CBRS for two-way radio dealers: PAL, GAA and the device categories

The band and its three kinds of user

CBRS runs from 3550 to 3700 MHz (47 CFR 96.11). Incumbent users, including federal radar, are protected first. Priority Access users hold licenses in the lower 100 MHz, 3550 to 3650 MHz. General Authorized Access (GAA) users may operate anywhere from 3550 to 3700 MHz on whatever the higher tiers are not using.

None of them picks a channel. A Spectrum Access System (SAS), a database-driven coordinator, assigns every channel and can move it to protect a higher tier (47 CFR 96.25(b)(2)).

PAL and GAA

A Priority Access License (PAL) is a 10 MHz channel in one license area, a county, for a ten-year term, renewed under the same rule as any other wireless license (47 CFR 96.25(b)(3)). The SAS assigns the actual channel, so a PAL names no fixed frequency. By the end of its first term the licensee must show substantial service in the license area, and for a mobile or point-to-multipoint system, signal coverage and service to at least half the population of the area is a safe harbor (47 CFR 96.25(b)(4)).

GAA needs no individual license. Any eligible party can operate a device on a GAA basis, provided the device registers with an SAS and follows its instructions (47 CFR 96.33). For most private networks a dealer will build, GAA is where the system lives.

Every device registers

A CBRS base station or access point is a CBSD, and every CBSD must register with and be authorized by an SAS before it first transmits (47 CFR 96.39(c)). Registration reports the device's location, its antenna height above ground, its category, whether it seeks Priority Access or GAA, its FCC ID and its contact information.

Category A and Category B

The category sets the power ceiling (47 CFR 96.41(b)):

Two things make a device Category B whatever it was sold as: operating above the Category A power, and operating outdoors with the antenna more than 6 meters above average terrain (47 CFR 96.43(a) and (c)). The second catches a great many sites. A modest mast on high ground, or a panel on an existing tower, clears 6 m of height above average terrain long before it clears the tower's first platform.

A Category B device must be professionally installed, operates outdoors only, and registers its antenna gain, beamwidth, azimuth, downtilt and height (47 CFR 96.45). That is why a CBRS study should know the sector layout, not just a power figure.

The two signal levels the SAS works with

A PAL is protected inside its PAL Protection Area. By default the SAS draws it as the -96 dBm per 10 MHz contour around each of the licensee's registered devices, combines overlapping ones, and never lets it run past the licensee's own license area (47 CFR 96.25(c)(2) and (3)). A device that has not contacted the SAS for seven days drops out of the calculation (47 CFR 96.25(c)(1)(ii)).

Inside a co-channel PAL's protection area, the combined signal from everyone else's devices must not exceed -80 dBm per 10 MHz, measured 1.5 m above ground, unless the affected PAL holders agree to another limit (47 CFR 96.41(d)(1)). A planning study can estimate where both lines fall for one site. The SAS calculates the real ones, for every device in the area at once, and its answer governs.

What changes for a land mobile shop

• Coverage at 3.5 GHz is decided by trees and buildings far more than at VHF or UHF, so a study needs land-cover losses modeled for the band, not a UHF figure scaled up.
• Sites are usually sectored, and the category depends on the height above average terrain, so the height and the sector layout belong in the first conversation, not the last.
• Nobody owns a channel outright. Design to the capacity the SAS is likely to grant, and check which PALs are licensed in the county before promising a customer anything in the lower 100 MHz.