A communication satellite function as an overhead wireless repeater station that provides a microwave communication link between two geographically remote sites. Due to its high altitude, satellite transmissions can cover a wide area over the surface of the earth. Each satellite is equipped with various “transponders” consisting of a transceiver and an antenna tuned to a certain part of the allocated spectrum. The incoming signal is amplified and then rebroadcast on a different frequency. Most satellites simply broadcast whatever they receive, and are often referred to as “bent pipes”. These were traditionally used to support applications such as TV broadcasts and voice telephony. In recent times, the use of satellites in packet data transmission has been on the rise. They are typically used in WAN networks where they provide backbone links to geographically dispersed LAN’s and MAN’s.

Satellite-based telecommunication systems offer two important advantages, i.e.
• independence of terrestrial infrastructure and
• global coverage.

Satellite communication channels are characterised by:
• Wide Area coverage of the earth’s surface.
• Long transmission delays.
• Broadcast transmission.
• Large Channel Bandwidth.
• Transmission costs independent of Distance.

The received microwave power involved in satellite links is typically very small (of the order of a few 100 picowatts). This means that specially designed earth stations that keep C/N (carrier to noise ratio) to a minimum are used to transmit/receive satellite communications. The front-end receiver is the most crucial part of the transceiver and is a major factor in the overall cost of the satellite Earth Station. It typically employs a large antenna (Gain of a parabolic antenna is proportional to the square of its diameter) and a highly linear, low noise microwave amplifier (LNA).
Satellite links can operate in different frequency bands and use separate carrier frequencies for the up-link and down-link. The use of C bands was most common in 1st generation Satellite systems. However this band is already crowded as terrestrial microwave links also use these frequencies. The current trend is towards the higher frequencies of Ku and Ka bands. Attenuation due to rain is a major problem in both of these bands. Also due to the higher frequencies, microwave equipment is still very expensive, especially in the Ka band.
Modern Satellites are often equipped with multiple transponders. The area of the earth’s surface covered by a satellite’s transmission beam is referred to as the “footprint” of the satellite transponders. The up-link is a highly directional, point to point link using a high gain dish antenna at the ground station. The down-link can have a large footprint providing coverage for a substantial area or a “spot beam” can be used to focus high power on a small region thus requiring cheaper and smaller ground stations. Moreover, some satellites can dynamically redirect their beams and thus change their coverage area.

Satellite Constellations

Satellites can be positioned in orbits with different heights and shapes (circular or elliptical). Based on the orbital radius, all satellites fall into one of the following three categories;

LEO: Low Earth Orbit.
MEO: Medium Earth Orbit.
GEO: Geostationary Earth Orbit.

The orbital radius of the satellite greatly affects its capabilities and design. Satellites are also classified in terms of their payload. Satellites that weigh in the range of 800-1000 kg fall in the “Small” class, whereas the heavier class is named as “Big” satellites. GEO satellites are typically “Big” satellites, whereas LEO satellites can fall in either class

Possible System Solutions

Taking into account the topography of the area of operation of the demonstrator, all possible satellite solutions are described. There are four possible solutions available Inmarsat, Thuraya, Iridium, and Globalstar.

Inmarsat
Inmarsat was the world’s first global mobile satellite communications operator and is still the only one to offer a mature range of modern communications services to maritime, land-mobile, aeronautical and other users.
Formed as a maritime-focused intergovernmental organization over 20 years ago, Inmarsat has been a limited company since 1999, serving a broad range of markets. Starting with a user base of 900 ships in the early 1980s, it now supports links for phone, fax and data communications at up to 64kbit/s to more than 250,000 ship, vehicle, aircraft and portable terminals. That number is growing at several thousands a month.
Inmarsat Ltd is a subsidiary of the Inmarsat Ventures plc holding company. It operates a constellation of geostationary satellites designed to extend phone, fax and data communications all over the world. The constellation comprises five third-generation satellites backed up by four earlier spacecraft.

