The objective of this activity is the development of a software library for signal processing in order to create a transponder for satellite communications (TT & C, telemetry, tracking and command transponders), compatible with European standards (ECSS). This library will be used in a hardware-in-the-loop test system to develop and validate new ground modems or satellite transponders. The validation of the software will be performed with a radio frequency development platform and the operational conditions for the transponder will be reproduced using a simulator. The project is realized in collaboration with the European Space Agency which will support the testing and validation phase of the software produced.