Introduction to VTSAT and SATELLITE COMMUNICATION

WHAT IS VSAT Stands for “Very Small

Aperture Terminal” and refers to receive/transmit terminals installed at dispersed sites connecting to a central hub via satellite using small diameter antenna dishes (0.6 to 3.8 meter). @ C and KU

Band Frequencies

BROADCASTING ONLY Stock market & other news

broadcasting Training or continuing

education from a distance Distribute financial trends &

analyses Introduce new products at

geographically dispersed locations

Distribute video or TV programs

Distribute music in stores & public areas

Relay advertising to electronic signs in retail stores

Transmit/Receive..... Interactive computer

transactions Internet Video Teleconferencing Bank transactions, ATM Reservation systems Distributed remote process

control and telemetry Voice communications Emergency services Electronic fund transfer at

Point-of-Sale Medical data transfer Sales monitoring & stock

control

VSAT SERVICES

Equipments required for VSAT network ANTENNAS HIGH POWER AMPLIFIER LOW NOISE AMPLIFIER UP & DOWN CONVERTER ECHO-CANCELLER MODEMS Power spliter POWER SYSTEM

Satellite network TO link LAN between offices

Satellite-Terrestrial Networkingused to share the data from offices

FDMA (Frequency Division Multiple Access )

TDMA (Time Division Multiple Access )

CDMA (Code Division Multiple Access )

Multiple Access

Frequency Division Multiple Access

(FDMA) – An approach to sharing a channel by

separating the simultaneous users in frequency

FDMA

Frequency

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Time division multiple access (TDMA) – Approach for allotting single-channel

usage amongst many users, by dividing the channel into slots of time during which each user has access to the medium.

TDMA

TDMA/FDMA Combination

Frequency

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FDMA

Each Channel in turn assigned to 8 subscribers on TDMA mode

200 KHz

TDMA Tipical TDMA IN TRANSPONDAR

Code Division Multiple Access (CDMA) – Spread spectrum technique using

high-speed pseudo random (PN) codes to scramble data words and spread spectral occupancy for added robustness.

CDMA

The Signal Path

TECHNOLOGY SIMPLIFIED – SCPC (DAMA/PAMA)

Pre – assigned multiple accesses. (PAMA): In Pre – assigned multiple accesses the frequency allotted is fixed. Suppose we want to call any place, then the frequency of call signal is fixed. This results in less number of calls. Pre – assigned multiple accesses is used to send the data or other any signal.

Demand assigned multiple accesses (DAMA): In Demand assigned multiple accesses frequency allotted is controlled by Master Signaling Channel Unit (MSCU). Suppose if we want to call any place then a request is send to MSCU. MSCU allots frequency the frequency which is free. Then the call is establish between that two places by using allotted frequency. Once the call is complete is over, then the frequency is left free so that it can be used again by other caller. So now there can be many numbers of connections as compared in PAMA. The satellite earth station where there is MSCU is called as master’s station or HUB station.

Main Components (cont)Main Components (cont) Master site contains:

Redundant call processing computers An administration and maintenance

terminal An antenna A redundant RF subsystem Master signaling channel units

FeaturesFeatures DAMA System features enhance

configurations and simplify network operation. Features include:

Universal telephone interface Digitized voice with Group III fax Voice/data circuits can be added Traffic analysis and billing data collection Monitoring and control of remote stations Priority call handling Redundant common equipment Flexible, configurable channel units

Remote Signaling Remote Signaling (cont’d)(cont’d)

Typical 24 channel C-band transponder frequency plan