A method and device for suppressing simultaneous and same-frequency external interference using auxiliary antennas

Abstract

The present invention discloses a method and device for simultaneously suppressing co-frequency external interference using an auxiliary antenna. The method comprises the following steps: S1. Interference capture is performed using the interference capture method of the auxiliary antenna or the interference capture method of the reused main antenna; S2. Interference reconstruction and cancellation are performed in the RF front end or intermediate frequency portion. RF interference reconstruction techniques are divided into two categories based on the feed method of the RF interference reconstruction signal: direct-coupled RF interference reconstruction and digital-assisted RF interference reconstruction; S3. After RF domain interference suppression, the received signal is down-converted and analog-to-digital converted into the digital domain, and then digital domain interference reconstruction and cancellation are performed. The present invention effectively eliminates interference signals transmitted by hostile jammers through RF front-end interference reconstruction and cancellation suppression processing, and performs digital domain residual interference cancellation.

Description

Technical Field

[0001] The present invention relates to wireless communications, and in particular to a method and device for suppressing simultaneous and same-frequency external interference using an auxiliary antenna. Background Art

[0002] Wireless communication receivers are a crucial component of modern wireless communication systems. Due to their open nature and wireless transmission, receivers are susceptible to interference from various external wireless signals. These interference signals can come from other wireless devices, electromagnetic noise, and natural sources. Interference signals can disrupt the receiver's ability to receive the target signal, leading to problems such as degraded signal quality, increased bit error rates, and communication interruptions. Therefore, to improve receiver performance and stability, effective interference suppression techniques are necessary to reduce or eliminate interference from external wireless signals.

[0003] For example, in a communication reconnaissance confrontation scenario, the detected party usually uses a hostile jammer to transmit a high-power suppressive jamming signal to hide the useful signal and prevent the useful signal from being captured by other communication receiving equipment.

[0004] In this case, the signal received by the receiver is often a mixed signal affected by interference. To address this problem, interference cancellation technology has become an important solution. Interference cancellation uses signal reconstruction to create an estimated sample of the interfering signal, which is then used to offset the interfering signal in the received signal, thereby suppressing interference. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method and device for suppressing external interference at the same time and frequency using an auxiliary antenna. The interference signal emitted by the hostile jammer is effectively eliminated by reconstructing and suppressing the interference through the RF front-end interference and performing digital domain residual interference cancellation.

[0006] The object of the present invention is achieved through the following technical solution: a method for suppressing simultaneous and co-frequency external interference using an auxiliary antenna, assuming that the signal m(t) obtained by the receiver is a target signal to be detected and a mixed hostile interference signal through an unprocessed channel, expressed as:

[0007]

[0008] in, represents convolution, i(t) represents the hostile interference signal; u(t) represents the desired reconnaissance signal; represents Gaussian additive white noise; h1(t) represents the interference channel between the interference source and the main antenna; g1(t) represents the expected channel from the source to be detected to the main receiving antenna;

[0009] The method comprises the following steps:

[0010] S1. Interference capture using the auxiliary antenna or multiplexing the main antenna interference capture mode for interference capture;

[0011] S2. Interference reconstruction and cancellation are performed in the RF front end or IF section. Based on how the RF interference reconstruction signal is fed, RF interference reconstruction techniques are categorized into two types: direct-coupled RF interference reconstruction and digitally assisted RF interference reconstruction.

[0012] S3. After interference suppression in the RF domain, the received signal is down-converted and converted to digital domain, where it is then reconstructed and canceled.

[0013] A simultaneous and co-frequency external interference suppression device using an auxiliary antenna, comprising:

[0014] An interference capture module is used to perform interference capture using the interference capture mode of the auxiliary antenna and the interference capture mode of the multiplexed main antenna;

[0015] The RF domain interference reconstruction and cancellation module is used to perform interference reconstruction and cancellation in the RF front end or intermediate frequency part. Based on the feeding method of the RF interference reconstruction signal, RF interference reconstruction technology is divided into two categories: direct coupling RF interference reconstruction and digitally assisted RF interference reconstruction;

[0016] The digital domain interference reconstruction and cancellation module, after the RF domain interference is suppressed, the received signal enters the digital domain through down-conversion and analog-to-digital conversion, and then performs digital domain interference reconstruction and cancellation.

[0017] The beneficial effects of the present invention are: 1. Only a set of initial parameter values ​​need to be input, and the system can perform adaptive adjustments according to the algorithm;

[0018] 2. By utilizing the difference in the directional patterns of the main antenna and the auxiliary antenna, the auxiliary antenna can receive interference signals more accurately, achieving a certain degree of interference separation;

[0019] 3. Reducing interference power in the RF domain can avoid saturation of the LNA and ADC in the receiving channel, making the cancellation results more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of desired channel and interference channel;

[0021] Figure 2 Schematic diagram of the architecture for simultaneous co-channel interference suppression using auxiliary antennas;

[0022] Figure 3 This is the block diagram of the energy detection system;

[0023] Figure 4 To identify the overall idea of ​​disturbance;

[0024] Figure 5 Schematic diagram of the interference suppression method architecture for multiplexing the main receiving antenna;

[0025] Figure 6 Reconstruct the architecture diagram for RF multi-tap interference;

[0026] Figure 7 A schematic diagram of the architecture of a digital preprocessing-assisted radio frequency and digital domain interference suppression method;

