Electronic Attack

The electronic attack means degrading, neutralizing, or destroying the opponent’s warfare capability with the use of anti-radiation weapons, directed energy, or electromagnetic en- ergy [16,23]. In the electronic attack operations, the attacks are against facilities, personnel, or equipment and it includes actions that reduce or prevent the opponent’s electromagnetic spectrum usage [16, 18]. These are depicted in Fig. 2.11. The directed energy is um- brella term for applications that produce beam of concentrated electromagnetic energy or atomic/subatomic particles [16,23]. It requires more considerable amount of energy than physical-layer jamming, and its task is to destroy or harm the opponent’s communication equipment [53]. For example lasers, with long distance, precision and accuracy properties, are used as the directed energy weapon to cause fatal damage to the opponent [35]. The electromagnetic weapons, on the other hand, are used primary for countermeasures and they include both defensive and offensive activities [23].

The countermeasures, as a part of the electromagnetic weapons, are techniques and devices whose objective is to offset or counter functional capability of the opponent from acting [16,18,23]. Offensive electronic attack [23] contains, e.g., opponent’s radar or electronic C2 system jamming, usage of the anti-radiation missiles against the radars of opponent’s air defenses, and utilization of an electronic deception to cause false information to the opponent’s intelligence. Also, the offensive electronic attack includes the operations related to surveillance and reconnaissance systems, and usage of earlier mentioned the directed- energy weapons. Differently, defensive electronic attack contains, i.e., expendables (flares, active decoys, et cetera), the improvised explosive device systems and self-protection to defend equipment, facilities, personnel, and capabilities [18].

Physical-Layer Jamming

As mentioned earlier, the offensive electronic attack contains physical-layer jamming. The physical-layer jamming is covered in more detail next because of its importance to the final work of this thesis and it is displayed in Fig. 2.12.

EA

(Electronic Attack)

(Electronic Protection) (Electronic Warfare

Support)

Defensive

activities Offensive activities

Countermeasures

Directed energy Electromagnetic weapons

Jamming Tune Jammer

Swept Jammer

Barrage Jammer

Adaptive Jammer

Figure 2.12. The physical-layer jamming as a part of the offensive electronic attack operations.

The primary goal of jamming is to prevent an opponent from using radio links for freely exchanging tactical information [26]. It has been shown [3,26,52,53] that denying at least one-third of tactical transmissions is substantially efficient against uncoded or coded digital data communications. Basically, the jamming is all about getting sufficient amount of energy into the opponents’ receivers at the right time and place [26]. It serves much larger purpose than just denying the tactical communication. Such purpose [44] could be denying

wireless users access to the particular network with strong privacy and authentication mechanisms while allowing entrance to different network with inadequate security measures.

Cyberattacks, on the other hand, are attack vectors launched through the network and they can be used, f.e., in MANETs [44]. However, here only physical-layer jamming is being discussed.

There are several possible ways of jamming against opponent’s communication systems where some of them are more effective than others. However, one should perform following steps [44] before launching the jamming attack: sense and detect signals over the spectrum of the interest, choose whether an individual signal will be jammed, and select the best jamming strategy for the preferred signal. In this thesis, only best-known and the most relevant jamming strategies will be discussed. Those aretune jammer, swept jammer, barrage jammer, andadaptive jammer. Their working principles can be seen in Fig. 2.13.

The perspective here is overlapping opponent’s tactical signal with the jamming signal in time or frequency domain [44]. Other features, such as antenna characteristics and modulation type of the jammer also affect a jammers efficiency [44].

a) Tune Jammer b) Swept Jammer

c) Barrage Jammer d) Adaptive Jammer

PowerPower FrequencyPower

Frequency Time

Frequency Frequency

Jamming signal

Jamming signal

Jamming signals Jamming signal

Figure 2.13. Jamming strategies

The most simplest one is called astune jammer[3,26,52,53] in Fig. 2.13(a). Here, jammer operator tunes its exact jamming frequency and bandwidth according to the measured opponent’s transmission. Periodically the jammer is switched on and off to see if the opponent’s signal is still there. If the tune jammer can be tuned rapidly, it is called as follower jammer, and it is incredibly efficient against FH radios [44,52,53]. For example, Link 16 uses such of the FH patterns.

When there is a need to jam multiple signals, or the opponent’s signal is changing in the frequency,swept jammer[26,53] in Fig. 2.13(b) can be used. Saw type sweep is mostly used, but any type of sweep can be utilized. Since the opponent’s tactical signal is swept, the full range of frequencies can be jammed in a short period. The swept must be fast enough ensuring that the whole band is covered in sufficiently short period to prevent the opponent from communicating. Also, it is possible sectoring the jammer to avoid certain bands that are used by the allied team.

Another type for jamming wide bandwidth is to utilizebarrage jammer[26,44,52,53] in Fig. 2.13(c) which simultaneously jams broad band of the spectrum. The barrage jammers are efficient in cases where the opponents’ spectrum usage is unknown. Also, the barrage jammers can be used to jam the FH signals; however, they require very high powers because energy is spread over the full bandwidth. If the opponent’s bandwidth is known, it is not necessary to jam the bandwidth entirely with this type of the jammer. As mentioned earlier, one third is enough [3,26,52,53].

Finally, if more than one frequency needs to be jammed,adaptive jammer[26,53] shown in Fig. 2.13(d) can be used. This type of the jammer splits available power into the required number of channels to jam several signals simultaneously. Because of power splitting ability, new channel addition reduces available jamming power for each channel. Also, this adaptivity can be further developed forlearning [44] to which cognitive properties can be attached. This learning means that the jammer can modify its behavior according to past experiences in real time. Also, if the technology of opponent’s radio system is known, smart jamming[26,53] techniques can be utilized. These smart jammers rely on detailed knowledge of network operation, and then vulnerable parts of the system can be jammed.

Usually, terrorists use commercial products, e.g., in their RC improvised explosive devices.

These remotely activated explosives can be easily countered with the smart jammers [26].