| Conventional P-code acquisition relies on the hand over from an acquired C/A code because the amount of search from a C/A code is finite and bounded. When the C/A code is not available, direct acquisition of P(Y)-code is the only option available. The GPS P(Y)-code offers improved cross-correlation property and higher precision than C/A code. The direct P(Y)-code acquisition improves the robustness of the GPS receiver. The design techniques used for direct P(Y)-code acquisition can also be applied to the acquisition of pulsed pseudolites that transmit wideband (shifted P-code) signals.; In order to achieve a fast acquisition code phase search, the direct average method was proposed. Both of them use a small size FFT and IFFT to facilitate the hardware design in FPGA. Due to averaging, the signal detection probability is decreased. Both methods require high carrier to noise ratio. The code phase search of 10 s signals only needs around 3 s.; A group of mathematical equations were presented to initialize the different registers and counters in the P-Code generator, which was capable to start P-Code generation at any time of the week. This is very useful when there is approximate time and satellite location information.; The synthesizable design direct GPS P-Code acquisition design was downloaded to the Xilinx VirtexE chip on the Nallatech FPGA board. The design results were verified. The final FPGA results showed the correct correlation peak amplitude value and code phase shift result. |
