Digital
Broadcast Re-Transmission
Over Cable Networks
Digital satellite broadcasting
is to begin in December,
2000, followed by digital
terrestrial broadcasting.
In order to make the new
services that digital
broadcasting will bring
about, such as data broadcasts
and EPG, available to
cable TV network subscribers
as well, the digitization
of cable TV network broadcasting
facilities and equipment
is indispensable.
1. Present Conditions
of Cable Television and
Its Digitization Trends
|
Figure
1: Reception condition
of terrestrial/satellite
broadcasting |
The diffusion ratio of cable
TV networks in Japan (Figure
1) shows that the households
subscribing to cable TV
networks, including larger
apartment buildings, accounted
for 50% of terrestrial broadcast
reception and 30% of satellite
services. It is expected
that diffusion will reach
up to 30 million households
(60 % of the total number
of households) by the year
2010.
Larger scale providers are
extending their businesses
toward communication services
such as the Internet for
their survival. Some have
started giving serious consideration
to the expansion of their
service area and its digitization.
Cable TV service providers
seem to be setting goals
for facility upgrades to
correspond with the digitization
of BS and terrestrial broadcasting.
2. Re-transmission systems
for digital satellite broadcasting
The maximum transmission
capacity of a transponder
for one digital BS channel
is 52Mbps. 6MHz digital
cable TV has a capacity
of 39Mbps, which is not
capable of efficiently and
directly re-transmitting
digital BS services. The
transmission system for
digital BS broadcasting
is designed with the capacity
to transmit data for one
channel on multiple TSs
(Transport Stream).
|
Figure
2: Digital BS broadcasting
re-transmission schemes
over cable TV networks |
As Figure 2(a) shows, this
will enable digital cable
networks to transmit data
for one channel utilizing
several individual TSs.
Figure 2(b) shows a possible
future system that uses
a 12MHz band, which is same
as two 6MHz channels, and
re-transmits the entire
data steam of a digital
BS transponder.
In order to diffuse a common
digital broadcast receiver,
NHK has proposed re-transmission
plans corresponding to cable
TV networks. |