The reflexive assumption of exclusive high-powered spectrum is now being questioned.
Spectrum sharing is not new
Sharing spectrum between different users and applications is not a new idea. Many existing frequency allocations have multiple users that coexist in space or time. Unlicensed (ISM) bands have a diverse range of technologies and business models sharing spectrum, based on appropriate power limits or permitted duty cycles. Wi-Fi is a prime example and arguably the greatest sharing success for spectrum to date.
But until recently, it has been rare for cellular wireless systems to share frequencies with other users and systems. Most 2G, 3G, 4G and 5G deployments have had exclusive use of their main bands, across defined regional areas or nationwide at high power that excluded the possibility of other services in the bands. Network operators (MNOs or carriers) have typically obtained such exclusive spectrum via auction processes, with previous tenants in the band being cleared out and their operations shifted to alternative frequency ranges at significant cost.
Given the reality of the limited spectrum available and evolving technologies and needs, the reflexive assumption of exclusive high-powered spectrum is now being questioned. New approaches to spectrum allocation are allowing 4G/5G networks to coexist with existing incumbents – especially the military, which is a major user of the spectrum most desirable for commercial use. The initial CBRS band between 3.55-3.7GHz is the obvious example of this, successfully employing sensing and coordination systems between the Navy and other tiers of users. This is unlocking more efficient use of spectrum, while serving national security interests and also democratizing access to a much wider group of network owners and investors.
CBRS is a major success and is now evolving further in multiple ways
To date, CBRS has been a huge success. There are now around 400,000 active CBRS access points (technically called CBSDs), spread across about 1000 different network owners / operators from a variety of sectors. The ecosystem includes traditional mobile carriers, hybrid MNO/MVNO operators, enterprises, government bodies and local municipalities, school authorities, and utility companies. Innovation continues with experimentation by small businesses and decentralized collectives of network owners.
However, the revolution in shared spectrum access and adoption is just getting started. It is a trend that already is developing a strong roadmap, with new sharing models expected to play a vital role for spectrum assignment into the 6G era and beyond.
In particular, there are four evolution vectors for the current CBRS spectrum sharing model, all of which are being developed in tandem and serve as an important touchstone for all forms of dynamic sharing being discussed and considered:
- Improved usability and accessibility through the updated CBRS 2.0 rules and future enhancement plans. After analyzing the initial deployments in CBRS, the protection areas (DPAs) have been reduced in size, improved interference models have allowed more-relaxed rules on small cell deployments and spectrum “grants” from SAS’s have been extended in length up to 24 hours. As a result, 72 million additional people and their employers, for a total of 240 million people nationwide, can now use CBRS in an unencumbered fashion. The collaborative process between the stakeholders is now proven, with high levels of mutual trust, meaning there is now an expectation of future CBRS 3.0 iterations and beyond offering even better access.
- New CBRS use-cases are continually being commercialized by enterprises, CSPs and municipalities. As deployment and operational experience grows and the ecosystem deepens, a variety of new CBRS applications are being deployed in production networks, as well as ongoing trials and tests for the “bleeding edge”. Distance learning and broadband inclusion are enabled for school districts. In-building coverage is being enhanced by CBRS-based “neutral hosts,” with carriers allowing their subscribers to “roam” onto third-party infrastructure. Advanced MVNOs are combining CBRS with Wi‑Fi access and their host MNOs’ wide-area cellular services, giving consumers additional competitive options for mobile service. Industrial and manufacturing enterprises are adding extra device and application categories to their CBRS networks via “use-case stacking”.
- Additional bands are being considered for CBRS-type sharing, notably the Lower 3 GHz band, currently used by the military and under review by a federal study group. A recent DoD report, the EMBRSS feasibility assessment, highlighted the need for a sophisticated coordination framework. In addition, future bands highlighted in the NTIA National Spectrum Strategy (NSS), such as 7.1-8.4GHz, may also benefit from similar sharing approaches – perhaps in conjunction with unlicensed elements.
- International coordination with other global regulators on dynamic spectrum sharing is moving forward. Many other nations are watching the US model and leadership in shared spectrum and have examined the CBRS concept. Several have created and started to iterate their own locally licensed spectrum regimes. A number are now looking at dynamic and database-driven approaches, as well as scope for sharing between their own military and commercial organizations, which also makes sense given harmonized spectrum for international military coordination, such as NATO. The UK, EU and others have spectrum sharing high on their agendas. While there are still some differences between technical approaches, there is an acknowledgement that sharing spectrum is critical for the future and will provide a pathway towards greater alignment and perhaps eventual harmonization with other countries.
Conclusion
There is no more “greenfield” spectrum for exclusive licensing and easy re-farming. Not only does every band have incumbent users, but almost all of these users want more spectrum in addition to keeping their existing assets. In particular, wireless connectivity is becoming ever more important to the military, while indoor gigabit broadband connectivity for consumers and businesses relies heavily on wireless technology (e.g., Wi-Fi and wireless offload), connected to the deepening fiber broadband infrastructure.
We would benefit greatly by thinking of smart spectrum policy in terms of precision irrigation, providing the right frequencies, in the right places at the right times and under conditions that serve diverse users and services.
Moreover, the type of advanced sharing scenarios envisaged in the NSS provide a path for freeing up spectrum quickly, while not displacing important national security interests. The process that recently led to CBRS 2.0 is a recognition that collaboration and sharing with the military is working even better than expected and that initially cautious restrictions loosen over time. Future innovations in CBRS should enable better coexistence between neighbouring GAA users, or perhaps even less-constrained indoor usage.
In parallel, new uses for CBRS are being continually developed, tested and deployed. Indeed, the success of collaboration and technology development for CBRS, between commercial users and incumbents, bodes well for other bands and models of spectrum sharing in the future.
Democratization of spectrum access also assists innovation and competition in mobile more broadly. It allows whichever parties have suitable backhaul, power and siting to build 5G infrastructure for themselves or others.
A final advantage is the strong US position in spectrum sharing platforms and technology, whether that is in databases and access systems, sensing technologies, commercial vendor ecosystems, or AI-centric innovations in spectrum management. This is potentially a completely new wireless industry domain that can yield both strategic and commercial advantage over global rivals.
Taken together, this discussion highlights the continued growth in importance of spectrum sharing. It is important that the cellular industry understands and actively participates in this sharing evolution – especially given the likely pathway to 6G. To be sure, exclusive licensed bands will continue to play a role for generic cellular services, but the future is as much about localized and specialized networks, and coexistence with incumbents.
