CN111835314A - Anti-interference extractor for extracting any multiple between 1-2 times and design method thereof - Google Patents
Anti-interference extractor for extracting any multiple between 1-2 times and design method thereof Download PDFInfo
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- CN111835314A CN111835314A CN202010781798.3A CN202010781798A CN111835314A CN 111835314 A CN111835314 A CN 111835314A CN 202010781798 A CN202010781798 A CN 202010781798A CN 111835314 A CN111835314 A CN 111835314A
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Abstract
An anti-interference extractor for extracting any multiple between 1-2 times and a design method thereof. The anti-interference decimator comprises an anti-aliasing low-pass filter and a polynomial interpolation filter; the design method comprises the following steps: determining the passband cutoff frequencies of the anti-aliasing low-pass filter and the polynomial interpolation filter; determining a stopband cut-off frequency of the anti-aliasing low-pass filter and a first stopband frequency range of the polynomial interpolation filter; determining the number and the order of polynomials used by the polynomial interpolation filter; calculating coefficients of the anti-aliasing low-pass filter and the polynomial interpolation filter; calculating the amplitude-frequency response of the anti-interference extractor; judging whether the amplitude-frequency response reaches a preset interference suppression level threshold value in an interference frequency band: if not, re-executing the steps; if so, the anti-interference extractor is successfully designed. The anti-interference extractor designed by the method has the advantages of simple structure, convenient realization and effective interference suppression.
Description
Technical Field
The invention relates to the field of digital signal processing, in particular to multi-rate signal processing, and specifically relates to an anti-interference extractor for extracting any multiple between 1-2 times and a design method thereof.
Background
Digital Down Converters (DDCs) are an important component of all-digital communication receivers. The multi-channel multi-factor interpolation filter is generally composed of a cascade integration comb filter (CIC), a plurality of half-band extractors and a polynomial interpolation filter, wherein the CIC is used for realizing large integral multiple extraction, the half-band extractors are used for realizing 2 times of extraction, and the polynomial interpolation filter is used for realizing 1-2 times of extraction.
The polynomial interpolation filter is usually implemented by a classical Farrow filter structure, as shown in fig. 1 and 2.
However, it is a drawback to use only one polynomial interpolation filter to achieve 1-2 times decimation: after the decimation, the interference signal in a specific frequency band is mixed into the frequency band of the baseband signal, causing interference. Specifically, as shown in fig. 3, the signal bandwidths involved are normalized bandwidths, and assuming that the bandwidth of the baseband signal before extraction is B, the frequency band distribution of the baseband signal is [ -B, B]The decimation multiple of the polynomial interpolation filter is x, and x belongs to [1, 2]]. According to the multi-rate signal processing theory, after the baseband signal is extracted by x times, the bandwidth of the baseband signal is widened to xB, so that the frequency band distribution range of the baseband signal is expanded to [ -xB, xB]. Because the extraction of the signal by the polynomial interpolation filter is realized by resampling, the frequency band [1-xB,1+ xB ] is obtained after resampling the signal according to the sampling theorem]The inner signal (if present) may mix into the frequency band of the baseband signal, causing interference. And band [1-xB,1+ xB]The inner signal is exactly the frequency band
The inner signal is obtained after x times of extraction. Therefore, frequency band
The distribution interval of the interference signal.
When x is in the interval [1, 2]]When the value is arbitrarily selected, the frequency band range of the interference signal is all the frequency band intervals
Is a union of
Where, U represents the union of sets. Due to the fact thatIn order to ensure that the baseband signal is not interfered by other signals after being extracted, the extractor needs to filter out the frequency band
All of the signals in.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the anti-interference extractor for extracting any multiple of 1-2 times and the design method thereof.
In order to realize the purpose of the invention, the following scheme is adopted:
a design method of an anti-interference extractor for extracting any multiple between 1-2 times is characterized in that the anti-interference extractor comprises the following steps: an anti-aliasing low-pass filter and a polynomial interpolation filter;
the design method comprises the following steps:
s100, determining design parameters of an anti-aliasing low-pass filter and a polynomial interpolation filter, comprising the following steps of:
determining the passband cut-off frequency of the anti-aliasing low-pass filter and the passband cut-off frequency of the polynomial interpolation filter according to the normalized bandwidth of the input signal;
selecting two frequency values in a preset frequency range, determining the stop band cut-off frequency of the anti-aliasing low-pass filter according to one frequency value, and determining a first stop band frequency range of the polynomial interpolation filter according to the other frequency value;
determining the number and the order of polynomials used by the polynomial interpolation filter;
s200, calculating coefficients of an anti-aliasing low-pass filter and a polynomial interpolation filter;
s300, respectively calculating the amplitude-frequency responses of the anti-aliasing low-pass filter and the polynomial interpolation filter, and correspondingly multiplying the amplitude-frequency response of the anti-aliasing low-pass filter and the amplitude-frequency response of the polynomial interpolation filter according to frequency points to obtain the amplitude-frequency response of the anti-interference extractor;
s400, judging whether the interference suppression capability of the amplitude-frequency response of the anti-interference extractor in an interference frequency band reaches a preset interference suppression level threshold value:
if not, returning to the step S100, and re-executing the steps S100 to S400;
and if so, the anti-interference extractor is successfully designed.
