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7 February 2018

Charter touts CBRS as ‘6G’, but is the shared band really the new face of spectrum?

As if the US’s CBRS band in 3.5 GHz hasn’t been hyped enough as the future face of mobile spectrum, cableco Charter Communications has placed it at the center of what it shamelessly dubbed its ‘6G’ trial. This seemed to ignore the fact – much bewailed by T-Mobile USA – that the US regulator, the FCC, has actually focused on LTE usage in this band, rather than 5G.

That is shortsighted, TMO argues, because elsewhere in the world, the C-Band spectrum (various bands between 3.4 GHz and 4.2 GHz) is being earmarked as a pioneer band for 5G. That is being driven heavily by China and Japan, but is also seen as a way to accelerate early 5G deployments, because in many countries, 3.5 GHz is already available for fixed wireless.

However, the FCC has undoubtedly set valuable precedents with its flexible, multi-tiered licensing approach for CBRS, which will resonate well beyond the specific frequency or radio technology. But they are only the start of a discussion which needs to be held urgently by regulators round the world, especially in the run-up to the World Radio Conference next year (WRC-19), at which global and regional 5G spectrum bands will be identified.

For 5G to be more than just another radio upgrade, largely focused on boosting mobile broadband capacity and increasing cost efficiency (just as 4G did), there need to be new approaches to spectrum licensing. The regulatory frameworks will need to acknowledge the needs of a far wider variety of operators and spectrum owners than just the established MNOs. Shared and unlicensed spectrum, dynamically allocated short term licenses, geographically specific allocations, not to mention the array of regulatory issues raised by network slicing – these will all be important matters to support if 5G is to be effective in enabling a wide range of services and service providers. And this, in turn, will be essential to fulfil its potential to transform enterprise and Internet of Things (IoT) businesses – not just to improve the core consumer mobile broadband business case for MNOs.

Charter has that right at least, in its ‘6G’ hype. It is looking for a spectrum regime which gives it more predictability and quality than the unlicensed free-for-all of 2.4 GHz and 5 GHz; more capacity than the sub-6 GHz cellular band allocations; and does not require it to shell out many millions of dollars on those frequencies.

On its quarterly earnings call last week, CEO Tom Rutledge said: “Our 5G wireless tests are going well, as are our 6G tests. This is our pre-spec definition of the integration of small cell architecture using unlicensed and licensed spectrum working together interchangeably with our advanced DOCSIS roadmap to create high capacity, low latency product offerings. We expect that over time our existing infrastructure will put us in a unique position to economically deploy new powerful products that benefit from small cell connectivity.”

Of course, this has nothing to do with 6G. Integrating dense, localized mobile networks with advanced cable is at the heart of many 5G visions, and even some forward looking 4G projects. Cellular in shared spectrum will support better manageability and quality of service than WiFi in unlicensed, the argument goes, and since most of these shared bands are relatively high frequency, they will be best suited – especially indoors, where the power limits are strict – to small cells. The mixture of these low cost small cell networks and advanced wireline connectivity will enable enterprises or specialized vertical market providers to create optimized ‘sub-nets’ for a city, corporation or industrial zone, while leaving the wide area mobility in the hands of the MNO and its licensed airwaves.

This is an opportunity the US cablecos are watching closely. In particular, Charter will leverage the CBRS spectrum to support its own wireless services (expanding on those it plans to launch this year via its MVNO agreement with Verizon) and to expand these into vertical and business markets.

“Charter is in the process of transitioning its wireless network from a nomadic WiFi network to one that supports full mobility by combining its existing WiFi assets with multiple 4G and 5G access technologies,” Charter said in comments on an FCC notice of proposed rulemaking about CBRS. “In navigating this technological transition, Charter is concentrating on an ‘Inside-Out’ strategy, initially focusing on advanced wireless solutions inside the home and office, and eventually expanding outdoors.”

The 3.5 GHz band is important to this strategy, and to reducing the reliance on the MVNO deal (and the fees payable). But the terms and conditions for the PAL tier are proving contentious, even setting aside the argument that the system should be focused on 5G not 4G. Charter has petitioned the FCC to regulate the 3.5 GHz spectrum based on areas “no larger than counties”. It insists that it “plans to use the 3.5 GHz band in conjunction with its WiFi network to improve network performance and expand capacity to offer consumers a superior wireless service. Charter’s intended use of this band, however, requires rules facilitating new entrants’ access to this critical spectrum.”

CBRS is a step in the right direction to opening up the ecosystem, but only if it has flexibility in its licensed, as well as shared, layers, and its licenses are both affordable for new entrants, and suited to the needs of localized sub-nets. That is why the FCC is considering licensing rules around relatively small geographic areas and short time periods, rather than the long term national or large-market licenses of the traditional cellular auction.

