By Barry Flynn, Contributing Editor
European TV standards body DVB is predicting that terrestrial broadcast networks will need to be nearly twice as efficient in the future as they are now to cope with the 700MHz sell-off.
The calculation â€“ which applies to European territories â€“ represents one initial result from a wide-ranging research study the DVB is conducting into the long-term future of terrestrial broadcasting.
Graham Mills, chairman of DVBâ€™s commercial module, said the research project, entitled DVB â€“ Long Term Vision for Terrestrial Broadcast, addressed the question: â€œhow much spectrum will the broadcasting community, and the viewers, want us to sustain and retain for the future?â€
Mills said the DVBâ€™s prediction was based on a model which estimated extra future demand for terrestrial capacity from new services, including HD and UHD TV as well as applications such as â€˜file-castingâ€™ â€“ and then compared that figure with the decrease in the overall supply of capacity implied by selling off the 700MHz frequencies to mobile operators.
The results show a projected increase in demand of 125% across Europe as a whole, averaging out territories at the bottom end â€“ which will actually require up to 30% less capacity because of compression and transmissions efficiency gains â€“ with those at the top end, which will require up to 160% more.
The supply side of the equation is easier to determine, since the amount of spectrum to be sold off in different countries is already precisely known, and works out at a decrease in the overall supply of capacity of 30%.
By marrying up demand and supply, the DVB model implies an overall capacity short-fall of 180% (100% at the bottom end and 230% at the top), which the DVB reckons can only be met through gains in technical efficiency over and above those currently available. (The large spread is the result of some European territories â€“ like Switzerland â€“ having very low terrestrial TV penetration, while others â€“ like Spain â€“ have a large majority of households with rooftop aerials).
It appears that one significant assumption built into the DVB model is that mobile operators will not make use of their new 700MHz frequencies to launch new broadcast TV services.
Peter Siebert, Director of the DVB Project Office, said that â€œas far as I understand the study is not really analysing whether the mobile broadcasters can do this or can not do this,â€ adding that his personal view was that â€œyou can always build a mobile network that will provide you with UHD services. The question is, is it commercially feasible?â€
Siebert argued that cellular networks were much more expensive to build and operate than the high-power, high tower networks used by broadcasters. â€œFor me, my impression is that the discussion [about mobile operators using technologies like LTE to broadcast TV on their networks] is mostly pushed by the manufacturers who want to sell equipment â€“ not by the operators.â€
If mobile operators donâ€™t address some of the demand for new terrestrial broadcast services, then the supply short-fall can only be met by a 1.8 times gain in technical efficiency, the DVB concludes.
But where will that come from? Siebert believes that â€œwe have to rely on a new video coding standard. Personally, I think that there is still room for another improvement. [â€¦] Letâ€™s hope that in 2023 we get an H.266 which will give us, again, double the capacity at the same data rate!â€
Other possibilities include MIMO (Multiple Input Multiple Output), says Siebert, originally considered for the DVB-T2 spec but rejected. In a broadcast application, MIMO could potentially double available capacity, but would imply two antennas at both the transmit and receive ends. The fact that all roof-top aerials would need to be changed to use DVB-T2 counted heavily against it.
Another possibility is planning networks in a different way and using â€˜time frequency slicingâ€™, which Siebert describes as â€œa kind of frequency hoppingâ€. This also improves capacity, but, Siebert points out, also implies a different network.
â€œMy strongest bet personally is the efficiency improvement in the video coding,â€ he concludes.