Like most areas of technology, depth of understanding usually has its genesis in definition of terms.
This is certainly true with satellite communications. It’s especially important to know two terms:
A high-Earth orbit is called geosynchronous if the satellite is synchronized with Earth’s rotation. But a geostationary orbit is, as the name implies, when a satellite stays over the same point on Earth all the time. Communication satellites are often placed in a geostationary orbit so that Earth-based satellite antennas do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located.
Weather satellites are also placed in this orbit for real time monitoring and data collection, as well as navigation satellites to provide a known calibration point and enhance GPS accuracy.
Geostationary satellites are launched from as close to the equator as possible to provide the maximum launch boost and to limit the amount of inclination change needed later. Satellites in geostationary orbit must all occupy a single ring above the equator.
The requirement to space these satellites apart to avoid harmful radio-frequency interference during operations means that there are a limited number of orbital “slots” available, and thus only a limited number of satellites can be operated in geostationary orbit.
Along those lines, it’s also important to know that the satellite industry abides by certain standards. GMR for example is a standard for satellite phones created by ETSI (The European Telecommunications Standards Institute). The GMR-1 air interface specifications were first published in 2001 (GMR-1 Release 1) based on the GSM protocol architecture with satellite specific optimizations.
The objective is to allow mobile satellite service (MSS) operators to provide forward-looking IMS (IP Multimedia Subsystem) based services. Key features included in this air interface are:
- Robust waveforms for link closure with terrestrial form-factor MESs.
- IPv6 compatibility.
- Spectrally efficient multi-rate VoIP with zero-byte header compression.
- Up to 592 kbps throughput.
- Multiple carrier bandwidth operation.
- Multiple terminal types such as hand-held terminals, PDA, vehicular, portable and fixed.
Want more? Tonex offers Technical Aspects of Satellite Communications Training for non-Engineers, a 4-day course designed to provide a general technical overview of Satellite Communications and GMR-1 family of technologies for non-technical professionals including sales, marketing, product managers, finance, project and program managers, and executive management. Note: This course can be customized.