CN104215976A - Narrow-band interference resisting system based on cascaded wave traps - Google Patents

Abstract

The invention provides an anti-narrowband interference system based on cascaded notch filters. The received signal x(k) first passes through the first notch filter to obtain the output e(k), and the output e(k) passes through the first adaptive iteration The module controls the iterative update of the first notch filter parameter ω1(k), and at the same time outputs e(k) as the input of the second notch filter to obtain the final output signal y(k), and the output signal y(k) passes through the second notch filter The output signal controls the iterative update of the second notch filter parameter ω2(k); the first notch filter parameter ω1(k) and the second notch filter parameter ω2(k) respectively control the first notch filter and the second notch filter Complex coefficients for the notch filter. The invention has higher anti-interference tolerance, faster convergence speed, and lower signal loss, so that the circuit has the characteristics of miniaturization, low power consumption, chip realization and the like.

Description

An anti-narrowband interference system based on cascaded notch filters

technical field

The invention belongs to the technical field of satellite navigation, and relates to an anti-narrow-band interference system applied to a satellite navigation receiver system.

Background technique

In the satellite navigation system, because the power of the satellite signal is very low, usually lower than the space white noise, it is easily affected by external hostile and non-hostile interference signals or harmonics in the same frequency band during space propagation, causing the receiver to receive signal distortion. , the normal solution and positioning function cannot be completed, so the anti-jamming technology is the key technology in the satellite navigation system. In the current anti-interference signal processing method, there are mainly the following key problems:

(1) Removing interference signals in the time domain requires real-time processing of received signals, which will lead to a significant increase in circuit scale, power consumption and other indicators, which limits engineering implementation.

(2) Removing interference signals in the frequency domain will usually cause damage to the satellite navigation signal itself, resulting in a decrease in the signal-to-noise ratio, an increase in the bit error rate, and a limited improvement in the interference tolerance of the system.

(3) The convergence speed of the anti-jamming algorithm will directly affect the sensitivity of the receiver to capture and track signals, and has a key impact on the performance of the entire satellite guidance system.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides an anti-narrowband interference system based on cascaded notch filters. The anti-interference processing module has higher anti-interference tolerance, faster convergence speed, and lower signal loss. The circuit has the characteristics of miniaturization, low power consumption, chip implementation and the like. With the help of existing technical methods such as complex notch filter and LMS iterative algorithm, it can be applied to small systems such as hand-held receivers, and has broad application prospects.

The technical solution adopted by the present invention to solve its technical problems is: comprise two wave notch filters, described wave notch filter adopts complex number self-adaptive wave filter; Received signal x (k) first passes through the first wave notch filter, obtains the output e(k), the output e(k) controls the iterative update of the first notch filter parameter ω1(k) through the first adaptive iterative module, and at the same time outputs e(k) as the input of the second notch filter to obtain the final The output signal y (k), the output signal y (k) controls the iterative update of the second notch filter parameter ω2 (k) through the second output signal; the first notch filter parameter ω1 (k) and the second notch filter The filter parameter ω2(k) controls the complex coefficients of the first notch filter and the second notch filter respectively, the zero point of the notch filter is located on the unit circle, and the pole is on the connecting line between the zero point and the center of the circle and in the unit circle; The adaptive iterative module adopts LMS algorithm.

The beneficial effects of the present invention are:

(1) Only two stages of first-order complex notch filters are needed to process two interference signals with large amplitude differences; the circuit scale is reduced, and engineering implementation is more convenient.

(2) The initial frequency point of the search can be set arbitrarily, so the initial position and step size of the search can be set according to the feedback result of the front-end interference detection module to reduce the number of iterations of the algorithm.

(3) In the case of interference of the same size, the convergence speed of the present invention is about four times that of the traditional matrix notch filter, has good convergence performance, and improves the capture and tracking capability of the receiver.

(4) The notch is only performed at the interference frequency point, which reduces the damage to the broadband signal input to the notch filter.

Description of drawings

Fig. 1 is a first-order complex adaptive notch filter structure;

Fig. 2 is the structure of two cascaded adaptive notch filters;

Figure 3 is a flowchart of the LMS algorithm;

Figure 4 is a block diagram of the system-level application of the anti-jamming algorithm.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, and the present invention includes but not limited to the following embodiments.

