Interference is one of the major concerns in using the global positioning system (GPS) for civilian and military applications. In this paper, a closed form analytical expressions for the continuous wave interference (CWI), and matched spectrum interference (MSI) power at correlator output are derived. The post-correlation carrier to noise ratio (C/No)
for the GPS L1 coarse acquisition (C/A) signal is analytically derived in the presence of CWI, and MSI. The effect of the GPS correlator coherent integration time is also investigated under the impact of these interferences. The derived analytical formulas are verified by extensive the computer based simulation result.