3650-3700 MHz Band Rules Released

The rules for the new Wireless Broadband Service 3650 to 3700 MHz band are included in the FCC Report and Order and Memorandum Opinion and Order released last week.

Rules for the new service are contained in Part 90, subpart Z. Modulation methods are not specified, but applications for certification of all transmitters "must describe the methodology used to meet the requirement that each transmitter employ a contention based protocol." The FCC defines a contention-based protocol as "a protocol that allows multiple users to share the same spectrum by defining the events that must occur when two or more transmitters attempt to simultaneously access the same channel and establishing rules by which a transmitter provides reasonable opportunities for other transmitters to operate. Such a protocol may consist of procedures for initiating new transmissions, procedures for determining the state of the channel (available or unavailable), and procedures for managing retransmissions in the event of a busy channel."

The certification applications for mobile transmitters "must identify the base stations with which they are designed to communicate and describe how the requirement to positively receive and decode an enabling signal is incorporated." Applications for fixed transmitters "must include a description of the installation instructions and guidelines for RF safety exposure requirements that will be included with the transmitter." Transmitters are subject to the RF exposure requirements in Sections 1.1307(b), 2.1091 and 2.1093 of the FCC rules.

Base and fixed stations are limited to 25-watts/25 MHz equivalent isotropically radiated power (EIRP) and the peak EIRP power density may not exceed 1 watt in any 1-MHz slice of spectrum. The FCC makes some exceptions for stations that use antenna systems that emit multiple directional beams. If the multiple directional beams are not emitted simultaneously, the rules state: "the total output power conducted to the array or arrays that comprise the device, i.e., the sum of the power supplied to all antennas, antenna elements, staves, etc. and summed across all carriers or frequency channels, shall not exceed the limit specified in paragraph (a) of this section, as applicable." The limit referred to is 25 watts/25 MHz.

The FCC states directional antenna gain in dBi, "shall be calculated as the sum of 10 log (number of array elements or staves) plus the directional gain, in dBi, of the individual element or stave having the highest gain." It will accept lower values for antenna gain if evidence is submitted that the actual gain is lower because of factors such as shading of the array or coherence loss in the beam forming. The rules are similar for antennas that can operate simultaneously in multiple directional beams, with the added requirement that if any of the beams overlap, the combined EIRP can't exceed the 25 watts/25 MHz EIRP limit, as calculated above, and the sum of all the beams, whether they overlap or not, cannot exceed that level by more than 8 dB.

Mobile and portable stations are limited to 1 watt/25 MHz EIRP and peak power density is not allowed to exceed 40 milliwatts in any 1-MHz slice of spectrum.

Out of band emissions must be attenuated by at least 43 + log (P) dB, where P is the transmitter power measured in watts. If interference results, the FCC can require greater attenuation.

In addition to the rules prohibiting base and fixed stations within 150 km of any grandfathered satellite earth station operating in the 3650-3700 MHz band unless coordinated with the licensee of the satellite earth station, the rules specify the coordinates of the three Federal Government radiolocation facilities that have 80 km radius protection zones. These facilities are located in St. Inigoes, Md., Pascagoula, Miss., and Pensacola, Fla. The rules warn broadband wireless system licensees that Federal Government radar systems in other areas could affect their operations.

The rules state "fixed devices generally must be located at least 8 kilometers from the U.S./Canada or U.S./Mexico border if the antenna of that device looks within the 160 degree sector away from the border. Fixed devices must be located at least 56 kilometers from each border if the antenna looks within the 200 degree sector towards the border."

For a details on the reasoning behind the rules and the FCC discussion and action on comments filed in the proceeding, see the FCC Report and Order and Memorandum Opinion and Order. For a summary of the FCC 3650-3700 MHz Orders, see RF Report for March 15, 2005.