Study And Applications Of Weak Signal Acquisition Techniques In GNSS System

Positioning and Navigation is of crucial importance in the business and war. Peoplehave been always seeking for better methods of navigation . In the last decades, theemergence of Global Navigation Satellite Systems(GNSS) made a revolutionary changein the experience of navigation. Nowadays the numerous applications is far beyond thethe initial expectation of GNSS which is not only a challenge but also an opportunity.From the perspective of signal processing, the massive attenuation of the signal pow-er , radio frequency interference(RFI) and multipath fading is the root of problem . Es-pecially the massive attenuation hinders receiver's operation of civil signals. Hence, highsensitivity GNSS technique is researched to deal with the weak signal in this dissertation.In this dissertation , a unified and complete GNSS signal detection theory is es-tablished based on the generalized likehood ratio test from signal detection and esti-mation theory aspect. Thus, classical matched filter, post-correlation noncoherent andpost-correlation di?erential detection is analyzed through reasonable approximation. Theprobability of false alarm ,the probability of detection and the PSNR is used as the judg-ment.Each algorithms are discussed both in theory and simulation and they are the foun-dation of the new algorithms .In accordance with the post-correlation noncoherent detection a?ected by the squareloss and the post-correlation di?erential detection a?ected by the data transition anddoppler frequency, based on the generalized likehood ratio test , a new design called coop-erative post-correlation di?erential detection(CPDD) is proposed utilizing the periodicityof C/A code. In the cooperative post-correlation di?erential detection,the doppler fre-quency embedded in the complex rotation of di?erent di?erential channel. Subsequently,a FFT operation will finish the coherent accumulation and fine frequency estimation si-multaneously. Thus ,the noise is suppressed e?ectively.As the prior-correlation di?erential detection proceeds the delay in the chip lev-el,the correlation is retained . Further more, the Gold sequences takes advantagesof its DAM(delay-and-multiply) property. Because of the chip level delay, the prior-correlation di?erential detection is almost immune to the doppler frequency but with theworst noise suppression as without matched filter, so multi prior-correlation di?erentialdetection(MPDD) is proposed. With the pre-filter introduced, the multi prior-correlation di?erential detection improves the noise suppression. Moreover , it retains ability of thefine frequency estimation. And then an deep investigation of C/A code is carried out toreduce the complexity of multi prior-correlation di?erential detection.Aiming at the ?aw of half-bit detection , the double di?erential full bit(DDFB) de-tection is proposed. Unlike the half-bit detection, DDFB use the whole power of thereceived signals rather than half of the power.The e?ective integration time is increasedthrough the double di?erential channel and DDFB avoids square loss due to the di?eren-tial operation . Thus the half samples discarded in the half-bit detection is compensatedand is fully utilized. More over , to reduce the computing complexity, the pre-filter isimplemented in the DDFB. Then , the PAR(peak to average ration ) is treated as the de-cision statics. Through the simulation, the PDF and the ROC(receiver operation curve) isobtained. In the end , the DDFB is implemented in the prototype receiver.For the modern GNSS signals , the time domain and frequency domain propertiesis analyzed. Then the cooperative post-correlation di?erential detection is extended foracquiring L2C signal and the multi prior-correlation di?erential detection is extended foracquiring L5 signal. Contrasted with the traditional methods, the acquisition sensitivityimproves .In the dissertation, each algorithm analyzed in theoretical derivation.Moreover, ancompleted performance test is carried out on the software receiver development platform.For convenience, the PSNR is used as the criterion. Some of these algorithms have beentransplanted into FPGA and implemented in the receiver.