Digital Satellite Communication – Definition and Advantages:
With the developments in digital electronics technology, access techniques and possibility of expanded communication network, digital signaling techniques have been introduced in communication by the satellite. Some of the advantages of digital satellite communication are :
- Increased efficiency of multiplexing multiple signals or handling digital messages in packets for convenient switching.
- Relative insensitivity of digital circuits for retransmission.
- Potential for extremely low error rate and high fidelity through error detection and correction.
- Communications privacy.
- Flexibility of digital hardware implementation and it permits the use of microprocessors and miniprocessors, digital switching and use of large scale integrated circuits (LSI).
So digital transmission techniques have gained increased usage for satellite communication, microwave relay or waveguide transmission.
In analog communication system frequency division multiplexing—frequency modulation–frequency division multiple access (FDM–FM–FDMA) has been widely used and provides good quality satellite links, but the number of earth stations are limited.
A Digital Satellite system such as that using quaternary phase shift keying–time division multiple access (QPSK-TDMA) can accommodate a large number of earth stations with a small loss in transponder capacity and the system can quickly respond to traffic variation. Efficiency can be further increased by demand assignment and digital speech interpolation. Digital communication techniques use onboard switching and processing, multiple spot beams and beam hopping and such digital systems are capable of serving a mixture of large, medium and small earth stations with high efficiency. The recent technique of code division multiple access has allowed use of microearth stations (0.5 m antenna) at an extremely low cost with a good quality service. ISDN system will further enhance the importance of digital communication networking with satellites.