CN117200813B - Method and system for detecting burst signal of radio navigation system - Google Patents
Method and system for detecting burst signal of radio navigation system Download PDFInfo
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Abstract
The invention relates to the field of radio navigation system testing, in particular to a method and a system for detecting burst signals of a radio navigation system. According to the method, based on burst signals of noise statistics, noise is separated from output signals, gain is adjusted to enable I, Q two paths of digital baseband signals to reach reference amplitude, the output signal value is used as a comparison reference, the performance of a demodulator is guaranteed, a modulation domain detection unique code can effectively improve the demodulation performance of the burst signals and reduce the loss rate of the burst signals, an adaptive threshold correlation detection algorithm is adopted to reject analog source noise of navigation signals received by the signals and compare the threshold of the signals, the resource consumption is low, the quantization error is small, the response speed and the convergence speed are faster, the signal processing is more stable, and the method has strong anti-interference and anti-interception capabilities.
Description
Technical Field
The invention relates to the field of radio navigation system testing, in particular to a method and a system for detecting burst signals of a radio navigation system.
Background
In recent years, many scholars have proposed a signal energy-based detection algorithm, a time domain data-based algorithm, a frequency domain data-based detection algorithm, a short-time self-phase function-based energy statistics algorithm, a high-order statistics method, and a zero-crossing detection algorithm; the detection algorithm based on signal energy has great relevance between the setting of the decision threshold and the environmental noise, and a general decision threshold is not selected, so that the energy detection method also loses the application value; the double sliding window method is most commonly used in a detection algorithm based on signal energy, the algorithm is easy to realize, but the threshold selection of the algorithm is related to the gain of a receiver, the final detection effect can be influenced by the signal-to-noise ratio, and the performance is slightly poor when the signal-to-noise ratio is low. The detection algorithm based on the frequency domain data mainly comprises a frequency domain energy statistical method and a cyclic spectrum estimation algorithm. The detection method based on the frequency domain data has stronger noise suppression capability, but has large data volume requirement, can be used for detecting burst signals with larger burst interval and lower signal-to-noise ratio, and is not applicable to the system; the detection method based on the time domain data needs small data volume, but requires high signal-to-noise ratio, and is suitable for the real-time detection of burst interval small signals; the short-time white sum closing method needs to calculate the correlation function of the signal, has large calculated amount and is not beneficial to hardware realization; the total algorithm is poor in performance or large in calculation amount, and the requirement of high-speed burst signal detection is difficult to meet. In the above detection scheme, one link is to compare the peak value after matching correlation with a set threshold. In detecting the unique code by using the correlation method, if a fixed threshold is adopted, the detection is difficult to be correctly performed.
Disclosure of Invention
Aiming at the situation that burst communication is more and more, the invention aims at the problems that the energy detection method in burst signal detection has low detection probability and the stable detection method is complex in calculation, and aims at improving the detection performance and processing real-time performance, the invention provides the detection method and the detection system for the burst signals of the radio navigation system, which separate noise from output signals based on noise statistics, adjust gain to enable I, Q digital baseband signals to reach reference amplitude, and take the output signal value as a comparison reference, thereby ensuring the performance of a demodulator, effectively improving the demodulation performance of the burst signals and reducing the loss rate of the burst signals by detecting unique codes in a modulation domain, adopting an adaptive threshold correlation detection algorithm to reject the analog source noise of the navigation signals received by the signals and comparing the threshold of the signals, and has the advantages of low resource consumption, small quantization error, faster response speed and convergence speed, more stable signal processing and strong anti-interference and anti-interception capability.
The invention has the following specific implementation contents:
a method for detecting a burst signal of a radio navigation system, the method comprising:
firstly, extracting a radio frequency signal received from an antenna, converting the frequency of the radio frequency signal, and filtering and amplifying; down-converting the radio frequency signals after filtering and amplifying to generate intermediate frequency analog signals; converting the intermediate frequency analog signal into an intermediate frequency digital signal, and converting the intermediate frequency digital signal into an I-path quadrature baseband digital signal and a Q-path quadrature baseband digital signal;
Modulating and demodulating the I-path quadrature baseband digital signals and the Q-path quadrature baseband digital signals to obtain navigation characteristic signals and noise signals; counting the noise amplitudes of the navigation characteristic signals and the noise signals, filtering the noise signals according to the noise amplitudes, and taking the noise amplitudes of the navigation characteristic signals as comparison reference values;
then filtering analog source noise in the navigation characteristic signals by using a self-adaptive threshold detection algorithm, detecting the threshold of the navigation characteristic signals, and judging that a unique code is detected if the threshold is exceeded; otherwise, generating an adjusting signal, adjusting the level of the radio frequency signal, and obtaining an adjusted navigation characteristic signal;
and finally, detecting the adjusted navigation characteristic signals by using a frequency domain data detection algorithm, and generating detection test results.
In order to better implement the present invention, further, the comparing the noise amplitude of the navigation feature signal as the reference value includes:
and judging whether the navigation signal is a navigation characteristic signal or a noise signal according to the comparison reference value, if the navigation signal is larger than the comparison reference value, judging the navigation signal as the navigation characteristic signal, otherwise, directly filtering the navigation signal as the noise signal.
In order to better realize the invention, further, after statistics of the navigation characteristic signal and the noise amplitude of the noise signal, if the arrival time of the antenna is uncertain and the duty ratio is small, the self-adaptive threshold correlation detection algorithm is adopted to remove the analog source noise of the navigation characteristic signal, the navigation characteristic signal is subjected to threshold comparison, if the navigation characteristic signal exceeds the threshold, the detection of the unique code is judged, otherwise, the detection is judged not, the gain of the quadrature baseband digital signal is adjusted, a gain control signal is generated to adjust the quadrature baseband digital signal to the reference amplitude, the gain control is carried out by adopting a numerical control mode in combination with the characteristics of the signals transmitted by all navigation subsystems, and the gain of a receiver is controlled.
In order to better realize the invention, further, after taking the noise amplitude of the navigation characteristic signal as a comparison reference value, if the duty ratio of an antenna is small, calculating a new duty ratio W=n/3T, calculating the ratio of the new navigation characteristic signal amplitude to the normal navigation characteristic amplitude according to the new duty ratio, then adopting a time domain averaging method to calculate the noise level value of a navigation subsystem, estimating the amplitude values of the first n sample points of the navigation characteristic signal, calculating the average value of the amplitude values, carrying out time domain averaging on the navigation characteristic signal according to the average value to obtain a noise level value which is larger than the average value of the amplitude values and is far smaller than the navigation characteristic signal amplitude, and taking the noise level value as the comparison reference value; wherein n is the number of pulses, and T is the total period of the pulses.
In order to better implement the present invention, further, after the filtering the noise signal, the method includes:
generating a control voltage, adjusting the amplitude of the radio frequency signal and generating a gain according to the control voltage;
detecting the level of the radio frequency signal, and comparing the level with a set reference level after filtering to obtain an error signal;
generating a direction control signal according to the error signal; the direction control signal is used for indicating the adjustment direction of the gain;
selecting an adjustment step length according to the error values of the direction control signal and the error signal, setting a gain step amount according to the adjustment step length, comparing a reference signal with set target energy, calculating to obtain a gain value adjustment step length according to a comparison result, and calculating a gain value according to the gain value adjustment step length;
and performing proportional integral filtering processing on the energy of the error signal, controlling the gain value according to the proportional integral to obtain an energy adjustment coefficient, and multiplying the energy adjustment coefficient by a navigation characteristic signal to obtain an analog output signal level.
