In its proposal, Google said that it would be willing to maintain "open geo-databases" to support this function, as well as provide intellectual property, reference designs, and technical support to other companies.

A second tool would be aimed at protecting the wireless microphones commonly used by news crews, conference speakers, and others, all of which today send signals over parts of the vacant TV spectrum.

Following earlier suggestions, Google is proposing the creation of an inexpensive "beacon" device, which would let microphone users broadcast the fact that a particular channel, in a particular area, is in use. White-space devices would be required to monitor and respect these active beacon signals, and to avoid broadcasting on the same channel.

Lastly, channels 36 through 38 would be set aside as a "safe harbor," to be used only by wireless microphones.

"We think Google did a good job of recognizing the high level of protection provided through this approach," says Steve Sharkey, senior director of regulatory and spectrum policy for Motorola, which submitted a proposal with similar features last year. "There is no question that this will be able to fully protect the [TV broadcast] incumbents and the devices that are supposed to be protected."

Others are less convinced.

"There is nothing in [Google's proposal] other than a laundry list of so-called protections that quite candidly have been debated for the last several years," says David Donovan, president of Maximum Service Television, a lobbying group that works closely with broadcasters. "There is no new technical information. There is no evidence put forth by Google, nor is there evidence in the record that any of this actually works."

At this date, with analysis of spectrum-sensing prototype devices still under way, and the alternative proposals still untested, there is no guarantee that the big technology companies, such as Google and Motorola, will have their way.

Indeed, this week the Cellular Telephone Industry Association (CTIA) offered an alternative proposal, under which the white-space channels would be used instead by licensed operators--much as cell-phone frequencies are used today--to offer broadband services. Broadcasters have said that they are more willing to accept this model, since any TV interference could be tracked immediately to a licensee, instead of to an unknown, unlicensed device.

However, the allure of spectrum-sensing devices hasn't diminished, despite testing hiccups and Google's new compromise proposal.

Google's proposal itself envisions a transition system, in which new devices' spectrum-sensing features could be continually checked against the information in the TV database, and any mismatches could be used to improve the technology.

Once spectrum sensing does mature, whole new generations of devices will be able to comb the airwaves looking for unused space, even beyond the TV channels now under discussion, the company says. Google has outlined a way of allocating this unused spectrum on the basis of "dynamic auctions," in which network service providers would bid for and gain access to the unused spectrum on a real-time basis, using an online auction tool.

Any such system would face considerable regulatory and technical hurdles, and it would almost certainly inspire political opposition from other, more traditional wireless users. But the idea of broadband devices that can find and utilize virtually any vacant spectrum has inspired technologists who see a more efficient use of the airwaves as a way to eliminate bandwidth constraints.

"We soon could see a low-cost and open infrastructure, supporting a near-unlimited bandwidth Internet service, improving every year as computer and radio technologies continue to evolve," wrote Google's Whitt. "This would be akin to a faster, longer range, higher data rate Wi-Fi service--'Wi-Fi 2.0' if you will."