5G Broadcast: Part 4 - 5G Broadcast Challenges Digital Terrestrial

Fast growing traction for 5G Broadcast and Multicast has the potential to disrupt over the air broadcasting by presenting an alternative to the established digital terrestrial networks just as they progress to the next generation. Yet the two may end up in harmony by combining DTT for delivery to TVs with 5G Broadcast/Multicast to reach mobile devices.

5G Broadcast is coming beyond all doubt and the question is how it will dovetail with established over the air distribution networks, and whether it will completely usurp digital terrestrial transmission, or merely reuse the infrastructure. The phrase High Power High Tower (HPHT) has evolved to describe a model where 5G Broadcast/Multicast distribution is overlaid on top of cellular networks to provide a new infrastructure also catering for unicast delivery, with support for interactive services.

HPHT is effectively synonymous with existing DTT infrastructure comprising traditional tall and powerful transmitters. Low Power Low Tower (LPLT) is then just another name for cellular infrastructure comprising the familiar masts, including these days small cells installed on street furniture such as lamp posts.

As we described in an earlier article of this series, many broadcasters are enthusiastic about 5G Broadcast because it gels with their progression towards IP based delivery over the internet, enabling them to reach a plethora of mobile devices. But there is still some division within the DTT camp itself, with the DVB more accommodating towards 5G Broadcast than the Advanced Television Systems Committee (ATSC), which seems to view it as an unwelcome distraction to ATSC 3.0, aka Next Gen TV.

Certainly a lot of work has gone into ATSC 3.0, which like DVB-T2 employs orthogonal frequency-division multiplexing (OFDM) modulation with low-density parity-check code (LDPC) FEC (Forward Error Correction) codes for highly efficient signal transmission. It uses 6 MHz channels and supports data rates up to 57 Mbs, depending on the parameters used.

A key enhancement is use of a bootstrap signal for discovery and identification of signals that are being transmitted, which is significant because it gives freedom to change signal type in future. These advances helped gain limited traction outside North America, with South Korea in fact being first to deploy ATSC 3.0 in May 2017, in preparation for the 2018 Winter Olympics.

But since then ATSC 3.0 has run into various headwinds that have delayed its implementation and derailed its progress. It has been beset by the sort of licensing issues that have bedevilled MPEG codecs, which critically has led to some TV makers either delaying supporting ATSC 3.0, or not doing so at all. Without such support ATSC 3.0 could be mortally wounded, leaving the door open for 5G Broadcast to come in and fill the breach as a unifying delivery method, also capable of reaching mobile devices where an increasing proportion of viewing takes place.

It is true that support from TV makers has been slowly coming as earlier ditherers like Sony and Hisense come on board. Sony is now supporting ATSC 3.0 in all of its models, and Hisense does in most of its TVs. TCL has also announced that it will support ATSC 3.0 in some TVs later this year.

However, Samsung has so far confined support to its top end models, while LG revealed in a filing with US regulator FCC in September 2023 that it was dropping it altogether as a result of a patents dispute. This followed a court case which LG lost against a holder of patents linked to ATSC 3.0.

ATSC 3.0 support is also absent from most budget TVs from the likes of Toshiba, Vizio and RCA. At the same time, owners of high-end TVs that do support ATSC 3.0 still cannot access some premium content because distributors have employed DRM to protect their assets. This has left many consumers with NextGen TVs unable to watch programs broadcast by local stations at the highest quality. This in turn has delayed development of ATSC 3.0 hardware further while manufacturers work out how to handle encrypted broadcasts.

ATSC 3.0 does still score for performance though, as was confirmed by a study published in a recent IEEE Transactions on Broadcasting paper.  This found that ATSC 3.0 generally outperformed 5G Broadcast because its BICM (Bit Interleaved Coded Modulation) components were superior, as was the interleaver itself usually.

The idea of interleaving is to dilute the impact of errors during transmission, especially in this context those associated with Rayleigh fading, a term for the random signal degradation that occurs during RF transmission through a medium. Interleaving alternately takes bits from two input numbers, and combines them into a single stream. Errors resulting are then allocated between the two, making it easier for them to be corrected by FEC.

Such studies usually omit to point out though that 5G Broadcast is work in progress and so the performance deficit will narrow, if not disappear entirely, under forthcoming releases of the 3GPP 5G standards, which we discuss in some detail in the next article of this series. The aforementioned paper admitted that already 5G Broadcast outperforms ATSC 3.0 over non line of sight (NLOS) channels, especially in “mobility situations”, usually when receiving devices are moving at a significant speed in trains or automobiles. This is because 5G Broadcast achieves path diversity by combining two data bearing channels known as Physical Downlink Shared Channels (PDSCH). That scores when there is no direct line of sight.

The debate in the USA particularly has seen some passionate communications with ATSC 3.0 defending its corner with the zeal broadcasters were more widely applying to DTT spectrum a decade ago. But even in the US, compromise is quite probable, largely because a split looks likely to develop where 5G Broadcast is available on newer mobile devices but not TV sets, while for ATSC 3.0 it is the other way round.

Indeed, it is technically possible for TV stations in the US to transmit both simultaneously over the same channel, although in practice this would probably require switch off of legacy ATSC 1.0 services to liberate enough spectrum.

In Europe though compromise has been built into discussions from the start, partly because there has been more pressure from broadcasters to accommodate 5G Broadcast. This shaped the hand of the EBU (European Broadcasting Union), which in September 2021 published two new reports concluding that a 5G Broadcast system could be introduced safely alongside existing DTT in the contested UHF band. In Europe that is 470 MHz to 694 MHz (470 – 608 MHz in the USA).

The idea was that existing broadcast towers could be used to significantly enhance coverage and minimize cost of rollout. 5G Broadcast would then add the unicast dimension, helping broadcasters migrate to internet distribution, without need for additional receiver components to be built into handsets.

The DVB also latched on to 5G Broadcast as a key component of its DVB-I technology designed to combine linear broadcast with the internet without any sacrifice in quality. DVB-I was subsequently extended to incorporate 5G Broadcast.

This led to a technical report published by ETSI (European Telecommunications Standards Institute), inspired by collaboration between the DVB Project and 5G-MAG (Media Action Group) to define how DVB-I could provide a service layer for any IP-based system. This specifically included both unicast 5G media streaming and 5G Broadcast.

This sprung from a Joint Task Force between DVB and 5G-MAG set up in in 2022 to shape the Commercial Requirements for DVB-I service support over 5G networks and systems (DVB BlueBook C100) into a set of deployment guidelines. The report now available includes high-level summaries of technologies from DVB (DVB-I, codecs, and delivery formats such as DVB-DASH, DVB-MABR and DVB Native IP), from 3GPP (5G System, 5G Media Streaming, eMBMS or 5G Broadcast and enhanced TV), and LTE-Based 5G Broadcast from ETSI JTC Broadcast.

This maps into three detailed service scenarios, one being standalone DVB-I service using 5G Broadcast, another DVB-I service using 5G Media Streaming, and the third DVB-I service available simultaneously over broadcast and unicast. The latter is of immediate interest since that represents the future of broadcast distribution. But the other two are inseparable from that because so many broadcast and unicast transmissions will go over 5G, irrespective of whether DTT is still in the frame.

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