Satellite On-Board Connectivity

Satellite Networking
Sukiswo
[email protected]
Komunikasi Satelit, Sukiswo, ST, MT
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Outline
 Network Refference Model
 Architecture for Satellite Network
 Basic Characteristic of Satellite Network
 Satellite On-Board Connectivity
 Connectivity Through Intersatellite Links
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OSI Refference Model
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TCP/IP Refference Model
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Architecture for Satellite Networks
 Satellite networks are used to provide two major types of
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service: TV services (associated with broadcast services)
and telecommunication services (associated with two-way
communication services, symmetric—telephony—or
asymmetric—Internet access).
One or more satellite networks can be deployed under the
coverage of a single satellite and operated by a satellite
network operator.
It relies on a ground segment and utilises some satellite
on-board resources (through the satellite channels that are
used).
The ground segment is composed of a user segment and a
control and management segment.
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Architecture for Satellite Networks
 In the user segment, one finds satellite terminals (ST)
connected to the end-user customer premises equipment
(CPE), directly or through a LAN and hub or gateway
stations, sometimes called network access terminals
(NAT), connected to terrestrial networks.
– Satellite terminals are earth stations connected to CPE, sending
carriers to or receiving carriers from a satellite. They constitute the
satellite access points of a network; when the satellite network is a
DVB-RCS network (designed according to the DVB-RCS
standard), satellite terminals are also called Return Channel
System Terminals (RCST).
– CPE are also called user terminals (UT) and they include
equipment such as telephone sets, television sets and personal
computers. User terminals are independent of network technology
and can be used for terrestrial as well as satellite networks.
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Architecture for Satellite Networks
– CPE are also called user terminals (UT) and they include
equipment such as telephone sets, television sets and personal
computers. User terminals are independent of network technology
and can be used for terrestrial as well as satellite networks.
– The gateway earth station (GW) provides internetworking
functions between the satellite network and the Internet or a
terrestrial network.
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Architecture for Satellite Networks
 The control and management segment consists of:
– a mission and network management centre (MNMC) in charge of
non-real-time, high-level management functions for all the satellite
networks that are deployed in the coverage of a satellite.
– network management centres (NMC), also called interactive
network management centres (INMC), for non-real-time
management functions related to a single satellite network.
– network control centres (NCC) for real-time control of the
connections and associated resources allocated to terminals that
constitute one satellite network.
 A satellite network (also called a satcom network)
comprises a set of satellite terminals, one or more
gateways and one NCC that is operated by one operator
and uses a subset of the satellite resources (or capacity).
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Satellite Network Components
NMC=network management
NAT=centres network access terminals
NCC =network control centres
GW=gateway earth station
MNMC =mission and network management centre
ST =satellite terminals
INMC =interactive network management centres
CPE=customer premises equipment
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Characteristic of Satellite Network
 Satellite networks are characterised by their topology
(meshed, star or multi-star), the types of link they support
and the connectivity they offer between the earth stations.
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Meshed Satellite Topology
 A meshed satellite network consists of a set of earth
stations which can communicate one with another by
means of satellite links consisting of radio-frequency
carriers.
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Meshed Satellite Topology
 A meshed satellite network can rely on a transparent or a
regenerative satellite.
 In the case of a transparent satellite, the radio-frequency
link quality between any two earth stations in the network
must be high enough to provide the end users with a
service achieving the target bit error rate.
 This implies sufficient EIRP and G/T for each earth
station, given the satellite transponder operating point.
 In the case of a regenerative satellite, the on-board
demodulation of the signal puts fewer constraints on the
EIRP and G/T of the earth stations.
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Star Satellite Topology
 In a star network, each node can communicate only with a single
central node, often called the hub.
 A star satellite network consists of earth stations which can
communicate only with a central earth station called the hub.
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Star Satellite Topology
 Hub is a large earth station (antenna size from a few meters to
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more than 10 m) with higher EIRP and G/T than the other earth
stations in the network.
A star network topology places fewer constraints on the EIRP
and G/T of the earth stations than a meshed network topology
relying on a transparent satellite, due to the fact that the earth
stations communicate with a large earth station (the hub).
