Intelligent anti-interference method based on interference deletion

Abstract

The invention relates to the technical field of communication, in particular to an intelligent anti-interference method based on interference deletion. Comprising the following steps: S1, carrying out signal scrambling on sending source data, and then carrying out turbo coding on the scrambled data; s2, carrying out OFDM (Orthogonal Frequency Division Multiplexing) modulation on the data blocks subjected to turbo coding; s3, controlling the transmitting end to transmit frequency hopping; s4, the receiving end obtains demodulated data; s5, adjusting the demodulated data obtained from the step S4; s6, carrying out amplitude limiting on the adjusted signal; s7, obtaining a signal-to-noise ratio mean value; s8, screening the demodulated data obtained from the step S4 according to a signal-to-noise ratio threshold; and S9, performing turbo decoding and signal descrambling on the data after interference deletion. The method has the advantages of simple algorithm, less resource consumption, adaptive threshold adjustment and the like.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to an intelligent anti-interference method based on interference cancellation. Background Art

[0002] With the continuous development and innovation of information systems, wireless communication technology has also experienced a leap from early simple radio communications to today's highly complex, diversified information systems that use radio as the core transmission medium. These systems are widely used in many key areas such as data link communications, navigation and control, intelligence reconnaissance, and friend-or-foe identification, greatly improving the efficiency and flexibility of military, civilian and commercial activities. However, while enjoying the convenience brought by technological progress, wireless communications are also facing severe challenges brought by their essential characteristics.

[0003] Due to the spatial openness of wireless communications, that is, the signal can be easily received by any device within the signal coverage during the transmission process, which makes the security boundary of information blurred. In addition, the non-cooperative nature of spectrum resources, that is, limited spectrum resources need to be shared by multiple users, and the lack of a central coordination mechanism leads to competition and conflict for spectrum resources, further exacerbating the uncertainty of information transmission. These factors provide a convenient path for various intentional or unintentional interference sources and unexpected signals to enter the information system, seriously threatening the reliability and security of information transmission.

[0004] Especially in recent years, with the continuous advancement of reconnaissance technology, the intelligent development of jamming technology and the significant improvement of communication equipment performance, the means of jamming wireless communication systems have become more efficient, covert and intelligent. Advanced reconnaissance equipment can accurately locate and analyze communication signals, while intelligent jamming systems can dynamically adjust jamming strategies according to real-time conditions, effectively weakening or even blocking communication links. In addition, some new types of network attacks, such as man-in-the-middle attacks and signal injection attacks, pose unprecedented challenges to the security of wireless communication systems.

[0005] In response to the requirements of anti-interference, the industry currently widely uses spread spectrum communication systems or frequency hopping communication systems as effective means to improve anti-interference capabilities. These two methods mainly use spread spectrum gain to improve the signal's recognition in noise, or quickly change the operating frequency to avoid conflicts with interference signals in the same frequency band, thereby effectively reducing the impact of interference signals on normal communications. However, although these methods have achieved remarkable results in improving anti-interference performance, they mainly focus on the technical implementation of the physical layer and have not yet fully realized higher-level intelligent processing of received signals. Summary of the invention

[0006] The present invention provides an intelligent anti-interference method based on interference cancellation, which aims to solve the problem that the prior art has not yet realized anti-interference processing of received signals.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] The present invention provides an intelligent anti-interference method based on interference deletion, comprising the following steps:

[0009] S1. Scramble the source data signal, the scrambling sequence is a specific PN code sequence, and then turbo encode the scrambled data;

[0010] S2. Interleave the turbo-encoded data, modulate it through phase coding, and then perform OFDM modulation in blocks;

[0011] S3. Control the transmitter to ensure that the duration of each frequency point covers an OFDM symbol by transmitting frequency hopping;

[0012] S4. The receiving end obtains demodulated data through capture, timing, frequency calibration, and OFDM demodulation;

[0013] S5. For the demodulated data obtained from S4, a certain mapping is performed according to the size and modulation type of the I and Q signal components of the data to adjust the I and Q signals of the demodulated signal;

[0014] S6. Limit the adjusted signal. If any signal of the I or Q channel exceeds the threshold, the signal at that moment is set to zero. In this way, the large interference signal is deleted first.

