Download - Telecom Fundamentals3
-
8/14/2019 Telecom Fundamentals3
1/37
Copyright 2003 P K Divakara
VSATVSAT
P K Divakaran
-
8/14/2019 Telecom Fundamentals3
2/37
Copyright 2003 P K Divakaran
What is VSAT?What is VSAT?
Very Small Aperture Terminal (VSAT) is a
small fixed Earth station.
It provides a satellite based communication
network
The communication could be voice, data or
videoconferencing
-
8/14/2019 Telecom Fundamentals3
3/37
Copyright 2003 P K Divakaran
VSATVSAT
-
8/14/2019 Telecom Fundamentals3
4/37
Copyright 2003 P K Divakaran
Why VSAT?Why VSAT?
Irregular terrain, where terrestrial network
rollout is difficult
For remote/ rural area communications
Large geographic area to be covered
For data traffic on Point to Multipoint basis
To avoid Last mile problem
-
8/14/2019 Telecom Fundamentals3
5/37
Copyright 2003 P K Divakaran
Applications of VSATApplications of VSAT
ATM Terminals (Banking)
Credit Authorisations
Play Win type of gaming terminals
To network farflung offices of a Company (Voice+ Data)
Inventory Management
Remote location connectivity
Remote process control/ Telemetry
Rural Telephony
Distance education/ Training
-
8/14/2019 Telecom Fundamentals3
6/37
Copyright 2003 P K Divakaran
Components of a VSATComponents of a VSAT
systemsystemSpace segment
Satellite and the Transponders on it
(Transponders are leased by VSAT serviceproviders)
Ground Segment
VSAT Earth stations Hub & Control centre
-
8/14/2019 Telecom Fundamentals3
7/37
Copyright 2003 P K Divakaran
Satellite CommunicationSatellite Communication
Earth Station
Satellite (Space Segment)
Hub & Control Centre
Earth
Statiouplink
Down
link
-
8/14/2019 Telecom Fundamentals3
8/37
Copyright 2003 P K Divakaran
Space SegmentSpace Segment
Space segment
Satellites are generally owned by organisations like
ISRO, INTELSAT, EUROPESTAR etc Transponders are electronic repeaters in the satellite .
The functions of transponders are Signal reception from Earth station
Frequency translation- The frequency of the received signal is
translated to a different frequency called Downlink
frequency. This avoids frequency interference .
Amplification of signals for transmission on the Downlink
-
8/14/2019 Telecom Fundamentals3
9/37
Copyright 2003 P K Divakaran
Space SegmentSpace Segment
Space Segment
Each transponder has a Bandwidth of 40 Mhz.
Typically there are 12-18 Transponder in INSATsatellites
The Frequency band used in India are 6.725 Ghz to
7.025 GHz Uplink and 4.5 Ghz to 4.8 Ghz
Downlink . (Extended C Band)
Ku band (11/14 Ghz) has just been permitted for VSAT
in India. Ku band needs only small antenna size Earth
station
-
8/14/2019 Telecom Fundamentals3
10/37
Copyright 2003 P K Divakaran
Space SegmentSpace Segment
Extended C band. Unique to India
Ku Band
Uplink 14 Ghz to 14.5 Ghz
Downlink 10.95 Ghz to 11.7 Ghz
Susceptible to rain attenuation
-
8/14/2019 Telecom Fundamentals3
11/37
Copyright 2003 P K Divakaran
Types of VSAT NetworksTypes of VSAT Networks
A
B
A & B are VSATs. For communicating between them , they
have to go thru the Hub.