[0027] Figure 8 Optimize the model graph for adaptive weights;

[0028] Figure 9 Schematic diagram of the adaptive transverse filter structure;

[0029] Figure 10 Schematic diagram of digital domain interference reconstruction architecture. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0031] 1. Scenario Introduction

[0032] In the communication reconnaissance confrontation scenario, in order to prevent the useful signal from being captured by other communication equipment, the detected party uses the hostile jammer to transmit a high-power suppressive jamming signal i(t) to hide the useful signal u(t) transmitted by the transmitter to be detected. Therefore, Figure 1 As shown, the signal m(t) obtained by the receiver is the target signal to be detected through the non-preprocessing channel and the mixed hostile interference signal, which is expressed as

[0033]

[0034] in, represents convolution, i(t) represents the hostile interference signal; u(t) represents the desired reconnaissance signal;

[0035] represents Gaussian additive white noise; h1(t) represents the interference channel between the interference source and the main antenna; g1(t) represents the expected channel from the source to be detected to the main receiving antenna.

[0036] To address this problem, the present invention proposes a method and device for simultaneously suppressing external interference at the same frequency using auxiliary antennas based on interference signal identification and positioning, thereby effectively eliminating the interference signal i(t) emitted by the hostile jammer.

[0037] 2. Invention Steps

[0038] By performing beamforming on two receive antenna arrays, the directional patterns of the two arrays are generated. The two received signals are beamformed using the MMSE method to separate the partial interference signals mixed in by the main receive array and the target signals mixed in by the auxiliary receive array. By selecting appropriate gain, the interference auxiliary channel is less likely to saturate, allowing strong interference signals to enter the digital domain directly. In the RF interference cancellation architecture, an antenna array (i.e., multiple receive antennas) is used to receive the same signal. The received signal is then processed to reduce or eliminate interference. Multi-tap interference cancellation technology is employed. The signals received by these receive antennas are fed into a processor, which weights and subtracts them. By simply varying the weighting coefficients for each receive antenna, the processor optimizes the signal cancellation effect. The optimal weights can be determined using various optimization algorithms. If a large number of multipath paths introduces significant system complexity, digitally assisted interference cancellation can be employed. Feedback control in the residual interference signal detection unit can simultaneously control the RF adaptive interference reconstruction parameters and the RF adjustments to the reconstructed interference amplitude (A) and delay (d), or it can control either parameter independently.

[0039] The present invention proposes a simultaneous and co-frequency external interference suppression architecture using auxiliary antennas. Figure 2 shown.

[0040] The method of the present application mainly includes three steps: interference signal capture, RF domain interference reconstruction and cancellation, and digital domain interference reconstruction and cancellation.

[0041] 2.1 Interference Capture

[0042] According to the interference signal capture method, interference capture can be divided into an interference capture method using an auxiliary antenna and an interference capture method using a multiplexed main antenna.

[0043] 2.1.1 Interference capture using auxiliary antennas

[0044] (1) Interference detection

[0045] Use Figure 3 The energy detection algorithm shown in FIG1 performs interference signal detection on the signal received by the main antenna. Figure 3 As shown in Figure 1, the signal m(t) captured by the main antenna is the target signal to be detected through the non-preprocessing channel and the mixed hostile interference signal:

[0046] By calculating the energy of the signal received by the main antenna within a certain period of time and comparing it with a preset threshold value, if the result is greater than the threshold value, it is determined that there is an interference signal in the received signal, otherwise there is no interference signal.

[0047] (2) Interference separation

[0048] Interference is separated using a blind source separation algorithm based on the independent component analysis (ICA) model. Based on the statistical independence of different signals, a linear separation matrix W is constructed using maximum likelihood estimation. This linear transformation is then applied to the main antenna received signal m(t), separating the mixed signal m(t) into independent signal components y(t) = Wm(t). The ICA method can be viewed as a process of finding an optimal solution. By iteratively updating the value of W according to a set objective function, the target signal and interference signal are separated to the maximum extent possible. The separated interference signal is then passed to the subsequent interference cancellation system.

[0049] (3) Interference positioning

[0050] Before interference location, the signals received by the primary and auxiliary antennas are a mixture of the target and interference signals. However, because the two signals arrive from different directions relative to the primary and auxiliary antenna arrays, their directivity patterns differ. Beamforming is performed on the receiving antenna arrays to obtain the directivity patterns of the two arrays. By comparing these directivity patterns, the difference between them is identified and the direction of the signal source is determined.

[0051] (4) Interference capture

[0052] After determining the direction of the interference signal source, the geographical location of the interference source is determined through positioning, and the auxiliary antenna is aimed at the interference source to capture the interference signal.

[0053] The signal s(t) captured by the auxiliary antenna is as follows: Figure 3 As shown, the hostile interference signal and the incoming jammer in the channel are

[0054] Part of the target signal to be detected entering the channel:

[0055]

[0056] in, represents Gaussian additive white noise; h2(t) represents the interference channel between the interference source and the auxiliary antenna; g2(t) represents the expected channel from the source to be detected to the auxiliary receiving antenna.

[0057] (5) Interference separation

[0058] After the interference signal is detected, it is necessary to effectively identify the interference signal. Active interference identification can be regarded as a pattern recognition problem. The overall idea of ​​interference identification is as follows: Figure 4 shown.

