 three tiers are defined as follows: First tier is an incumbent user, e.g. the federal government. Table 2.2 LSA VS. CBRS. Tier access First tier: incumbent user First tier: incumbent user Second tier: (co-primary) licensee Second tier: primary access license Third tier: general authorized access Operating band 2.3-2.4 GHz (LTE band 40) 3.55-3.7 GHz (LTE bands 42/43) Incumbent Using database Using sensing and database protection Licensing period To be negotiated (target: > >10 years) 10 years (PAL) LTE, Long-Term Evolution. PAL, Priority Access License. 2.4 New Spectrum Models Second is PAL users - licensed users who acquire spectrum, e.g. through an auction. PAL users must protect incumbent Tier 1 users from harmful interference. Third tier is General Authorized Access (GAA) users, who may operate through regis- tration. GAA users must protect both first tier incumbents and second PAL users from harmful interference. LSA and CBRS may have RAN impact not only due to increased spectrum availability, but also because of special incumbent protection requirements, such as sensing and usage of a database for spectrum availability. Furthermore, while CBRS network architecture is essentially based on 3GPP, there are certain differences, such as for example the usage of Spectrum Access System (SAS), which controls access to CBRS spectrum. A CBRS base station connects to a SAS (which is a network node unique to CBRS and not present in the 3GPP architecture) when it is powered on. The base station provides its coordinates and an identifier to the SAS. The SAS uses this information to provide to the base station the CBRS frequencies it can use, that is, those which are currently not in use by the first tier incumbent users. Since as of now CBRS is not slated to use NR, 5 further details on SAS are beyond the scope of this book. Furthermore, shared spectrum as described here may give rise to new RAN deployment options such as neutral host. The neutral host concept extends the idea of RAN sharing and "tower business model." A