Digital Satellite Broadcasting Practical
There are some standards to follow in carrying out digital broadcasting:
the Ministerial Ordinances/Notifications and the standards established
by the Association of Radio Industries and Businesses (ARIB), based
on such governmental guidance. These standards contain a large range
of selections that have to be narrowed down for the start of digital
satellite broadcasting services in 2000. At the end of September in
1999, the BS-P Consortium, formed by satellite broadcasters, completed
an 800 page manual of detailed practical rules with the cooperation
of the Electronic Industry Association of Japan (EIAJ). These practical
rules were reported to the ARIB and published as a Technical Report
Starting with this issue, the Broadcast Technology will present a two
part report regarding the new digital services broadcasting environment
being realized by these practical rules. The following themes will be
featured in these issues:
- New types of programming services not possible in the analog era.
- Electronic Program Guides (EPG) which help a viewer to select programs
- Receiver specifications such as for remote controllers and interface
This issue will introduce the first, Programming Services. The next
edition of the Broadcast Technology will contain an article developing
the latter two themes.
1. Programming Services
Digital satellite broadcasting which is to start in the year 2000 enables
new broadcast programming services. This was first made possible by
the practical rules which established what exactly each service would
provide as well as what their necessary transmission signals and receiver
functions would accordingly be. In this article, we will explain "provisional
programming service," "multi-view TV," "hierarchical modulation service,"
and "emergency alert broadcasts."
The provisional programming service creates a new temporary programming
channel while maintaining regular programming but reducing the bit rate.
For example, when the time slot for a live Hi-Vision (HDTV) baseball
relay is extended due to the game, this service will reduce the HDTV
bit rate to create an SDTV channel for the continuation of the baseball
game. In this case, while the picture quality of the HDTV program will
not be as magnificent as it usually is, the next scheduled program can
begin on the HDTV channel without any delay. As Figure 1 shows, selecting
the regular HDTV channel or a provisional channel when a second channel
is provided is the choice of the viewer. The viewers will be notified
by an announcement or closed-captioning during the HDTV program they
are currently watching. As the program on the provisional channel ends,
the channel will automatically switch back to regular HDTV programming.
Moreover, a timer recording selection will make possible a continuous
recording (relay recording) of the baseball game which was transferred
to the provisional channel during its broadcast.
When this service is provided, the HDTV and SDTV picture quality will
depend on the bit rate allocation of each channel. Balancing out the
picture quality with data transmission is a problem that is under consideration.
The Multi-View TV is an application that divides one regular HDTV
channel into a maximum of three SDTV channels. This is to broadcast
program related information on multiple channels simultaneously with
the main program. Using a broadcast golf game for an example, this function
can be used to broadcast three locations at the same time on two additional
channels: General channel (main channel), 17th Hole (sub-channel one),
and the 18th Hole (sub-channel two). In this case, the multi-view program
starts on the General channel, allowing the viewer to freely switch
between the main and sub channels during the program. As the multi-view
program ends, the screen will automatically return to the next HDTV
program on the main channel. Regarding recording of the program, the
conventional VCRs will only record the main channel. A future digital
video recording system may be equipped with a function enabling the
recording of all the multi-view program channels.
The multi-view TV function can be applied to theater relays and dramas,
as well as sports programs. This function has a possibility of expanding
the viewer's selections and providing new information. On the other
hand, because of flexible viewing styles of those watching, program
information may not be delivered accurately or as the producers intended.
These drawbacks should be considered thoroughly at the time of production.
|Figure 1. Provisional
programming service example
|Figure 2. Multi-view
|Figure 3. Hierarchical
On satellite digital broadcasting, radio waves are affected by heavy
rain causing abrupt video/audio blackouts (video: freezing, sound: muting,
etc.). Broadcasting of a program using the modulation (low hierarchical)
which is resistant to interference by multipaths along with the regular
modulation (high hierarchical) will enable the transmission of information
during rainfalls. Although this low hierarchical modulation is resistant
to rain, the amount of information that can be transmitted decreases,
which means that only necessary information will be sent on this system.
We describe this in Figure 3. A program which is normally in an HDTV
video form could be broadcast with reduced sharpness, as reduced size
video, or as HDTV still images. A receiver will evaluate reception quality
and automatically (or manually) switch between these hierarchies.
Since sound data is smaller, sound service can be sent by means of low
hierarchical transmission. However, this low hierarchical transmission
is not capable of transmitting numerous data broadcasting programs,
resulting in the broadcast of only important programs such as emergency
The following two functions are under consideration regarding emergency
alert services on digital satellite broadcasting.
- A signal of emergency alert broadcasting is able to activate a turned-off
(stand-by) receiver for emergency alert broadcasting.
- If an emergency broadcast starts while you are watching a program,
the screen will automatically switch to the emergency programming.
However, due to the energy saving policy being promoted nationally,
it is expected that this function 1 will not be included on a standard
receiver. Function 2 will be activated and automatic switching to the
emergency channel will occur only when the viewer is watching NHK's
HDTV, simultaneous broadcast channel, S1 and S2. In the case the viewer
is watching another, commercial, channel when NHK issues an emergency
broadcast, the function will not be activated or change the current
channel to NHK.