Deere: LightSquared Causing Massive GPS Interference

Deere & Co., a major provider of precision agriculture equipment and services, notified the FCC May 26 of substantial interference with its GPS receivers by the LightSquared signal. Deere receivers registered impact of and interference by the LightSquared signal as far away as 22 miles from a transmitter. Further, the company has found no practicable technical solution to the problem. Deere met with an FCC legal advisor to report on its analysis of recent New Mexico tests of the Lightsquared signal and effects on GPS equipment.

The U.S. military conducted anechoic chamber tests at a White Sands facility and open-air tests at Holloman Air Force Base in April. The tests, which simulated various cellular base station transmission schemes proposed by LightSquared in L-band frequencies between 1525-1559 MHz, without exception demonstrated severe interference to Deere’s high-precision GPS receivers.

The tests included configurations where the simulated emission was reduced in bandwidth and/or assigned to frequencies in the lower part of the L-band. The Deere presentation contains an interesting graphic showing how high-precision receivers are more affected by the proposed LightSquared signals than are consumer grade receivers. The reasons:

  • Modern high-precision receivers use filters that cover MSS, GPS, and GLONASS bands
  • Wideband filters are required for higher rate, precision codes

Deere owns NavCom Technology and operates the StarFire Network, a global satellite-based augmentation system providing decimeter positioning accuracy on a worldwide basis, enabling users to roam freely while maintaining precise positioning information. The Starfire service and GPS equipment are used in precision agriculture and other applications of precise machine control, survey (land and air), marine navigation, unmanned vehicles, and continuously operating reference stations, among other applications.

Deere explained that, in the course of its technical analysis, the company’s engineers have determined that there is currently no practicable technical solution, or solutions in combination, available to avoid or substantially mitigate interference from LightSquared’s base stations to Deere’s existing precision GPS system and to similar systems operated by others, particularly in the agriculture and construction industries.

Deere also confirmed that while there are important potential mitigation strategies that may be worth exploring with respect to future generations of GPS receivers, no single interference mechanism — such as repositioning LightSquared’s operating frequencies, modestly reducing transmitter power, and so on — and no combination thereof, has been examined such that it can be deemed to provide meaningful protection for precision farming operations essential to today’s U.S. agricultural sector. Similarly, no potentially effective mitigation solution, alone or in combination, has been examined such that it can be deemed to protect other precision GPS users in the construction sector or GPS in other applications.

Deere emphasized that, based on this data and analysis, permitting LightSquared to operate its network as proposed or any variant of its currently proposed network will create massive interference into Deere’s StarFire system and other similar systems risking serious harm to the U.S. agriculture industry.

Deere expressed its support for expanding wireless broadband services, particularly in rural areas, so long as initiatives to provide new wireless service do not compromise critical and irreplaceable GPS and/or space-to-earth MSS services essential to the nation’s agricultural community.

Deere suggested that, in the absence of short-term solutions, should the Commission decide to pursue a new use of L-Band spectrum as a long-term option, the Commission should do so in Commission rulemaking proceedings allowing for full public input, technical examination, product and development time, and appropriate testing. Given the critical importance of the L-Band interference to Deere’s agricultural (and other customers), Deere would expect to participate in such proceedings.

(Source: GPS World)

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