The ascent of CBRS as a medium of shared mid-band spectrum is sending ripples through the wireless industry. In doing so, it is upending spectrum policy across the globe and spawning a new ecosystem of use cases, from fixed wireless access to private cellular and neutral host networks.
Undoubtedly, this interest in spectrum sharing is an apt one given the parallel development and commercialisation of 5G NR. Wireless operators now require access to an unprecedented breadth of spectrum assets in order to facilitate new and evolving demands for network resources.
Paving a path towards incorporating shared spectrum across newly refreshed Radio Access Networks (RANs) means breaking free from the rigidity of licensed spectrum and from the unreliability of unlicensed spectrum. The net effect can be a more diverse network that proactively responds to the demands being placed on it.
Understanding the fundamentals of the Spectrum Sharing Concept
Put simply, the sharing concept seeks to maximise efficiency in the use of spectrum – a finite resource – through a dynamic system that enables users to opportunistically tap spectrum assets which the incumbents are not using.
CBRS, for example, takes advantage of the fact that spectrum is traditionally licensed to specific users (e.g, the United States Armed Forces) and/or for specific uses (e.g, fixed satellite services and ship-based radar). A large proportion of the spectrum, however, remains underutilised because the incumbents operate only at specific times and in specific areas.
The sharing framework, which fits in between the extremes of licensed and unlicensed assignments, challenges exclusivity by making spectrum available to the users that require it and have the capabilities to exploit it. At the same time, this framework achieves equal access while also ensuring reliability in the transmission of high-priority and high-value traffic.
A real-time coordination system (such as the Spectrum Access System with CBRS) enables the enforcement of priorities and power levels. This dynamic optimisation of spectrum utilisation to minimise interference can be achieved through the use of a sensor-based feedback loop (such as the Environmental Sensing Capability with CBRS).
Spectrum Sharing in Europe: Germany and the United Kingdom
The aforementioned ripple effect of CBRS is, perhaps, most evident in Europe. Since 2012, the European Union (EU) has encouraged Member States to “foster the collective and shared use of spectrum where appropriate” through its Radio Spectrum Policy Programme (RSPP).
Notably, policymakers in Europe and further afield are being drawn to spectrum sharing by the understanding that it can act as a springboard for economic growth. The use cases that sharing enables, such as private enterprise networks, can act as a competitive differentiator in the global market.
Some of the fruits of this policy position have been laid bare in Germany’s approach to the assignment of 5G spectrum. In addition to the traditional licensing of spectrum to incumbent wireless operators there, the Federal Ministry of Economics and Technology (BMWi) made private licenses available exclusively to German enterprises.
These licenses were located in small portions of the 3.7-3.8 GHz band, and have equipped companies such as Bosch and Siemens with the tools to deploy private enterprise networks on their campuses for highly bespoke cellular connectivity.
In the United Kingdom, conversely, its foray into spectrum sharing has been driven by goals to enhance rural connectivity in underserved areas. The vision is that new mobile network deployment models such as neutral host can co-exist with and complement traditional ones in striving to reduce the digital divide.
The Office of Communications (Ofcom) opened an application process in July of 2019 to provide co-ordinated and localised access to spectrum in portions of the 1800 and 2300 MHz and 3.8-4.2 GHz bands. MmWave spectrum in the 24.25-26 GHz band was also added to the regulator’s spectrum sharing framework for indoor-only use.
These access licenses are broken into two distinct types: the Shared Access License and the Local Access License. With the former, both low (per area license) and medium power (per base station license) options were made available. Meanwhile, the Local Access License constitutes access to unused licensed spectrum held by the UK’s mobile operators.
Spectrum Sharing in other bands: 6 GHz and the C-Band
Regulators in the United States, in particular, and across the world are also exploring the potential to enable spectrum sharing in other bands. The 6 GHz band (5.925-7.125 GHz), which encompasses a massive 1,200 MHz of spectrum, is attractive because of the sheer amount of capacity that it can offer and because of its favourable mid-band signal propagation characteristics.
This band is currently used for a multitude of services in the US including microwave backhaul. The Federal Communications Commission (FCC) is currently assessing how to best open up the band to new uses while also protecting the incumbents by potentially breaking it into unlicensed and licensed portions for both Wi-Fi and cellular networks.
Separately, the C-Band (4-8 GHz) is poised for increased sharing as the FCC continues its engagement with stakeholders to clear some of the spectrum (3.7-4.2 GHz). Satellite operators (which form part of the C-Band Alliance) are the incumbent users of this band, providing cable and broadband programming services.
These incumbents are, however, seeking compensation for an early transition of their spectrum within and/or out of the C-Band. It is expected that this transition process will bear fruits within the next two to three years.
Conclusion: Spectrum Sharing redefines access to a finite resource
While CBRS is still in its infancy as a commercially deployed medium of mid-band spectrum, it has blazed a trail in redefining access to a finite resource through dynamic sharing. This framework is built on a foundation of equal access and it is now being considered across numerous bands globally.
In maximising the efficient use of spectrum, sharing can provide tremendous value for consumers, operators and the underlying use case ecosystem. The arrival of 5G NR with support for unlicensed (NR-U), along with both asynchronised and synchronised sharing, only serves to expedite this trend.