Target recognition based on phase noise of received laser
signal in lidar jammer
Mahdi Nouri, Mohsen Mivehchy*, and Mohamad Farzan Sabahi
Department of Electrical Engineering, University of Isfahan, Isfahan, Iran
*Corresponding author: mivehchy@eng.ui.ac.ir
Received March 22, 2017; accepted June 6, 2017; posted online July 11, 2017
In this Letter, a method based on the effects of imperfect oscillators in lasers is proposed to distinguish targets in
continuous wave tracking lidar. This technique is based on the fact that each lidar signal source has a specific
influence on the phase noise that makes real targets from the false ones. A simulated signal is produced by complex
circuits, modulators, memory, and signal oscillators. For example, a deception laser beam has an unequal and var-
iable phase noise from a real target. Thus, the phase noise of transmitted and received signals does not have the
same power levels and patterns. To consider the performance of the suggested method, the probability of detection
(P
D
) is shown for various signal-to-noise ratios and signal-to-jammer ratios based on experimental outcomes.
OCIS codes: 030.5630, 050.5080, 060.5625, 070.1170, 070.6020.
doi: 10.3788/COL201715.100302.
Nowadays, coherent Doppler tracking lidars are exten-
sively used due to their low required signal power in veloc-
ity and range measuring of moving targets
[1–5]
. Idyllically,
a speckle noise free signal with Doppler frequency can
be denoted with a spectral frequency lin e
[6]
. A narrower
linewidth laser source with linear frequency-modulated
continuous-wave (LFMCW) modulation is extensively
employed in several applications. Particularly, when
the accurate velocity and range is required in the lidar
system
[7–10]
. To confuse the tracking lidars, deception laser
beam (DLB) systems are used to produce false signals by
storage, velocity and distance of signal processing, and
sending back the lidar and radar signal
[11]
.InaDLB
system, the input laser beam (LB) signal is first downcon-
verted to an intermediate frequency (IF) by a laser local
oscillator (LO) in a coupler. Then, an analog-to-digital
converter (ADC) quantizes and samples these IF signals.
Then, they are rescheduled to produce the DLB signal
properties like amplitude, frequency, and phase. After
digital-to-analog conversion (DAC), the fake signal is up-
converted by the LO signal with a false Doppler frequency,
through a single-sideband (SSB) modulator, to send back
to a hostile transmitter
[12–14]
. The DLB recognition is one
of the serious problems of tracking lidar systems. The au-
thors in Ref. [
15] proposed an arbitrarily phase-coded
method that could be utilized to decline the replicas. Some
techniques focus on the characteristics of the lidar signal.
One of these techniques is proposing a cone class to
categorize the DLB signals based on the number of
DAC quantization levels
[16]
. Another method
[17]
utilizes a
support vector machine (SVM) with kernel linear
discriminator analysis (KLDA) feature extraction to sep-
arate the targets.
In this Letter, a discrimination method is proposed to
recognize the beat frequency signal (BFS) generated by
a DLB that has a higher−order nonlinearity (phase noise)
of transmitting light from false signals. This method con-
centrates on various phase noise levels of the DLB block
and a hostile lidar. In a CW tracking lidar, the master
oscillator (MO) produces the lidar signal due to its own
phase noise. In other words, this signal is signified with
particular phase noise characteristics by the laser oscilla-
tor. The MO of tracking lidars has low-phase noise level
oscillators. On the other hand, the DLB jammer has a
high−phase noise level since several kinds of subsystems
exist in the DLB structure. A simulated DLB signal made
through complex circuits has higher phase noise levels and
diverse patterns in comparison to a real signal target. It
should be noted that the power spectrum of the phase
noise is measu red by the same set of circuits.
The CW transmitted signal with laser frequency modu-
lation (LFM) can be expressed as
xðtÞ¼
E
s
p
e
j½2πf
c
tþπμt
2
þφ
MO
ðtÞ
; (1)
where E
s
, f
c
, μ, and φ
MO
ðtÞ are the lidar signal power,
the lidar central frequency, the frequency chirp rate,
and the instantaneous phase of the MO of lidar, respec-
tively. The received real and DLB signal in the IF band
can be written as
y
φ
ðtÞ¼
E
s
p
~
a
r
expfj½2πðf
IF
þ f
d
r
Þt þ πμt
2
þ 2πμτ
r
t þ φ
MO
ðt − τ
r
Þ − φ
r
LO
ðtÞg þ νðtÞ: Real Target;
E
J
p
~
a
J
expfj½2πðf
IF
þ f
d
J
Þt þ πμt
2
þ 2πμτ
J
t þ φ
MO
ðt − τ
δ
− τ
J
Þ − φ
J
LO
ðt − τ
f
Þþφ
J
LO
ðt − τ
J
Þ − φ
LO
ðtÞg þ νðtÞ: DLB;
(2)
COL 15(10), 100302(2017) CHINESE OPTICS LETTERS October 10, 2017
1671-7694/2017/100302(4) 100302-1 © 2017 Chinese Optics Letters