Understanding Satellite Link Emulators: Basics and Applications

This page covers the basics of satellite link emulators. It mentions an application note from dBm Corporation on how to use a satellite link emulator to model the satellite channel for testing satellite ground station equipment.

As we know, satellite communication systems use different frequency bands for communication, such as L Band (1-2GHz), C band (4 to 8GHz), Ku band (12 to 18GHz), and Ka band (26.5 to 40GHz). A portion of the L band is used in Inmarsat.

Image alt: satellite communication system

The figure above illustrates two modes used in satellite communication: star and mesh.

The link between a VSAT terminal and a satellite, and from the satellite to the VSAT terminal (i.e., ground station), is simulated for testing purposes. In such testing, real-time testing with a live satellite is not required, saving considerable time while achieving the same test performance.

In Iridium satellite systems, different bands are used between the user and the satellite, the gateway and the satellite, the satellite and the gateway, and between satellites (inter-satellite links). Inter-satellite links use the 22.55 to 23.55 GHz range. This satellite-to-satellite link can also be simulated using a satellite link emulator.

There are different satellites for different applications, such as:

• Communications satellites (used for VSAT-based communication)
• Remote sensing satellites
• Weather satellites
• GPS satellites

All types of satellites have two major elements:

• Payload: The equipment the satellite needs to do its job. This includes cameras, antennas, radar, and electronics. All satellites have different payloads. For example, a communication satellite has antennas as a payload, while a weather satellite has cameras.
• Bus: The part of the satellite that carries the payload and its equipment into space for launching. The bus provides power and keeps all the parts together. It also has equipment for the satellite to communicate with earth station equipment.

Application Note: How to Use a Satellite Link Emulator from dBm Corporation

dBm Corporation provides SLE9000 series satellite link emulators for testing VSAT and earth station equipment in simulated real-time mode. This application note covers the features of the dBm satellite link emulator. The satellite link emulator provides RF link emulation for VSAT terminal or payload development.

SLEs are used for the following applications:

• Earth Station testing
• Satellite payload testing
• Mobile transceiver testing
• Satellite system integration tests
• Satellite to UAV tests

It provides emulation for the following links and orbit modes:

• Earth to satellite to earth (in mesh mode)
• Earth to satellite links
• Low Earth Orbit
• Medium Earth Orbit
• Geostationary orbit and Geosynchronous orbit
• Satellite to satellite links

Image alt: satellite link emulator set up

Satellite link emulators can simulate propagation delays, path loss, flat fading, phase shift, and different Doppler frequency shifts. Optional features such as multipath fading (Rician and Rayleigh) and AWGN are available. In multipath fading, up to 6 paths can be simulated per channel.

dBm Corporation offers external frequency converters to extend the testing coverage in a wide variety of radio frequency bands used in satellite applications.

dBm satellite channel emulators come with easy-to-use GUI software that helps in setting up various parameters in a handy manner. It helps in programming all the orbits as well as any earth station coordinates. Various satellite systems such as Iridium®, ICO®, Globalstar®, and Inmarsat® can be simulated. The GUI software runs on any Windows-based computer.

Figure-2 (not provided in the original text) depicts a test bed for testing VSAT ground equipment.

In earlier days, a TLT (Test Loop Translator) was used, which housed only an LO that converted 6 GHz frequency to the corresponding 4 GHz frequency. Nowadays, satellite link emulators introduce all sorts of impairments, such as frequency offset, phase noise, time delay, and channel models, to simulate the real-time test scenario.

Another manufacturer/vendor of satellite link emulators is Polaris. They have various models like PSLE-L-10D, 100D, 200D, and so on.