基于DSP＋FPGA＋USB2.0开发板GPS卫星导航定位系统的开发

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huangkun315

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Selected GPS Receiver Enhancements for Weak Signal Acquisition and Tracking
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 dif-
ferential 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 im-
provement ranging from 1.2 dB to 1.6 dB for a given probability of false alarm and mi-
ssed detection.   
Based on an analysis of the Costas-family PLLs, carrier tracking is enhanced by optimiz-
ing loop configurations. The decision-directed loop , exhibits a 2  -dB sensitivity im-
provement 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 im-
proves 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 car-
rier tracking error. This leads to a 4 dB and 7 dB sensitivity improvement during weak
and strong amplitude ionospheric scintillations, respectively.