CN113852383B - Anti-interference processing system for VHF frequency band burst signals - Google Patents
Anti-interference processing system for VHF frequency band burst signals Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
- H04B1/1036—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B17/00—Monitoring; Testing
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
- H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
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Abstract
The invention discloses an anti-interference processing system for VHF frequency band burst signals, which comprises a DBF module, a DDC module, an energy detection module, a carrier synchronization module, a symbol synchronization module, a channel estimation module, a self-adaptive equalizer, a frame synchronization module, a CRC module, a spectrum identification module and a null filter. The invention adopts multi-antenna reception, obtains certain anti-interference capability by DBF beam synthesis, has a time domain signal energy detection function and eliminates signals with abnormal lengths. And sending the signals extracted after detection to a carrier synchronization and symbol synchronization module to obtain synchronized baseband signals, further reducing the interference of the signals by adopting a self-adaptive equalizer, optimizing the frequency spectrum of the signals, carrying out frequency spectrum detection and identification on the signals which do not pass through CRC demodulation, carrying out null filtering on the signals according to the interference position if narrow-band interference exists in the signals, and finally sending the signals after interference suppression to the synchronization module again for demodulation.
Description
Technical Field
The invention relates to the technical field of communication in a VHF frequency band, in particular to an anti-interference processing system for a burst signal in the VHF frequency band.
Background
The very high frequency VHF (very high frequency) band is a frequency band with a frequency range of 30MHz to 300MHz, and is located between an HF band and a UHF band, and a signal of the frequency band is not easily affected by weather changes, and has a fast information transmission rate and a small delay.
In the actual project test process, it is found that some interference signals are often mixed in the frequency band, which is due to multiple factors such as frequency band allocation, time slot collision, and the like, and it is difficult to avoid interference or malicious damage from other wireless communication systems. Of these interferences, the narrowband interference usually causes more serious deterioration to the system than other interference such as additive noise, and the narrowband interference tends to change with time, which also has a considerable effect on the stability of the system performance. In order to further reduce the error rate, it is necessary to take certain measures to suppress such narrow-band interference.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides an anti-interference processing system for VHF frequency band burst signals, which can avoid interference as far as possible while not influencing the normal receiving function and has the capability of processing certain interference signals.
In order to achieve the above purpose, the technical solution for solving the technical problem is as follows:
the utility model provides a VHF frequency channel burst signal's anti-interference processing system, includes DBF module, DDC module, energy detection module, carrier synchronization module, symbol synchronization module, self-adaptation equalizer, frame synchronization module, CRC module, spectrum identification module and null filter, wherein:
the output end of the DBF module is connected with the DDC module and is used for carrying out DBF digital multi-beam synthesis on the VHF frequency band burst signals received by the multiple antennas so as to enhance the signal intensity in the incoming wave direction;
the input end of the DDC module is connected with the DBF module, the output end of the DDC module is connected with the energy detection module, and the DDC module is used for performing down-conversion on the DBF module DBF digital multi-beam synthesized signal and transmitting the signal to the energy detection module;
the input end of the energy detection module is connected with the DDC module, the output end of the energy detection module is connected with the carrier synchronization module, and the energy detection module is used for carrying out energy detection on the received burst signal, acquiring the data length, further carrying out interference elimination processing on the signal with abnormal length, and simultaneously transmitting the normally received signal to the carrier synchronization module;
the input end of the carrier synchronization module is connected with the energy detection module, and the output end of the carrier synchronization module is connected with the symbol synchronization module, and the carrier synchronization module is used for estimating and compensating carrier frequency offset:
the input end of the symbol synchronization module is connected with the carrier synchronization module, the output end of the symbol synchronization module is connected with the adaptive equalizer, and the symbol synchronization module is used for outputting a baseband signal with twice symbol rate after symbol synchronization, extracting a signal with single symbol rate and transmitting the signal to the adaptive equalizer;
