Mobile satellite communication

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Mobile satellite communication vsat
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• Supervised by
• Dr. Hasan Abbas
• Presented by
• E. Nagham Abbas

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• WHY SATELLITE?
• As internet traffic continues to grow at
  exponential rates world wide, internet services
  providers (ISPS) everywhere are faced with the
  challenge of keeping up with demand for network
  bandwidth . Satellite-based internet connections
  are one of those solutions . Vsat has offered
  ISPS and telecommunications service providers
  easily scalable.

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KEY BENEFITS

• 1- faster installation
• Satellite services are usually activated much
  more quickly
• than terrestrial fiber. An antenna , modem and
  satellite
• circuit can be provisioned in a few weeks.
• As a network grows, additional capacity can be
  obtained
• in just as short a time.

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2-better network performance

• Satellite connections enhance network performance
  by linking directly
• to an internet backbone, bypassing congested
  Terrestrial lines and
• numerous router hops. In addition, dedicated
  Space segment, local
• loop circuits and ports into a major Internet
  backbone mean ISPs
• do not share infrastructure, Another reason for
  slow or degraded
• connections over the traditional fiber line.

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3-lower network costs

• The broadcast nature of satellites allows for the
  simultaneous
• delivery of information to wide geographic areas
  without regard
• to terrestrial infrastructure or geographic
  barriers.
• This translates into a pricing structure that is
  distance insensitive,
• keeping costs down for international ISPs, in
  addition, satellite
• capacity is easily matched to actual traffic
  patterns, meaning ISPs
• pay only for what they need.

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Network architecture

• the network architecture consists of the three
  entities
• user segment
• ground segment
• space segment.

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Network Architecture (cont)

• The User Segment The user segment comprises of
  user terminal units
• Terminals can be categorised into two main
  classes
• Mobile terminals Mobile terminals can be
  divided into two categories mobile personal
  terminals and mobile group terminals.
• Mobile personal terminals often refer
  to hand-held and palm-top devices, on board a
  mobile platform, such as a car.
  

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The User Segment (cont)

• 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.
• Portable terminals lap-top computer.

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• The Ground Segment
• The ground segment consists of three main network
  elements
• gateways, sometimes called fixed Earth stations
  (FES)
• the network control centre (NCC)
• the satellite control centre (SCC).

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• the ground segment
• Gateways provide fixed entry points to the
  satellite access network by public switched
  telephone network (PSTN) and public land mobile
  network (PLMN) .
• Figure 2.2 shows a gateways internal
  structure

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• the ground segment
• the traffic channel equipment (TCE) and RF/ IF
  components
• together form the gateway transceiver
  subsystem (GTS).
• The gateway subsystem (GWS) consists of both the
  GTS and the
• gateway station control (GSC).
• The NCC, also known as the network management
  station
• (NMS) is connected to the Customer information
  Management
• System (CIMS) to co-ordinate access to the
  satellite resource and
• performs the logical functions associated with
  network
• management and control.

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the ground segment

• these two logical functions can be summarized as
• follows
• Network management functions The network
  management functions include
• Development of call traffic profiles
• System resource management and network
  synchronisation
• Operation and maintenance (OAM) functions
• Congestion control
• Provision of support in user terminal
  commissioning
• Call control functions include
• Common channel signalling functions
• Definition of gateway configurations

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• the ground segment
• The SCC monitors the performance of the satellite
  constellation and controls a satellites position
  in the sky.
• The CIMS is responsible for maintaining gateway
  configuration data and processing call detail
  records.
• The Space Segment
• The space segment provides the connection between
  the users of
• the network and gateways.
• The space segment consists of one or more
  constellations of
• satellites each with an associated set of orbital
  and individual
• satellite parameters.

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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
• 1. LEO Low Earth Orbit.
• 2. MEO Medium Earth Orbit.
• 3. GEO Geostationary Earth Orbit.
• The orbital radius of the satellite greatly
  effects 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

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Satellite Constellations (cont)
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Satellite Constellations

• Table 2 summarizes the design issues related to
  different type of satellite constellations.

