Democratising the spectrum through dynamic spectrum access

Just like real estate, there is a finite amount of spectrum, so we must ensure that it is owned by the right organization and optimally used by government and private companies. Of course, there needs to be enough of it available for commercial usage. But government departments must also have the spectrum they need to keep the country safe, develop future policies, and ensure capabilities that take many years to develop.

Which government agencies use spectrum in the UK?

MOD: The MOD’s job is to keep our country safe. It holds the majority of all publicly-held spectrum and one-third of all spectrum below 15GHz.

UK space agency: The UK space agency works on a range of activities involving space exploration, satellite technology, and commercial space ventures. It indirectly but significantly contributes to the UK economy as services from satellites support many industrial activities, which contribute at least £370 billion to UK GDP (17.7%).

Met Office: The Met Office is tasked with making advances in weather and climate predictions by remotely observing the environment. It ensures continuous progress through extensive use of radio frequencies. Without spectrum access, we risk avoidable damage from weather.

Digital terrestrial television: The government-funded BBC (and other public service and private broadcasters) operate many television channels and radio broadcasting services—providing something for every member of the UK’s diverse population. They have vital but unmeasurable societal value and require different frequency bands for terrestrial broadcasting, satellite broadcasting, and digital platforms like DAB (Digital Audio Broadcasting) or DAB+ (an enhanced version of DAB).

Sitting on opposite sides of the spectrum

Traditionally, government agencies have been large owners of spectrum. And they have not been incentivized to use it efficiently. Currently, there is an all-or-nothing approach to spectrum, as certain bands function as excludable goods.

Mobile network operators have campaigned against this large government ownership model as they demand large swathes of spectrum, mainly to satiate the public’s demand for mobile data, but also to score spectrum as a valuable asset on their balance sheets—the 2000 3G spectrum auction raised over £20bn. They have pressured government agencies to sell parts of spectrum that are not in permanent use or that they wish to use.

And the knee-jerk reaction has been for the Treasury to sell, leading to a 2010 initiative to release or share 500 MHz of spectrum below 5 GHz, called the Public Sector Spectrum Release Programme; this was extended in 2016 to 750 MHz below 10 GHz by 2022. Spectrum released has enabled Ofcom to conduct auctions which raised money for HM Treasury.

The 2014 UK Government Spectrum Strategy focused on spectrum sharing as the most efficient use of spectrum. Yet, public services are still being squeezed out of bands to meet demands for cleared spectrum and to generate auction receipts. The country is itching for a new approach that enables sharing whilst protecting public services and capabilities.

Focusing on mobile at the expense of the country

The current shared assumption is, as Matt Galligan, co-founder of Circa puts it, that “the future of mobile is the future of everything”. And as mobile has an insatiable thirst for spectrum, spectrum allocation should be permanently diverted their way.

However, this path of no return hurts the government’s ability to deliver its policies and key capabilities, including defence, meteorology, research and development, and space.

This situation is particularly acute for the Ministry of Defence. While mobile network operators must provide excellent data services for the UK’s economy to prosper, without defence, there is no country. Mobile cannot outvie defence; Ukraine will attest to that.

But the MOD has a complicated relationship with spectrum. For instance, although a new-generation fighter aircraft might take fifteen years to enter service, it is essential to acquire the frequency bands the systems will use at the beginning of the design stage. If those frequency bands are sold off and reassigned to mobile operators midway through the process, the program will incur additional costs at a cost for the taxpayer. Budgets are tight—and unnecessary expenses are unacceptable.

Focusing on mobile at the expense of television is a different but equally significant example. Television is a social mechanism that has myriad benefits for a country, including binding the community together, offering a shared cultural experience, and providing elderly people with a vital service. Not giving television the spectrum it needs could mean damaging the fabric of society.

Value is what people are willing to pay for it

Despite our thirst for mobile, how much are people willing to pay for increased data consumption? According to Ofcom’s Communications Market Report 2022, the average person used 5.6GB of data per month in 2021: a 24% increase on the 4.5GB used per month in 2020, which is a 27% increase on the 3.6GB used per month in 2019. However, the average monthly spend on mobile and voice data has steadily decreased from a high in 2015 of £48.11 to £36.32 in 2021.

