Aerospace and Electronic Systems Magazine August 2017 - 66

An Approach to Detect GNSS Spoofing
tive code delay is changing. The advantage of this approach is that
by reducing the Doppler difference of the spoofing and authentic
signal, the tracking loop can maintain carrier tracking, thus loss of
lock does not happen. However, if a receiver compares the carrier
and code Doppler values, there will be an inconsistency between
these values, which can be a sign of a spoofing attack. In the case
of consistent Doppler spoofing, the Doppler frequency and code
delay rates of spoofing signals are consistent. The consistent Doppler spoofing scenario is similar to a multipath interference case.

Relative Power
Spoofing power is an essential feature to misdirect a target receiver.
The relative power level of spoofing signals with respect to that of
the authentic ones can highly affect the effectiveness and error limit
of spoofing interference. Adjustment of the spoofing power level at
a target receiver is challenging since it requires information about
the propagation channel between the spoofer and target receiver,
the antenna gain pattern, and its orientation. Spoofing interference
can generate a dominant correlation peak that is more powerful than
the authentic peak and can mislead the tracking point of the target
receiver into an arbitrary point determined by spoofing signals.
In an ideal case, the power level of the spoofing signal should
be slightly higher than that of the authentic signals but it should not
excessively overpower the authentic peak in order to avoid being
detected by power monitoring techniques. A low power spoofing
interference is not able to take away the tracking point of the receiver but it can distort the shape of the correlation peak and lead
to a biased pseudorange measurement. This type of spoofing interference has a similar effect to that of multipath interference and
may lead to several metres of pseudorange measurement error [5].

Relative Delay

This section focuses on different spoofing detection methods
based on monitoring the received signal strength. These techniques generally rely on the assumption that interfering signals
are more powerful than the authentic ones. Predespreading methods evaluate the overall power content of the received signal set
without separately analyzing different PRN signals. This category of detection looks for any abnormal variation in the received
signal power prior to the despreading process in the receiver. At
this stage, the GNSS signals are buried under the noise floor and
a detection test is performed based on the analysis of the power
content of received baseband signals. Three spoofing detection
metrics are analyzed here.

Baseband Variance Analysis
This method continuously monitors the variance of baseband signals in order to detect additional power injected by interfering signals. Most commercial GNSS receivers are equipped with an AGC
module that adaptively changes the receiver input gain based on
the variance of the received signal in order to efficiently use the
quantization levels of the input analog-to-digital convertor (ADC)
module. A feedback circuit controls the AGC gain and monitoring
of this gain value is used to detect an inclined signal variance due
to the presence of spoofing interference [3]. In the case of fixed
AGC gain and adequate digitizer bits, the intermediate frequency
(IF) sample variance can be used to monitor the excessive power in
the band. Assuming that the received signal is zero mean, the input
signal variance σ2 can be represented as

σ2 =

The main goal of a spoofing attack is to misdirect the observations of a target receiver and this is associated with the relative
delays of spoofing signals with respect to those of the authentic
ones. A spoofing signal may slightly change its relative code delay
with respect to the authentic signal in order to gradually take away
the tracking point of the target receiver's delay lock loop (DLL)
without causing loss of lock. An accurately designed spoofing attack can change its relative power level as it changes its relative
delay with respect to that of the authentic ones. One of the main
differentiation factors of the spoofing and multipath signals is that
the former tries to gain control of the receiver tracking point and
slowly take the spoofing correlation peak away from the authentic
one to minimize the interference between authentic and spoofing
signals. However, in the multipath case, depending on the reflectors' geometry, multipath delays may vary within a certain range
depending on the operating environment.

DETECTION METRICS
Several spoofing detection metrics in different operation layers of a
receiver have been proposed. These metrics can generally be divided
into two categories, namely predespreading and postdespreading. In
the following, the metrics used in this investigation are defined.
66

PREDESPREADING DETECTION

1
N

N

 r (nT ) × r (nT )
n =1

s

∗

s

(3)

where r is the IF sample and N is the number of temporal samples
over which the expectation is calculated. This method does not
take advantage of any spoofing signal features and simply assumes
that the spoofing signals' power content elevates the ambient noise
floor. A spoofing (or generally interference) attack will be detected if the estimated variance is higher than a predefined detection
threshold. Defining a proper detection threshold requires an initial
power level calibration in the presence of clean signals in a typical
operational environment. As mentioned before, this method cannot
be used to distinguish spoofing from other interfering sources.