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• Operational Frequency
• Mobile-satellite systems now operate in a variety
  of frequency bands,
• depending on the type of services offered.
• Communications between gateways and satellites,
  known as feeder
• links, are usually in the C-band or Ku-band,
  although recently the
• broader bandwidth offered by the Ka-band has been
  put into operation
• by satellite-personal communication Network
  (S-PCN) operators.

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Table 2.1 summarises the nomenclature used to
categorise each particular frequency band.
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Logical Channels

• Traffic Channels
• Mobile-satellite networks adopt a similar channel
  
• structure to that of their terrestrial
  counterparts.
• They are divided into traffic channels and
  control
• channels.
• Satellite-traffic channels (S-TCH) are used to
  carry
• either encoded speech or user data.

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• traffic channel (Cont )
• Four forms of traffic channels
• Satellite full-rate traffic channel (S-TCH/F)
  Gross data rate of 24 kbps
• Satellite half-rate traffic channel (S-TCH/H)
  Gross data rate of 12 kbps
• Satellite quarter-rate traffic channel
  (S-TCH/Q) Gross data rate of 6 kbps
• Satellite eighth-rate traffic channel (S-TCH/E)
  Gross data rate of 3 kbps

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• traffic channel (Cont)
• These traffic channels are further categorised
  into speech traffic channels and data traffic
  channels.
• Table 2.2 summarises each category.

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Control Channels

• Control channels are used for carrying signalling
  and
• synchronisation data.
• Table 2.3 summarises the different categories

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Control Channels
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Control Channels
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Control Channels
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Logical Channels (cont)

• Additional logical channels in the physical layer

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Land Mobile Channel Characteristics

• Introduction
• there are two types of channel to be considered
  the mobile channel, between the mobile terminal
  and the satellite.
• the fixed channel, between the fixed Earth
  station or gateway and the satellite. The basic
  transmission chain is shown in Figure 4.1.
• In a mobiles case, the local operational
  environment has a significant impact on the
  achievable quality of service (QoS).
• In the mobile-link, a service availability of
  8099 is usually targeted, whereas for the
  fixed-link, availabilities of 99.999.99 for the
  worst-month case can be specified.

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Local Environment

• The received land mobile-satellite signal
  consists of the combination of three components
• the direct line-of-sight (LOS) wave.
• the diffuse wave.
• the specular ground reflection.
• The direct LOS wave arrives at the receiver
  without reflection from
• the surrounding environment. The only L-/S-band
  propagation
• impairments that significantly affect the direct
  component are free
• space loss (FSL) and shadowing. FSL is related to
  operating
• frequency and transmission distance. Systems
  operating at above
• 10 GHz need to take into account tropospheric
  impairments
• Shadowing occurs when an obstacle, such as a tree
  or a building,
• impedes visibility to the satellite.

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Local Environment

• The diffuse component comprises multipath
  reflected signals
• from the surrounding environment, such as
  buildings, trees and
• telegraph poles.
• The specular ground component is a result of the
  reception of the
• reflected signal from the ground near to the
  mobile.
• three broad categories
• Urban areas, characterised by almost complete
  obstruction of the direct wave.
• Open and rural areas, with no obstruction of
  the direct wave.
• Suburban and tree shadowed environments, where
  intermittent
• partial obstruction of the direct wave occurs.

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Local Environment
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Channel Characteristics

• if the signal power can be reduced while
  maintaining the same
• grade of service (BER).
• This can be achieved by adding extra or redundant
  bits to the
• information content, using a channel coder.
• The two main classes of channel coder are block
  encoders and
• convolutional encoders. At the receiver, the
  additional bits are
• used to detect any errors introduced by the
  channel.
• There are two techniques employed in satellite
  communications
• to achieve this
• Forward error correction (FEC), where errors
  are detected and
• corrected for at the receiver
• Automatic repeat request (ARQ), where a high
  degree of
• integrity of the data is required, and latency is
  not a significant
• factor.

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Location Management

• Operations
• Location management is concerned with network
  functions that allow
• mobile stations to roam freely within the
  network coverage area. It is
• a two-stage process that allows the network to
  locate the current
• point of attachment The first stage is location
  registration or location
• update, while the second stage is the call
  delivery as shown in Figure
• (6.3) .
• In the location registration stage, the mobile
  station periodically
• notifies the network of its new point of
  attachment, allowing the
• network to authenticate and to update the users
  location profile.
• In the call delivery stage, the network queries
  the users location
• profile and locates the current position of the
  mobile terminal by
• sending polling signals to all candidate access
  ports through which
• an MS can be reached.

