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With mobile devices overtaking TVs for video viewing in countries such as the USA and UK – and fast catching up elsewhere – it is not surprising that broadcasters have been scrambling to square that circle between the big and the small screen.

Some broadcasters, such as the BBC, have pivoted towards mobile first strategies, while next generation platforms like ATSC 3.0 are attempting to cater for this trend to varying degrees.

Earlier in this miniseries we have also discussed how the challenge of integrating mobile with TV delivery is being addressed by 5G Broadcast with an attempt to apply cellular 3GPP standards to broadcast transmission over DTT type infrastructures, bypassing established 5G networks.

Yet none of these efforts currently reconcile the differing requirements of streaming services from mass live broadcast down to niche, on-demand content. For the latter, broadcast delivery to all devices is inefficient and not economically viable.

Perhaps the 3GPP missed an opportunity with 5G Broadcast by pitching too hard at broadcasters and ignoring the requirements of numerous streaming outlets seeking an efficient way of delivering less popular services that cannot justify full broadcast delivery. 5G Broadcast does address TVs and mobiles, and it is true that chipsets for the latter can quite readily be adapted to receive the services as it is couched in 3GPP protocols. But it does not support unicast transmission to single devices, or multicast to a subset of the total viewing community.

Let’s examine the multicast landscape first.

Multicast

The multicast proposition is simple enough, which is to cater for delivery of data, content or services to significant numbers of users while remaining well short of all possible recipients on a network. In that case, broadcasting the same content to all users would consume more bandwidth than necessary. Similarly, transmitting the data separately to each user in unicast mode would also be inefficient.

Multicast resolves this conundrum by sending only one copy of each data down every link of a network leading towards at least one downstream recipient. Then at each node, that data is replicated onto output ports or links leading to a downstream recipient, and pruned from the rest. In this way, all redundant transmission is eliminated.

But this approach only works in this way over a fixed network comprising point to point links between nodes. Indeed, multicast transmission evolved in particular for fixed IP networks in the infancy of mobile data and video.

Although multicast was not developed originally with wireless networks in mind, subsequent technical developments are making it possible. The first point to note is that cellular networks comprise of fixed point to point networks downstream as far as each individual wireless cell.

Within the cell, data is normally transmitted within dedicated slots consuming a portion of the overall signal bandwidth, even though it is usually targeted at just a single end device in unicast mode. But it is possible to transmit data down as far as each cell in multicast mode, originating in an operator’s core network and then reaching cell towers over a backhaul network. The latter may be based on optical fiber, or microwave radio, but it is always in point-to-point mode so that multicast operations such as “join”, where a host receiver signals its desire to start receiving traffic for a specific multicast group, can be executed.

The challenge comes within the wireless plane, given that it has historically transmitted signals without any direction for reception by any device within range. However, it is now possible to direct radio signals towards individual receivers, and this has become a major part of wireless transmission over both WiFi and cellular through MIMO (Multiple Input Multiple Output) technologies.

MIMO

This has evolved into Massive MIMO at higher radio frequencies, at which the shorter wavelengths enable the use of smaller antenna. This in turn allows individual transmitters, and even receivers such as smart phones, to incorporate larger numbers of antennas. In principle, each antenna is capable of transmitting in point-to-point mode, allowing spatial multiplexing where a given channel band can be reused multiple times within a cell. In effect this allows wireless to operate like a wired network.

The impact of MIMO allied to beamforming techniques to focus the signals tightly is transformative for RF (Radio Frequency) network performance and capacity. It also allows multicasting to be extended across the wireless domain of mobile networks right to the end device.

Certainly MIMO, and recently by extension Massive MIMO which can support in the region of 100 ports to significantly boost capacity, has been widely adopted in cellular networks. But the motivation so far has been for increased capacity, reach and efficiency, rather than to deploy multicast for video.

While mobile operators have acknowledged the potential of multicast for efficient delivery of video in combination with unicast to serve content of widely varying popularity efficiently, they have been deterred by the complexity and costs. Meanwhile, alternative ways of meeting the same objectives have evolved that avoid the need to engage with those complexities.

