The 3.5 GHz band gains in significance, but no global alignment

As mobile stakeholders continue to lobby the FCC either to speed up progress on opening up the 3.5 GHz CBRS band, or to change the rules, there is significant progress in making the shared spectrum system commercially workable. However, while stakeholders like Google press the FCC to speed up its efforts, the CTIA is concerned that the US is, once again, adopting a band plan which does not align with the global norm, and that may create a disadvantage in 5G.

Federated Wireless is one of two companies which are trialling spectrum access systems (SAS) to manage the sharing of airwaves and prevent interference (the other being Google). It says it has now racked up about 40 trials, including technology and operational tests, and expects the FCC to certify its spectrum controller before the end of this year. The controller, which underpins the SAS, gained conditional certification in February.

Federated CEO Iyad Tarazi – formerly in charge of the Network Vision modernization program at Sprint – expects to see commercial services in the CBRS spectrum in late 2017 or early 2018, starting with wireless ISPs, followed by MNOs.

Last year, Federated and Alphabet/Google demonstrated interoperability between their SAS platforms. The former is now also working on providing sensors for the Environmental Sensing Capability (ESC), which is a requirement under the FCC’s sharing system.

This system allows three levels of access to the 3.5 GHz spectrum (3550-3700 MHz). The top level is for the incumbent users, mainly in naval radar (so the airwaves are often very little used away from the coast). They will be protected from interference from any other users.

The next is for priority or licensed access. These priority access licences (PALs) will be assigned by auction in the 3550-3650 MHz portion of the band. Each licence will be a non-renewable authorization to use a 10 MHz channel in a single census tract for three years. Up to seven PALs may be assigned in any given census tract with up to four PALs going to any single applicant. The PAL holders will be protected from interference from the general access users. No date has yet been set for these auctions.

The General Authorized Access (GAA) tier allows any users to use any portion of the 3550-3700 MHz band not assigned to a higher tier user and may also operate opportunistically on unused Priority Access channels.

Despite progress on the SAS front, which is essential to protect the rights of the various tiers of users and prevent interference between unlicensed operators, many organizations are frustrated at slow movement elsewhere. Last month, members of the CBRS Alliance, which mainly represents stakeholders interested in the GAA portion of the band, called on the FCC to move more quickly to complete certification of the SAS and environmental sensing systems so that services can begin. A group of companies, including Google, Microsoft, Boingo and American Tower, also recently called on the FCC to stick to the rules it set out in 2016. There have been fears that the change of administration, and the new FCC leader, Ajit Pai, might lead to modifications of those initially proposed rules, creating uncertainty and further delay.

The main reason why adjustments might be made to the rules would be to align them more closely with international practice. T-Mobile USA, in particular, has pointed out that many regulators are earmarking 3.5 GHz as a core 5G band – auctions have been conducted or planned, on that basis, in several European countries, for instance, including France, Sweden and Ireland (see below). TMO argues that the US will miss an opportunity if it does not align itself with global 5G requirements, and that this would make the priority access layer more attractive to investors.

The mobile operators’ trade alliance in the US, CTIA, has also recently urged the FCC to adopt changes in order to spur investment in 3.5 GHz, particularly towards 5G. The GAA tier is seen as a band in which near term deployments could be made with LTE small cells, though its disruptive potential will be maximized when the MulteFire technology -which allows LTE to run in unlicensed bands such as 5 GHz and 3.5 GHz GAA – is commercial. This will enable non-MNOs to build cellular networks, perhaps as subnets for particular enterprises, cities or vertical industries.

Meanwhile, the PAL layer is being seen as a candidate for early 5G. The 3.5 GHz spectrum is well suited to densification with its relatively short range and high capacity, and the CBRS plan claims it will greatly increase spectral efficiency compared to that in current LTE bands. And it carries fewer uncertainties and propagation challenges than the millimeter wave bands in which some US carriers plan to deploy early 5G.

CTIA, then, wants to keep the PAL layer in the control of its members and maximize its attraction for them. In a recent filing with the FCC, it recommended longer licensing terms for the spectrum; strengthened privacy and property rights; and simplification of licence terms based on Partial Economic Areas (PEAs) rather than census tracts.

“These reforms are important because if we get our spectrum and wireless infrastructure policy right, 5G is forecast to be a $500bn shot in the arm to American’s economy, creating 3m jobs and enabling smart city solutions that could produce $160bn in benefits and savings for communities across the country,” CTIA said in a statement.

