A wifi jammer can interfere with the proper functioning of a system in a number of ways. If remote access to the control center can be achieved, for example, turning the antenna toward null can effectively mute the link. This issue is becoming increasingly important as more and more of our critical infrastructure is placed online and transmitted to the cloud, creating loopholes for those seeking to cut power, redirect links, or even shut it down.
Local jamming is a more direct approach since the target may be in motion. Here, higher power levels than the initial signal when transmitting in a particular frequency band can overwhelm the receiver and block communications. The spark gap emits noise, presenting energy in every band and at every frequency. However, noise in narrower frequency bands can also wreak havoc. For example, naughty people design, build, demo, and even provide simple wifi signal jammers to ruin other people's day.
Smart wifi jammer technology
In addition to power and frequency-based interference, smart wifi blockers are also a problem. Here, jamming techniques aim to disrupt wireless protocol operation rather than overwhelm the receiver with noise. For example, with 802.11-centric Ethernet and IP protocols, you can violate interframe spacing rules and spoof RTS/CTS messages to make the channel appear to be busy all the time. If you have wireless access to a layer 3 router, you can even redirect traffic, intercept it, disrupt it, and send it out.
This is becoming an increasingly effective technique. It can be stealthy because it uses less energy and is less visible to the victim. As forward-looking military and defense systems increasingly rely on RF links, encryption and frequency hopping alone may not be good enough.
Interfering signals on the jamming band can cause the transmitter to remain on for longer than normal, even when the data is not being extracted or altered. The cumulative effect will drain the battery faster than expected, shutting down remote or hidden links.
For these reasons, the U.S. Defense Advanced Research Projects Agency (DARPA) is looking for innovative anti-jamming solutions and is soliciting requests under its Ultra Wideband Radio Frequency Messaging (HERMES) Program 3. The entire federal government, including law enforcement, military, communications, and control, has rights to only 1.4 percent of the total spectrum. This can make military spectrum management difficult, especially as the threat of signal cannibalism or jamming grows. This aligns with a 2010 presidential decree to make an additional 500 MHz of spectrum available for commercial use by 2020, and to use that spectrum more efficiently and to make it more immune to interference.