These discussions relate to the second of CBRS’s three tiers of access. At the top is assured access for incumbent federal users; then priority access (PAL), which is based on regional and relatively short term auctioned licenses (terms to be decided); and then general authorized access (GAA), in effect unlicensed. A Spectrum Access System (SAS) enforces the prioritization of traffic from any of the three tiers and informs a GAA device which channels are free to use without interference to federal or PAL users, or to other shared spectrum services. Currently there are two commercially tested SAS platforms, from Google and Federated Wireless, and these have also demonstrated interoperability.

Charter continued in its most recent FCC filing: “Small cells are not well suited for large geographic license areas because, as a matter of design and engineering, these cells provide less coverage than traditional macrocells. Importantly, smaller license sizes will enable new entrants to more efficiently leverage their existing infrastructure in those counties that encompass their networks. Utilizing existing networks would enable new entrants such as Charter to rapidly deploy 3.5 GHz radios throughout these county-sized licensing areas for the provision of wireless broadband service. This results in more wireless service options with better throughput for more consumers in a shorter period of time.”

On the other hand, increasing the geographic size of a PAL to a ‘partial economic area’ (PEA) – as backed by the MNOs – would restrict access to large wireless incumbents, Charter argued. “With larger license areas to cover, only those companies with national scale and an already significant wireless network presence throughout a PEA will be in a position to invest in expensive new licenses.”

The CTIA, which represents US carriers, has backed TMO’s proposal for larger geographic license sizes and claims they would be more spectrally efficient and still enable deployment by providers of all sizes. It says larger areas will reduce the risk of interference or congestion from too many CBRS devices in close range, and allow systems to run near borders at full power. It also argues that smaller areas will be
challenging for the Spectrum Access System (SAS) administrators to manage, because channels will be reused less often, which in turn, will leave fewer channels vacant for GAA.

As well as small cells, Charter is currently testing in the 3.5 GHz Band to assess its value to support rural broadband and possibly extend its overall footprint. It says it has determined that it can provide speeds of at least 25/3Mbps at “significant distances”. It continued: “To deliver ubiquitous connectivity to our customers, we will rely increasingly on next generation wireless technologies like 5G, and significantly improve and expand the reach of our wired broadband network.” The cableco said it is working with eight different vendors on the 3.5 GHz tests for fixed and mobile wireless use cases. It is testing mobile solutions in Tampa, Florida and Charlotte, North Carolina, and fixed wireless in six other markets (Orlando, Florida; Reno, Nevada; Clarksville, Tennessee; Columbus, Ohio; Bakersfield, California; and Grand Rapids, Michigan).

IT and Internet firms lobby for 6 GHz to be open for sharing in the US:

Expansion of the 5 GHz unlicensed band in the US, and the multi-tiered CBRS band, have both been heavily driven by the Internet community and now the same names are at it again, this time focusing on 6 GHz.

Representatives from Apple, Broadcom, Cisco, Hewlett Packard Enterprise, Facebook, Google, Intel, MediaTek, Microsoft and Qualcomm met with FCC staff last Thursday to plead the case for expediting the opening of the 6 GHz band, supporting unlicensed services to coexist with incumbent users.

There has been lobbying for wider usage of this band before, but this latest activity is based around a detailed study by RKF Engineering Solutions, of how unlicensed and existing services – including satellite, microwave and mobile – could coexist without interference.

The companies said that providing a detailed engineering analysis at this early stage – before the FCC issues a Notice of Proposed Rulemaking – should reflect the urgency of the issue and help accelerate the process.

In the US, the 5.925-7.125 GHz spectrum (the 6 GHz band) is shared primarily by two services – Fixed Satellite Service (FSS) uplinks and fixed microwave (Fixed Service or FS) links. Portions of the band are also used by Mobile Service (MS) designated for public safety and electronic news gathering applications.

RKF analyzed the potential impact of unlicensed radio devices on existing 6 GHz operations in the 48 mainland states. It concluded that a national deployment, using established RLAN mitigation techniques, and rules similar to those in the 5 GHz band, would not cause harmful interference to incumbent services.

The vendor group points out that the WiFi Alliance has concluded that between 500 MHz and 1 GHz of additional unlicensed spectrum may be needed by 2020 to support the growth of WiFi.

At a Spectrum Management Conference last year, FCC Commissioner Michael O’Rielly said that the large swathe of spectrum from 5925 to 7125 MHz is not homogenous and different sub-bands may need different sharing mechanisms.

“Commenters seem confident that the Part 15 rules, along with additional coexistence mechanisms, should allow for sharing, but similar to the mid-bands, it is necessary to determine exactly what is needed to protect incumbent uses,” he said at the time. “Hopefully, further analysis will ease the minds of those entities that have expressed concerns about the ability to protect existing operations.”