[0059] Feature extraction is equivalent to a nonlinear transformation, which transforms the signal into a suitable space for processing and extracts important information with classification significance from the signal. Feature parameter extraction is an optimization process, which removes redundancy and decorrelation of features from the perspective of improving classification efficiency and saving memory resources, and quantifies some essential characteristics of abstract signals to achieve the purpose of distinguishing signals according to signal characteristics. Currently, common feature parameters include the signal time domain autocorrelation coefficient, the 3dB bandwidth of the signal normalized spectrum, the signal power spectrum density, the signal energy concentration, etc. In addition, since the Fourier transform can only obtain the frequency components of a signal as a whole, but has no knowledge of the time when each component appears, two signals with a large difference in time domain may have different spectra. Figure 1 Therefore, we can use the short-time Fourier transform signal to perform time-frequency analysis. Short-time Fourier transform (STFT) is a commonly used time-frequency analysis method to extract signal features. Its basic transformation formula is:

[0060] F(ω,τ)=∫ R f(t)g*(t-τ)e -jωt dt

[0061] Where f(t) is the signal to be analyzed, g(t) is a time-finite function with compact support, and the short-time Fourier transform is the local spectrum of the signal f(t) near the analysis time τ.

[0062] The extracted characteristic parameters are classified and decided using algorithms such as decision trees to achieve interference classification. Finally, the interference signal parameters are estimated to obtain specific interference parameters, further determining the type of interference signal. Based on the decision tree concept, the characteristic parameters of the interference signal are used as the attribute value of each node to compare and judge with the preset threshold. Those greater than the threshold belong to category set A, and those less than the threshold belong to category set B. Then, the comparison and judgment are made again in category sets A and B respectively, forming new category sets C and D or category sets E and F. This cycle is repeated until each category set has only one element, that is, only one interference type. In this way, the interference signal can be identified.

[0063] 2.1.2 Interference Capture of Multiplexed Main Antenna

[0064] In addition to using auxiliary antennas to capture interference signals, it is also possible to Figure 5 The method shown in the figure reuses the main antenna to establish an additional RF channel to capture, reconstruct, and suppress interference signals. Unlike interference capture using auxiliary antennas, since there is no additional antenna to receive the interference signal, there is no need to locate the interference source. Interference capture using the main antenna reuses the following steps:

[0065] (1) Interference detection

[0066] The main antenna receives the signal m(t) and converts it into a digital signal m(n) after sampling by the ADC. The digital signal m(n) is processed as follows: Figure 2 The energy detection algorithm shown here performs interference signal detection by calculating the energy of the received signal within a certain time period and comparing it with a preset threshold. If the result is greater than the threshold, it is determined that an interference signal exists in the received signal; otherwise, no interference signal exists.

[0067] (2) Interference separation

[0068] In order to accurately reconstruct the interference signal on the auxiliary channel, it is necessary to artificially separate the target signal and the interference signal in the received signal. On the one hand, this can improve the accuracy of interference reconstruction cancellation, and on the other hand, it can also reduce the loss of the target signal in the interference cancellation.

[0069] The blind source separation algorithm is also used to separate the target signal and the interference signal. The separated interference signal is used as the interference signal captured by the auxiliary channel for subsequent RF domain and digital domain interference reconstruction and cancellation.

[0070] (3) Interference feature analysis

[0071] Feature analysis primarily involves mathematical analysis of interference signals, extracting characteristic parameters (amplitude, phase, frequency, power spectrum, and other aspects of the interference signal) from samples across multiple transform domains. Based on features such as the signal's power spectrum, the general characteristics of the interference signal are initially extracted. Decision tree algorithms, for example, are then used to classify the extracted characteristic parameters. Parameter estimation of the interference signal yields specific interference parameters, further enabling the determination of the interference signal's type.

[0072] 2.2 RF Domain Interference Reconstruction and Cancellation

[0073] RF domain interference reconstruction and cancellation involves performing interference reconstruction and processing in the RF front-end or intermediate frequency (IF) section to avoid saturation of the ADC in the receiver's analog channel and meet the ADC's input signal dynamic range requirements. RF interference reconstruction techniques can be categorized into two types based on how the RF interference reconstruction signal is fed: direct-coupled RF interference reconstruction and digitally assisted RF interference reconstruction. Direct-coupled RF interference reconstruction can be categorized into single-tap and multi-tap based on the number of taps. The single-tap interference reconstruction suppression architecture can be considered a special case of the multi-tap interference reconstruction suppression architecture.

[0074] 2.2.1 Direct-Coupled RF Interference Reconstruction and Cancellation

[0075] The direct-coupled RF interference reconstruction and cancellation method using an auxiliary antenna includes the following sub-steps:

[0076] (1) Active signal attenuation

[0077] In order to enable the auxiliary antenna to reconstruct the received signal s(t) in the digital domain through the ADC, an attenuator is used in the RF receiving channel at the auxiliary antenna receiving end to avoid ADC blocking and saturation;

[0078] (2) Interference reconstruction

[0079] Single-tap interference reconstruction suppression is mainly used to suppress the strongest direct path interference or interference channels with only one path. However, due to the influence of multipath effects, single-tap interference suppression often cannot meet the requirements. For multipath interference signals, multi-tap interference suppression methods are used.

