Mobile Satellite Services

 

Mobile Satellite  

Services(MSS)

Riadh Abdul-Hussain Mahdy  Mahdy  PhD student  student  2013   2013

 

Introduction 

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Mobile Satellite Service (MSS) is the term used to describe telecommunication services delivered via satellite to or from mobile users. MSS extendsconstraints mobile communications the range of terrestrial beyond based wireless systems and allows mobile-to-fixed and mobile-to-mobile voice and data communications worldwide. MSS can be used in remote areas where wired networks do not exist or to serve public safety needs where terrestrial lines and portable radios are emergency situations.

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Introduction 

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Technology advances in satellite and antenna designs have overcome many of the limitations associated with providing satellite access to a mobile user. MSS fill the gaps in wireless voice telephony and complement existing terrestrial wireless. MSS services include voice, low-speed data, fax, paging, high speed data, and broadcast and video on demand; specific services may vary among MSS providers.

 

Network Architecture 

the network architecture consists of the three entities: 1-User segment. 2-Ground segment. 3-Space segment.

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The basic network architecture of a mobilesatellite access network is shown Figure1.

 

Network Architecture  

 

The User Segment 

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The user segment comprises of user terminal units.  A terminal’s characte characteristics ristics are highly related to its application and operational environment. Terminals can be categorized into two main classes: 1-Mobile terminals. 2-Portable terminals.

 

Mobile terminals 

Mobile terminals are those that support full mobility during operation. They can be further divided into two categories: 1- mobile personal terminals and 2-mobile group terminals. 1-Mobile 1Mobile personal terminals often refer to handheld and palm-top devices ,Other mobile personal terminal categories include those situated on board a mobile platform, such as a car. car. Mobile group terminals are designed for group 2-Mobile 2usage and for installation on board a collective transport system such as a ship, cruise liner, liner, train, bus or aircraft.

 

Portable terminals 

Portable terminals are typically of a dimension similar to that of a briefcase or lap-top computer. As the name implies, these terminals can be transported from one site to another, however, operation while mobile will not normally be supported.

 

Segment  The Ground Segment  

The ground segment consists of three main network elements: 1-Fixed Earth stations (FES) or (Gateways). 2-Network control centre (NCC). 3-Satellite control centre (SCC).

 

Gateways 

Gateways provide fixed entry points to the satellite access network by providing a connection to existing core networks (CN), such as the public switched telephone network (PSTN) and public land mobile network (PLMN), through local exchanges.

 

Network control centre (NCC) 

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The network control centre (NCC) is connected to the Customer Information Management System (CIMS) To regulate access to the satellite resource  To perfor perform m the logical functions associat associated ed with network management and control. NCC performs two main functions: 1- Network management functions. 2- Call control functions .

 

Network control centre (NCC) 

Network management functions include : 1-Development of call traffic profiles. 2-System resource management and network synchronization. 3-Operation and maintenance (OAM) functions. 4-Management of inter-station signaling links. 5-Congestion control. 6-Providing the support for user terminal.

 

Network control centre (NCC) 

The call control functions include: 1-Common channel signaling functions 2-Gateway selection for mobile origination 3-Definition of gateway configurations

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The Satellite control centre (SCC) monitors The  (SCC) monitors the performance of the satellite constellation and controls a satellite’s position in the sky.

 

Segment  The Space Segment  

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The space segment provides the connection between the users of the network and gateways. Direct connections between users via the space segment is also achievable using the latest generation of satellites. The space segment consists of one or more constellations of satellites, each with an associated set of orbital and individual satellite parameters.

 

Segment  The Space Segment  

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In order to provide continuous global coverage, the satellite constellation has to be designed very carefully, taking into account technical network. and commercial requirements of the There are many options for the satellite architecture : -Transparent payload. -Transparent -On-board processing pr ocessing (OBP) capability. capability. -Inter-satellite links (ISL) within the constellation, or inter-constellation links with other data relay satellites to carry traffic and

signaling.  

satellite architecture 

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a)Transparent transponders are used in the space a)Transparent segment and the network relies on the ground segment to connect gateways. Satellites do not have the capability to perform ISLs and the delay in a mobile-to-mobile call is equal to at least two NGEO hop-delays plus the fixed network delay between gateways.

 

satellite architecture 

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b)Uses a GEO satellite to satellite to provide connectivity among Earth stations. As with option (a), no ISL technology is employed. The geostationary satellite is used to reduce the dependency on the terrestrial network, which may otherwise be needed to transport data over long distances delay between gateways.

 

satellite architecture 

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(c) uses ISLs ISLs to  to establish links with other satellites within the same orbital configuration. the need for gateways is reduced.  A mobile-to-mob mobile-to-mobile ile call may have have delays of varying varying duration depending on the route chosen through the ISL .

 

satellite architecture 

(d), Hybrid satellite network is formed through the use of a hybrid constellation. Interconnection Interconnection between NGEO satellites is established through ISL and intersatellite inter-orbit links (IOL) (ISL-IOL) via a data relay geostationary satellite is employed.

