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5G at 3.5 GHz: The Global Opportunity

Nokia has long been an advocate of opening the entire 3.5 GHz range of bands, from 3.3 to 4.2 GHz, for 5G use. Indeed, the speed of 5G network deployment in the mid-bands, such as 3.5 GHz, can be significantly faster due to its propagation characteristics, which generally permit the reuse of the existing macro site grid that uses 1.8 GHz spectrum.

In addition, the bands’ capacities can be significantly higher than those of lower frequency bands. This is due to the ability to use massive MIMO antennas, for which antenna sizes are practical at this frequency, and the higher bandwidths typically available compared to most bands lower than 3.5 GHz. This provides a good balance of both capacity and coverage, while also allowing  rapid initial 5G rollout and fast introduction of services, both vital in all markets.

We expect the 3.5 GHz range of bands will support a variety of applications, including enhanced Mobile Broadband, Fixed Wireless Access and Industry 4.0, with an ecosystem driven by two 3GPP defined bands: n77 (3300-4200 MHz) and n78 (3300-3800 MHz). 

Addressing some of the technical challenges of 3.5 GHz

Compared to lower frequency bands such as 1.8 GHz, 3.5 GHz presents some coverage challenges, as higher frequencies lead to lower signal propagation. This can be compensated for by using massive MIMO antennas, which can provide higher beamforming gain compared to typical passive antennas at 1.8 GHz because 5G coverage is uplink limited.

It is important to note that 5G networks using 3.5 GHz employ Time Division Duplex (TDD), in contrast to most 4G networks globally that use Frequency Division Duplex (FDD) technology.  TDD inherently brings new requirements for deployments. Chief among these are network synchronization and inter-operator coordination, to mitigate interference between TDD operators and achieve efficient use of spectrum.

Nokia has addressed these issues in the white papers published today.

Innovative regulatory approach to address incumbents

We are encouraged by the efforts of regulators worldwide to make spectrum in the 3.4-4.2 GHz range available for 5G deployments. Examples include:

  • South Korea auctioned 3.42-3.7 GHz in July 2018 and is studying 3.4-3.42 GHz and 3.7-4.2 GHz.
  • China issued 5G licenses in June 2019 for 3.4-3.6 GHz. 3.3-3.4 GHz is being studied.
  • Japan awarded 3.6-4.1 GHz in April 2019.
  • In the U.S., the 3.55-3.7 GHz band, also known as the Citizens Broadband Radio Service (CBRS) band is being made available. The U.S. is also studying the 3.7-4.2 GHz range where 200 MHz or more could be cleared in the medium term and 3.45-3.55 GHz offered as a longer-term candidate.
  • 3.4-3.8 GHz is a 5G pioneer band in Europe, where several countries, like the UK, Finland, Italy, Spain and Germany have conducted auctions and others like France are planning them.
  • Countries in the Middle East and Africa as well in Latin/South America are similarly exploring various parts of the 3.5 GHz range for 5G deployment.

As we unlock this important frequency range for 5G, regulators need to ensure that they do not impose constraints that would devalue this band. Central to this requirement is how to manage incumbents, which include Fixed Satellite Service (FSS) and Fixed Service and Radiolocation Service.  Regulators should clear the band of incumbents as much and as quickly as possible to enable the full potential of 5G. The U.S. is looking at this for FSS incumbents on the 3.7-4.2 GHz band.

Regulators also need to abandon the use of large, permanent exclusion zones to mitigate interference with these incumbents in the same or adjacent spectrum blocks.Accurate modeling of the 5G systems, incumbent systems and propagation environment should be considered when determining if interference can occur. 5G base station filtering, as well as network management techniques such as beam nulling towards the incumbent systems and power control could be used to mitigate interference. Where clearing the band is not possible, spectrum sharing could be explored using novel schemes such as those developed for the U.S. CBRS band, which involves sharing with incumbent Federal radar systems and fixed satellite Earth stations.

The characteristics of the 3.5 GHz range of bands make them ideal for 5G use, from initial rollout onwards. Using this band can help scale deployments and aid rapid adoption of 5G by both consumers and industry.

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Prakash  Moorut

About Prakash Moorut

Prakash is currently the Head of Spectrum Standardization for Nokia and has been passionate about unlocking spectrum bands for the past 22 years to unleash the full potential of wireless technologies globally.

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