Military Communications and Information Technology: A Trusted ...

Chapter 1: Concepts and Solutions for Communications and Information Systems
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impossible and meaningless, because it would block own radio links. Therefore
it is, necessary to provide a selective distortion emission, based on information
obtained from the electromagnetic spectrum monitoring.
III. Jamming principles and techniques
In this chapter we discuss basic techniques and parameters of jamming signal.
In order to disrupt radio signals there are applied devices which ensure appropriate
parameter values of jamming signals. The major parameter determining the degree
to which jamming will be successful is jamming (J) to signal (S) ratio JSR, described
by the general formula shown below [5]
JSR[dBm] = ERP J – ERP S – L J + L S + G RJ – G R (1)
ERP J – effective radiated power of jamming station in dBm;
ERP S – effective radiated power of transmitter signal in dBm;
L J – propagation loss from jamming station in dB;
– propagation loss from transmitter signal in dB;
L S
G RJ
G R
– jammed receiver antenna gain in the direction of jamming station in dBi;
– jammed receiver antenna gain in the direction of transmitter station in dBi.
The minimum value of JSR is dependent on the signal type which is jammed,
signal propagation and jamming technique.
Jammer designers can use various techniques of jamming. All techniques
have their own advantages and disadvantages and application each of them is directly
associated with type of jammed signal. The basic techniques include: noise
jamming, tone jamming, swept jamming, pulse jamming, follower jamming and
smart jamming [3].
A. Noise jamming
Noise jamming is based on jamming carrier signal which is modulated with
a random (Gaussian) noise waveform. This technique causes disruption of communication
between transmitter and receiver by inserting high level noise. A bandwidth
of jamming signal can have different width. Depending on the bandwidth occupied
by noise jamming signal, it can be distinguished the following types of signals:
broadband noise (BBN), partial-band noise (PBN) and narrowband noise (NBN).
BBN places noise energy inside entire bandwidth used by the communication
system which is planned to jam. Generally BBN jamming signals fills the channel
capacity. If the noise power is raised by inserting BBN signals into the channel,
the signal to noise decrease and according to Shannon theorem, channel capacity
also decrease [4].
PBN places noise energy inside multiple channels indicated to disrupt.
The channels may be contiguous or noncontiguous.