Hub
STAR TOPOLOGY
Path thru Satellite
-
8/14/2019 Telecom Fundamentals3
12/37
Copyright 2003 P K Divakaran
VSAT Star TopologyVSAT Star Topology
VSAT A
Satellite (Space Segment)
Hub & Control Centre
VSAT
Buplink
Down
link
Two hops thru satellite between A &B
-
8/14/2019 Telecom Fundamentals3
13/37
Copyright 2003 P K Divakaran
Star TopologyStar Topology
-
8/14/2019 Telecom Fundamentals3
14/37
Copyright 2003 P K Divakaran
VSAT Star TopologyVSAT Star Topology
Makes use of a Central Hub station for
communication between VSATs
Satellite double hop transmission is used
Time delay introduced due to double hop
transmission
Hence more suited for data applications
than voice
-
8/14/2019 Telecom Fundamentals3
15/37
Copyright 2003 P K Divakaran
VSAT Star TopologyVSAT Star Topology
Smaller VSAT antenna size can be used (1.2m).Comparitively less costly VSATs
High Central Hub investment . Antenna size 5-11m
Hub is installed and maintained by the VSATOperator and shared by different VSAT users
(Shared Hub)Or the Hub could be for a Single large User
community (Dedicated Hub). For eg. VSATnetwork of National Stock Exchange with more
than 800 VSAT terminals
-
8/14/2019 Telecom Fundamentals3
16/37
Copyright 2003 P K Divakaran
Mesh TopologyMesh Topology
A B
A & B are VSATs which communicate with each other directly
without going through a Hub. Only one Hop transmission
thru satellite is required
Thru satellite
-
8/14/2019 Telecom Fundamentals3
17/37
Copyright 2003 P K Divakaran
Mesh TopologyMesh Topology
VSAT A
Satellite (Space Segment)
Network Control
System
VSAT
Buplink
Down
link
-
8/14/2019 Telecom Fundamentals3
18/37
Copyright 2003 P K Divakaran
Mesh TopologyMesh Topology
The transmission between two VSATs isdirect thru a one hop transmission thru
satelliteThe Network control centre assists in
setting up the communication but is not partof the traffic path
One hop transmission is suited for voiceand video application because of less delays
-
8/14/2019 Telecom Fundamentals3
19/37
Copyright 2003 P K Divakaran
VSAT TechnologiesVSAT Technologies
TDM/TDMA (Time Division Multiplex/
Time Division Multiple Access)
DAMA (Demand Assignment Multiple
Access
-
8/14/2019 Telecom Fundamentals3
20/37
Copyright 2003 P K Divakaran
TDM/TDMATDM/TDMA
Star Topology
Double hop Satellite system
Suited for interactive data applications
speed upto 19.2 kbps
All VSATs in the system share satellite
resources on a Time slot basis
-
8/14/2019 Telecom Fundamentals3
21/37
Copyright 2003 P K Divakaran
TDM/TDMATDM/TDMA
Communications method VSATs to HubInbound Routes using
TDM/TDMA on a carrierTime slots assigned to each VSAT for transmission
on the Inbound RoutesSeveral VSATs share an Inbound Route
Hub to VSATs Outbound Route on aCarrier
Time synchronisation very critical
-
8/14/2019 Telecom Fundamentals3
22/37
Copyright 2003 P K Divakaran
Types of TDMATypes of TDMA
Fixed Assigned TDMA Each VSAT assigned a Fixed Time Slot for
transmission on the In Route
Used when traffic on all Vsats are balanced
Slotted Aloha VSATs can access any Time Slot at any time on the In
Route randomly
Suitable for short bursty transmissions
Need to have collission resolution mechanismbetween VSAT transmissions
-
8/14/2019 Telecom Fundamentals3
23/37
Copyright 2003 P K Divakaran
Types of TDMATypes of TDMA
Dynamic Reservation
Switch between a Slotted Aloha mode to
Fixed Assigned Mode depending on trafficgrowth
Performed dynamically depending on traffic
