Spectrum sharing: getting the balance right

At the ITU World Radiocommunication Conference 2023, a number of topics proved hugely contentious, reflecting not just national disagreements but also inter-sector battles over spectrum allocation. Looking to the future, new forms of consensus-building and mutual understanding are needed if the existing regulatory processes remain workable nationally and internationally.  

 Two conferences in the second half of 2024, the DSA (Dynamic Spectrum Alliance) Summit in Geneva and the Spectrum Americas congress in Washington DC, highlighted three important underlying trends: 

• Universal demands for more spectrum from virtually every sector of use, reflecting a huge explosion in applications for wireless connectivity and other uses of radio resources. 

• Increasing awareness among regulatory attendees of the growing importance of spectrum sharing and coexistence. A word frequently used has been the need for “balance” between different user groups and applications of spectrum. 

• Additional emphasis on the specific need for sharing between commercial wireless sectors and military users of spectrum.  

It is worth dissecting each point. 

Weights on the scales: every sector wants more spectrum 

Perhaps the root cause of the problem is that there is much more demand than supply for spectrum, especially in prime bands with good propagation characteristics. Every sector is talking about growing usage and new and innovative applications. The days of simple reallocation of incumbent users’ frequencies, clearance of bands, and fresh awards of national exclusive licenses, especially for cellular/IMT, are either over or heading rapidly in that direction.  

The mobile industry is looking ahead to later versions of 5G, followed by 6G / IMT2030. It attempts to identify new bands for capacity and new use cases, ideally with enough spectrum for multiple competing MNOs and with large, contiguous, and exclusive bands for maximum throughput and efficient frequency reuse. Advocates continue to point to growth in cellular data traffic driving spectrum demand, although others now believe it to be plateauing. 

The Wi-Fi industry is pushing for more unlicensed spectrum and the ability to use it at higher power levels where conditions permit. The growth of broadband access and especially fibre continues to fuel demand for unlicensed spectrum for Wi-Fi, plus Bluetooth and other uses in homes and business premises. Some countries have already made the entire 6GHz band available on an unlicensed low-power basis, while others have released the lower 500MHz of the band and are still debating what to do with the upper 6GHz part. The WRC outcome was something of a fudge, allowing for multiple options.  

The satellite industry has increasing requirements for both spectrum and orbital slots, especially with the rise of large constellations of Low Earth Orbit (LEO) craft. The recent emergence of “direct to device” concepts to connect from space directly to smartphones or IoT systems is adding a new set of variables, as is the quiet renaissance of “high altitude platforms” such as stratospheric aircraft or balloons for communications purposes, which some see as pivotal for “connecting the unconnected”. Space-based agenda items dominate the WRC-27 agenda. 

At the same time, many historic incumbent spectrum user groups want to maintain access to their existing bands or even obtain/protect more. Fixed links, event audiovisuals, and defence (see more below) all have clear and urgent requirements for radio resources, while even the broadcast sector is arguing for maintaining access to its historical frequencies.  

Critical sectors such as rail and utilities have expanded the need for connectivity, which often cannot be satisfied by other terrestrial networks such as commercial mobile. Aviation and maritime sectors must maintain safety and support new wireless applications, such as the growth of autonomous or remote-piloted drones and vessels. 

Less visible but important, passive spectrum use, typically for scientific, environmental, or earth-observation purposes, is also becoming more critical and accessible. Its users are keen to ensure that terrestrial wireless does not destroy the ability to monitor the earth or space, especially for scrutiny of climate change indicators. 

Demand claims are facing more scrutiny 

As a result, public conferences continue to show vigorous—and sometimes vitriolic—debate over bands such as upper 6GHz, lower 3GHz (especially in the US), and now the 7–8GHz range being studied for possible IMT identification at WRC-27. Sector-specific lobbyists often have detailed and persuasive analyses of why their preferred technology and applications deserve more spectrum or looser rules. 

That said, regulators are increasingly exasperated with overblown forecasts and demands for spectrum, often made in the expectation that initial claims will be negotiated down. Even if one acknowledges that all arguments are valid, that does not help if demand far exceeds supply. 

Matching demand and supply means that regulators need more “balance.” That can be achieved by dividing bands into sub-bands, sharing frequencies between multiple users, or combining applications.   

