The Inadequacy Of The Spectral Separation Coefficient And Aggregate Gain Factor For Quantifying The Effects Of Gps C/A Code Self Interference

Some would call C/A Code self-interference by the name cross-correlation. Indeed, that is a more-correct characterization. Unlike most other GNSS codes, the C/A code is a short code (1023 chips). It was designed in the early 1970s for aiding acquisition of the much longer GPS P(Y) code. Since the P(Y) code is not available for civil applications (except in a semi-codeless mode), the C/A code eventually became the standard for civil applications. It comes with the short code disadvantages, but disadvantages that receiver designers have overcome to the point where the use of the GPS C/A code has been certified for aviation applications. One of these short code disadvantages, multipath errors, has been mitigated to the point that the C/A code now provides accuracy nearly equal to that of most longer modernized codes in receivers with similar bandwidths. However, C/A cross correlation effects are still worse than those for more recently designed RNSS signals (GPS L1C and L5, Galileo, etc.). At this point in time, some of these signals don't exist, so aviation applications can only use the "legacy" GPS C/A code. Also, since it will take years to certify and install receivers that use the modernized signals, the GPS C/A code will be the "legacy" code for aviation for another 20 to 30 years. Thus, the purpose of this paper is to clarify some common misunderstandings regarding the performance of the legacy C/A code.