Software-based GIC/GNSS compatible GPS receiver architecture using TMS320C30 DSP processor

The Global Navigation Satellite System (GNSS) refers to a world wide position and time determining system that uses satellite ranging signals to determine user position. It encompasses all satellite ranging technologies including GPS and additional satellites. The GNSS integrity channel (GIC) uses a network of ground stations at known locations to determine the status of every GNSS satellite in view of the network. Satellite health is then broadcast to GNSS users in real time via geostationary satellites. The paper describes the architecture of a software based GIC/GNSS compatible GPS receiver using the TMS320C30 DSP processor. The architecture is compatible with GPS, INM-3 GIC, the US WAAS GSO satellites and takes into account the future GNSS lightsats with GPS compatible architecture and carrier frequency offset from GPS L/sub 1/ frequency by approximately 1.023 MHz. The processor is used for correlation, filtering, decimation, demodulation, Viterbi decoding and navigation. The paper emphasises the Viterbi (k=7, r=1/2) decoder implementation in software for the WAAS and GIC satellites.