Satelltie Access Methods
Channel Controller
Saturday, January 16th, 2010The Channel Controller will act as interface between the Resource Controller and the satellite channel. It will provide timing and control information to user terminals, and will forward user access requests to the Resource Controller. There will be a Channel Controller for each satellite channel.
Demand Assigned Multiple Access Subsystem (DAMA)
Wednesday, December 30th, 2009As satellite requirements have increased, UHF satellite capacity has been quickly saturated. The available frequencies to support UHF SATCOM are limited and only the efficient use of those frequencies can satisfy the increasing demands of the war-fighter. Demand Assigned Multiple Access (DAMA), a method of gaining efficiency in the use of UHF SATCOM channels, is automated channel sharing. “Demand based assignment” means that unused transponder space can be dynamically reallocated real-time on the basis of precedence. These channels can be assigned on demand, hence the term Demand Assigned. Many users who are capable may, at any one time, be actively accessing these channels, so the system is said to provide “Multiple Access.” DAMA allows multiple users to access simultaneously the UHF SATCOM pool of channel resources on demand. DAMA improves the efficiency of satellite resources by ensuring that channels are not wastefully idle when nets assigned to the channels are not communicating.
Time Division Multiple Access (TDMA)
Monday, December 28th, 2009The first attempt at using the transponders more efficiently was in the form of a TDMA scheme. TDMA is still in use. In this scheme, each ground terminal is allocated a “block” or “slot” of time in which to transmit a message. A message can be transmitted only during the terminal’s assigned time slot. If the terminal does not have a message to transmit, its time slot is wasted.
Frequency Division Multiple Access (FDMA)
Wednesday, December 23rd, 2009FDMA has been the most frequently used technique primarily because it is the simplest to implement. With FDMA, each earth terminal accessing a satellite merely transmits on a different frequency. The available bandwidth is subdivided into smaller frequency bands, or subchannels, in which each subchannel is assigned to a specific user.
SATELLITE MULTIPLE ACCESS METHODS
Monday, December 21st, 2009For economic and technical reasons, a separate satellite or satellite transponder must be made available for each pair of earth terminals that require a communication link. In most communications systems, several terminals must use the same transponder. The transponder must be able to receive, translate, amplify, and transmit signals from several earth terminals through the satellite is referred to as multiple access. A military, or commercial communications channel can potentially be used by numerous earth terminals within its coverage area. Various multiple access control techniques have been developed to enable many earth terminals to share the capacity of a single satellite communications channel.