[0015] S7. Estimate the signal-to-noise ratio of the amplitude-adjusted data by OFDM symbol; obtain the signal-to-noise ratio of each OFDM symbol and the mean signal-to-noise ratio of all symbols, and calculate the first threshold Th1;

[0016] S8. The demodulated data obtained from S4 is screened according to the signal-to-noise ratio threshold. If the signal-to-noise ratio of the OFDM symbol is lower than Th1, 0 with the same length as the demodulated signal is output; if the signal-to-noise ratio of the OFDM symbol is higher than the first threshold Th1, it is determined whether the signal-to-noise ratio of the OFDM symbol is higher than the second threshold Th2. If it is higher, data is output, otherwise 0 with the same length as the demodulated signal is output;

[0017] S9. Perform turbo decoding and signal descrambling on the data after interference removal to obtain required data.

[0018] Furthermore, Turbo coding selects a 1 / 3 code rate.

[0019] Furthermore, OFDM modulation is selected to be performed using IFFT.

[0020] Furthermore, OFDM demodulation is performed using FFT.

[0021] Furthermore, the first threshold Th1 is set to 1 / 4 of the mean value of the signal-to-noise ratio.

[0022] The beneficial effects achieved by the present invention are:

[0023] (1) The present invention is based on the FH_OFDM system and utilizes a frequency hopping communication method to reduce the impact of interference signals on the communication system.

[0024] (2) The present invention first limits the amplitude of the demodulated signal to avoid the maximum value caused by interference, which affects the subsequent signal-to-noise ratio estimation and ensures accurate signal-to-noise ratio calculation.

[0025] (3) The signal-to-noise ratio of each OFDM symbol is dynamically calculated based on actual data, and the mean value of the signal-to-noise ratio is used as the first threshold. The threshold value also changes dynamically and can adapt to different situations.

[0026] (5) The second threshold is a smaller signal-to-noise ratio value, which is suitable for situations where all frequencies are interfered with, to avoid the continued transmission of erroneous data and reduce processing pressure; it plays a role of double protection.

[0027] (6) By comparing the signal-to-noise ratio of each OFDM symbol with the threshold, the signal with less interference is intelligently selected, and the performance of the turbo code is utilized to achieve final data recovery.

[0028] (8) Since the intelligent interference cancellation method is based on the FH_OFDM system, the frequency of interference can be intuitively determined according to the data output to the turbo decoding module by each OFDM symbol.

[0029] (9) The method for calculating the signal-to-noise ratio requires less computational effort. Based on the original communication system, only fewer resources are needed to complete the signal-to-noise ratio estimation calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0031] Figure 1 It is a flow chart of the method disclosed in the present invention; in the figure, the Y branch is a branch above the threshold, and the output is the demodulated data; the N branch is a branch below the threshold, and the output is 0 of the same length as the signal.

[0032] Figure 2 It is the constellation diagram before BPSK processing.

[0033] Figure 3 It is the constellation diagram before QPSK processing.

[0034] Figure 4 It is the constellation diagram after BPSK adjustment.

[0035] Figure 5 It is the constellation diagram after QPSK adjustment.

[0036] Figure 6 This is a flow chart of the present invention for screening demodulated data according to the signal-to-noise ratio threshold.

[0037] Figure 7 This is a bit error rate simulation experiment data diagram of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention (the following will be combined with the embodiments of the present invention to describe the technical solutions of the present invention). Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0040] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] In order to improve the anti-interference capability of the system, for the FH_OFDM system, the present invention provides an intelligent anti-interference method based on interference cancellation, such as Figure 1 As shown, the following steps are included:

[0042] S1. Scramble the source data, the scrambling sequence is a specific PN code sequence, and then turbo encode the scrambled data.

[0043] Among them, Turbo coding selects 1 / 3 code rate.

[0044] S2. Interleave the turbo-encoded data, perform phase coding modulation, and then perform OFDM modulation in blocks.

[0045] Among them, OFDM modulation is completed by using IFFT (Inverse Fast Fourier Transform).

[0046] S3. Control the transmitter to ensure that the duration of each frequency point covers an OFDM symbol through transmission frequency hopping, so as to reduce the interference effect through frequency hopping.

[0047] S4. The receiving end obtains demodulated data through capture, timing, frequency calibration, and OFDM demodulation.

[0048] Among them, OFDM demodulation is completed using FFT, and signal demodulation adopts the demodulation method corresponding to the transmitting end.

[0049] S5. For the demodulated data, a certain mapping is performed according to the size of the I and Q signal components of the data and the modulation type (specifically, since the process signal is a vector, direct superposition will result in loss of signal energy, so it is mapped to a fixed quadrant based on the amplitude and phase of the signal), and the I and Q signals of the demodulated signal are adjusted.