To better implement the invention, further, after said deriving the analog output signal level, it comprises:
Generating a gain control signal and an AGC feedback control signal according to the noise level value and the analog output signal level;
multiplying the navigation characteristic signal with the gain factor after feedback according to the AGC feedback control signal, squaring the amplitude, and comparing with a set reference level;
subtracting the reference signal from the AGC feedback control signal, subtracting the signal amplitude to obtain a compensation signal, determining the size of a product factor according to time average by the compensation signal, and estimating average energy;
selecting a corresponding gain factor according to the speed, and multiplying the gain factor by the compensation signal to obtain a gain variation;
generating a next gain value according to the gain variation, the gain value and the integral initial value;
multiplying the gain value with the I baseband digital signal and the Q baseband digital signal; and obtaining the I baseband digital signal and the Q baseband digital signal after gain adjustment, and finishing feedback regulation.
The system comprises a gain controllable amplifying unit, a down-conversion unit, an intermediate frequency digitizing unit and a digital signal processing unit which are connected in sequence;
The gain controllable amplifying unit is used for extracting the radio frequency signal received from the antenna, converting the frequency of the radio frequency signal and filtering and amplifying;
the down-conversion unit is used for down-converting the radio frequency signals after filtering and amplifying to generate intermediate frequency analog signals;
the intermediate frequency digitizing unit is used for converting the intermediate frequency analog signal into an intermediate frequency digital signal and converting the intermediate frequency digital signal into an I-path quadrature baseband digital signal and a Q-path quadrature baseband digital signal;
the signal processing unit is used for modulating and demodulating the I-path quadrature baseband digital signals and the Q-path quadrature baseband digital signals to obtain navigation characteristic signals and noise signals; counting the noise amplitudes of the navigation characteristic signals and the noise signals, filtering the noise signals according to the noise amplitudes, and taking the noise amplitudes of the navigation characteristic signals as comparison reference values; filtering analog source noise in the navigation characteristic signals by using a self-adaptive threshold detection algorithm, detecting the threshold of the navigation characteristic signals, and judging that a unique code is detected if the threshold is exceeded; otherwise, generating an adjusting signal, adjusting the level of the radio frequency signal, and obtaining an adjusted navigation characteristic signal; and detecting the adjusted navigation characteristic signals by using a frequency domain data detection algorithm, and generating detection test results.
In order to better realize the invention, the signal processing unit further comprises an amplitude demodulation unit, a noise statistics unit, a signal comparison unit and a digital AGC unit which are connected in sequence;
the amplitude demodulation unit is used for judging whether the navigation characteristic signal or the noise signal is the navigation characteristic signal according to the comparison reference value, if the comparison reference value is larger than the comparison reference value, the navigation characteristic signal is judged, and if the comparison reference value is not the navigation characteristic signal, the noise signal is directly filtered.
In order to better realize the invention, further, the noise statistics unit counts the noise amplitude, the signal comparison output unit eliminates the analog source noise of the navigation characteristic signal by adopting a self-adaptive threshold correlation detection algorithm under the condition that the arrival time of an antenna is uncertain and the duty ratio is small, and carries out self-threshold comparison on the navigation characteristic signal, if the self-threshold comparison exceeds the threshold, the detection of the unique code is judged, otherwise, the detection is not judged, the digital AGC unit adjusts the gains of the I-path digital baseband signal and the Q-path digital baseband signal, generates a gain control signal, adjusts the I-path digital baseband signal and the Q-path digital baseband signal until reaching the reference amplitude, and carries out gain control in a numerical control mode according to the characteristics of the signals transmitted by each navigation subsystem.
In order to better realize the invention, further, the noise statistics unit calculates a new duty ratio w=n/3T according to the small duty ratio of the antenna signal, calculates the ratio of the new navigation characteristic signal amplitude to the normal navigation characteristic amplitude according to the new duty ratio, then calculates the noise level value of the navigation subsystem by adopting a time domain averaging method, estimates the amplitude values of the first n samples of the navigation characteristic signal, calculates the average value of the amplitude values, performs time domain averaging on the navigation characteristic signal according to the average value to obtain a noise level value which is larger than the average value of the amplitude value and is far smaller than the navigation characteristic signal amplitude, and takes the noise level value as a comparison reference value; wherein n is the number of pulses, and T is the total period of the pulses.
In order to better realize the invention, the signal comparison output unit is further characterized in that the signal comparison output unit processes antenna signals with burstiness, low duty cycle and large dynamic variation;
the signal comparison output unit comprises a gain controlled amplifying circuit and a control voltage forming circuit, and an electric control attenuator is inserted between all stages of amplifiers of the gain controlled amplifying circuit to form an AGC detector and a low-pass smoothing filter;
After the AGC detector detects and filters low-frequency modulation components and noise through the low-pass smoothing filter, the control voltage of the control gain controlled amplifying circuit is generated and output to the gain controllable amplifying unit, and the amplitude of the radio frequency signal is adjusted and gain is generated;
the gain controllable amplifying unit controls the level detection circuit to perform level detection, and the level detection circuit is compared with a set reference level after filtering to obtain an error signal; generating a direction control signal according to the error signal, wherein the direction control signal is used for indicating the adjustment direction of the gain; and selecting an adjustment step length according to the error values of the direction control signal and the error signal, setting a gain stepping amount according to the adjustment step length, comparing a reference signal with target energy, calculating a gain value adjustment step length according to a comparison result, calculating a gain value, performing proportional integral filtering processing on the error energy, controlling the gain value according to the proportional integral to obtain an energy adjustment coefficient, and multiplying the energy adjustment coefficient with an input signal to obtain an analog output signal level.
In order to better realize the invention, further, the digital AGC unit generates a gain control signal and an AGC feedback control signal according to the noise level value from the noise statistics unit and the level of the analog output signal output by the signal comparison unit, extracts the AGC feedback control signal, multiplies the navigation characteristic signal by the gain factor after feedback, squares the amplitude and then compares the amplitude with the set reference level;
Subtracting the reference signal from the feedback signal, subtracting the amplitude of the output signal to obtain a compensation signal, determining the magnitude of a product factor by time average of the compensation signal, estimating average energy, controlling a gain controllable amplifying unit according to the average energy, selecting a corresponding gain factor according to the speed, multiplying the gain factor with the compensation signal to obtain a gain variation, and generating a next gain value according to the gain variation, the gain value and an integral initial value;
multiplying the gain value with the I baseband digital signal and the Q baseband digital signal; and obtaining the I baseband digital signal and the Q baseband digital signal after gain adjustment, and completing the feedback regulation function of the digital AGC unit.
The invention has the following beneficial effects:
(1) The invention uses digital intermediate frequency sampling to replace the prior frequency conversion and filtering in analog AGC, the signal received by the antenna is filtered, amplified, down-converted after the digital intermediate frequency sampling, and the noise of the signal receiving problem is removed and the signal is compared under the condition that the arrival time is uncertain and the duty ratio is small, thereby controlling the gain of the receiver.
(2) The invention completes the signal AGC control jointly through noise statistics, amplitude demodulation, digital AGC control and signal comparison output, breaks through the real-time key technology of the high-dynamic and high-precision navigation signal, and has the technical indexes that: the pseudo-range phase control precision is better than 0.01m, the speed resolution is 1mm/s, and the acceleration resolution is 10mm/s 2 Jerk resolution 10mm/s 3 The diversity and accuracy of the satellite navigation field simulation scene are improved. The resource consumption of a Global Navigation Satellite System (GNSS) receiver and the system thereof in the links of development, experiment, production, test, application and the like is greatly reduced.
(3) The invention ensures that the baseband input signal keeps proper amplitude level, is beneficial to the baseband processing to avoid overload and fully utilizes quantization bits to reduce quantization errors as much as possible. The digital AGC overcomes the defects of the traditional AGC system to a certain extent, the response speed and the convergence speed are higher, and the system performance is more stable. Has important significance for reducing the pressure of the analog AGC part and ensuring the processing precision of the DSP.