This architecture is popular among networks populated with
small earth stations (antenna size of about 1 m) called very
small aperture terminals (VSAT) [MAR-02].
The link from any earth station to the hub is called an inbound
link or return link.
The link from the hub to the other earth stations is called the
outbound link or forward link.
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Types of link
 Two types of link can be established through a satellite
network: unidirectional links, where one or several stations
only transmit and other earth stations only receive, and
bidirectional links, where earth stations both transmit and
receive.
 Unidirectional links are usually associated with a star
topology, in satellite broadcast-oriented networks.
 Bidirectional links can be associated with a star or meshed
topology and are required to transport any two-way
telecommunication services.
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Types of Network Connectivity
 Connectivity characterises the way nodes of a network are
connected to each other.
 When a communication link is established through a
satellite network, two levels of connectivity need to be
distinguished: the connectivity required at the service level
and the connectivity required on board the satellite.
 The connectivity at the service level defines the type of
connection that is necessary between CPEs or network
equipment, and between satellite terminals or gateways, to
provide the service required by end users.
 This connectivity is principally processed on the ground
and relies on ‘identifiers’ associated with sessions, layer 3
and layer 2 connections.
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Types of Network Connectivity
 Satellite on-board connectivity defines how the satellite
network resources are switched on board in order to meet
the service-level connectivity requirements.
 It therefore depends on how the satellite resources (beams,
channels, carriers, etc.) are organised on both satellite upand downlinks and, primarily, on the type of coverage that
the satellite system provides.
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Satellite On-Board
Connectivity
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Satellite On-Board Connectivity
 Satellite on-board connectivity can be provided at the
following levels:
– Spot-beam: The whole frequency resource allocated to a beam is
switched on board; this can correspond to a channel or several
channels (typically 125 or 250MHz in Ka band).
– Channel: This is equivalent to the frequency resource that is
classically transmitted through a transponder (typically 36 or 72
MHz).
– Carrier: This can be an FDMA carrier transmitted by a satellite
terminal or earth station, or an MF-TDMA carrier that is shared by
several satellite terminals (typically from a few kHz up to tens of
MHz depending on the earth station radio capability).
– Time slot: This corresponds to TDM or TDMA time slots.
– Burst, packet or cell: This corresponds to any type of layer 2
packet, up to IP datagrams.
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Satellite On-Board Connectivity
 Figures below correspond to different levels of granularity
and they imply different types of processing
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Satellite On-Board Connectivity
 Depending on the on-board processing capability
and the network layer, different techniques are
considered for interconnection of coverage:
– transponder hopping (used when there is no on-board
processing);
– on-board switching (used when there is transparent and
regenerative processing);
– beam scanning.
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Connectivity With Transponder Hopping
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Connectivity With Transponder Hopping
 Interkoneksi ini digunakan jika jumlah beam
sedikit
 Bandwidth total sistem dibagi menjadi beberapa
sub-band sebanyak jumlah beam
 Terdapat sejumlah filter secara onboard disatelit
untuk memisahkan carrier yang berhubungan
dengan jumlah sub-band yang digunakan
 Output dari tiap filter terhubung ke antena beam
tujuan melalui transponder
 Jumlah filter dan transponder minimal sama
dengan kuadrat dari jumlah beam
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Connectivity With Transponder Hopping
 Stasiun bumi harus mampu
mengirimkan/menerima dalam beberapa frekuensi
dan beberapa polarisasi agar proses interkoneksi
disatelit dapat melompat dari transponder satu ke
transponder lainnya (transponder hopping)
 Interkoneksi ini biasanya digunakan jika jumlah
beam sedikit
 Jika jumlah beam banyak maka penggunaan
interkoneksi transponder hopping tidak lagi
optimal karena jumlah transponder minimum sama
dengan kuadrat dari jumlah beam→satelite mjd
berat
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Connectivity On With
Transparent Processing
 Beam switching by transponder hopping is a
solution when the number of beams is low.
 Because the number of transponders increases at
least as the square of the number of beams, with a
large number of beams the satellite payload
becomes too complex and too heavy.
