Page 28 - ITU Kaleidoscope 2016

2016 ITU Kaleidoscope Academic Conference

Figure 6: The footprint of Astra 2E carrying FreeSat TV
Figure 5: UHF FreeView coverage of Mux A from Crystal services
Palace.
doubling up of these channels, with a consequential increase the
Figure 5 shows the coverage achieved by the Arqiva transmitters power consumed by transmitters. The same platform may even
for UK FreeView at the Crystal Palace site in south London and eventually carry Ultra High Definition pictures and sound.
the supporting network of infill or relay transmitters. This “one Additionally efficient systems design has resulted in terrestrial and
too many” broadcasting, approach is never more true than when satellite TV infrastructures sharing several components. For
using a satellite system. Here, in the case of the UK, the beam of a example the coding and multiplexing technology - that is the way
single geostationary satellite is able to illuminate the whole that the services are data compressed (or coded) and bundled
country with FreeSat. The footprint for Astra’s 2E Satellite is together into bit streams (or multiplexed) - is the same for both
shown in figure 6. This has its drawbacks though because if you platforms.
want to deliver a regional service, this can only be achieved by There are 1,182 FreeView transmitter sites across the whole of the
delivering to the whole footprint or by using more satellites. The UK but for the BBC 83 of these are the most significant in terms
BBC has a history of regularly “opting” local TV transmitters to of the size of audience they serve and the power that they consume
carry local services for short periods. Local news bulletins for to do this. As you might imagine with a system that has gown over
example are broadcast at the end of the national news programme a number of years and developed across a number of technologies
by briefly breaking the national network in to a number of smaller there are a range of efficiencies but typically the transmitters have
networks, each carrying programme focused on events with the an ERP (Effective Radiated Power) of between 20-100kW with a
smaller service area. This continues to work well on FreeView but range of efficiencies between 10-30%. At the top end is the
on FreeSat the opting approach is problematic and so the 18 Crystal Palace transmitter, which serves London, with an ERP of
regional news programmes can only be delivered by creating 17 200kW. It covers 4.9 million homes or about a fifth of the UK
extra versions of BBC One, which are broadcast all the time. Not population. In simple terms this makes it a very efficient way of
the most bandwidth efficient approach. delivering TV to a large number of homes (i.e. 0.04 W/home).
The simple systems diagram in figure 4 shows the main power A number of strategies are being considered to improve the energy
consuming elements that BBC R&D used when modeling the efficiency of these transmitters and perhaps the most obvious is
carbon footprint of TV broadcasting. The production element is replacing older equipment with modern, more efficient, amplifiers,
not part of the distribution chain and so is not included in this part modulators and antenna. In some cases transmitter efficiency can
of the footprint but we have already discussed the impact of be raised to 38% but even then the significant capital outlay and
production earlier. The BBC funded infrastructure components are the large number of sites means that it could take over 20 years to
show in dark grey whilst those that are provided by the viewer are produce a financial pay back. A more effective approach is to re-
lighter grey. You can see that DTT & DST technologies have assign efficient, existing equipment to where it can be more
several advantages from a sustainability point of view. Firstly the effective and swap out the less efficient units to less critical or
system components can be clearly identified, measured and back up roles. In fact resilience is another area where cost
modeled. Secondly, although there is a significant investment in effective improvements in power consumption can be achieved at
setting up the infrastructure, they have a long life and a constant a moderate increase in risk, for example by running back up
operating power consumption regardless of the number of systems as lower power or even off when not in use. Most main
viewers. The UK FreeView infrastructure has already made one sites have 2 transmitters, each with a backup in a 2N + 2
major technology step by moving from Standard Definition TV configuration, so perhaps a 2N + 1 configuration, where the
with stereo audio to High Definition TV (or T2) with surround backup is shared, would be nearly as effective but save 25% of the
sound and this was achieved without a significant increase in the operating energy. Other techniques being considered include
power consumed. Partially this was possible because of the increasing the Forward Error Correction producing a more robust
inherent characteristics and strengths of the technology but also signal, which needs less radiated power to achieve the same
because of the improved performance of Video Coding coverage (although be it with an increased delay) and a feedback
technology. It should however be noted that at the moment all system using receivers across the coverage area to allow the
major services are transmitted in both SD & HD to maintain transmit power to be turned down when the atmospheric
compatibility with older television receivers and this does mean a conditions allow good propagation, only turning up the transmitter
power when the reverse is the case. The size of the impact of these

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