A natural ability of satellites to distribute signals to large areas of the Earth surface has been utilized for broadcasting of analog television and radio for decades. This ability mainly relates to geostationary satellites that are placed in a geostationary orbit i.e. in distance about 36000 km (over the equator).
Each geostationary satellite appears for Earth user fixed in the sky so there is no need for an antenna tracking system.
On the other hand satellite transmissions suffer from error prone satellite links therefore every signal before transmitting has to be adapted for such difficult propagation conditions.
A communication payload of satellites consists of transponders. Their function is to receive, restore, amplify, process, re-modulate and send signal back to Earth. Currently, the conventional geostationary satellite contains about 20 to 30 transponders and a single transponder can most often have a bandwidth ranging from 26 to 72 MHz (e.g. 36 MHz on the ASTRA 3A satellite). In satellite analog television a single transponder took care of one TV channel.
Applying the DVB technology a single 36 MHz satellite transponder can carry a number of TV channels (4 – 20, depending on resolution, video coding and bit rates) or radio channels (150).
Currently, the satellite systems provide DVB services all over the world. DVB-S standard came in 90s and uses MPEG-2 for video coding. In DVB-S transmitter a transport stream is equipped by an outer Reed Solomon code (with a coding rate 188/204), interleaved (resistance to block errors) and encoded by an inner convolutional code (with a coding rate from 1/2 to 7/8). Afterwards, the encoded transport stream is modulated by QPSK (Quaternary Phase Shift Keying) modulation [1].
DVB-S2 (DVB – satellite 2nd generation) is based on DVB-S but integrates new features and algorithms [8]. It relies on the same FEC codes as DVB-T2 (LDPC+BCH). QPSK and 8-PSK modulations are used for TV broadcasting, 16-APSK and 32-APSK (Amplitude and Phase Shift Keying) modulations for professional applications (interactive services, news gathering). In order to allow backwards compatibility with DVB-S it also can use the hierarchical modulation.
DVB-S2 also allows adaptively changing the coding and modulation (ACM) parameters to adapt signal to actual transmission conditions (frame by frame) for each particular user (interactive and point-to-point services). DVB-S2 increases the transmission efficiency by 30% (compared with DVB-S).
DVB-S2X (standardized in 2014) extends DVB-S2 specification by additional framing, coding and modulation options to increase the spectral efficiency, better support for UHD TV and future broadband interactive networks.