Further, in step S100, the passband cut-off frequency of the anti-aliasing low pass filter
Passband cut-off frequency of sum polynomial interpolation filter
Equal to the normalized bandwidth B of the input signal, i.e.
Further, in step S100, in the frequency range
Internally picking two frequency values Δ f1And Δ f2The stop band cut-off frequency of the anti-aliasing low-pass filter is set to be
The first stop band frequency range of the polynomial interpolation filter is [ 1-Deltaf2,1+Δf2]。
Further, in step S400, the interference band is:
the utility model provides an anti-interference decimator that is used for arbitrary multiple extraction between 1~2 times which characterized in that includes:
the anti-aliasing low-pass filter is used for filtering partial interference signals in the interference frequency band; and
the polynomial interpolation filter is connected with the anti-aliasing low-pass filter and is used for cooperating with the anti-aliasing low-pass filter, filtering the residual interference signals in the interference frequency band and realizing 1-2 times of signal extraction in a resampling mode;
the anti-interference extractor is obtained by the design method of the anti-interference extractor for extracting any multiple between 1-2 times.
The embodiment of the invention has the beneficial effects that:
the anti-interference extractor for extracting any multiple between 1-2 times, which is obtained by the design method, solves the problem that interference signals in a certain specific frequency band can be mixed into the frequency band of baseband signals to cause interference after 1-2 times of extraction in the prior art, effectively inhibits the interference, and has the advantages of simple structure and convenient implementation.
Drawings
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
FIG. 1 is a schematic diagram of a Farrow filter of type I for performing polynomial interpolation, where N is N1+N2+1 is the number of polynomials and M is the order of the polynomials.
FIG. 2 is a type II Farrow filter for polynomial interpolation, where N is N1+N2+1 is the number of polynomials and M is the order of the polynomials.
FIG. 3 is a schematic diagram of the adjacent channel interference phenomenon occurring when the polynomial interpolation filter performs 1-2 times of decimation.
FIG. 4 is a structural diagram of the anti-interference extractor for extracting any multiple between 1-2 times according to the present invention.
Fig. 5 is an amplitude-frequency response of an exemplary interference rejection decimator design of the present invention.
Detailed Description
In order to make the purpose, technical scheme and advantages of the invention clearer, a design example of an anti-interference extractor for extracting any multiple between 1-2 times is given according to the method disclosed by the invention.
The structure diagram of the anti-interference extractor for extracting any multiple between 1-2 times provided by the invention is shown in fig. 4, and the anti-interference extractor comprises an anti-aliasing low-pass filter and a polynomial interpolation filter.
The design example of the anti-interference extractor for extracting any multiple between 1-2 times provided by the invention is as follows:
1. the normalized bandwidth B of the input signal is determined.
In this example, the normalized bandwidth of the input signal is taken to be 0.12, i.e., B ═ 0.12.
2. The interference rejection decimator's suppression level of the interference signal is determined.
In this example, the interference suppression level is taken to be 50 dB.
3. And jointly designing the coefficients of the anti-aliasing low-pass filter and the polynomial interpolation filter.
And 3.1, determining design parameters of the anti-aliasing low-pass filter and the polynomial interpolation filter.
a. Passband cutoff frequency of anti-aliasing low pass filter
Passband cut-off frequency of sum polynomial interpolation filter
Equal to the normalized bandwidth of the input signal, i.e.
b. Two frequency values were taken within the frequency range [0.12, 0.38): Δ f10.175 and Δ f20.2425. Let the stop band cut-off frequency of the anti-aliasing low-pass filter be
The first stop band frequency range of the polynomial interpolation filter is [ 1-Deltaf2,1+Δf2]I.e., [0.75752,1.2425]。
And c, determining the number N and the order M of the polynomials used by the polynomial interpolation filter. In this example, N is 4 and M is 3.
