VSAT

Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: MCE203A
VSAT & DSB-TV
5/11/2020 1Arpan Deyasi, RCCIIT, MCE203A

Very Small Aperture
Terminal for small,
software-driven
Earth stations
Small satellite dish
capable of both
transmitting and
receiving radio
signals
VSAT

5/11/2020 Arpan Deyasi, RCCIIT, MCE203A 3
Mostly designed at 6/4 GHz, 14/11-12 GHz and
30/20 GHz frequency bands
Involves FDMA or TDMA techniques
Date rate: 4 Kbps – 16 Mbps
Used for reliable transmission of data, voice, video,
audio via satellite
VSAT

VSAT
Transceiver Terminal device
. placed outdoor with direct
line of sight with satellite
. receives/sends signal to
transponder
. placed at indoor to interface
the transceiver with end
user’s communications
Components of VSAT

Working of HUB
Every end user is interconnected with hub via satellite through star
topology
Hub controls entire network operation

Configuration of VSAT
1. STAR topology:
All the communications occur
through Hub station using
multi-hop communication
Higher propagation delay
Smaller antenna size

Used by TDMA VSATs
High central hub investment
1. STAR topology:
Ideally suited for interactive
data applications
Large organizations demand it
for centralized data processing
requirements
Classified into Shared Hub and
distributed Hub types

• In Shared Hub Network type, one large hub station is used and
all the VSATs are divided into sub-networks
• Each sub-network is assigned to particular CUG (Closed User
Group)
• Different CUG is created for all the clients separately
• Each CUG will have their own inbound and outbound RF carriers
VSATs in all the CUGs use the same one Hub station
1. STAR topology:
o In Distributed Hub Network type, each network will have its
own hub station known as "min-Hub“
o This mini hub is located near the client's premises
o In this network, all the clients will have its own traffic hub
dedicated to its own CUG

2. MESH topology:
All the communications occur
directly between VSATs without
need of any central Hub station
Mesh type is called point-to-point
configurations. In this mesh type
network configuration, Earth
stations communicate directly via
satellite and will have only one
hop communication
Configuration of VSAT

Used for telephony applications
2. MESH topology:
Lower propagation delay
Used by FDMA VSATs
Lower central hub investments
Larger antenna size
Suited for high data-traffic

minimize overall cost of network
improves data communication
3. Combination of STAR & MESH topology:

Multiple Access Techniques in VSAT
[i] PAMA: Permanently Assigned Multiple Access
[ii] DAMA: Demand Assigned Multiple Access

In PAMA, every user is assigned a fixed channel, irrespective of
whether it is used or not
This is very inefficient as the channels are allotted to users even
when there is no requirement
PAMA is also known as Fixed Assigned Multiple Access (FAMA)
PAMA protocols are considered the most effective techniques for
those satellite networks with a small number of terminals
Permanently Assigned Multiple Access (PAMA)

Permanently Assigned Multiple Access (PAMA)
Advantages of PAMA:
Perfect for constant-bit-rate-type sources
Straightforward scheduler
Channel usage is contention-free
Disadvantages of PAMA:
Considerable bandwidth usage
Not flexible while working with terminals having
variable bit rates

Demand Assigned Multiple Access (DAMA) is a protocol used in
satellite communications, particularly VSAT systems
DAMA enables efficient and instantaneous assignment of
transponder channels on a first come, first served basis
according to data priority
Typical VSAT systems use DAMA for point-of-sale (POS)
transactions, such as credit card, polling or radio frequency
identification; remote location Internet access and mobile
maritime communications
Demand Assigned Multiple Access (DAMA)

Characteristics of VSAT systems
1. Reliable communication: error-free digital communication
with more than 99.7% reliability
2. Remote communication: remote diagnosis, monitoring and
data streaming services are possible
3. Network management: Easier network monitoring and
control

4. Time: deployment takes 1-1.5 months
5. Maintenance: single point contact for operation,
maintenance, fault isolation, trouble shooting
6. Cost: Comparatively less compared with leased line
7. Flexibility: enormous expansion capability even in
remote places
Characteristics of VSAT systems

Advantages of VSAT
Brings service directly to end-user by reducing
hierarchical distribution network and therefore,
hierarchical cost

Limitations of VSAT
High initial cost for launching satellite in Geo-synchronous orbit
Requires clear line of sight between dish and satellite
Higher latency
Probability of damaging of antenna
Rain attenuation detoriates performance

Uses of VSAT
Receiving internal communications
Interactive distance learning courses
Financial management
Data processing
Telemetry & Data collection
Virtual Private Network
Remote location access

Satellite television
Television programming delivered through
satellite communications and received by
outdoor antenna
R-S Encoder Interleaver
Rate ¾
convolutional
encoder
Convolutional
Decoder
de-Interleaver R-S Decoder
Data i/p
Data
o/p

Working principle
Uplink dish is pointed towards a specific satellite and uplink
signal is transmitted within a frequency range
Signal received by transponder and send to satellite
Transponder re-transmit the downlink signal to Earth
Set-top box demodulates and converts it in desired form

Features of Satellite TV
High definition
Simple user interface
Internal drive
Remote management
Digital video recorder
Detailed program information
Keyword search
Favorite list

https://www.rfwireless-world.com/Tutorials/satellite-network-
configuration.html
https://www.techopedia.com/
A. K. Maini, V. Agarawal, “Satellite Communications”, Wiley, 1st Ed.,
2019
T. Pratt, C. Bostian, J. Allnutt, “Satellite Communications”, John
Wiley & Sons, 2nd Ed., 2003
References

VSAT

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VSAT