| The sensitivity of a baseband signal processing unit, including both acquisition and tracking, is critical for a GPS receiver to function in perturbed signal enviroments such as indoors and under ionospheric scintillation. To improve acquisition sensitivity, the differential combining approach, which allows a 2.5 dB improvement in processing loss as compared to noncoherent methods, is proposed herein. This results in a sensitivity improvement ranging from 1.2 dB to 1.6 dB for a given probability of false alarm and missed detection.;Based on an analysis of the Costas-family PLLs, carrier tracking is enhanced by optimizing loop configurations. The decision-directed loop, exhibits a 2-dB sensitivity improvement as compared to other types of PLLs. Bandwidth and root deviation caused by bilinear or boxcar transforms are solved by implementing a root-controled method. Using this design makes the bandwidth of the digital loop close to desired values, and thus improves carrier tracking by another 1 to 2 dB. A Kalman Filter adopts a soft-mode to deal with the bit sign uncertainty and adjusts the bandwidth to minimize the mean square carrier tracking error. This leads to a 4 dB and 7 dB sensitivity improvement during weak and strong amplitude ionospheric scintillations, respectively. |
