Here are three words that aren’t at the tip of your average tongue when talking about 5G: Dynamic Spectrum Sharing (DSS). Yet, in this early stage of 5G, DSS could provide an important stepping stone to rolling out broader 5G coverage more quickly. And it could be a temporary lifeline for Verizon, given the dose of reality we’re seeing with millimeter wave and the fact that new, mid-band spectrum won’t be commercially available for a couple of years.
Put simply, Dynamic Spectrum Sharing allows a spectrum band to be shared by both 4G and 5G. An operator can add a coverage layer for 5G New Radio (NR) in low-band frequencies without having to refarm the spectrum.
To understand the importance of this, a quick tutorial is in order, using Verizon as an example. Today, Verizon’s 5G Ultra Wideband service is offered on the operator’s high frequency millimeter wave (28 GHz) band. 4G LTE, in Verizon’s other bands, is used as the coverage layer, which is especially important right now given the limited coverage (and rollout) of its mmWave. A 5G network that still uses the 4G LTE core network is referred to as 5G ‘non standalone’ (NSA). In order to add 5G to the lower bands, which is critical to achieving greater coverage, Verizon has two options: refarming the spectrum for 5G, or using DSS. Refarming would require Verizon to allocate some of its channels in the lower band (likely the 850 MHz band) permanently to 5G. It’s a simpler and cleaner approach, more of a fast cut. The drawback is that Verizon would lose the capacity in those channels for LTE, which is what most of its subscribers (and devices) are still using.
DSS offers a more elegant approach. It allows Verizon to split the band between 4G and 5G, so that it gains 5G coverage in the low bands, while still keeping some capacity for LTE. The channels (‘carriers’, in industry parlance) can be allocated between 4G and 5G dynamically, as traffic demands. DSS is important to operators such as Verizon, since the operator has far less capacity per subscriber (outside of mmWave) than its competitors, and the prospects for acquiring more spectrum lie in the [more complex] CBRS PAL auctions later this year and future C-band auctions.
DSS is expected to become available later in 2020, in line with the availability of devices that support both 5G and LTE in the low bands. Ericsson Spectrum Sharing and Nokia Dynamic Spectrum Sharing require a software upgrade on the network side and devices that support DSS. Those devices require Qualcomm’s newer X55 chip, which is available on a handful of phones today, with more expected throughout the year.
The ability to offer DSS is critical to operators’ extending 5G to their lower band holdings. However, the need for DSS, and how it will be deployed, is highly situational. In the United States, DSS is especially important for Verizon, because of the combination of the natural coverage limitations of mmWave bands, its lack of mid-band holdings, and capacity challenges relative to its number of subscribers and data demand. Verizon needs to roll out 5G at its lower band holdings in order to claim ‘nationwide’ coverage of 5G, which will be critical later this year as more 5G devices, including a likely 5G iPhone, are launched. In fact, there’s a chance that the 2020 iPhone won’t offer support of 5G in the mmWave bands, which makes Verizon’s rollout of 5G in the 850 MHz band even more critical.
AT&T is also looking at DSS, although its relative capacity position is more favorable, which means refarming certain lower and mid bands for 5G is a viable strategic option, as well. T-Mobile’s strategy with regard to DSS hinges on the outcome of the Sprint deal. For its current 5G coverage, T-Mobile allocated 20 MHz of its new 600 MHz band spectrum. If the Sprint deal goes through, T-Mobile will accelerate the rollout of 5G on Sprint’s 2.5 GHz bands, which is ideal spectrum for 5G. If the Sprint merger is blocked, T-Mobile will need to look at adding DSS to its 700 MHz and 1900 MHz holdings, in addition to acquiring spectrum in future C-band auctions. Sprint, for the time being, is focused on its 2.5 GHz band for 5G, and is not seriously considering adding 5G at the lower bands.
DSS will also play a role in the next phase of 5G networks, which will be the rollout of what’s called 5G Standalone (SA). This involves moving to a 5G Core network, rather than today’s NSA framework of 5G NR radio using a 4G LTE core. 5G SA is required in order to introduce some of the game-changing capabilities that have been touted for 5G, such ultra-low latency, support for massive IoT, and network slicing. The capabilities of DSS, as they mature and are deployed commercially, will be employed in network slicing, which allows operators to deploy certain network functions to particular customers or market segments, such as higher speed bandwidth or lower latency capabilities. But for now, expect to hear more about DSS from certain operators as they roll out 5G coverage and add capacity over the coming months.