CN103078661A - An Interference Suppression Method for Spread Spectrum System Based on Iterative Threshold - Google Patents

Abstract

The invention provides a spread spectrum system interference inhibition method based on an iteration threshold. The method comprises the following steps of: calculating a mean value of a sequence obtained through FFT (Fast Fourier Transform) of a received signal sequence; setting an interference detection threshold to carry out interference judgment; utilizing a threshold clamping algorithm to obtain a new sequence, and calculating a mean value of the new sequence; and setting a new threshold to carry out secondary interference judgment and inhibition according to the mean value until a maximum value of a correlation peak of the updated signal sequence and the set local sequence is more than 2.5 times of a second maximum value. Through multiple iteration, a threshold suitable for a current jamming-to-signal condition is obtained, the calculation is simple, and the anti-interference ability is good.

Description

A kind of spread spectrum system disturbance restraining method based on the iteration thresholding

Technical field

The present invention relates to a kind of disturbance restraining method of spread spectrum system.

Background technology

Determine that it is the key of spread spectrum system interference suppression algorithm that suitable threshold filter disturbs.Because if the thresholding setting is too high, has to disturb and leak; The thresholding setting is too low, can produce distortion to desired signal again.Disturb in the reality and signal becomes when all being, and filter out portions of the spectrum what follow the energy of the energy of interference signal and useful signal relevant.

Document 1 " Suppression of Multiple Narrowband Interference in a Spread SpectrumCommunication System[IEEE J; 2000; SAC-18 (8); 1347-1356] " discloses several thresholding computational algorithms commonly used, first moment threshold algorithm TH=Ku particularly, wherein k is the thresholding optimized coefficients, and u is for receiving the signal average.The thresholding optimized coefficients choose normally that value rule of thumb obtains, but owing to can't determine the prior information of the form disturbed, adopt this thresholding to disturb inhibition, under dynamic interference environment, can not obtain preferably interference free performance.

The document 2 Suppression of narrow band interference research [electronic information countermeasure techniques; pp; 51-53; 2009] of adaptive threshold " under the low signal-to-noise ratio based on " is by calculating the model of narrowband Gaussian noise, thresholding optimized coefficients K in the proposition first moment threshold algorithm 〉=8 o'clock, under the condition of noiseless existence, can not cause damage to useful signal.Simultaneously, disclose a kind of segmentation interference suppression algorithm, chosen different thresholdings by the power that calculates current demand signal.This algorithm complex is high, and expense is large.Under dynamic interference environment, be difficult to equally obtain preferably interference free performance.

Existing technology does not all adopt the interference mitigation technology of iteration, is difficult to obtain to disturb preferably rejection under the dynamic disturbance environment

Summary of the invention

In order to overcome the deficiencies in the prior art, the invention provides a kind of for spread spectrum system interference mitigation technology thresholding iterative calculation method, consider implementation complexity and interference suppressioning effect, take the first moment threshold algorithm as the basis, through iteration repeatedly, to reach the adaptive thresholding of choosing when disturbing inhibition, finish the inhibition to interference signal.The computational methods of this thresholding have lower complexity, can obtain preferably interference free performance based on the interference suppression algorithm of this thresholding, and go in the dynamic disturbance environment.

The technical solution adopted for the present invention to solve the technical problems may further comprise the steps:

Step 1. is carried out the FFT conversion with the burst { r (l) } that receives, and obtains burst { R (k) }, asks its average

Wherein, l=0,1,2 ... N-1, k=0,1,2 ... N-1, N are the signal figure places of burst;

Step 2. is set interference detection threshold TH1=KM1, and judgement is disturbed in K 〉=8, and usage threshold clamper algorithm obtains new burst $R_1\left(k\right)=\left\{\begin{array}{cc}\mathrm{TH}1& R\left(k\right)\≥\mathrm{TH}1\\ R\left(k\right)& \mathrm{else}\end{array}\right.;$

Step 3. is calculated burst { R ₁(k) } average

Step 4. is set interference detection threshold TH2=KM2, disturbs judgement, the burst after obtaining upgrading

$R_2\left(k\right)=\left\{\begin{array}{cc}\mathrm{TH}2& R\left(k\right)\≥\mathrm{TH}2\\ R_1\left(k\right)& \mathrm{else}\end{array}\right.;$

Step 5. repeating step 3 and 4 is until the maximum of the relevant peaks of the local sequence of the burst after upgrading and setting is more than 2.5 times of second largest value.

