Post Detection Integration Strategies for GPS L2C Signal Acquisition

L2C is the second civilian signal introduced on the modernized block of Global Positioning System (GPS) satellites. The two PN sequences employed in L2C, named CM and CL, have periods of 20 milliseconds and 1.5 seconds respectively. With longer PN codes, the search space for L2C acquisition becomes huge. In this paper, the Generalized Post Detection Integration (GPDI) technique is introduced to enhance the L2C acquisition sensitivity. The GPDI combines available correlator-output samples in several ways to maximize the processing gain. Monte Carlo simulations verify a GPDI gain of approximately 0.7 dB, over non-coherent techniques, in the L2C detection probability. Time-domain partial correlations are investigated for efficient acquisition of L2C signal. It is identified that a coherent integration interval of 1 millisecond with 20 correlator-output samples combined through GPDI is good enough to detect the L2C signal with C/N0 level of 33.82 dB-Hz or above (covering outdoor range), making it 20 times faster than conventional coherent integration over CM code period. On the other hand, for signals as weak as 17.55 dB-Hz (nominal indoor level), it is shown that coherent integration interval of 20 milliseconds with 75 correlator-output samples combined through GPDI is a better acquisition strategy than coherent integration with pilot code.