How Dynamic Spectrum Sharing Enables Fast 5G Deployments

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For wireless service providers (WSPs) looking to jump start their 5G rollouts, dynamic spectrum sharing (DSS) offers an-attractive alternative to building a standalone (SA) 5G network from scratch.

Fundamentally, DSS allows WSPs to share existing 4G LTE spectrum and wireless infrastructure with 5G. New non-standalone (NSA) 5G services can be deployed on existing cell sites and in existing frequency bands simultaneously with 4G LTE. The good news is that DSS can be activated at each cell site by a software upgrade from the network core, saving significant field work.

DSS affords WSPs tremendous opportunity to roll out 5G quickly over wide areas, ultimately nationwide or wherever they already provide 4G LTE coverage. More important, DSS enables 5G service without either activating new dedicated frequency bands or installing 5G radio access network (RAN) equipment.

Building out 5G is complex enough on all fronts. For full SA 5G operation, WSPs need new spectrum, new infrastructure, and a dedicated user equipment (UE) ecosystem to deliver high data throughput, and low latency across multiple use cases. Early 5G deployments are in high-band millimeter wave (mmW) and mid-band sub-6 GHz spectrum that deliver high bandwidth over relatively short distances. With few exceptions, WSP holdings lack low-band sub-1 GHz spectrum that can provide wide area coverage.

Conversely, 4G LTE operates predominantly in low bands such as 700 or 800 MHz. Tapping into existing 4G LTE frequencies gives WSPs a fast start to making 5G available over wide areas and avoid re-farming of existing low-band frequencies used for other purposes. Ultimately, 5G will cover the same nationwide footprint as 4G LTE. 

Spectrum sharing can be either static or dynamic. Static sharing basically splits the communications channel, say, a 20 MHz channel, and allocates a fixed 10 MHz to each 4G LTE and 5G. However, with more 4G LTE smartphones and devices in service than 5G UEs, the allocated 4G capacity becomes overused while the 5G portion is underused.

Dynamic sharing, as the name implies, efficiently allocates spectrum and network resources on demand. This allocation is across the whole 20 MHz channel in 1 millisecond (ms) intervals using timing and signaling algorithms to support the UEs in the cell site coverage area at any given point. DSS continually optimizes the channel split as the UE base shifts from 4G LTE to 5G, making it easier to transition to 5G.

DSS is traffic-aware and its performance depends on how quickly traffic demand changes and the corresponding resource allocations. A shared arrangement likely will not yield peak specified 5G performance, though the tradeoff may be small. Independent analyses suggest that NSA 5G performance may be off by 10-15 percent of peak.

Once the 5G UE base reaches a critical mass, WSPs can migrate to a SA 5G architecture involving a dedicated 5G Core and 5G New Radio (NR) gNodeB base stations. SA architecture is more efficient than 4G LTE and improves data throughput by leveraging low-, mid-, and high-band frequencies.

But getting to full nationwide SA operation will take billions in capital expenditures and years to achieve. WSPs must decide where and when to install 5G NRs and whether to leave the 4G LTE sites operational or decommission them. Here, DSS buys them time to plan and fund a full SA 5G buildout.

Major radio OEMs – Ericsson, Nokia, Huawei, and ZTE – already are field trialing and deploying DSS with their respective national WSP customers around the world, notably AT&T and Verizon (USA), Bell (Canada), Vodafone and Swisscom (Europe), Telstra (Australia) and China Mobile, China Unicom and China Telecom (China).   

By John Celentano, Inside Towers Business Editor

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