[0050] S6. Limit the adjusted signal. If any signal of the I or Q path exceeds the threshold, the signal at that moment is set to zero. In this way, the large interference signal is deleted first.

[0051] Specifically, the above two steps are to adjust the demodulated data according to the orthogonal two-way signal. The demodulated signal can be expressed as R(i)=I(i)+1i*Q(i); wherein R(i) is the demodulated signal, and I(i) and Q(i) are two orthogonal components. abs(I(i)) and abs(Q(i)) are the modulus values ​​of the two signal components. First, delete the large signal. The operation can be expressed as (abs(I(i))>th)||(abs(Q(i))>th), R(i)=0, wherein th is the judgment threshold (this judgment threshold is an empirical value, and the selected limit depends on the bit width limit of subsequent processing). Since the large signal is generally generated by an external interference signal, resulting in excessive signal energy at this moment, setting the data at this moment to zero can avoid the signal-to-noise ratio being affected by the extreme value and ensure the accuracy of the signal-to-noise ratio calculation.

[0052] In order to avoid the energy loss caused by vector summation, the signal energy is then concentrated. Due to the phase coding adopted, R(i) is currently distributed according to the phase modulation method of the transmitter, such as Figure 2 and 3 shown.

[0053] For BPSK signals, the adjustment method can be expressed as:

[0054] I(n)<0, Rb(n)=-I(n)+1i*Q(n)

[0055] For QPSK signals, the adjustment method can be expressed as:

[0056] abs(I(n))>=abs(Q(n)), I(n)>=0:Rb(n)=I(n)+1i*Q(n);

[0057] abs(I(n))>=abs(Q(n)), I(n)<0:Rb(n)=-I(n)-1i*Q(n);

[0058] abs(I(n))<abs(Q(n)),Q(n)> =0:Rb(n)=-1i*I(n)+Q(n);

[0059] abs(I(n)) <abs(Q(n)),Q(n)<0:Rb(n)=1i*I(n)-Q(n);

[0060] Among them, Rb(n) is the adjusted data. The adjusted signal constellation diagram is as follows Figure 4 and 5 shown.

[0061] S7. Estimate the signal-to-noise ratio of the amplitude-adjusted data by OFDM symbol; obtain the signal-to-noise ratio of each OFDM symbol and the average signal-to-noise ratio of all symbols, and calculate the first threshold Th1 based on this.

[0062] Specifically, the signal-to-noise ratio is calculated; the expression of the adjustment amplitude data Rb(n) is Rb(n)=X(n)+N(n); wherein n=1, 2, ..., N; X(n) represents the actual effective signal; N(n) represents random noise, and in order to simplify the derivation, additive white Gaussian noise with a mean of 0 is selected; n represents the signal position; and N represents the length of a single OFDM symbol.

[0063] The signal energy Ps can be approximately expressed as:

[0064]

[0065] in, Utilize the properties of additive white Gaussian noise.

[0066] The total signal power P can be expressed as:

[0067]

[0068] Therefore, the noise power Pn can be expressed as Pn=P-Ps.

[0069] The signal-to-noise ratio calculation expression is:

[0070]

[0071] Among them, fix means rounding; c is the adjustment coefficient, which is related to the phase encoding method. The signal-to-noise ratio of each OFDM symbol is calculated by the formula. Since the number of OFDM blocks sent by the sending module at a time is fixed, the receiving end can calculate the mean signal-to-noise ratio of the OFDM symbols received at one time, and use this mean as the subsequent decision threshold Th1.

[0072] S8. Filter the demodulated data obtained from S4 according to the signal-to-noise ratio threshold. If the signal-to-noise ratio of the OFDM symbol is lower than Th1, output 0 of the same length as the demodulated signal. If the signal-to-noise ratio of the OFDM symbol is higher than the first threshold Th1, determine whether the signal-to-noise ratio of the OFDM symbol is higher than the second threshold Th2. If it is higher, output data. Otherwise, output 0 of the same length as the demodulated signal. Specifically, use the threshold Th1 to filter the OFDM signal. If the signal-to-noise ratio of the OFDM symbol is lower than Th1, determine that the symbol is significantly interfered, and the data of the symbol will not participate in subsequent processing. If the signal-to-noise ratio of the OFDM symbol is higher than the first threshold Th1, determine whether the signal-to-noise ratio of the OFDM symbol is higher than the second threshold Th2. If it is lower than the threshold Th2, it is considered that all frequency points of the entire FH_OFDM system are interfered, and select the signal with better signal quality.

