The Federal Communications Commission’s (FCC) vision of making spectrum available on a shared basis was realized in Q1 2020 with the commercial release of mid-band spectrum. The Citizens Broadband Radio Service (CBRS) band includes 150 megahertz of spectrum in the 3.5 GHz band (3550 MHz-3700 MHz). This band has historically been occasionally used by U.S. federal government with radar systems (Navy) and a few fixed satellite receivers. As well, some wireless internet service providers and other private network operators were able to lightly license 50Mhz (3660MHz-3700Mhz) of spectrum for fixed access deployments. CBRS is an attempt to combine the freedom of unlicensed access with the guarantees of licensed access, in a technology-neutral approach that can be shared by multiple technologies in any given deployment area.
CBRS is designed with a three-tiered spectrum sharing framework. In this framework, the Incumbent Tier (Tier 1) are given the highest priority access to the CBRS spectrum. This is specifically allocated to existing users of the band, including Department of Defense personnel and U.S. Naval Radar, who will receive permanent priority and site-specific protection. A Priority Access tier (Tier 2) is available to organizations that pay a fee for a Priority Access License (PAL). There is a maximum of seven 10Mhz channels (70Mhz) that can be purchased for any given PAL area. These PAL licenses are purchased at FCC auction for 10-year increments with limited renewal rights. The final tier (Tier 3) is General Authorized Access (GAA) users, which can access the spectrum on an opportunistic basis, will have access to 80 megahertz of spectrum in every market as well as the 70 megahertz of PAL spectrum when it is not being used by PAL licensees.
As is nearly always the case, there are tradeoffs to be made between system cost and performance when it comes to solving the problem intent of the network deployment. Striking the proper balance for the targeted market segment is key to creating a network solution that can be successfully implemented. Due to the tremendous excitement surrounding CBRS in USA, there are standards-based and non-standards-based solutions that can be used to solve the problem statement for a network deployment.