CN110690911B - Self-adaptive threshold method for effectively coping with pulse type interference - Google Patents
Self-adaptive threshold method for effectively coping with pulse type interference Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/7163—Spread spectrum techniques using impulse radio
- H04B1/719—Interference-related aspects
Abstract
The invention discloses a self-adaptive threshold method for effectively dealing with impulse type interference, which comprises the steps of carrying out weighted operation on input signal data and carrying out difference on an initial value of threshold calculation to obtain a first incremental value; summing the second increment obtained by the weighting operation of the first increment and the initial threshold calculation value to obtain the initial threshold value after the increment is overlapped and updating the initial threshold calculation value; performing weighted operation on the first incremental value to obtain a third incremental value; delaying input signal data to obtain a second matching signal; obtaining an interference peak value and performing weighting operation on the interference peak value to obtain a weighted peak value; if the pulse interference is detected, the current threshold value is equal to the updated initial threshold calculation value and the sum of the third increment and the weighted peak value is added; the threshold value is adaptively made to track corrections based on the updated input of the input signal. The invention ensures that the system keeps proper detection probability and false alarm probability, effectively improves the anti-pulse interference performance of the threshold, and ensures that the detection sensitivity cannot be lost under the condition of no interference.
Description
Technical Field
The invention relates to the field of digital communication, in particular to an adaptive threshold method for effectively coping with pulse type interference.
Background
In spread spectrum communication systems, digital matched filtering is typically used to achieve acquisition of the PN code. Because the power of the received signal may change with the change of the relative position of the receiver and the transmitter, the fixed threshold cannot effectively adapt to the dynamic change of the channel environment, the situations of high false alarm probability, high missed detection probability, incapability of correctly detecting the signal by the system, and the like easily occur, and the detection performance is often poor. To effectively solve these problems, adaptive threshold techniques may be employed. Namely, the decision threshold value is adaptively corrected according to the strength of noise or signal power, so that the system keeps proper detection probability and false alarm probability, thereby improving the capture performance. Meanwhile, in a communication system, it is often necessary to cope with various forms of interference. When receiving and capturing spread spectrum signals, if the spread spectrum signals are affected by impulse type interference signals, false alarm conditions that the detection threshold is mistakenly exceeded may occur, and the receiving system may affect effective receiving of the system due to false capturing.
Document 1 (poppy, aging, royal cloud, etc..) sets a pseudo code parallel capture threshold based on a constant false alarm criterion [ J ] data acquisition and processing, 2010,25(2): 234-. When the false alarm probability is changed, numerical simulation is not needed in the method, but the correction of the algorithm needs to be completed through statistical calculation, which is not beneficial to the realization of rapid capture, and meanwhile, the anti-interference is not designed.
Document 2 (shang kuang, guo ying, wangjinjiang, etc.. signal-to-noise ratio-based adaptive threshold decision PN code capture algorithm [ J ]. the university of post and telecommunications, south kyo 2014,34(4):88-93) proposes an adaptive change method for adjusting a threshold based on a signal-to-noise ratio by parameter setting to realize a decision threshold. Meanwhile, the method combines a median filtering algorithm and an amplitude limiting filtering algorithm to reduce the probability of false alarm caused by threshold burrs. The method considers the anti-interference and has stronger inhibition capacity on the narrow-band interference, but the pulse interference signal with stronger correlation easily breaks through the threshold after smoothing, and the method is difficult to deal with.
Patent application 1 (lacquer poplar, king diplonta. adaptive threshold controller and control method, direct sequence spread spectrum signal detection method and circuit, 201510624507.9, 2015) proposes an adaptive threshold controller and control method. Counting the number N of the current group of signals to be detected, calculating the shift correlation values of the N signals to be detected and the local spread spectrum sequence, judging whether the shift correlation values exceed the threshold, and counting the number N of the shift correlation values exceeding the threshold. And correcting the threshold based on the number N of the signals to be detected and the number N of the correlation values exceeding the threshold, and taking the corrected threshold as the threshold of the next group of signals to be detected. The method can effectively improve the detection probability and reduce the false alarm probability under the condition of large signal amplitude dynamic range, but a plurality of pulses need to be detected for correcting the threshold, and the threshold convergence speed is low.
Patent application 2 (shorea, a method of using adaptive thresholds in multipath searching, 02103918.6, 2003) provides a method of using adaptive thresholds in multipath searching. The method adopts a constant false alarm probability method based on screening average to calculate the threshold in the multipath search, and compared with the multipath search algorithm of a fixed noise threshold, the detection probability is improved by 5 percent. The method establishes the threshold by eliminating a plurality of peak values brought by multipath, avoids the influence brought by the multipath, but the performance of the threshold is reduced under the condition that a plurality of pulse interference peak values of relevant interference exist.