(4) The invention can ensure the performance of the demodulator by separating noise from the output signal of the amplitude demodulation unit, and the modulation domain can effectively improve the demodulation performance of the burst signal and reduce the loss rate of the burst signal by detecting the unique code. Meanwhile, the characteristics of intermediate frequency digitization of the receiver are fully utilized, the noise amplitude is counted, the gain adjustment speed is increased, and the signal searching time is shortened.
(5) The invention can improve the signal receiving effect of the receiver, enhance the adaptability of the receiver under different environments and improve the performance of the receiver. The method solves the problem of large dynamic receiving of the sudden characteristic navigation signal when the transmission signal of the navigation signal is 80dB changed in an airport system consisting of a plurality of system navigation subsystems.
Drawings
Fig. 1 is a schematic block diagram of a detection system for burst signals of a radio navigation system according to an embodiment of the present application;
fig. 2 is a schematic block diagram of a signal processing unit according to an embodiment of the present application.
Detailed Description
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it should be understood that the described embodiments are only some embodiments of the present invention, but not all embodiments, and therefore should not be considered as limiting the scope of protection. All other embodiments, which are obtained by a worker of ordinary skill in the art without creative efforts, are within the protection scope of the present invention based on the embodiments of the present invention.
In the description of the present invention, it should be noted that, unless explicitly stated and limited otherwise, the terms "disposed," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; or may be directly connected, or may be indirectly connected through an intermediate medium, or may be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
Navigation systems play an important role in aircraft, submarines, ships, etc. Radio navigation is performed by measuring electrical signal parameters, such as amplitude, frequency, phase, etc., of electromagnetic waves as they propagate in space. In integrated navigation systems, the specific gravity of data communication is larger and larger, the data transmission rate is higher and higher, and the output values of various navigation subsystems show strong correlations, and the correlations provide necessary information redundancy for fault detection, such as inertial navigation systems, global positioning systems and Doppler speed sensors, which can provide the speed of a navigation body. Under normal conditions, the difference between these measurements is within a certain range, and if a navigation subsystem fails, the normal correlation with other subsystems will be destroyed. Because the operation environment is complex and special, once the components in the operation environment fail, decision-making personnel can be misled to make wrong decisions, economic loss is caused, and the accident of machine destruction and human death is caused. Therefore, the failure hazard is large. The inertial navigation system installed on the airplane is fixedly connected with the airplane body, is greatly influenced by the vibration of the airplane and is usually in a high dynamic environment. Under the high altitude environment, the components of the navigation equipment are subjected to various environmental factors such as high and low temperature, noise, electromagnetism, space particle radiation, vibration, space environment chemical pollution and the like, so that the output parameters of the navigation system have great errors compared with the output under the laboratory condition. The errors generated are mainly as follows: cone error, pitch error, and scroll error. These errors add difficulty to fault detection and diagnosis. The data processing capability of the airborne navigation computer is limited, and the airborne resources are limited, so that the excessively complex fault diagnosis method cannot be adopted in order to achieve the real-time performance and accuracy of fault detection and diagnosis in comparison with ground equipment. The general fault detection and diagnosis method cannot be directly applied to the navigation system. The occurrence of faults is abrupt, such as the failure of an inertial navigation system mounted on an aircraft, which cannot be handled during the flight due to limited manual intervention capacity, which may lead to a task failure.
At present, a multi-body satellite navigation signal simulation technology and multi-body navigation signal simulation source equipment are widely applied. The multi-body navigation signal simulation source can simulate navigation scenes in various environments such as cities, suburbs, canyons, oceans and the like in a laboratory environment, so that the consumption of resources in links such as development, experiments, production, testing and application of a GNSS receiver and a system thereof is greatly reduced, and the performance of the multi-body navigation signal simulation source can directly influence the satellite navigation terminal product to participate in a plurality of key technologies such as navigation satellite orbit high precision, navigation signal generation, carrier phase precise control and transmission error simulation. To overcome the effects of external factors on the receiver input signal, automatic gain control techniques are required. The automatic gain control system comprises two parts, namely radio frequency gain control and baseband gain control. The radio frequency front end employed by the receiver system provides only a variable gain amplifier but no automatic gain control function. Among them, the automatic gain control AGC is an automatic control method that causes the gain of an amplifying circuit to be automatically adjusted according to the signal strength. In an analog AGC unit in the automatic gain control technology, the level value of a comparator in a level detection/comparison circuit is analog, and is easy to be influenced by temperature and circuit component performance to cause fluctuation, and the fluctuation change can cause the comparator to judge delay when a received signal is in a low level state, so that the received signal is lost. The dynamic range low end of the analog AGC can typically only be 30dB. The digital AGC unit level detection/comparison circuit is implemented by a DSP. The general DSP signal processing program does not consider the intermittence of navigation signal emission and the complexity of signal format, and can cause decoding errors in the test of a microwave landing system MMS, a rangefinder system DME system and an air traffic control system ATC. Because of the guiding continuity characteristic of the navigation signal and the ground air loss, the transmitting power of the ground station is always small in long distance and large in short distance, and because the acting distances of the navigation subsystems are different from each other, the transmitting signal power of the subsystems is far different even on the same test point. For each navigation subsystem, the duty ratio of the signals is different, the obtained noise level value and gain are also different, and the obtained digital AGC control level is used as a signal comparison reference and is not a fixed value but is related to the characteristics of each subsystem. In burst communication mode, the output level of the receiver depends on the input signal level and the gain of the receiver, and the signal strength received by the receiver varies greatly with the channel environment and the receiving condition. For various reasons, the input signal of the receiver often has a large variation range, and the signal can be one microvolts or tens of microvolts when weak, and can reach hundreds of millivolts when strong. The strongest signal and the weakest signal may differ by up to several tens of decibels, a variation range referred to as the dynamic range of the receiver. When the transmitter is operated at a distance of, for example, several hundred meters, the signal power received by the receiver exceeds the dynamic range of the rf front-end chip, which can disable the AGC in the rf front-end, so that the amplitude of the output signal is not constant, and the amplifier may be burned out due to the oversized input signal. If the amplifier output signal exceeds the dynamic range of the radio frequency front end AGC, the amplitude of the intermediate frequency continuous signal exceeds the normal amplitude, and the duty ratio of the MAG output signal is directly caused to exceed 1/3. The ratio of the intermediate frequency output continuous signal amplitude to the normal signal amplitude is related to the duty cycle of the output signal at the MAG end, so the key of the AGC control module is to design a circuit to detect the duty cycle of the output signal.
Factors influencing the input signal of the receiver are numerous, such as the magnitude of the power of the transmitting station, the distance of the receiver from the transmitting station, variations in propagation conditions of the signal during propagation, such as ionosphere and troposphere disturbances, weather variations, variations in the environment of the receiver, and the effect of artificially generated noise on the receiver, etc. If the signal suddenly experiences a relatively large change, the discontinuous transmission DTX situation cannot be timely determined, but is processed according to the conventional signal, the gain value is increased. The terminal receiving device may also encounter a large attenuation condition of the received signal, for example, when the variation range is within 40dB, the gain of the AGC cannot be kept up in time, so that the received signal of the AGC is too small or supersaturated, and the subsequent signal processing will be seriously affected.
