Dynamic spectrum sharing (DSS) is an important element in the Release 15 5G standards, because it makes it easier and cheaper for operators to deploy 5G base stations within 4G networks, upgrading their capabilities and use cases before they need to migrate from the LTE core.
DSS enables MNOs to transform 4G base stations via a software upgrade to become hybrid 4G/5G base stations supported by a common LTE core. Users of DSS-capable 5G NR devices can then access 5G services where they are available, while the MNO can allocate its existing spectrum flexibly across many bands, dynamically switching between LTE and 5G based on traffic demand.
Qualcomm has announced an extended partnership with testing company Keysight to help accelerate commercialization of DSS, and therefore to speed up 5G roll-outs in general, especially by that second tier of operators which lack the resources or confidence to invest in large quantities of customization, or untried new architectures, in order to be in the first wave of deployers.
The cooperation will use Keysight’s 5G network emulation solutions to accelerate the ability for Qualcomm’s Snapdragon 5G Modem-RF System to support DSS.
“Our continued collaboration with Keysight on 5G technology, which was initiated in 2015, has enabled Qualcomm Technologies to accelerate the implementation of DSS, a critical feature that will help mobile operators quickly transition to 5G,” said Jon Detra, VP of engineering at Qualcomm. “Keysight helps us develop and validate our Snapdragon 5G Modem-RF System designs at a pace that will help accelerate 5G commercialization.”
Mechanisms like DSS will also help operators to make far better use of underused spectrum assets. Contrary to the myth of a spectrum famine, most MNOs – at least outside very congested urban centers – have all kinds of airwaves gathering dust on the shelf. Many of these are licences for unpaired spectrum – such as the TDD portion of the 2.6 GHz and even 2.1 GHz bands – which has only really come into its own in 5G, which is driven by TDD technology and its flexibility to support asymmetric data uplink and downlink.
Others are small slivers of spectrum, or those without significant device support. In 5G, far greater degrees of carrier aggregation are standardized than in 4G, so operators will eventually be able to combine up to 16 different bands, even when non-contiguous, to form larger, and more useful, chunks of capacity – and to reduce the need to spend large sums on new spectrum in future.
Some of the UK operators are pushing ahead with innovative approaches to spectrum efficiency. Three UK has scored a major advantage over its rivals by acquiring UK Broadband and its substantial holdings in the key first-wave 5G band, 3.5 GHz (assets which have been extremely underused up until now). The smallest MNO is also harnessing its 1.4 GHz spectrum to add further 5G capacity.
Meanwhile, Vodafone says it will make some of its underused 2.6 GHz spectrum available for use by fixed wireless access (FWA) providers in rural communities. The UK operators have toyed with various ideas for improving rural coverage by sharing airwaves – largely as a way to bat away regulator Ofcom’s proposal to impose compulsory roaming. They are also discussing placing a small amount of their 2G spectrum into a shared network which would support GSM-based machine-to-machine services, notably the smart metering program, indefinitely, allowing the MNOs to refarm the rest of their 2G assets for 4G or 5G.
In a rather less dramatic move, but an interesting sign of possible things to come, Vodafone will share some of its excess 2.6 GHz spectrum with StrattoOpencell, which provides FWA services as well as enterprise small cell networks and other wireless solutions for areas where the conventional MNO model tends to run out. The three-year deal will initially focus on services in the south western county of Devon. StrattoOpencell will also deploy 4G small cells to deliver connectivity to a holiday site in the county.
The FWA offering will deliver speeds of up to 120Mbps, said Vodafone, whose CEO Nick Jeffery said: “Vodafone has a long history of innovation, from sending the first text message to conducting the first 5G holographic call. We are delighted to become the first mobile company in the UK to share some of our spectrum to extend rural coverage.”
The move Ofcom’s decision, earlier this year, to change its rules to permit MNOs to share spectrum, in order to improve connectivity in rural and remote communities.
“Our new sharing approach aims to help more people access the airwaves they need to create local networks around the UK, including improving connections in rural areas. Vodafone and StrattoOpencell are the first to take advantage of this. We look forward to seeing how others use our new spectrum access approach to support innovation and enable local communities to have better connections,” said Philip Marnick, group director of spectrum at Ofcom.
Under Ofcom’s new rules, a telco has to seek permission from Ofcom to license spectrum to a third party, and the decision will be made on a case-by-case basis, depending on the band, location, bandwidth and power required, and the risk of interference.
Of course, the USA’s CBRS scheme in 3.5 GHz is the industry’s poster child for flexible spectrum usage and sharing. Initial commercial deployment (ICD) in the general access tier of the band was recently announced, though auctions for the licensed portion will only take place next year. This is another approach to DSS – unlike fully unlicensed spectrum, usage in CBRS is actively mediated by a database that allocates channels according to the priority of the user (federal incumbents take first place, then licence owners, then general access users). The database calculates propagation models based on geolocation, tilt, height and other variables in order to guard against interference.
The CBRS experiment is being closely watched round the world, and spawning a host of start-ups, both service providers and technology providers, including the most prominent of the database administrators, Federated Wireless. One of the start-ups is Celona, a Silicon Valley start-up which has raised $10m in Series A funding, with a plan to combine cloud, edge and AI technology to support CBRS services.
It was co-founded by CEO Rajeev Shah, formerly at Federated Wireless, and CTO Mehmet Yavuz, formerly at Qualcomm. They claim to be developing a “fresh technology stack” to make LTE and 5G more easily consumable by enterprises, since the model in which MNOs manage enterprise networks as extensions of their own macrocells does not work. Yavuz said: “Really two different worlds. Even just to extend the coverage of the macro network operator to indoors has been very hard.”
New Street Research has identified three main categories of use case for CBRS – densification in urban environments; fixed wireless access (FWA) in rural markets; and enterprise. Analyst Spencer Kurn wrote in a research note: “AT&T plans to deploy CBRS spectrum for FWA in rural markets. They will use a traditional RAN architecture on 1,100 macro sites (2% of total). Their ultimate goal is to use CBRS in conjunction with the C-Band to significantly boost capacity.” He believes cablecos will harness CBRS to extend their wireless activities cost-effectively, complement WiFi and their own cable grids, and penetrate all three use cases. “Overall, the insights from the event support our view that cable companies stand to benefit the most from CBRS,” stated Kurn. “We estimate this could enable cable companies to pass an incremental 6-7m homes.”
New Street’s models assume that cable may be able to reduce its MVNO costs by roughly two-thirds over the next several years “boosting EBITDA per sub by ~$10 per month, on average”.