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Location Management (cont)
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Handover Management

• Phases of Handover Handover management ensures
  that an active call connection is maintained when
  the mobile terminal moves and changes its point
  of attachment to the network. Three main phases
  are involved in handover
• handover initiation.
• handover decision .
• handover execution.
• The main task involved in the handover initiation
  phase is
• gathering of information such as the radio link
  measurements.

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• phases of handover (Cont)
• If the radio link quality falls below a
  predefined threshold, a
• handover will be initiated.
• Based on measurements, the handover decision
  phase will select
• the target resources.
• In handover execution, new connections are
  established and old
• connections are released by performing signalling
  exchanges
• between the mobile terminal and the network .
• A handover can be initiated due to poor radio
  link performance
• or other QoS degradation.

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Handover types

• Stand-alone Satellite Network handover occurs
  due mainly to
• the motion of the satellite.
• there are two main handover categories
• 1-Intra-FES Handover This type of handover
  occurs due to
• the change of spot-beams caused by the motion of
  the satellite.
• The satellite motion sults in a change or
  degradation in the radio
• link quality, rewhich is then used to determine
  whether a handover
• should be initiated.
• This type of handover is further divided into
• inter-beam handover.
• inter-satellite handover.

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• intra FES handover
• Inter-beam handover refers to the transfer of a
  call from one
• spot-beam to another of the same satellite.
• Such handover is due mainly to the satellite
  motion.
• Inter-satellite handover refers to the transfer
  of a call from
• one satellite to another, This type of handover
  is due to the
• low elevation angle as a result of the satellite
  motion.
• As the elevation angle becomes lower, the
  propagation path
• loss and the depth of shadowing increase,
  resulting in a
• decrease in the received power.

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Inter-beam handover
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Inter-satellite handover
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Inter-FES Handover

• Inter-FES handover refers to the change from one
  FES to another
• during a call. in order to avoid frequent changes
  in the signalling
• and traffic link, it is usual that the call would
  still carry on with
• the original FES. This FES is called the anchor
  FES during the
• handover process.

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inter FES Handover (Cont )
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• inter FES Handover (Cont )
• inter-FES handover is rare only mobile
  terminals associated
• with a high degree of mobility, such as in high
  speed trains or
• aero planes, may experience this type of
  handover.
• Unlike intra-FES handover, which affects mainly
  on-going calls,
• inter-FES has a great impact on the network as it
  implies a transfer
• of routing control from one FES to another.

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S-PCN Interfaces and Signalling Protocol
Architecture

• use the GSM protocols as the baseline protocols
  for carrying out the satellite network control
  functions.
• Figure 6.2 shows the network interfaces. A brief
  description on the
• interfaces follows
• S-Um-interface used for signalling between a
  Gateway Transceiver System (GTS) and an MS.
• A-interface between (GWS) ,(GMSC) This interface
  is used to carry information on GWS management,
  call handling and mobility management .
• Abis-interface this is an internal GWS
  interface linking the GTS part to the GSC part.
• used to support the services offered to the
  users.
• B-interface uses the MAP/B protocol allowing the
  GMSC to retrieve or update local data stored in
  the VLR.

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S-PCN Interfaces and Signalling Protocol
Architecture (cont)

• C-interface uses the MAP/C protocol allowing the
  GMSC to interrogate the appropriate HLR in order
  to obtain MS location information.
• D-interface uses the MAP/D protocol to support
  the exchange of data between an HLR and VLR of
  the same GMSC.
• E-interface uses the MAP/E protocol to support
  the exchange of messages between the relay GMSC
  and the anchor GMSC during an inter-GMSC
  handover.
• F-interface between the GMSC and the AuC/EIR. It
  uses the MAP/F protocol for user authentication.
• G-interface uses the MAP/G protocol between VLRs
  of different GMSCs in order to transfer
  subscriber data.

