IEEE - Aerospace and Electronic Systems - April 2023 - 19

Huang et al.
Figure 4.
Extracted features from the Frank code PSK signal using (a) VMD and EMD, (b) WVD, (c) CWD, and (d) wavelet transform.
wavelet transform is used so that the joint time-frequency
representation can be obtained and further used as the
wavelet features to be put into the classifier. In FALPINE,
the Morse wavelets are selected as they are commonly
used in time-frequency analysis [27]. The wavelet features
can be obtained by the following equations:
Wðj; kÞ¼
X
j
cjkðnÞ¼ 2 cð2jn kÞ
j
2
X
k
sðkÞcjkðnÞ
(8Þ
(9)
where sðkÞ is the signal samples, Wðj; kÞ are the wavelet
transform coefficients, cjkðnÞ is the mother wavelet, and j
and k are the scale parameter and shift parameter, respectively.
Figure 4(d) shows the wavelet feature of the Frank
code PSK signal.
FEATUREEVALUATION
The feature evaluation for each feature aims to obtain the
performance sense of the features going beyond the fusion
operations. To obtain the LPI signal recognition performance
ofeach feature, all the types ofthe generated LPI signals
including Frank, P1-P4 coded, and noise radar signals
are used for the feature evaluation. A simple three-layered
CNN model is used in the feature evaluation process. For
each feature, the CNN model is trained and tested for optimal
recognition performance. First, the number of adaptive
APRIL 2023
features from EMD and VMD is determined, as a different
number of IMFs contain variant amounts of characteristics
from the original signals, the number of IMFs contained in
the adaptive features will affect the classification performance
to some extent. Take theVMD feature as an example.
In our work, we look at the data with SNR levels of-15, -17,
and -18 dB, so that the number ofVMD features will have
significant differences in the classification performance. The
number ofVMD features is set to be from 2 to 6 and are put
into the CNN model. Figure 5 shows the results ofdifferent
numbers of VMD features. The results show that five features
are better than the other number of features for the
Figure 5.
Accuracy with different number ofVMD features.
IEEE A&E SYSTEMS MAGAZINE
19

IEEE - Aerospace and Electronic Systems - April 2023

Table of Contents for the Digital Edition of IEEE - Aerospace and Electronic Systems - April 2023

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