DIGITAL VIDEO BROADCASTING (DVB)

DIGITAL VIDEO BROADCASTING (DVB)

                   Once the video is encoded in the desired format (MPEG-2 or MPEG-4/H.264 AVC) will have to be put on the network to be distributed and transported to the end user. In this field there are different connections, satellite, terrestrial, cable, etc., Depending on the type of means used in transport will have different formats, but mostly in terrestrial digital television will use a terrestrial connection (DVB-T) mixed with a connection via satellite (DVB-S). These connections will be in charge of transmitting the digital signal to the end user, but first this signal must be created, since only at this point you have video signals, audio and data. Digital Video Broadcasting (DVB) has become the synonym for digital television and for data broadcasting world-wide. DVB services have recently been introduced in Europe, in North- and South America, in Asia, Africa and Australia.DVB is the technology that makes possible the broadcasting of “data containers“ in which all kinds of digital data up to a data rate of 38 Mbit/s can be transmitted at bit-error rates in the order of 10^-11.

BASEBAND PROCESSING

                   The transmission techniques developed by DVB are transparent with respect to the kind of data to be delivered to the customer. They are capable of making available bit streams at (typically) 38 Mbit/s within one satellite or cable channel or at 24 Mbit/s within one terrestrial channel. On the other hand a digital video signal created in today’s TV studios comprises of 166 Mbit/s and thus cannot possibly be carried via the existing media. Data rate reduction or “source coding“therefore is a must for digital television.

            One of the fundamental decisions which were taken during the early days of DVB was the selection of MPEG-2 for the source coding of audio and video and for the creation of programme    elementary   streams, transport streams etc. - the so-called systems level. Three international standards describe MPEG-2 systems, video and audio. Using MPEG-2 a video signal can be compressed to a datarate of for example 5 Mbit/s and still can be decompressed in the receiver to deliver a picture quality close to what analogue television offers today.

            The term “channel coding” is used to describe the algorithms used for adaptation of the source signal to the transmission medium. In the world of DVB it includes the FEC (Forward Error Correction) and the modulation as well as all kinds of format conversion and filtering.

DVB-S2: THE SECOND GENERATION STANDARD FOR SATELLITE BROAD-BAND SERVICES

                        DVB-S2 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 theoretical limit for such systems. Satellite transmission was the first area addressed by the DVB Project in 1993 and DVB standards form the basis of most satellite DTV services around the world today, and therefore of most digital TV in general. DVB-S2 will not replace DVB-S in the short or even the medium term, but makes possible the delivery of services that could never have been delivered using DVB-S. 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. Further additions were made with the emergence of DVB-DSNG (Digital Satellite News Gathering), for example allowing the use of 8PSK and 16QAM modulation. DVB-S2 benefits from more recent developments and has the following key technical characteristics:

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.