FCC Releases NPRM for 3.65 GHz Unlicensed Operation

April 27, 2004
The FCC has released the Notice of Proposed Rulemaking (NRPM) to maximize the use of the 3.65-3.70 GHz band and foster the introduction of new and advanced services. As reported in last week's RF Report, the NPRM proposes allowing the use of unlicensed fixed and mobile devices in the 3.65 GHz band. The NPRM addressed concerns about interference to C-band TVRO downlinks in the 3.7 to 4.2 GHz band, proposed requirements for protecting existing Fixed Satellite Service (FSS) operations sharing the 3.65-3.70 GHz band and proposed power limits for fixed and mobile devices.

The NPRM said the Satellite Industry Association (SIA) expressed concern that emission from devices in the 3.65 GHz band could interfere with FSS operations in the 3.7-4.2 GHz. band. However, the Coalition of Program Networks and Distributed Broadcast Networks and Distributors, Broadcast Networks, Satellite Operators and Others (Coalition) did not oppose unlicensed use of the band but cautioned "sufficient technical analysis should be undertaken to establish suitable power levels, modulation types and antenna configurations for unlicensed devices that would prevent interference."

The NPRM concluded, "We reject SIA's argument against the feasibility of unlicensed operation because we tentatively conclude that mechanisms exist, as discussed below, that will provide for unlicensed use of the 3650 MHz band without causing interference to licensed FSS operations. This view is also shared by several commenters. For example, AT&T states that geographic and power limitations and other restrictions should be sufficient to permit unlicensed devices to operate successfully in this band without causing interference to licensed FSS users in this band."

The NPRM proposed two approaches for protecting FSS earth stations and Federal Government operations in the 3.65 GHz band. Fixed unlicensed devices would require professional installation of fixed unlicensed devices to ensure they would not result in interference to any FSS earth station. Both fixed and non-fixed unlicensed devices would require the devices to detect the presence and strength of RF transmissions from operating FSS earth stations (including those on uplink frequencies outside the 3.65 GHz band) and automatically adjust the effective radiated power to prevent interference. Both fixed and non-fixed unlicensed devices would also have to transmit a device identification signal to make it easier to track down interfering devices.

A maximum effective isotropic radiated power (EIRP) of 25 watts (14 dBW) is proposed for fixed unlicensed devices in this band. Any combination of antenna gain and transmitter power would be allowed, including sectorized or phased array antennas, as long as the 25-watt EIRP level was not exceeded. The NPRM said omnidirectional antennas would likely be used to provide "uniform coverage of a particular geographic area." The FCC requested comment on whether it would be beneficial to specify power by other means, such as transmitter output power and antenna gain. For non-fixed unlicensed devices, a maximum EIRP of 1 watt is proposed.

To protect licensed operations in adjacent bands, the NPRM proposes "to require that new unlicensed operations in the 3650 MHz band limit emissions into the adjacent 3600-3650 MHz and 3700-4400 MHz bands to spurious emissions only (i.e., emissions with a maximum field strength of 500 microvolts/meter measured at 3 meters)." The FCC noted that a similar situation exists in the 2400-2483.5 MHz unlicensed band and manufacturers have been able to design devices with sufficient filtering to meet these requirements.
For information on the proposed transmitter identification systems and additional information on requirements for protecting existing earth stations, refer to the Notice of Proposed Rulemaking FCC-04-100.

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