Two important indicators of AGC block design are stability and response speed. Stability requires that the AGC control voltage jitter be small when in operation and not susceptible to pulse disturbances. The response speed requires that the AGC circuit amplify and attenuate the input signal to the normal range as soon as possible at the moment of start-up and keep up with the low frequency variations in signal amplitude during operation. A precondition is that the gain of the receiving-end automatic gain control unit remains constant during reception of the burst communication signal. But in actual implementation, the above conditions cannot be maintained. These two indicators are in fact contradictory. The burst signal receiving system includes two parts, including RF system and baseband system, and the RF system is used to complete the analog-to-digital conversion and signal demodulation of the intermediate frequency signal. The baseband system is responsible for converting the radio frequency signal into an intermediate frequency signal, and has the functions of filtering, amplifying, frequency conversion and the like. The receiver receives the signal, mainly considers that the noise is introduced to the minimum and the interference signal is restrained to the minimum while the function of the radio frequency system is completed. The individual devices in the radio frequency module can be divided into two types, active and passive. The active device must produce a certain noise at normal temperature due to its own characteristics, while the passive device does not have a specific noise like the active device, but the attenuation caused by it is also a phase-change noise introduction. In reality, noise sources are various, the mechanism and the characteristics of the generation are complex, and the reasonable arrangement of the performance trade-off and matching among the modules is required in the design. The interference signals are mainly divided into three cases: co-channel interference, adjacent channel interference and image interference. Co-channel interference is not hardware resolved and can only be avoided by directional antennas, which fails if the interference is from the same direction as the received signal. For adjacent channel interference, besides intermodulation and intermodulation interference usable signals, if the interference signals are strong, the amplifier can be caused to enter a saturated state, the gain is reduced, and the sensitivity of the system is reduced. The receiver therefore needs to employ a bandpass filter to suppress the strong interference of the adjacent channels. When a receiving system is to filter out a narrow channel signal with high frequency and large interference, a filter is required to have a very high Q value, and usually, the filter is difficult to realize, even if the cost is very high, and attenuation of the filter with high Q value in a passband is large, which causes deterioration of noise coefficient of the system and reduces the receiving sensitivity of the system. It is therefore desirable to select a reasonable reception scheme to suppress interference while maintaining high sensitivity of the system.
In a wireless burst communication channel, for burst signals, if a demodulator for continuous signals is used to demodulate burst signals, the following problems must occur: when the signal exists, the demodulator accurately locks, and the signal can be accurately demodulated; when the signal disappears and only noise is present, the demodulator will drift. The conventional receiver employs a feedback type analog AGC unit, an analog AGC unit and a digital AGC unit, respectively. The analog AGC unit includes controllable gain amplifying circuit, level detecting circuit or envelope detector, filter, comparator, control signal generating circuit, etc. Because of the strong multipath interference in the wireless burst communication channel. In order to obtain certain anti-interference capability and confidentiality, a spread spectrum technology is generally adopted, so that the input signal-to-noise ratio of the system is low, the dynamic range is larger, a common Automatic Gain Control (AGC) circuit is difficult to adapt to the system, meanwhile, the communication distance and the channel environment are easy to change due to movement, and particularly, the system transmits data in a random burst mode, so that the input signal is extremely intense and rapid, and in the case, the system works stably and reliably, very strict requirements are definitely put on the automatic gain control circuit, and the following main points are included:
(1) Since the dynamic range of the input signal is wide, the dynamic range of the AGC is necessarily required to be wide in order to prevent signal distortion and noise saturation;
(2) Particularly, when working in a burst mode, because the time slot or frame is very short, the synchronous signal in the time slot or frame is shorter, so that each time slot or frame can be correctly received, the control speed of the AGC becomes the primary problem to be considered;
(3) The AGC system of the receiver not only controls the level to the detector, but also operates under the following conditions: i: when the desired signal is absent and a significant amount of noise is present due to interference, the AGC must control the signal level to prevent false target recognition; ii: when the desired signal is present, the AGC must have the output level only a function of the input signal, independent of other signals; iii: the AGC must provide near critical damping characteristics to prevent pulse stretching and avoid false sync indications.
A burst signal is a signal that is very difficult to understand literally. Generally, a burst signal is a sequence of signal components calculated as one unit according to a specific criterion or metric in data communication. In most cases, the burst signal is short-lived, and thus is a continuous signal of relatively long duration. The starting point and the starting position of the burst signal are uncertain. Burst signals cannot generally be handled in a conventional manner. In general, for processing of continuous signals, one is less concerned about the start and end of the signal, but in the case of non-cooperative communication for burst signals, since there is no accurate a priori knowledge of the occurrence of the signal, it is sometimes necessary to judge the start of the signal, and also the end of the signal. Signal detection may be performed in the passband or in the baseband. Each hop of the frequency-hopped signal can be seen as a short burst signal. These known structures are difficult, if not impossible, to obtain for non-cooperative recipients, and particularly for communication systems employing interactive training, because the non-cooperative recipients cannot participate in the communication session of the communication, and even if they grasp part of the information structure, they cannot successfully utilize the known information. The burst signal has the characteristics of burst and transient, and a certain method is needed to be adopted before demodulation to judge whether the received signal is noise or a signal carrying data. Therefore, related detection algorithms are designed to detect burst signals rapidly and accurately, otherwise, signal loss is caused, which is a problem of burst signal detection.
In recent years, many scholars have proposed a signal energy-based detection algorithm, a time domain data-based algorithm, a frequency domain data-based detection algorithm, a short-time self-phase function-based energy statistics algorithm, a high-order statistics method, and a zero-crossing detection algorithm; the detection algorithm based on signal energy has great relevance between the setting of the decision threshold and the environmental noise, and a general decision threshold is not selected, so that the energy detection method also loses the application value; the double sliding window method is most commonly used in a detection algorithm based on signal energy, the algorithm is easy to realize, but the threshold selection of the algorithm is related to the gain of a receiver, the final detection effect can be influenced by the signal-to-noise ratio, and the performance is slightly poor when the signal-to-noise ratio is low. The detection algorithm based on the frequency domain data mainly comprises a frequency domain energy statistical method and a cyclic spectrum estimation algorithm. The detection method based on the frequency domain data has stronger noise suppression capability, but has large data volume requirement, can be used for detecting burst signals with larger burst interval and lower signal-to-noise ratio, and is not applicable to the system; the detection method based on the time domain data needs small data volume, but requires high signal-to-noise ratio, and is suitable for the real-time detection of burst interval small signals; the short-time white sum closing method needs to calculate the correlation function of the signal, has large calculated amount and is not beneficial to hardware realization; the total algorithm is poor in performance or large in calculation amount, and the requirement of high-speed burst signal detection is difficult to meet. In the above detection scheme, one link is to compare the peak value after matching correlation with a set threshold. In detecting the unique code by using the correlation method, if a fixed threshold is adopted, the detection is difficult to be correctly performed.
Example 1:
the embodiment provides a method for detecting burst signals of a radio navigation system, which specifically comprises the following steps:
step 1: extracting a radio frequency signal received from an antenna, converting the frequency of the radio frequency signal, and filtering and amplifying.
Step 2: down-converting the radio frequency signals after filtering and amplifying to generate intermediate frequency analog signals;
step 3: and converting the intermediate frequency analog signal into an intermediate frequency digital signal, and converting the intermediate frequency digital signal into an I-path quadrature baseband digital signal and a Q-path quadrature baseband digital signal.
Step 4: and modulating and demodulating the I-path quadrature baseband digital signals and the Q-path quadrature baseband digital signals to obtain navigation characteristic signals and noise signals.
Step 5: and counting the noise amplitudes of the navigation characteristic signals and the noise signals, filtering the noise signals according to the noise amplitudes, and taking the noise amplitudes of the navigation characteristic signals as comparison reference values.
In step 5, after statistics of the navigation characteristic signal and the noise amplitude of the noise signal, if the arrival time of the antenna is uncertain and the duty ratio is small, the self-adaptive threshold correlation detection algorithm is adopted to reject the analog source noise of the navigation characteristic signal, the navigation characteristic signal is subjected to threshold comparison, if the navigation characteristic signal exceeds the threshold, the detection of the unique code is judged, otherwise, the detection is judged not to be detected, the gain of the quadrature baseband digital signal is adjusted, a gain control signal is generated to adjust the quadrature baseband digital signal to the reference amplitude, and the gain control is performed in a numerical control mode by combining the characteristics of the signals transmitted by all navigation subsystems, and the gain of a receiver is controlled.
