Where has the BBC found space for additional HD channels?

REFERENCE Over the past two years, the BBC has been ensuring that it has sufficient capacity on terrestrial and satellite to be able to widen its HD offering. a516digital takes a look at where the extra space has been found:

Terrestrial
The BBC, Channel 4 and Arqiva released plans last year to secure currently unused frequencies for extra HD channels. In the proposals, the BBC announced that it intended to use two of the ten slots for its own use. Ofcom agreed with the proposals and is awarding a licence to Arqiva to run the extra multiplexes of channels. Meanwhile, the fifth slot on the existing Freeview HD multiplex was put up for sale following Channel 5's rejection of the slot. No buyers came forward, and the BBC secured this slot as well, giving it three extra HD slots.

This is how the HD channels could be divided up between the existing Freeview HD multiplex and the two new multiplexes.


Existing Freeview HD Multiplex
“Mux 7” / ARQ-C *
“Mux 8” / ARQ-D *
98.5% population coverage
Up to 70% population coverage
Up to 70% population coverage
BBC One HD
BBC Four HD/ CBeebies HD

BBC Two HD
BBC News HD

itv HD (or STV/UTV HD)
(Channel 4 service)

Channel 4 HD
(Channel 4 service)

BBC Three HD/CBBC HD



The table shows how the existing Freeview HD multiplex will look once the new services start and is based on the information released 16th July 2013. The breakdown of Mux 7 and 8 remains unclear, but is based on what limited information there is available at the moment. Channel 4 announced their intention to launch extra HD services on the extra multiplexes, but as of the time of publication, it is not known which extra channels it is bringing to the platform, or whether they will reside on Mux 7 or Mux 8.

*For the time being, a516digital has named the multiplexes "Mux 7" and "Mux 8", as they are the seventh and eighth national multiplexes. They could also be referred to as "Arqiva C and D", as they would become the third and fourth Arqiva-operated multiplexes, after Arqiva A and B.

Satellite
Last year, changes to BBC services on satellite resulted in two satellite transponders being put in use for HD channels, giving the BBC the potential to carry eight HD channels - four across each transponder. BBC One HD was given four slots, to cater for national variants of the channel, which launched between October 2012 and January 2013. One slot was set aside for BBC HD, which become BBC Two HD, leaving enough spare bandwidth for three more slots.


Transponder: 50
Astra 1N 28.2 East 
BBC DSAT 4
Transponder: 61
Astra 2F 28.2 East 
BBC DSAT 8
Frequency
10847
Frequency:
11023
Polarisation:
V
Polarisation:
H
Mode:
DVB-S2, 8PSK
Mode:
DVB-S2, 8PSK
Symbol Rate:
23000
Symbol Rate:
23000
FEC:
2/3
FEC:
2/3
BBC One HD
BBC One Scotland HD
BBC One NI HD                
BBC One Wales HD
BBC Two HD  
BBC Four HD / CBeebies HD
BBC Three HD / CBBC HD
BBC News HD

The table above shows how the services might be split over the BBC's two satellite transponders earmarked for HD. Services already on air are highlighted in bold. Transponder 50 has room for one more HD channel, and transponder 61 room for two more services, once current BBC Red Button HD transmissions end. (BBC Red Button HD is currently scheduled to end in September.)

This is based on each transponder carrying four HD channels each. Some satellite TV providers including Sky are putting up to five channels on a transponder with similar or identical configurations.  However, when a broadcaster uses capacity for national/regional variants of the same channel - in this case BBC One HD - care has to be taken not to put too many services on the same transponder. This is because the bandwidth allocated to each channel varies depending on what is shown at the time in order to maximise available bandwidth.

During the times when all variants of BBC One are showing the same programme, the encoder has to supply identical bandwidth for all variants, plus enough remaining bandwidth for other channels. Fast moving material, such as music and sports events require sudden peaks of increased bandwidth. All versions of BBC One HD would require extra bandwidth at the same time. So if too many services were put on the same transponder, there would be a "crunch point" when the encoder wouldn't be able to provide enough bandwidth to maintain HD picture quality during these simultaneous peaks in demand. Therefore, the BBC has split the variants of BBC One over two transponders, with a slight time delay, and only needs to carry four rather than five channels per transponder, leaving it with sufficient bandwidth to maintain good picture quality. Encoder improvements may facilitate extra services in the future.


See also:
Where are the extra Freeview HD channels going to be available? >
List and map showing the transmitter sites where Freeview HD is going to get extra channels.




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