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
Echo Location in Bats and Radar
Finding Dory: Echo Location in Beluga Whale
Whale Songs
• Communication: "grunts", "groans", "snorts" and "barks“
• Music: 'for art's sake’ (untestable question)
• Serving multiple purposes simultaneously: echo location/navigation, communication, etc
Bird Communication via Chirping Sound
Chickadee
Yellow Warbler
• Proclaim and defend their territories•Attract and impress
potential mates
•A fast-approaching predator is detected.
Birds Communication
• Multiple layers
• Across species
• Within the same species
• Only understood by a few individuals
• Secure communication
Security and LPD RF Waveform
• Security of information (bits): encryption
• Security of communication itself: low probability of detection
Traditional Low Probability of Detection (LPD) Waveform Design
8
• Spread spectrum
• Noise-like waveform
• Both
Spread Spectrum
Noise-like Waveform Design
• White Gaussian noise waveform
• Chaotic waveform
• Animal sound waveform
Problem
• Cyclostationary analysis will reveal digital modulation
New LPD Waveform Design
• Do not hide waveform itself
• Hide communication in an existing RF signal
• RF Steganography
Joint radar/comm waveform design
Linear Frequency Modulation (LFM) Chirp
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
Up Chirp and Down Chirp
Chirp Modulation
• Long-short Chirp Modulation
1 0 0 0 1 1
• Up-down Chirp Modulation
1 0 0 0 1 1
BPSK-Chirp Modulation
Chirp (LFM Signal)
BPSK Signal
BPSK Modulated Chirp
Ambiguity Function (AF)
Un-modulated Radar Chirp Signal
LFM AF Plot LFM AF Plot - Top View
Ambiguity Function (AF)
BPSK Modulated Radar Signal
LFM AF Plot LFM AF Plot - Top View
Spectrum Correlation Function (SCF)
LFM Radar Signal
SCF of BPSK Modulated LFM Chirp
BPSK Modulated Radar Signal
High SNR for Comm
Reduced Phase Shift Keying
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
Reduced PSK Modulation
Constellation of Reduced phase shift keying modulation
Reduced PSK-Chirp Modulation
Chirp (LFM Signal)
BPSK Signal
RPSK Modulated Chirp (ϕ =15o)
Ambiguity Function (AF)
RBPSK modulated Radar Signal (ϕ =15o)
LFM AF Plot LFM AF Plot - Top View
SCF of RPSK Modulated LFM Chirp
RPSK Modulated Radar Signal
Variable Symbol Duration (VSD) RPSK
Fixed symbol duration
Variable symbol duration
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
SCF of VSD-RPSK modulated Radar Signal
SCF Comparison between VSD-RPSK and Un-modulated Chirp Signal
Un-modulated Chirp
VSD-RPSK
Cognitive Radio (CR)
Cognitive Network (CN)
• Pioneering work of Ryan Thomas
• Network of CR vs CN
• Cognition
From XGtechnology
Cognitive Cycle
Cognitive RF
• Combining communication/radar/navigation/EW
Sponsors
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
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.
