Wireless, Satellite Industries Continue to Implement Ways to Protect GPS Band
The wireless and engineering industry put protective measures in place to shield the GPS band from interference, wireless industry and engineering executives said Friday during a GPS receiver workshop at the FCC. The FCC Wireless Bureau gets “very few GPS interference complaints and the few we get have to do with intentional jamming,” said Chris Helzer, bureau chief engineer.
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As long as there is a reasonable guard band, broadcast auxiliary service (BAS) stations shouldn’t present interference into GPS, said Andy McGregor, Ericsson systems engineer. It’s feasible to use BAS station filtering to reduce out-of-band-emissions (OOBE) limits into the GPS receiver band, he said. Because BAS station transmitters use the GPS band, they must prevent damage from their own transmission, he said. There are receivers for BAS stations “that provide extra isolation and give good solid performance,” he said.
T-Mobile also has operations in the GPS band, said Nelson Ueng, T-Mobile principal engineer. T-Mobile’s LTE network runs in synchronous mode and “every smartphone we carry has a GPS receiver inside,” he said. “So we have an interest in protecting this band.” The wireless company’s bands are distant from radio navigation satellite service and GPS, he said.
Services operating in bands adjacent to GPS comply with FCC and Third Generation Partnership Project (3GPP) rules to keep emissions from spilling over into the GPS band, the executives and engineers said. T-Mobile protects GPS by meeting FCC OOBE rules and the spurious emissions requirements of 3GPP, said Ueng. “We're confident that our transmissions won’t violate rules."
In-device interference to GPS is a key driver for the way Qualcomm ensures that GPS is protected from mobile phone transmissions, said Cormac Conroy, vice president-engineering and product management at Qualcomm. A lot of radios are operating simultaneously, he said. Qualcomm operates in a band that is close in frequency to GPS and to supersensitive receivers, he said.
Due to its close proximity to the GPS band, LightSquared voluntarily accepted a more restricted OOBE limit of -95 dBw/MHz, said Geoff Stearn, vice president-spectrum development at LightSquared. This limit is much stricter than others that are in place today, he said. Emissions from consumer devices were measured by NASA in 2004 and 2005, he said. It demonstrated that “in this crowded neighborhood … LightSquared can be the quietest of neighbors in this band,” he said. The wholesale satellite capacity company can meet terrestrial OOBE limits in its devices by using radio frequency technology, he added: “It doesn’t require new research and development on our part.”
Some of the panelists said that the FCC OOBE limits are adequate, while others disagreed. “They seem to be adequate,” said James Campion, principal action officer, office of the DOD chief information officer. But it remains to be seen what the plans are for changing them, he said. The FCC limits are not OK, said Paul Galyean, consultant for Deere. The -70 dBw/MHz “is far too high if you want to protect GPS,” he said. “If you want increased precision and accuracy, you have to have the wider bandwidth.”