The tide among European broadcasters is flowing away from DTT towards 5G for over the air video transmission, encouraged by the EU’s reallocation of the upper high-quality 700 MHz band (694-790 MHz) from digital terrestrial to cellular that must be completed by 2022 at the latest. This has been reflected in a change of stance by leading broadcasters and also the pubcasters body, the EBU (European Broadcasting Union). Originally the EBU lobbied hard to defend DTT spectrum from mobile invasion but has more recently been focusing on influencing the development of 5G in favor of broadcasting, through a variety of projects.
Regional public broadcaster WDR was the first in Germany to come out for 5G by starting trials with Vodafone Deutschland in January 2019 for both linear and VoD transmissions. Running until 2020, WDR and Vodafone are testing delivery of high-quality content featuring 4K and HDR to moving receivers in vehicles and trains, as well as mobile devices in apartments. They have set up a dedicated TV studio for the project firstly in Düsseldorf, then the 5G Mobility Lab in Aldenhoven before extending to the city center of Cologne over Vodafone’s 5G network on the WDR campus.
Then in the last week, broadcaster Bayerischer Rundfunk (BR) has aired its view that 5G will replace the DVB-T2 transmission infrastructure currently widely used in the country – by 2030 at the latest if not earlier. BR’s head of syndication and transmission Helwin Lesch has echoed the EBU in highlighting the importance of playing a major part in the standardization of 5G. BR has also aped the EBU over the timeline in light of the latter’s recent study suggesting that by 2030 5G networks would have achieved widescale coverage in Europe providing a viable infrastructure for broadcasting.
The EBU is now rather on the fence over 5G, arguing correctly that unicast cellular 5G alone cannot replace existing broadcasting networks and that the first use cases will be in content production where high speed and flexible one-to-one communications from the field are often required. On this front, broadcasters will utilize not just public 5G networks, but also private ones set up either temporarily or permanently in venues, for example.
However, the EBU has come around to the idea that new broadcast modes could fit well with 5G for serving areas within range of the cellular network but where population densities are lower. It is investigating several ways of adding broadcast capabilities to 5G networks, including low earth orbiting satellites interconnected by laser-based optical mesh backbones offering much lower latency than higher orbit satellites can provide. It is also examining deployment of high-powered 5G base stations in existing broadcast towers.
This seems at odds with views expressed recently by the EBU’s own Peter MacAvock, Head of its Distribution, Platforms as well as chair of the DVB Project. He argues that 5G is unlikely ever to replace DTT because the economics of the latter have been perfected over decades, while attempts to develop multicast over cellular have consistently failed. He argues that DVB now approaches optimum efficiency over terrestrial as well as satellite and cable networks and is the best way of broadcasting any signal to many people. He notes that the DVB, as opposed to the EBU, is studying how to combine a DVB network with a 5G network, implying that spectrum would continue to be reserved for broadcasting. “There will be many markets where DVB and 5G co-exist,” he insists.
However, the EBU’s Technical Review conducted by its spectrum project manager Marcello Lombardo identifies two scenarios neither of which would see DVB holding onto spectrum indefinitely. Under one, DVB would become effectively one of various virtual networks hosted by 5G infrastructures, in which case the spectrum would still go. The second scenario envisages DTT being phased out altogether and replaced totally by 5G.
Yet DTT would, in a sense, live on under the cloak of 5G, because the mechanisms it has perfected would still be required for efficient multicasting. Already the Further evolved Multimedia Broadcast Multicast Service (FeMBMS), specified in 3GPP Release 14 in June 2017, supports the High Power High Tower (HPHT) transmission model alongside cellular cells, which is derived from DTT. This creates overlay networks able to provide the required coverage more cost effectively for popular linear content in both rural and urban areas. Alongside this is support for greater Inter-Site Distance (ISD) at high spectral efficiency, with ability to allocate all of the eMBMS carrier bandwidth if required to create dedicated broadcast networks, rather than just 60% of total capacity previously. The new model also supports hybrid services where on demand content can still be unicast over the cellular network.
With support for HPHT combined with dynamic re-allocation of downstream bandwidth between broadcast and unicast operation, eMBMS is now better placed to support converged mobile/broadcast services. The MBMS operation on demand (MOOD) mechanism allows dynamic switching from unicast delivery to multicast when the number of devices accessing the same content within a given cell exceeds a defined threshold.
HPHT is one reason BR has decided to come out for 5G and it is no surprise perhaps that Germany has been at the forefront of testing so far. At the recent NAB 2019, Munich-based electronics group Rohde & Schwarz discussed its participation in the Bavarian research project ‘5G Today’, which is investigating TV broadcast transmission in the FeMBMS mode in a HPHT 5G field broadcast trial. Rohde & Schwarz noted that the HPHT concept gives 5G networks the advantages already established for DTT broadcasting. The point then is that 5G is not replacing DTT but absorbing it, although in practice DTT will live on until 2030, or even longer in some isolated pockets.