While Low-Band Spectrum Is "beachfront property," Mid-Bands Offer Higher Capacities Needed For 5G

And some mid-bands are more accessible with better ecosystem support

Rather like with real estate, while beachfront properties are coveted, properties elsewhere providing more space and better access can be the most useful.

Cellular technologies have improved to utilize the greater capacity in the larger bandwidths—including in mmWave bands with 5G—that is needed to satisfy the massive growth in mobile data. Much of the radio spectrum—including frequencies between 2.5 GHz and 3.5 GHz—that used to be deemed less than ideal for cellular and which were termed “high-band” are now very highly sought-after and defined as “mid-band.” 

The newly-announced US FCC allocation of an additional 117 MHz bandwidth at 2.5 GHz is in response to strong carrier demand for mid-band spectrum. While spectrum allocations vary from nation to nation, the supply ecosystem for chips and devices is driven by scale of demand globally. Band support is fastest and strongest where most large nations are deploying, as with Band n78 at 3.5 GHz for 5G.

But the physics of radio waves has not changed: propagation characteristics of the lower bands continue to make them most suited for broad rural coverage and penetration into buildings where most mobile data is consumed. Thankfully, however, even mmWave deployments within buildings, along with WiFi can satisfy most demand there. 

Service expectations of consumers and governments are rising in all respects, as is the need for a wide range of frequency band allocations. Regulators, including the FCC, and the market are responding accordingly with an ever-increasing supply of spectrum for 5G.

Lows and alternative highs

Carriers today generally deploy frequencies below 2 GHz, and ideally sub gigahertz, to provide a coverage beachhead including in-building penetration. 

In the FCC’s 2014 Report and Order entitled Policies Regarding Mobile Spectrum Holdings Expanding the Economic and Innovation Opportunities of Spectrum Through [600MHz] Incentive Auctions it defined low-band as spectrum below 1GHz and used the term high-band implicitly to mean everything above that. 

AT&T and Verizon were limited by FCC in their eligibility to bid in auction for the 600MHz spectrum because they were deemed by FCC to hold 73 percent of all “suitable and available” spectrum below 1 GHz.

In drumming-up interest and demand for that auction, the FCC stated in its report that the “Incentive Auction represents the last opportunity in the foreseeable future for providers to acquire licenses for below-1-GHz spectrum at auction.”

It was not until a couple of years later that significant consideration was given to using mmWave for cellular, with these wavelengths first being included for standardization, in 5G, in 2018 with 3GPP’s Release 15.  In my September 2018 Analyst Angle, I explained how crucially important mmWave spectrum is for expansion of network capacity and how this is ensuring deployment and success of 5G technology. According to a report by 5G Americas, a total of between 5.5 GHz to potentially 9.4 GHz of spectrum bandwidth could become available in the US.

While addition of such high-band spectrum is highly desirable or essential, it is insufficient. Carriers also need spectrum below 6GHz for capacity or coverage expansion.

Two-way street

The upcoming release of more 2.5 GHz spectrum will be in county-sized licenses in two 50 megahertz blocks and one 16.5 megahertz block. According to FCC Chairman Ajit Pai, “This is the single largest contiguous swath of mid-band spectrum below 3 gigahertz in the nation.”  Sprint already has more than 150 MHz in this band and covers 100 US metro areas. 

This spectrum band was unusable with mobile technologies until the introduction of mobile WiMAX around 2008 because it was unpaired spectrum requiring Time Division Duplex technology. Hitherto, even WiMAX provided only fixed-wireless access. All the mainstream 2G and 3G cellular technologies including CDMA, GSM and WCDMA were only available with Frequency Division Duplex mode of operation, which required the use of paired spectrum. LTE was standardized including FDD and TDD modes.  Use of unpaired spectrum with LTE-TDD is now quite common and TDD mode is also used in 5G. 

The chip and device supply ecosystem stepped up in response to widespread carrier demand for LTE-TDD, significantly driven by the large Chinese market from the end of 2013.

Digital divide

Mobile broadband is increasingly the means by which many people everywhere —particularly those in rural areas or on low incomes—access the Internet primarily, or at all. Many have no wireline Internet access—by choice, or because it is not available where they are.

The aforementioned 2014 FCC report noted the US Department of Justice’s ‘concern that because of the superior propagation characteristics of low-band spectrum, a service provider’s holdings of such spectrum may be an important factor in determining its “ability to compete in offering coverage across a broad service area, including its ability to provide coverage efficiently in rural areas.”’ However, while limited amounts of low-band spectrum could reduce the number of carriers able to provide service in rural areas, capacity is not a constraint where there are relatively few users.  It is the low population densities and overall low subscriber numbers that make rural deployments economically challenging for carriers.

Re-farming to reach the ranch

There is still enormous potential to open up large amounts of additional spectrum to 5G in mmWave spectrum bands, and moderate potential to do so in the mid-bands. While the physics also dictates there is less bandwidth below 1 GHz than in higher bands, it is remarkable how much low-band spectrum has been re-farmed for mobile communications from other uses such TV broadcasting in the last 15 years and how new technologies have dramatically increased spectral efficiencies in all bands. As technologies developed in cellular communications are increasingly adopted elsewhere, this will allow economic forces to continue to encourage all spectrum users—including government and commercial—to upgrade to more bandwidth-efficient technologies and release spectrum from low-, medium-, and high-bands to where its use is most valuable.  Multi-billion-dollar auction receipts for a wide range of frequency bands show that cellular continues to be where such value lies. 

The FCC is now optimistic about the outlook for the new licensing of low-, medium- and high-band spectrum. In its December 2018 Communications Marketplace Report, it stated the “the Commission will continue to make available a significant amount of additional spectrum over the next two years across a range of low-, mid-, and high-band frequencies to ensure a vibrantly competitive mobile wireless services marketplace.”

Low-, mid- and high-band spectrum are all important for 5G. Shared and unlicensed spectrum is supplementing licensed allocations for mobile communications. To support the wide range of applications and services envisaged including eMBB, IoT, connected cars and a whole lot more, regulators, including the FCC, and the market are responding. The supply of spectrum for 5G will continue to increase substantially in the coming years.

Keith Mallinson has more than 25 years of experience in the Telecommunications Industry: as a research analyst, consultant and testifying expert witness. Complementing his industry focus, he has a broad skill set including technologies, market analysis, regulation, economics and finance. Prior to founding WiseHarbor in 2006, Mallinson led Yankee Group's global Wireless/Mobile research and consulting team as Executive Vice President, based in Boston, from 2000. Until then, he had overall responsibility for the firm's European division, as Managing Director from 1995. Prior to that he was the European Research Director.

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