High quality / Service Flexibility
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.
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.
|Number of lines||525||525||750||1125|
|Number of active lines||483||483||720||1080|
|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 /
|Sampling frequency||Luminance signal||13.5MHz||27MHz||74.25 /
|Color-difference signals||6.75MHz||13.5MHz||37.125 /
|Numbers of samples per line||Luminance signal||858||858||1650||2200|
|Numbers of samples per active line||Luminance signal||720||720||1280||1920|
|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(∗)|
∗ : These figures are downloaded from List of Standards for Broadcasting (ARIB website) (You will leave the DiBEG website). → As shown “ARIB STD-B32 Part 1, chapter 2.4” .
|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
|Recommended audio mode||mono, stereo, multichannel stereo (3/1, 3/2, 3/2+LFE(Note 2)),
2-audio signals (dual mono)
∗ : Above table is downloaded from List of Standards for Broadcasting (ARIB website) (You will leave the DiBEG website). → As shown “ARIB STD-B32 Part 2, chapter 5.1” .
3/1 = 3 front + 1 rear
3/2 = 3 front and 2 rear
As described above, by adopting ISDB-T, any type of broadcasting service is possible in one receiver.
(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.
(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.