Despite the growing recognition that compromise is important, working out a “fair” balance is extremely hard. Inevitably, some parties will be disappointed, either in terms of absolute amounts of spectrum or in rules put in place to enable coexistence without harmful interference. Reducing power levels or using new mechanisms for signalling and coordination can reduce efficiencies, limit theoretical performance, or increase deployment and operation costs. 

But that is what balance implies—there can be no “winner take all” mentality. 

One “balancing act” is certain: greater use of spectrum sharing is inevitable and necessary. National or large-area exclusive licenses, used by many IMT networks, seem inefficient and inflexible, especially where data suggests there may be 1000x difference in usage levels between dense urban and remote areas.  

There are several ways spectrum could be “balanced” via sharing: 

• Divide frequency bands, from <1GHz to >100GHz, based on what is optimal for particular applications. More data and insight into the real needs and current usage are needed to determine baselines. 

• Consider the range of physical scales and location types where spectrum is made available for both fixed and moving applications. For instance, while broadband TV and mobile broadband generally need nationwide access, fixed links or rail/utility controls are used along linear corridors. At the same time, some applications can be limited to indoor or site-specific use. 

• Consider temporary access to bands and predictable, stable access needed for significant investments in infrastructure. Any well-balanced spectrum policy understands multiple time spans from minutes/hours to years/decades.  

• Balance old and new, reflecting different historical licensing conditions, usage models, and expectations/needs of incumbents versus new application operators or sharing partners. 

In sum, balancing mechanisms are likely to be complicated and require substantial amounts of real-world data and credible predictions and forecasts. Ideally, this data will reflect actual spectrum usage patterns rather than vague and debatable assumptions linking traffic use or other adjacent metrics to spectrum requirements.  

Defence spectrum needs a particularly good sense of “balance” 

Defence is perhaps a particular case for spectrum. The military controls large amounts of the radio spectrum, which it uses for a diverse and growing set of applications. Real-time communications are central to terrestrial, aviation, naval, and space forces. Multiple sensing functions—notably radar but also signals intelligence and monitoring—are used extensively from many different platforms.  

Telemetry, navigation, and the growing use of remote/autonomous systems require ultra-reliable connectivity, especially as the importance of video, augmented reality, and complex integrated systems increases. The ability to shift frequencies and obfuscate wireless usage is also critical in an age of surveillance and signal jamming. In addition to operational use, spectrum access is needed for training, testing, innovation/labs, and security.  

This means that “efficiency” has a different meaning or calculus for the military than mainstream commercial usage. Throughout 2024, organisations such as the US DoD, NATO, and UK MoD have highlighted the need for maintaining defensive abilities and supporting more new wireless applications. 

In the military context, balance refers as much to maintaining national and international security as it does to tangible commercial outcomes and immediate social benefit and inclusion. While every sector claims to have unique requirements, there is a strong argument that defence is genuinely different. However, it is also willing to share spectrum if it retains rights as the keystone user. The Citizens Broadband Radio Service (CBRS) model in the US and the recent UK policy for sharing 2.3GHz are good examples, as well as various instances of sharing with Programme Making and Special Events applications (PMSE) for events’ wireless cameras and microphone needs.    

Does “balance” always imply spectrum sharing?  

A balanced approach to spectrum assignment does not necessarily mean multiple users sharing a given band, either in space or time. It can relate to policymakers giving a fair amount of attention and analysis to each stakeholder group—rather than allowing the conversation to be dominated by whichever has the loudest PR, the greatest volume of reports, or the most insistent lobbying. 

A key point is maintaining optionality and recognising that forecasts are rarely accurate. Although some sectors are fast-moving, such as commercial cellular, enterprise wireless, and satellite communications, hasty decision-making can sometimes yield bad outcomes. For instance, several early awards of mmWave spectrum for 5G are now being reversed. 

A more fitting measure might be agility in spectrum management, a crucial element in disciplines requiring delicate balance, such as gymnastics. The ability to monitor and correct outcomes as needed is valuable, and better sensing, analytics, and database functions for spectrum could be essential. 

Conclusion 

Policymakers are increasingly looking at new methods of spectrum management to solve the multiple, overlapping claims of the need for new radio resources. Better data about how spectrum is currently used and how that changes over time or in different locations will be an important input for such decision-making (and enforcement). A key element of that will be sensing, ideally distributed in a way that gives good granularity regarding location, direction, frequency, and usage.