Ericsson promotes dynamic spectrum sharing to reduce 5G cost and risk

Until the 5G core and surrounding cloud-native platform are fully developed and available, the business benefits an operator can gain from early 5G deployment remain limited, and it is essential to keep costs under control.

While the 5G core and fully disaggregated RAN promise to enable the operator to target many new revenue streams in a flexible, cost-efficient way, the Non-Standalone 5G network can only realistically enhance existing mobile broadband services – with, perhaps, some incremental revenue uplift from applications like augmented reality – and support fixed wireless as a new revenue stream for selected operators.

So a large-scale 5G roll-out in new spectrum and on a new grid of sites and backhaul will not be justified by such marginal revenue gains, and many of the early business benefits of 5G will come from improving other KPIs such as churn reduction or customer satisfaction. Most early movers, apart from the US operators with their millimeter wave roll-outs, are installing 5G radios and antennas on existing 4G sites, using the same fiber and power, and are not yet virtualizing the baseband.

One way to enhance performance while keeping additional cost low is to ensure LTE and 5G interwork smoothly and their resources are aggregated to limit the need to invest in extra 5G capacity or sites. Ericsson is promoting a dynamic spectrum approach which it says will help address this challenge. It has worked with Qualcomm to develop technology for spectrum sharing between 4G and 5G, on an FDD low band, without the need to refarm spectrum. The test took place using Ericsson Radio System (ERS), which supports 4G with 5G features, such as new bands and Massive MIMO, upgradeable in software. This was working with a mobile test device powered by Qualcomm’s Snapdragon X55 5G modem/RF solution.

Ericsson said this would 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 ERS software, 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.

The Dynamic Spectrum Sharing (DSS) system uses Ericsson’s 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.

Other vendors are also pushing DSS, which is part of 3GPP standards, 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 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. However, Weldon says it could also help with interoperability, as 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.”