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S-PCN Interfaces and Signalling Protocol
Architecture (cont)
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S-PCN Interfaces and Signalling Protocol
Architecture (cont)

• H-interface between the HLR and the AuC .
• When an HLR receives a request for authentication
  and
• ciphering data for a mobile subscriber and if
  the data
• requested is not held at the HLR, it will send a
  request
• to the AuC to obtain the data.
• Figure 6.2 Functional interfaces of a system

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VSAT Networks

• due to high performance requirements, design of
  earth station is
• quite complicated. This increases the costs and
  the need for
• maintainence. Very Small Aperture Terminals
  (VSAT) provides a
• solution to this problem.
• The key point in VSAT networks is that either the
  transmitter or
• the receiver antenna on a satellite link must be
  larger.
• In order to simplify VSAT design, a lower
  performance microwave
• transceiver and lower gain dish antenna (smaller
  size) is used.
• They act as bidirectional earths stations that
  are small, simple and
• cheap enough to be installed in the end user's
  premise.

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What is vsat?

• It is an earthbound station used for satellite
  communications of data, voice and video signals.
• A vsat consists of two parts
• A transceiver that is placed outdoors
• Device that is placed indoors to interface the
  transceiver with the end users communications
  device.
• Vsat can handle up to 1 MBPS (1 million bits per
  second).
• Vsat systems can be relatively small (1-2 meter
  antenna ) and easily installed.

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What is vsat?

• The transceiver receives or sends a signal to a
  satellite
• transponder in the sky. The satellite sends and
  receives signals
• from a ground station computer that acts as a
  hub for the system.
• Each end user is interconnected with the hub
  station via the
• satellite, forming a star topology. The hub
  controls the entire
• operation of the network. For one end user to
  communicate with
• another, each transmission has to first go to
  the hub station that
• then retransmits it via the satellite to the
  other end user's VSAT.

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How does it work?

• For best results, the network should be designed
  to exploit the
• Unique virtue of satellite in geostationary orbit
  namely that
• it can be a shared resource available, as needed,
  to many users
• spread Over a very large proportion of the
  earths surface.
• This is the concept of bandwidth-on demand.
• Satellite internet
• The data travels from the satellite equipment at
  the customers location to the satellite, and then
  to the teleport for routing to the internet.

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Turbo Internet

• With the increasing popularity of the World Wide
  Web, the
• demand for speedy downloads is increasing. The
  main
• bottleneck is the analog telephone line, which is
  incapable of
• supporting higher data rates.
• An end user overcomes the telephone line barrier
  and is capable
• of receiving data at 400 kbps. This is much
  faster than typical
• analog modems (28.8 kbps), A connection is setup
  with the local ISP using the analog telephone
  line modem.
• Instead of directing the data to the requesting
  node, data is
• directed to the Network Operations Centre (NOC).

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Turbo Internet
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Operation of VSAT Networks

• VSAT networks are typically arranged in a star
  based topology,
• where each remote user is supported by a VSAT.
• The Earth hub station acts as the central node
  and employs a
• large size dish antenna with a high quality
  transceiver.
• The satellite provides a broadcast medium acting
  as a common
• connection point for all the remote VSAT earth
  stations.
• Typical examples are central office, Banking
  institutions with
• branches all over the country, backbone links
  for an ISP and
• Airline ticketing system.
• since all connections must pass through the hub
  ES node. The
• data link supported from the hub to the VSAT is
  typically slower
• (19.2 kbps) than that in the reverse direction
  (512kbps).

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Operation of VSAT Networks
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Benefits of vsat

• Our vsat technology offers many advantages
• Ease of implementation
• After the order is placed, putting up a vsat
  network can be done
• in a matter of days.
• the antenna dish can be installed virtually
  anywhere, the size of
• the antenna dish ranges from 1.8m to 2.4m in
  diameter depending
• on the type of the applications .
• Likewise, moving the vsat unit to a new location
  can be done very
• quickly.

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availability 2-

• The wireless nature of vsat system allows its
  installation at
• virtually any location within the footprint of
  the Satellite .
• With this advantages, customers may setup offices
  in a promising
• location without being constrained by the
  availability of terrestrial
• lines. At the same time, customers may relocate
  offices to a lower
• cost area and still maintain the communication
  link with the use of
• our Vsat links.

