The CBRS Band
spectrum for the Citizens Broadband Radio Service
The CBRS band – Citizens Broadband Radio Service – is a spectrum plan that tasked the FCC and Department of Commerce’s NTIA sub agency to find an additional 500 MHz that could be re-allocated to serve the public interest, specifically in advancing broadband deployment. The FCC and the NTIA were able to work with the military to decide that current military spectrum allocation from 3.55-3.65 GHz could be re-worked to permit commercial use.
The CBRS Band will cover 3.55 – 3.65 GHz.
What makes the CBRS spectrum different than the LTE radio interface of licensed spectrum, or the unlicensed 5 GHz band, lies within the spectrum assignment. To use the CBRS spectrum you must request and be assigned a band by the SAS (Spectrum Allocation Server). This process of assigning spectrum is automated through the SAS and works to coordinate spectrum use. Then, when the spectrum is no longer required for use, the channel is freed up so other users can operate with minimal interference.
Currently, the FCC Rules Part 96 defines three levels of priority access for use in the CBRS spectrum.
3 Levels of Priority Access
2. Priority Access Licenses (PALs)
3. General Authorized Access (GAA)
This is the highest tier and therefore has the highest priority for protection. This group protects fixed satellite users in the NN area and DoD users, and site specific protection of existing registered NN locations.
PALs will be made available through an undetermined auction process. No single entity (including through layers of shells or subsidiaries) may obtain more than 4 PALs to operate within a limited geographic area for 3 years.
This is the lowest tier, and operates almost exactly like the current 3.65 GHz band. Coexistence issues will be determined by the SAS for spectrum allocation.
Of these, protection for Fixed Satellite and DoD users is permanent, while NN sites registered before April 17, 2015 have their protection expiring mid-April 2020. Remember, under current NN rules registered sites have no protection as is, so this is beneficial to existing NN users.
PALs will only exist in the lower 100 MHz of the CBRS band range – 3.55-3.65 GHz. Within that range there will be UP TO 7 PALs, each 10 MHz in size, for a total PAL availability of 70 MHz of the 100 MHz-wide band. These PALs will be proportional in price to the population density of the geographic location, allowing rural operators to protect their licenses at a lower cost.
No other GAA has priority over another, and they all have to try to cooperate to co-exist. 30 MHz are available for GAA use, on top of the 3.65-3.750 MHz range, which will stay all GAA. As well, anything not bought as a PAL gets thrown into the GAA pool, making even further spectrum available for GAA use. This means there will be 80 MHz minimum that will always be available for GAA in the entire 3.55-3.70 GHz range compared to the 50MHz currently available in the NN band.
Benefits of CBRS
The CBRS Band should significantly lower the costs of entry for non-traditional wireless carriers, and the propagation characteristics of the 3.5 GHz spectrum rivals current WiFi networks. There is an expectation of wide availability of PALs at extremely low cost, since large carriers want the band mostly for small cell use in urban corridors to “densify” their LTE networks and alleviate demand pressure on their traditional spectrum. In rural areas these pressures are not acute, and even non-existent so there is little motivation for large carriers to invest in PALs in rural markets. And, even if they do, they are limited to 4 PALs, so even non PAL GAA users will be able to compete.
In addition, this band sits directly below and adjacent to the current NN Rural Broadband band of 3.65-3.70 GHz, making it easy for rural operators to adopt the new spectrum. This, plus the fact that the band range is already in commercial use around the world, creates a global opportunity for a level of regulatory harmony that could spur mass adoption of vendors and markets at large.
How does this work?
In practice, network owners essentially deploy the CBRS spectrum similar to WiFi. Operators will buy the gear, which will already be certified by the FCC under the new CBRS Part 96 rules and thus confirmed to perform with a SAS, and then simply go online to register the equipment as they do now. Then they will select one of the SAS vendors to which the base stations will connect in the cloud and then it’s done. The SAS will do the work to keep operators off incumbent protected users. If the operator is not using a PAL, they are able to use 20 MHz channels. If they are using PALs, then they can use 10 MHz channels or do carrier aggregation of two PALs, for example. Operators can even combine GAA and PAL use if they would like.