Calculating a new duty ratio W=n/3T based on the small duty ratio of an antenna, calculating the ratio of new navigation characteristic signal amplitude to normal navigation characteristic amplitude according to the new duty ratio, then calculating the noise level value of a navigation subsystem by adopting a time domain averaging method, estimating the amplitude value of the first n sample points of the navigation characteristic signal, calculating the average value of the amplitude values, carrying out time domain averaging on the navigation characteristic signal according to the average value to obtain the noise level value which is larger than the average value of the amplitude value and is far smaller than the navigation characteristic signal amplitude, and taking the noise level value as a comparison reference value; wherein n is the number of pulses, and T is the total period of the pulses.
After filtering the noise signal, step 5 includes:
generating a control voltage, adjusting the amplitude of the radio frequency signal and generating a gain according to the control voltage;
detecting the level of the radio frequency signal, and comparing the level with a set reference level after filtering to obtain an error signal;
generating a direction control signal according to the error signal; the direction control signal is used for indicating the adjustment direction of the gain;
selecting an adjustment step length according to the error values of the direction control signal and the error signal, setting a gain step amount according to the adjustment step length, comparing a reference signal with set target energy, calculating to obtain a gain value adjustment step length according to a comparison result, and calculating a gain value according to the gain value adjustment step length;
And performing proportional integral filtering processing on the energy of the error signal, controlling the gain value according to the proportional integral to obtain an energy adjustment coefficient, and multiplying the energy adjustment coefficient by a navigation characteristic signal to obtain an analog output signal level.
After said deriving the analog output signal level, comprising:
generating a gain control signal and an AGC feedback control signal according to the noise level value and the analog output signal level;
multiplying the navigation characteristic signal with the gain factor after feedback according to the AGC feedback control signal, squaring the amplitude, and comparing with a set reference level;
subtracting the reference signal from the AGC feedback control signal, subtracting the signal amplitude to obtain a compensation signal, determining the size of a product factor according to time average by the compensation signal, and estimating average energy;
selecting a corresponding gain factor according to the speed, and multiplying the gain factor by the compensation signal to obtain a gain variation;
generating a next gain value according to the gain variation, the gain value and the integral initial value;
multiplying the gain value with the I baseband digital signal and the Q baseband digital signal; and obtaining the I baseband digital signal and the Q baseband digital signal after gain adjustment, and finishing feedback regulation.
In step 5, after the noise amplitude of the navigation feature signal is used as the comparison reference value, the method comprises the following steps:
and judging whether the navigation signal is a navigation characteristic signal or a noise signal according to the comparison reference value, if the navigation signal is larger than the comparison reference value, judging the navigation signal as the navigation characteristic signal, otherwise, directly filtering the navigation signal as the noise signal.
Step 6: filtering analog source noise in the navigation characteristic signals by using a self-adaptive threshold detection algorithm, detecting the threshold of the navigation characteristic signals, and judging that a unique code is detected if the threshold is exceeded; otherwise, generating an adjusting signal, adjusting the level of the radio frequency signal, and obtaining an adjusted navigation characteristic signal.
Step 7: and detecting the adjusted navigation characteristic signals by using a frequency domain data detection algorithm, and generating detection test results.
According to the embodiment, based on the burst signal of noise statistics, noise is separated from an output signal, gain is adjusted to enable I, Q two paths of digital baseband signals to reach reference amplitude, the output signal value is used as a comparison reference, the performance of a demodulator is guaranteed, the modulation domain detection unique code can effectively improve the demodulation performance of the burst signal and reduce the burst signal loss rate, the adaptive threshold correlation detection algorithm is adopted to reject the analog source noise of the navigation signal received by the signal and compare the threshold of the signal, the resource consumption is low, the quantization error is small, the response speed and the convergence speed are faster, the signal processing is more stable, and the method has strong anti-interference and anti-interception capabilities.
Example 2:
in this embodiment, as shown in fig. 1 and 2, a system for detecting burst signals of a radio navigation system is provided based on embodiment 1.
Aiming at the situation that burst communication is more and more, the energy detection method in burst signal detection has low detection probability, the stable detection method has complex calculation and the like, and the defects existing in the prior art are overcome, so that the implementation is simpler and the system performance is more stable for improving the detection performance and processing instantaneity. The burst signal detection method of the radio navigation system has the advantages of low resource consumption, small quantization error, faster response speed and convergence speed, more stable signal processing and strong anti-interference and anti-interception capability, so as to solve the problem of large dynamic receiving of the burst characteristic navigation signal when the transmitted signal is 80dB changed under an airport system consisting of a plurality of system navigation subsystems.
The system for detecting burst signals of the radio navigation system comprises a gain controllable amplifying unit, a down-conversion unit, an intermediate frequency digitizing unit and a digital signal processing unit which are sequentially connected in series; after the antenna receives the radio frequency signal, the radio frequency system of the wireless receiver finishes the extraction of weak useful signals through the gain controllable amplifying unit, the gain controllable amplifying unit converts the frequency and filters and amplifies the frequency, the processed signals are input into the down-conversion unit, the down-conversion unit down-converts the radio frequency signal into intermediate frequency analog signals, the intermediate frequency analog signals are digitized in the intermediate frequency digitizing unit, the intermediate frequency analog signals are converted into digital signals through ADC sampling quantization, the noise and navigation signal information frequency domain received by the receiving antenna are digitized into I, Q two paths of quadrature baseband digital signals, the I, Q paths of quadrature baseband digital signals are input into the digital signal processing unit, the I, Q baseband digital signals are subjected to modulation demodulation through the amplitude demodulating unit of the digital signal processing unit, the modulated signals are subjected to A/D sampling and digital down-conversion to obtain navigation characteristic signals and noise signals containing pulse pairs and pulse string video signals of the characteristics of each navigation subsystem, the noise statistics unit and the signal comparison output unit are respectively sent to the noise statistics unit to count the noise amplitude, the noise statistics unit is based on the burst signals of the noise statistics, the noise is separated from the output signals of the amplitude demodulation unit, and the output signal value is used as a reference of the noise comparison unit; the signal comparison output unit eliminates the navigation signal analog source noise of the received signal and carries out threshold comparison on the signal by adopting a self-adaptive threshold correlation detection algorithm under the condition that the arrival time of an antenna is uncertain and the duty ratio is small, if the signal comparison output unit exceeds the threshold, the unique code is considered to be detected, otherwise, the signal comparison output unit does not detect the unique code, controls the ADC to sample the input signal level, and completes the amplitude control on the baseband signal; the digital AGC unit adjusts the gain of the digital baseband signal, generates a gain control signal to enable the gain control signal to reach a reference amplitude, performs gain control in a numerical control mode according to the characteristics of the transmitting signals of each navigation subsystem, further controls the gain of a receiver, sends the gain to the burst data frame head detection module, completes the detection of the burst signal based on the detection algorithm of the frequency domain data, and outputs the burst signal detection test result.
The digital signal processing unit judges whether the interference type is adjacent frequency interference or other radio interference, determines the type, polarization mode and modulation mode of the interference signal, judges the frequency, bandwidth and emission rule of the interference signal, calculates the field intensity and spectrogram of the interference signal generated by the radio monitoring system, compares the calculation result with the interfered frequency, determines the type, polarization mode and modulation mode of the interference signal, searches an interference source, deduces the polarization characteristic of the interference signal, finds the interference frequency by an elimination method, identifies the interference by the spectrogram, discriminates the interference signal and rapidly processes the interference.
