[jleader]

From the 2nd page of the article, quoting from the "Technical Working Group" (which supposedly included representatives from both LightSquared and the GPS industry):

"the interfering signal at a distance of 500 feet from the [cell] tower [was] up to 800 billion times more powerful than the distant GPS signals being received from space,"

and a mile away power levels were "400 million times those of the GPS signals."

That's a difference of ~87 to 120 dB, which seems consistent with the 90 dB difference you cite.

(edited: s/LightSpeed/LightSquared/)