Reply Comments on OET Unlicensed Device Testing

BEFORE THE
FEDERAL COMMUNICATIONS COMMISSION

In the Matter of Unlicensed Operation
in the TV Broadcast Bands, ET Docket No. 04-186

Additional Spectrum for Unlicensed Devices
Below 900 MHZ and in the 3 GHz Band, ET Docket No. 02-380

REPLY COMMENTS OF
New America Foundation
Media Access Project
Cuwin Foundation
Michael Marcus, Sc.D., F-IEEE
Dr. Paul Kolodzy
Dr. Joseph Evans

NAF, et al. again applauds the FCC Office of Engineering and Technology (OET) for the recent technical studies on initial measurements of prototype TV white space devices (WSD). NAF, et al. believe that the feasibility of personal/portable WSDs to both detect-and-avoid occupied channels and to transmit on unoccupied first adjacent channels without causing harmful interference with licensed services has been clearly demonstrated both by the recent OET report, in other studies, and in deployments in other bands. The remaining challenge for OET and the Commission is to define the explicit operating parameters that will govern device certification, so that a broader array of industry players can embark on the R&D necessary to refine personal/portable devices to meet those standards. We look forward to continuing to assist the Commission in developing WSD rules that will foster a new age in consumer applications and wireless technologies.

In these comments we respond to certain claims of incumbent interests opposed to opening the band’s unused capacity for unlicensed access and clarify several important facets of the current WSD discussion, including issues related to: (1) adjacent channel interference parameters and a proposal for use of adjacent channel leakage ratios (as exemplified by the 3G industry); (2) efforts to select appropriate protection levels for out of band emissions, particularly with respect to the distance between devices: (3) wireless microphone sensing feasibility and a proposal for a protected transition for microphone licensees; and (4) MST/NAB measurement artifacts and inconsistencies, particularly as it relates to assumptions concerning detection thresholds based on building propagation loss.

With regard to the overall TV Whitespace Proceeding, the OET has sought to address two essential but separate questions: first, what operational parameters provide sufficient protection to licensed services from harmful interference; and second, whether the technology for WSDs to meet those parameters is technically feasible. It is important to bear in mind that “sufficient protection” from harmful interference is not a simple technical matter but a complex question of weighing potential benefits, risks and user expectations. For example, while broadcasters would set standards sensitive enough to protect every out of market signal – however distant – from the risk of intermittent interference, to do so would create such enormous costs and so limit the availability of the spectrum as to render such rules effectively unworkable.

OET found that the Philips device (Prototype “B”) was 100 percent reliable in lab testing for detection of DTV signals at -114 dBm. However, a policy that required detection of a signal that is roughly 1,000 times weaker than what a DTV tuner requires to display a picture represents an unacceptable opportunity loss in terms of spectrum efficiency and a concomitant loss of benefits from broadband and wireless innovation for all Americans. As we show below, the credible empirical studies of which we are aware provide no basis for precluding low-power WSD use of a channel where DTV signals are detected at thresholds as weak as -114 dBm. At all times, OET must recall that the relevant test for harmful interference is user expectation. Because receivers of such weak signals via over the air transmission are accustomed to intermittent interference from routine atmospheric conditions, or from operation of home computers or other consumer devices certified pursuant to Section 302a, an increase in the risk of interference from mobile and very low-power WSDs is not “harmful interference” within the meaning of the Communications Act or past Commission precedent.

In the real world, there is never zero “interference” between systems and services operating in spectral or physical proximity – which is why “harmful interference” is the statutory qualifier that routinely requires the Commission to balance competing considerations and probabilities in the public interest.

To view the full comments, please see the PDF document linked below.