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All radio frequency (RF) links are subject to distortion due to the physics of the transmission media, as well as the physical environment in which the link is operating. While designers take these effects into account when developing communication systems, actual testing with these distortions realistically applied to the system under test can be problematic and costly, unless RF channel simulation is utilized.

Margin testing of a transmitter/receiver pair can occur throughout the design phase. Typically, this is done with signal generators substituting for the transmitter portion of the design and spectrum analyzers or vector signal analyzers acting as receivers. However, even with the most sophisticated equipment, this testing is typically performed in static conditions, possibly stressing a few worst, best cases, and nominal operating conditions. For many communication system designs, especially those where one or both of the ends of the communication path are in motion, maintaining realistic RF test conditions offers unique challenges. Static testing can miss communication issues related to the way the signals are impacted by the actual operating environment.

This article discusses how a new category of test tools, called channel simulators, are used in the laboratory and QA areas to create RF signals that match those that occur when communication systems are deployed on platforms in motion. Sometimes channel simulators will be referred to as link emulators, channel emulators or link simulators, depending on region and specific application. Channel simulators provide engineers with an effective and economical way of verifying and optimizing the operation and quality of communication devices, where one or more nodes are in motion.

Channel simulators do exactly what the name implies; they emulate the distortions on an RF signal when receivers and transmitters move with respect to one another. The reasoning behind utilizing a channel simulator in this case is that there are no simple alternatives. The engineering team could finish their design and place the communication system on an aircraft or satellite, thereby putting it into motion and creating realistic conditions. However, the risks of this approach can be disastrous and almost certainly costly. Consider the condition where the link is used for control of the moving platform. It is easy to see where realistic emulation in a controlled environment is a preferred approach, over a possible loss of the communication link and therefore control of the platform. A channel simulator can be utilized throughout the design phase to realistically impair signals, just as if they were in their intended operating environment, whether that environment relates to a drone flying overhead or a mission to the edge of the solar system.