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Is 3.5GHz the end to the spectrum conundrum?

Posted by Narayan Menon on 1 June 2017

The desperate need for more spectrum means there has been much talk in the industry about the Citizens’ Broadband Radio Service (CRBS) and the 3.5 GHz spectrum band. Rather than simply licensing the spectrum in a national auction or give it over to unlicensed use, the plan will use a mix of these in the hope of creating networks run by new operators.

But how likely is it that new players will be attracted by CBRS? Will this band not just be more spectrum for the incumbent operators?

Firstly, it’s worth understanding a bit more how the band will work. The 3.5GHz spectrum consists of a three-tier access model:

  • Tier 1 access is automatically granted to the government and military groups that already have access to this band, so this band is essentially protected.
  • Tier 2 is licensed, but this will work differently from other licenses. Up to seven blocks of spectrum per “census tract” (about the size of a small town) will be awarded to the highest bidders.
  • Tier 3 is “General Authorized Access”, where no license is required – similar to how Wi-Fi works.

It’s also important to note that each tier is protected from interference by the tier below by the Spectrum Allocation Service (SAS). This means that the military and government will have priority over everyone, and those who have paid for licenses for Tier 2 access will have priority over general unlicensed access in Tier 3.

But this does raise the question of who will apply for Tier 2 licenses?

Well, a few scenarios could materialize. It could be that these granular, localized licenses will lead to the creation of private networks that take advantage of the lack of interference and the cheaper price tag. Enterprises with large campuses could develop wireless networks for their own use, or large venues and shopping malls could use this band to offer wireless services to customers.

But a lack of device support for the 3.5GHz bands could pose a problem, which means the band might end up being mostly used for specialist use cases – so more like connected medical devices in a large hospital, where owning a license would have previously been cost-prohibitive.

There is a third possibility: the 3.5GHz band will drive innovation and create services that are tailored to specific audiences, or that have a limited geographic reach – meaning operators from outside the established license holders will create these services.

While these scenarios are all viable possibilities, it’s also important to understand how gaining access to Tier 2 will work. Tier 2 licenses will need to be renewed every three years, and they will cost as much as people are willing to pay for them — with all the complications this brings. If the band becomes popular with a mix of both established and new players, then the price of a license could rise beyond what is affordable for a local service. Which means anyone creating a ‘Tier 2’ service would need assurance that the Wi-Fi-like ‘Tier 3’ could still be viable.

Tier 3 licenses need to be attractive, but if incumbent mobile operators turn to CBRS to offload mobile traffic or provide more coverage in congested areas, their buying power will outstrip new players, leaving their services using a band available to all and with no protection against interference.

This is something that can be improved with smart radio management – schemes that allocate CBRS channels intelligently to mitigate interference. These will be invaluable at Tier 3 where access is open, but also necessary for Tier 2 users to enable more efficient use of the spectrum available.

CBRS does have the potential to attract new players, but preventing interference from lower tiers is simply not enough. Anyone looking to make the most of CBRS needs to treat intelligent radio management as seriously as operators do with cellular networks.

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