Patent application 3 (yao is as noble, chen 36191, li gunn, etc.) provides an interference suppression method of a spread spectrum system based on an iteration threshold, which is a spread spectrum system interference suppression method based on an iteration threshold, and the method comprises the steps of calculating the average value of a sequence after FFT conversion of a received signal sequence, then setting an interference detection threshold to carry out interference judgment, obtaining a new sequence by using a threshold clamping algorithm and calculating the average value, setting the new threshold according to the average value to carry out secondary interference judgment and suppression until the maximum value of the correlation peak values of the updated signal sequence and the set local sequence is more than 2.5 times of the second largest value. The interference suppression algorithm based on the threshold can obtain better anti-interference performance and can be suitable for a dynamic interference environment. However, the method is only suitable for the case that the interference is greater than the signal power, and the applicability to the strong correlated interference of weak power is not strong.
Disclosure of Invention
The invention aims to provide a self-adaptive threshold method for effectively coping with impulse type interference, which effectively improves the anti-impulse interference performance of a threshold by simultaneously using an interference signal and a noise signal as input of threshold generation, and simultaneously ensures that the detection sensitivity is not lost under the condition of no interference without using noise peak weighted superposition when the interference is not detected.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method of efficiently coping with an adaptive threshold for impulsive interference, the method comprising the steps of:
input signal data d (n) and a first weighting factor w1Multiplying to obtain a first matching signal w after weighting operation1D (n), and the first matching signal w1D (n) and the current threshold to calculate the initial value gamma0Performing difference to obtain a first increment value delta for threshold accumulation;
comparing the first delta value Δ to a second weighting factor w2Multiplying to obtain a second increment value w after weighting operation2Δ, and said second increment value w2Δ and threshold calculation initial value γ0Summing to obtain the second threshold initial value gamma after the increment is superimposed0+w2Δ; using the second threshold initial value gamma0+w2Δ update the original threshold calculation initial value γ0The second threshold is initially limited by gamma0+w2The value of delta is assigned to the initial value gamma of threshold calculation0Completing the primary operation of the accumulation operation branch;
multiplying the first delta value Δ by a third weighting factor w3To obtain a third incremental value w after weighting operation3Delta, completing direct operation branch calculation;
delaying input signal data d (n) for a fixed time to obtain a delayed second matching signal;
carrying out interference peak value extraction operation on the delayed second matching signal to obtain an interference peak value, and multiplying the interference peak value by a fourth weighting factor w4Obtaining a weighted peak value;
when pulse interference is detected, the weighted peak value is superposed on the threshold value, so that the current threshold value gamma is equal to the updated initial threshold calculation value gamma0Adding the third increment value w simultaneously3The sum of Δ and the weighted peaked value;
comparing the delayed second matching signal of the spread spectrum system with the current threshold value gamma to judge whether the receiver receives the signal sent by the transmitting terminal or not to obtain a capturing judgment result;
the above process is repeated according to the updated input of the input signal d (n), and the threshold value gamma is adaptively tracked and corrected.
Preferably, the current threshold value γ is equal to γ when detecting the absence of impulse interference0+w3·Δ。
Preferably, the method for adaptive threshold further comprises the following steps:
delaying the input signal data d (N) by N0A sampling clock, the delayed second matching signal is d (N-N)0)；
The peak value of the interference is marked as p (N-N)0) The weighted peaked value is w4·p(n-N0) The current threshold value gamma is equal to gamma0+w3·Δ+w4·p(n-N0)。
Preferably, the method for adaptive threshold further comprises the following steps:
using the matched signal data after matched filtering as input signal data d (n); the spread spectrum system matches the received original signal to obtain a spread spectrum gain, and uses the matched and filtered data as the input signal data d (n).
Preferably, the first increment value Δ ═ w1·d(n)-γ0。
Preferably, the first initial value of the threshold calculation initial value is set to be half of the maximum value of the correlation peak of the receiver through correlation matching of the spread spectrum signal.
Preferably, the third weighting factor w3Is set to the second weighting factor w2One tenth of the total.
Preferably, when said second matching signal d (N-N)0) When the signal is larger than the threshold value gamma, the receiver captures a signal transmitted by a transmitting end; when the second matching signal d (N-N)0) When the value is less than the threshold value gamma, the receiver is notCapturing the signal transmitted by the transmitting end.
Compared with the prior art, the invention has the beneficial effects that: the self-adaptive threshold technology for effectively coping with the pulse type interference effectively utilizes the strength change of noise and signal power to adaptively correct the judgment threshold value, so that a system keeps proper detection probability and false alarm probability, simultaneously utilizes the peak characteristic of pulse noise, and when an interference signal is detected, noise peaks are weighted and superposed on a receiving threshold, so that the pulse interference resistance of the threshold can be effectively improved, and simultaneously, when the interference is not detected, the weighted superposition of the noise peaks is not used, so that the detection sensitivity is not lost under the condition of no interference.
