CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20151 Wei Su and John Kosinski U.S. ARMY CECOM RDEC Intelligence and Information

CECOM Bottom Line: THE WARFIGHTERFile Name.PPT - Briefer’s Name - Briefed 04/21/231

Wei Su and John Kosinski

U.S. ARMY CECOM RDEC

Intelligence and Information Warfare Directorate

Fort Monmouth, New Jersey

COMPARISON AND SIMULATION OF DIGITAL MODULATION RECOGNITION

ALGORITHMS


signal

center frequency

Cooperative Communication

Non-cooperative Communication

symbol rate

signal

? ?Signal processing

Statistical estimation

pulse shaping

?

Demodulated

signal

Modulation recognition

modulation type

?

Automated Signal Exploitation and Modulation Recognition

Automated Signal Exploitation and Modulation Recognition


Factors Affect the Modulation Recognition Results

Factors Affect the Modulation Recognition Results

Residual carrier frequency estimation Carrier frequency and phase tracking Baud rate estimation and pulse

timing Pulse shaping recovery Channel distortion


PSK8 signal with phase shift produced by center frequency offset

A PSK8 signal

Center frequency offsetCenter frequency offset


4 samples per symbol 10/3 samples per symbol

Re-sampling will be necessary if the symbol frequency divided by sample frequency is not an integer

Error is introduced in re-sampling

After re-sampling

Before re-sampling

Pulse TimingPulse Timing


Before 16-QAM After

Transmitter Radio Channel

RF Receiver Equalizer Decision Maker

An adaptive filter (lower figure) is used to eliminate the multiple channel distortion in wireless communication. A distorted 16-QAM signal (left figure) is blindly equalized to give a correct output (right figure) before recognition process

Channel DistortionChannel Distortion


A web site search of “modulation recognition” gave 52,500 hits.

More than a hundred publications on modulation recognition.

Many GOTS and COTS products available for various applications.

Literature SearchLiterature Search


Modulation feature extraction I-Q Analysis Zero-crossing Power-law

Modulation classification Pattern recognition Maximum likelihood

Some Well-known Approaches


Deferent modulation type Deferent assumption Deferent signal environment Deferent specification

Problems in Algorithm Comparison

PSK2

PSK8

PSK4

FSK8

FSK4

FSK2

ASK4

ASK8

ASK2

32QAM

CW

UNKNOWN

64QAM

16QAM

MSK

PSK

PSK

FSK


Based on signal parameter variances and variance thresholds

CW PSK2PSK4ASK2ASK4FSK2FSK4

Base Band Signal

reco

gniti

on

tree

thresholds

x

xix )( s.t.d.

abs

frequency phase

amplitude

Azzouz and Nandi’s Method


Phase Variance is affected by the Center Frequency Offset

Phase Variance is affected by the Center Frequency Offset

BPSK with residual carrier after phase tracking and compensation

unwrapped phase trackingphase tracking


Phase Variance is Affected by Pulse Shaping (/4 DQPSK)

Phase Variance is Affected by Pulse Shaping (/4 DQPSK)


Phase Variance is Affected by Phase Wrap


Limitation in Azzouz and NandiLimitation in Azzouz and Nandi

Not robust to center frequency offset Not robust to pulse shaping Not robust to phase wrap Thresholds depend on SNR level Restricted in modulation types (2 bits)


Liedtke’s MethodLiedtke’s Method

I

/

( )2

( )2

+

tan-1

amplitude

IF

sqrt

timing circuit

Q

t2

T

Freq.

delta phase

BPFbaud rate detector

hist

ogra

ms

CW PSK2 PSK4 PSK8 ASK2 FSK2

templates

reco

gniti

on tr

ee

s.t.d

Based on delta-phase and histogram correlation


Limitation in Liedtke’s Method Limitation in Liedtke’s Method

Manual tuning of center frequency Manual tuning of the time-recovery band

pass filter Limited in modulation types


IF

s.t.d.

delta-phase histogram

frequency estimation

phase estimation

histogram templates

zero-crossing counter

reco

gniti

on tr

ee PSK2 PSK4 PSK8 FSK2 FSK4 FSK8

templates

Zero-crossing Detection Method

Based on zero-crossing phase, and delta phase histogram


Not robust to multiple frequencies Need high SNR Need high sampling rate

Limitation in Zero-Crossing Method


signal ( )2

( )4

FFT peak detection

envelope s.t.d.

PSK2 PSK4 ASK2 FSK2

reco

gniti

on tr

ee

Power-Law Classification Method

Based on power spectrum analysis


Need very high sampling rate Affected by pulse shape Limited in modulation types Noise is amplified with high order

Limitation to Power-Law Method


CW PSK2PSK4PSK8ASK2ASK4FSK2FSK4

IF

I

/

( )2

( )2

+

tan-1

amplitude

down demodulation

sqrt

Q

frequency

phase


reco

gniti

on tr

ee

adaptive thresholds

x

xix )(s.t.d.

abstiming

recovery

track and

correct phase

x

xix )(s.t.d.

abs

x

xix )(s.t.d.

abs

x

xix )(s.t.d.

abs

X2

phasex2

Modified Azzouz and NandiModified Azzouz and Nandi


Before BPSK After

The unwanted phase rotation (left figure) is corrected adaptively (right figure) by a modified blind carrier phase tracker (upper figure) so that the feature variation methods can be used robustly for modulation recognition

)(

)(

2

1

ximag

xreal

x

xx

symbol xVx

z

zz

2

1

01

10)()( 2

22121 zzzzzG

2

)( 22

2121 zzzz

VzGI

V

1

)(Estimated

phase

Center Frequency Offset CorrectionCenter Frequency Offset Correction

Method 1:

Method 2: CFO = angle( (yky*k-1)fs/2/ k = 1, 2, …, N

yk is a sample at k fs is the sampling frequency


Modified LiedtkeModified Liedtke

I

/

( )2

( )2

+

tan-1

amplitude

down demodulation

sqrt

timing circuit

QT

frequency

delta phase

varia

nce

test

CW PSK2PSK4PSK8ASK2ASK4ASK8FSK2FSK4FSK8


peak detector

reco

gniti

on tr

ee

templates

IF


There are many publications but most of them are related to base band symbol recognition

Center frequency offset (CFO), pulse shape, timing, and channel fading can be estimated but the estimates will not be perfect

Signal type UNKNOWN should be defined in all algorithms

A good modulation recognition algorithm should be robust to CFO, timing error, and fading

Summary

Documents

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20151 Wei Su and John Kosinski U.S. ARMY CECOM RDEC Intelligence and Information