As shown in fig. 2, the digital signal processing unit includes: the device comprises an amplitude demodulation unit, a noise statistics unit, a signal comparison unit and a digital AGC unit which are sequentially connected in series; after A/D sampling and digital down-conversion, the modulated signals generated by the amplitude demodulation unit are respectively sent to the noise statistics unit and the signal comparison output unit to obtain pulse pairs containing the characteristics of each navigation subsystem and navigation characteristic signals and noise signals in the pulse train video signals. The noise statistics unit counts the noise amplitude, the signal comparison output unit eliminates the navigation signal analog source noise of the received signal and compares the signal by threshold by adopting a self-adaptive threshold correlation detection algorithm under the condition that the arrival time of the antenna is uncertain and the duty ratio is small, and the noise exceeds the threshold, namely the unique code is considered to be detected, otherwise, the digital AGC unit adjusts the gain of the digital baseband signal to generate a gain control signal so as to enable the gain control signal to reach the reference amplitude, and the gain of the receiver is controlled by adopting a numerical control mode according to the characteristics of the signal transmitted by each navigation subsystem.
The signal output by the amplitude demodulation unit is compared with the comparison standard obtained before through the signal comparison output unit, and if the signal is larger than the comparison standard, the signal is considered to be a useful signal and is sent to a lower-level circuit for processing; the signal below the comparison reference is a noise signal and is filtered out.
In this embodiment, the noise statistics unit calculates a new duty ratio w=n/3T based on the characteristic that the duty ratio of the received signal is small, calculates a ratio of a new input signal amplitude to a normal signal amplitude, then calculates a noise level value of the navigation subsystem by using a time-domain averaging method, estimates the first N sample amplitude values of the input signal, calculates an average value, and performs time-domain averaging on the sampled signal by using the input signal and the average value for a relatively long time to obtain a noise level value which is greater than the average value of the noise amplitude and far less than the signal amplitude, and uses the noise level value as a comparison reference for a signal comparison and automatic gain control link, where N is the number of pulses, and T is the total period of the pulses. The noise level value is related to the transmit power of the navigation subsystem.
The signal comparison output unit separates the antenna signal with burstiness, low duty ratio and large dynamic change from the output signal of the amplitude demodulation unit in figure 2, and divides the antenna signal into two parts of a gain controlled amplifying circuit and a control voltage forming circuit, an electric control attenuator is inserted between each stage of the amplifier to form an AGC detector and a low-pass smoothing filter control voltage, the voltage used for controlling the gain controlled amplifier is generated after the low-frequency modulation component and noise are filtered by a filter after detection, two paths of output signals are obtained, the signal output is sent to a post gain controllable amplifying unit for continuous processing, gain is generated and signal amplitude adjustment is completed, the gain controllable amplifying unit controls a level detection circuit for level detection, the level detection is compared with a reference level to obtain an error signal after filtering, the error signal is obtained, the error signal is processed, a direction control signal is directly generated, the direction of gain adjustment is indicated, then an adjustment step length is selected according to the direction indication signal and the error value, the reference signal is compared with the target energy, the gain value adjustment step length is calculated, the gain value is obtained after calculation, the gain value is obtained, the gain energy is proportional integral filtered, the current signal is obtained, the gain energy is obtained, the current proportional integral and the gain energy is processed, the digital integral signal is obtained, and the digital signal is used for obtaining the corresponding digital signal. This embodiment focuses on proportional control of the current value, reducing the steady state error of the system. When the input signal changes, the system can quickly respond to the error, so that the system generates a control signal to control the change of the input signal, thereby reducing steady-state error.
The digital AGC unit generates a gain control signal and an AGC feedback control signal according to the noise level value from the noise statistics unit by utilizing the signal comparison output unit, extracts the feedback signal, multiplies the input signal by the gain factor after feedback, squares the amplitude of the output signal, compares the output signal with an ideal reference level, subtracts the reference signal from the feedback signal, subtracts the amplitude of the output signal to obtain an error signal, time-averages the error signal to determine the size of a product factor, estimates the average energy of the signal, controls the gain controllable amplifying unit, selects the corresponding gain factor according to the speed, multiplies the gain factor by the error signal to obtain the gain variation, and generates the next gain value according to the current gain variation value, the current gain value and the integral initial value; when the controllable gain amplifier at the front end of the receiver selects 50dB, the controllable gain amplifier is matched with the 100dB dynamic of the digital intermediate frequency, the receiving dynamic range of 80dB can be obtained, the autocorrelation function of the signal is used as judgment statistics, the existing gain amplifier for detecting the burst signal multiplies the input IQ baseband signal according to the gain value output by the error integration module to obtain the output IQ baseband signal after gain adjustment, and the feedback regulation function of the digital AGC unit is completed. The sampling is multiplied by a gain factor, which is equivalent to multiplying this gain factor simultaneously for each frequency in the frequency domain. The setting of the gain factor corresponds to the action of a low-pass filter, if the gain factor is set larger, the more sensitive the AGC system is to the error signal, the higher the cut-off frequency of the low-pass filter is; the smaller the gain factor, the more insensitive the AGC system is to the error signal, which corresponds to a lower cut-off frequency of the low pass filter. Meanwhile, the size of the gain factor directly influences the stability time of the AGC system, and the larger the gain factor is set, the shorter the stability time of the system is. The smaller the gain factor, the more gain adjustments are needed, i.e., the longer the system settling time, with the same error.
The digital AGC unit performs gain control according to the characteristics of the signals transmitted by the navigation subsystems, and adopts the following rules to judge and output corresponding control signals: when the signal is not output and the statistical noise is not greater than the comparison reference threshold, increasing the channel gain; when the signal is not output and the noise statistics are larger than a fixed threshold, reducing the channel gain; when the signal has an output and the signal amplitude is smaller than the comparison reference threshold, the channel gain is increased: and when the signal has output and the signal amplitude is larger than the comparison reference fixed value, reducing the channel gain.
The digital AGC unit calibrates a pointing beacon system MKR, an air traffic control system ATC, an instrument landing system ILS, a microwave landing system MMS, a TACN, a variable omni-directional beacon system VOR, a ground tower of a range finder system DME, an external field simulator and an internal field simulator, and repeats a noise spectrum extraction algorithm to correct the noise spectrum in time so as to obtain a new noise spectrum, or performs weighted average on new and old spectrums, and completely replaces the noise spectrum in use by the new noise spectrum.
The digital AGC unit adjusts the output signal by using the effective combination of linear amplification and compression amplification, and when a weak signal is input, the linear amplification circuit works to ensure the intensity of the output signal; when the input signal reaches a certain strength, the compression amplifying circuit is started to reduce the output amplitude, and the gain of the amplifying circuit is automatically adjusted along with the signal strength by changing the amplitude of the gain automatically controlled by the input-output compression ratio.
The embodiment adopts the antenna signal to pass through the gain controllable amplifying unit and the down-conversion unit, then the high-precision, high-dynamic and high-credibility satellite navigation signal is simulated to obtain the intermediate frequency analog signal, the signal is digitized after the down-conversion, the noise and navigation signal information frequency domain received by the receiving antenna is digitized into I, Q two paths of quadrature baseband digital signals, the digital intermediate frequency sampling replaces the prior frequency conversion and filtering in the analog AGC, the signal received by the antenna is filtered, amplified, down-converted and the like after the digital intermediate frequency sampling, and under the condition that the arrival time is uncertain and the duty ratio is small,and eliminating noise of the signal receiving problem and comparing the signal to control the gain of the receiver. The signal AGC control is completed jointly through noise statistics, amplitude demodulation, digital AGC control and signal comparison output, and the real-time key technology of the high-dynamic and high-precision navigation signal is broken through, and the technical indexes are as follows: the pseudo-range phase control precision is better than 0.01m, the speed resolution is 1mm/s, and the acceleration resolution is 10mm/s 2 Jerk resolution 10mm/s 3 The diversity and accuracy of the satellite navigation field simulation scene are improved. The resource consumption of a Global Navigation Satellite System (GNSS) receiver and the system thereof in the links of development, experiment, production, test, application and the like is greatly reduced.
