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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

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.