profile so that VSATs have an assured amount
of Time slots for transmission
-
8/14/2019 Telecom Fundamentals3
24/37
Copyright 2003 P K Divakaran
DAMADAMA
Mesh topology (Single hop)
On Demand a pair of available Satellite Carrier
frequencies are assigned between two VSATs bythe Network Control System
After use, the Carrier frequencies are returned acommon pool
Ideally suited for Voice / data traffic in batchmode
Optimum utilisation of Satellite resources
-
8/14/2019 Telecom Fundamentals3
25/37
Copyright 2003 P K Divakaran
DAMADAMA
Network Control System (NCS) Receives requests for Frequency Channel from a VSAT
over a shared DAMA common signalling channel
NCS checks the validity of the request and allocatespair of Carrier frequencies between the RequestingVSAT and the Destination VSAT
After the call, NCS returns the frequencies to a
common poolNCS only performs control functions and System
performance monitoring and is NOT a part of theTraffic path
-
8/14/2019 Telecom Fundamentals3
26/37
Copyright 2003 P K Divakaran
PAMAPAMA
Pre Assigned Multiple Access (PAMA)
Mesh Topology
VSATs are pre allocated designated Carrierfrequencies
Equivalent to Terrestrial Leased connections
No call set up delays For constant use for high traffic volumes
-
8/14/2019 Telecom Fundamentals3
27/37
Copyright 2003 P K Divakaran
VSAT TerminalsVSAT Terminals
Constituent Parts
Outdoor Unit
Indoor Unit
-
8/14/2019 Telecom Fundamentals3
28/37
Copyright 2003 P K Divakaran
Outdoor UnitOutdoor Unit
Antenna System Feed horn
Directs Transmitted power towards the antenna dish( Reflector) and collects the Received power from itMounted on the antenna frame at its focal point by
means of support arms.
Antenna Dish (Reflector)Varies in size from 1.2 m diameter onwardsProvides Signal Gain in both Transmit & Receive
directions
-
8/14/2019 Telecom Fundamentals3
29/37
Copyright 2003 P K Divakaran
VSATVSATRFT
Feed horn
-
8/14/2019 Telecom Fundamentals3
30/37
Copyright 2003 P K Divakaran
Outdoor Unit (ODU)Outdoor Unit (ODU)
RFT
The Radio Frequency Trans Receiver unit
Connected to Feed Horn and mounted on theAntenna Frame
-
8/14/2019 Telecom Fundamentals3
31/37
Copyright 2003 P K Divakaran
RFTRFT
IF from
Indoor Unit(70 Mhz)
Up Converter(70 Mhz to
C Band)
Power
Amplifier
Feed HornLow Noise
Amplifier
(LNA)
Down
Converter ( C Band to
70 Mhz IF)
IF to IndoorUnit (70 Mhz)
Trans
Receive
-
8/14/2019 Telecom Fundamentals3
32/37
Copyright 2003 P K Divakaran
Indoor UnitIndoor Unit
Consists of
Modulators
Modulates the User Data/ signal to an IF of 70Mhz towards the RFT
Demodulators
Demodulates the IF received from RFTDetermines the Access Scheme (TDMA,
DAMA etc)
-
8/14/2019 Telecom Fundamentals3
33/37
Copyright 2003 P K Divakaran
Indoor Unit (IDU)Indoor Unit (IDU)
Interface towards the user end equipment
like LAN, PABX, Routers, Multiplexors
-
8/14/2019 Telecom Fundamentals3
34/37
Copyright 2003 P K Divakaran
IDUIDU
Access
Control&
User
Interface
Modulators
Demodulators
OD
U
Customer
Equipment
LAN, PABX etc
-
8/14/2019 Telecom Fundamentals3
35/37
Copyright 2003 P K Divakaran
Regulatory IssuesRegulatory Issues
CUG
Space Segment
Licence fee
-
8/14/2019 Telecom Fundamentals3
36/37
Copyright 2003 P K Divakaran
VSAT Service Providers inVSAT Service Providers in
IndiaIndiaHughes Escorts Communications Ltd
HCL Comnet
Comsat Max
Bharti Broadband
Telstra Vcom
-
8/14/2019 Telecom Fundamentals3
37/37
Copyright 2003 P K Divakaran
VSAT equipment VendorsVSAT equipment Vendors
Gilat
Hughes
Viasat