[0080] The interference signal m received by the main antenna I (t) The modeling expression is as follows:

[0081]

[0082] The target signal m received by the main antenna U (t) The modeling expression is as follows:

[0083]

[0084] Therefore, the signal received by the main antenna can be expressed as:

[0085]

[0086] Among them, M and N represent the multipath numbers of the interference signal and the desired signal to the main receiving antenna, respectively, and a m , τ m ,θ m Represent the transmission delay, amplitude attenuation and phase offset of the interference channel respectively. n , τ n ,θ n They represent the transmission delay, amplitude attenuation and phase offset of the desired channel respectively.

[0087] Interference signal s received by the auxiliary antenna I (t) The modeling expression is as follows:

[0088]

[0089] The target signal m received by the auxiliary antenna U (t) The modeling expression is as follows:

[0090]

[0091] Therefore, the auxiliary antenna receiving signal can be expressed as:

[0092]

[0093] RF multi-tap interference reconstruction architecture such as Figure 6 As shown in Figure 1, considering the need to suppress multipath interference signals, in the multi-tap interference suppression structure, the interference reconstruction channel consists of multiple analog taps including a time delay device with a fixed delay, an adjustable attenuator, and an adjustable phase shifter. The interference is reconstructed using the received signal s(t) of the auxiliary antenna as the reference signal. The reconstructed signal s r (t) can be expressed as:

[0094]

[0095] Among them, L represents the number of taps of the reconstruction channel, a l , τ l ,θ l Represent the transmission delay, amplitude attenuation and phase offset of the interference reconstruction channel respectively. r (t) represents the reconstructed interference signal, u r (t) represents the reconstructed expected signal, n r (t) is the interference reconstruction channel noise. In addition, where a l,p , a l,q , τ l,p , τ l,q ,θ l,p ,θ l,q Satisfy respectively

[0096] a l,p =a l a p (10)

[0097] a l,q =a l a q (11)

[0098] τ l,p =τ l +τ p (12)

[0099] τ l,q =τ l +τ q (13)

[0100] θ l,p =θ l +θ p (14)

[0101] θ l,q =θ l +θ q (15)h r (t) is the impulse response of the interference reconstruction channel, and its expression is:

[0102]

[0103] (3) Interference cancellation

[0104] Fine-tune the amplitude (A) and delay (d) of the reconstructed interference signal to be used for the main antenna receiving signal in the RF domain.

[0105] Row offset:

[0106] s c (t)=As r (td) (17)

[0107] Among them, s r (t) is the interference signal reconstructed by the multi-tap model, s c (t) is the value of s r (t) The reconstructed signal after fine-tuning. At the front end of the RF receiving channel of the near-end device, the reconstructed interference signal s c (t) is subtracted from the received signal m(t) to complete the interference

[0108] Suppression, the received signal c(t) after interference suppression is:

[0109]

[0110] where i c (t) is the residual interference signal that is not completely suppressed, u c (t) is the remaining target signal, n c (t) represents the residual signal noise.

[0111] The main signal c(t) after RF cancellation is converted into a digital signal c(n) by the ADC and used as the input of two channels:

[0112] a) As the input for digital domain interference reconstruction, the residual interference after RF cancellation is reconstructed in the digital domain to complete further cancellation;

[0113] b) As the input of the energy detection module unit, the parameters of the control interference reconstruction are searched through the RF domain adaptive interference suppression algorithm.

[0114] (4) Residual interference signal detection

[0115] The residual interference signal detection module mainly implements the calculation of the residual interference signal energy and the adaptive search of the adjustable attenuator and adjustable phase shifter based on the gradient descent idea. The ultimate goal is to minimize the residual interference energy that enters the digital domain interference cancellation.

[0116] The goal is to minimize the residual interference signal energy. According to formula (18), the residual interference i c (t) can be expressed as:

[0117]

[0118] Among them, h1(t) and h2(t) represent the impulse responses of the interference channel when the interference signal reaches the main receiving antenna and the auxiliary antenna, respectively.

[0119] h r (t) is the impulse response of the interference reconstruction channel.

[0120] In the energy detection period T, the energy of the residual interference signal can be expressed as:

[0121]

[0122] The received signal c(n) after the ADC after the RF interference is cancelled can be expressed as:

[0123] c(n)=i c (n)+u c (n)+ε(n) (21)

[0124] Among them, u c (n) is the digital vector signal of the desired reconnaissance signal after quantization, ε(n) is the additive noise signal, i c (n) is the residual interference signal vector after analog domain interference cancellation. From the above formula, we can see that considering the delay is fixed, if we want to make the residual interference i c (n) The energy is minimum, and the RF reconstruction parameters A, d, and a l ,θ l The search is performed to realize the control of the interference reconstruction channel and the amplitude modulation and phase modulation after reconstruction, thereby realizing direct-coupled RF domain adaptive interference suppression.

[0125] 2.2.2 Digitally Assisted RF Interference Reconstruction and Cancellation

[0126] In addition to the direct RF coupling interference suppression method, considering the situation where the signal bandwidth is large and there are many multipath components, in order to reduce complexity and improve engineering feasibility, the digital preprocessing-assisted interference reconstruction method can be used to reconstruct and offset the interference signal.