In the embodiment, the digital AGC is adopted in the all-digital receiver to realize the further control of the signal level, the frequency is converted and amplified, the I, Q baseband digital signal demodulates the burst signal through the amplitude demodulation unit, the modulated signal is subjected to A/D sampling and digital down-conversion to obtain the characteristic signal and noise signal of the navigation system comprising the pulse pair and pulse series video signal of the characteristics of each navigation subsystem, and the program is downloaded to a chip, so that the digitization of an algorithm is completed, and the processing pressure of the front-stage AGC is reduced. The scheme is simple to realize and occupies less hardware resources. And carrying out digital AGC processing on the AD sampled data, and adjusting the gain of a front-end amplifier according to the average amplitude of the signal sampled by the A/D, so that the baseband input signal keeps proper amplitude level, thereby being beneficial to the baseband processing, avoiding overload and fully utilizing quantization bits to reduce quantization errors as much as possible. The digital AGC overcomes the defects of the traditional AGC system to a certain extent, the response speed and the convergence speed are higher, and the system performance is more stable. Has important significance for reducing the pressure of the analog AGC part and ensuring the processing precision of the DSP.
According to the embodiment, based on the burst signal of noise statistics, noise is separated from an output signal of an amplitude demodulation unit, gain is adjusted to enable a digital baseband signal to reach a reference amplitude, and the output signal value is used as a comparison reference of a signal and noise comparison unit, so that the performance of a demodulator can be ensured, and the demodulation performance of the burst signal can be effectively improved and the burst signal loss rate can be reduced by detecting a unique code in a modulation domain. Meanwhile, the characteristics of intermediate frequency digitization of the receiver are fully utilized, the noise amplitude is counted, the gain adjustment speed can be increased, and the signal searching time is shortened. Due to the existence of the noise statistics function, when the signal and noise are suddenly enhanced, the gain of the receiving channel can be timely reduced, and the receiving signal can be effectively prevented from suddenly becoming larger to block the receiver. The control voltage jitter of the AGC is small when the AGC works, and the AGC is not easily affected by pulse interference. The method can effectively improve the demodulation performance of the burst signal and reduce the loss rate of the burst signal. The noise statistics method can adopt a time domain averaging method, namely based on the characteristic that the duty ratio of the received signal is small, the sampled signal is subjected to time domain averaging in a relatively long time, the obtained average value is necessarily larger than the noise amplitude and is far smaller than the signal amplitude, and then the average value is a relatively proper noise level value at the moment.
In the embodiment, under the condition that the arrival time of an antenna is uncertain and the duty ratio is small, the self-adaptive threshold correlation detection algorithm is adopted to reject the navigation signal analog source noise received by the signal and compare the signal with the threshold, if the signal exceeds the threshold, the unique code is considered to be detected, otherwise, the unique code is considered to be not detected; when the received signal is less than a threshold, the AGC circuit acts as an amplifier: when the received signal is larger than a certain threshold, the AGC circuit is equivalent to an attenuator, so that the input of a subsequent processing circuit is ensured to be relatively constant, and the signal processing is more stable.
According to the embodiment, gain control is performed in a numerical control mode according to the characteristics of the signals transmitted by the navigation subsystems, so that the gain of a receiver is controlled, the gain is transmitted to a burst data frame head detection module, and a burst signal detection test result is output based on a frequency domain data detection algorithm. According to the method, a spectrum set with burst signals possibly exists is provided according to a judging result of initial energy detection, and a comparison function of the method with the traditional method in terms of detection accuracy and operand is provided according to a judging flow. Under a severe channel environment, the method has strong anti-interference and anti-interception capabilities, and burst signal detection can be well completed. Theoretical analysis and simulation results show that the detection method can effectively improve the detection probability of the burst signal and reduce the calculation complexity. The signal receiving effect of the receiver can be improved, the adaptability of the receiver under different environments can be enhanced, and the performance of the receiver can be improved. The method solves the problem of large dynamic receiving of the sudden characteristic navigation signal when the transmission signal of the navigation signal is 80dB changed in an airport system consisting of a plurality of system navigation subsystems.
Other portions of this embodiment are the same as those of embodiment 1 described above, and thus will not be described again.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent variation, etc. of the above embodiment according to the technical matter of the present invention fall within the scope of the present invention.
Claims (10)
1. A method for detecting a burst signal in a radio navigation system, comprising:
firstly, extracting a radio frequency signal received from an antenna, converting the frequency of the radio frequency signal, and filtering and amplifying; down-converting the radio frequency signals after filtering and amplifying to generate intermediate frequency analog signals; converting the intermediate frequency analog signal into an intermediate frequency digital signal, and converting the intermediate frequency digital signal into an I-path quadrature baseband digital signal and a Q-path quadrature baseband digital signal;
modulating and demodulating the I-path quadrature baseband digital signals and the Q-path quadrature baseband digital signals to obtain navigation characteristic signals and noise signals; counting the noise amplitudes of the navigation characteristic signals and the noise signals, filtering the noise signals according to the noise amplitudes, and taking the noise amplitudes of the navigation characteristic signals as comparison reference values;
Then filtering analog source noise in the navigation characteristic signals by using a self-adaptive threshold detection algorithm, detecting the threshold of the navigation characteristic signals, and judging that a unique code is detected if the threshold is exceeded; otherwise, generating an adjusting signal, adjusting the level of the radio frequency signal, and obtaining an adjusted navigation characteristic signal;
finally, detecting the adjusted navigation characteristic signals by using a frequency domain data detection algorithm, and generating detection test results;
the step of taking the noise amplitude of the navigation characteristic signal as a comparison reference value comprises the following steps:
and judging whether the navigation signal is a navigation characteristic signal or a noise signal according to the comparison reference value, if the navigation signal is larger than the comparison reference value, judging the navigation signal as the navigation characteristic signal, otherwise, directly filtering the navigation signal as the noise signal.
2. The method for detecting burst signals of a radio navigation system according to claim 1, wherein after the statistics of noise amplitudes of the navigation feature signal and the noise signal, if an antenna arrival time is uncertain and a duty ratio is small, an adaptive threshold correlation detection algorithm is adopted to reject analog source noise in the navigation feature signal, a threshold of the navigation feature signal is compared with a set threshold, if the threshold exceeds the set threshold, it is determined that a unique code is detected, otherwise it is determined that no unique code is detected, a gain of an orthogonal baseband digital signal is adjusted, a gain control signal is generated to adjust the orthogonal baseband digital signal to a reference amplitude, and a numerical control mode is adopted to perform gain control in combination with characteristics of signals transmitted by each navigation subsystem.
3. The method for detecting burst signals of a radio navigation system according to claim 2, wherein after taking the noise amplitude of the navigation feature signal as a comparison reference value, if the duty ratio of an antenna is small, calculating a new duty ratio w=n/3T, calculating a ratio of the new navigation feature signal amplitude to the normal navigation feature amplitude according to the new duty ratio, then calculating a noise level value of a navigation subsystem by a time-domain averaging method, estimating amplitude values of the first n samples of the navigation feature signal, calculating an average value of the amplitude values, performing time-domain averaging on the navigation feature signal according to the average value to obtain a noise level value which is larger than the average value of the amplitude values and smaller than the navigation feature signal amplitude, and taking the noise level value as the comparison reference value; wherein n is the number of pulses, and T is the total period of the pulses.