the input end of the self-adaptive equalizer is connected with the symbol synchronization module, and the output end of the self-adaptive equalizer is connected with the frame synchronization module, and the self-adaptive equalizer is used for obtaining a convergent filter coefficient through iteration of a known training sequence so as to filter a received signal to improve the demodulation probability;
the input end of the frame synchronization module is connected with the self-adaptive equalizer, and the output end of the frame synchronization module is connected with the CRC module and is used for identifying frame header position information and extracting a completed frame sequence;
the input end of the CRC module is connected with the frame synchronization module, the output end of the CRC module is connected with the spectrum identification module and is used for performing CRC on the received signal, the signal passing the CRC is a successfully demodulated signal and is output, and if the CRC does not pass, the signal is sent to the spectrum identification module;
the input end of the spectrum identification module is connected with the CRC module, the output end of the spectrum identification module is connected with the null filter, and the spectrum identification module is used for performing spectrum detection on the signal which does not pass the CRC check, identifying whether the narrow-band interference exists in the spectrum of the signal, and if the narrow-band interference exists, sending the signal into the null filter;
the input end of the null filter is connected with the spectrum identification module, the output end of the null filter is connected with the carrier synchronization module, and the null filter is used for carrying out spectrum identification on data packet signals which are not demodulated, and for narrow-band interference appearing in a band, a null filtering method is adopted to inhibit interference signals so as to send the signals after interference inhibition into the carrier synchronization module again for subsequent demodulation.
The system further comprises a channel estimation module, wherein the input end of the channel estimation module is connected with the symbol synchronization module, the output end of the channel estimation module is connected with the DBF module, and the channel estimation module is used for receiving the single symbol rate signal sent by the symbol synchronization module and estimating the channel quality through detecting the signal-to-noise ratio and the amplitude of the received signal so as to adjust the DBF beam gain and improve the demodulation probability, and meanwhile, the threshold value of the energy detection module is adjusted so as to improve the detection probability.
Preferably, a plurality of groups of filter coefficients are prestored in the anti-interference processing system, and a corresponding null filter is selected according to the interference center position detected by the frequency spectrum.
Further, recursive least squares RLS is used to derive the filter coefficients for faster convergence, and assuming that the observed signal vector is x (l), and l is 0,1, etc., the objective function of RLS is such that the weighted mean square is
The method is characterized in that the minimum value is reached, lambda (0 < lambda < 1) is a forgetting factor, the weight of the latest data point is emphasized, so that the filter coefficient can adapt to the time-varying data statistical characteristic, n is 0,1,2 … and L-1 are taken as a group of input sequences, a predistortion model is tested and verified, the optimal performance can be achieved when the polynomial order is k and the memory depth is q, and the number of predistortion coefficients is m is k;
the algorithm of RLS is described as:
initializing coefficient vectors and correlation matrices: w is a m (0)＝0；R m (0)＝1/δI m ；
Where δ is a small positive number;
calculating predistorter output:
and (3) error estimation:
calculating a Kalman gain vector:
k ml (n)＝R m (n-1)U lm ′(n)/λ+U lm (n)R m (n-1)U lm ′(n)
update the inverse of the correlation matrix:
R m (n)＝1/λ(R m (n-1)-K ml (n)U lm (n)R m (n-1))
updating a coefficient vector: w is a m (n+1)＝w m (n)+K ml (n)e l (n)
Wherein R is m Is the inverse of the signal (estimate) correlation matrix, I m Is to R m And (5) performing initialized identity matrixes.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
because the communication system of the VHF frequency band is widely used by a frequency modulation broadcast channel, a television broadcast channel, a military radio channel, an air traffic control communication, an air navigation system, and the like, there are many conflicts in a time slot and a frequency band in an actual communication system, and interference signals are also various. The anti-interference processing system for the VHF frequency band burst signals adopts multi-antenna receiving, obtains certain anti-interference capability by DBF beam synthesis, has a time domain signal energy detection function, and eliminates signals with abnormal lengths. And sending the signals extracted after detection to a carrier synchronization and symbol synchronization module to obtain synchronized baseband signals, further reducing the interference of the signals by adopting a self-adaptive equalizer, optimizing the frequency spectrum of the signals, carrying out frequency spectrum detection and identification on the signals which do not pass through CRC demodulation, carrying out null filtering on the signals according to the interference position if narrow-band interference exists in the signals, and finally sending the signals after interference suppression to the synchronization module again for demodulation.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:
FIG. 1 is a schematic diagram of an overall framework of an anti-interference processing system for VHF band burst signals according to the present invention;
FIG. 2 is a signal energy detection diagram in an anti-interference processing system for VHF frequency band burst signals according to the present invention;
FIG. 3 is a signal head and tail recognition diagram in an anti-interference processing system for burst signals in VHF frequency band according to the present invention;
FIG. 4 is an error convergence diagram of an RLS algorithm in the anti-interference processing system for burst signals in VHF band according to the present invention;
FIG. 5 is a diagram of a useful signal superimposed with a narrow-band interference signal in an anti-interference processing system for a VHF band burst signal according to the present invention;
fig. 6 is a frequency response diagram of a null-notch filter in an anti-interference processing system for VHF band burst signals according to the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the present embodiment discloses an anti-interference processing system for VHF band burst signals, which includes a DBF module, a DDC module, an energy detection module, a carrier synchronization module, a symbol synchronization module, an adaptive equalizer, a frame synchronization module, a CRC module, a spectrum identification module, and a null filter, wherein:
the output end of the DBF (Digital Beam Forming or Digital Beam synthesizing) module is connected with the DDC module and is used for carrying out DBF Digital multi-Beam synthesis on the VHF frequency band burst signals received by the multi-antenna so as to enhance the signal intensity in the incoming wave direction;
the input end of the DDC module is connected with the DBF module, the output end of the DDC module is connected with the energy detection module, and the DDC module is used for performing down-conversion on the DBF module DBF digital multi-beam synthesized signal and transmitting the signal to the energy detection module;
the input end of the energy detection module is connected with the DDC module, the output end of the energy detection module is connected with the carrier synchronization module, and the energy detection module is used for carrying out energy detection on the received burst signal, acquiring the data length, further carrying out interference elimination processing on the signal with abnormal length, and simultaneously transmitting the normally received signal to the carrier synchronization module;
the input end of the carrier synchronization module is connected with the energy detection module, and the output end of the carrier synchronization module is connected with the symbol synchronization module, and the carrier synchronization module is used for estimating and compensating carrier frequency offset:
the input end of the symbol synchronization module is connected with the carrier synchronization module, the output end of the symbol synchronization module is connected with the adaptive equalizer, and the symbol synchronization module is used for outputting a baseband signal with twice symbol rate after symbol synchronization, extracting a signal with single symbol rate and transmitting the signal to the adaptive equalizer;
the input end of the self-adaptive equalizer is connected with the symbol synchronization module, and the output end of the self-adaptive equalizer is connected with the frame synchronization module, and the self-adaptive equalizer is used for obtaining a convergent filter coefficient through iteration of a known training sequence so as to filter a received signal to improve the demodulation probability;
the input end of the frame synchronization module is connected with the self-adaptive equalizer, and the output end of the frame synchronization module is connected with the CRC module and is used for identifying frame header position information and extracting a completed frame sequence;
the input end of the CRC module is connected with the frame synchronization module, the output end of the CRC module is connected with the spectrum identification module and is used for performing CRC on the received signal, the signal passing the CRC is a successfully demodulated signal and is output, and if the CRC does not pass, the signal is sent to the spectrum identification module;
the input end of the spectrum identification module is connected with the CRC module, the output end of the spectrum identification module is connected with the null filter, and the spectrum identification module is used for performing spectrum detection on the signal which does not pass the CRC check, identifying whether the narrow-band interference exists in the spectrum of the signal, and if the narrow-band interference exists, sending the signal into the null filter;
the input end of the null filter is connected with the spectrum identification module, the output end of the null filter is connected with the carrier synchronization module, and the null filter is used for carrying out spectrum identification on data packet signals which are not demodulated, and for narrow-band interference appearing in a band, a null filtering method is adopted to inhibit interference signals so as to send the signals after interference inhibition into the carrier synchronization module again for subsequent demodulation.
