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 Warfare Directorate Fort Monmouth, New Jersey COMPARISON AND SIMULATION OF DIGITAL MODULATION RECOGNITION ALGORITHMS

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20152 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

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20153 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

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20154 PSK8 signal with phase shift produced by center frequency offset A PSK8 signal Center frequency offset

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ 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 Timing

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20156 Before 16-QAM After Transmitter Radio Channel RF ReceiverEqualizer 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 Distortion

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20157  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 Search

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20158 Modulation feature extraction  I-Q Analysis  Zero-crossing  Power-law Modulation classification  Pattern recognition  Maximum likelihood Some Well-known Approaches

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/20159  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 FSK

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Based on signal parameter variances and variance thresholds CW PSK2 PSK4 ASK2 ASK4 FSK2 FSK4 Base Band Signal recognition tree thresholds s.t.d. abs frequency phase amplitude Azzouz and Nandi’s Method

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Phase Variance is affected by the Center Frequency Offset BPSK with residual carrier after phase tracking and compensation unwrapped phase tracking phase tracking

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Phase Variance is Affected by Pulse Shaping (  /4 DQPSK)

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Phase Variance is Affected by Phase Wrap

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Limitation 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)

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Liedtke’s Method I / ( ) 2 + tan -1 amplitude IF sqrt timing circuit Q Freq. delta phase BPF baud rate detector histograms CW PSK2 PSK4 PSK8 ASK2 FSK2 templates recognition tree s.t.d Based on delta-phase and histogram correlation

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Limitation in Liedtke’s Method  Manual tuning of center frequency  Manual tuning of the time-recovery band pass filter  Limited in modulation types

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ IF s.t.d. delta-phase histogram frequency estimation phase estimation histogram templates zero-crossing counter recognition tree PSK2 PSK4 PSK8 FSK2 FSK4 FSK8 templates Zero-crossing Detection Method Based on zero-crossing phase, and delta phase histogram

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/  Not robust to multiple frequencies  Need high SNR  Need high sampling rate Limitation in Zero-Crossing Method

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ signal ( ) 2 ( ) 4 FFT peak detection envelopes.t.d. PSK2 PSK4 ASK2 FSK2 recognition tree Power-Law Classification Method Based on power spectrum analysis

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/  Need very high sampling rate  Affected by pulse shape  Limited in modulation types  Noise is amplified with high order Limitation to Power-Law Method

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ CW PSK2 PSK4 PSK8 ASK2 ASK4 FSK2 FSK4 IF I / ( ) 2 + tan -1 amplitude down demodulation sqrt Q frequency phase frequency estimation recognition tree adaptive thresholds s.t.d. abs timing recovery track and correct phase s.t.d. abs s.t.d. abs s.t.d. abs X2 phasex2 Modified Azzouz and Nandi

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ 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 symbol x Estimated phase Center Frequency Offset Correction Method 1: Method 2: CFO = angle(  (y k y * k-1 )f s /2/  k = 1, 2, …, N y k is a sample at k f s is the sampling frequency

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/ Modified Liedtke I / ( ) 2 + tan -1 amplitude down demodulation sqrt timing circuit Q frequency delta phase variance test CW PSK2 PSK4 PSK8 ASK2 ASK4 ASK8 FSK2 FSK4 FSK8 frequency estimation peak detector recognition tree templates IF

CECOM Bottom Line: THE WARFIGHTER File Name.PPT - Briefer’s Name - Briefed10/12/  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