[0127] Digitally assisted RF interference suppression architectures such as Figure 7 As shown in the RF interference reconstruction and cancellation section, the method mainly reconstructs the interference signal in the baseband digital domain, converts it into an RF signal through a DAC, and then performs interference suppression in the receiving channel. The direct coupling RF interference reconstruction and cancellation method using the auxiliary antenna includes the following sub-steps:

[0128] (1) Active signal attenuation

[0129] In order to enable the auxiliary antenna to reconstruct the received signal s(t) in the digital domain through the ADC, an attenuator is used in the RF receiving channel at the auxiliary antenna receiving end to avoid ADC blocking and saturation.

[0130] (2) Adaptive Interference Reconstruction

[0131] The auxiliary antenna receives the signal s(t) through an attenuator, down-conversion, and filtering, and then converts it into a digital signal s(n) through an ADC. Due to the existence of multipath effects, a digital domain adaptive transversal filter is combined with radio frequency interference cancellation. Using the digital signal s(n) as the reference signal, the digital domain adaptive transversal filter reconstructs the multipath reference signal and converts it to the radio frequency domain to eliminate the interference signal.

[0132] The adaptive transversal filter structure is as follows Figure 8 As shown. Among them, the input signal x(n), the output signal y(n) and the expected signal d(n), and the error signal e(n) = d(n) - y(n). N is the filter length, which is also the number of filter taps. In this patent, the filter input signal is the digital signal vector s(n) of the auxiliary antenna receiving signal, and the output signal is the reconstructed signal s r (n), the expected signal is the digital signal vector m(n) of the signal received by the main antenna. Figure 9 The LMS algorithm shown is an adaptive algorithm that iteratively solves the filter tap coefficients. The LMS algorithm process is as follows:

[0133] s r (n) = s T (n)ω(n) (22)

[0134] e(n)=m(n)-s r (n) (23)

[0135] ω(n+1)=ω(n)+2μe(n)ω(n) (24)

[0136] Where μ is the convergence factor (step size) and ω(n+1) is the filter tap weight for the next iteration. The cost function of the adaptive adjustment is expressed as the energy of the error signal e(n), that is,

[0137] J(ω)=E[|e(n)| 2 ] (25)

[0138] The result of adaptive adjustment makes the cost function J(ω) reach the minimum value at which the optimization algorithm converges.

[0139] (3) Interference cancellation

[0140] The multipath reconstructed signal s obtained by adaptive interference reconstruction r(n) Convert the signal into an analog signal through DAC r (t), at the front end of the RF receiving channel, the interference signal s is reconstructed r (t) is subtracted from the received signal m(t) to complete the interference suppression and obtain the suppressed signal c(t).

[0141] 2.3 Digital Domain Interference Reconstruction and Cancellation

[0142] The digital domain interference suppression of the present invention adopts time domain interference suppression. After the radio frequency domain interference suppression, the received signal enters the digital domain through down-conversion and analog-to-digital conversion. Figure 10 As shown, the digital domain simultaneous co-channel interference reconstruction and cancellation method for auxiliary antennas includes the following sub-steps:

[0143] (1) Delay alignment

[0144] To further suppress residual interference, the reference signals are first aligned in the digital domain. Because the signals reach the primary and auxiliary receive antenna arrays over different propagation distances and paths, there is a time delay between the signals received by the two receive antenna arrays. This time difference can lead to phase differences, which in turn affect signal demodulation and further processing. Therefore, time synchronization of the signals received by the two receive antenna arrays is also required.

[0145] Perform correlation operation on the main receiving antenna digital signal c(n) and the auxiliary receiving antenna digital signal s(n):

[0146]

[0147] Where τ is the delay to s(n). The delay τ corresponding to the maximum correlation value is m As the delay for s(n) synchronization alignment.

[0148] (2) Frequency alignment

[0149] Considering that the auxiliary antenna and the main antenna use non-cognate local oscillators and there is Doppler frequency shift, the received interference signal inevitably has a frequency offset. The frequency coarse synchronization algorithm based on FFT spectrum analysis is used to estimate the frequency offset.

[0150] The frequency offset estimation algorithm based on FFT is as follows:

[0151]

[0152] Where Δf is the frequency offset, m is the modulation order, N is the number of FFT points, R sym is the symbol rate, and s(n) is the received signal.

[0153] After frequency error compensation and frequency stepping based on FFT spectrum analysis, the remaining frequency error and phase error can be compensated and tracked using phase-locked loops (PLLs).

[0154] The auxiliary antenna receiving signal after time alignment and frequency alignment is expressed as:

[0155]

[0156] Among them, τ m is the time alignment delay, Δf m and θ are the frequency offset and phase offset compensated by the phase-locked loop after the frequency offset is roughly estimated.

[0157] (3) Nonlinear interference reconstruction

[0158] Considering that the radio frequency interference cancellation introduces additional signal nonlinear distortion due to the large power of the interference signal and the nonlinear characteristics of the radio frequency device, further reconstruction of the nonlinear characteristics is required.

[0159] The residual interference signal after RF domain interference suppression is:

[0160] c(t)=m(t)-s r (t) (29)

[0161] Where m(t) is the multipath signal received by the main receiving antenna, s r (t) is the reconstructed interference signal output by the RF domain interference suppression channel.

