Satellite phone
A satellite phone provides a link for voice or data for two-way satellite communication . The connection to the end device (telephone, "cell phone") is made via radio directly to a satellite. In theory, calls can be made anywhere in the world and even in areas without terrestrial cellular coverage. The satellite forwards the incoming call to an earth station, which feeds the call into the public telephone network.
History of the Satellite Phones
As early as the late 1970s, satellites were used for communication over long distances. However, the transmitting and receiving systems of these systems were very large and stationary. It was not until the International Maritime Satellite Organization ( Inmarsat ) that a system was made available for mobile devices from 1982 onwards, which was mainly used in maritime shipping . The first devices for mobile land use were available from 1989.
In the late 1980s, Canada was the first country to use satellite telephones to supply large, sparsely populated areas with telecommunications, without having to provide complex, ground-based infrastructure . A similar system was started shortly afterwards in the USA . The satellites used were in geostationary positions.
From 1985 Motorola developed the Iridium communication system , whose satellites orbit the earth from pole to pole. This means that the polar regions can also be covered, which are not served by the geostationary satellites, which are always above the equator.
By establishing networks with satellites in low orbits ( LEO , MEO ), it was possible to significantly reduce the distance between satellite and end device and thus reduce the necessary transmission power in the end device. Only this generation of devices was able to measure itself in weight and size with the now established mobile phones , but was unable to displace them from the market because, on the one hand, the end devices and the connection charges of these networks are far too expensive for them, and on the other, completely different framework conditions, such as . B. a clear view of the sky are necessary. In the meantime, extremely powerful satellites (e.g. Thuraya ) in a geosynchronous / geostationary orbit have been able to reduce the size of the end devices even further.
In the meantime, the first providers are also daring the balancing act “cell phone and satellite phone”. One of the pioneers of this approach is the company Spot LLC, a subsidiary of the satellite operator Globalstar, which recently introduced a device called "SPOT Connect". This enables satellite connections via a normal, modern smartphone . This is made possible via a Bluetooth connection between the device and a standard smartphone with an installed mobile phone app .
Also, Apple set up a working group of engineers of the satellite, aerospace and antenna industry to the possibilities of satellite telephony for the iPhone to let explore. The five-year project aims to take into account the lessons learned from previous failures such as Iridium, Globalstar and Teledesic, which could not have developed viable business plans. Possibly even a separate satellite infrastructure should be built. When expanding the network, the group could fall back on extensive financial reserves currently amounting to over 200 billion dollars.
application
Satellite telephones enable voice telephony even in regions without cell phone reception. Satellite phones generally do not offer worldwide reception. Before using a satellite phone, it should be clarified whether reception is even available with the satellite phone to be used and whether the operator of the satellite network covers this region. The position of the satellite in the sky should also be clarified for the region of operation. With a smart phone - app for satellite tracking , the current location of the satellite can be calculated in the sky. The satellite tracking app requires current TLE data to calculate the current satellite location.
Sky position Thuraya 2 in Bern on April 29, 2012 at 10:50 pm
For reliable satellite communication, there must be a line of sight from the antenna of the satellite telephone to the satellite and the first Fresnel zone must be free of any obstacles.
Satellite phones use L-band radio frequencies . In the dense forest with tall trees, the connection reserve of the satellite telephones is insufficient. Satellite phones do not allow voice communication in the thick forest with tall trees. Long-wave radio signals can penetrate dense forests with tall trees better. That is why satellite communication systems with long-wave radio signals around 300 MHz (lower UHF frequency band) are better suited for satellite communication in the forest than L-band satellite communication systems. That is why, for example, the emergency radio beacons alarming via the global COSPAS-SARSAT satellite network and the MUOS do not use the L-band, but rather long-wave radio signals around 300 to 450 MHz ( UHF frequency band).
In areas with terrestrial radio reception in the VHF or UHF frequency band , terrestrial radio should always be used. An example of terrestrial radio is mobile radio . Terrestrial radio in the VHF or UHF frequency band is more reliable than any satellite communication with portable handheld devices. Terrestrial radio shows significantly larger average link margins in the inner area of a radio cell than satellite communication. With large link margins, a radio link is possible even if there is no line of sight, for example if a hill , forest or building interrupts the line of sight between the transmitting and receiving antennas. The Earth's atmosphere and the Van Allen Belt protect terrestrial radio from cosmic disturbances such as solar weather and cosmic radiation .
Current systems
| system | cover | prefix | Tel | SMS | Data | Type of satellites | Customers |
|---|---|---|---|---|---|---|---|
| iridium | worldwide | +881 6 +881 7 |
Yes | Yes | 2.4 kbit / s | LEO | 359,000 |
| Thuraya | Europe, Africa (excluding Southern Africa), Near and Middle East, Asia (excluding NE Siberia), Australia, Oceania | +882 16 | Yes | Yes | 9.6 to 444 kbit / s | geosynchronous | 250,000 plus roaming users |
| Global star | worldwide, without polar regions and high seas | +881 8 +881 9 |
Yes | Yes | 9.6 kbit / s | LEO | |
| Inmarsat | worldwide, excluding polar regions | +870 | Yes | Yes | 2.4 to 420 kbit / s | geostationary |
Web links
Individual evidence
- ↑ Elke Schwan: SPOT Connect - satellite reception for cell phones. January 31, 2011, accessed November 20, 2012 .
- ↑ Achim Sawall: Apple develops satellite technology for the iPhone. December 22, 2019, accessed on December 23, 2019 (German).
- ↑ https://funkperlen.blogspot.ch/2017/11/wenn-baume-den-wellen-im-wege-haben.html Anton's Funkperlen - When trees stand in the way of the waves
- ↑ Archived copy ( Memento of the original from May 28, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Lockhead Martin - MUOS factsheet
- ↑ https://web.archive.org/web/20090227003825/http://www.research.telcordia.com/society/TacCom/papers99/36_2.pdf Geosynchronous Satellites for MUOS
- ↑ http://www.milsatmagazine.com/2013/MSM_Apr2013.pdf MilsatMagazine - April 2013 - Satellite Spotlight - Understanding + Using MUOS (from page 72)
- ↑ ITU: List of ITU-T Recommendation E.164 Assigned Country Codes. (PDF; 178 kB) May 1, 2005, accessed on November 20, 2012 (English).
- ↑ Archived copy ( memento of the original from April 1, 2018 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Iridium - Press Release - Iridium Announces Fourth-Quarter and Full-Year 2017 Results; Company Issues 2018 Outlook
- ^ Network Coverage. Thuraya, accessed February 19, 2016 .
