| At present, Global Positioning System (GPS) has got wide applications in thewhole world. However, it is mainly used in the environments where GPS signals appeargood. In those environments such as indoor, in forests and in cities, it can not be wellused because of the negative effects to the GPS signals caused by shading, multipath,interference and so on. But, these environments are the main areas where humans live in,and thus there are a lot of application requirements for GPS in these environments. Thehigh performance navigation receiver is studied to meet these requirements, and it hasbecome a main research direction in GPS navigation. In this thesis high-sensitivityacquisition and subchip multipath separation technologies are studied, aiming for thehigh performance navigation receiver in weak signal environments. The main topics andachievements of the study are as follows:1. A lot of high sensitive GPS signal acquisition algorithms are studied, such ascoherent integration, non-coherent integration, differential coherent integration andcircular correlation algorithms. Their advantages and disadvantages are discussed. TheDoppler frequency error and Doppler effect of C/A code are analyzed in some highsensitive GPS signal acquisition algorithms. A new acquisition method is proposed,which takes use of FFT transform, double block zero padding (DBZP), differentialcoherent algorithm and frequency error correction technology. Its acquisitionperformance is also analyzed through detection probability, false alarm probability, falsedismissal probability and SNR.2. The stochastic resonance(SR) phenomenon, created by cooperation of the threeparts of the bistable system，noise and an input signal, is investigated under thecondition of small parameters. The SR mechanism is analyzed through the structures oftime domain and frequency spectrum. The basic theories of adaptive SR and twicesampling SR are discussed. And their applications are also studied in weak signaldetection. Then, a weak GPS signal acquisition method based on SR is proposed. Thismethod is different from the traditional acquisition methods. In it SR can not onlysuppress noise but also turn parts of noise energy into signal energy to greatly improveGPS signal acquisition sensitivity. The proposed acquisition method is also analyzed inthe measured data sets and simulated data sets, and its advantages are validated.3. The technology for weak signal detection based on array bistable SR is studied.By introducing stationary auto-covariance, we study the SNR gain by using boththeoretical and numerical arguments. It is found that the noise in array bistable SR systems can be used to further enhance the ability of weak signal detection over isolatedbistable one. Based on this study, we analyze the effects of array noise, external noiseand array sizes on detection performance. A new acquisition method based on arraybistable SR is proposed. It is validated by experiments in the measured data sets andsimulated data sets that acquisition performance of the proposed method is muchimproved by using an array bistable SR than an isolated bistable one under the sameconditions.4. The characteristics of multipath signals and the error model are both discussed.Multipath effects on receiver performance are analyzed. Subchip multipath time delay(MTD) estimation algorithm based on projection onto convex sets (POCS) is studied. Anew MTD estimation algorithm is proposed based on constrained incremental Wienerfilter. By utilizing the time-delay priori estimation of GPS C/A code, the supportinterval and magnitude constraints are applied in the time-delay estimation andattenuation coefficient estimation in multipath impulse channels, respectively. Thesubchip MTD can be estimated through an iteration process of the incremental Wienerfilter under the constraint conditions. Theoretical analysis and numerical simulationresults show that the proposed algorithm has a low temporal complexity, spatialcomplexity, fast convergence, and high resolution in low SNR condition. |
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