Dynamic spectrum sharing (DSS) is an important way to improve interworking between LTE and 5G in 5G Non-Standalone environments, which still use the 4G core. Operators are looking to DSS to optimize spectrum utilization, by using the same airwaves for 4G and 5G, and prepare the path for migration to Standalone 5G networks based on a 5G core – and it may also make it smoother to swap out a 4G baseband in order to introduce a new vendor at the early 5G stage.
Although DSS is a 3GPP standard which all the major OEMs will support, Ericsson has led the way in commercializing the technology and has already announced some firm customer commitments, including one by Verizon, which will implement DSS from next year.
Last week, Ericsson and Qualcomm said they completed the first over-the-air 5G data call using DSS with a service provider, working with another 5G frontrunner, Swisscom. The two vendors had previously achieved a DSS 5G data call, in September, in their own labs, but this was the first with an operator partner.
Swisscom launched Switzerland’s first 5G services in April in 3.6 GHz spectrum, with Ericsson as its only 5G equipment vendor. It plans to deploy Ericsson Spectrum Sharing (ESS) software in December, and says this will be important to its goal of covering 90% of the country’s population with 5G this year.
“With Ericsson Spectrum Sharing, service providers can reuse their Ericsson Radio System investments on bands currently used for LTE, to support a fast introduction of 5G,” said Hannes Ekström, head of product line 5G RAN at Ericsson, in a statement.
Qualcomm said Ericsson’s DSS solution is compatible with all 5G FDD smartphones and other devices based on its Snapdragon 5G platform. The chip provider’s VP of technology for Europe, Dino Flore, said: “Coverage is the next killer app for 5G, and we congratulate Ericsson and Swisscom on this significant milestone. Spectrum sharing will be a key catalyst for nationwide 5G coverage, helping deliver ubiquitous 5G services to consumers.”
Ericsson says DSS will be an important technology to enable 5G to be rolled out more quickly and cheaply, using FDD bands which the operator already has. It stated: “Traditionally, new generation radio access technologies are deployed on separate spectrum blocks – as was the case with 2G, 3G and 4G. This would require operators to buy new spectrum or refarm the existing spectrum to allocate the new generation. This is a very slow and costly process.”
Refarming could take a decade whereas spectrum sharing can be activated, in software embedded in the Ericsson Radio System, overnight, and the resources can then be dynamically allocated between 4G and 5G in the same band based on demand from the users or applications. This could also be important for operators in countries where auctions of new 5G spectrum are not planned in the near term. Ericsson’s implementation of DSS uses its own intelligent scheduler algorithms to decide on optimal use of both LTE and 5G in a single block of spectrum.
Another option is to extend coverage for a 5G network in a midband or millimeter wave band – with their limited range – by adding interband NR carrier aggregation of a lower frequency band. This enables 4G spectrum to be used to double the coverage area of a new 5G cell, or improve indoor penetration, without the need to switch off LTE altogether.
DSS offers many benefits for 5G NSA economics:
Other vendors are also pushing DSS as a way to encourage MNOs to accelerate 5G deployments – as well as a way to ease the path to introducing alternative suppliers to their networks. In the Non-Standalone environment, 5G and 4G base stations both connect to the LTE core using Dual Connectivity. However, most of the options for deploying this work more efficiently if both base stations come from the same supplier, which causes issues for MNOs which want to migrate to a new vendor for their first-stage 5G RANs. This predicament has been highlighted by the risk that operators in some countries may be barred from buying RAN gear from Huawei – Huawei users such as VHA in Australia now have to make a difficult migration to a different vendor to comply with government restrictions.
The use of DSS can help with this, argue both Ericsson and Nokia (see Wireless Watch April 10 2019). Nokia has described a solution based on DSS which allows the existing LTE to communicate with the new base stations without using the X2 interface (which has been implemented in incompatible ways by different vendors).
With DSS, spectrum can be reallocated to different radios every millisecond. It allows an MNO to move spectrum between different radio technologies as required, and was designed mainly to give greater flexibility and efficiency in spectrum usage, in high bandwidth situations. And an MNO could buy 5G equipment, with DSS support, from a new vendor and initially run the system in 4G mode, using some existing 4G spectrum.
This overlay would support interoperability between the incumbent 4G and the new 5G systems, with roaming between the two 4G radios happening at packet core level as usual.
“We don’t think X2 is the way forward because it would slow things down and be expensive,” Thomas Noren, Ericsson’s head of 5G commercialization, said. “DSS is a much better way forward. It means you can be totally flexible between 4G and 5G and allow any mix of the two to run in a band.”