As spectrum becomes a scarce resource in some urban areas, sharing bands between different services is becoming a priority for many regulators. The FCC is carrying out various trials with a view to opening up some federal spectrum, notably in 3.5GHz and parts of 5GHz, for technologies such as WiFi or LTE small cells.
Having unveiled plans to open up the 5850MHz-5925MHz frequencies for licence-exempt use – with an extension of 5GHz WiFi seen as the primary candidate – the US administration’s latest step is to create a spectrum sharing testbed within a major city, to experiment with sharing policies and technologies.
The idea was mooted in July by the FCC and the NTIA (National Telecommunications and Information Administration), which have now published comments on the proposal. The ‘model city’, within a real metropolis, could “include large scale sustainable facilities for systems-level testing in real world environments across multiple frequency bands, including public safety and selected federal bands”, says the proposal.
AT&T was prominent among the commentators, though it led on its predictable view that there must be more spectrum opened up for exclusive licensed use too. It wants multiple testbeds to be established, so that many approaches can be modelled, and it hopes that successful sharing techniques mean that “additional spectrum can be cleared for commercial mobile broadband use” and “transitional sharing can be used to allow commercial wireless licensees to access new spectrum bands prior to the relocation of incumbent users” – in other words, simplifying and accelerating existing processes for licensed band users.
The so-called Model City would be likely to test various bands and technologies, and in its own comments, the cellcos’ representative body, the CTIA, comments that “even as testing progresses additional candidate bands may be identified”. However, 5GHz WiFi (and perhaps LTE-Unlicensed) are sure to be a major component of any test, though the inclusion of as many technologies and bands as possible will provide richer data to feed into future HetNet deployments. Of course, another key issue will be ways to mitigate interference between different technologies.
Nokia Networks called on federal agencies to help fund the initiative, rather than leaving it entirely to private companies, and commented: “It would be very beneficial to those who design and manufacture radio equipment to have reasonably validated propagation models in order to innovate and seek good solutions to the challenges of sharing spectrum with disparate systems ideally to the point of coexisting with those systems rather than trying to simply avoid them.”
Cities positioning themselves for consideration as the program’s test bed, include Chicago; Cincinnati; Kansas City, Missouri; Madison, Wisconsin; and Washington DC.