Mobile satellite communication & vsat Supervised by: Dr. Hasan Abbas Presented by: E. Nagham Abbas WHY SATELLITE?
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Dr. Hasan Abbas
E. Nagham Abbas
As internet traffic continues to grow at exponential rates world wide, internet services providers (ISP’S) 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 ISP’S and telecommunications service providers easily scalable.
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 ISP’s
do not share infrastructure, Another reason for slow or degraded
connections over the traditional fiber line.
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 ISP’s, in addition, satellite
capacity is easily matched to actual traffic patterns, meaning ISP’s
pay only for what they need.
the network architecture consists of the three entities:
Terminals can be categorised into two main classes:
Mobile personal terminals :often refer to hand-held and palm-top devices, on board a mobile platform, such as a car.
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
The ground segment consists of three main network elements:
Figure 2.2 shows a gateway’s internal structure:
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).
(NMS) is connected to theCustomer information Management
System (CIMS) to co-ordinate access to the satellite resource and
performs the logical functions associated with network
management and control.
these two logical functions can be summarized as
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
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
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
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.
Mobile-satellite networks adopt a similar channel
structure to that of their terrestrial counterparts.
They are divided into traffic channels and control
Satellite-traffic channels (S-TCH) are used to carry
either encoded speech or user data.
Four forms of traffic channels :
These traffic channels are further categorised into speech traffic channels and data traffic channels.
Table 2.2 summarises each category.
Control channels are used for carrying signalling and
[Table 2.3 summarises the different categories]
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 mobile’s case, the local operational environment has a significant impact on the achievable quality of service (QoS).
In the mobile-link, a service availability of 80–99% is usually targeted, whereas for the fixed-link, availabilities of 99.9–99.99% for the worst-month case can be specified.
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.
The diffuse component comprises multipath reflected signals
from the surrounding environment, such as buildings, trees and
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.
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 coderare: 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
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
notifies the network of its new point of attachment, allowing the
network to authenticate and to update the user’s location profile.
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.
The main task involved in the handover initiation phase is
gathering of information such as the radio link measurements.
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.
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:
spot-beam to another of the same satellite.
Such handover is due mainly to the satellite motion.
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.
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
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.
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
used to support the services offered to the users.
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
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.
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.
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 earth’s surface.
This is the concept of bandwidth-on demand.
Satellite internet :
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).
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).
Our vsat technology offers many advantages
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
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.
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.
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
Satellite networks offer excellent security against on authorized access.
Gaining access to a vsat system is virtually impossible Without authorization.
corporate communications can be divided into the following categories :
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.
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.
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.
a recent file transfer application requires support offile 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.
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.
long satellite-to-earth path and to the longer distance between the
FES and the user terminal.
to the longer propagation delay.
Coverage resulting in lower inter-spot-beam handover probability.
the satellite power is shared by all the spot-beams over the entire
coverage area .
compensate for the high attenuation in the radio signal in
contrast to the use of multipath signals in terrestrial cellular
of power and cellular radius; whereas adjacent spot- beam
interference is a function of power and sidelobe characteristics
of the satellite antenna Array.
networks in contrast to terrestrial network access in which the user
terminal in any given cell can only access an MSC associated with that
the call to the nearest gateway to the called party. This is impossible
in existing GSM networks.
during the initial period of operation.