Satellite Phone Industry Term Glossary
Bent Pipe Technology: The Globalstar satellites are simple repeaters or mirrors in the sky. Globalstar calls this “bent pipe” technology. Voice and data transmissions come up from the satellite phone or data device to one of the 40 satellites, that signal is then bounced back down to one of the ground gateways where it is transferred to the public switched telephone network and/or the Internet.
BGAN: Broadband Global Area Networks (BGAN) The Inmarsat IP based BGAN network uses the new I-4 satellites offering a shared channel IP packet switched service up to 492 Kbits and streaming IP service from 32 to 256 Kbits. Some terminals offer mobile ISDN service at 64 Kbits while also offering voice service at 4.8 Kbits.
CDMA: Code division multiple access (CDMA) is a channel access method used by numerous radio communication technologies. CDMA allows several transmitters to send information at the same time over one single communication channel. This allows numerous users to share the bandwidth of different frequencies which is called multiplexing. CDMA uses spread spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same channel. Globalstar uses a version of Code Division Multiple Access (CDMA) technology based upon the IS-95 CDMA standard. Globalstar uses a combination of CDMA with FDMA and spread spectrum modulation enabling it to support multiple users simultaneously.
Encryption: Encryption which is used by a number of satellite providers is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special key to decrypt the information making the information readable again. Satellite providers use encryption to protect data in transit in their satellite network.
FDMA: Frequency Division Multiple Access (FDMA) is a channel access method used in multiple access protocols. FDMA users are given an individual allocation of one to several frequency bands. Multiple access systems coordinate access between multiple users. Communication with the Iridium network is done using a TDMA and FDMA based system using L band spectrum between 1616 and 1626.5MHz. Iridium controls 7.775MHz of this.
Fixed Site Units: This is a term given to a satellite phone if normally fixed to a building. These fixed site units have an external antenna giving line-of-site to one of the satellites that provides service to the phone. Most Fixed Site Units have a RJ-11 phone connection which provides an analog phone line with dial tone. A standard off the shelf home phone can be used with most Fixed Site Units or most PBX systems have an analog connection allowing a line to come in for emergency use.
Geostationary Satellites: Geostationary satellites do not orbit the earth like low earth orbiting satellites. They are stationary over one region of the earth which can give line-of-site to many countries. They provide communication across this one area much like shining a giant flash light over the earth. Everywhere the flash light can shine that is where communication is provided. Geostationary satellites used by satellite phones are usually large and capable of handling large amounts of voice and data. Low earth orbiting satellites are smaller and not capable of handing as much volume. The Inmarsat I-4 constellation is made up of three large and powerful geostationary satellites that are placed in high earth orbit… 22,240 statute miles above the Earth. The I-4 satellite’s powerful features incude a very large body close to the size of a double-decker bus. Solar arrays with an immense wing span of 45 meters. A digital signal processor controls the beam forming the antennas and the channel allocation. The 9 meter wide reflector when deployed unfurls in orbit like a giant flower. There are both chemical and plasma ion thrusters that keep the satellite in its geostationary orbit.
GOCC: Ground Operations Control center (GOCC) is responsible for controlling the use of satellites by gateway terminals and coordinating with Satellite Operations Control Center (SOCC). The GOCC controls the allocation of satellite resources for each gateway. The Globalstar gateways are a very important part of the ground segment which includes Ground Operations Control Center (GOCC), Globalstar Data Network (GDN) and Satellite Operations Control Center. Each gateway or ground station is owned and operated by a service provider which receives transmissions from orbiting satellites and switches the calls to the appropriate ground network.
Handheld Satellite Phone: Satellite phone providers including Iridium, Globalstar and Inmarsat all provide handheld satellite phones that look similar to an early cellular phone which would be larger than today’s cellular phones. Most handheld satellite phones have a stick antenna that must be raised or deployed so the phone can receive a signal. These antennas can be as large as a hot dog. With any handheld satellite you must have line-of-site to a satellite that provides service to the phone for it to function. This in most cases required you to be outside with an 80% view of the sky away from tall structures and trees. The more you reduce this view of the sky the more likely you will receive periods of no service and dropped calls.
