INTRODUCTION OF SATELLITES
Most communication satellites are geostationary the like, are placed in an orbit so as to have a rotation period equal to that of our planet. Thus the angular velocity of rotation is equal to the Earth. Seen here is like being stuck in space.
The International Telecommunications Union (ITU) divided the space geostationary orbital positions 180, each separated from another by an angle of 2 ° (two degrees). The Brazil pleaded 19 orbital positions with the ITU.
The transponder is the device responsible for retransmission of the received signal consists of a set of electronics that receives the Earth signal (uplink) and after processing as power gain, filtering and frequency translating retransmits the planet (link descent).
A satellite is usually composed of several transponders act as independent of repeat units, each occupying a unique range of frequencies, it is important to increase its reliability and versatility.
A VSAT station is composed of two distinct physical units, Outdoor Unit (ODU - "outdoor unit") and the Indoor Unit (IDU - "indoor unit"). In ODU are the antenna feeder and the RF part of the transmitter and receiver. In the IDU is the entire baseband part consisting essentially modem.
The IDU connects to the ODU via coaxial cables where transmission is made at the level of intermediate frequency (IF), usually in the 2 GHz band. The maximum distance that can be ODU IDU ranges from 50 to 100 meters.
ACCESS METHODS SATELLITE
Multiple accesses require precise management by the operator of the satellite company, in order to avoid mutual interference between different stations. Access can be:
TDMA (“Time Division Multiple Access") multiple access or time division in which each channel is assigned a time interval which is repeated periodically;
FDMA (“Frequency Division Multiple Access") or multiple access by frequency division, each channel is associated with a frequency; It is the only one that supports analog signals;
FTDMA (“Frequency Time Division Multiple Access") or multiple access frequency division and time, which is a combination of the two, where each channel is associated with an ordered pair of time and frequency interval;
CDMA ( "Code Division Multiple Access") or multiple access code division, which uses spread spectrum technique ( "spread spectrum") where each channel is assigned a code, which is the decryption key that channel.
SCPC (single channel per carrier) is intended for the transmission of digitized voice at 64kbps (or data at speeds up to 2048Kbps) in duplex mode.
APPLICATIONS FOR SATELLITE
The applications of satellite communication technology are as follows:
For very large geographic regions and to reach remote areas as mining camps, logging, rural and suburban properties and stations on highways;
Where a quick or occasional use deployment is necessary, as for concerts, rodeos, car racing;
Military applications such as defense of borders, etc;
For air transport and maritime.
Telecommunications, television, internet, etc.
Communication satellite systems in the Ku and Ka bands are a modern technology and great potential in terms of telecommunications services. Due to the high frequency telecommunications services such as telephone, data and television can be carried out through networks with topology consisting star small terminal stations called VSAT ( "Very Small Aperture Terminal"), coupled to a station central master ( "master" or "HUB").
The VSATs networks are a technical-economical solution interesting for countries like Brazil, because it has large areas with remote and isolated communities.