While 5G presents some big opportunities for wireless operators in terms of new services and capabilities, it also requires that operators have access to large amounts of spectrum — specifically mid-band spectrum — to make it a reality. 

Dynamic spectrum sharing (DSS) is an important part of the 5G roadmap because it makes it possible for a mobile operator to flexibly allocate spectrum across low-, mid-, and high-band frequencies and dynamically switch between LTE and 5G New Radio coverage based upon their network traffic demands. That means that an operator can leverage DSS to deliver the best possible performance and coverage on their network for the mix of 4G and 5G subscribers that they have. 

GlobalData senior analyst Ed Gubbins says that the value of DSS really depends upon the operator’s spectrum assets and its 5G rollout plans. For example, some operators aren’t going to use overlapping spectrum for 4G and 5G so they won’t need DSS. Others, however, will want to use existing 4G spectrum for 5G and DSS will allow them to share the same spectrum and make adjustments based upon how quickly customers are migrating from 4G to 5G. The ability to make adjustments on the fly is critical because it allows operators to be more efficient with their spectrum. 

It often takes years for these regulatory authorities to make spectrum available for mobile use.

Scarce resources 

According to the GSMA, a global wireless industry trade group, mobile operators need between 80-100 MHz of contiguous mid-band spectrum and about 1 GHz of high-band spectrum, such as millimeter wave (mmWave), to deploy 5G. Low-band spectrum is also needed for 5G coverage across urban, suburban and rural areas and to provide support for such services as the Internet of Things.  

But spectrum is a finite resource that is carefully managed by governments and regulatory authorities around the world. It often takes years for these regulatory authorities to make spectrum available for mobile use. Because of this, many wireless operators are lacking enough spectrum to quickly deploy 5G across a broad footprint. Regulators are scurrying to make more spectrum available. In the U.S. the Federal Communications Commission (FCC) is currently holding an auction of 70 MHz of the 3.5 GHz Citizens Broadband Radio Services (CBRS) spectrum and in December it plans to hold another auction of 280 MHz of C-band spectrum, which is between the 3.7 GHz and 4.2 GHz bands.

However, in some regions of the world spectrum auctions are being postponed because of the COVID-19 pandemic. For example, Canada postponed its 5G spectrum auction of 3.5 GHz spectrum that was originally scheduled for late this year until June 2021. India also is delaying its 5G auction of 5G spectrum in the 3.3 GHZ- 3.6 GHz range that was originally scheduled for April. It will likely now occur in September or later. And Poland’s regulatory commission has suspended the deadline for operators to submit bids for its 5G spectrum auction in the 3.6 GHz band. A new deadline has not yet been determined. 

DSS today

In the U.S. market, AT&T in June became the first mobile operator to deploy DSS but so far it has only deployed it in portions of its network in Texas and Florida. But AT&T insists that DSS will play an important role in its nationwide 5G plans. In a blog post written by Igal Elbaz, senior vice president of wireless technology and experience delivery at AT&T, he called DSS a “stepping stone” on AT&T’s path to nationwide 5G and said it enabled AT&T to bypass the process of refarming spectrum and make it faster for the company to get transition to 5G. In late July AT&T announced that its 5G network was now available nationwide, covering 205 million customers. 

Verizon also has been an outspoken proponent of DSS. In June the operator announced it was actively testing DSS on its network and plans to deploy it throughout its network later this year. In the company’s second quarter earnings call with investors on July 24, CEO Hans Vestberg said that the company’s tests with DSS are going very well and hinted that it will be using the technology for the company’s nationwide 5G network this year. Verizon has mmWave-based mobile 5G service available in parts of 35 cities and plans to expand that to 60 cities by the end of the year.  

Other operators around the world have also expressed interest in deploying DSS in their networks. Swisscom in Switzerland announced last November that it had completed the first over-the-air 5G data call using DSS. The call was conducted at the company’s Digital Lab and used the 3.6 GHz spectrum. 

Mark Lowenstein, managing director of Mobile Ecosystem, said in a blog post that most DSS solutions just require a software upgrade on the network side and devices that support DSS. Those devices require Qualcomm’s newer X55 chipset, which is available in a handful of phones today with more expected later this year. 

Infrastructure vendor Nokia says that a form of DSS actually was first deployed back in the 4G era when some of its operator customers wanted to use the low-band spectrum they were currently using for 2G services for 4G. Instead of refarming all the spectrum for 4G, Nokia’s 2G-4G DSS solution made it possible for an operator to deploy LTE and increase its voice-over-LTE traffic and also boost data traffic while at the same time maintaining the same quality of service for its existing legacy 2G users.  In a blog post written by Harry Kuosa, Nokia’s head of single RAN and zero emissions marketing, he said Nokia has commercialized three different DSS solutions that support different frequency bands. 

Potential downside 

But DSS may have a downside. As more consumers flock to 5G and consume more bandwidth, that could have an impact on the user experience for both the 4G customers and the 5G customers. T-Mobile’s President of Technology Neville Ray alluded to this problem during the company’s fourth quarter 2019 earnings call. “It’s going to be a tough year on DSS,” Ray said. And while he admitted that T-Mobile has been a proponent of the technology, he added that as they started testing it, they noticed potential issues with spectrum capacity. 

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“We’re seeing as we learn more, that as you deploy DSS it kind of eats away on the net capacity of the shared radio,” Ray said. 

Of course, T-Mobile, with its recent acquisition of Sprint, now has access to about 175 MHz of 2.5 GHz spectrum in major markets around the U.S. making it less dependent upon DSS to deploy nationwide 5G than some of its competitors. 

Other operators such as Verizon and AT&T disagree with Ray’s assessment and say they have not seen any capacity issues in their DSS tests. 

Potential bandwidth issues aside, DSS offers operators an elegant way to use existing 4G spectrum to deploy 5G and acts as a stopgap measure to meet consumer demand for 5G without waiting for additional spectrum to be made available through auctions.  DSS will likely be a technology that we will hear more about in the months ahead as operators begin to expand their 5G reach.