 

Frequency  Operational Frequency  

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Mobile-satellite systems operate in a variety of frequency bands, depending on the type of services offered. Originally, the International Telecommuni-cation Union (ITU) allocated spectrum to mobile-satellite services in the L/S-bands. Communications

between

gateways

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satellites, known as feeder links, are usually in the C-band or Ku-band. 

Recently the broader bandwidth offered by the Ka-band has been put into operation by satellite-PCN ( personal communication

networks) operators.

 

Traffic Channels Channels   

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Mobile-satellite use a similar channel structure to that networks of their terrestrial networks.  As an example, the following considers the channels recommended by ETSI ETSI   (European Telecommunications Standards Institute) under its geo mobile radio (GMR) specifications. Satellite-traffic channels (S-TCH) are used to carry either encoded speech or user data. The traffic channels in ETSI’s ETSI’s   GMR-2 specifications are organized to be as close as possible to those of GSM. They are divided into traffic channels and control channels.

 

Channels  Traffic Channels   

There are four forms of traffic :

Satellite full-rate traffic channel (S-TCH/F): data rate of 24 kbps

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Satellite half-rate traffic channel (S-TCH/H): data rate of 12

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kbps Satellite quarter-rate traffic channel (S-TCH/Q): data rate of 6 bps

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Satellite eighth-rate traffic channel (S-TCH/E): data rate of 3 kbps

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These traffic channels are categorized into speech traffic channels and data traffic channels.. Table channels Table 2 summar summarizes izes each ca category tegory..

 

Channels  Traffic Channels 

 

Channels  Control Channels  

Control channels are used for carrying signaling and synchronization data. As in GSM, the GMR specifications categories control channels into broadcast, control and dedicated . Table3 summarizes the different categories as defined in the GMR specifications.

 

Types  Orbital Types  

MSS systems can be categorized their orbital altitude: geostationary orbit (GEO), by medium earth orbit (MEO), and low earth orbit (LEO). Geostationary Orbit  A geostationary satellite system orbits approximately 22,300 miles (or 35,970 kilometers) from Earth.  At this height and location, the satellite moves at the same speed as the Earth rotates.

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Geostationary satellites can provide coverage to a large portion of the earth using a small number of satellites (3 or 4). Geostationary satellite systems have inherent transmission time delays and require terminal equipment with large RF power amplifiers.

 

Types  Orbital Types  

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Middle (or Medium) Earth Orbit :are : are located between 3,125 and 9,375 miles (or 5,040 and 15,121 kilometers) from the Earth. MEOs have lower orbits than GEO satellites, which reduces RF power requirements and transmission delays.  A constellation of about about 12 satellites can provide global coverage.  coverage. 

 

Types  Orbital Types  

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Low Earth Orbit : LEO satellites orbit at altitudes between 500 and 1,250 miles (or 8,065 and 2,016 kilometers) from the Earth. LEOs have lower orbits than MEOs, which reduces RF power requirements and transmission delays when compared to MEOs and GEOs. LEO systems require many more satellites (from 20 to more than 100) to cover the earth.

 

Types  Orbital Types 

 

Types  Orbital Types  

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Low Earth Orbit : LEO satellites orbit at altitudes between 500 and 1,250 miles (or 8,065 and 2,016 kilometers) from the Earth. LEOs have lower orbits than MEOs, which reduces RF power requirements and transmission delays when compared to MEOs and GEOs. LEO systems require many more satellites (from 20 to more than 100) to cover the earth.

 

Systems  Commercial MSS Systems  

GEO MSS Systems: 1-International Maritime Satellite (INMARSA (INMARSAT) T) 2-American Mobile Satellite System (AMSC)

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INMARSAT offers several different mobile systems designed to provide users with a wide variety of terminals and services. The units and costs are illustrated in Table 4.

 

Table 4 Standard INMARSAT Terminal Cost and Capabilities  

 

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 American Mobile Satellite System (AMSC), user terminal equipment for Skycell Plus is defined by application and varies with each application. Their capabilities and costs are shown in T Table able 5.

 

Systems  Commercial MSS Systems  

MEO Systems : The system capabilities of three MEO systems : Odyssey, ICO Global, and Ellipso. are shown in Table 6.

Table6 MEO System Cost and Capabilities  

 

Systems  Commercial MSS Systems  

LEO Systems : There are a number of LEO systems currently under development. Table 7 lists some general characteristics of four proposed LEO systems.

Table 7 LEO Systems Cost and Capabilities 

 

Limitations  Benefits & Limitations   

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Benefits of MSS  Provide access diversity to public switched network (PSN) services . provide communications in remote areas or areas where terrestrial communications networks are not available. Provide a worldwide services. Limitations of MSS  Line-of-Sight Requirement. High cost compared communication systems.

with

terrestrial

 

References: References:   

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Mobile Satellite Communication Networks/Ray E.Sheriff and Y.Fun Hu  Mobile Satellite Services /Public Safety Wireless Network (PSWN) http://www.skyhelp.net http://www .skyhelp.net / globalstar / globalstar globalstar.htm .htm