[0073] Since the interfered OFDM symbols are deleted, the influence of erroneous data on turbo decoding is avoided. Since turbo coding is interleaved, there is still a probability to recover the source data after deleting the interference signal.

[0074] The first threshold Th1 is a threshold obtained according to the mean value of the signal-to-noise ratio, which is generally 1 / 4 of the mean value of the signal-to-noise ratio. The second threshold Th2 is an empirical value, which selects a very small signal-to-noise ratio.

[0075] The first threshold is an adaptive threshold, which selects data with less interference according to the signal-to-noise ratio and deletes signals with severe interference, thereby ensuring the correctness of turbo decoding. If signals with severe interference participate in turbo decoding, the performance of turbo decoding will be reduced.

[0076] For the second threshold, all frequencies are considered to be interfered. At this time, the signal-to-noise ratio is poor, and the interference removal effect brought by the first threshold is poor. According to the second threshold, all OFDM symbols with low signal-to-noise ratio are directly deleted to ensure the integrity of interference removal. Figure 6 shown.

[0077] Specifically, two scenarios are considered: in the first scenario, if a few frequencies are occasionally interfered, the signal-to-noise ratio of the interfered frequencies is low, and Th1 can be used to delete the interfered frequencies; in the second scenario, all communication frequencies are interfered, and the estimated signal-to-noise ratios of all frequencies are very low at this time. In this scenario, find a signal with a large signal-to-noise ratio for subsequent processing; so TH2 needs to select a lower value, which is an empirical value and has no relationship with TH1.

[0078] S9. Perform turbo decoding and signal descrambling on the data after interference removal to obtain the required data; use the same PN code sequence as the transmitting end to perform the descrambling operation.

[0079] The simulation parameters are as follows: sampling rate 12.8MHz, source data 256bit, 1 / 3 code rate Turbo coding, DBPSK debugging of the coded data, data divided into 4 OFDM symbols. The bit error rate performance of different OFDM symbols with different interference removal at the receiving end is simulated respectively. Figure 7 It can be seen that in the FH_OFDM system, OFDM symbols of some frequencies are interfered, but the source signal can still be recovered, which has good anti-interference ability. However, as more OFDM symbols are deleted, the recovery ability decreases.

[0080] The above embodiments can be extended to FH_OFDM communication systems with different debugging modes, and have the advantages of simple algorithm, low resource consumption, and adaptive threshold adjustment.

[0081] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. An intelligent anti-interference method based on interference cancellation, characterized in that: The following steps are involved: S1. Scramble the source data signal, the scrambling sequence is a specific PN code sequence, and then turbo encode the scrambled data; S2. Interleave the turbo-encoded data, modulate it through phase coding, and then perform OFDM modulation in blocks; S3. Control the transmitter to ensure that the duration of each frequency point covers an OFDM symbol by transmitting frequency hopping; S4. The receiving end obtains demodulated data through capture, timing, frequency calibration, and OFDM demodulation; S5. After demodulation, the data is mapped according to the size and modulation type of the I and Q signal components of the data, and the I and Q signals of the demodulated signal are adjusted; S6. Limit the adjusted signal. If any signal of the I or Q channel exceeds the threshold, the signal at that moment is set to zero. In this way, the large interference signal is deleted first. S7. Estimate the signal-to-noise ratio of the amplitude-adjusted data by OFDM symbol; obtain the signal-to-noise ratio of each OFDM symbol and the mean signal-to-noise ratio of all symbols, and calculate the first threshold Th1; S8. The demodulated data obtained from S4 is screened according to the signal-to-noise ratio threshold. If the signal-to-noise ratio of the OFDM symbol is lower than Th1, 0 with the same length as the demodulated signal is output; if the signal-to-noise ratio of the OFDM symbol is higher than the first threshold Th1, it is determined whether the signal-to-noise ratio of the OFDM symbol is higher than the second threshold Th2. If it is higher, data is output, otherwise 0 with the same length as the demodulated signal is output; S9. Perform turbo decoding and signal descrambling on the data after interference removal to obtain required data.

2. The intelligent anti-interference method based on interference cancellation according to claim 1, characterized in that: Turbo coding selects 1 / 3 bit rate.

3. The intelligent anti-interference method based on interference cancellation according to claim 1 is characterized in that: OFDM modulation is performed using IFFT.

4. The intelligent anti-interference method based on interference cancellation according to claim 1 is characterized in that: OFDM demodulation is done using FFT.

5. The intelligent anti-interference method based on interference cancellation according to claim 1 is characterized in that: The first threshold Th1 is 1 / 4 of the mean value of the signal-to-noise ratio.

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