[0162] After quantization by the ADC, the digital baseband signal c(n) of the main receiving channel can be expressed as:

[0163] c(n)=m(n)-s r (n) (30)

[0164] Considering the nonlinear distortion generated by the RF part, the MP (polynomial) model of the RF domain interference reconstruction signal is:

[0165]

[0166] Among them, K is the nonlinear order of the interference reconstruction channel, and Q is the memory depth of the interference reconstruction channel. In order to eliminate the residual interference signal and the resulting nonlinear distortion in the digital domain, it is only necessary to use the auxiliary receiving channel baseband signal To reconstruct the interference signal, subtract the reconstructed interference signal from the baseband signal c(n), so only the following criteria need to be met:

[0167]

[0168] Among them, h is the interference signal reconstruction parameter matrix, |*|2 is the square of the modulus value. In order to meet the above criteria, use

[0169] The least squares method is used to estimate h, namely:

[0170]

[0171] Then the nonlinear estimation signal is:

[0172]

[0173] The signal after nonlinear interference suppression is recorded as:

[0174] c D (n) = c(n) - s nc (n) (35)

[0175] Thus, the nonlinear signal caused by the interference reconstruction channel is suppressed. To improve the interference cancellation capability and accuracy, the energy detection module can be used to feedback control the interference suppression parameters in the digital domain, just like in the RF domain.

[0176] In an embodiment of the present application, the frequency domain characteristic parameters of the interference feature analysis can be replaced by effective characteristic parameters in the time domain, wavelet transform domain, and bispectral transform domain; the interference identification algorithm can be replaced by other supervised learning decision algorithms, such as support vector machines, BP neural networks, etc.; the algorithm of the energy detection unit can be replaced by Newton's method, simulated annealing algorithm (SA), particle swarm algorithm (PSO), genetic algorithm (GA), etc.; the algorithm of digital domain interference reconstruction can be replaced by adaptive algorithms such as least mean square algorithm (LMS) and recursive least squares algorithm (RLS); the number of taps in both RF domain and digital domain interference reconstruction can be adjusted according to actual needs; when the number of multipaths is large or the signal bandwidth is wide, digital domain interference suppression can be replaced by frequency domain interference suppression method.

[0177] The foregoing description is a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Instead, the present invention can be used in other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for suppressing simultaneous and co-frequency external interference using an auxiliary antenna, characterized in that: Assume that the signal m(t) obtained by the receiver is the target signal to be detected and the mixed hostile interference signal through the unprocessed channel, which can be expressed as: in, represents convolution, i(t) represents the hostile interference signal; u(t) represents the desired reconnaissance signal; represents Gaussian additive white noise; h1(t) represents the interference channel between the interference source and the main antenna; g1(t) represents the expected channel from the source to be detected to the main receiving antenna; The method comprises the following steps: S1. Interference capture using the auxiliary antenna interference capture mode interference capture mode; S2. Interference reconstruction and cancellation are performed at the RF front end. Based on the method of feeding the RF interference reconstruction signal, RF interference reconstruction techniques are divided into two categories: direct-coupled RF interference reconstruction and digitally assisted RF interference reconstruction. S3. After interference suppression in the RF domain, the received signal undergoes downconversion and analog-to-digital conversion into the digital domain, where it undergoes digital domain interference reconstruction and cancellation. The step S3 comprises: S301. Delay alignment First, perform digital domain linear synchronization alignment on the reference signal. Because the signals reach the main and auxiliary receiving antenna arrays over different propagation distances and paths, there is a time delay between the signals received by the two receiving antenna arrays. Therefore, the signals received by the two receiving antenna arrays need to be time synchronized. Perform correlation operation on the main receiving antenna digital signal c(n) and the auxiliary receiving antenna digital signal s(n): Where τ is the delay to s(n); the delay τ corresponding to the maximum correlation value m As the delay of s(n) synchronization alignment; S302. Frequency alignment Considering the case where the auxiliary antenna and the main antenna use non-cognate local oscillators and Doppler shift exists, the received interference signal inevitably has a frequency offset. A coarse frequency synchronization algorithm based on FFT spectrum analysis is used to estimate the frequency offset. The FFT-based frequency offset estimation algorithm is as follows: Where Δf is the frequency offset, m is the modulation order, N is the number of FFT points, R sym is the symbol rate, s(n) is the received signal; After frequency error compensation and frequency stepping based on FFT spectrum analysis, the remaining frequency error and phase error are compensated and tracked using a phase-locked loop. The auxiliary antenna receiving signal after time alignment and frequency alignment is expressed as: Among them, τ m is the time alignment delay, Δf m and θ are the frequency offset and phase offset after coarse frequency offset estimation and compensation by the phase-locked loop; S303. Nonlinear Interference Reconstruction Considering that the large power of the interference signal and the nonlinear characteristics of the RF device cause the RF interference cancellation to introduce additional signal nonlinear distortion, it is necessary to further reconstruct the nonlinear characteristics: The residual interference signal after RF domain interference suppression is: c(t)=m(t)-s r (t) (5) Where m(t) is the multipath signal received by the main receiving antenna, s r (t) is the reconstructed interference signal output by the RF domain interference suppression channel; After quantization by the ADC, the digital baseband signal c(n) of the main receiving channel can be expressed as: c(n)=m(n)-s r (n) (6) Considering the nonlinear distortion generated by the RF part, the MP (polynomial) model of the RF domain interference reconstruction signal is: Among them, K is the nonlinear order of the interference reconstruction channel, and Q is the memory depth of the interference reconstruction channel. In order to eliminate the residual interference signal and the nonlinear distortion generated in the digital domain, it is necessary to use the auxiliary receiving channel baseband signal The interference signal is reconstructed and subtracted from the baseband signal c(n), so only the following criteria need to be met: Where h is the interference signal reconstruction parameter matrix, |*| 2 Expressed as the square of the modulus value; in order to meet the above criteria, the least squares method is used to estimate h, that is: Then the nonlinear estimation signal is: The signal after nonlinear interference suppression is recorded as: c D (n)=c(n)-s nc (n) (11) At this point, the nonlinear signal caused by the interference reconstruction channel is suppressed.