“Nations around the world are accelerating the development and deployment of 5G by streamlining access to bands like 3.5 GHz. China, for example, is testing 5G already and has allocated 300 MHz of 3.5 GHz and spectrum for 5G use. With 3.5 GHz as the only midband spectrum in the pipeline in the US, we need a licensing framework that facilitates investment, cements our lead in 5G and maintains our position as the global leader in wireless.”

The FCC’s three-tiered approach has attracted high levels of interest round the world, and various forms of shared access are being discussed and tested in various regions. In Europe, Licensed Shared Access is the likely mechanism, but this is initially targeted at the 2.3-2.4 GHz band, using the recently finalized ETSI specs.

In many areas of the world, 3.5 GHz will be allocated for 5G, but not necessarily in a shared way. The spectrum has generally been assigned in the past for fixed wireless, and now regulators are starting to add mobility rights, and consider repurposing some or all of the band for 5G.

For instance, French telecoms regulator ARCEP last week pledged to make available 300 MHz of contiguous 3.5 GHz spectrum for 5G by 2020 – clearly earmarking the mobile usage of this band for next generation wireless rather than for LTE densification.

In some markets, 3.5 GHz is seen as an ideal way to add capacity to 4G via small cells, but as MNOs in Europe have often not reached capacity and density limits in their 2.6 GHz holdings, there is a tendency to look ahead to 5G for the 3.5 GHz spectrum. Regulators in the UK, Sweden and Ireland have already identified the band for 5G use.

ARCEP has identified a sub-band of 80 MHz of spectrum at 3.6 GHz to be used for near term 5G trials. The first cities named to host these trials are Lyon, Nantes, Lille, Le Havre, Saint-Étienne and Grenoble.

The decision arose from ARCEP’s public consultation on spectrum for 5G, Internet of Things, fixed wireless and private radio, which ran from January to May of this year. The regulator received submissions from 66 stakeholders, including local authorities, operators, trade associations and vendors.

The first priority is to support “urgent needs” for fixed wireless and private mobile radio (PMR) systems in the 3.5 GHz band (3,400–3,800MHz) and then to look ahead to using these airwaves for 5G also. Within the 3.5 GHz band, 40 MHz will be earmarked for fixed wireless, and possibly an additional 10 MHz depending on demand. These licences will be geared to underserved rural areas and will be subject to
“ambitious roll-out obligations”, ARCEP said.

The fixed wireless and PMR requirements will also be supported by new allocations in the unpaired portion of the 2.6 GHz band this year. While most European regulators auctioned 2.6 GHz FDD airwaves in the early stages of 4G, the unpaired spectrum was sometimes left on the table. In France, some of this spectrum is already used for PMR.

A decade ago, most MNOs were still mainly interested in paired spectrum, but now there is rising demand for unpaired frequencies, which can support densification, and services which are downlink-heavy (because the uplink and downlink can be configured asymmetrically in TDD).

Existing licences in the 3.4 GHz to 3.6 GHz band will be regrouped to form contiguous blocks, towards the bottom of the band. This should make it possible to have more than 300 MHz of contiguous spectrum available for 5G by 2020, and 340 MHz by 2026 (or up to 390 MHz where fixed wireless is not in use). Work will begin this year on upgrading part of the 3.5 GHz network, and the 2.6 GHz TDD band, to “superfast” networks.

A consultation on the system to allocate the 3.5 GHz band will be held next month, with a view to begin assigning spectrum from September. Allocation of the PMR frequency will take place by the end of this year, with a consultation held on its distribution in the autumn.

The consultation also gathered information on the targeted use of other bands for 5G, IoT, PMR or fixed access – those were 1.4 GHz band, 2.3 GHz band, the supplemental downlink portion of the 700 MHz band, 400 MHz band and 26 GHz band. No decisions have yet been taken about the use of these bands as yet.

ARCEP said in a statement that is “welcomes all and any queries from players interested in conducting 5G trials. Based on these trials, Arcep could then begin preparing for the frequency allocation procedure that would enable 5G services to launch in France, starting in 2018.”

French operators have been active in pre-5G trials – earlier this year, Bouygues hit speeds of 25Gbps while Orange reached 10Gbps, both working with Ericsson in various spectrum bands including millimeter wave.