Efficient differentially coherent code/Doppler acquisition of weak GPS signals

Differentially coherent combining of correlation results is proposed for the acquisition of weak GPS signals, i.e. signals down to -147 dBm received power. It is shown that, with a combined coherent/differentially coherent acquisition scheme, GPS signals can be acquired in 200 msec without any assistance data. By complementing the proposed scheme with methods to estimate the fractional delay, the acquisition unit can provide high quality Doppler and delay estimates such that additional tracking units seem obsolete. Since the need for a complex FFT post-processing of correlation results is avoided, the proposed scheme offers an efficient way of implementing a rapid acquisition GPS receiver in hardware.