It is very clear that many of the use cases and applications for 5G will not be viable in rural scenarios. This is because those use cases and applications rely on mm-wave spectrum to achieve sufficient bandwidth, hence capacity—noting that 5G New Radio carriers at mm-wave frequencies might be as large as 400 MHz not even considering supported aggregation options. Propagation range in mm-wave spectrum might be a few hundred metres. Deploying a base station every few hundred metres or every kilometre or so in rural scenarios will not be economically viable, as the number of customers/users per base station will be very small. Achieving 20 Gbps+ backhaul to each such base station will also not be economically viable. It is therefore necessary to maximise the use of sufficient bandwidth at the far-better propagation lower frequencies to provide good bandwidth coverage with a far lower density of base stations.
As part of the Department for Digital Culture Media and Sport 5G Testbeds & Trials Programme, this report investigates the use of TV White Space to assist 5G through opening up more spectrum at lower frequencies. Its content is based on general thoughts and analysis, as well as the experiences within the 5GRIT project of TV White Space deployments serving its use cases. Such alternative mid- and low-band spectrum might achieve propagation of several km, or 10 km or more in the case of the low-band. However, the carrier bandwidths in 5G mid- and low-bands are very small in comparison with mm- wave, and such frequencies are less amenable, or not amenable at all in the case of the low-band, to spatial reuse solutions such as beamforming. For example, the largest- bandwidth license awarded in the recent 3.4 GHz auction in the UK was only 50 MHz.
Given that all such low- and mid-band spectrum is already assigned (usually licensed), spectrum sharing is the necessary solution to open up more such spectrum. The purpose of this report is to understand the use of low-band spectrum to assist 5G through spectrum sharing, particularly TV White Space. It is noted, however, that TV White Space is just an initial example of spectrum sharing achieved through the far more broadly-applicable spectrum database-driven sharing concept, with oversight, definition and in some cases direct real-time input of the regulator. The Citizens Broadband Radio Service in the US is a further example, with many strong parallels to the operation of TV White Space frameworks. The emphasis here is that spectrum database-driven sharing in general, not just TV White Space, is the basis to achieve spectrum sharing at lower frequencies supporting 5G, and we are only investigating TV White Space as an initial example.
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