Section 90.1338 - Grandfathered operation and transition to Citizens Broadband Radio Service(a) Fixed and base station registrations filed in ULS on or before April 17, 2015 that are constructed, in service, and fully compliant with the rules in part 90, subpart Z as of April 17, 2016 will be afforded protection from harmful interference caused by Citizens Broadband Radio Service users until the end of their license term (with one exception that fixed and base stations registered under licenses issued after January 8, 2013 will only be afforded protection until April 17, 2020), consistent with § 90.1307 . Protection criteria for such registered base stations are described in § 96.21of this chapter. Registrations originally filed after April 17, 2015 will only be afforded protection from harmful interference under this section within the licensee's Grandfathered Wireless Protection Zone, as defined in §§ 96.3 and 96.21 of this chapter.(b) Existing licensees as of April 17, 2015 may add new mobile or portable stations (as defined in § 90.1333 ) and/or add new subscriber units that operate above the power limit defined in § 90.1333 , only if they can positively receive and decode an enabling signal from a base station. Such units will be afforded protection within the licensee's Grandfathered Wireless Protection Zone (as defined in §§ 96.3 and 96.21 of this chapter) until April 17, 2020 or until the end of their license term, whichever is later (with one exception that mobile and portable stations associated with licenses issued after January 8, 2013 will only be afforded protection until April 17, 2020).80 FR 36222, June 23, 2015