 It is therefore necessary to consider on-board
switching at a lower granularity, and shift from
beam switching to channel switching.
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Connectivity On With
Transparent Processing
 Two types of technology can provide this
kind of connectivity:
– analogue technology using an intermediate
frequency-switching matrix, one example of
which is known as satellite switched/TDMA
(SS/TDMA),
– digital technology using baseband processing
equipment, in particular digital transparent
processors (DTP).
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Connectivity On Board Switching (SS/TDMA)
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Connectivity On Board Switching (SS/TDMA)
 Pada payload terdapat programable switch matrix yang
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mempunyai jumlah input = jumlah output = jumlah beam
Switch matrix ini menghubungkan tiap up beam ke down
beam dan jumlah repeater sama dengan jumlah beam
DCU (Distribution Control Unit) berfungsi untuk mengatur
switch matrix pada proses pembangunan koneksi
Jika koneksi antar 2 beam adalah cyclic (berulang) maka
stasiun DCU akan menyimpan trafik dari banyak user dan
mengirimkan trafik dalam bentuk burst jika interkoneksi
antar beam telah selesai
Jenis interkoneksi ini digunakan pada transmisi digital dan
jenis multiple access TDMA →SS-TDMA (Satellite
Switched Time Division Multiple Access)
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Frame Organisation on SS/TDMA
 Tiap frame berisi field sinkronisasi dan field trafik
 Contoh organisasi frame untuk 3 beam :
 Window : durasi (lama) waktu koneksi dari satu up beam
ke satu down beam
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Window Organisation on SS/TDMA
 Pengaturan burst pada
interval waktu satu window
 Gambar disamping
menunjukkan burst –burst
yang akan yang akan
ditransmisikan oleh stasiun
A,B dan C pada window yang
berhubungan dengan koneksi
dari beam 3 ke beam 2
 Masing–masingburst yang
ditransmisikan oleh stasiun
pada selang waktu window
berisi beberapa sub burst yang
berisi informasi stasiun ke
stasiun
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Synchronisation On Processing SS TDMA
 Ada2 aspek sinkronisasi:
– Sinkronisasi antar stasiun bumi
– Sinkronisasi antara stasiun bumi dengan satelit
 Sinkronisasi antar stasiun bumi:
– Sinkronisasi antar stasiun bumi menggunakan
single beam TDMA. Ada2 teknik:
• Sinkronisasi closed loop
• Sinkronisasi open loop
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Synchronisation On Processing SS TDMA
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Close Loop Synchronisation
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Open Loop Synchronisation
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Open Loop Synchronisation
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Sinkronisasi Antara Stasiun Bumi Dengan Satelit
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Troughput Frame pada On Board
Processing
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Digital transparent switching
 Digital technology, relying on digital filtering and
switching.
 The principle of a digital transparent processor
that enables the switching of uplink carriers from
one spot beam to another spot beam and the
transposition of frequency.
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Digital transparent switching
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Connectivity With Regenerative
Processing
 The availability on board the satellite of
binary digits obtained after demodulation
and decoding, offers several opportunities,
and in particular allows the introduction of
some layer 2 switching on board the
satellite.
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On Board Processing
 Proses yang terjadi secara on board
disatelit:
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Downlink Coding
Baseband switching
Rate Convertion
Beam Scanning
Proses FDMA/TDM
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Downlink Coding
 Pada arah downlink encoder ditempatkan secara on board
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disatellite dan diaktivasi oleh telecommand
Akan menghasilkan decoding gain dan laju transmisi akan
bertambah(sebanding dg 1/code rate)
Sehingga pd arah downlink dibatasi oleh power bukan
bandwidth
Jika link dibatasi oleh bandwidth maka laju transmisi harus
dimaintained sehingga laju informasi akan turun
Akibat penggunaan encoder pd arah downlink adalah akan
terdapat margin C/Noyang dapat digunakan untuk
mengantisipasi redaman hujan
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Baseband Switching
 Proses switching antara antena kirim dan
antena terima dilakukan dilevel baseband
setelah proses modulasi dan demodulasi
 Dilakukan pada data rate yang rendah
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Baseband switching
 The availability of bits on board the satellite at the
output of the uplink carrier demodulators permits
switching between receiving and transmitting
antennas to be no longer at radio frequency but at
baseband.
