FCC STAFF REPORT UNDERSCORES CONSERVATIVE ASSUMPTIONS FOR UWB

Report described measurement effort as “first step” in collecting data to reassess UWB standards. When FCC adopted UWB order earlier this year, it committed to re-examine what it said were “ultraconservative” limits within 6-12 months. Report said existing ambient emissions in GPS spectrum were found to be up to 3,000 times greater than interference threshold that was used as basis for UWB limits at some outdoor test sites.

Long-awaited report, for which FCC seeks comments by Nov. 22, said measurement effort focused on pre-existing emissions and related power density levels in frequency bands such as GPS that were identified as needing extreme protection from potential UWB interference. Before release of report, testing drew early controversy involving wireless carriers, GPS interests and airline and satellite industries that expressed concerns that Commission was testing hair dryers rather than actual UWB devices. Results of measurement effort are expected to play important role in how FCC evaluates pending petitions for reconsideration of UWB report, which it’s expected to address in Feb., industry sources said. Report said few UWB devices had hit market yet, so FCC decided as first step to focus on some of assumptions that were integral to development of emission limits for UWB devices. One industry source said report didn’t answer concerns of some critics about impact of aggregation of UWB communications devices, which has been concern of parties that have challenged limits at FCC.

Report pointed to balancing act FCC attempted to strike in UWB proceeding between protected critical systems such as GPS and allowing new technology to move forward. “The Commission recognizes the growing importance of GPS in everyday life and is committed to ensuring that the GPS signals are not degraded or interrupted as a result of radio frequency interference,” report said. It said FCC also wanted to foster “promising” new technology. “It is in the public interest that appropriate limits be developed to provide adequate protection but not overprotect these services, particularly to an extent that overly encumbers the development of new technologies,” report said.

UWB order had created limits in form of application- based emissions masks, with limits in 960-1610 MHz range based on protecting current and future GPS operations. Limits were designed to address interference susceptibility of GPS receivers to various classifications of UWB emissions, such as broadband noise. NTIA had stressed need for additional protection against potential interference to emerging GPS receiver technology, such as that used in Enhanced 911 location solutions. FCC measured existing level of ambient radio frequency activity in specific GPS bands, looking at both indoor and outdoor locations. Outdoor sites included airports, seaports and train yards, all of which were chosen because GPS was navigational component in such transportation systems. Indoor environments included office buildings and factory installations and were chosen because they were representative of scenarios in which GPS could be used in E911 applications alongside UWB-based systems.

In case of such ambient emissions, “these measurements were intended to determine the amplitude of existing ambient emissions as would be experienced at the measurement location by a GPS receiver,” report said. Those measured levels then were compared with “theoretical GPS interference criterion” backed by NTIA and used in setting emissions limits for UWB devices. In case of radiated emissions, spurious emissions generated by common consumer electronic and electric devices were examined in different GPS bands. Devices included desktop and laptop PCs, personal digital assistant, electric drill, hair dryer, vacuum cleaner.

Study found GPS L1 and L2 bands to be relatively quiet on existing radio frequency activity. L1 band falls within 1559-1610 MHz restricted band and is used exclusively for radio navigation satellite links. There are no authorized frequency assignments to terrestrial-based systems. L2 band is within 1215-1240 MHz restricted band, shared by Defense Dept. and FAA radar systems. GPS modernization efforts will include addition of new civil signal to GPS L2 carrier. GPS L5 band showed greater level of radiofrequency (RF) activity. That band also is part of GPS modernization effort, report said. Measurements in lower ARNS band at 960-1160 MHz showed high level of RF activity, it said.

“At all measurement sites, significant emissions were observed in the band, with associated power levels well in excess of the assumed interference threshold,” study said of outdoor measurement sites. Existing ambient emissions were observed in band with associated power levels more than 3,000 times greater than interference threshold assumed in designing UWB emissions limits for that band. In some cases, source of these emissions was readily identifiable, including Air Traffic Control Radio Beacon System, report said. In many other cases, source wasn’t easily pinpointed, it said.

At indoor sites, trend emerged that was different from outdoor testing, report said. At many of indoor measurement locations, narrow-band emissions were observed at levels exceeding assumptions for GPS interference by more than 5,600 times, it said. Study didn’t pinpoint sources of emissions, but said they were presumed to come from existing electronic devices such as computers and copiers. In case of narrow- band spurious emissions from consumer-grade electronic devices tested as part of effort, power density levels were low relative to Part 15 limits but were up to 500 times greater than UWB emissions limits. “Stated another way, each of the devices measured complies with the applicable emissions limits in the frequency bands under examination; however, if they were subjected to the emission limits for UWB, most of the devices examined would fail a compliance test,” report said.