FCC'S MSS DECISION DIFFERED FROM NTIA ON GPS PROTECTION LIMITS

“This was an agreement between the agencies to get an order out quickly on MSS and to explore some of the issues that are important in a separate notice and later proceeding,” Victory told us Tues. Rather than delay resolution of complicated MSS proceeding, agencies decided public notice on GPS protection levels would be issued soon. “Additional questions remain,” Victory said. “We would have liked to resolve these issues.” She said agreement showed reluctance of both agencies to hold up outcome of entire order on single issue for which follow-up was pledged.

GPS protection limits set for ancillary terrestrial component (ATC) service were issue in MSS proceeding for agencies such as FAA, NASA and Defense Dept., which remain concerned about outcome of order, several sources said. Qualcomm Vp-Federal Govt. Affairs Jonas Neihardt said his company, which develops GPS location technology for wireless phones, believed NTIA’s analysis on E911 impact was correct. “The FCC should have adhered to the NTIA’s recommendation,” he said. “We agree with their analysis and share their concern that an ATC phone operating in the [GPS] L1 band will cause interference to GPS devices and therefore degrade the accuracy of Enhanced 911-equipped cell phones.” As for PCS protection limits, Neihardt said Qualcomm had told FCC that - 90 dBW/MHz was needed to limit out-of-band emissions from ATC phones into PCS band but agency chose -70 dBW instead. In proceeding, Qualcomm raised concerns about harmful interference to PCS phones from ATC handsets at 2 GHz. Qualcomm said its analysis found that PCS phones could suffer interference from ATC phones at lower protection limits approved by Commission, he said.

For GPS band, at issue were out-of-band emission limits into that spectrum from ATC base stations and terminals. What those power levels, or equivalent isotropically radiated power (EIRP) limits, should be were among myriad policy areas debated in reaching 132-page order that allowed MSS operators to deploy ancillary terrestrial services under certain conditions. Order upheld FCC’s existing GPS protection limits of -70 dBW/MHz for ATC operations, saying agency planned to “continue to assess the appropriate interference protection levels for GPS.” OET will release public notice on potential need for changes in future for GPS protection levels. That level is less restrictive than agreement on out-of-band emission limits reached last summer by U.S. GPS Industry Council and Mobile Satellite Ventures (MSV), with blessing of DoD. Those limits were -100 dBW/MHz for ATC base stations and initially -90 dBW/MHz for terminals operating in ATC mode. For new terminals, July 2002 pact would have tightened proposed limits to -95 dBW within 5 years from start of MSV service. Current MSS emission limit is -70 dBW/MHz to protect aviation GPS from satellite-based services. Industry agreement in that area had involved MSV’s ATC proposal, which would operate next door to GPS operations. Other planned ATC operations wouldn’t be in adjacent bands and wouldn’t be affected, industry source said.

“NTIA believes that the protection of safety-of-life aviation and safety-related terrestrial services is essential and suitable accommodation should be made,” NTIA Acting Assoc. Administrator of Office of Spectrum Management Fredrick Wentland wrote to OET Chief Edmond Thomas Jan. 24. NTIA said that to maintain “desired performance availability” of GPS receivers to meet certain E-911 accuracy requirements, power limit for ATC mobile limits should be -95 dBW/MHz. NTIA made “preliminary calculations” to evaluate effect that various power limits would have on ability of GPS receivers to meet E-911 requirement of locating 95% of callers within 150 meters.

NTIA told Thomas it previously backed limits of -70 dBW/MHz to protect GPS reception in aviation scenarios involving MSS earth stations and 700 MHz commercial base stations and mobile transmitters. That was based on “only known safety-of-life application of GPS” at time, which was for aviation, NTIA said. But it said different protection levels were required for aviation vs. terrestrial GPS receivers, such as those used in wireless phones with E-911 caller location capability. “The aviation scenario considered an aircraft in the final phase of flight, during which the GPS receiver will be in the tracking mode of operation as opposed to the more sensitive acquisition mode of operation. The GPS signals seen by the aircraft receive antenna are essentially unobstructed,” NTIA said. But GPS receivers for terrestrial applications use signals “barely above” receiver’s tracking and acquisition thresholds, it said. “The technical factors when considering interference to GPS receivers in the aviation and terrestrial scenarios are clearly very different, and emission limits based on aviation applications will not protect terrestrial applications of GPS from received interfering signal levels above the acceptable level at separation distance less than 30 meters from the MSS ATC stations,” NTIA said.

FCC order acknowledged ATC concerns on out-of-band emissions in 1559-1605 MHz band. “The limits spelled out in the agreement are well below the GPS protection limits contained in the GMPCS [Global Mobile Personal Communications by Satellite] order and contained in the Commission rules,” Commission said. “We recognize the importance of the GPS system to commercial, government and consumer users. We fully support and encourage negotiations among parties whose operations may affect GPS,” it said, adding that agency would continue to evaluate appropriate interference protection levels for GPS.

NTIA official said agency’s evaluation had examined potential impact of terrestrial system and receivers on GPS during FCC’s ultra-wideband proceeding. Analysis led to adoption of emission limits appropriate to 2 m separate distance in L1, L2 and L5 GPS frequency bands, NTIA said. While separation distance for UWB systems examined what protection levels were needed at distance of 2 m and power level of -105 dBW/MHz, official said, that scenario was seen as “tall pole in the tent,” meaning that if that protection level were satisfied, “we would protect everything else.” For potential ATC impact, NTIA also examined separation distance of 6 m between ATC mobile terminal and GPS receiver. If protection distance were increased to 6 m, power limits could be raised to 10 dB, which in L1 band of GPS would shift restrictions from -105 dBW/MHz to -95 dBW/MHz. If protection distance widened to 107 m, power limit would be -70 dBW/MHz, NTIA said.

Federal agencies expressed concerns on UWB devices’ potential interference with GPS spectrum. “It has all sorts of implications,” govt. source said of MSS decision, noting that protection levels were substantially lower than those adopted in Europe to protect Galileo, which is rival system to GPS. One issue that worried some federal agencies about GPS was interference temperature concept raised in FCC’s Spectrum Policy Task Force report. “One of the issues is when do you fight this battle, is this the place,” source said of MSS order.

Victory said she hoped notice would produce full discussion of GPS protection issues. “I can’t say if we will be able to come up with a number that’s going to fit in every situation,” she said. “You cannot be applying a number that you got in a prior proceeding blindly.”