Drawings
FIG. 1 is a schematic block diagram of an adaptive threshold method for efficiently handling impulsive interference according to the present invention;
FIG. 2 is a schematic block diagram of an orthogonal four-channel correlator according to the present invention;
FIG. 3 is a diagram illustrating the relationship between the threshold and the position of the matching signal according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the present invention provides an adaptive threshold method for effectively dealing with impulse type interference, which comprises the following steps:
firstly, a spread spectrum system matches signals received by a communication receiver to obtain spread spectrum gain; and using the matched and filtered data d (n) as input signal data for subsequent calculation of the decision threshold. Where n is the discrete time after the matching data is normalized with respect to the matching signal sampling time interval. The input signal is typically the output signal of an orthogonal four-channel correlator, and the functional block diagram of the orthogonal four-channel correlator is shown in fig. 2, that is, the invention uses a four-channel matched filter to implement pseudo code correlation operation to obtain the receiving spread spectrum gain.
The four-channel correlator respectively matches the I path and Q path received data after the down-conversion of the receiver with the I path and Q path PN codes to form four matching channels; the matching process is to multiply the PN code and then calculate the accumulated sum; and finally, squaring and summing the values after matching the four channels to obtain a complete correlation peak value after PN code matching.
(II) weighting the input matched filtered data d (n) to obtain a weighted matched signal w1D (n), and the weighted matching signal w1D (n) and threshold calculation initial value γ0And performing difference calculation to obtain an increment value delta for threshold accumulation, wherein the delta is w1·d(n)-γ0。
Thirdly, weighting the increment value delta, namely multiplying the increment value delta by the weight w2Obtaining a weighted incremental value w2Δ, and increment the value w2Δ and threshold calculation initial value γ0Summing, i.e. performing accumulation operation on the initial threshold calculation value to obtain the initial threshold value gamma after the increment is overlapped0+w2·Δ。
(IV) using the initial threshold value gamma after the superposition increment0+w2Δ update original threshold calculation initial value γ0And completing one operation of the accumulation operation branch.
The first initial value of the initial threshold calculation value can be set to be half of the maximum value of the correlation peak, so that the noise signal is not over-threshold, and the correlation peak is not submerged. Through the accumulation operation branch, the initial threshold calculation value is smoothly changed along with the size of the input matching signal.
And (V) simultaneously directly carrying out weighting operation on the increment value delta obtained by calculation in the step (II), namely multiplying the increment value delta by the weight w3Obtaining a weighted delta value w3And delta, completing direct operation branch calculation.
Wherein the weighting factor w3General settingsIs a weighting factor w2And the specific values of other weighting factors in the graph are determined according to the signal full-range energy value and the weight relationship of contribution of each branch to the threshold value.
Sixthly, delaying the matching signal d (N) which is input at the beginning by a fixed time through a delay unit, namely delaying by N0A sampling clock to obtain a delayed matched signal d (N-N)0)。
The basis of the delay time setting is as follows: the envelope of the delayed matched signal with a certain pulse width is within the envelope interval of the threshold, and the specific delay time length needs to be determined according to the pulse width of the signal, as shown in fig. 3, that is, the matched output signal needs to be within the envelope of the threshold. Since the input signal is delayed, the threshold will increase before the signal and decrease after the signal, and will only quickly break the threshold when a matching peak signal occurs and be detected.
(seven) pairs of delayed matched signals d (N-N)0) Extracting interference peak value to obtain interference peak value p (N-N)0) The extraction of the peak can be realized by signal truncation or high-pass filtering and the like; and will interfere with the spike p (N-N)0) Multiplied by a weighting value w4To obtain a weighted peaked peak w4·p(n-N0) (ii) a Then judging whether impulse interference is detected: if impulse interference is detected, peak value w is weighted4·p(n-N0) Is sent to a summation unit for calculating a threshold value, namely, the following step (eight) is carried out, and the peak value w is weighted4·p(n-N0) Superimposing the threshold value; if no interference is detected, the step (eight) is not executed, i.e. noise spike weighted superposition is not used, and the current threshold value is equal to that when gamma is equal to gamma0+w3Δ, which ensures that no loss of detection sensitivity occurs without interference. Wherein the superimposed weighted spikes p (N-N)0) It will be possible to effectively filter out the impulsive interference spikes and prevent the interference spikes from crossing the threshold causing false alarms, as shown in fig. 3.
