White Spaces: Austere And Somewhat Unclear Microphone Embraces

A front-page cover story in the October edition of Pro Sound News magazine, an abridged version of which I eventually found online after much searching of the publication’s byzantine, frustrating website, sheds more (and more encouraging) light on the way forward for wireless microphone manufacturers in the embryonic White Spaces era. As I mentioned a month back, the final FCC ruling negated an earlier tentative requirement that White Spaces devices regularly sense the spectrum they’re inhabiting and, if necessary, relocate themselves to avoid destructive-interference conflicts with other transmitters. Instead, White Spaces equipment, containing GPS receivers for location cognizance, will only be required to monitor and appropriately respond to the information contained in a regularly updated online database of close-proximity broadcasters. Back then, I wrote:

The finalized FCC rules (DOC) retained the location database-cognizance aspect of the 2008 proposal, but did away with the spectral sensing portion. Part of the reason, apparently, was that White Spaces developers were concerned about bill-of-materials cost, form factor, and power consumption impacts due to the inclusion of the spectral sensing feature. Given my positive experiences with Avnera- and ISM-based wireless audio transmitter/receiver equipment, for example, I can’t help but wonder if the White Spaces folks were sandbagging their estimates here. On the other hand, I wholeheartedly agree with their other argument; they’d be inappropriately saddled with protecting wireless microphones and other gear that shouldn’t be broadcasting, anyway, since its owners ignored Part 74 licensing requirements. Licensed installations (concerts, sports events, etc) can petition the FCC’s administrators for database inclusion; assuming Google et al. react with sufficient speed (which I realize, mind you, is a sketchy assumption), the microphones and other stuff should still work fine.

What I didn’t realize at the time, but the Pro Sound News piece clarifies, is that wireless microphones have another path to ongoing operation. Senior Editor Clive Young notes (bolded emphasis is mine):

A primary concern for the pro audio community, however, has been that such devices would create interference with critical equipment, such as wireless microphones. After considerable lobbying from the pro audio community, NAB, end users, broadcasters and others, the FCC would appear to have taken those concerns to heart with the new rules. As part of the Order, two channels will be set aside nationwide for wireless mic use-a move that the FCC expects will allow between 12 to 16 mics in a given area to operate simultaneously without interference from devices that will use the newly released spectrum. If a production requires more spectrum for an event such as a sports game or concert, it can petition for a temporary expansion of allocated frequencies during performance times by electronically filing a request with the FCC at least 30 days in advance. A condition of the additional spectrum being granted will be that users will have to prove that the additional channels have been exhausted, but critically, a wireless mic user does not have to be a licensed operator to register with the database.

Cynically speaking, this loophole is still a big win for the wireless microphone suppliers, since a notable percentage of customers’ existing equipment will still no longer be spectrally acceptable, thereby forcing upgrades. Shure’s Chris Lyons, Manager of Technical and Educational Communications and quoted in the Pro Sound News piece, alludes to this reality albeit in a likely intentionally obscure manner (again, bolded emphasis is mine):

First, wireless mic users should determine which TV channels are occupied by TV stations, and which will be reserved for wireless mic use in their location. Second, take inventory of wireless gear and determine how many of your existing systems can fit into those reserved channels. Third, plan ahead for large events that will need extra TV channels; registering in the database can protect those systems. Applying for a wireless mic license can’t hurt.

Regarding the two above bolded highlights, the FCC seems to have inserted some wiggle room in its prior party line of a Part 74 licensing requirement for wireless microphone use. Young notes:

Most wireless mic end-users are unlicensed; with the Order not requiring database registrants to be licensed, the FCC would appear to be sidestepping the intimidating effort that would be required to license hundreds of thousands of users. While this would appear to let wireless mic operators off the hook, fine print within the Order indicates that getting licensed might still be more beneficial in the long run. To wit, Mark Brunner, senior director of global brand management at Shure, remarked, “There’s some interesting language regarding the database application process that could be interpreted as ‘hurdles’ for entry. Based on oft-stated objections from TVBD [BD note: TV-band device, aka White Spaces] proponents regarding non-licensed wireless microphone users’ access to the database, one could presume that licensed users may face less scrutiny, and NBC, for example, may be granted a registration request more quickly than the local Ribfest. Also, as is the case today, Part 74 licensees have operating priority over Part 15 (non-licensed) users and are able to take advantage of some of the benefits afforded to this Part status, such as a 250 mW operating power limit vs. 50 mW for Part 15. For these reasons alone, for eligible parties, pursuing a Part 74 license may be a worthwhile endeavor.”

Or maybe not, Young counters, using an argument that will be familiar to anyone designing equipment for use in the spectrally crowded, therefore intentionally transmission power-constrained, ISM and U-NII bands:

Ironically, given the congestion that might occur for wireless microphones when potentially hundreds of mics start vying for the same limited spectrum space, the Order creates a situation where wireless mic systems with smaller or more limited ranges might be more preferable, as since they had less range, they would they be less likely to overlap with other mics from other productions. Of course, that holds true even today, as Sennheiser’s [Joe] Ciaudelli noted, “In some applications less power is helpful: the Broadway district is a good example. Hundreds of mics are used within a small geographic area, yet reliable, interference-free systems are configured, largely because the transmitters are operated at 10 to 50mW. Of course, good planning, natural shielding from the theater walls and cooperation among productions also contribute. Generally, you only need higher power for long-distance applications, such as a golf tournament, or if there is a high RF noise floor in the environment. These principles hld true regardless of the presence of TVBDs (WSDs [White Space Devices]).”