Introduction to VTSAT and SATELLITE COMMUNICATION
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