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Dynamic Spectrum Sharing

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One of the first 5G specifications that will be implemented in cell sites is dynamic spectrum sharing (DSS). This technology allows a cellular carrier to use a block of spectrum for both 4G LTE and 5G customers. Without DSS, a carrier could only use 5G in existing blocks of spectrum by subdividing the spectrum and allocating a portion of the spectrum specifically and exclusively to 5G. Since 4G networks are already overloaded today it’s not practical to subdivide existing spectrum.

With DSS, a carrier can use spectrum in the manner being requested by a customer handset. A handset seeking a 4G connection will get a traditional 4G channel of bandwidth. If a handset asks for a 5G connection, then that phone can connect as 5G and can provide whatever 5G features are available at a cell site.

For now, there are almost no 5G features implemented in cell sites, so at first a 4G and 5G connection will be nearly identical. Over time 5G features will be coming. The most powerful 5G feature will be frequency slicing where the cell site provides each customer with the bandwidth they need. If somebody only needs a tiny sliver of bandwidth, then the cell site can operate more efficiently by not wasting a full 4G channel on the customer. If a customer wants to download a large file, the cell site will provide a burst of high bandwidth by assigning more than a typical 4G channel of capacity.

This means that DSS needs to be one of the earliest features introduced because it prepares a cell site for the introduction of other 5G features by allowing 5G to be used across multiple bands of spectrum. A carrier doesn’t have to use DSS if they instead plan to use separate bands of frequency for 5G and 4G.

Ericsson and Qualcomm had their first successful test of DSS in September and they think the technology will be made available to US cellular providers sometime in the second half of 2020.

Like all 5G features, DSS will only work with 5G phones that are enable to use the technology. This means all of the phones being sold as 5G today won’t have the DSS capability. The cellular carriers are handling early 5G deployment by having 5G phones only use new blocks of spectrum. T-Mobile is using 600 MHz spectrum and AT&T is using 850 MHz. All the big carriers are also offering separate millimeter wave spectrum phones. Until DSS is implemented, 5G phones will be routed to use the new blocks of spectrum.

To some degree, the cellular world is gaming the system to make 5G feel better than 4G. For now, callers connecting to one of the largely empty new spectrum bands will have a guaranteed full-bandwidth connection, due mostly to there being few other customers using the spectrum at the same time. As the dedicated 5G spectrum bands get busier, the 5G connection experience will begin to feel more like 4G. The same thing happened when 4G was introduced and for the first 6 months of the new 4G technology, customers reported fast 4G data speeds that still can’t be matched today.

DSS can allow carriers to play the same game with existing bands of spectrum. The first 5G customers to make a DSS connection using the existing 4G spectrum can be given priority routing to make sure they have a high-quality connection.

Most of the 5G features that will make 5G special are still three years or more into the future. For now, the carriers are selling 5G phones that don’t include 5G features. The carriers are instead placing the supposed 5G customers into new spectrum bands to give them a good data experience. Over time, as 5G features are introduced, 5G should have better performance than 4G. What the carriers are not telling the public, though, is that the majority of cellular connections made for the next decade are going to be 4G.

5G will be introduced in fits and starts. Carriers will release a 5G feature, but when first introduced almost no handsets will be able to use it. The first customers with phones enabled for a given feature will have a great experience. Over time, as more people use the new 5G features, the higher traffic volumes will lower the performance seen by the early adapters. We’re going to go through this cycle over and over until a decade from now the handsets sold will include the full set of 5G features. The uneven performance for 5G will baffle customers when they don’t get the same features and experience as others that own slightly newer phones.

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