Mobile Satellite Services

8/12/2019 Mobile Satellite Services

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Mobile Satellite

Services(MSS)

Riadh Abdul-Hussain Mahdy

PhD student2013


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Introduction

Mobile Satellite Service (MSS) is the termused to describe telecommunication servicesdelivered via satellite to or from mobile users.

MSS extends mobile communications beyond

the range constraints of terrestrial basedwireless systems and allows mobile-to-fixedand mobile-to-mobile voice and datacommunications worldwide.

MSS can be used in remote areas wherewired networks do not exist or to serve publicsafety needs where terrestrial lines andportable radios are unavailable during

emergency situations.


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Introduction

Technology advances in satellite and antennadesigns 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 broadcastand video on demand; specific services may

vary among MSS providers.


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Network Architecture

the network architecture consists of the threeentities:

1-User segment.

2-Ground segment.3-Space segment.

The basic network architecture of a mobile-

satellite access network is shown Figure1.


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Network Architecture


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The User Segment

The user segment comprises of user terminalunits.

A terminals characteristics are highly related

to its application and operational environment. Terminals can be categorized into two main

classes:

1-Mobile terminals.

2-Portable terminals.


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Mobile terminals

Mobile terminals are those that support fullmobility during operation. They can be further

divided into two categories: 1- mobile personal

terminals and 2-mobile group terminals.

1-Mobile personal terminals often refer to hand-

held and palm-top devices ,Other mobile personal

terminal categories include those situated on

board a mobile platform, such as a car.

2-Mobile group terminals are designed for group

usage and for installation on board a collective

transport system such as a ship, cruise liner, train,

bus or aircraft.


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Portable terminals

Portable terminals are typically of a dimensionsimilar 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.


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The Ground Segment

The ground segment consists of three mainnetwork elements:

1-Fixed Earth stations (FES) or (Gateways).

2-Network control centre (NCC).3-Satellite control centre (SCC).


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Gateways

Gateways provide fixed entry points to thesatellite 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.


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Network control centre (NCC)

The network control centre (NCC) isconnected to the Customer Information

Management System (CIMS)

To regulate access to the satellite resource To perform the logical functions associated

with network management and control.

NCC performs two main functions:

1- Network management functions.

2- Call control functions .


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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.


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The call control functions include:

1-Common channel signaling functions

2-Gateway selection for mobile origination

3-Definition of gateway configurations TheSatellite control centre (SCC)monitors

the performance of the satellite constellation

and controls a satellites position in the sky.


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The Space Segment

The space segment provides the connectionbetween the users of the network and

gateways.

Direct connections between users via thespace segment is also achievable using the

latest generation of satellites.

The space segment consists of one or more

constellations of satellites, each with anassociated set of orbital and individual satellite

parameters.


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The Space Segment

In order to provide continuous globalcoverage, the satellite constellation has to bedesigned very carefully, taking into accounttechnical and commercial requirements of the

network. There are many options for the satellite

architecture :

-Transparent payload.

-On-board processing (OBP) capability.

-Inter-satellite links (ISL) within theconstellation, or inter-constellation links withother data relay satellites to carry traffic andsignaling.


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satellite architecture

a)Transparent transponders are used in the space

segment and the network relies on the groundsegment 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 networkdelay between gateways.


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b)Uses a GEO satelliteto provide connectivity among

Earth stations. As with option (a), no ISL technology isemployed.

The geostationary satellite is used to reduce the

dependency on the terrestrial network, which may

otherwise be needed to transport data over longdistances delay between gateways.


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(c) uses ISLsto establish links with other satellites

within the same orbital configuration.

the need for gateways is reduced.

A mobile-to-mobile call may have delays of varying

duration depending on the route chosen through the

ISL .


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(d), Hybrid satellite network is formed through the use

of a hybrid constellation. Interconnection betweenNGEO satellites is established through ISL and inter-

satellite inter-orbit links (IOL) (ISL-IOL) via a data relay

geostationary satellite is employed.


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Operational Frequency

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 and

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.


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Traffic Channels Mobile-satellite networks use a similar channel

structure to that of their terrestrial networks.As an example, the following considers the

channels recommended by ETSI (EuropeanTelecommunications Standards Institute)

under its geo mobile radio (GMR)specifications.

Satellite-traffic channels (S-TCH) are usedto carry either encoded speech or user data.

The traffic channels in ETSIs GMR-2specifications are organized to be as close aspossible to those of GSM. They are dividedinto traffic channels and control channels.


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Traffic Channels

There are four forms of traffic :

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

kbps

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

kbps

Satellite quarter-rate traffic channel (S-TCH/Q): data rate of6 bps

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

kbps

These traffic channels are categorized intospeech traffic channels and data traffic

channels. Table 2 summarizes each category.


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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 categoriesas defined in the GMR specifications.


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Orbital Types MSS systems can be categorized by their orbital

altitude: geostationary orbit (GEO), medium earthorbit (MEO), and low earth orbit (LEO).

Geostationary Orbit

A geostationary satellite system orbitsapproximately 22,300 miles (or 35,970 kilometers)from Earth.

At this height and location, the satellite moves atthe same speed as the Earth rotates.

Geostationary satellites can provide coverage to a

large portion of the earth using a small number ofsatellites (3 or 4).

Geostationary satellite systems have inherenttransmission time delays and require terminalequipment with large RF power amplifiers.


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Orbital Types

Middle (or Medium) Earth Orbit :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 andtransmission delays.

A constellation of about 12 satellites can

provide global coverage.


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Orbital Types

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 andtransmission delays when compared to MEOs

and GEOs.

LEO systems require many more satellites

(from 20 to more than 100) to cover the earth.


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Orbital Types


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Commercial MSS Systems

GEO MSS Systems:

1-International Maritime Satellite (INMARSAT)

2-American Mobile Satellite System (AMSC)

INMARSAT offers several different mobile

systems designed to provide users with a widevariety of terminals and services. The units and

costs are illustrated in Table 4.


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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 eachapplication. Their capabilities and costs are

shown in Table 5.


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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


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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


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Benefits & Limitations

Benefits of MSS

Provide access diversity to public switchednetwork (PSN) services .

provide communications in remote areas orareas where terrestrial communicationsnetworks are not available.

Provide a worldwide services.

Limitations of MSS

Line-of-Sight Requirement. High cost compared with terrestrial

communication systems.


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References:

Mobile Satellite Communication Networks/Ray E.Sheriff and

Y.Fun Hu Mobile Satellite Services /Public Safety Wireless Network

(PSWN)

http://www.skyhelp.net / globalstar / globalstar.htm


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Mobile Satellite Services

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