(VIII) calculating the threshold of the accumulation operation branch to obtain an initial value gamma0(i.e., the updated initial threshold calculation value described in step four)) Directly calculating the weighted incremental value w obtained by the branch3Δ and weighted peak value w of the impulsive interference peak extraction branch4·p(n-N0) Summing the three, and calculating to obtain the current threshold value gamma, namely gamma is gamma0+w3·Δ+w4·p(n-N0)。
(nine) matching signal d (N-N) after time delay of spread spectrum system0) And comparing with the threshold value gamma in the step eight to judge whether the receiver receives the signal sent by the transmitting terminal. When matching the signal d (N-N)0) If the signal is greater than the judgment threshold gamma, the receiver captures the signal transmitted by the transmitting end; when matching the signal d (N-N)0) And if the signal is smaller than the judgment threshold gamma, the signal of the sending end is not captured.
And (ten) with the updated input of the matching signal d (n), the threshold value gamma adaptively follows the amplitude change of the input matching signal d (n) according to the interaction of the accumulation operation branch and the direct operation branch. That is, the matching signal d (n) becomes larger and smaller as it becomes larger. Accordingly, the threshold value γ will implement the function of adaptively tracking d (n) and modifying its own size.
In summary, the present invention provides an adaptive threshold method for effectively dealing with impulse type interference, which effectively utilizes the variation of noise and signal power to adaptively modify the decision threshold value, so that the system maintains proper detection probability and false alarm probability, and simultaneously utilizes the peak characteristic of impulse noise, when an interference signal is detected, the noise peak is weighted and superposed on the receiving threshold, thereby effectively improving the anti-impulse interference performance of the threshold, and when no interference is detected, the weighted superposition of the noise peak is not used, thereby ensuring that the detection sensitivity is not lost under the condition of no interference.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (8)
1. A method for efficiently coping with an adaptive threshold for impulsive interference, the method comprising:
input signal data d (n) and a first weighting factor w1Multiplying to obtain a first matching signal w after weighting operation1D (n), and the first matching signal w1D (n) and the current threshold to calculate the initial value gamma0Performing difference to obtain a first increment value delta for threshold accumulation;
comparing the first delta value Δ to a second weighting factor w2Multiplying to obtain a second increment value w after weighting operation2Δ, and said second increment value w2Δ and threshold calculation initial value γ0Summing to obtain the second threshold initial value gamma after the increment is superimposed0+w2Δ; using the second threshold initial value gamma0+w2Δ update the original threshold calculation initial value γ0The second threshold is initially limited by gamma0+w2The value of delta is assigned to the initial value gamma of threshold calculation0Completing the primary operation of the accumulation operation branch;
multiplying the first delta value Δ by a third weighting factor w3To obtain a third incremental value w after weighting operation3Delta, completing direct operation branch calculation;
delaying input signal data d (n) for a fixed time to obtain a delayed second matching signal;
carrying out interference peak value extraction operation on the delayed second matching signal to obtain an interference peak value, and multiplying the interference peak value by a fourth weighting factor w4Obtaining a weighted peak value;
when pulse interference is detected, the weighted peak value is superposed on the threshold value, so that the current threshold value gamma is equal to the initial threshold value gamma calculated by the threshold0Adding the third increment value w simultaneously3The sum of Δ and the weighted peaked value;
comparing the delayed second matching signal of the spread spectrum system with the current threshold value gamma to judge whether the receiver receives the signal sent by the transmitting terminal or not to obtain a capturing judgment result;
the above process is repeated according to the updated input of the input signal d (n), and the threshold value gamma is adaptively tracked and corrected.
2. The method for adaptive thresholding of claim 1,
when detecting the absence of impulse interference, the current threshold value gamma is equal to gamma0+w3·Δ。
3. The method for adaptive thresholding of claim 1,
delaying the input signal data d (N) by N0A sampling clock, the delayed second matching signal is d (N-N)0)；
The peak value of the interference is marked as p (N-N)0) The weighted peaked value is w4·p(n-N0) The current threshold value gamma is equal to gamma0+w3·Δ+w4·p(n-N0)。
4. The method of adaptive threshold according to claim 1 or 2 or 3,
the threshold input signal data d (n) is the signal data output by the orthogonal four-channel correlator matching.
5. The method for adaptive thresholding of claim 1,
first increment value Δ ═ w1·d(n)-γ0。
6. The method for adaptive thresholding of claim 1,
the first initial value of the threshold calculation initial value is set to be half of the maximum value of a correlation peak of a receiver through matching spread spectrum signals.
7. The method for adaptive thresholding of claim 1,
the first mentionedThree weighting factors w3Is set to the second weighting factor w2One tenth of the total.
8. The method of adaptive threshold of claim 3,
a second matching signal d (N-N) after time delay of the input signal data d (N)0) When the signal is larger than the threshold value gamma, the receiver captures a signal transmitted by a transmitting end;
a second matching signal d (N-N) after time delay of the input signal data d (N)0) And when the signal is smaller than the threshold value gamma, the receiver does not capture the signal transmitted by the transmitting end.
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