2. The method for suppressing simultaneous and co-frequency external interference using an auxiliary antenna according to claim 1, characterized in that: In step S1, the interference capture method using the auxiliary antenna includes: A1. Interference detection: Use energy detection algorithm to detect interference signals on the main antenna receiving signal: The signal m(t) captured by the main antenna is the target signal to be detected and the mixed hostile interference signal through the non-preprocessing channel: By calculating the energy of the signal received by the main antenna within a certain period of time and comparing it with the pre-set threshold value, if it is greater than the threshold value, it is determined that there is an interference signal in the received signal, otherwise there is no interference signal; A2. Interference separation: The blind source separation algorithm based on the independent component analysis model is used to separate the target signal and the interference signal, and the separated interference signal is used for interference identification, interference reconstruction and cancellation; A3. Interference positioning: Before interference location is performed, the signals received by the main antenna and the auxiliary antenna are a mixture of the target signal and the interference signal. However, since the two signals come from different directions relative to the main antenna array and the auxiliary antenna array, the radiation patterns are different. Perform beamforming on the receiving antenna array to obtain the directional patterns of the two arrays. By comparing their directional patterns, find the difference between them and determine the direction of the signal source; A4. Interference capture: After determining the direction of the interference signal source, locate the geographical location of the interference source through positioning, and aim the auxiliary antenna at the interference source to capture the interference signal: Assume that the signal s(t) captured by the auxiliary antenna is the hostile interference signal in the channel of the hostile jammer and the target signal to be detected that enters the channel: in, represents Gaussian additive white noise; h2(t) represents the interference channel between the interference source and the auxiliary antenna; g2(t) represents the expected channel from the source to be detected to the auxiliary receiving antenna; A5. Interference identification: After detecting the interference signal, it is necessary to effectively identify the interference signal. The overall idea of ​​interference identification is: Feature extraction: Feature extraction of the interference signal separated in A2 is performed based on short-time Fourier transform; Then, the extracted feature parameters are classified by the decision tree algorithm to achieve the classification of interference. Finally, the interference signal parameters are estimated to obtain specific interference parameters and further determine the type of interference signal: According to the idea of ​​decision tree, the characteristic parameters of the interference signal are used as the attribute value of each node to compare and judge with the preset threshold. The value greater than the threshold belongs to category set A, and the value less than the threshold belongs to category set B. Then, the comparison and judgment are made again in category sets A and B respectively to form new category sets C and D or category sets E and F. Multiple cycles are performed until there is only one element in each category set, that is, there is only one interference type, so as to realize the identification of the interference signal.