Furthermore, the anti-interference processing system further comprises a channel estimation module, wherein an input end of the channel estimation module is connected with the symbol synchronization module, and an output end of the channel estimation module is connected with the DBF module, and the channel estimation module is used for receiving the single symbol rate signal sent by the symbol synchronization module and estimating the channel quality through detecting the signal-to-noise ratio and the amplitude of the received signal so as to adjust the DBF beam gain and improve the demodulation probability, and meanwhile, the threshold value of the energy detection module is adjusted so as to improve the detection probability.
Example (b):
assuming that the frequency band of a signal transmitted by a transmitting end is 160MHz and the bandwidth is 50k, a TDMA method is adopted, data is transmitted according to time slots, the data frame is 1024 code words, the modulation method is QPSK modulation, the preamble sequence is 128 code words, and the modulation method is BPSK.
A receiving end adopts eight antennas for receiving, eight-beam DBF beams are used for synthesizing single-beam signals, so that the received signals obtain higher gain and have certain anti-interference capability, a channel estimation module calculates the amplitude and the signal-to-noise ratio of the signals to obtain the conditions of the signals and the channels at the moment, the DBF gain can be adjusted under the condition that the signal-to-noise ratio meets the index but the signal amplitude is abnormal, the gain in the signal receiving direction is improved, if the gain is too large, data overflow can be caused, if the gain is too small, the signals can not be demodulated, a feedback signal is given to the DBF module by a channel detection module, the gain of the DBF module is controlled to be adjusted upwards or downwards in a first gear, the feedback signal is obtained by evaluating whether the amplitude of the signals is in an effective range (between the maximum amplitude and the minimum amplitude of the signals which can be demodulated), if the amplitude exceeds the effective range, the feedback signal is adjusted downwards, if the amplitude is lower than the effective range, the feedback signal is adjusted upwards, the feedback signal simultaneously adjusts the threshold value of the energy detection module by using the same principle, and the detection probability is improved.
Meanwhile, the system has a time domain signal energy detection function, and signals with abnormal lengths are removed. The energy detection module firstly detects the square accumulation addition of data according to the movement of a sliding window, as shown in figures 2 and 3, when the head of a signal is detected, a head mark is generated, when the tail of the signal is detected, a tail mark is generated, if the signal only has one head mark and one tail mark, the position of the head mark is subtracted from the position of the tail mark to obtain the length of the data, and if the length of the data is less than the length of a known data frame, the data is considered to be an abnormal signal in the environment, and the interference signal is removed. However, it is complicated, if the data length is greater than the data frame length, it may be the superposition of useful signals caused by time slot collision, at this time, the data cannot be removed, the signal often has more than one data header, as shown in fig. 2 and 3, two data headers and one data tail appear, at this time, the signal is intercepted according to the finally appearing data header identifier, because the signal energy is strongest at this time, the position of the header identifier is subtracted by the position of the tail identifier, then the data length is judged, and the signal with normal data length is sent to the back-end processing module.
The signals extracted after energy detection are sent to a carrier synchronization module and a symbol synchronization module, the signals with single symbol rate are extracted and sent to a self-adaptive equalizer, the coefficient of an equalization filter is converged by using the convergence of a training sequence, and the self-adaptive equalizer can further reduce the interference of the signals and optimize the frequency spectrum of the signals.
