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