The Federal Communications Commission (FCC) has adopted several changes to its Part 90 rules governing the Private Land Mobile Radio (PLMR) services. These new rules will become effective 30 days after publication in the Federal Register, which has not yet occurred.
These revisions are designed to clarify the rules under Section 90.187 for trunked systems operating on frequencies between 150 and 512 MHz. The FCC has revised the process for coordinating these systems and clarified which incumbent licensees are deemed “affected licenses” for purposes of frequency coordination. The FCC has also changed its rules to permit digital transmission of station identification by PLMR stations with exclusive use of their spectrum.
Section 90.187 of the FCC’s rules specifies the manner in which trunking may be accomplished in the PLMR frequency bands below 800 MHz. A trunked radio system employs technology that can search two or more available channels and automatically assign a user an open channel. The FCC made the following changes:
Added specific definitions of “centralized” and “decentralized” trunked stations in Section 90.7 of the FCC’s rules. In a “centralized” trunked system, the base station controller provides dynamic channel assignments by automatically searching all channels within the system and assigning an open channel to a user. In a “decentralized” trunked system, the system monitors the assigned channels for activity both within and outside the trunked system and transmits only when an open channel is found.
Clarified that Section 90.187 does not require applicants for decentralized trunked systems in the PLMR frequency bands below 800 MHz to obtain consent from affected licensees, and that decentralized trunked systems must monitor frequencies prior to transmitting.
Under Section 90.187, trunked systems operating on frequencies between 150 and 512 MHz must employ equipment that prevents transmission on a trunked frequency if the signal from another system is present on that frequency. The purpose of this rule is to ensure that trunked systems operating in a shared frequency environment would not have a detrimental impact on the operation of existing systems. However, this monitoring requirement does not apply if certain conditions are met. Applicants for centralized trunked systems that do not have the exclusive use of a channel must obtain the written consent of “affected licensees.” Previously, applicants could choose between alternate methods of determining which incumbents are considered affected licensees by using either a distance analysis based on mileage separation or a contour analysis based on protecting incumbents’ service contours. The FCC has eliminated the distance analysis option.
Previously, the contour analysis needed to be performed only to demonstrate that the proposed system’s interference contour does not overlap any incumbent system’s service contour. Applicants for a new centralized trunked system will now be required to also demonstrate the reverse, i.e., the contour analysis must also demonstrate that the proposed system’s service contour will not be overlapped by any affected licensee’s interference contour. The FCC stated it will permit applicants with legitimate reasons for seeking authorization for service contours overlapped by incumbents’ interference contours to seek case-by-case waivers.
Whether an incumbent is an affected licensee also depends on spectral separation. The FCC revised its rules such that an incumbent 25 kHz bandwidth station will be deemed an affected licensee if its assigned frequency is 15 kHz or less from the assigned frequency of a proposed 12.5 or 6.25 kHz bandwidth station. Incumbents will be deemed affected licensees with respect to a proposed 12.5 kHz bandwidth station if the assigned frequencies are with 15 kHz (for 25 kHz bandwidth incumbents) or 7.5 kHz (for 12.5 kHz or 6.25 kHz bandwidth incumbents). Incumbents will be deemed affected licensees with respect to a proposed 6.25 kHz bandwidth station if the assigned frequencies are within 15 kHz (for 25 kHz bandwidth incumbents), 7.5 kHz (for 12.5 kHz bandwidth incumbents) or 5 kHz (for 6.25 kHz bandwidth incumbents).
The FCC previously clarified that frequency coordinators must base their contour calculations for systems that have no permanent base stations on mobile units operating at the edge of the authorized service area in the direction of the proposed or incumbent station, utilizing any propagation curves and derating factors adopted by the coordinators. The FCC has revised this rule to treat mobile-only stations as follows: For purposes of determining whether an incumbent licensee’s written consent is required, a mobile-only system’s authorized operating area will be used as both the station’s service contour and its interference contour, regardless of whether that licensee has defined its operating area as a radius around geographic coordinates or by jurisdictional boundaries (e.g., licenses authorizing operation within a particular county or state).
Station Identification VHF or UHF PLMR licensees in the bands between 150 and 512 MHz that are licensed on an exclusive basis can transmit the required station identification using digital signals instead of Morse code, on the condition that the licensee provide the FCC with information sufficient to decode the digital transmission to ascertain the call sign transmitted. PLMR licensees may also use a single call sign for commonly owned facilities that are operated as part of a single system, as is currently allowed for CMRS licensees.
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