DSP-based real time ZFFT method

Abstract

The invention discloses a DSP-based real time ZFFT method comprising the following three steps: (1) a filter coefficient and a frequency shift coefficient of a ZFFT are calculated offline and temporarily stored according to application needs; (2) data sampling operation is carried out while online ZFFT data selecting, filtering and frequency shift operation is conducted; (3) after a result of step (2) is subjected to offline FFT operation, refined spectral line with required bandwidth can be obtained. According to the DSP-based real time ZFFT method, ZFFT operation characteristics and strong digital processing capability of a DSP are effectively utilized; ZEET data selecting and sampling are combined, and filtering and frequency shift operation is performed after being dispersed to a plurality of sampling periods; a refined spectral line in an analyzed bandwidth scope can be obtained with only an FFT of a Q point when sampling operation ends; compared with a conventional ZFFT method, the DSP-based real time ZFFT method is advantaged by small occupied memory space, good real-time property, and capability of meeting requirements of online monitoring and real time signal analyzing and processing systems.

Description

technical field [0001] The invention belongs to spectrum refinement analysis technology, in particular to a DSP-based real-time spectrum refinement method. Background technique [0002] ZFFT, also called Zoom-FFT, is a complex modulation spectrum refinement method. In the case of limited memory and FFT calculation length, it is contradictory to increase the frequency resolution without reducing the frequency analysis range; for this reason, various frequency resolutions based on different principles have appeared successively since the 1970s. It is a chemical analysis method whose main purpose is to identify the fine structure on the spectrum. For example: sweep-frequency narrow-band analysis method, Zoom-FFT method based on complex modulation, direct sampling method, phase compensation refinement and local representation of maximum spectrum, etc. The most commonly used methods are complex modulation Zoom-FFT and phase compensation refinement. However, the ideal method in...

AI Technical Summary

Problems solved by technology

Due to the huge memory space required to store intermediate data, the maximum refinement multiple is limited

[0010] 2) The characteristics of the low-pass filter limit the accuracy and the maximum refinement multiple. The actual low-pass filter has a transition band. When the refinement multiple is larger, the width of the transition band has a greater impact on the filtering accuracy, which will make the band selection analysis The analysis accuracy at both ends is greatly reduced, and frequency aliasing occurs

When the refinement multiple reaches a certain value, the entire band selection analysis frequency band will produce a large analysis error, this method can not be realized in practice, especially when it is implemented by software

[0011] 3) The amount of calculation is large. In the previous (1)~(3) steps, the low-pass filtering and re-sampling are completed together, that is, the selected sampling point is determined first, and the low-pass anti-aliasing filter is only performed on the selected sampling point; but it must Perform frequency shift processing on all analysis points. When the selection multiple is large, the amount of calculation in this step is quite large.

[0012] 4) The adjustment of frequency components is more complicated. The process of adjusting the frequency components obtained by FFT and spectral analysis to the frequency components of the selected frequency band is more complicated, especially to avoid frequency aliasing caused by the edge error of the low-pass anti-aliasing filter, such as performing Only 400 spectral lines in the center frequency band are displayed during 1024-point spectral analysis, and the process is more complicated

For monitoring systems with high real-time requirements, the current ZFFT method is powerless; whether a real-time ZFFT method can be invented has not been solved by the scientific and technological circles at home and abroad, and there is no relevant research report.

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