And 3.2, calculating the coefficients of the anti-aliasing low-pass filter and the polynomial interpolation filter based on a least square criterion or a best consistent approximation criterion. In this example, the coefficients of the anti-aliasing low-pass filter calculated according to the least squares criterion are
The coefficients of the polynomial interpolation filter are of two types:
in this example, the coefficients for the type I Farrow filter calculated according to the least squares criterion are
For a type II Farrow filter, the coefficients are
And 3.3, calculating the amplitude-frequency response of the anti-interference decimator.
First, the amplitude-frequency response of the anti-aliasing low-pass filter and the polynomial interpolation filter are calculated respectively.
And then, multiplying the amplitude-frequency responses of the two signals by the frequency point correspondingly to obtain the amplitude-frequency response of the anti-interference extractor.
In this example, the amplitude-frequency response of the interference rejection decimator is shown in fig. 5.
3.4 judging the amplitude-frequency response of the anti-interference extractor in the interference frequency band
Whether the internal interference suppression capability meets design requirements.
Fig. 5 shows the amplitude-frequency response of the interference rejection decimator of this embodiment.
The solid line in the figure represents the amplitude-frequency response of the interference rejection decimator, and the dashed line represents the amplitude-frequency response of the polynomial interpolation filter.
As can be seen from the figure, the power gain of the anti-interference extractor in the interference frequency band [0.38,1.12] (the area between two black vertical lines in the figure) is < -50dB, namely, the interference suppression capability reaches more than 50dB, and the design requirement is met. Therefore, the interference signal can be effectively suppressed.
The power gain of the polynomial interpolation filter in the adjacent frequency band [0.38,0.5] of the input signal is > -8dB, and the suppression effect on the interference signal is poor.
The foregoing is merely a preferred embodiment of this invention and is not intended to be exhaustive or to limit the invention to the precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention.
Claims (5)
1. A design method of an anti-interference extractor for extracting any multiple between 1-2 times is characterized in that the anti-interference extractor comprises the following steps: an anti-aliasing low-pass filter and a polynomial interpolation filter;
the design method comprises the following steps:
s100, determining design parameters of an anti-aliasing low-pass filter and a polynomial interpolation filter, comprising the following steps of:
determining the passband cut-off frequency of the anti-aliasing low-pass filter and the passband cut-off frequency of the polynomial interpolation filter according to the normalized bandwidth of the input signal;
selecting two frequency values in a preset frequency range, determining the stop band cut-off frequency of the anti-aliasing low-pass filter according to one frequency value, and determining a first stop band frequency range of the polynomial interpolation filter according to the other frequency value;
determining the number and the order of polynomials used by the polynomial interpolation filter;
s200, calculating coefficients of an anti-aliasing low-pass filter and a polynomial interpolation filter;
s300, respectively calculating the amplitude-frequency responses of the anti-aliasing low-pass filter and the polynomial interpolation filter, and correspondingly multiplying the amplitude-frequency response of the anti-aliasing low-pass filter and the amplitude-frequency response of the polynomial interpolation filter according to frequency points to obtain the amplitude-frequency response of the anti-interference extractor;
s400, judging whether the interference suppression capability of the amplitude-frequency response of the anti-interference extractor in an interference frequency band reaches a preset interference suppression level threshold value:
if not, returning to the step S100, and re-executing the steps S100 to S400;
and if so, the anti-interference extractor is successfully designed.
2. The design method of the anti-interference decimator for decimating any multiple between 1-2 times as claimed in claim 1, wherein in step S100, the passband cut-off frequency of the anti-aliasing low pass filter
Passband cut-off frequency of sum polynomial interpolation filter
Equal to the normalized bandwidth B of the input signal, i.e.
3. The method for designing an anti-interference extractor for extracting any multiple between 1-2 times as claimed in claim 1, wherein in step S100, in the frequency range
Internally picking two frequency values Δ f1And Δ f2The stop band cut-off frequency of the anti-aliasing low-pass filter is set to be
The first stop band frequency range of the polynomial interpolation filter is [ 1-Deltaf2,1+Δf2]。
4. According to claimThe method for designing an anti-interference extractor for extracting any multiple between 1-2 times as claimed in claim 1, wherein in step S400, the interference frequency band is:
5. the utility model provides an anti-interference decimator that is used for arbitrary multiple extraction between 1~2 times which characterized in that includes:
the anti-aliasing low-pass filter is used for filtering partial interference signals in the interference frequency band; and
the polynomial interpolation filter is connected with the anti-aliasing low-pass filter and is used for cooperating with the anti-aliasing low-pass filter, filtering the residual interference signals in the interference frequency band and realizing 1-2 times of signal extraction in a resampling mode;
the anti-interference extractor is obtained by the design method of the anti-interference extractor for extraction of any multiple between 1-2 times according to any one of claims 1-4.
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