Shatrunjay Rawat, IIIT Hyde rabad VSAT Communication System
Nov 16, 2014
Shatrunjay Rawat, IIIT Hyderabad
VSAT Communication System
Limitations of Guided Media
Fixed positions – lack of mobility Installation time is high Difficult to install in some terrain
– Hills, jungles, etc. Maintenance is difficult Frequent cable faults
Unguided Media - Characteristics
Flexible Fast deployment No cable faults Easy maintenance Lower costs Limited bandwidth Interference
Wireless Characteristics
At lower frequencies– Easy to generate
– Travel long distances
– Penetrate buildings
– Omnidirectional
– Interference between users
– Absorption by earth surface
Wireless Characteristics
At higher frequencies– Unidirectional
– Antenna needs to be aligned
– Less interference from neighbours
– Line of sight communication
– Reflected from buildings
April 8, 2023 6
Very Small Apperture Terminal(VSAT)
Man Made Satellite
Satellite
Repeater in the sky Broadcast medium High Bandwidth High reliability Fast deployment
Type of Satellites
Based on Usage– Communication Satellites
– Military Satellites
– Remote Sensing Satellites
Type of Satellites
Based on orbit– GEO
• 36000 Km
– MEO• 10000-15000 Km
– LEO• <5000 Km
VSAT
Can be easily deployed any where within footprint of satellite
Reachability in hostile terrain and remote areas
Cost of communication independent of distance
High network reliability( > 99.7%) Enormous expansion capabilities- additional
VSATs can be rapidly installed Change in traffic loads can be easily
accommodated
VSAT Network Topology
STAR:– VSATs communicate to a central HUB (single
hop)
– VSATs communicate with each other through the central HUB( double hop)
MESH Network– VSAT to VSAT communication without a HUB
– Useful for high volume traffic
Inroute and Outroute
INROUTE OUTROUTE
Hub VSAT
Frequency of Operation
Ext C-Band–Tx: 6.725 GHz-7.025GHz, Rx: 4.5GHz –4.8GHz
–Shares frequencies with terrestrial transmission systems
–Typical antenna sizes are 1.8m/2.4m Ku-Band
–Tx: 14.0GHz-14.5GHz; Rx: 10.95-11.7GHz, 11.7-12.2GHz, 12.25-12.75GHz
–With heavy rain, fog or clouds, signal strength falls
–Typical antenna sizes are 1.2m/1.8m
–Cheaper end equipment
EIRP Footprint Comparison
GE-1AGE-1A INSAT-3BINSAT-3B
TDM/TDMA– (Time Division Multiplexing/Time Division
Multiple Access) SCPC DAMA/PAMA
– (Single Channel per Carrier : Demand Assigned Multiple Access/ Permanent Assigned Multiple Access)
DVB/RCS Broadband VSAT– (Digital Video Broadcast/Time Division Multiple
Access - Return Channel Satellite)
VSAT Technologies
TDM/TDMA Technology
Out Routes:– Outroute access based on Synchronous TDM
(Time Division Multiplexing)
– Data to multiple VSATs multiplexed in synchronous time slots sent as a single packet
– Remote VSATs receive complete packet,but pickup only slots which contain data addressed to them
– Typical information data rates: 512 kbps - 2Mbps
TDM/TDMA Technology
In Routes:– Time Division Multiple Access (TDMA) access
method
– Multiple versions of TDMA access methods (like Slotted Aloha, Reservation Aloha etc.)
– VSATs transmit bursts in an assigned time division slots
– Typical Rates 64 kbps, 128 kbps
– Multiple In-routes for one Out-route and multiple VSATs for one In-route
TDMA Access Techniques
Slotted Aloha– Each burst must begin and end transmission on
predefined time slots
– If collision occurs then bursts must be retransmitted
– Suited for short , uniform message lengths with rapid response-time requirements
TDMA Access Techniques
Stream Transmission:– Fixed allocation of bandwidth to a VSAT port
– Excellent performance for heavy and continuous data transfer
Transaction Reservation:– VSAT sends request to Hub to reserve capacity
– Hub assigns time slots on inroute for transmission
– Suited for long and varying message types
TDM/TDMA Technology
Best suited for bursty Traffic Transaction processing Double hop delay for VSAT to VSAT voice links
(~500 msec, exclusive of processing delay) 1.8/2.4 meter VSAT antenna Low cost end user equipment Large population of remote users are served by
single HUB
SCPC/DAMA Technology
Single hop communication (delay ~ 250 msec) Shared pool of frequency pairs User demands a frequency pair Frequency pair assigned by Central Controller After use, frequency is released to shared pool Central Controller only involved in call
management
SCPC/DAMA Technology
Best suited for continuous stream of information
Suitable for voice and video conferencing Typical data rates are as low as 8Kbps for
voice, upto 64Kbps for data and 384Kbps for video
Antenna size - 3.8 mtrs (Ext-C) / 2.4m (Ku) RF capacity chosen depending on speed and
number of carriers being uplinked (typical sizes 5W, 10W,20W)
End user equipment is expensive
Broadband VSAT - The need for Speed
High speed asymmetrical architecture– 2- 45Mb/s Downstream– Upto 256Kbps on the Upstream– Simultaneous Video, Audio, IP Data
Internet Surfing IP Multicast applications
– Video/Audio Streaming– Web Content Distribution
Broadcast quality Video/audio
Broadband Advantage
DVB/RCS is and industry standard– Non-proprietary as in case of other
systems– Broad Market acceptance– Lower cost as market demand increases
Deploy in any existing network– Two-way or one-way– Not locked into vendor’s proprietary system
Broadband VSAT
Video
IDU
Ethernet Port
HostHost
Audio
Front End Server
1.2/1.8m Antennawith
2-way ODU
Serial Ports
LAN
IF Interface
Dedicated vs Shared Hub
Dedicated Hub:
– Suitable when number of sites is more than >300
– High Capital Costs
– Services can be added depending on requirements
– Network is more secure Shared Hub :
– Hub equipment is installed, maintained and operated by a Service Provider
– Required number of VSATs can be procured from the Service Provider
– Several customers run on the same Hub and share the same resources
Shared Hub Service Providers
HECL Bharti Tatanet Essel Shyam GNFC HCL Comnet Comsat
VSAT Network Implementation
RF/Baseband Rack
1.2m Antenna
IDU
TDM/TDMA VSATIDU
1.2m Antenna Antenna
Remote Site #1
Remote Site#n
Outbound ( DVB or TDM)TDMA Inbound
1.2m Antenna
IDU
Service Provider’s Hub
Central Location
VSAT Equipment Configuration
VSAT configuration– 1.2m Antenna– 1 W SSPA– IDU with 1 LAN port– IFL cable
Implementation Scenario
RF/Baseband Rack
1.2m Antenna
IDU
DVB/TDMA VSATIDU
1.2m Antenna Antenna
Service Provider’s Hub
Central Site
Nx64 Kbps LL
SCPC Backhaul to SP Hub
RF/Baseband Rack
1.2m Antenna
IDU
TDM/TDMA VSATIDU
1.2m Antenna Antenna
Remote site #1
Remote site # n
Outbound ( DVB or TDM)TDMA Inbound
2.4m Antenna
IDU
Service Provider’s Hub
Central Location
SCPC Backhaul