People are using more data, requiring more spectrum, purchased at great expense by mobile operators but paying less for it. Even Ofcom claims that “Mobile customers can often get more while paying less, particularly those buying services with a large data allowance.” With this more-for-less culture, it will be hard for mobile companies to sell the idea to customers that they should be paying more for the industry’s increased use of spectrum.

An economically efficient strategy would involve giving the public the amount of mobile data they are willing to pay for whilst protecting government capabilities. An optimal strategy is not a situation where only one actor can use spectrum but one where spectrum can be used dynamically.

What is dynamic spectrum access?

Dean Bubley, the founder of Disruptive Analysis, believes that, in the future, “Spectrum is shared much more, and more dynamically, for multiple uses, in multiple bands. Near real-time monitoring & AI models help minimise interference. Dedicated exclusive licenses still exist, but are rarely nationwide, and are the exception rather than default”.

Dynamic spectrum access is a strategy for optimizing spectrum use, allowing for efficient and flexible access to the electromagnetic spectrum. The strategy permits users to access spectrum on an opportunistic basis.

For example, if the new generation of fighter jets is not in service until 2040, their allocated frequency band will lie idle until they are in the air. Instead of being warehoused, this spectrum could be shared or leased, or released temporarily. Mobile network operators could have almost twenty years of spectrum use through dynamic spectrum access, which could be based on geolocation or time separation.

Based on geolocation, dynamic spectrum access is a system where wireless devices or networks dynamically access and use available spectrum resources based on their specific geographic position.

Conversely, based on time separation, dynamic spectrum access is a system where wireless devices or networks dynamically access available spectrum during specific time intervals. For example, spectrum used for military planes is only needed when a plane is flying. When it is not, the spectrum could be used by other users. Military missions are generally flown between working hours, while the internet rush hour is between 4–11 pm.

How could dynamic spectrum access work?

If all government spectrum was put into a ‘pot’, a tool such as game theory could be used to guide dynamic spectrum access—democratizing the spectrum by allowing multiple actors to use it.

The goal would be to allocate the finite resource in a way that maximizes overall efficiency and minimizes interference among users. Game theory can help to design strategies to achieve these objectives.

For example, if spectrum is unused by one government agency from 5 pm to 9 am, it could be auctioned and allocated to users based on their bids, which represent the value they place on spectrum use at one particular time. By formulating the auction as a game, different users would determine their bids strategically based on their own valuations and expectations of others' behaviour.

Auctioning is one tool; however, game theory provides a set of tools to analyse the strategic interactions and decision-making processes involved in dynamic spectrum access, enabling the design of mechanisms that encourage efficient spectrum usage among multiple users.

In fact, game theory has previously been used in the UK to manage the use of white spaces in television broadcasting frequency bands. The White Spaces Database (WSDB) model is a regulatory framework and database developed by the Federal Communications Commission (FCC) in the United States and Ofcom in the United Kingdom. The database uses algorithms influenced by game theory to dynamically allocate available white spaces among different users, ensuring interference-free coexistence.

AI is another available tool to help organize dynamic spectrum access. In a situation where bidding is not the best system due to insufficient demand, companies needing spectrum could enter into a computer program where they want to operate geographically and at what frequency range. Available spectrum could be used flexibly, and if the exact spectrum was not available, the system could make suggestions about other locations, frequencies, and power levels. This tool is already available but not used.

Sometimes, however, the best solution is the simplest one: spectrum could be made available for a minimal license cost, adjustable when demand gets too high.

The best outcome for the UK

Dynamic spectrum access is a flexible system for which more spectrum is available for more users at more times. In one case, a mobile operator might be granted a license for the next fifteen years. In another, a company might be able to gain additional spectrum capacity during internet rush hours. And in another, a user might be able to use 10 MHz of spectrum at one time during the day and a different 10 MHz in the same band at a different time. So long as users can be agile, they can access spectrum dynamically.

