Methods Of Signal Frequency Measurement And Implementation Based On Nonuniform Sampling

With the development of computer and signal processing technical, digital instruments has been used in more and more fields, it has been attached more importance to signal sampling and signal processing. The nonuniformly sampled signal is an importance research component of digital signal sampling and processing subject. This thesis studies some key issue of nonuniformly signal sampling theory and its application. The main contributions of this thesis are given as follows:The theory of nonuniformly sampling can process signals with components whose frequencies exceed the Nyquist limit. The disadvantage of nonuniformly sampling is there exists the noise in spectrum analysis. A novel method for nonuniform sampling based on amplitude of signals is proposed in this thesis. This new method combines sampling rate with amplitude of signals. It make the most of some special samples that it is help to process signal so it is very effective to suppress noise. It is an effective signal processing method for weak signal detection and it can estimate exactly the frequency of sinusoidal signal hidden beneath the noise when Signal-to-Noise Ratio (SNR) is below -15dB.The disadvantage of nonuniformly sampling is there exists the noise in spectrum analysis, so it's difficult to detect the low amplitude signals. Two methods have been studied in this thesis. Firstly, a novel nonuniform periodically sampling method is proposed in this thesis. The samples are uniform in one period, but the samples are nonuniform in different periods, so these samples posses the merits of uniform and nonuniform sampling. It can estimate exactly the frequencies of sinusoidal signals when the ratio of amplitude of signal exceeds 10.A novel notch filter method for nonuniform sampling is studied in chapter 5 of this thesis. This method is very effective to suppress noise of spectrum by filtering the signal with the maximal amplitude so that it can detect the low amplitude signal. The fundamental of notch filter and threshold filtering are introduced, the characteristics of the notch filter are analyzed, and the processing procedure of notch filter is presented. It can estimate exactly the frequencies of sinusoidal signals when the ratio of amplitude of signal exceeds 100.A novel nonuniform sampling digital spectrum processing method based on wavelet transform is studied in chapter 6 of this thesis. The fundamental principle of nonuniform sampling wavelet transform and the processing procedure from the uniform wavelet to nonuniform wavelet is presented. The nonuniform sampling wavelet transform method is applied to the frequency detection.The results of the experiments of every method have been given in this thesis according to different signal, the results show that these methods are effective methods for nonuniform sampling signal detection and it can exactly estimate the frequencies of sinusoidal signals and rectangular signal.A real time nonuniform sampling and signal processing system based on a digital signal processor is developed in this thesis. This system includes a Tms320C6211 digital signal processor (DSP), an analog signal input and analog to digital converter (AD) part, a nonuniform clock generator, a data transfer part, etc. We use a complex programmable logic device (CPLD) to generate the nonuniform clock for AD, then AD sampling the signal according to this clock. The sampled data are processed by DSP used the nonuniform sampling algorithm.The method of nonuniform sampling based on amplitude of signals is tested in this system. It can estimate exactly the frequency of signal hidden beneath the noise when Signal-to-Noise Ratio (SNR) is below -15dB. The system can detect the signal above 18MHz at the maximal sampling of 1.5MHz, achieving 24 times the bandwidth of a classic uniformly digital signal processing (DSP) system that only can detect the signal above 0.75MHz at the sampling of 1.5MHz. This system process signals in real time, and the system is small-sized because it adopts a DSP.Finally, the main contributions in t...