FCC asks for more information on LightSquared, GPS
A article published today cited that the head of the FCC’s Office of Engineering and Technology, Julius Knapp, sent a letter to LightSquared and the GPS Council asking for more information on which devices were specifically interfered with by LightSquared, ane the effects of LightSquared’s new proposal to use only the lower portion of their licensed band (1,526 MHz to 1,536 MHz). This is a valid, and not unexpected, question from the FCC especially since the Technical Working Group Report randomized the devices so that no correlation could be made between the device, device manufacturer and the test result. This is understandable since the GPS receiver manufacturers likely want to preserve their proprietary performance from public disclosure to their competitors. However, as Questiny looked at the data, we could not correlate the measured performance to the device characteristics. For example, some of the receivers use automatic gain control (AGC) and 3-bit analog to digital convertors (A/Ds) , whereas other receivers use no AGC, and a 1-bit A/D. The performance between these two devices is predictably differerent (the 1 bit A/D will be more sensitive to overload). The figure shows the results of static tests performed for the General Navigation Class of GPS Receivers where the LightSquared power level was measured at the device such that the GPS carrier-to-noise level was reduced by 1 dB (or 25%). As the figure shows, the range of power needed to create the same degradation across receivers varied by more than 70 dB (10 million time). This is a huge difference in performance. As the TWG only provided an index for the device, their technical characteristics could not be correlated to account for this range of performance difference. (Note gaps in the measurements indicated devices that did not suffer any loss or were not tested.)
Regardless of the previous results of the TWG. LightSquared essentially nullified their relevance when they proposed a new frequency plan on June 15. Now, as expected, the FCC has ordered additional testing for this new LightSquared frequency plan, and they have reassured the GPS community that they will not impact the GPS performance. As my colleague at TMF points out, this could put severe pressure on LightSquared vis-a-vis Sprint’s ability to back out of their deal should LightSquare be unable to raise additional capital and make their required payments.
Received Power (at Device) Required for 1 dB loss in GPS in C/N0 for General Navigation Devices