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3-Reliability

• Satellite communication is extremely reliable.
  our vsat system has
• a Bit Error Rate (BER) of approaching 1x10-9.
• our vsat master Earth station has built-in
  redundancy that ensures
• continuous operations in case of failure.
• regardless of where the sites are located, each
  vsat remote unit
• receives the same level of performance and signal
  quality.
• 4-lower cost
• As customers add more services, they will find
  that the
• incremental cost is very low compared to
  terrestrial networks.
• the monthly service fees are fixed and priced
  according to the
• network capacity, not the distance between the
  head-office
• and branch locations.
• As a result, customers pay only for the amount of
  data throughput
• used.

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• 5-security
• Satellite networks offer excellent security
  against on authorized access.
• Gaining access to a vsat system is virtually
  impossible Without authorization.

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Typical vsat applications

• corporate communications can be divided into the
  following categories
• 1-interactive applications
• The interactive applications can be based on
  centralized
• or distributed concept. In a centralized system,
  all terminals in the
• offices operate on-line and communicate
  intermittently with the
• host of servers at the data center.
• In a distributed system, each remote office has
  terminals linked to
• its local host or servers.

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• interactive application( Cont )
• the servers then communicate with each other in a
  (WAN).
• Besides real-time data applications, our Vsat
  network supports two-
• way voice capability for telephone or facsimile,
  remote offices can
• make phone calls to each other or to central
  headquarters by passing
• the local public phone network.
• 2-File transfer
• These applications send a large amount of data in
  one transaction.
• These include the use of the TCP/IP file transfer
  protocol (FIP) to
• transfer files and the printing of a large
  reports.

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• 3- file broadcast
• a recent file transfer application requires
  support of file broadcast
• or IP multicast these applications send the data
  to multiple sites
• in one transaction.
• Using a vsat network, a large file can be
  distributed to hundreds
• of sites simultaneously, our vsat network
  Supports IP multicast,
• which improves broadcast performance even more.

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Similarities and differences between a
mobile-satellite network and a GSM network

• Similarities The frequency re-use concept
  adopted in the GSM
• network can be applied to the S-PCN.
• A satellite spot-beam coverage is equivalent to a
  GSM cell coverage.
• Higher layer protocols of the GSM network may be
  adopted in the
• S-PCN with possible modifications.
• Differences Longer propagation delays in the
  S-PCN due to the
• long satellite-to-earth path and to the longer
  distance between the
• FES and the user terminal.
• Higher attenuation in the radio signal .
• Larger variations in conversational dynamics in
  voice communications.
• Increased echoes .

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Similarities and differences between a
mobile-satellite network and a GSM network (cont)

• Delay in double-hop connection for
  mobile-to-mobile call may become
• Unacceptable.
• Higher attenuation in the radio signal in the
  satellite network due
• to the longer propagation delay.
• A spot-beam coverage is much larger than a
  terrestrial cellular
• Coverage resulting in lower inter-spot-beam
  handover probability.
• A power control mechanism is required in a
  satellite network as
• the satellite power is shared by all the
  spot-beams over the entire
• coverage area .
• Line-of-sight operation is required in a
  satellite network in order to
• compensate for the high attenuation in the radio
  signal in
• contrast to the use of multipath signals in
  terrestrial cellular
• mobile networks.

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Similarities and differences between a
mobile-satellite network and a GSM network (cont)

• Adjacent cell interference in a terrestrial
  cellular network is a function
• of power and cellular radius whereas adjacent
  spot- beam
• interference is a function of power and sidelobe
  characteristics
• of the satellite antenna Array.
• User terminals can access by any one of the
  gateways in satellite
• networks in contrast to terrestrial network
  access in which the user
• terminal in any given cell can only access an MSC
  associated with that
• cell.
• Optimum call routing is possible in satellite
  networks by routing
• the call to the nearest gateway to the called
  party. This is impossible
• in existing GSM networks.
• Doppler shift can be considerable in a satellite
  network especially
• during the initial period of operation.

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References

• mobile satellite communication networks
• http//www.wiley.co.uk or http//www.wiley.com 
• mobile satellite
• http//www.cs.berkeley.edu/randy/courses/cs294.596
  /cs294-7.s96.html
• mobile communicationsatellite system-jochen
  schillerr
• http//www.jochenschiller.de