I-4 constellation: In March 2005 the first I-4 satellite is launched from Cape Canaveral propelled by the Atlas five rocket. The I-4 satellites are sixty times more powerful than their predecessors. The I-4 satellites are the most advanced satellites ever launched. In November of 2005 on converted oil platform in the Pacific Ocean a second I-4 satellite was successfully launched giving Inmarsat 85% coverage of the earth's landmass and 98% of the world's population. In August 2008 in Kazakh the third and final I-4 satellite is successfully launched. With all three I-4 satellites fully operational, Inmarsat is able to provide seamless broadband satellite communication globally. The I-4 constellation performs 20,000 system checks every 20 seconds bringing reliability and performance to the core of the I-4 system. The I-4 constellation provides communication for the new Inmarsat IsatPhone Pro and the Inmarsat BGAN satellite terminals. The I-4 has a life span of 20 years.
Ka-band intersatellite links: The Iridium satellites communicate with each other using Ka-band intersatellite links. Each satellite has four intersatellite links, two to the fore and aft satellites in the same orbital plane and two to the satellites in orbital plane to either side. These intersatellite links allow calls to be routed among the Iridium satellites before being transferred to a ground station. This intersatellite links makes Iridium impervious to natural disasters like hurricanes or earthquakes which can damage a ground station. If a ground station is damaged the Iridium satellites can rout the call to another ground station.
Landline: A landline simply put is the public phone system that is based on earth. Even though your landline phone provider may use a satellite to transfer the calls to their destination the call always ends up back on the earth using everyday phone lines.
Line-of-Site: In many forms of communication which includes most forms of satellite voice, data and video you must have line-of-site to the satellite you are trying to communicate with. That is why satellite TV dishes or satellite phone antennas must not be obstructed by trees or buildings. Even though you may not be able to see the satellite with naked eye you must have an unobstructed path to transmit and/or receive a signal.
Low Earth Orbiting Satellites (LEO): Satellite phones use two types of satellites or spacecraft low earth orbiting (LEO) or geostationary which are much larger. The Globalstar constellation has 40 satellites in low earth orbit. The Globalstar constellation orbits at an altitude of approximately 1,500 kilometers of (876 miles). First generation Globalstar satellite weighed 550 kg. Their second generation satellites will weigh substantially more. Globalstar satellites orbit with an inclination of 52 degrees. Because of this and the fact the satellites lack inter satellite linking the constellation picks up signals from over 80% of the planet excluding the extreme polar regions and some ocean regions. The Iridium constellation includes 66 satellites flying in six orbital planes with 11 satellites equally spaced apart from each other in that orbital plane. The satellites have polar orbits at an altitude of 485 miles. One advantage of (LEO) satellites include if one fails the others should keep the network functional. Another advantage is these satellites are orbiting or moving constantly. If you do not have line-of-site to receive a signal you can simply wait till a satellite moves enough to establish the line-of-site required to receive a signal.
Satellite Phone Network: A satellite phone network includes a satellite or a constellation of satellites that transmits and receives voice and data signals from the phones which communicate with gateway or number of gateways on earth. These gateways will either access the Internet for data transmissions or in the case of voice communication switches the call to the public phone system sending the call to a landline or cellular network till it reaches its call destination.
SOCC: Satellite Operations Control Center (SOCC) manages the constellation by tracking satellites, providing telemetry, controlling their orbits and command services for the constellation. Each Globalstar satellite constantly transmits telemetry data providing on board health reports for each satellite. The SOCC oversees satellite launch and deployment.
TDMA: Time division multiple access (TDMA) is a channel access method for shared medium networks. TDMA allows numerous users to share the same frequency channel. This is done by dividing the signal into different time slots. The user transmits in rapid succession each using his own time slot. TDMA allows multiple stations to share the same radio frequency channel while only using a part of the channel capacity. Communication with the Iridium network is done using a TDMA and FDMA based system using L band spectrum between 1616 and 1626.5MHz. Iridium controls 7.775MHz of this. TDMA is also used in the digital 2G cellular systems.