FCC Suggests Alternative Spectrum for Wireless Microphones

The same day the FCC released its Notice of Proposed Rulemaking (NPRM) regarding unlicensed and wireless microphone operations in the 600 MHz band, it also released an NPRM on “promoting spectrum access for wireless microphone operations.” The NPRM asks many questions but provides few answers. It gives some insight into the options the commission is considering for wireless microphones.

One solution would be to encourage wireless microphone use in available spectrum outside the TV bands. These include existing licensed broadcast auxiliary service spectrum at 26 MHz, 161 MHz, 450/455 MHz, and 950 MHz, where broadcasters currently use wireless microphone and IFB systems as well as certain licensed Part 90 Business Radio spectrum. The 6875-7125 MHz BAS microwave band appears in one list. Several bands available for unlicensed use are also discussed. These include the 88-108 MHz FM band, 902-928 MHz band, the 2.4 GHz and 5 GHz bands commonly used for Wi-Fi, the 1920-1930 MHz unlicensed PCS band and ultrawide band systems using 3.1 to 10.6 GHz. Other bands include 1435-1524 MHz, where wireless microphone operations have been allowed on a temporary basis under special temporary authority for certain events, and the 3.5 GHz band.

The NPRM seeks comment on the different groups of wireless microphone operators and how they use wireless microphones, “including the particular applications served by the microphones, the types and number of devices used, the extent to which the devices are analog or digital, the settings in which they are used, and the frequency bands they use. We ask that the different user groups, or the manufacturers of products for these groups, provide detailed information about the particular nature of wireless microphone uses by different groups of users.”

The list of questions continues for several pages. There are several specific questions on advances in wireless microphone technologies. The FCC focuses on ways to increase the spectrum efficiency of wireless microphone use.

“While we recognize, as discussed more fully below, that analog devices may be appropriate or necessary at this time for certain types of applications, digital devices can be effective for others, and we seek comment on the range of efficiency gains that may be possible depending on whether analog or digital devices, or a mix of the two, are used,” the NPRM states. Specific questions include, “To what extent does the number of wireless microphones that can be deployed on a channel number depend on the power levels used, other operational factors, or the specific application(s) for which the wireless microphone is being used? Similarly, how many digital devices can operate on a television channel, and what operational factors or use factors might affect this number?”

The NPRM mentions “Use of general purpose wireless standards,” noting that “the past several decades have seen widespread development and deployment of ‘general purpose’ wireless technology standards that may be used for a wide variety of end-user applications. For example, the 802.11 family of standards serves as the basis of Wi-Fi technologies in the 2.4, 5 GHz bands, and other bands; the DECT standard provides for digital audio transmission in the 1920-1930 MHz band; and the LTE standard serves, increasingly, as a basis for broadband transmissions in several different licensed spectrum bands. We inquire about the extent to which these, and other, general purpose technologies are now, or will be in the future, suitable for use in the wireless microphone context. We are specifically interested to understand what kinds of use cases are appropriate for general-purpose wireless technologies and which are not. To what extent do general purpose technologies increase the ability of wireless microphones to share spectrum with other kinds of applications (e.g., in the Wi-Fi bands, discussed below), thereby potentially increasing the quantity of spectrum available for wireless microphones? Could the use of such technologies potentially improve performance and reduce cost of wireless microphone equipment? Should the commission endeavor to promote the use of general purpose wireless technologies by wireless microphone users? What are the trade offs?”

Controlling access to spectrum by wireless microphones is considered in the NPRM, with the FCC asking about the possible use of databases to coordinate operations as is an “electronic key or similar mechanisms” that would restrict operation to certain areas or frequencies and provide protection to other users with primary or superior spectrum rights.

The NPRM notes that the out-of-band emission rules for wireless microphones operating under Part 74 are the same for analog and digital and have not changed since 1987. It seeks comment whether the U.S. should adopt the ETSI emission mask standards for analog and digital wireless microphones and the benefits and disadvantages of adopting the mask.

A large portion of the NPRM is devoted to how to transition users out of the 600 MHz band and specifying information and notification requirements for manufacturers. While the NPRM asks many questions about how wireless microphone use can be accommodated in less spectrum, the proposed rules listed in Appendix A of the NPRM take up less than two pages and do not provide any new regulatory relief to existing wireless microphone users.

The changes include adding Section 74.832(d), “Cable television operations, motion picture and television program producers, large venue owners or operators, and professional sound companies may be authorized to operate low power auxiliary stations in the bands allocated for TV broadcasting and in the 944-952 MHz band.” (Note that the 944-952 MHz band is also used for radio broadcast STL links.)

The only technical change is in Section 74.861, which adds the requirement “Effective as of [___], emissions within the band from one megahertz below to one megahertz above the carrier frequency shall comply with the emission mask in Section 8.3 of ETSI EN 300 422-1, Electromagnetic compatibility and Radio spectrum Matters (ERM); Wireless microphones in the 25 MHz to 3 GHz frequency range; Part 1: Technical characteristics and methods of measurement.”

Section 74.841 “Certification of equipment; prohibition on manufacture, import, sale, lease, offer for sale or lease, or shipment of devices that operate in the 700 MHz Band or the 600 MHz Band; labeling for 700 MHz or 600 MHz band equipment destined for non-U.S. markets; disclosures.” describes the deadlines after which devices operating in the repurposed 600 MHz band as defined in Section 74.801” may no longer be certified, manufactured, imported, sold, leased or shipped and requirements for labeling devices destined for non-U.S. markets that are capable of operating the repurposed 600 MHz band.

While I suspect some non-broadcast, unlicensed wireless microphone users continue to use wireless microphones they purposed before the DTV transition on spectrum above 698 MHz, the costs incurred by licensed wireless microphone users to transition out of the channel 52-69 spectrum was significant and not that long ago. The cost to move wireless microphones out of 600 MHz spectrum reallocated to wireless broadband and away from high power TV operations on lower TV channels is likely to be as expensive, perhaps higher if it requires transitioning to wireless microphones in bands outside those traditionally used or to digital technologies. It isn't too early to start preparing!

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.