Editing Satellite modem (section)

== Features ==
The main functions of a satellite modem are modulation and demodulation. Satellite communication standards also define [[error correction]] codes and [[framing (World Wide Web)|framing]] formats.

Popular modulation types being used for satellite communications:
* Binary phase-shift keying ([[BPSK]]);
* Quadrature phase-shift keying ([[QPSK]]);
* Offset quadrature phase-shift keying ([[OQPSK]]);
* [[8PSK]];
* [[Quadrature amplitude modulation]] (QAM), especially 16QAM.

The popular satellite error correction codes include:
* [[Convolutional code]]s:
** with [[constraint length]] less than 10, usually decoded using a [[Viterbi algorithm]] (see [[Viterbi decoder]]);
** with [[constraint length]] more than 10, usually decoded using a [[Fano algorithm]] (see [[Sequential decoder]]);
* [[Reed–Solomon error correction|Reed–Solomon]] codes usually concatenated with convolutional codes with an [[forward error correction#Interleaving|interleaving]];
* New modems support superior error correction codes ([[turbo code]]s and [[LDPC]] codes).

Frame formats that are supported by various satellite modems include:
* Intelsat business service (IBS) framing
* Intermediate data rate (IDR) framing
* [[MPEG-2]] transport framing (used in [[Digital Video Broadcasting|DVB]])
* [[E-carrier|E1]] and [[Digital Signal 1|T1]] framing

[[High-end]] modems also incorporate some additional features:

* Multiple data interfaces (like [[RS-232]], [[RS-422]], [[V.35 (recommendation)|V.35]], [[G.703]], [[LVDS]], [[Ethernet]]);
* ''Embedded Distant-end Monitor and Control'' (EDMAC), allowing to control the distant-end modem;
* ''Automatic Uplink Power Control'' (AUPC), that is, adjusting the output power to maintain a constant [[signal-to-noise ratio|signal to noise]] ratio at the remote end;
* [[Drop and insert]] feature for a [[multiplexing|multiplexed]] stream, allowing to replace some channels in it.