According to the NASA news article NASA’s NavCube Could Support an X-ray Communications Demonstration in Space — A NASA First:
The new technology, called NavCube, combines NASA’s SpaceCube, a reconfigurable and fast flight computing platform, with the Navigator Global Positioning System (GPS) flight receiver. Navigator
“A Match Made in Heaven”
As part of the potential XCOM demonstration, NavCube will drive the electronics for a device called the Modulated X-ray Source, or MXS, which generates rapid-fire X-ray pulses, turning on and off many times per second.
From this article I understand that NavCube is a unique, fast computer for space applications, combined with a unique, sensitive GPS receiver also optimized for space applications.
The X-ray communications investigation/demonstration will put an X-ray transmitter at one end of the ISS and an X-ray receiver at the other. In this case the receiver will be NICER, an array of X-ray telescopes that will primarily be used to study astronomical sources such as neutron stars, and to look into the possible use of timing from pulsars as a deep space positioning system for navigation.
Would NavCube then actually just serve as a signal generator for some high-speed pulsed X-ray generator?
above: "NavCube, the product of a merger between the Goddard-developed SpaceCube 2.0 and Navigator GPS technologies, could play a vital role helping to demonstrate X-ray communications in space — a potential NASA first. Credits: NASA/W. Hrybyk" from here
above: NICER X-ray timing telescope/concentrator array, from About NICER.