 The constraint of immediate routing of received
information to the destination downlink disappears.
 This permits earth stations to transmit all their
information in the same burst and hence to transmit
only a single burst per frame. The number of bursts
per frame is reduced and the efficiency of the frame
increases.
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Baseband switching
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Rate Convertion
 Satelit tipe transparent repeater :
Terdapat link terestrial dan terjadi 2 hop
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Rate Convertion
 Satelit tipe regenerative repeater :
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Beam Scanning Satelite
 Single beam yg dihasilkan satelit akan melakukan scan terhadap area
servis secara sekuensial
 Keuntungan: Akan mengurangi Co-channel interference karena
pengalokasian beam yang dinamik
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Beam Scanning Satelite
 Contoh: NASA ATCS (Advance Technology Communication
Sattelite) Satellite; Menggunakan 2 beam untuk scanning (uplink dan
downlink)
 Payload :
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FDMA/TDM
 Satelit tipe regenerative mempunyai kelebihan:
– Dapat mereduksi EIRP stasiun dan G/T stasiun bumi
– Dapat mengimplementasikan FDMA pd arah uplink danTDM pd
arah downlink
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Connectivity With Beam Scanning
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Connectivity With Beam Scanning
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Connectivity Through
Intersatellite Links
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Connectivity Through
Intersatellite Links
 Intersatellite links (ISL) can be considered as
particular beams of multibeam satellites; the
beams in his case are directed not towards the
earth but towards other satellites.
 For bidirectional communication between
satellites, two beams are necessary—one for
transmission and one for reception.
 Network connectivity implies the possibility of
interconnecting beams dedicated to intersatellite
links and other links at the payload level.
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Connectivity Through
Intersatellite Links
 Three classes of intersatellite link can be
distinguished:
– links between geostationary earth orbit (GEO)
and low earth orbit (LEO) (inter-orbital links
(IOL);
– links between geostationary satellites (GEO–
GEO);
– links between low orbit satellites (LEO–LEO).
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Links between GEO–LEO
 This type of link serves to establish a permanent
relay via a geostationary satellite between one or
more earth stations and a group of satellites
proceeding in a low earth orbit at an altitude of the
order of 500 to 1000 km.
 One or more geostationary satellites are therefore
used; they are permanently and simultaneously
visible both from stations and low earth orbit
satellites and serve to relay communications.
 This technique also permits overcoming possible
limitations of the terrestrial network.
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Links between GEO–LEO
Example :
 NASA tracking network by means of the tracking
and data relay satellites (TDRS) which, in
particular, provide communication with the
International Space Station.
 European programme has successfully launched a
data relay payload (ARTEMIS satellite) to provide
communications between the ground and low
earth orbit spacecrafts.
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Increasing the capacity of a system
Second satellite is launched to increase the capacity of
the space segment—the stations must be equipped
with two antennas
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Increasing the capacity of a system
 With an intersatellite link, only the stations of the
most heavily loaded region must be equipped with
two antennas;
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Increasing the Capacity of a System
 The stations are distributed between the two
satellites. The intersatellite link carries the traffic
between the two groups of stations.
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Extending the coverage of a system
Interconnecting the stations of each coverage
by an intersatellite link
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Extending the coverage of a system
interconnecting, without an intersatellite link, by
a station common to the two networks
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Extending the coverage of a system
interconnecting, without an intersatellite link, by
a terrestrial network
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Global network
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Links between LEO–LEO
 Satellites orbiting in low earth orbit present the
advantage of significantly minimising the
transmission delay, which is of high interest for
some services (typically voice).
 However, a single satellite is visible from earth
during a very short period of time thus limiting the
duration of communication.
 An example of a network of this type is proposed
in [BRA-84; BIN-87].
 The IRIDIUM system is another example of a
deployed constellation of 66 satellites.
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