The satellites are controlled from Inmarsat’s headquarters in London, which is also home to Inmarsat Ventures as well as the small IGO created to supervise the company’s public-service duties for the maritime community (Global Maritime Distress and Safety System) and aviation (air traffic control communications). Inmarsat has regional offices in Dubai, Singapore and India.
Today’s Inmarsat system is used by independent service providers to offer a range of voice and multimedia communications. Users include ship owners and managers, journalists and broadcasters, health and disaster-relief workers, land transport fleet operators, airlines, airline passengers and air traffic controllers, government workers, national emergency and civil defence agencies, and peacekeeping forces.
The Inmarsat business strategy is to pursue a range of new opportunities at the convergence of information technology, telecoms and mobility while continuing to serve traditional maritime, aeronautical, land-mobile and remote-area markets.
Keystone of the strategy is the new Inmarsat I-4 satellite system, which from 2005 will support the Inmarsat Broadband Global Area Network (B-GAN) – mobile data communications at up to 432kbit/s for Internet access, mobile multimedia and many other advanced applications.
Inmarsat’s Maritime Safety Services continue to ensure that Inmarsat’s Public Service Obligations in respect of the Global Maritime Distress and Safety System (GMDSS) are carried out, not just to “The letter of the law”, but to the fullest possible extent using all available Inmarsat resources.
The Inmarsat Maritime Safety Services department liaises with all entities involved in the operation of the GMDSS involving Inmarsat services to ensure that they operate without any problems.
The Global Maritime Distress and Safety System (GMDSS) is an international system that uses terrestrial and satellite technology and ship-board radio systems to ensure rapid, automated alerting of shore-based communication and rescue authorities, in addition to ships in the immediate vicinity, in the event of a marine distress.
Under the GMDSS, all cargo ships of 300 gross registered tonnes and upwards and all passenger ships engaged on international voyages must be equipped with radio equipment that conforms to international standards as set out in the system. The basic concept is that search and rescue authorities ashore, as well as shipping in the immediate vicinity of the ship in distress, will be rapidly alerted through satellite and terrestrial communication techniques so that they can assist in a co-ordinated search and rescue operation with the minimum of delay.
The satellites are controlled from the Satellite Control Centre (SCC) at Inmarsat HQ in London. The control teams there are responsible for keeping the satellites in position above the Equator, and for ensuring that the onboard systems are fully functional at all times.
Data on the status of the nine Inmarsat satellites is supplied to the SCC by four tracking, telemetry and control (TT&C) stations located at Fucino, Italy; Beijing in China; Lake Cowichan, western Canada; and Pennant Point, eastern Canada. There is also a back-up station at Eik in Norway.
Traffic from a user terminal passes via a satellite and then down to a land earth station (LES), which acts as a gateway into the terrestrial telecoms networks. There are about 40 LESs, located in 30 countries.
The flow of communications traffic through the Inmarsat network is monitored and managed by the Network Operations Centre (NOC) at Inmarsat HQ.
The NOC is supported by network co-ordination stations (NCS). Their primary role is to help set up each call by assigning a channel to the MES and the appropriate LES. There is one NCS for each ocean region and for each Inmarsat system (Inmarsat A, B, C, etc). Each NCS communicates with all the land earth station operators in its ocean region, the other NCS and the NOC, making it possible to distribute operational information throughout the system.