Further, recursive least squares RLS is used to derive the filter coefficients for faster convergence, and assuming that the observed signal vector is x (l), and l is 0,1, etc., the objective function of RLS is such that the weighted mean square is
To the minimum, λ (0 < λ < 1) is a forgetting factor, weighting the nearest data points so that the filter coefficients can adapt to the time-varying data statistics, with n being 0,1,2 …, L-1, the input sequence being a set, and the pre-distortion model being passed throughTesting and verifying, wherein the optimal performance can be achieved when the polynomial order is k and the memory depth is q, and the number of predistortion coefficients is m-k-q;
the algorithm of RLS is described as:
initializing coefficient vectors and correlation matrices: w is a m (0)＝0；R m (0)＝1/δI m ；
Where δ is a small positive number;
calculating predistorter output:
and (3) error estimation:
calculating a Kalman gain vector:
K ml (n)＝R m (n-1)U lm (n)/λ+U lm (n)R m (n-1)U lm ′(n)
update the inverse of the correlation matrix:
R m (n)＝1/λ(R m (n-1)-K ml (n)U lm (n)R m (n-1))
updating a coefficient vector: w is a m (n+1)＝w m (n)+K ml (n)e l (n)
Wherein R is m Is the inverse of the signal (estimate) correlation matrix, I m Is to R m And (5) performing initialized identity matrixes.
From the simulation of the embodiment, it can be seen in fig. 4 that the RLS algorithm starts to converge within 100 data points, and the data tracking condition is good after convergence. Thus, in this embodiment, a 100 symbol point training sequence is required to converge the adaptive equalizer and then perform equalization filtering on the useful data frame signal.
And (3) carrying out spectrum detection and identification on the signal which does not pass the CRC demodulation, and if the signal has narrow-band interference, as shown in figure 5, carrying out null filtering on the signal according to the interference position. The adopted null filter needs to prestore a plurality of groups of coefficient values in a receiving system, a corresponding null filter is selected according to the central position of an interference signal detected by a frequency spectrum, as shown in figure 6, the null filter can inhibit the interference while inhibiting the useful signal, the null filter is set in an interference simulation test, the depth of the null is based on demodulation which does not affect the useful signal under the condition of no interference, the coefficient values are quantitatively stored after the setting, the corresponding null filter is selected according to the corresponding position of the interference, the signal after the interference is inhibited is sent to a carrier synchronization for demodulation again, and if the demodulation is still unavailable after optimization, the signal is not subjected to multiple cycles and is regarded as packet loss processing.
The anti-interference processing system for the VHF frequency band burst signals adopts multi-antenna receiving, obtains certain anti-interference capability by DBF beam forming, has a time domain signal energy detection function, and eliminates signals with abnormal lengths. And sending the signals extracted after detection to a carrier synchronization and symbol synchronization module to obtain synchronized baseband signals, further reducing the interference of the signals by adopting a self-adaptive equalizer, optimizing the frequency spectrum of the signals, carrying out frequency spectrum detection and identification on the signals which do not pass through CRC demodulation, carrying out null filtering on the signals according to the interference position if narrow-band interference exists in the signals, and finally sending the signals after interference suppression to the synchronization module again for demodulation.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (4)
1. The utility model provides a VHF frequency channel burst signal's anti-interference processing system which characterized in that, includes DBF module, DDC module, energy detection module, carrier synchronization module, symbol synchronization module, self-adaptation equalizer, frame synchronization module, CRC module, spectrum identification module and null notch filter, wherein:
the output end of the DBF module is connected with the DDC module and is used for carrying out DBF digital multi-beam synthesis on the VHF frequency band burst signals received by the multiple antennas so as to enhance the signal intensity in the incoming wave direction;
the input end of the DDC module is connected with the DBF module, the output end of the DDC module is connected with the energy detection module, and the DDC module is used for performing down-conversion on the DBF module DBF digital multi-beam synthesized signal and transmitting the signal to the energy detection module;
