BeiDou Navigation Satellite System:

The investigation of the transmitted signals started immediately after the launch of Compass -M1 on 14 April 2007. Soon after in June 2007, engineers at CNES reported the spectrum and structure of the signals. A month later, researchers from Stanford University reported the complete decoding of the “I” signals components. The knowledge of the codes allowed a group of engineers at Septentrio to build the COMPASS receiver and report tracking and multipath characteristics of the “I” signals on E2 and E5B.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Knowing the codes allowed Stanford researchers to build the NERF receiver and report what?
unanswerable