4. A method for detecting a burst signal in a radio navigation system according to claim 3, comprising, after said filtering out said noise signal:
generating a control voltage, adjusting the amplitude of the radio frequency signal and generating a gain according to the control voltage;
detecting the level of the radio frequency signal, and comparing the level with a set reference level after filtering to obtain an error signal;
Generating a direction control signal according to the error signal; the direction control signal is used for indicating the adjustment direction of the gain;
selecting an adjustment step length according to the error values of the direction control signal and the error signal, setting a gain step amount according to the adjustment step length, comparing a reference signal with set target energy, calculating to obtain a gain value adjustment step length according to a comparison result, and calculating a gain value according to the gain value adjustment step length;
and performing proportional integral filtering processing on the energy of the error signal, controlling the gain value according to the proportional integral to obtain an energy adjustment coefficient, and multiplying the energy adjustment coefficient by a navigation characteristic signal to obtain an analog output signal level.
5. The method for detecting a burst signal in a radio navigation system according to claim 4, comprising, after the obtaining of the analog output signal level:
generating a gain control signal and an AGC feedback control signal according to the noise level value and the analog output signal level;
multiplying the navigation characteristic signal with the gain factor after feedback according to the AGC feedback control signal, squaring the amplitude, and comparing with a set reference level;
Subtracting the reference signal from the AGC feedback control signal, subtracting the signal amplitude to obtain a compensation signal, determining the size of a product factor according to time average by the compensation signal, and estimating average energy;
selecting a corresponding gain factor according to the speed, and multiplying the gain factor by the compensation signal to obtain a gain variation;
generating a next gain value according to the gain variation, the gain value and the integral initial value;
multiplying the gain value with the I-path quadrature baseband digital signal and the Q-path quadrature baseband digital signal; and obtaining the I-path quadrature baseband digital signal and the Q-path quadrature baseband digital signal after gain adjustment, and finishing feedback regulation.
6. The system for detecting the burst signal of the radio navigation system is characterized by comprising a gain controllable amplifying unit, a down-conversion unit, an intermediate frequency digitizing unit and a digital signal processing unit which are connected in sequence;
the gain controllable amplifying unit is used for extracting the radio frequency signal received from the antenna, converting the frequency of the radio frequency signal and filtering and amplifying;
the down-conversion unit is used for down-converting the radio frequency signals after filtering and amplifying to generate intermediate frequency analog signals;
The intermediate frequency digitizing unit is used for converting the intermediate frequency analog signal into an intermediate frequency digital signal and converting the intermediate frequency digital signal into an I-path quadrature baseband digital signal and a Q-path quadrature baseband digital signal;
the signal processing unit is used for modulating and demodulating the I-path quadrature baseband digital signals and the Q-path quadrature baseband digital signals to obtain navigation characteristic signals and noise signals; counting the noise amplitudes of the navigation characteristic signals and the noise signals, filtering the noise signals according to the noise amplitudes, and taking the noise amplitudes of the navigation characteristic signals as comparison reference values; filtering analog source noise in the navigation characteristic signals by using a self-adaptive threshold detection algorithm, detecting the threshold of the navigation characteristic signals, and judging that a unique code is detected if the threshold is exceeded; otherwise, generating an adjusting signal, adjusting the level of the radio frequency signal, and obtaining an adjusted navigation characteristic signal; detecting the adjusted navigation characteristic signals by using a frequency domain data detection algorithm, and generating detection test results;
the signal processing unit comprises an amplitude demodulation unit, a noise statistics unit, a signal comparison unit and a digital AGC unit which are connected in sequence;
The amplitude demodulation unit is used for judging whether the navigation characteristic signal or the noise signal is the navigation characteristic signal according to the comparison reference value, if the comparison reference value is larger than the comparison reference value, the navigation characteristic signal is judged, and if the comparison reference value is not the navigation characteristic signal, the noise signal is directly filtered.
7. The system according to claim 6, wherein the noise statistics unit counts the noise amplitude, the signal comparison output unit eliminates the analog source noise of the navigation feature signal by using an adaptive threshold correlation detection algorithm under the condition of uncertain antenna arrival time and small duty ratio, and compares the navigation feature signal with the threshold of the signal, if the noise is greater than the threshold, the signal detection unit determines that the unique code is detected, otherwise, the signal detection unit determines that the unique code is not detected, the digital AGC unit adjusts the gains of the I-path quadrature baseband digital signal and the Q Lu Zhengjiao-path quadrature baseband digital signal, generates a gain control signal, adjusts the I-path quadrature baseband digital signal and the Q-path quadrature baseband digital signal until reaching a reference amplitude, and performs gain control by using a numerical control mode according to the characteristics of the transmission signal of each navigation subsystem.
8. The system according to claim 7, wherein the noise statistics unit calculates a new duty ratio w=n/3T according to a duty ratio of the antenna signal, calculates a ratio of a new navigation feature signal amplitude to a normal navigation feature amplitude according to the new duty ratio, calculates a noise level value of the navigation subsystem by using a time-domain averaging method, estimates amplitude values of the first n samples of the navigation feature signal, calculates an average value of the amplitude values, time-domain averages the navigation feature signal according to the average value, and obtains a noise level value which is larger than the average value of the amplitude values and smaller than the navigation feature signal amplitude, and uses the noise level value as a comparison reference value; wherein n is the number of pulses, and T is the total period of the pulses.
9. The system for detecting a burst signal in a radio navigation system according to claim 8, wherein the signal comparison output unit processes an antenna signal having a burst, a low duty cycle, and a large dynamic variation;
the signal comparison output unit comprises a gain controlled amplifying circuit and a control voltage forming circuit, and an electric control attenuator is inserted between all stages of amplifiers of the gain controlled amplifying circuit to form an AGC detector and a low-pass smoothing filter;
after the AGC detector detects and filters low-frequency modulation components and noise through the low-pass smoothing filter, control voltage of the gain controlled amplifying circuit is generated and output to the gain controllable amplifying unit, and the amplitude of the radio frequency signal is adjusted and gain is generated;
the gain controllable amplifying unit controls the level detection circuit to perform level detection, and the level detection circuit is compared with a set reference level after filtering to obtain an error signal; generating a direction control signal according to the error signal, wherein the direction control signal is used for indicating the adjustment direction of the gain; and selecting an adjustment step length according to the error values of the direction control signal and the error signal, setting a gain stepping amount according to the adjustment step length, comparing a reference signal with target energy, calculating a gain value adjustment step length according to a comparison result, calculating a gain value, performing proportional integral filtering processing on the error energy, controlling the gain value according to the proportional integral to obtain an energy adjustment coefficient, and multiplying the energy adjustment coefficient with an input signal to obtain an analog output signal level.
10. The system according to claim 9, wherein the digital AGC unit generates a gain control signal and an AGC feedback control signal according to a noise level value from the noise statistics unit and a magnitude of an analog output signal level output from the signal comparison unit, extracts the AGC feedback control signal, multiplies a navigation feature signal by a gain factor after feedback, squares an amplitude, and compares the squared amplitude with a set reference level;
subtracting the reference signal from the feedback signal, subtracting the amplitude of the output signal to obtain a compensation signal, determining the magnitude of a product factor by time average of the compensation signal, estimating average energy, controlling a gain controllable amplifying unit according to the average energy, selecting a corresponding gain factor according to the speed, multiplying the gain factor with the compensation signal to obtain a gain variation, and generating a next gain value according to the gain variation, the gain value and an integral initial value;
multiplying the gain value with the I-path quadrature baseband digital signal and the Q-path quadrature baseband digital signal; and obtaining the I-path quadrature baseband digital signal and the Q-path quadrature baseband digital signal after gain adjustment, and completing the feedback regulation function of the digital AGC unit.
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