This flexible spectrum use method will allow commercial actors to dynamically use more spectrum whilst the country can still deliver a government policy that matters. NATO is also advocating for its members to adopt a Dynamic Spectrum Management philosophy “to optimize the use of RF spectrum and to extend spectrum sharing between the different military communities and between the military and civil users” to avoid military users from competing with global commercial players and to promote cooperation and coordination with civil administrations.

Government departments must retain control

Government departments must be able to use the spectrum when required. Dynamic spectrum sharing means that even if spectrum has been made available on a semi-fixed basis, if or when the security or geopolitical situation changes, the spectrum will be immediately returned to the government department without them incurring additional costs or having to be allocated different spectrum.

Unfortunately, in 2023, it is uncomfortably easy to imagine a situation in which the UK is at a heightened state of alert or must defend itself. In this context, all government departments will have increased communication needs, which understandably take priority over private citizens’ right to consume mobile data.

To avoid degrading national capabilities and potentially putting lives at risk, government departments must have the certainty that there will not be transmissions on the spectrum they need as this will cause interference which degrades their capabilities.

Prior notice is an important consideration in dynamic spectrum access. In some situations, it will be possible to issue a fifteen-year license—the spectrum may only need to be returned when a new airplane comes into service, for example. However, on other occasions, depending on the use case, government departments might only be able to give one month or 24 hours prior warning. The key is being sure that they can use the spectrum when they need it—if they have this assurance, they are likely to be enterprising when granting sharing access.

In situations when mobile network providers needed to ‘return’ the spectrum to government agencies, they would not need to switch off mobile. The time and date could be logged in a database, and the mobile network could automatically power down to an extent where it is still operational but not affecting military users.

Of course, there may be objections from commercial players who want unfettered access to bands without the caveats of dynamic spectrum sharing; however, national communications regulators must stipulate that spectrum sharing between different users is the default option—this would become the baseline situation.

Has dynamic spectrum access been successfully implemented?

In the US, the Citizens Broadband Radio Service (CBRS) is a wireless communication band that operates between 3550–3700 MHz. The FCC established CBRS to share spectrum dynamically between multiple entities, including government agencies, commercial users, and other organizations.

CBRS’s unique design has a three-tiered access framework: The first tier is reserved for users, such as government radar systems that have primary access to the band and are protected from interference. Second-tier licenses are auctioned and then allocated to specific entities. And the third tier allows unlicensed users to access the CBRS spectrum on a shared basis.

CBRS has been a success by providing a logical hierarchy of spectrum access and opening up new opportunities for innovative wireless services. Its greatest boon is having expanded a finite spectrum for different users and industries.

What essential elements can make dynamic spectrum access a reality?

Dynamic spectrum access is not easy to implement. There are several technical issues, such as ensuring the sensing receivers pick up priority signals with a very high probability, overcoming inefficiencies with the data transmission protocol, and addressing changes in the regulations or changes of frequency bands.

Moreover, the specific requirements will vary depending on the implementation approach and the specific goals of the dynamic spectrum access system.

As such, no one silver RF device can overcome all the challenges inherent in implementing a dynamic spectrum access programme. It is likely that a combination of paper regulations, Listen Before Talk (LBT) etiquette, and RF spectrum sensing receivers will be needed. 

However, efficient spectrum sensing is a fundamental part of the process as it involves detecting and monitoring the availability and occupancy of spectrum bands.

Therefore, easy-to-use spectrum sensing hardware, such as radio frequency receivers and high-end software defined radios, are excellent tools for capturing and analysing radio signals in a given frequency band.

Any spectrum sensing receiver for dynamic spectrum access must have high sensitivity, be easy to install, have networked control of all sensing receivers, and be durable and long-lasting.

Conclusion

Government and business need not compete. By finding and implementing dynamic and flexible ways to share resources they both rely on, they can strengthen the UK’s economy, security, and society. Implementation will not be easy, but a successful dynamic spectrum access programme would allow the country to share a vital and limited resource.