Satellite Communication System Tutorial
This tutorial section on satellite basics covers following sub topics:
Main Page About satellite Bands Parts Orbits Services Types capacity allocations network configurations Applications Satellite TTC Remote sensing VSAT basics
This satellite tutorial covers satellite transponder,satellite frequency bands,network, parts,orbits,services,satellite types,capacity allocation,network configurations,applications etc.
In satellite based wireless communication system, the information(data,voice,image,video) is transmitted at microwave frequency using high gain directional parabolic antenna from ground station to the satellite antenna on spacecraft orbiting in the geosynchronous orbit.
The received signal on the satellite is frequency converted and translated to the downlink frequency as per the C band or Ku band. This translated frequency is passed through the low noise amplifier and transmitted back to the earth. The input frequency from the earth is about 6 Ghz and after passing through the mixer and beating with the LO of 2225 MHz, the frequency is abour 4 Ghz which is sent back as mentioned after amplification. This frequency conversion helps avoiding interference between uplink and downlink signals. Also the frequencies are chosen such that they incur less attenuation and absorption losses through the atmosphere.
For signals having lesser bandwidth VSAT is used for interfacing with satellite. For signals having more bandwidth Hub station or Ground station is used for interfacing with satellite. VSAT usually will have smaller diameter antenna 3.7 or 4.2 meter, while Hub station will have larger diameter antenna usually 7.5 or 11.2 meter.
The satellite is used for long distance telephone calls and for relaying TV signals to broad area of the earth. It is mainly used for providing communication in the hilly and mountain areas where other means of communication is difficult to provide.
The satellites orbit at the height of 35800 km in the geosynchronous orbit at the speed of 11000km/hr. Due to satellite having in the geosynchronous orbit it is visible all the time from the earth and no tracking is needed. The entire earth can be covered by 3 such satellites orbiting around the earth in Geo-Stationary orbit. The stage which does the uplink to downlink frequency conversion is referred as transponder, for more refer page as mentioned below on the topic "what is satellite".
A satellite usually will have 12 transponder having 36 MHz bandwidth each.The total bandwidth on satellite is about 500 MHz. For C band satellite it is from 5925 to 6425 MHz uplink and 3700 to 4200 MHz downlink. For Ku band satellite it is from 14 to 14.5GHz uplink and 11.45 to 11.7 GHz downlink.
What is satellite?
The main function of satellite is to receive
signal from earth and transmit the same signal to broad area of the earth.
Satellite does frequency conversion and amplification of the received signal
before relaying back to the earth.
Satellite specification for C band operation
Frequency band of operation: C band
Uplink frequency(from ground station to the satellite): 6 GHz
Downlink frequency(from satellite to the ground station): 4 GHz
Input Carrier saturation flux density: -85 dBW/meter*meter
Input carrier backoff: -10dB
G/T of satellite antenna receive : -5 dB/deg.K
Single carrier saturated flux density output: 32 dBW
Output backoff: 4.5 dB
Uplink path loss : 199.6 dB
Downlink Path loss: 196.0 dB
Satellite Intermodulation noise density : -100 dB/Hz