There is a need for a long haul communication process for
cities or places that are far from reach by cables or any wireline technologies.
Terrains may be a factor that other wireless technologies may not be efficient.
So satellite communication comes in to minds of the carries to provide means of
voice, data and other communication access.
Low Earth Orbit
(LEO) refers to a satellite which orbits the earth at altitudes between (very
roughly) 200 miles and 930 miles.
Low Earth Orbit
satellites must travel very quickly to resist the pull of gravity —
approximately 17,000 miles per hour. Because of this, Low Earth Orbit satellites
can orbit the planet in as little as 90 minutes.
Low
Earth Orbit has been used for both military and aeronautical purposes. Military
rocketry and missiles have long taken advantage of this orbit to launch
missiles and rockets over long distances. Other than lunar flights Low
Earth Orbit defines the boundary of all human space exploration. This shows the major
technical and financial obstacles that need to be overcome in order to make
even nearby interplanetary travel possible. However there is promise in the
technologies used to send satellites into Geostationary Orbit and beyond.
LEO provides
features that other wireless technologies may not provide for remote areas.
There
are two types of LEOs - little LEOs and Big LEOs.
Big LEO
Big LEOs are used for technology devices such as high-speed,
high-bandwidth data communications, and video conferencing. They carry voice
and high-speed data services. They are aimed at data communications and
real-time voice into hand-held devices. Big LEO can also offer global services,
which are also subject to regulatory requirements. There have been five Big LEO
already licensed. The five Big LEO are Iridium, Global Star, Odyssey, ICO
Global Communications, Teledesic.
Little LEO
Little LEOs are required to offer non-voice services for example
vehicle tracking, environmental monitoring and two-way data communication. A
little LEO is a constellation of small, low-earth orbiting satellites, used for
short, narrowband communications. Little LEOs are a small, low-cost, class of
satellites. LEOs are to use a spectrum allocated between 137-138MHz for
space-to-Earth downlinks, and 148-150.05 MHz for Earth-to-space uplinks.
Advantages to LEO Satellite Telemetry
- Global applications
in developing a remote environmental monitoring communication system.
- Two-way
communications
- Easy to set up
and low maintenance costs
- Low profile,
non-directional whip helix antenna
- Easy access to
data
- No FCC or other
governmental agency requirements for data transmission
- Coverage in very
remote areas
- Data is
proprietary
- Stevens is able
to quickly detect any problems with transmission of data
- Systems verifies
that data has been transmitted which minimizes risk of missing data.
- Event
notification on line, by pager, etc.
- Lower power
transceivers compared to GEO transmitters.
- LEO Transceivers
hardware system is lower in cost than a GEO transmitter system.
Disadvantages to LEO Satellite Telemetry
- Monthly service
fee which could be expensive with frequent transmissions of data.
- Power outage at
GCC would shut down the communication server, which could delay
transmission of data to end user until power is restores. However, no data
is lost.
- LEO satellites
have a much shorter life span (five to eight years) than GEO satellites.
Reference:
http://www.stevenswater.com/telemetry_com/leo_info.aspx
http://www.tech-faq.com/low-earth-orbit.html