Power Spectral Density Analysis
Narrowband and partial band interference signals are more observable in the frequency domain using a spectrogram operator. The
latter is the optimal detector when the interference is a sinusoid of
unknown amplitude, phase and frequency [9], [18]. The detection
test statistic can be written as
Γ PSD

2
 N s −1
 2π nk  

= max   r n exp  − j
 
k
N s  

 n = 0


IEEE A&E SYSTEMS MAGAZINE

(4)
AUGUST 2017



Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine August 2017

No label
Aerospace and Electronic Systems Magazine August 2017 - No label
Aerospace and Electronic Systems Magazine August 2017 - Cover2
Aerospace and Electronic Systems Magazine August 2017 - 1
Aerospace and Electronic Systems Magazine August 2017 - 2
Aerospace and Electronic Systems Magazine August 2017 - 3
Aerospace and Electronic Systems Magazine August 2017 - 4
Aerospace and Electronic Systems Magazine August 2017 - 5
Aerospace and Electronic Systems Magazine August 2017 - 6
Aerospace and Electronic Systems Magazine August 2017 - 7
Aerospace and Electronic Systems Magazine August 2017 - 8
Aerospace and Electronic Systems Magazine August 2017 - 9
Aerospace and Electronic Systems Magazine August 2017 - 10
Aerospace and Electronic Systems Magazine August 2017 - 11
Aerospace and Electronic Systems Magazine August 2017 - 12
Aerospace and Electronic Systems Magazine August 2017 - 13
Aerospace and Electronic Systems Magazine August 2017 - 14
Aerospace and Electronic Systems Magazine August 2017 - 15
Aerospace and Electronic Systems Magazine August 2017 - 16
Aerospace and Electronic Systems Magazine August 2017 - 17
Aerospace and Electronic Systems Magazine August 2017 - 18
Aerospace and Electronic Systems Magazine August 2017 - 19
Aerospace and Electronic Systems Magazine August 2017 - 20
Aerospace and Electronic Systems Magazine August 2017 - 21
Aerospace and Electronic Systems Magazine August 2017 - 22
Aerospace and Electronic Systems Magazine August 2017 - 23
Aerospace and Electronic Systems Magazine August 2017 - 24
Aerospace and Electronic Systems Magazine August 2017 - 25
Aerospace and Electronic Systems Magazine August 2017 - 26
Aerospace and Electronic Systems Magazine August 2017 - 27
Aerospace and Electronic Systems Magazine August 2017 - 28
Aerospace and Electronic Systems Magazine August 2017 - 29
Aerospace and Electronic Systems Magazine August 2017 - 30
Aerospace and Electronic Systems Magazine August 2017 - 31
Aerospace and Electronic Systems Magazine August 2017 - 32
Aerospace and Electronic Systems Magazine August 2017 - 33
Aerospace and Electronic Systems Magazine August 2017 - 34
Aerospace and Electronic Systems Magazine August 2017 - 35
Aerospace and Electronic Systems Magazine August 2017 - 36
Aerospace and Electronic Systems Magazine August 2017 - 37
Aerospace and Electronic Systems Magazine August 2017 - 38
Aerospace and Electronic Systems Magazine August 2017 - 39
Aerospace and Electronic Systems Magazine August 2017 - 40
Aerospace and Electronic Systems Magazine August 2017 - 41
Aerospace and Electronic Systems Magazine August 2017 - 42
Aerospace and Electronic Systems Magazine August 2017 - 43
Aerospace and Electronic Systems Magazine August 2017 - 44
Aerospace and Electronic Systems Magazine August 2017 - 45
Aerospace and Electronic Systems Magazine August 2017 - 46
Aerospace and Electronic Systems Magazine August 2017 - 47
Aerospace and Electronic Systems Magazine August 2017 - 48
