At a recent Cambridge Wireless event Damian Bevan, Wireless System Analyst at Real Wireless, posed the question “Can NTN D2D be used to further extend outdoor mobile coverage beyond what the Shared Rural Network will provide?”
The event ‘When Networks Collide: Merging of Terrestrial and Non-Terrestrial Networks’, held at the Institute for Communication Systems (ICS) at the University of Surrey was attended by over a hundred experts and enthusiasts from the non-terrestrial networks (NTN) community, including representatives from mobile network operators (MNOs), equipment vendors, consultancies, government and academia, some of whom also delivered informative slide presentations to explain their own organisations’ perspectives on the topic.
Damian addressed the question head-on by looking at ‘geographical coverage’ in regions such as Scotland. They proceeded by presenting the current ‘Shared Rural Network’ (SRN) programme, which aims to address so-called ‘Partial Notspots’ (PNS) and ‘Total Notspots’ (TNS) in rural areas of the UK. The SRN programme uses a mixture of MNO and government investment into shared infrastructure (>£1B), employing a conventional ‘old-school’ approach – i.e. by constructing new ‘High-Power-High-Tower’ mobile network sites using sub 1 GHz spectrum to achieve extended coverage.
He went on to explore whether emerging satellite-based ‘direct-to-device’ (D2D) architectures can be used to extend and enhance the terrestrial based SRN, potentially giving even better geographical coverage at a lower cost. Beyond questions about what orbits, waveforms and radio spectrum might be deployed, and what might be the mechanism for paying for this enhanced coverage, a key issue is exactly what we mean here by ‘coverage’. Part of the SRN programme definition of its intended coverage target is that SRN aims to provide a ‘>2Mbps download speed with >95% reliability’. Early D2D solutions look to offer what we might call ‘basic’ (i.e. ‘GSM-style’) coverage of 2-way messaging, potentially along with voice and low-rate data.
However, while some of the leading D2D ‘players’ such as Starlink and AST appear to be claiming that more enhanced ‘SRN-style’ coverage (i.e. including higher-rate data) is part of their roadmap, only time will tell whether they are truly able to deliver on that tantalising promise.
Also at the event, key MNO representative Rowan Chesmer, an R&D Future Technologies researcher from Vodafone, asked and answered the question, ‘How will satellite connectivity be integrated into mobile networks?’ – a problem that Vodafone is trying to solve. This is particularly relevant in remote regions such as Africa, where 1 billion people remain unconnected, 95% live in rural areas, and conventional terrestrial cell-sites in those areas have double the cost and 1/10th of the revenue of urban sites.
However, Vodafone noted that satellites are evolving, and a new generation of LEO satellites is emerging with higher capacity and lower latency compared to older MEO and GEO systems. These new technologies give opportunities in D2D services, mobile backhaul, broadband and Enterprise/IoT. Rowan explored how the satellites can fit into Vodafone’s network plan over the above range of applications for a range of deployment types, from dense urban to rural to ‘very remote’.
For much of the network, Vodafone stated that terrestrial networks are still the best option. However, satellite will be a great complementary and cost-effective option for providing near 100% geographical coverage for low population density and hard-to-reach areas. In the later Q&A panel session, Rowan reiterated that terrestrial networks will never be totally replaced by satellites, but that satellite is a great complement. He went on to tease that we could in the future be seeing 100% geographical coverage due to satellites in remote areas such as Scotland – ‘sooner than you might think’!
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