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Bio-Inspired RF Steganography via Linear
Chirp Radar Signals
Zhiping Zhang, Michael Nowak, Michael Wicks, Zhijin Wu, Zhiqiang Wu
Wright State University, Air Force Research LaboratoryUniversity of Dayton, Brown University
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Echo Location in Bats and Radar
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Finding Dory: Echo Location in Beluga Whale
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Whale Songs
• Communication: "grunts", "groans", "snorts" and "barks“
• Music: 'for art's sake’ (untestable question)
• Serving multiple purposes simultaneously: echo location/navigation, communication, etc
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Bird Communication via Chirping Sound
Chickadee
Yellow Warbler
• Proclaim and defend their territories•Attract and impress
potential mates
•A fast-approaching predator is detected.
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Birds Communication
• Multiple layers
• Across species
• Within the same species
• Only understood by a few individuals
• Secure communication
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Security and LPD RF Waveform
• Security of information (bits): encryption
• Security of communication itself: low probability of detection
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Traditional Low Probability of Detection (LPD) Waveform Design
8
• Spread spectrum
• Noise-like waveform
• Both
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Spread Spectrum
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Noise-like Waveform Design
• White Gaussian noise waveform
• Chaotic waveform
• Animal sound waveform
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Problem
• Cyclostationary analysis will reveal digital modulation
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New LPD Waveform Design
• Do not hide waveform itself
• Hide communication in an existing RF signal
• RF Steganography
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Joint radar/comm waveform design
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Linear Frequency Modulation (LFM) Chirp
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Linear Chirp for Radar and Communication
• Instantaneous frequency
• Waveform of a Chirp Signal
• Up-Chirp (k >0)
• Down-Chirp (k <0)
( )0
f t f kt
( ) 2
0 02x t f t kt
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Up Chirp and Down Chirp
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Chirp Modulation
• Long-short Chirp Modulation
1 0 0 0 1 1
• Up-down Chirp Modulation
1 0 0 0 1 1
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BPSK-Chirp Modulation
Chirp (LFM Signal)
BPSK Signal
BPSK Modulated Chirp
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Ambiguity Function (AF)
Un-modulated Radar Chirp Signal
LFM AF Plot LFM AF Plot - Top View
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Ambiguity Function (AF)
BPSK Modulated Radar Signal
LFM AF Plot LFM AF Plot - Top View
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Spectrum Correlation Function (SCF)
LFM Radar Signal
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SCF of BPSK Modulated LFM Chirp
BPSK Modulated Radar Signal
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High SNR for Comm
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Reduced Phase Shift Keying
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Reduced PSK Modulation
Constellation of Reduced phase shift keying modulation
• When ϕ = π/2, RPSK becomes conventional BPSK
min / sin ( ) sin ( )( ) ( ) ( )
2 2
0
2 2 bd A EQ Q Q
N
• BER in AWGN channel
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Reduced PSK Modulation
Constellation of Reduced phase shift keying modulation
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Reduced PSK-Chirp Modulation
Chirp (LFM Signal)
BPSK Signal
RPSK Modulated Chirp (ϕ =15o)
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Ambiguity Function (AF)
RBPSK modulated Radar Signal (ϕ =15o)
LFM AF Plot LFM AF Plot - Top View
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SCF of RPSK Modulated LFM Chirp
RPSK Modulated Radar Signal
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Variable Symbol Duration (VSD) RPSK
Fixed symbol duration
Variable symbol duration
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Variable Symbol Duration (VSD) RPSK
sin [( ) / ]
sin ( )
2
2
2i
L Hb b
i
T T
sin ( ) sin ( ) ... sin ( )2 2 2
1 1 2 2b b bi iT T T
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SCF of VSD-RPSK modulated Radar Signal
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SCF Comparison between VSD-RPSK and Un-modulated Chirp Signal
Un-modulated Chirp
VSD-RPSK
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Cognitive Radio (CR)
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Cognitive Network (CN)
• Pioneering work of Ryan Thomas
• Network of CR vs CN
• Cognition
From XGtechnology
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Cognitive Cycle
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Cognitive RF
• Combining communication/radar/navigation/EW
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Sponsors
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Summary
• RF steganography: concealing communication information in a linear chirp radar signal.
• Reduced phase shift keying (RPSK) modulation
• Variable symbol duration: removing cyclostationary features
• Joint radar/comm/navigation
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Published Paper[1] Z. Zhang, M. Nowak, M. Wicks and Z. Wu, “Bio-inspired RF
Steganography via Linear Chirp Radar Signals,” IEEE Communications Magzine, pp. 2-6, June 2016.
[2] M. Nowak, Z. Zhang, M. Wicks and Z. Wu, “Co-Designed Radar-Communication Using Linear Frequency Modulation Waveform,” accepted for publication in IEEE Aerospace and Electronic Systems Magazine.
[3] M. Nowak, Z. Zhang, L. LoMonte, M. Wicks and Z. Wu, “Mixed-Modulated Linear Frequency Modulated Radar-Communications,” accepted for publication in IET Radar, Sonar & Navigation.
[4] J. Ellinger, Z. Zhang, M. Wicks and Z. Wu, “Multi-Carrier Radar Waveforms for Communications and Detection,” accepted for publication in IET Radar, Sonar & Navigation.
[5] M. Nowak, Z. Zhang, M. Wicks and Z. Wu, “Co-Designed Radar-Communication Using Linear Frequency Modulation Waveform,” accepted for Milcom 2016.