Cross-correlation performance assessment of global positioning system (GPS) L1 and L2 civil codes for signal acquisition

Owing to imminent availability of global positioning system (GPS) L2C full constellation, low-cost dual-frequency GPS L1/L2C receivers are likely to appear on the market in the near future. The L1 C/A, L2 CM and L2 CL are the code choices available to combat the `near-far` problem in such a receiver. The published average cross-correlation protection figures of these codes (C/A: 22 dB, CM: 28 dB and CL: 45 dB) are not sufficient to determine the right code choice for different acquisition scenarios. The aim of this study is to evaluate the robustness of each code to the near`far problem and develop recommendations for code/frequency selection in a given acquisition scenario. For comparison of L2C and C/A codes, multiple C/A periods are to be considered, in order to be consistent with the signal observation interval. It is shown that the cross-correlation performance of multiple C/A periods is strongly dependent on the relative Doppler offset between local and interfering signals, and consequently it is much superior to that of the single C/A period. It is concluded that the C/A code is more robust to the near`far problem in the assisted acquisition scenarios including warm start, hot start, assisted-GPS and reacquisition, whereas L2 CM is the best code choice for the cold startup.