Testers & Simulators

Aeronautical Ground Data Unit (GDU)

Aeronautical Ground Data Unit (GDU)

Square Peg Communications Inc.’s Aeronautical Ground Data Unit (GDU) is a software application that runs on the generic Physical Layer Tester (PLT) platform. The GDU supports the testing of physical layer performance and protocol operation for Ground Earth Stations (GESs) and Aeronautical Earth Stations (AESs) implementing Inmarsat Aero services.

The GDU supports all of the Classic Aero channel types and also implements the Inmarsat Aero link layer. Interfaces are provided for external devices, including codecs, to be connected through the GDU to the equipment under test.

The GDU can run autonomously under external control. Alternatively a familiar Windows based user interface provides easy access to test functions. A powerful scripting language allows every feature of the GDU and equipment under test to be exercised in automated test cases and suites.

A complete set of Inmarsat AATS scripts is available, eliminating the requirement for a separate Micro-VAX. Scripts are also available to automate physical layer testing. For testing of normal operation and end-to-end connectivity, a GES emulator is also available.

Key Features

Integrates with legacy Inmarsat Access Approval Test System for link layer and network layer testing of AESs.
Protocol Testing can also be performed using only the GDU.


Drop in replacement for TRL and SkyWave Ground Data Units.

Transmit Capabilities

Modulators1 – 5 simultaneous (1 – 4 on PLT-H platform) 
Channel Types & Rates
  • P, R and T Channels: 600, 1200, 2400, 4800 and 10,500 bps
  • C Channels: 8400 and 21000 bps
Channel impairments

Independently-specifiable parameters:

  • Fixed carrier frequency error
  • Doppler rate, peak offset
  • Reacquisition carrier offset
  • Adjacent channel interference level and frequency offse
  • Co-channel interference level
  • I/Q gain and phase imbalance
  • Continuous phase noise spectrum, level
  • Discrete phase noise level
  • Fading model, bandwidth, C/M ratio, differential delay
  • Phase/amplitude jump distribution, magnitude, interval
  • Transmission path delay
  • Symbol rate error
  • HPA non-linearity
  • AWGN
Link LayerEmbedded implementation of Aero Link Layer

Receive Capabilities

Demodulators1 – 5 simultaneous (1 – 4 on PLT-H platform)
Channel Types & Rates
  • P, R and T Channels: 600, 1200, 2400, 4800 and 10,500 bps
  • C Channels: 8400 and 21000 bps
Link LayerEmbedded implementation of Aero Link Layer

Ethernet Interface Capabilities


Serial Interface Capabilities

FunctionalityGESTE interface, AES control interface

Avionics Interface Capabilities

MediumARINC-429 (with PCI ARINC-429 card)
FunctionalityLabel transmission / reception, Williamsburg bit-oriented protocol file transfer

Logging Capabilities

GeneralGESTE interface messages
Transmitted/received SUs
Test sequence progress and outcome
System events, faults, and abnormal conditions 

Script Capabilities

GeneralProcedure-based (like Basic, C or Pascal)
Functions for string processing, math, user interaction, logging, I/O (serial, TCP/IP, GPIB)
Integrated development environment
GDU-specificConfiguring and controlling modems
Flexible definition of SU formats
Formatting and sending SUs
Receiving SUs
Sending and receiving link layer LSDUs
Generating signal blockage events

Physical Layer Tester (PLT-M)

Physical Layer Tester (PLT-H)

  • Requires MSS L-band Radio Frequency Unit (RFU) for operation at L-band

Physical Layer Tester (PLT-L)

MSS L-band Radio Frequency Unit (RFU)

ATC Interface Unit (AIU)

Square Peg Communications Inc.
4017 Carling Avenue, Suite 200 
Ottawa, ON, Canada K2K 2A3
Tel + 1 613 271 0044
Fax+ 1 613 271 3007
Contact us for more information: