Spectrum in the USA - an overview of today and a new tomorrow.

This week (Week 17, 2023), I submitted my comments and advice titled "Development of a National Spectrum Strategy (NSS)" to the United States National Telecommunications & Information Administration (NTIA) related to their work on a new National Spectrum Strategy.

Of course, one might ask why, as a European, bother with the spectrum policy of the United States. So hereby, a bit of reasoning for bothering with this super interesting and challenging topic of spectrum policy on the other side of the pond.

A European in America.

As a European coming to America (i.e., USA) for the first time to discuss the electromagnetic spectrum of the kind mobile operators love to have exclusive access to, you quickly realize that Europe's spectrum policy/policies, whether you like them or not, are easier to work with and understand. Regarding spectrum policy, whatever you know from Europe is not likely to be the same in the USA (though physics is still fairly similar).

I was very fortunate to arrive back in the early years of the third millennium to discuss cellular capacity and, as it quickly evolves ("escalates"), too, having a discussion of available cellular frequencies, the associated spectral bandwidth, and whether they really need that 100 million US dollar for radio access expansions.

Why fortunate?

I was one of the first (from my company) to ask all those "stupid" questions whenever I erroneously did not just assume things surely must be the same as in Europe and ended up with the correct answer that in the USA, things are a "little" different and a lot more complicated in terms of the availability of frequencies and what feeds the demand ... the spectrum bandwidth. My arrival was followed by "hordes" of other well-meaning Europeans with the same questions and presumptions, using European logic to solve US challenges. And that doesn't really work (surprised you not should be). I believe my T-Mobile US colleagues and friends over the years surely must have felt like Groundhog Day all over again at every new European visit.

Comparing apples and oranges.

Looking at US spectrum reporting, it is important to note that it is customary to provide the total amount of spectrum. Thus, for FDD spectrum bands, including both the downlink spectrum portion and uplink spectrum part of the cellular frequency band in question. For example, when a mobile network operator (MNO) reports that it has, e.g., 40 MHz of AWS1 spectrum in San Diego (California), it means that it has 2x20 MHz (or 20+20 MHz). Thus, 20 MHz of downlink (DL) services and 20 MHz of uplink (UL) services. For FDD, both the DL and the UL parts are counted. In Europe, historically, we mainly would talk about half the spectrum for FDD spectrum bands. This is one of the first hurdles to get over in meetings and discussions. If not sorted out early can lead to some pretty big misunderstandings (to say the least). To be honest, and in my opinion, providing the full spectrum holding, irrespective of whether a band is used as FDD or TDD, is less ambiguous than the European tradition.

The second "hurdle" is to understand that a USA-based MNO is likely to have a substantial variation in its spectrum holdings across the US geography. An MNO may have a 40 MHz (i.e., 2x20 MHz) PCS spectrum in Los Angeles (California) and only 30 MHz (2x15 MHz) of the same spectrum in New York or only 20 MHz (2x10 MHz) in Miami (Florida). For example, FCC (i.e., the regulator managing non-federal spectrum) uses 734 so-called Cellular Market Areas or CMAs, and there is no guarantee that a mobile operator's spectrum position will remain the same over these 734 CMAs. Imagine Dutch (or other European) mobile operators having a varying 700 MHz (used for 5G) spectrum position across the 342 municipalities of The Netherlands (or another European country). It takes a lot of imagination ... right? And maybe why, we Europeans, shake our heads at the US spectrum fragmentation, or market variation, as opposed to our nice, neat, and tidy market-wise spectrum uniformity. But is the European model so much better (apart from being neat & tidy)? ...

... One may argue that the US model allows for spectrum acquisition to be more closely aligned with demand, e.g., less spectrum is needed in low-population density areas and more is required in high-density population areas (where demand will be much more intense). As evidenced by many US auctions, the economics matched the demand fairly well. While the European model is closely aligned with our good traditions of being solid on average ... with our feet in the oven and our head in the freezer ... and on average all is pretty much okay in Europe.

Figure 1 and 2 below illustrates a mobile operator difference between its spectrum bandwidth spread across the 734 US-defined CMAs in the AWS1 band and how that would look in Europe.

Figure 2 below is visually an even stronger illustration of mobile operator bandwidth variation across the 734 cellular market areas. The dashed white horizontal line is if the PCS band (a total of 120 MHz or 2x60 MHz) would be shared equally between 4 main nationwide mobile operators ending up at 30 MHz per operator across all CMAs. This would resemble what today is more or less a European situation, i.e., irrespective of regional population numbers, the mobile operator's spectrum bandwidth at a given carrier frequency would be the same. The European model, of course, also implies that an operator can provide the same quality in peak bandwidth before load may become an issue. The high variation in the US operator's spectrum bandwidth may result in a relatively big variation in provided quality (i.e., peak speed in Mbps) across the different CMAs.

There is an alternative approach to spectrum acquisition that may also be more spectrally efficient, which the US model is much more suitable for. Aim at a target Hz per Customer (i.e., spectral overhead) and keep this constant within the various market. Of course, there is a maximum realistic amount of bandwidth to acquire, governed by availability (e.g., for PCS, that is, 120 MHz) and competitive bidders' strength. There will also be a minimum bandwidth level determined by the auction rules (e.g., 5 MHz) and a minimum acceptable quality level (e.g., 10 MHz). However, Figure 2 below reflects more opportunistic spectrum acquisition in CMAs with less than a million population as opposed to a more intelligent design (possibly reflecting the importance of, or lack of, different CMAs to the individual operators).

Thirdly, so-called exclusive use frequency licenses (as opposed to shared frequencies), as issued by FCC, can be regarded accounting-wise as an indefinitely-lived intangible asset. Thus, once a US-based cellular mobile operator has acquired a given exclusive-use license, that license can be considered disposable to the operator in perpetuity. It should be noted that FCC licenses typically would be issued for a fixed (limited) period, but renewals are routine.

This is a (really) big difference from European cellular frequency licenses that typically expire after 10 - 20 years, with the expired frequency bands being re-auctioned. A European mobile operator cannot guarantee its operation beyond the expiration date of the spectrum acquired, posing substantial existential threats to business and shareholder value. In the USA, cellular mobile operators have a substantially lower risk regarding business continuity as their spectrum, in general, can be regarded as theirs indefinitely.

FCC also operates with a shared-spectrum license model, as envisioned by the Citizens Broadband Radio Service (CBRS) in the 3.55 to 3.7 GHz frequency range (i.e., the C-band). A shared-spectrum license model allows for several types of users (e.g., Federal and non-Federal) and use-cases (e.g., satellite communications, radar applications, national cellular services, local community broadband services, etc..) to co-exist within the same spectrum band. Usually, such shared licenses come with firm protection of federal (incumbent) users that allows commercial use to co-exist with federal use, though with the federal use case taking priority over the non-federal. A really good overview of the CBRS concept can be found in "A Survey on Citizens Broadband Radio Service (CBRS)" by P. Agarwal et al.. Wireless Innovation Forum published on 2022 a piece on "Lessons Learned from CBRS" which provides a fairly nuanced, although somewhat negative, view on spectrum sharing as observed in the field and within the premises of the CBRS priority architecture and management system.

Recent data around FCC's 3.5 GHz (CBRS) Auction 105 would indicate that shared-licensed spectrum is valued at a lower US$-per-MHz-pop (i.e., 0.14 $-per-MHz-pop) than exclusive-use license auctions in 3.7 GHz (Auction 107; 0.88 $-per-MHz-pop) and 3.45 GHz (Auction 110; 0.68 $-per-MHz-pop). The duration of the shared-spectrum license in the case of the Auction 105 spectrum is 10 years after which it is renewed. Verizon and Dish Networks were the two main telecom incumbents that acquired substantial spectrum in Auction 105. AT&T did not acquire and T-Mobile US only picked close to nothing (i.e., 8 licenses).

The state of cellular performance - in the United States and the rest of the World.

Irrespective of how one feels about the many mobile cellular benchmarks around in the industry (e.g., Ookla Speedtest, Umaut benchmarking, OpenSignal, etc...), these benchmarks do give an indication of the state of networks and how those networks utilize the spectral resources that mobile companies have often spend hundreds of millions, if not billions, of US dollars acquiring and not to underestimate in cost and time, spectrum clearing or perfecting a "second-hand" spectrum may incur for those operators.

So how do US-based mobile operators perform in a global context? We can get an impression, although very 1-dimensional, from Figure 1 below.

Ookla's Speedtest rank (see Figure 3 above) positions the United States cellular mobile networks (as an average) among the Top-20. Depending on the ambition level, that may be pretty okay or a disappointment. However, over the last 24 months, thanks to the fast 5G deployment pace at 600 MHz, 2.5 GHz, and C-band, the US has leapfrogged (on average) its network quality which for many years did not improve much due to little spectrum availability and huge capital investment levels. Something that the American consumer can greatly enjoy irrespective of the relative mobile network ranking of the US compared to the rest of the world. South Korea and Norway are ranked 3 and 4, respectively, regarding cellular downlink (DL) speed in Mbps. The above figure also shows a significant uplift in the speed at the time of introducing 5G in the cellular operators' networks worldwide.

How to understand the supplied cellular network quality and capacity that the consumer demand and hopefully also enjoy? Let start with the basics:

We might be able to understand some of the dynamics of Figure 3 using Figure 4, which illustrates the fundamental cellular quality (and capacity) relationship with frequency bandwidth, spectral efficiency, and the number of cells (or sectors or sites) deployed in a given country.

Thus, a mobile operator can improve its cellular quality (and capacity) by deploying more spectrum acquired on its existing network, for example, by auctions, leasing, sharing, or other arrangements within the possibilities of whatever applicable regulatory regime. This option will exhaust as the operator's frequency spectrum pool is deployed across the cellular network. It leaves an operator to wait for an upcoming new frequency auction or, if possible, attempt to purchase additional spectrum in the market (if regulation allows) that may ultimately include a merger with another spectrum-rich entity (e.g., AT&T attempt to take over T-Mobile US). All such spectrum initiatives may take a substantial amount of time to crystalize, while customers may experience a worsening in their quality. In Europe, the licensed spectrum becomes available in cycles of 10 - 20 years. In the USA, exclusive-use licensed spectrum typically would be a once-only opportunity to acquire (unless you acquire another spectrum-holding entity later, e.g., Metro PCS, Sprint, AT&T's attempt to acquire T-Mobile, ...).

Another part of the quality and capacity toolkit is for the mobile operator to choose appropriately spectral efficient technologies that are supported by a commercially available terminal ecosystem. Firstly, migrate frequency and bandwidth away from currently deployed legacy radio-access technology (e.g., 2G, 3G, ...) to newer and spectrally more efficient ones (e.g., 4G, 5G, ...). This migration, also called spectral re-farming, requires a balancing act between current legacy demand versus the future expectations of demand in the newer technology. In a modern cellular setting, the choice of antenna technology (e.g., massive MiMo, advanced antenna systems, ...) and type (e.g., multi-band) is incredibly important for boosting quality and capacity within the operators' cellular networks. Given that such choices may result in redesigning existing site infrastructure, it provides an opportunity to optimize the existing infrastructure for the best coverage of the consolidated spectrum pool. It is likely that the existing infra was designed with a single or only a few frequencies in mind (e.g., PCS, PCS+AWS, ...) as well as legacy antennas, and the cellular performance is likely improved by considering the complete pool of frequencies in the operator's spectrum holding. The mobile operator's game should always be to achieve the best possible spectral efficiency considering demand and economics (i.e., deploying 64x64 massive MiMo all over a network may be the most spectrally efficient solution, theoretically, but both demand and economics would rarely support such an apparently "silly" non-engineering strategy). In general, this will be the most frequently used tool in the operators' quality/capacity toolkit. I expect to see an "arms race" between operators deploying the best and most capable antennas (where it matters), as it will often be the only way to differentiate in quality and capacity (if everything else is almost equal).

Finally, the mobile operator can deploy more site locations (macro and small cells), if permitting allows, or more sectors by sectorization (e.g., 3 → 4, 4 → 5 sectors) or cell split if the infrastructure and landlord allows. If there remains unused spectral bandwidth in the operator's spectrum pool, the operator may likely choose to add another cell (i.e., frequency band) to the existing site. Particular adding new site locations (macro or small cell) is the most complex path to be taken and, of course, also often the least economic path.

Thus, to get a feeling for the Ookla Speedtest, which is a country average, results of Figure 3, we need, as a starting point, to have the amount of spectral bandwidth for the average cellular mobile operator. This is summarised in below's Table 1.

It does not take too long to observe that there is only an apparently rather weak correlation between spectrum bandwidth (sub-total and total) and the observed DL speed (even after rescaling to downlink spectrum only). Also, what is important is, of course, how much of the spectrum is deployed. Typically low and medium bands will be deployed extensively, while other high-frequency bands may only have been selectively deployed, and the C-band is only in the process of being deployed (where it is available). What also plays a role is to what degree 5G has been rollout across the network, how much bandwidth has been dedicated to 5G (and 4G), and what type of advanced antenna system or massive MiMo capabilities has been chosen. And then, to provide a great service, a network must have a certain site density (or coverage) compared to the customer's demand. Thus, it is to be expected that the number of mobile site locations, and the associated number of frequency cells and sectors, will play a role in the average speed performance of a given country.

Figure 5 shows that load (e.g., customers per site) and available capacity (e.g., sites x bandwidth) relative to customers are strongly correlated with the experienced quality (e.g., speed in Mbps). The comparison between the United States and China is interesting as both countries with a fairly similar surface area (i.e., 9.8 vs. 9.6 million sq. km), the USA has a little less than a quarter of the population, and the average mobile US operator would have about one-third of the customers compared to the average Chinese operator (note: China mobile dominates the average). The Chinese operator, ignoring C-band, would have ca. 25 MHz or ~+20% (~50 MHz or ca. +10% if C-band is included) more than the US operator. Regarding sites, China Mobile has been reported to have millions of cell site locations (incl. lots of small cells). The US operator's site count is in the order of hundreds of thousands (though less than 200k currently, including small cells). Thus, Chinese mobile operators have between 5x to 10x the number of site locations compared to the American ones. While the difference in spectrum bandwidth has some significance (i.e., China +10% to 20% higher), the huge relative difference in site numbers is one of the determining factors in why China (i.e., 117 Mbps) gets away with a better speed test score that is better than the American one (i.e., 85 Mbps). While theoretically (and simplistically), one would expect that the average Chinese mobile operator should be able to provide more than twice the speed as compared to the American mobile operator instead of "only" about 40% more, it stands to show that the radio environment is a "bit" more complex than the simplistic view.

Of course, the US-based operator could attempt to deploy even more sites where it matters. However, I very much doubt that this would be a feasible strategy given permitting and citizen resistance to increasing site density in areas where it actually would be needed to boost the performance and customer experience.

Thus, the operator in the United States must acquire more spectrum bandwidth and deploy that where it matters to their customers. They also need to continue to innovate on leapfrogging the spectral efficiency of the radio access technologies and deploy increasingly more sophisticated antenna systems across their coverage footprint.

In terms of sectorization (at existing locations), cell split (adding existing spectrum to an existing site), and/or adding more sophisticated antenna systems is a matter of Capex prioritization and possibly getting permission from the landlord. Acquiring new spectrum ... well, that depends on such new spectrum somehow becomes available.

Where to "look" for more spectrum?

Where would more spectrum come from?

Within the so-called "beachfront spectrum" covering the frequency range from 225 MHz to 4.2 GHz (according to NTIA), only about 30% (ca. 1GHz of bandwidth within the frequency range from 600 MHz to 4.2 GHz) is exclusively non-Federal, and mainly with the mobile operators as exclusive use licenses deployed for cellular mobile services across the United States. Federal authorities exclusively use a bit less than 20% (~800 MHz) for communications, radars, and R&D purposes. This leaves ca. 50% (~2 GHz) of the beachfront spectrum shared between Federal authorities and commercial entities (i.e., non-Federal).

For cellular mobile operators, exclusive use licenses would be preferable (note: at least at the current state of the relevant technology landscape) as it provides the greatest degree of operational control and possibility to optimize spectral efficiency, avoiding unacceptable levels of interference either from systems or towards systems that may be sharing a given frequency range.

The options for re-purposing the Federal-only spectrum (~800 MHz) could, for example, be either (a) moving radar systems' operational frequency range out of the beachfront spectrum range to the degree innovation and technology supports such a migration, (b) modernizing radar systems with a focus of making these substantially more spectrally efficient and interference-resistant, (c) migrated federal-only communications services to commercially available systems (e.g., 5G federal-only slicing) similar to the trend of migrating federal legacy data centers to the public cloud. Within the shared frequency portion with the ~2 GHz of bandwidth, it may be more challenging as considerable commercial interests (other than mobile operators) have positioned that business at and around such frequencies, e.g., within the CBRS frequency range. This said, there might also be opportunities within the Federal use cases to shift applications towards commercially available communication systems or to shift them out of the beachfront range. Of course, in my opinion, it always makes sense to impose (and possibly finance) stricter spectral efficiency conditions, triggering innovation on federal systems and commercial systems alike within the shared portion of the beachfront spectrum range. With such spectrum strategies, it appears compelling that there are high likelihood opportunities for creating more spectrum for exclusive license use that would safeguard future consumer and commercial demand and continuous improvement of customer experience that comes with the future demand and user expectations of the technology that serves them.

I believe that the beachfront should be extended beyond 4.2 GHz. For example aligning with band-79, whose frequency range extends from 4.4 GHz to 5 GHz, allows for a bandwidth of 600 MHz (e.g., China Mobile has 100 MHz in the range from 4.8 GHz to 4.9 GHz). Exploring additional re-purposing opportunities for exclusive use licenses in what may be called the extended beachfront frequency range from 4.2 GHz up to 7.2 GHz should be conducted with priority. Such a study should also consider the possibility of moving the spectrum under exclusive and shared federal use to other frequency bands and optimizing the current federal frequency and spectrum allocation.

The NTIA, that is, the National Telecommunications and Information Administration, is currently (i.e., 2023) for the United States developing a National Spectrum Strategy (NSS) and the associated implementation plan. Comments and suggestions to the NSS were possible until the 18th of April, 2023. The National Spectrum Strategy should address how to create a long-term spectrum pipeline. It is clear that developing a coherent national spectrum strategy is critical to innovation, economic competition, national security, and maybe re-capture global technology leadership.

So who is the NTIA? What do they do that FCC doesn't already do? (you may possibly ask).

Who manages what spectrum?

Two main agencies in the US manage the frequency spectrum, the FCC and the NTIA.The Federal Communications Commission, the FCC for short, is an independent agency that exclusively regulates all non-Federal spectrum use across the United States. FCC allocates spectrum licenses for commercial use, typically through spectrum auctions. A new or re-purposed commercialized spectrum has been reclaimed from other uses, both from federal uses and existing commercial uses. Spectrum can be re-purposed either because newer, more spectrally efficient technologies become available (e.g., the transition from analog to digital broadcasting) or it becomes viable to shift operation to other spectrum bands with less commercial value (and, of course, without jeopardizing existing operational excellence). It is also possible that spectrum, previously having been for exclusive federal use (e.g., military applications, fixed satellite uses, etc..), can be shared, such as the case with Citizens Broadband Radio Service (CBRS), which allows non-federal parties access to 150 MHz in the 3.5 GHz band (i.e., band 48). However, it has recently been concluded that (centralized) dynamic spectrum sharing only works in certain use cases and is associated with considerable implementation complexities. Multiple parties with possible vastly different requirements co-existence within a given band is very much work-in-progress and may not be consistent with the commercialized spectrum operation required for high-quality broadband cellular operation.