3. The method for suppressing simultaneous and co-frequency external interference using an auxiliary antenna according to claim 1, wherein: In step S2, the reconstruction cancellation method under direct coupling radio frequency interference reconstruction includes: C1. Active signal attenuation: In order to enable the auxiliary antenna to reconstruct the received signal s(t) in the digital domain through the ADC, an attenuator is used in the RF receiving channel at the auxiliary antenna receiving end to avoid ADC blocking and saturation; C2, Interference Reconstruction: Single-tap interference reconstruction suppression is mainly used to suppress the interference of the strongest direct path or the interference channel with only one path. For multipath interference signals, a multi-tap interference suppression method is used: The interference signal m received by the main antenna I (t) The modeling expression is as follows: The target signal m received by the main antenna U (t) The modeling expression is as follows: Therefore, the main antenna received signal is expressed as: Among them, M and N represent the multipath numbers of the interference signal and the desired signal to the main receiving antenna, respectively, and a m , τ m ,θ m Respectively represent the transmission delay, amplitude attenuation and phase offset of the interference channel; a n , τ n ,θ n They represent the transmission delay, amplitude attenuation and phase offset of the desired channel respectively; Interference signal s received by the auxiliary antenna I (t) The modeling expression is as follows: The target signal m received by the auxiliary antenna U (t) The modeling expression is as follows: Therefore, the auxiliary antenna receiving signal is expressed as: In the multi-tap interference suppression structure, the interference reconstruction channel consists of multiple analog taps including a time delay device with fixed delay, an adjustable attenuator and an adjustable phase shifter; the interference is reconstructed using the received signal s(t) of the auxiliary antenna as the reference signal, and the reconstructed signal s r (t) is expressed as: Among them, L represents the number of taps of the reconstruction channel, a l , τ l ,θ l Represent the transmission delay, amplitude attenuation and phase offset of the interference reconstruction channel respectively; i r (t) represents the reconstructed interference signal, u r (t) represents the reconstructed expected signal, n r (t) is the interference reconstruction channel noise, in addition, where a l,p , a l,q , τ l,p , τ l,q ,θ l,p ,θ l,q Satisfy respectively a l,p =a l a p (20) a l,q =a l a q (21) t l,p =t l +t p (22) t l,q =t l +t q (23) i l,p =θ l +θ p (24) i l,q =θ l +θ q (25) h r (t) is the impulse response of the interference reconstruction channel, and its expression is: C3. Interference cancellation Fine-tune the amplitude (A) and delay (d) of the reconstructed interference signal to offset the main antenna receiving signal in the RF domain: s c (t)=As r (t-d) (27) Among them, s r (t) is the interference signal reconstructed by the multi-tap model, s c (t) is the value of s r (t) reconstructs the signal after fine-tuning; at the front end of the RF receiving channel of the near-end device, the interference signal s is reconstructed c (t) is subtracted from the received signal m(t) to complete the interference suppression. The received signal c(t) after interference suppression is: where i c (t) is the residual interference signal that is not completely suppressed, u c (t) is the remaining target signal, n c (t) represents the residual signal noise; The main signal c(t) after RF cancellation is converted into a digital signal c(n) by the ADC and used as the input of two channels: a) As the input for digital domain interference reconstruction, the residual interference after RF cancellation is reconstructed in the digital domain to complete further cancellation; b) serving as the input of the energy detection module unit, searching for parameters that control interference reconstruction through the RF domain adaptive interference suppression algorithm; C4. Residual interference signal detection: The residual interference signal detection module mainly realizes the calculation of the residual interference signal energy and the adaptive search of the adjustable attenuator and adjustable phase shifter based on the idea of ​​gradient descent. The ultimate goal is to minimize the residual interference energy that enters the digital domain interference cancellation; With the goal of minimizing the residual interference signal energy, according to formula (28), the residual interference i c (t) is expressed as: Among them, h1(t) and h2(t) represent the impulse responses of the interference channel of the interference signal reaching the main receiving antenna and the auxiliary antenna respectively, and h r (t) is the impulse response of the interference reconstruction channel; In the energy detection period T, the energy of the residual interference signal is expressed as: The received signal c(n) after the ADC after the RF interference is cancelled is expressed as: c(n)=i c (n)+u c (n)+ε(n) (31) Among them, u c (n) is the digital vector signal of the desired reconnaissance signal after quantization, ε(n) is the additive noise signal, i c (n) is the residual interference signal vector after analog domain interference cancellation. Considering the delay is fixed, if the residual interference i c (n) The energy is minimum, and the RF reconstruction parameters A, d, and a l ,θ l The search is performed to realize the control of the interference reconstruction channel and the amplitude modulation and phase modulation after reconstruction, thereby realizing direct-coupled RF domain adaptive interference suppression.

4. The method for suppressing simultaneous and co-frequency external interference using an auxiliary antenna according to claim 1, wherein: In step S2, the reconstruction cancellation method under digitally assisted radio frequency interference reconstruction includes: D1, active signal attenuation In order to enable the auxiliary antenna to reconstruct the received signal s(t) in the digital domain through the ADC, an attenuator is used in the RF receiving channel at the auxiliary antenna receiving end to avoid ADC blocking and saturation; D2, Adaptive Interference Reconstruction The auxiliary antenna receives the signal s(t) through an attenuator, down-conversion, and filtering, and then converts it into a digital signal s(n) through an ADC. Due to the presence of multipath, a digital domain adaptive transversal filter is combined with RF interference cancellation. Using the digital signal s(n) as a reference signal, the digital domain adaptive transversal filter reconstructs a multipath reference signal and converts it to the RF domain to eliminate interference signals. Assume the input signal x(n), output signal y(n), desired signal d(n), and error signal e(n) = d(n) - y(n) of the adaptive transversal filter. N is the filter length, which is also the number of filter taps. The filter input signal is the digital signal vector s(n) of the auxiliary antenna receiving signal, and the output signal is the reconstructed signal s r (n), the desired signal is the digital signal vector m(n) of the signal received by the main antenna; the LMS algorithm is used as the adaptive algorithm to iteratively solve the filter tap coefficients: The LMS algorithm process is as follows: s r (n)=s T (n)ω(n) (32) e(n)=m(n)-s r (n) (33) ω(n+1)=ω(n)+2μe(n)ω(n) (34) Among them, μ is the convergence factor, ω(n+1) is the filter tap weight of the next iteration, and the cost function of adaptive adjustment is expressed as the energy of the error signal e(n), that is, J(ω)=E[|e(n)| 2 ] (35) The result of adaptive adjustment makes the cost function J(ω) reach the minimum value at which the optimization algorithm converges; D3, Interference Cancellation The multipath reconstructed signal s obtained by adaptive interference reconstruction r (n) Convert the signal into an analog signal through DAC r (t), at the front end of the RF receiving channel, the interference signal s is reconstructed r (t) is subtracted from the received signal m(t) to complete the interference suppression and obtain the suppressed signal c(t).

5. A device for suppressing simultaneous and co-frequency external interference using an auxiliary antenna, using the method according to any one of claims 1 to 4, characterized in that: include: An interference capture module is used to capture interference using the interference capture method of the auxiliary antenna; The RF domain interference reconstruction and cancellation module is used to perform interference reconstruction and cancellation in the RF front end. Based on the feeding method of the RF interference reconstruction signal, RF interference reconstruction technology is divided into two categories: direct coupling RF interference reconstruction and digitally assisted RF interference reconstruction; The digital domain interference reconstruction and cancellation module, after the RF domain interference is suppressed, the received signal enters the digital domain through down-conversion and analog-to-digital conversion, and then performs digital domain interference reconstruction and cancellation.

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