High quality / Service Flexibility

High quality

Japan started the research and development for HDTV in 1964, and has the advantages HDTV hardware/software technologies. (Because of these background, High quality of the picture is the most important requirement for digital broadcasting system. In satellite broadcasting in Japan, started from 1989, HDTV service is a real broadcasting service, so, even in digital terrestrial broadcasting service, HDTV is also adopted.)
Japan developed ISDB-T system adopting MPEG-2 for HDTV/SDTV compression system. So both HDTV/SDTV are supported in ISDB-T.

Service flexibility

ISDB-T system, realizes service flexibility by 2 technologies below.

(1) MPEG-2 video coding technology/ MPEG-AAC audio coding technology

MPEG-2 video coding technology, which is adopted in Japanese digital broadcasting, supports many kinds of video quality/format. For video quality/format, Japanese digital broadcasting adopts many kinds of video quality/format described in Table 1.
For audio system, MPEG-AAC, the highest compression and quality audio coding system, is adopted for digital broadcasting in Japan. MPEG-AAC also supports many kinds of audio quality/format. In Table 2, audio quality/format specified in Japanese digital broadcasting are shown.

Digital broadcasting receiver in Japan should be specified to decode any kinds of video/audio quality/format described in Table 1 and Table 2.
In addition above, digital receiver specification specifies that the video output format to display should be selectable according to display specification.

So, following format conversion is possible, (1)HDTV → SDTV, (2)SDTV → HDTV.
As described above, ISDB-T receiver has a flexibility for video/audio quality/format.
And it is possible to enjoy HDTV program on SDTV display by converting video format. Therefore, ISDB-T receiver can support the variation of broadcasting service, such as, HDTV, HDTV+SDTV, multi-SDTV, etc, by one receiver.

For audio system, many quality/format, such as monaural/stereo/bi-lingual/multi-channel stereo are supported, and more, down-mix from multi-channel to monaural and stereo is specified, so, legacy audio system can be used.

Table 1: Video quality/format (adopted in digital broadcasting)
Number of lines 525 525 750 1125
Number of active lines 483 483 720 1080
Scanning system Interlaced Progressive Progressive Interlaced
Frame frequency 30 / 1.001Hz 60 / 1.001Hz 60 / 1.001Hz 30 / 1.001Hz
Field frequency 60 / 1.001Hz 60 / 1.001Hz
Aspect ratio 16 : 9 or 4 : 3 16 : 9 16 : 9 16 : 9
Line frequency  fH 15.750 /
31.500 /
45.000 /
33.750 /
Sampling frequency Luminance signal 13.5MHz 27MHz 74.25 /
74.25 /
Color-difference signals 6.75MHz 13.5MHz 37.125 /
37.125 /
Numbers of samples per line Luminance signal 858 858 1650 2200
Color-difference signals 429 429 825 1100
Numbers of samples per active line Luminance signal 720 720 1280 1920
Color-difference signals 360 360 640 960
Filter characteristics See Fig. 1() See Fig. 2() See Fig. 3()
Line synchronizing signal See Fig. 4() See Fig. 5() See Fig. 6()
Field synchronizing signal See Fig. 7() See Fig. 8() See Fig. 9() See Fig. 10()

Table 2: Audio quality/format (adopted in digital broadcasting)
Parameter Restriction
Audio mode     Possible audio mode mono, stereo, multichannel stereo (3/0, 2/1, 3/1, 2/2, 3/2, 3/2+LFE) (Note 1), 2-audio signals (dual mono), multi-audio (3 or more audio signals) and combinations of the above
Audio mode Recommended audio mode mono, stereo, multichannel stereo (3/1, 3/2, 3/2+LFE(Note 2)), 2-audio signals (dual mono)
Emphasis None
  (Note 1)   Number of channels to front/rear speakers:     Example: 3/1 = 3 front + 1 rear
3/2 = 3 front and 2 rear
  (Note 2)   LFE = Low frequency enhancement channel

As described above, by adopting ISDB-T, any type of broadcasting service is possible in one receiver.

(note) In South America, Dolby 5.1 surround system is already used. For compatibility between MPEG-AAC and Dolby surround, A AC/DTS converter assure the compatibility. (In Brazil, reached to above conclusion in March, 2007)

(2) MPEG-2 systems for multiplex

ISDB-T adopts MPEG-2 systems as multiplex technology. In MPEG-2 systems, all broadcast contents, video/audio/data are multiplexed by Transport stream Packet format. Therefore, any type of contents/service can be multiplexed.
The concept of Multiplex is shown in Figure 1.

Multiplexed format In ISDB-T system
Figure 1  Multiplexed format In ISDB-T system
(Note) Signal format of PES, TS and Section area is defined in ARIB STD-B32, based on MPEG-2 systems.
(Note) PSI is defined in both STD-B32 and STD B10. In STD-B32, only outline related to MPEG-2 systems is defined.

As shown in Figure 1, stream type contents, such as video, audio and stream type data, are converted to PES (Packet Elementary Stream) format and finally converted to TS format and Multiplexed, on the other hand, non stream type data contents are converted to Section format and finally converted to TS format and multiplexed.