Content Delivery Network Caching

Foremost among these is CDN (Content Delivery Network) caching, which has the advantage of exploiting the scale and efficiency of third party CDN network providers. This offers great scalability and is often more efficient for serving content to multiple subscribers simultaneously down as far as the wireless domain. Combined with unicast, CDN caching also caters for delivery of personalized content, which multicast does not because the identity of receivers is masked from the origin servers.

CDN caching can also improve QoS (Quality of Service) by cutting down on latency for on demand content as this can be delivered from servers closer to the user.

It is true CDN caching does not address capacity issues within the radio domain. But MIMO allows unicast traffic to be delivered on a point-to-point basis within radio cells.

There is still the possibility of a more radical overhaul of mobile network structure in the future, when multicast transmission could come back into contention. One such radical option currently subject to research and development is cell-free Massive MIMO, where the existing boundaries between radio cells are eliminated to be replaced with a flat structure of distributed antennas. These antennas would cooperate with the help of AI machine learning for tuning and optimization.

Then, multicasting would almost come out in the wash as an integral part of the architecture, ensuring efficient allocation of RF bandwidth and resources. It would be complex, but a lot of that could be automated with emerging AI techniques; some AI techniques can automate and optimize the operation of multicasting, a key one being mathematical graph theory for representing multicast trees. Under graph theory, nodes are connected by edges in point-to-point mode, which can be directed and weighted with a body of established algorithms for fundamental calculations. These include finding the shortest route between two network nodes, and trimming graphs back to the minimum number of edges needed to connect all the nodes.

Such algorithms enable network routes to be optimized on the basis of varying priorities and service guarantees, including multicast trees, but determining how to apply these algorithms most effectively is still work in progress, and the future structure of mobile networks remains uncertain.

And there are additional challenges to overcome.

Other Challenges

Perhaps the biggest lies in extending these algorithms into the production domain and incorporating them within broadcast workflows. This hurdle has held back multicast generally and AI raises the bar further, while a lack of standardized interfaces and availability of open-source software capable of being tailored for specific broadcast environments has strengthened the challenge.

The situation has not been helped by confused positioning by 3GPP as the arbiter of cellular standards of its MBMS (Multimedia Broadcast Multicast Services), which has been rolling out over the last two releases of its platform, Rel 17 and Rel 18. With critical refinements still being worked out, it is not surprising mobile operators have been hesitant over committing to MBMS. Note that MBMS is distinct from 5G Broadcast; the first is pitched at mobile operators, the second at broadcasters.

The other outstanding question is whether, and if so when, some form of multicast will be incorporated with next generation broadcast. That does not appear anywhere on the agenda at present, especially considering the January 2026 report commissioned by Broadcast Networks Europe (BNE) contending that 5G Broadcast could become a strategic pillar of Europe’s media, communications and civil protection infrastructure.

The BNE argued this would combine the reach and resilience of terrestrial broadcasting with the flexibility of mobile technology. That study, called “5G Broadcast: Horizons for Europe”, laid out a roadmap for deployment, urging coordinated action by policymakers, broadcasters and industry players. But as before there seems to be no room for mobile operators in the discussion. Indeed, the report positions 5G Broadcast as a Free To Air SIM-free service capable of delivering live TV, radio and data directly to smartphones and other mobile devices, completely bypassing mobile networks.

It would use existing digital terrestrial television infrastructure in the lower UHF band, with a focus on delivering ancillary services such as emergency use, enhanced experiences at sports and cultural events, large-scale file delivery for software updates, and emerging uses such as geolocation back-up and drone navigation.

The report does highlight the multicast nature of broadcast, but without addressing the radio domain, or any suggestion of synergy with MBMS. This would not be an efficient vehicle for delivery of niche content to relatively few subscribers and would leave broadcast and mobile networks operating as parallel delivery mediums. 5G Broadcast remains dependent on smartphone chipsets being upgraded.

Without access to the phone’s SIM card there is limited scope for integration at the service level. It all means that there is still a lot up in the air over the future of mobile broadcast in its broad sense.

Nevertheless, it is clear that mobile networks will continue to be optimized and automated as far as possible for delivery of video content to multiple receivers, irrespective of the exact underlying mechanisms. Standards will solidify and mobile networks will become better suited for large scale delivery of video content in all categories.