DVB-S2

DVB-S2简介

2nd

Generation Satellite

What is DVB-S2?

DVB-S2 (EN 302 307) 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 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 gradually replace DVB-S in the future, as new HD services entice users to upgrade their receivers to more efficient DVB-S2 models.

Background

The world’s first digital satellite TV services were launched in Thailand and South Africa at the end of 1994 and both used the newly released DVB-S system. Over time it has become the most popular system for the delivery of digital satellite television, with well over 100 million receivers deployed around the world. Nonetheless, with the system being more than ten years old, it is not surprising that the industry eventually decided the time was right to update. Thus DVB-S2 was developed, with the DVB Technical Module sub-group responsible for the work being chaired by Dr. Alberto Morello of RAI. The work would take 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, e.g., 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. 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:

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.

SatelliteEIRP(dBW)System

Modulation&CodingSymbolRate(Mbaud)C/N(in27.5MHz)(dB)UsefulBitrate(Mbit/s)NumberofSDTVProgrammesNumberofHDTVProgrammes

DVB-SQPSK2/327.5(α=0.35)

5.133.87MPEG-215AVC1-2MPEG-23-4AVC

51

DVB-S2QPSK3/430.9(α=0.2)

5.146(gain=36%)10MPEG-221AVC2MPEG-25AVC

DVB-SQPSK7/827.5(α=0.35)

7.844.410MPEG-220AVC2MPEG-25AVC

53.7

DVB-S28PSK2/329.7(α=0.25)

7.8

58.8(gain=32%)13MPEG-226AVC3MPEG-26AVC

Figure 1. Example comparison between DVB-S and DVB-S2 for TV broadcasting (Source: EBU Technical Review 10/04)

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