Partial Differential Postcorrelation Processing for GPS L2C Signal Acquisition

L2C is the second civilian signal introduced on the modernized block of GPS satellites. The two PRN sequences employed in L2C, named civil moderate (CM) and civil long (CL), have periods of 20 ms and 1.5 s, respectively. Stemming from the fact that using a full code period (CM or CL) for signal acquisition in GPS L2C receivers might not be necessary in normal situations (e.g. outdoor, light indoor, etc.), in this paper, we introduce a partial acquisition architecture using specially-designed matched filters (MFs) in order to relieve the computational complexity of the acquisition stage. The partial correlation loss is compensated by differential postcorrelation techniques. Three techniques, namely conventional differential combination (CDC), generalized differential combination (GDC), and modified generalized differential combination (MGDC), are investigated in terms of detection probabilities and mean acquisition time leading to the selection of MGDC as the most suitable technique for the L2C partial acquisition. By using this technique, a 2-dB sensitivity improvement with respect to the conventional noncoherent combination and a 94.5% reduction in mean acquisition time in comparison with the full code acquisition are shown for 1-ms partial correlation.