264 Satellite Communication Engineering, Second Edition
Cryptographic key management: The generation, distribution, recognition,
and reception of the cryptographic keys (passwords).
Cryptography: A science that comprises encryption, decryption, and a
cryptographic key management unit.
Decoding: The process required to reconstruct the data bit sequence
encoded onto the carrier.
Decryption: The unlocking of the locked (decrypted) message; the reverse
Demodulation: A process by which the original signal is recovered from a
modulated carrier; the reverse of modulation.
Delay: Time a signal takes to go from the sending station through the satel-
lite to the receiving station.
Downlink: The space-to-earth telecommunication pathway.
Drag: The friction between a moving vehicle through the earth’s atmo-
sphere opposing the vehicle’s forward motion.
Earth station: A terrestrial terminal that provides a means of transmitting
the modulated radiofrequency (RF) carrier to the satellite within the
uplink frequency spectrum and receiving the RF carrier from the
satellite with the downlink frequency spectrum. It is the vital link
between satellite and communication users.
Encryption (enciphering): The process of converting messages, informa-
tion, or data into a form unreadable by anyone except the intended
Feed: The radiofrequency (RF) input/output device.
Footprint: An area on earth illuminated by a satellite antenna. Its shape and
size depend on a number of factors, including the antenna design
and the satellite’s angle of elevation.
Forward error correction: A transmission error detection and correction
technique that, in addition to detecting errors, also corrects errors at
the receive end of the link.
Frequency division multiple access: A technique by which the transponder
bandwidth is shared in separate frequency slots.
Frequency reuse: Using the same frequency band several times in such a
way as to increase the overall capacity of a network without increas-
ing the allocated bandwidth.
Functional group: A set of functions required for carrying out tasks in
cooperation with another functional element or group.
Gain: A measure of amplier power expressed in watts (W) or decibels (dB).
Gateway: A special switch used to link part of a network.
Geostationary satellite (GEO): A satellite placed in the geosynchronous
orbit in the equatorial plane. Although it appears not to be moving
when seen from the earth, its velocity in space equates to 3.076 km/s
Gigahertz (GHz): One billion (10
) cycles per second.
K21636_Book.indb 264 10/22/13 4:11 PM