsSelecting 1 Emitter at a Time
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0 1 2 3 4 5Emitter #
%
Predictor Effectiveness
Present Alone
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TDD ResultsSelecting 1 Emitter at a Time
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5Emitter #
%
Predictor Effectiveness
Present Alone
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Effects of Dropped PulsesSelecting Emitter 2 - Varying Drop Outs
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50
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0 2 5 7 10Drop Out %
% O
vera
ll
Predictor Effectiveness
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Effects of Dropped PulsesSelecting Emitter 2 - Varying Drop Outs
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0 2 5 7 10Drop Out %
% O
vera
ll
Predictor Effectiveness
Acquired on First Scan
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Application: System Control
• Controlling a Receiver / Transmitter using the Look-Through Method– Non coverpulse technique
– Cover Pulse Technique
Video Signal
Receiver Enable
Transmitter Enable
Video Signal
Receiver Enable
Transmitter Enable
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Application: Timesharing
• Use a single DRFM to jam multiple (scanning) radars simultaneously
• Encompasses both:– Real-time pulse train de-interleaving– Real-time control of DRFM Read and Write
• Algorithm calculates optimal allocation based on signal present, predictor accuracy, first come first served, scan priority
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Timeshare Application
• Weapon Systems that use separate Acquisition and Track radars– Acq can provide good set-on to Tracker
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Timeshare Track & Acq
Timeshare Results: Video #1 Non-scanning
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1 2 3 4 5 6
Video Generator
% C
orr
ect
Pre
dic
ito
ns
Tracking 1&2
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Application: Timeshare
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Application: Fade + Re-Acq
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Application: Head to Tail
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Application: CRBM
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Application: RGPI >> PRI
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Application: ESM / RWR
• A Multi-Channel Predictor used to de-interleave the Received Video could greatly speed up the identification of threats in order to begin jamming sooner
• Predictor could act as a real-time filter for known emitters and enable the ESM / RWR system to process the unknown faster
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PRED-5 Features
• Small 3” x 6” PMC format• Pod or lab use• 4 or more parallel channels – multi-threat
capability• Adaptive Acquisition• Constant, dwell shift, sliding, stagger (> 192
pos), embedded sine• Add or improve ECMs• RF prediction can be used to control VCO
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PRED-5 Features• Time domain or RF de-interleaving, timeshare &
controller• Embedded user memory• Available soon as chip set: Stratix II FPGA plus flash
memory
33 mm x 33 mm Chip PMC Card
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Prediction:Summary (1)
• No a-priori radar information is required– Real-time “learning”
• Easily added to a system– Variety of form factors
• Solves systems issues
Agile threatsScanning radarsMissing Pulses
Antenna isolationDRFM contaminationExtra pulses
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Summary (2)
• Applications Include:– Real-time de-interleaving– Rx/Tx switching (look-through)– Advanced ECM functions
• Up-range false targets
• CRBM
• CRV
– ECM Timesharing among multiple emitters– ESM/RWR pre-filter
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Acknowledgement
The authors would like to acknowledge the contributions of the other members of the MC Countermeasures team including:
• Dan Grise
• Colin Jackson
Questions
For further information, please feel free to contact us at:
MC Countermeasures Inc. http://www.mc-cm.com
260 Hearst Way, Suite 207
Kanata, Ontario, K2L 3H1 Canada [email protected]
Tel: +1 (613) 592-0818 [email protected]
Fax: +1 (613) 592-2818 [email protected]