30-03-2011, 11:32 AM
ABSTRACT
SATELLITE PHONES
A satellite telephone, satellite phone, or sat phone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions. Early satellite phones handsets had a large size and weight with a large retractable antenna. Recent sat phones are small in size comparable with the earlier sat phones. Sat phones are popular on expeditions into remote areas where terrestrial cellular service is unavailable. A fixed installation, such as one used aboard a ship, may include large, rugged, rack-mounted electronics, and a steer able microwave antenna on the mast that automatically tracks the overhead satellites. Some satellite phones use satellites in geostationary orbit, which are meant to remain in a fixed position in the sky at all times. Disadvantage of geostationary satellite systems is that in many areas—even where a large amount of open sky is present—the line-of-sight between the phone and the satellite is broken by obstacles such as steep hills and forest. This disadvantage can be overcome with the low earth orbit (LEO). The advantages include providing worldwide wireless coverage with no gaps. LEO satellites orbit the earth in high speed, low altitude orbits. Satellite phones are usually issued with numbers in a special country calling code. Most mobile telephone networks operate close to capacity during normal times and large spikes in call volumes caused by widespread emergencies often overload the systems just when they are needed the most. Also, terrestrial cell antennas and networks can be damaged by natural disasters. Satellite telephony can avoid this problem and be critical in natural disaster communications. Satellite phone networks themselves are prone to congestion as satellites and spot beams cover a very large area with relatively few voice channels.
SATELLITE PHONES
A satellite telephone, satellite phone, or sat phone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions. Early satellite phones handsets had a large size and weight with a large retractable antenna. Recent sat phones are small in size comparable with the earlier sat phones. Sat phones are popular on expeditions into remote areas where terrestrial cellular service is unavailable. A fixed installation, such as one used aboard a ship, may include large, rugged, rack-mounted electronics, and a steer able microwave antenna on the mast that automatically tracks the overhead satellites. Some satellite phones use satellites in geostationary orbit, which are meant to remain in a fixed position in the sky at all times. Disadvantage of geostationary satellite systems is that in many areas—even where a large amount of open sky is present—the line-of-sight between the phone and the satellite is broken by obstacles such as steep hills and forest. This disadvantage can be overcome with the low earth orbit (LEO). The advantages include providing worldwide wireless coverage with no gaps. LEO satellites orbit the earth in high speed, low altitude orbits. Satellite phones are usually issued with numbers in a special country calling code. Most mobile telephone networks operate close to capacity during normal times and large spikes in call volumes caused by widespread emergencies often overload the systems just when they are needed the most. Also, terrestrial cell antennas and networks can be damaged by natural disasters. Satellite telephony can avoid this problem and be critical in natural disaster communications. Satellite phone networks themselves are prone to congestion as satellites and spot beams cover a very large area with relatively few voice channels.
