Dynamic Spectrum Sharing (DSS) has garnered a lot of attention this year, highlighting complexity and a bit of mystery.
In February, T-Mobile’s president of technology predicted it would be a difficult year for technology. Lightning-fast and rivals AT&T and Verizon are already using DSS for lower-bandwidth 5G coverage. T-Mobile doesn’t need it that much because it has 5G in its 600 MHz spectrum.
Asked about DSS, Verizon CTO Kyle Malady recently said they see the types of speeds and performance they expected. Verizon unveiled the launch of DSS the same day Apple announced its first 5G phone, the iPhone 1
“We’ve spent a lot of time with our partners from Ericsson, Nokia, Samsung, as well as Qualcomm, and our OEMs like Apple. So we spent a lot of time on that and it works well, “said Melody at an investment event at Wells Fargo. “We will still optimize and work on it, as it is new, but at the moment it fully meets our target engineering requirements.”
Bottom line: This is in progress. Signals Research Group (SRG) published a report on its DSS study on December 1, in which the company said it was a fan of DSS because of the flexibility it provides to operators when migrating from LTE to 5G New Radio (NR), but disappointed with performance, which currently provides.
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Analysts also note that any low-frequency implementation of 5G NR, with or without DSS, cannot deliver the data rates that most users associate with 5G. T-Mobile is aggressively launching 5G, using the 2.5 GHz spectrum it acquired with Sprint, and thus has the ability to change the 5G landscape, according to SRG.
Mike Telander, CEO and founder of SRG, said he agreed with Ray when it came to performance issues related to dynamic spectrum sharing. “DSS definitely has its challenges,” Thelander told Fierce.
The opposite is that if the operator does not have DSS, it will crash and will have to turn off LTE to turn on 5G, which is not a good situation. “DSS is something like this tool that allows them to migrate from 4G to 5G data traffic, but there is definitely a penalty today that needs to be paid.”
SRG is testing DSS on the Verizon network in two markets: Minneapolis, where Ericsson is the provider, and Oklahoma City, where Nokia is the provider. In Plano, Texas, they tested DSS on the AT&T network, which uses Ericsson equipment.
AT&T is an example of an operator using DSS only when it needs to use it. Gordon Mansfield, AT&T’s vice president of mobility and access architecture, said during a recent Fierce 5G virtual event that DSS is a great tool that AT&T and others will continue to use.
In its report, SRG notes that there are at least two ways to implement DSS. In the Verizon markets where Ericsson is a provider, it uses something called a Cell Reference Signal (CRS). In its Nokia markets, it uses the Multicast Broadcast Single Frequency Network (MBSFN).
According to Thelander, CRS is what operators want, as it is most dynamic in terms of how they can allocate capacity between LTE and 5G when traffic shifts. “If you’re going to allocate spectrum or capacity between 4G and 5G, you want it to be as dynamic as the traffic on your network. That’s why the way Ericsson does it is what operators want. But this comes with this punishment, right now, because of interference, “he said.
Earlier this year, Ray from T-Mobile said that one of the major network equipment providers was “very late” with regard to DSS, and although he never identified the provider by name, many concluded that it was Nokia.
If it was Nokia, I can’t do it. In early February, some vendors were more aggressive than others in marketing their DSS solutions, but virtually 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 for both 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 tests around the world, but the implementation of commercial DSS is the most advanced in the US market.
“Both have their pros and cons,” Tavares told MBSFN and CRS. The iPhone 12 – Apple’s first 5G iPhone – supports both flavors of the DSS.
There are no 5G devices on the market that have the ability to cancel CRS interference, so there are performance issues with CRS speed compliance. CRS cancellation is not applied to the 5G chipset because there is no CRS with 5G, but with DSS it enters the picture and there the problem occurs. This applies to all chipsets, regardless of manufacturer, he said.
Putting them side by side, “we see that matching CRS speeds usually have 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 CRS signal strength of neighboring cells. But “this is a compromise,” he said, and the operator must decide what to do. “Our customers have both options.”
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The problem with MBSFN is that it is not so dynamic. “I’d call it semi-static, if you will,” Telander said. There is a lack of flexibility in this spectrum, which can be dedicated to 5G when there is no 5G traffic.
In summary, “5G NR DSS with CRS tariff matching is likely to become a long-term DSS choice for most operators, or at least this statement is true for AT&T and Verizon,” SRG said in its report. “However, the performance issues we saw in our testing will need to be resolved, especially when operators have 5G NR DSS in their mid-band spectrum, which carries most of the data traffic. 5G NR DSS with MBSFN should not have interference problems, but there are inherent inefficiencies associated with using a semi-static solution to handle the dynamic mix of 5G NR and LTE traffic. Take your poison! “
T-Mobile has said it will use DSS, but will do so strategically and does not need it for a national layer of 5G coverage because it already has it at 600 MHz.
“I guess T-Mobile doesn’t have to have as good an LTE network in many markets as the other two operators, so they need 5G to be successful,” Thelander said. “That’s why I think they’re focusing more on ‘our 5G network is great’ – to some extent it should be, because I don’t know that their LTE network is as big as it should be.”