The present invention is an interference suppression algorithm structure based on multi-cascaded complex notch filters. By taking the first-order self-adaptive complex notch filters as a unit and selecting a suitable convergence coefficient and cascading structure, the solution in the satellite navigation receiver is realized. Calculate the suppression of the narrowband interference signal by the front end.

The modulation method of spread spectrum communication is IQ modulation. The actual signal is divided into two orthogonal signal transmission channels. Each sampling point is a complex number, and its spectrum is similar to Gaussian white noise, so it can be processed by a complex adaptive notch filter. The structure of the complex adaptive notch filter is shown in Figure 1: x(k) and e(k) are the input and output sequences of the notch filter respectively, and ω is the convergence coefficient controlled by the iterative algorithm, which is iteratively modified until the algorithm converges. It controls the complex coefficient h in the transfer function of the notch filter, and A(Z)*B(Z) is the transfer function of the notch filter. The zero point of the notch filter is located on the unit circle, and the pole is on the line connecting the zero point and the center of the circle and within the unit circle. The notch filter can always work in a stable state. Due to the compensation of the amplitude-frequency characteristics and phase-frequency characteristics of the previous stage A(Z) by the latter stage B(Z), the whole notch filter only notches at the notch frequency, and the amplification of signals at other frequencies is basically 1 , the phase shift is approximately 0. Therefore, it can greatly weaken strong interference, and the introduced signal distortion is very small, so that the interference tolerance of the system is significantly improved.

The first-order notch filter is used as the notch unit, and the second-order complex notch filter is formed by cascading. The structure of the second-order notch filter is shown in Figure 2. The second-order notch filter is composed of two first-order notch filters. The received signal x(k) first passes through the first notch filter to obtain the output e(k), and e(k) controls the iterative update of the first notch filter parameter ω1(k) through an adaptive iterative algorithm, and its output As the input of the second notch filter, the final output signal y(k) is obtained, and y(k) controls the iterative update of the parameter ω2(k) of the second notch filter through an adaptive iterative algorithm.

The adaptive convergence algorithm adopts the LMS algorithm, and its idea is to use the output sequence of the notch filter as the error signal, and make the error signal converge through the closed-loop iterative algorithm. The calculation flow of the notch filter processing unit combined with the LMS algorithm is shown in Figure 3.

The power of the space satellite signal reaching the ground is about -130~-120dBm, and the interference-to-signal ratio required by the general satellite navigation receiver for the system's anti-interference tolerance is not greater than 85dB. Use the Armijo criterion to calculate and set the search step of the algorithm to 1e-11 ;The anti-jamming processing is carried out in the digital intermediate frequency domain, and the working frequency is usually not greater than 100MHz. Combined with the Nyquist criterion, the initial search frequency can be set arbitrarily within the clock operating frequency range; the hardware implementation based on the anti-jamming processing module is implemented in the entire satellite navigation The application scheme in the system is shown in Figure 4.

According to different interference signals, the algorithm can converge within 200 clock cycles, and the response speed is less than 10 milliseconds, so the algorithm structure can also be used to eliminate high-speed frequency sweep interference.

The present invention can also be applied to large-scale platforms. According to the requirements of the anti-interference ability of the system and the scale of the hardware platform, a higher-order notch filter cascade structure can be selected to configure hardware resources.

Claims (1)

1., based on an anti-arrowband EVAC (Evacuation Network Computer Model) for cascade trapper, comprise two trappers, it is characterized in that: described trapper adopts plural adaptive notch filter; Received signal strength x (k) is first by the first trapper, obtain exporting e (k), export e (k) controls the first trap parameter ω 1 (k) iteration renewal by the first adaptive iteration module, export the input of e (k) as the second trapper simultaneously, obtain final output signal y (k), output signal y (k) is upgraded by the iteration of the second output signal control second trap parameter ω 2 (k); Described first trap parameter ω 1 (k) and the second trap parameter ω 2 (k) controls the complex coefficient of the first trapper and the second trapper respectively, the zero point of trapper is positioned on unit circle, and limit is on the line in zero point and the center of circle and in unit circle; Described adaptive iteration module adopts LMS algorithm.