Dvb digital television
The DVB (Digital Video Broadcast) digital television (DTV) broadcast standard is used in most regions except the United States, Canada, South Korea, Taiwan, Brazil, and Argentina.
The DVB standard is actually a group of ETSI standards. A comparison of the DVB standards is given in Table 8.4. DVB uses a MPEG-2 transport stream to convey compressed digital video, compressed digital audio, and data over a 6-, 7- or 8-MHz channel. Multiple video streams, multiple audio streams, and/or data may be present in the MPEG-2 transport stream.
Table 8.4. Comparison of DVB Standards
| Parameter | DVB-T (Terrestrial) | DVB-C (Cable) | DVB-S/-S2 (Satellite) | DVB-H (Handheld) | DVB-SH (Handheld) |
|---|---|---|---|---|---|
| Video compression | MPEG-2, MPEG-4.10 (H.264), SMPTE 421M (VC-1) | MPEG-4.10 (H.264), SMPTE 421M (VC-1) | |||
| Audio compression | MPEG, Dolby® Digital, Dolby® Digital Plus, DTS®, MPEG-4 AAC, MPEG-4 HE-AAC v1/v2 | MPEG-4 AAC, MPEG-4 HE-AAC v1/v2, AMR-WB+ | |||
| Multiplexing | MPEG-2 transport stream | RTP-encapsulated MPEG-2 transport stream | |||
| Modulation | COFDM | QAM | QPSK | uses DVB-T | uses DVB-S |
| Channel bandwidth | 6, 7, or 8 MHz | 6, 7, or 8 MHz | – | 6, 7, or 8 MHz | – |
The MPEG-2 transport stream has a maximum bit-rate of ∼24.1 Mbps (8 MHz DVB-T) or ∼51 Mbps (8-MHz 256-QAM DVB-C). DVB-S bit-rates are dependent on the transponder bandwidth and code rates used, and can approach 54 Mbps (DVB-S2 offers a 25–35% bit-rate capacity gain over DVB-S). The bit-rate can be used in a very flexible manner, trading off the number of programs offered versus video quality and resolution.
DVB-H and DVB-SH for mobile applications use IP datacasting within DVB-T and DVB-S, respectively. RTP-encapsulated MPEG-2 transport streams are used.
Second generation versions of DVB-T and DVB-C (called DVB-T2 and DVB-C2, respectively) are being investigated.
Insider Info
Much like MPEG-2, DVB uses descriptors to add new functionality. In addition to various MPEG-2 descriptors, one or more of numerous DVB-specific descriptors may be included to extend data within the system information tables.
Video Capability
Although any resolution may be used as long as the maximum bit-rate is not exceeded, there are several standardized resolutions. Both interlaced and progressive pictures are permitted for most of the resolutions.
DVB-T, DVB-C, DVB-S, and DVB-S2 support MPEG-2 (MP@ML, MP@HL), MPEG-4.10 (MP@L3, HP@L4), and SMPTE 421M (AP@L1, AP@L3) video.
DVB-IP (“DVB over IP”, used by DVB-H, DVB-SH and DVB-IPTV) adds additional support for MPEG-4.10 (BP@L1b, [email protected], BP@L2) and SMPTE 421M (SP@LL, SP@ML, AP@L0) video.
Audio Capability
DVB-T, DVB-C, DVB-S, and DVB-S2 support MPEG-1 Layer II, MPEG-2 BC multi-channel Layer II, Dolby® Digital, Dolby® Digital Plus, DTS®, MPEG-4 AAC, and MPEG-4 HE-AAC v1/v2 audio.
DVB-IP (“DVB over IP”. used by DVB-H, DVB-SH and DVB-IPTV) adds additional support for AMR-WB+audio.
Application Block Diagrams
Figures 8.5 and 8.6 illustrate a typical DVB-S set-top box.
FIGURE 8.5. DVB Receiver Set-Top Box Block Diagram (Multicrypt).
FIGURE 8.6. DVB Receiver Set-Top Box Block Diagram (Simulcrypt).
