DVB-S2 (EN302 307) is a digital satellite transmission system developed by the DVB Project. It makes use of the latest modulation and coding techniques to deliver performance that approaches the theorectical limit for such systems.DVB-S2 will gradually replace DVB-S in the future, as new HD services entice users to upgrade their receivers to more efficient DVB-S2 models. DVB-S2 takes advantage of advanced techniques for channel coding, modulation and error correction to create a system that would make a range of new services commercially viable for the first time eg when combined with the latest video compression technology, DVB-S2 would enable the widespread commercial launch of HDTV services.

 

 How does it work?

The original DVB-S system, on which DVB-S2 is based , specifies the use of QPSK modulation along with various tools for channel coding and error correction. DVB-S2 benefits from more recent developments and has the following key technical characteristics:

There are four modulation modes available , with QPSK and 8PSK intended for broadcast applications in non-linear satellite transponders driven close to saturation. 16APSK and 32APSK, requiring a higher level of C/N, are mainly targeted at professional applications such as news gathering and interactive services.

DVB-S2 uses a very powerful Forward Error Correction scheme (FEC), a key factor in allowing the achievement of excellent performance in the presence of high levels of noise and interference. The FEC system is based on concatenation of BCH (Bose-Chaudhuri-Hcquengham) with LDPC (Low Density Parity Check) inner coding.

Adaptive Coding and Modulation (ACM) allows the transmission parameters to be changed on a frame by frame basis depending on the particular conditions of the delivery path for each individual user. It is mainly targeted to unicasting interactive services and to point-to-point professional applications.

DVB-S2 offers optional backwards compatible modes that use hierarchical modulation to allow legacy DVB-S receivers to continue to operate, whilst providing additional capacity and services to newer receivers.

DVB-S2 delivers excellent performance, coming close to the Shannon limit, the theorectical maximum information transfer rate in a channel for a given noise level. It  can operate at carrier-to-noise ratios from -2dB ( below the noise floor) with QPSK through to +16dB using 32AAPSK. Improvements in efficiecy that DVB-S2 delivers compared to DVB-S shows gains in the useful bitrate of more than 30% in each case.