Cross-correlation performance assessment of global positioning system (GPS) L1 and L2 civil codes for signal acquisition
Sana Ullah Qaisar, Andrew Graham Dempster · IET Radar Sonar & Navigation · 2011
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.