In parallel with the FCC, we have the National Telecommunications and Information Administration, NTIA for short. NTIA is solely responsible for authorizing Federal spectrum use. It also acts as the President of the United State's principal adviser on telecommunications policies, coordinating the views of the Executive Branch. NTIA manages about 2,398 MHz (69%) within the so-called "beachfront spectrum" range of 225 MHz to 3.7 GHz (note: I would let that Beachfront go to 7 GHz, to be honest). Of the total of 3,475 MHz, 591 MHz (17%) is exclusively for Federal use, and 1,807 MHz (52%) is shared (or coordinated) between Federal and non-Federal. Thus, leaving 1,077 MHz (31%) for exclusive commercial use under the management of the FCC. NTIA, in collaboration with the FCC, has been instrumental in the past in freeing up substantial C-band spectrum, 480 MHz in total, of which 100 MHz is conditioned on prioritized sharing (i.e., Auction 105), for commercial and shared use that subsequently has been auctioned off over the last 3 years raising US$ 109 billion (ca. $0.68 per MHz-pop vs $0.13 per MHz-pop in Europe and $0.23 per MHz-pop in APAC ... remember US spectrum can be regarded as an indefinite-lived intangible asset while European spectrum rights expire between 10 and 20 years).

NTIA and FCC jointly manage all the radio spectrum, licensed (e.g., cellular mobile frequencies, TV signals, ...) and unlicensed (e.g., WiFi, MW Owens, ...) of the United States, NTIA for Federal use, and FCC for non-Federal use (put simply). FCC is responsible for auctioning spectrum licenses and is also authorized to redistribute licenses.

Acknowledgment.

I greatly acknowledge my wife,?Eva Varadi,?for her support, patience, and understanding during the creative process of writing this article. Of course, throughout the years of being involved in T-Mobile US spectrum strategy, I have enjoyed many discussions and debates with US-based spectrum professionals, bankers, T-Mobile US colleagues, and very smart regulatory policy experts in Deutsche Telekom AG. I have the utmost respect for their work and the challenges they have faced and face. For this particular work, I cannot thank Roslyn Layton, PhD enough for nudging me into writing the comments to NTIA. By that nudge, this little article is a companion to my submission about the US Spectrum as it stands today and what I would like to see with the upcoming National Spectrum Strategy. I very much recommend reading Roslyn's far more comprehensive and worked-through comments to the NTIA NSS request for advice. A final thank you to John Strand (who keeps away from Linkedin;-) of Strand Consult for challenging my way of thinking and for always stimulating new ways of approaching problems in our telecom sector. I very much appreciate our discussions.

Additional material.

1. Ronald Harry Coase, "The Federal Communications Commission", The Journal of Law & Economics, Vol. 2 (October 1959), pp. 1- 40. In my opinion, a must-read for anyone who wants to understand the US spectrum regulation and how it came about.
2. Kenneth R. Carter, "Policy Lessons from Personal Communications Services: Licensed vs. Unlicensed Spectrum Access," 2006, Columbus School of Law. An interesting perspective on licensed and unlicensed spectrum access.
3. Federal Communication Commission (FCC) assigned areas based on the relevant radio licenses. See also FCC Cellular Market Areas (CMAs).
4. FCC broadband PCS band plan, UL:1850-1910 MHz & DL:1930-1990 MHz, 120 MHz in total or 2x60 MHz.
5. Understanding Federal Spectrum Use is a good piece from NTIA about the various federal use of spectrum in the United States.
6. Ookla's Speedtest Global Index for February 2023. In order to get the historical information use the internet archive, also called "The Wayback Machine."
7. I make extensive use of the Spectrum Monitoring site, which I can recommend as one of the most comprehensive sources of frequency allocation data worldwide that I have come across (and is affordable to use).
8. FCC Releases Rules for Innovative Spectrum Sharing in 3.5 GHz Band.
9. 47 CFR Part 96—Citizens Broadband Radio Service. Explain the hierarchical spectrum-sharing regime of and priorities given within the CBRS.