NPSTC Recommends Changes to LightSquared GPS/LTE Interference Study

LightSquared's final plan for testing L-band LTE network interference to GPS is better than initially proposed, but still could be improved, said the National Public Safety Telecommunications Council in an FCC filing posted Wednesday in docket 12-340. NPSTC met with LightSquared consultant Roberson Aug. 11 to voice concerns about the test methodology, such as the lack of any indication the testing would look at possible impacts to public safety and that the simulated LightSquared test signal levels -- -25 dBm to -30 dBm -- were lower than what would be expected in actual practice. The final test plan submitted in August by LightSquared (see 1508250070) includes a public safety portable radio and public safety mobile data terminal among those being used in the testing, though LightSquared may want to consider adding others, such as ankle bracelet tracking devices used in house arrests and limited releases, plus vehicular tracking devices, NPSTC said. The final test plan also raises the maximum level for the simulated LightSquared LTE signal to -20 dBm, which is an improvement, though any LightSquared operation that gets approved should be conditioned on a maximum power flux density at ground level that's comparable to the level used in testing, NPSTC said. LightSquared's testing plan indicates it may test in the 1545-1555 MHz band for LTE downlink operations, and though use of that spectrum "could cause significant impact on GPS," testing of that spectrum section is necessary if that sub-band does end up being used, NPSTC said. Any time to first fix testing of the devices needs to include signal levels up to -20 dBm or the equivalent level that matches the power flux density at ground level that's expected to be deployed if LightSquared gets FCC approval for its LTE operations, NPSTC said. While the firm plans to test only 10 MHz bandwidth version of LTE, smaller bandwidth variants can point to additional GPS sensitivity to out-of-band emissions and should also be tested if lower bandwidth versions of LTE may come, NPSTC said. In a statement Thursday, LightSquared said it was "critical that the interests of public safety are represented and satisfied, and over the past month [Roberson] and NPSTC have had a cooperative back and forth, which is both reflected in the test plan and ongoing today. The testing process is underway, but also iterative. [Roberson] has incorporated many of the NPSTC elements, and as additional feedback comes in, the test plan will continue to reflect that with the goal to establish how compatibility can be established between wireless broadband and GPS."