How Does Jamming Simulation Work?
Why are jamming simulators needed at all? Why not just use real jammers for testing and training? To be honest, there are some cases where “live” jamming is required. Usually this is due to accuracy (for certain tests) or exceptional transparency (the appearance of the “real thing”) during training.
There are, however, several problems with live jamming. Since it is indiscriminate, live jamming affects all users in the area. This includes government users that are not part of the testing or training scenario, as well as civilian users. These effects make it difficult to get clearance for live jamming, and such clearance often comes with an assortment of onerous conditions, such as odd hours of operation and reduced power levels and beam restrictions (which reduce accuracy or transparency). In the case of GPS jamming, civilian users must be warned, usually in the form of NOTAMS (notice to airmen). These conditions take extra time, and cost valuable testing and training dollars.
In addition to the costs and inconvenience, live jamming also, by it’s nature, transmits the threat which is expected in combat. If the threat to be tested or trained with is classified, an eavesdropper near the test area can intercept the jamming transmission and gain intelligence on the program at hand, not an acceptable situation. With a jamming simulator, all of these issues are avoided.
There are several ways to simulate jamming in communications and GPS systems. Some are more accurate than others, but each has a place in the testing and training environment. Sometimes highly accurate simulation is needed. Other times, low cost or ease of deployment is the driving requirement. For training, transparency is important, while this requirement is not as critical for the test environment. It is vital that the details of the application be considered when selecting the best method, or combination of methods.
Currently, there are several basic approaches to jamming simulation. They are:
- Beacon based jamming
In beacon based jamming, a specialized transmitter is used on a non-interfering frequency near the band of interest. The beacon contains information about the nature of the jamming, as well as some form of identification which ensures that only the correct signal is used to trigger the jamming simulator. The jamming simulator measures the strength of the beacon and injects a jamming signal into the target receiver that is proportional to the received level of the beacon. In this way the beacon appears, to the target radio, like a real jammer.
- Terrain-based jamming level prediction
In terrain-based, jamming level prediction systems, information from a topographic map of the target area is fed into a computer program which calculates jamming levels from a "virtual" jammer located at some point in the target area. The computer analyzes the distance from the specified jammer location to the target, includes information about the terrain from the map, and uses a sophisticated algorithm to determine the amount of jamming signal which is then fed to the target receiver. While not as accurate as beacon based jamming, it is easier to implement since no beacon is required.
- Location-based jamming
In location-based jamming, a map of the desired jammed area is programmed into the simulator. A GPS receiver feeds position information into the simulator, and whenever the target is within the specified area, a jamming signal is applied to the receiver. This method is accurate in determining where the jamming occurs, but does not accurately reflect the varying levels of jamming that may be encountered. The trade-off here is that this method is simple and relatively low in cost compared to more accurate methods.
- Manually controlled jamming
This is the simplest of all jamming simulation methods. A local jamming device is connected to a remote control system which allows the training controller to turn the jamming to the target receiver on and off at will. This method is not useful for testing, where accuracy is a concern, but has training value for those situations where budget or logistics are severely constrained.
All of these techniques have their advantages and disadvantages. Radio Design Group, Inc. has the experience to help you determine which system, or combination of systems, is right for your application.