Regional BGAN
Regional BGAN offers users high-speed internet access with coverage in up to 99 countries within the satellite footprint. This cost-effective service is delivered through a portable satellite IP modem the size of a notebook PC, making it ideal for professionals on the move.
Seamless access to applications
Regional BGAN is compatible with Microsoft Windows 98, Millennium Edition (ME), 2000, XP, NT and Mac OS 10.1. It also provides remote LAN and intranet access, and enables dedicated, secure links to be set up over a virtual private network (VPN).
It is also suitable for FTP, instant messaging, video streaming, e-commerce and transferring or sharing all kinds of data files with colleagues or clients.
Twice the speed of GPRS
The connectivity offered by Regional BGAN runs at more than twice the speed of current terrestrial GPRS mobile phone networks. The satellite footprint covers more than 99 countries stretching from western Europe and the northern half of Africa, across central and eastern Europe, the southern CIS countries, to the Middle East and the Indian sub-continent.
Avoids the need for a fixed line network
Regional BGAN is a high-speed Internet Protocol (IP) data service providing fast, reliable access to the Internet and corporate computer networks, even where the local telecom infrastructure is either poor, non-existent or expensive.
Easy to set up
The service is based around a lightweight satellite IP modem the size of a notebook PC. Weighing only 1.6Kg, the modem is portable and easy to use. The modem can be used with a single PC or connected to a local area network (LAN) through which it can be accessed by multiple devices.
Cost-effective packet data system
Another major benefit of Regional BGAN is its cost effectiveness. Connection to the Internet or a private network can be kept ‘always on’, and you only pay for the amount of data you send or receive, rather than the time spent online – making it an extremely effective business tool.
Connection compatibility
The Regional BGAN satellite IP modem can be connected using USB, Ethernet or Bluetooth technology. These area standard protocols for many computer peripheral devices.
Inmarsat’s satellite technology provides a fast, efficient connection, for example allowing the download of 50K files, e-mail or attachments in about 10 seconds.

lnmarsat has designed the entire end to end system in association with leading specialist communications companies including Hughes Network Systems and Ericsson.
The system infrastructure consists of advanced satellite bandwidth and an Inmarsat owned and operated Satellite Access Station (SAS) to be sited in Fucino, Italy. The SAS operates on industry standard General Packet Radio Services (GPRS) which enables inter-working with terrestrial services and operators. This facilitates competitive speeds for ‘fixed to mobile’ and ‘mobile to fixed’ communications. SIM Card roaming to and from the terrestrial GPRS services may also be supported.
Advanced spot-beam technology allows Inmarsat to maintain a footprint stretching across 99 countries. The maximum bandwidth within each spot-beam is 144kbit/s. However, because Regional BGAN is a packet data network, the average bandwidth available is shared among several connected users if they transmit data at the same time.
The Regional BGAN system allocates this capacity where needed – invisibly to the end-user. Based on forecasts of traffic and capacity, over a three-minute period it is estimated that users will consistently experience transfer rates equivalent to more than double those offered by current terrestrial GPRS services.

The Hardware
The Regional B-GAN proposition user equipment is a lightweight notebook-sized IP satellite modem which connects the end-user’s notebook PC with the satellite network. The IP satellite modem wilt be manufactured by Hughes Network Systems who have extensive experience in this technology arena, as well as a reputation for high quality manufacture.
The installation process is automated and end-users do not need extensive knowledge of satellite or modem operation, just simple plug and play. The Regional B-GAN IP satellite modem is treated as any other standard modem by the notebook PC, meaning end-users’ applications will automatically be configured to work with it. The IP satellite modem is designed to operate indoors and is capable of operating outdoors in extreme weather conditions. Antenna can be set up externally (on the roof) and the modem positioned internally to enable a semi-fixed remote office.
The Regional B-GAN IP satellite modem offers:
• data rates up to 144kbit/s
• connection via Universal Serial Bus (USB), Ethernet or Bluetooth
• direct compatibility with Windows operating systems
• IP Virtual Private Network (VPN) inter-connectivity
• portability and mobility as wet[ as fixed operation
• battery life – 1 hour of continuous peak data rate and 36 hours standby
• ability to work with standard encryption packages for secure working

The Regional B-GAN Proposition Features and Benefits
The exceptional features and benefits of the Regional B-GAN proposition make it the world’s most effective wireless IP data communication solution – both from the end-user’s perspective and the organisations in which they work.

Thuraya

Thuraya uses a Geo-stationary satellite system that has proven highly secure and reliable in terms of technology. GEO satellites are not expensive to maintain and are less likely to be replaced because of the longer life-span.
The Thuraya system has been adapted for efficient operation in both satellite and GSM environments. It provides high flexibility in managing network resources through a re-programmable satellite payload. This supports modifications to the system’s coverage area even in the post-launch period and optimises performance over high demand areas.
Thuraya’s satellites have been specially designed to achieve network capacity of about 13,750 telephone channels. Thuraya’s hand held mobile terminals are comparable to GSM handsets in terms of size and appearance, as well as in voice quality.