Aerospace and Electronic Systems Magazine August 2017 - 49
Aerospace and Electronic Systems Magazine August 2017 - 50
Aerospace and Electronic Systems Magazine August 2017 - 51
Aerospace and Electronic Systems Magazine August 2017 - 52
Aerospace and Electronic Systems Magazine August 2017 - 53
Aerospace and Electronic Systems Magazine August 2017 - 54
Aerospace and Electronic Systems Magazine August 2017 - 55
Aerospace and Electronic Systems Magazine August 2017 - 56
Aerospace and Electronic Systems Magazine August 2017 - 57
Aerospace and Electronic Systems Magazine August 2017 - 58
Aerospace and Electronic Systems Magazine August 2017 - 59
Aerospace and Electronic Systems Magazine August 2017 - 60
Aerospace and Electronic Systems Magazine August 2017 - 61
Aerospace and Electronic Systems Magazine August 2017 - 62
Aerospace and Electronic Systems Magazine August 2017 - 63
Aerospace and Electronic Systems Magazine August 2017 - 64
Aerospace and Electronic Systems Magazine August 2017 - 65
Aerospace and Electronic Systems Magazine August 2017 - 66
Aerospace and Electronic Systems Magazine August 2017 - 67
Aerospace and Electronic Systems Magazine August 2017 - 68
Aerospace and Electronic Systems Magazine August 2017 - 69
Aerospace and Electronic Systems Magazine August 2017 - 70
Aerospace and Electronic Systems Magazine August 2017 - 71
Aerospace and Electronic Systems Magazine August 2017 - 72
Aerospace and Electronic Systems Magazine August 2017 - 73
Aerospace and Electronic Systems Magazine August 2017 - 74
Aerospace and Electronic Systems Magazine August 2017 - 75
Aerospace and Electronic Systems Magazine August 2017 - 76
Aerospace and Electronic Systems Magazine August 2017 - 77
Aerospace and Electronic Systems Magazine August 2017 - 78
Aerospace and Electronic Systems Magazine August 2017 - 79
Aerospace and Electronic Systems Magazine August 2017 - 80
Aerospace and Electronic Systems Magazine August 2017 - Cover3
Aerospace and Electronic Systems Magazine August 2017 - Cover4
http://www.brightcopy.net/allen/aesm/34-2s
http://www.brightcopy.net/allen/aesm/34-2
http://www.brightcopy.net/allen/aesm/34-1
http://www.brightcopy.net/allen/aesm/33-12
http://www.brightcopy.net/allen/aesm/33-11
http://www.brightcopy.net/allen/aesm/33-10
http://www.brightcopy.net/allen/aesm/33-09
http://www.brightcopy.net/allen/aesm/33-8
http://www.brightcopy.net/allen/aesm/33-7
http://www.brightcopy.net/allen/aesm/33-5
http://www.brightcopy.net/allen/aesm/33-4
http://www.brightcopy.net/allen/aesm/33-3
http://www.brightcopy.net/allen/aesm/33-2
http://www.brightcopy.net/allen/aesm/33-1
http://www.brightcopy.net/allen/aesm/32-10
http://www.brightcopy.net/allen/aesm/32-12
http://www.brightcopy.net/allen/aesm/32-9
http://www.brightcopy.net/allen/aesm/32-11
http://www.brightcopy.net/allen/aesm/32-8
http://www.brightcopy.net/allen/aesm/32-7s
http://www.brightcopy.net/allen/aesm/32-7
http://www.brightcopy.net/allen/aesm/32-6
http://www.brightcopy.net/allen/aesm/32-5
http://www.brightcopy.net/allen/aesm/32-4
http://www.brightcopy.net/allen/aesm/32-3
http://www.brightcopy.net/allen/aesm/32-2
http://www.brightcopy.net/allen/aesm/32-1
http://www.brightcopy.net/allen/aesm/31-12
http://www.brightcopy.net/allen/aesm/31-11s
http://www.brightcopy.net/allen/aesm/31-11
http://www.brightcopy.net/allen/aesm/31-10
http://www.brightcopy.net/allen/aesm/31-9
http://www.brightcopy.net/allen/aesm/31-8
http://www.brightcopy.net/allen/aesm/31-7
https://www.nxtbookmedia.com