AT&T calls for higher power in CBRS to make it more 5G-centric

AT&T is leading the charge to allow a third category of equipment into the USA’s new CBRS spectrum band, supporting higher powered applications.

Members of the operator’s technical and regulatory staff met with FCC officials last week to propose increased power levels to enable a new type of CBRS small cell (called CBSDs), in the 3.5 GHz spectrum, which is being opened up for 4G and future 5G with a multi-tiered access system.

The FCC currently allows two categories of CBSDs. Category A refers to a lower power base station, mainly for indoor use, while Category B refers to an outdoor-only CBSD with higher maximum power limits.

AT&T wants a Category C product with even high power allowances – specifically, a maximum allowable EIRP of up to 62 dBm/10 MHz (EIRP refers to the total RF power radiated by the antenna). For Cat A devices, the EIRP limit is 30 dBm/10 MHz and for Cat B devices, it is 47 dBm/10 MHz.

The operator says the new category would allow for “operational, technical flexibility” and enable additional 5G use cases for CBRS.

This issue is important to the US operators, since – with the exception of Sprint – they are severely lacking in the midband spectrum which, in nearly every other world market, is the starting point for 5G. In most countries, spectrum around 3.5 GHz is supporting the first wave of 5G, as it provides high capacity for hotspot patterns of roll-out, but without the very constrained coverage, and engineering and device challenges, of millimeter wave.

Since 3.5 GHz is federal spectrum in the USA, AT&T and Verizon have focused their early 5G efforts mainly on the more economically challenging mmWave spectrum, while T-Mobile is opting for coverage-first, using its 600 MHz airwaves. Only Sprint, with its plentiful 2.5 GHz holdings, is really strongly positioned in the midband.

Therefore, the operators are keen that CBRS should be as well-tailored as possible to support at least some of their 5G needs. The band has a tiered set of access priorities with federal incumbents at the top. Exclusive (though fairly short term and geographically limited) licences will be auctioned later this year. These holders will get priority over users in the unlicensed or general access tier, though some of the spectrum is set aside purely for shared use.

There will not be standards for 5G in shared spectrum until the next 3GPP release, so for early 5G movers, the key is to get the licensed CBRS portion well-suited to 5G, hence AT&T’s proposal. The proposed Category C would have far better power levels than mmWave spectrum in the USA, though rather lower than LTE. It could reduce the advantage Sprint has over its rivals in the midband, and give T-Mobile a back-up option should its proposed takeover of the fourth MNO be blocked in the end (and assuming TMO succeeded in acquiring CBRS licenses).

This year, CBRS services should finally be deployed at some scale in the 80 MHz of spectrum allocated to General Authorized Access (GAA), though this is lagging a year behind initial expectations. And 70 MHz of spectrum will be auctioned as Priority Access Licenses (PAL) in 2019 or 2020.