Iridium

The Iridium System is a satellite-based, wireless communications network designed to permit voice and data transmission to and from anywhere on earth, at any time. Eighty-six percent of the world’s landmass and all of its oceans are in areas with inadequate landline service. The Iridium Satellite Solutions global service provides coverage across all ocean areas, air routes, and all landmasses, even the Poles. A host of Iridium Satellite Solutions equipment options exist to meet specific fixed-site and mobile communications needs.
The Iridium Satellite System is the only provider of global, truly mobile satellite voice and data solutions with complete coverage of the Earth (including oceans, airways and Polar regions). Through a constellation of 66 low-earth orbiting (LEO) satellites operated by Boeing, Iridium delivers communications services to and from remote areas where terrestrial communications are not available. The service is ideally suited for industrial applications such as heavy construction, defence/military, emergency services, maritime, mining, forestry, oil and gas and aviation. Iridium currently provides services to the United States Department of Defense and launched commercial service in March 2001.

Iridium World Data Services
Using your computer and an Iridium satellite phone, you can connect to the Internet or a corporate network from virtually anywhere in the world, allowing you to browse the web, send and receive email and transfer files. You can configure your computer for two different types of data calls, depending on your needs: Dial-Up Data or Direct Internet Data.

Globalstar

The Globalstar constellation consists of 48 Low Earth Orbiting (LEO) satellites, with an additional four satellites in orbit as spares.

The satellites utilize “bent-pipe” architecture. On any given call, several satellites transmit a caller’s signal via CDMA technology to a satellite dish at the appropriate gateway where the call is then routed locally through the terrestrial telecommunications system.
The system’s software resides on the ground, not on the satellites, which means fast and easy system maintenance and upgrades.
The Satellite Operations Control Center (SOCC) manages the Globalstar satellite constellation. Globalstar phones look and act like mobile or fixed phones. The difference is that they can operate virtually anywhere, carrying a voice call / data over an exceptionally clear, secure Code Division Multiple Access (CDMA) satellite signal.
Described as being ljavascript:popUp(’Constellation’)ike “bent-pipes” or mirrors in the sky, the Globalstar constellation of 48 Low Earth Orbiting (LEO) satellites picks up signals from over 80% of the Earth’s surface, everywhere outside the extreme polar regions and some mid-ocean regions. Several satellites pick up a call, and this “path diversity” assures that the call does not get dropped even if a phone moves out of sight of one of the satellites.
As soon as a second satellite picks up the signal and is able to contact the same terrestrial gateway, it begins to simultaneously transmit. If buildings or terrain blocks the phone signal, this “soft-handoff” prevents call interruption. The second satellite now maintains transmission of the original signal to the terrestrial “gateway”.
Additional advantages of using Low Earth Orbiting (LEO) satellites within the Globalstar system include no perceptible voice delay and lighter / smaller all-in-one phones.
Gateways process calls, then distribute them to existing fixed and cellular local networks. Terrestrial gateways are an important part of Globalstar’s strategy to keep key technology and equipment easily accessible and to integrate our services as closely as possible with existing local telephony networks. This makes the Globalstar system and its services simple to manage, expand and improve.
Gateways are an integral part of the Globalstar ground segment, and include the Ground Operations Control Center (GOCC), Satellite Operations Control Center (SOCC), and Globalstar Data Network (GDN).
Each gateway, which is owned and managed by the service provider for the country in which the gateway is located, receives transmissions from orbiting satellites, processes calls, and switches them to the appropriate ground network.
A gateway may service more than one country. Gateways consist of three or four dish antennas, a switching station and remote operating controls. Because all of the switches and complex hardware are located on the ground, it is easier for Globalstar to maintain and upgrade its system than it is for systems which handle switching in orbit.
Gateways offer seamless integration with local and regional telephony and wireless networks. They utilize a standard T1/E1 interface to the existing PSTN/PLMN systems. Encryption ensures voice and signalling security for individual transmissions.