INMARSAT-3 NAVIGATION SIGNAL C/A CODE SELECTION AND INTERFERENCE ANALYSIS

Inmarsat-3, the next generation of Inmarsat satellites, will carry a dedicated transponder package that will be capable of transmitting signals virtually identical to those of GPS at the L1 frequency (1575.42 MHz). This paper provides a brief functional description of the Inmarsat-3 navigation transponder. This is followed by a discussion of the results of two studies performed to determine the compatibility between the proposed Inmarsat-3 navigation signals and the GPS navigation signals. The first study resolved the issue of potential interference that may be caused by the Inmarsat-3 navigation signals to GPS receivers acquiring and tracking the GPS signals. The second study examined the selection of C/A-codes to be used by the Inmarsat-3 navigation payloads transmitting GPS lookalike signals. The properties of these codes were then applied to the expected signal levels of the Inmarsat-3 satellites to assess the interference potential to GPS. The results show that the proposed Inmarsat-3 signals will not adversely interfere with the GPS signals.