Aerospace and Electronic Systems Magazine November 2017 - 49

Leonardi et al.
After the injection of the jamming signals, the receiving detection and decoding algorithms (with or without EPA) are applied on
both the not jammed and the jammed signals. Then the decoded
data are compared to evaluate the algorithm performance.
Trials with four types of jammers were performed over about
400 real signals. For each signal, a jammer with the desired waveform and a SIR between -26 dB and 6 dB was digitally generated
with a random AOA (uniformly distributed in 0 − 2π). Various
types of jammers with various SIR were generated and analyzed.
To select the types of jamming signal to test, we considered jamming technology evolution in the Global Navigation Satellite System (GNSS) field and we selected three classes of jammer [30],
[31]. The cheapest "basic jammer" that uses a frequency tone in
the signal band was the first choice and we generated a tone on the
ADS-B nominal frequency (1090 MHz). The second most common type of jammer (more powerful than the first one but still
cheap) was the "Chirp modulated jammer". In our case the chirp
has a bandwidth of 2 MHz (from 1089 MHz to 1091 MHz) and
a repetition interval of 12.5 μs. Last, the EPA performance was
tested also with "smart jammers" (or spoofers) that emulate the
nominal signal characteristics. We generated a square wave signal
with pulse length equal to the pulse length of the ADS-B message
(0.5 μs) and a random PPM modulated data with the same characteristic as the nominal signal, i.e. the most harmful jammer illustrated in [19].

Jamming: The intentional
transmission of high power
harmful signals in the same
band as the ADS-B channel
in order to disable the air-
ground communication, for
a single receiver or in a
particular geographical area.
An example of the EPA algorithm evaluation is shown in
Figure 4, where it is possible to see the capability of the EPA algorithms to extract the two sources (the jammer and the legitimate
message) from the interfered signal. The envelope of the real jammer-free received signal is represented in (a). In (b), the envelope
of the corresponding jammed signal is shown; in this case the jammer is a PPM jammer with a SIR of 0 dB. The third (c) and the
fourth (d) parts show the two sources discovered and separated

Figure 4.

Example of the algorithm results for SIR = 0 dB and square wave jammer: (a) not jammed signal envelope, (b) jammed signal envelope, (c) and (d) two
sources envelope after their separation by using the EPA algorithm, where (d) is the degarbled ADS-B message quite similar to the original one (a).

NOVEMBER 2017

IEEE A&E SYSTEMS MAGAZINE

49



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