Inmarsat Aeronautical Ground Data Units (GDUs) are used to supervise the testing of Aeronautical Earth Stations (AESs) against requirements in the Inmarsat Aeronautical System Definition Manual (SDM) and to permit monitoring of Ground Earth Station (GES) and AES performance in an operational system.
In its base configuration, the GDU requires only one Channel Unit (CU); however, the IF Unit (IFU) or RF Unit (RFU) may also be utilized to integrate more of the required elements of a test bench. The GDU CU may be populated with one to four full-duplex channels. AES access approval testing can be performed using the configuration shown. The Inmarsat Access Approval Test System (AATS) serves as a protocol tester. The CU implements the aeronautical physical layer (and optionally the link layer) to the 70 MHz IF. The RFU performs the frequency conversion between IF and RF.