Upper bound on C/a code spectral separation coefficient

It is well known that spectral lines of the Global Positioning System (GPS) coarse acquisition (C/A) codes increase the amount of code division multiple access (CDMA) noise generated, occasionally far exceeding what is typically expected, depending on the user-satellite geometry. This degrades the available effective carrier-to-noise density ratio (C/N₀)_effective to a GPS receiver to a greater degree than when spectral line effects are ignored. (C/N₀)_effective is a key metric widely used to characterize the performance of the GPS receivers in terms of code acquisition, carrier loss of lock, and data bit error rates. Because of the short duration, limited geographical extent and a limited number of signals in the GPS frequency band that existed most analysis performed several years ago ignored the spectral line effects altogether. But in the changed signal environment with the growing number of Global Navigation Satellite Systems (GNSSs) in the Radio Navigation Satellite System (RNSS) band, there is a need to account for all the interference sources accurately to make sure that the intersystem and intrasystem Radio Frequency Compatibility (RFC) is achieved. Since C/A code is very widely used currently and will be used possibly in the foreseeable future in a number of applications, some of them of a critical nature, interference into C/A code receivers must be carefully considered. Since C/A code intrasystem interference is a significant contributor to (C/N₀)_effective, the focus of many studies done in the past couple of years have been on C/A code spectral line issues. A number of methods based on quasi-analytical models of the correlator output, simulation models of GPS satellite constellation and the receivers, and limited laboratory measurements were employed in earlier studies. In this paper we take a different approach to provide an upper bound on the C/A code spectral separation coefficient (CA-SSC) based on the code spectral line properties. This upper bound is computationally much simpler to obtain. This bound is also applicable to other spreading codes, resulting in spread-spectrum signals with spectral line effects.