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Dynamic Spectrum Sharing (DSS) has garnered a lot of attention this year, highlighting its complexity and a bit of mystery.
In February, T-Mobile’s chief technology officer predicted it would be a tough year for tech. Flash forward, and rivals AT&T and Verizon now use DSS for lower band 5G coverage. T-Mobile doesn’t need it as much as 5G is deployed across its 600 MHz spectrum.
When asked about DSS, Verizon CTO Kyle Malady recently said he sees the types of speeds and performance they expect. Verizon revealed the launch of DSS on the same day Apple announced its first 5G phone, the iPhone 12. DSS allows carriers to host 4G LTE and 5G services in the same band of spectrum.
“We’ve spent a lot of time on this with our supplier partners with Ericsson, Nokia, Samsung as well as Qualcomm, and our OEMs like Apple. So we’ve spent a lot of time on it and it’s working well, ”Malady said at a Wells Fargo investor event. “We will continue to optimize and work on it because it is new, but it absolutely meets our targeted engineering requirements for now.”
Bottom line: it’s a work in progress. Signals Research Group (SRG) released a report on its DSS study on December 1 in which the company said it is fans of DSS due to the flexibility it offers operators when migrating from LTE to 5G New Radio (NR ), but disappointed with the performance it currently offers.
RELATED: Verizon CTO: We’re Excited With DSS Performance
Analysts have also noted that any low-band 5G NR deployment, with or without DSS, cannot deliver data speeds that most consumers associate with 5G. T-Mobile is aggressively deploying 5G using the 2.5 GHz spectrum it acquired with Sprint, and with that, it has the ability to change the 5G landscape, according to SRG.
Mike Thelander, CEO and founder of SRG, said he agrees with Ray when it comes to performance issues related to dynamic spectrum sharing. “DSS definitely has its challenges,” Thelander told Fierce.
The reverse is that if an operator did not have DSS available, they would be stuck and would have to turn off LTE to enable 5G, and that’s not a good situation. “DSS is a kind of tool that allows them to migrate from 4G data traffic to 5G, but there is certainly a penalty to pay today.”
SRG has tested DSS on Verizon’s network in two markets: Minneapolis where Ericsson is the supplier and Oklahoma City where Nokia is the supplier. In Plano, Texas, they tested DSS on the AT&T network which uses Ericsson equipment.
AT&T is an example of an operator who only uses DSS when needed. Gordon Mansfield, vice president of mobility and access architecture at AT&T, told a recent Fierce 5G virtual event that DSS is a great tool that AT&T and others will continue to build on. use.
In its report, SRG noted that there are at least two ways to deploy DSS. In Verizon’s markets where Ericsson is the provider, it uses something called cellular reference signal rate (CRS) matching. In its Nokia markets, it uses the single-frequency multicast broadcast network (MBSFN).
According to Thelander, CRS is what operators want, as it is the most dynamic in terms of capacity allocation between LTE and 5G as traffic changes. “If you’re going to allocate spectrum or capacity between 4G and 5G, you want it to be as dynamic as your network traffic. That’s why the way Ericsson does it is what the operators want. But it comes with this penalty, right now, because of the interference, ”he said.
Advantages and disadvantages
Earlier this year, T-Mobile’s Ray said that one of the major network equipment vendors was “very late” on DSS, and although he never identified the vendor by his name, many have deduced that it was Nokia.
If it was Nokia, it isn’t. In early February, some vendors were more aggressive than others in marketing their DSS solutions, but in practice, no one had a ready-made commercial solution for the US market; which came later in the year, noted Sandro Tavares, global head of mobile network marketing for Nokia.
In fact, he said that Nokia has solutions available for MBSFN and CRS rate matching, and Verizon can use CRS rate matching in Nokia markets whenever it decides to go in that direction. The Finnish supplier has DSS trials all over the world, but the commercial DSS deployment is the most advanced in the US market.
“They both have their pros and cons,” Tavares said of the MBSFN and CRS rate pairing. IPhone 12 – Apple’s first iPhone 5G – supports both versions of DSS.
No 5G device on the market has the ability to cancel CRS interference, and that is why there are performance issues on matching CRS rates. CRS cancellation has not been implemented on the 5G chipset because there is no CRS with 5G, but with DSS it comes into the picture, and this is where the problem occurs. This applies to all chipsets regardless of the manufacturer, he said.
Putting them side-by-side, “we see that CRS rate match generally has 5G performance losses compared to MBSFN,” and if you get to a place with a lot of interference, that loss adds up pretty quickly. There are ways to optimize this, such as reducing the strength of the CRS signal on neighboring cells. But “it’s a compromise,” he said, and it’s up to the operator to decide what to do. “Our customers have both options available.”
RELATED: T-Mobile’s Ray: DSS Still ‘Bumpy’
The problem with MBSFN is that it is not as dynamic. “I’d call it semi-static, if you will,” Thelander said. There is a lack of flexibility in this spectrum that can be dedicated to 5G when there is no 5G traffic.
In summary, “5G NR DSS with CRS rate match is likely to become the long-term DSS solution of choice for most carriers, or at least that statement is true for AT&T and Verizon,” SRG said in its report. “However, the performance issues we observed in our testing will need to be addressed, especially when operators deploy 5G NR DSS in their mid-band spectrum that carries the bulk of data traffic. 5G NR DSS with MBSFN shouldn’t have interference-related issues, but there are inherent inefficiencies associated with using a semi-static solution to handle the dynamic mixing of 5G NR and LTE traffic. Choose your poison! “
T-Mobile has said it will use DSS, but it will do so strategically and it doesn’t need it for a nationwide 5G coverage layer, as it already has it with 600 MHz.
“My feeling is that T-Mobile doesn’t necessarily have an LTE network that is as good in many markets as the other two carriers, so they need 5G to be successful,” Thelander said. “That’s why I think they are focusing more on ‘our 5G network is wonderful’ – to some extent it must be because I don’t know their LTE network is as great as it should be. . “
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