Earth to Satellite Communications
How it works
Optical communications in free space and through the earth's atmosphere between a satellite and a ground station traditionally have used radio waves because of their ability to go through atmosphere. A system using optical frequencies requires the satellite to have both a transmitter and a receiver that typically share the optical antenna, and a mechanism for beam steering an on board laser. A beam splitter is also used at the receiving end: half the beam goes to the optical detector for demodulation and decoding, while the other half is used to adjust the receive antenna to make sure the beam is centered. The same system is required at the ground station.
Advantages/Disadvantages
Advantages:
- Much faster data rates than with RF
- Direct point-to-point signals at very high frequencies mean less interference with outside signals
- Cloud cover and Atmosphere can distort data being sent. If cloud cover is really heavy, no data can be recovered.
- transmitting in free space also introduces interference from background radiation, most notably the Sun.
- Point to-Point signals make it difficult to aim receiver at the very small beam being transmitted.
- A new system means new infrastructure which means new (expensive) equipment including telescopes, lasers, mirrors, detectors, a pointing and tracking system and control electronics