Described average $M$ $2=M1-\frac{1}{N}\underset{j=0}{\overset{L}{\mathrm{\Σ}}}(R\left(j\right)-\mathrm{TH}1),$ Wherein, L is that spectral line surpasses the quantity of disturbing suppression threshold, sequence { R _jDisturb the spectral line of the interference detection threshold of judgement when being current interference judgement greater than the last time.

The invention has the beneficial effects as follows: the algorithm that passes through the iterative computation thresholding that the present invention proposes, can adaptive setting interference detection threshold, compare with existing thresholding set algorithm, can pass through repeatedly iteration, obtain a thresholding that is fit to current jamming-to-signal ratio situation, calculate simply good in anti-interference performance.

Description of drawings

Fig. 1 is the spectrogram that receives signal;

Fig. 2 is the interference free performance schematic diagram after the iteration, wherein, (a) is the spectrogram of an iteration after anti-interference, (b) is the correlation circumstance figure of an iteration after anti-interference;

Fig. 3 is the interference free performance schematic diagram behind the second iteration, wherein, (a) is the spectrogram of second iteration after anti-interference, (b) is the correlation circumstance figure of second iteration after anti-interference;

Fig. 4 is three interference free performance schematic diagrames after the iteration, wherein, (a) is the spectrograms of three iteration after anti-interference, (b) is the correlation circumstance figures of three iteration after anti-interference.

Embodiment

The present invention is further described below in conjunction with drawings and Examples.

A kind of based on disturbing the iteration thresholding computational methods that suppress, calculation procedure is as follows:

Step 1. is calculated and is received burst

Sequence after the conversion

Average M1:

$\mathrm{<figure-callout\; id="1"\; label="M"\; filenames="HDA00002604359800011.png,HDA00002604359800012.png"\; state="\{\{state\}\}">M</figure-callout>}1=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left|R\left(k\right)\right|}^2$

Step 2. is set interference detection threshold TH1=KM1, K=8 according to the thinking of document 2.When disturbing judgement, usage threshold clamper algorithm, the interference spectral line that estimates is set to interference detection threshold, obtains new sequence { R ₁(k) }, that is:

$R_1\left(k\right)=\left\{\begin{array}{cc}\mathrm{TH}1& R\left(k\right)\&GreaterEqual;\mathrm{TH}1\\ R\left(k\right)& \mathrm{else}\end{array}\right.(k=\mathrm{0,1,2}...N-1)$

Step 3. obtains sequence { R ₁(k) } afterwards, calculate { R this moment ₁(k) } average M2:

$\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="HDA00002604359800011.png,HDA00002604359800012.png"\; state="\{\{state\}\}">M</figure-callout>}2=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left|R_1\left(k\right)\right|}^2$

Step 4. is set interference detection threshold TH2=KM2.Carry out disturbing judgement the second time and suppressing the sequence { R after obtaining upgrading with this new thresholding ₂(k) }, that is:

$R_2\left(k\right)=\left\{\begin{array}{cc}\mathrm{TH}2& R\left(k\right)\&GreaterEqual;\mathrm{TH}2\\ R_1\left(k\right)& \mathrm{else}\end{array}\right.(k=\mathrm{0,1,2}...N-1)$

Later interference judgement is similar with the second time with inhibition, repeats no more here.

