DVB-S2

Joshua Kline
ECEN 4242 - Communication Standards Survey

Introduction
Typical Applications
Frequency Band
Standard Body
Block Diagram
Error Control Coding
Constellations
I/Q
Multi-Access
References

Introduction

Digital Video Broadcasting - Satellite Generation 2 (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 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, and does so with a performance level that ensures that we won’t see a “DVB-S3” for a very long time, if ever!

DVB-S2 is not currently implemented. The conversion process from DVB-S to DVB-S2 is expected to take about 15 years—probably in sync with the coming of HDTV. DVB-S has proven to be a well designed and flexible standard, and this makes the upgrade process take longer for those delivering programming.

Typical Applications

Envisaged scenarios for DVB-S2 by the standard document are:

  • Broadcasting television services in SDTV or HDTV. Optionally, this transmission may be backwards compatible with DVB-S, but does not benefit from the 30% extra bandwidth.
  • Interactive services including Internet access. Data generated by the user may be sent by cable (copper/fibre optic), mobile wireless, or satellite uplink (DVB-RCS).
  • Professional applications, where data must be multiplexed in real time and then broadcast in the VHF/UHF band (e.g., digital TV contribution, satellite news gathering). These transmissions are not intended for the average viewer.
  • Large-scale data content distribution. These include point-to-point and multicast services, as well as transmission to head-ends for (re-)distribution over other media.

  • Frequency Band

    Standard Body


    The standard body is the European Telecommunications Standards Institute (ETSI). More information can be found at the etsi site
    The Digital Video Broadcasting (DVB) Project is an industry-led consortium of over 250 broadcasters, manufacturers, network operators, software developers, regulatory bodies and others in over 35 countries committed to designing open interoperable standards for the global delivery of digital media services. As DVB’s name suggests, these include broadcasting. Services using DVB standards are available on every continent with more than 500 million DVB receivers deployed.

    Block Diagram



    Error Control Coding

    Forward Error Correction (FEC) Encoding shall be carried out by the concatenation of BCH outer codes and LDPC (Low Density Parity Check) inner codes (rates 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10) to achieve quasi-error free (QEF) reception conditions on an AWGN channel.

    Depending on the application area, the FEC coded block shall have length nldpc = 64 800 bits or 16 200 bits. When VCM and ACM is used, FEC and modulation mode may be changed in different frames, but remains constant within a frame. For Backwards Compatible modes, the bit-stream at the output of the FEC encoder shall be processed according to annex F. Bit interleaving shall be applied to FEC coded bits for 8PSK, 16APSK and 32APSK.


    Format of data before bit interleaving. nldpc=64800 bits for normal FECFRAME, nldpc=16200 bits for short FECFRAME

    Constellations

    Possible Constellations are:

    QPSK and 8PSK are typically proposed for broadcast applications, since they are virtually constant envelope modulations and can be used in non-linear satellite transponders driven near saturation. For some specific broadcasting applications (i.e. regional spot beams) and interactive application operating with multi-beam satellites, 16APSK provides extra spectral efficiency with very limited linearity requirements if proper pre-distortion schemes are employed.

    32APSK modes, mainly targeted to professional applications, can also be used for broadcasting, but these require a higher level of available C/N and the adoption of advanced pre-distortion methods in the up-link station to minimize the effect of transponder non-linearity. While these modes are not as power efficient as the other modes, the data throughput is much greater. 16APSK and 32APSK constellations have been optimized to operate over a non-linear transponder by placing the points on circles. Nevertheless their performances on a linear channel are comparable with those of 16QAM and 32QAM respectively.

    All the modes are also appropriate for operation in quasi-linear satellite channels, in multi-carrier Frequency Division Multiplex (FDM) type applications.

    I/Q

    After randomization, the signals are be square root raised cosine filtered with roll-off factors a = 0,35, 0,25 and 0,20, depending on the service requirements.

    The baseband square root raised cosine filter isdefined by the following expression:

    Information found in ETSC 302 307

    Quadrature modulation shall be performed by multiplying the in-phase and quadrature samples (after baseband filtering) by sin (2pf0t) and cos (2pf0t), respectively (where f0 is the carrier frequency). The two resulting signals are added to obtain the modulator output signal. The specific I/Q parts of the signal could not be determined at this time.

    Multi-Access

    The DVB-S2 system may be used in "single carrier per transponder" or in "multi-carriers per transponder" (FDM) configurations.

    References

    DVB-S2 fact sheet
    Wikipedia
    ETSI EN 302 307
    ETSI TR 102 376