Owing to when carrying out disturbing judgement the second time and suppressing, need to repeat primary process, calculate M2, operand is larger, and the present invention proposes a kind of algorithm of simplification:

$\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="HDA00002604359800011.png,HDA00002604359800012.png"\; state="\{\{state\}\}">M</figure-callout>}2=M1-\frac{1}{N}\underset{j=0}{\overset{L}{\mathrm{\&Sigma;}}}(R\left(j\right)-\mathrm{TH}1)$

Wherein, L is that spectral line surpasses the quantity of disturbing suppression threshold, sequence { R _j, j=0,1 ... L is greater than the spectral line of TH1 when for the second time disturbing judgement.When calculating the average of the spectral line second time, utilize for the first time average M1 and TH1, will disturb in the judgement last time and find out greater than the point of thresholding, the formula of substitution calculating M2 gets final product.In like manner, this simplification computational methods can be used for the calculating of subsequent interference thresholding.This method has been avoided N point summation operation, a demand thresholding is outer count and, operand reduces greatly, is fit to use in the more situation of iterations in engineering is used.

Take Big Dipper C/A code sequence as example, sample frequency 62MHz, intermediate frequency 30.52MHz, arrowband jamming bandwidth 6M, signal interference ratio-30dB, signal to noise ratio-20dB.Receive the frequency spectrum of signal r (l)=s (l)+n (l)+j (l) as shown in Figure 1, when an iteration one time, namely adopt traditional first moment thresholding to carry out when anti-interference.

Through disturbing the sequence { R after suppressing ₁(k) } power spectrum and final correlated results as can be seen from Figure 2, because interference ratio is larger, cause average M1 also larger as shown in Figure 2 at this moment, and thresholding is too high, effectively do not suppress interference.Disturb maximum to only have several dB this moment.

When the iteration secondary, { R ₂(k) } power spectrum be final correlated results as shown in Figure 3, as can be seen from Figure 3, through second iteration, thresholding reduces, and again interference is suppressed.Disturb and dropped to below zero dB.Can find out that from correlated results this moment, the correlation of useful signal displayed, but relevant peaks not to give prominence to especially.

When through after the iteration for the third time, final sequence { R ₃(k) } power spectrum be final correlated results as shown in Figure 4, as can be seen from Figure 4, this moment is very effective to the inhibition of disturbing.Through after three iteration, basically disturb and all suppressedly fallen.And the result of its relevant peaks is very obvious.Disturb and suppress successfully.

Claims (2)

1. A spread spectrum system interference suppression method based on iterative threshold, is characterized in that comprising the steps: Step 1. Perform FFT transformation on the received signal sequence {r(l)} to obtain the signal sequence {R(k)}, and calculate its mean value

Wherein, l=0,1,2,...N-1, k=0,1,2,...N-1, N is the number of signal bits of the signal sequence; Step 2. Set the interference detection threshold TH1=K M1, K≥8, perform interference judgment, and use the threshold clamping algorithm to obtain a new signal sequence $R_1\left(k\right)=\left\{\begin{array}{cc}\mathrm{TH}1& R\left(k\right)\&Greater\; Equal;\mathrm{TH}1\\ R\left(k\right)& \mathrm{else}\end{array}\right.;$ Step 3. Calculate the mean of the signal sequence {R ₁ (k)} $m2=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left|R_1\left(k\right)\right|}^2;$ Step 4. Set the interference detection threshold TH2=K M2, perform interference judgment, and obtain the updated signal sequence ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}& \mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\\ {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; else</span>}\end{array}\right.<span\; class="notranslate">\; ;</span>$ Step 5. Repeat steps 3 and 4 until the maximum value of the correlation peak between the updated signal sequence and the set local sequence is more than 2.5 times the next maximum value. 2. the spread spectrum system interference suppression method based on iterative threshold according to claim 1, is characterized in that: described mean value

Among them, L is the number of spectral lines exceeding the interference suppression threshold, and the sequence {R _j } is the spectral line that is greater than the interference detection threshold of the previous interference judgment in the current interference judgment.

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