the input end of the energy detection module is connected with the DDC module, the output end of the energy detection module is connected with the carrier synchronization module, and the energy detection module is used for carrying out energy detection on the received burst signal, acquiring the data length, further carrying out interference elimination processing on the signal with abnormal length, and simultaneously transmitting the normally received signal to the carrier synchronization module;
the input end of the carrier synchronization module is connected with the energy detection module, and the output end of the carrier synchronization module is connected with the symbol synchronization module, and the carrier synchronization module is used for estimating and compensating carrier frequency offset:
the input end of the symbol synchronization module is connected with the carrier synchronization module, the output end of the symbol synchronization module is connected with the adaptive equalizer, and the symbol synchronization module is used for outputting a baseband signal with twice symbol rate after symbol synchronization, extracting a signal with single symbol rate and transmitting the signal to the adaptive equalizer;
the input end of the self-adaptive equalizer is connected with the symbol synchronization module, the output end of the self-adaptive equalizer is connected with the frame synchronization module, and the self-adaptive equalizer is used for obtaining a converged filter coefficient through iteration of a known training sequence so as to filter a received signal to improve demodulation probability;
the input end of the frame synchronization module is connected with the self-adaptive equalizer, and the output end of the frame synchronization module is connected with the CRC module and is used for identifying frame header position information and extracting a completed frame sequence;
the input end of the CRC module is connected with the frame synchronization module, the output end of the CRC module is connected with the spectrum identification module and is used for performing CRC on the received signal, the signal passing the CRC is a successfully demodulated signal and is output, and if the CRC does not pass, the signal is sent to the spectrum identification module;
the input end of the spectrum identification module is connected with the CRC module, the output end of the spectrum identification module is connected with the null filter, and the spectrum identification module is used for performing spectrum detection on the signal which does not pass the CRC check, identifying whether the narrow-band interference exists in the spectrum of the signal, and if the narrow-band interference exists, sending the signal into the null filter;
the input end of the null filter is connected with the spectrum identification module, the output end of the null filter is connected with the carrier synchronization module, and the null filter is used for carrying out spectrum identification on data packet signals which are not demodulated, and for narrow-band interference appearing in a band, a null filtering method is adopted to inhibit interference signals so as to send the signals after interference inhibition into the carrier synchronization module again for subsequent demodulation.
2. The system of claim 1, further comprising a channel estimation module, an input end of the channel estimation module is connected to the symbol synchronization module, and an output end of the channel estimation module is connected to the DBF module, for receiving a single symbol rate signal sent by the symbol synchronization module and estimating channel quality by detecting a signal-to-noise ratio and an amplitude of the received signal to further adjust a DBF beam gain to improve demodulation probability, and adjusting a threshold of the energy detection module to improve detection probability.
3. The system of claim 1, wherein a plurality of sets of filter coefficients are pre-stored in the system, and a corresponding null filter is selected according to the detected interference center position of the spectrum.
4. The system of claim 1, wherein the filter coefficients for deriving faster convergence are Recursive Least Squares (RLS), and if the observed signal vector is X (l), l is 0,1, and n, the objective function of RLS is such that the weighted mean square (weighted mean square) is used
Reaches the minimum, λ (0 < λ < 1) is a forgetting factor, emphasizes the weight of the nearest data point, so thatThe filter coefficients can adapt to the time-varying data statistical characteristics, n is 0,1,2 … and L-1 are used as a group of input sequences, the predistortion model is tested and verified, the optimal performance can be achieved when the polynomial order is k and the memory depth is q, and the number of predistortion coefficients is m is k q;
the algorithm of RLS is described as:
initializing coefficient vectors and correlation matrices: w is a m (0)＝0；R m (0)＝1/δI m ；
Where δ is a small positive number;
calculating predistorter output:
and (3) error estimation:
calculating a Kalman gain vector:
K ml (n)＝R m (n-1)U lm ′(n)/λ+U lm (n)R m (n-1)U lm '(n)
update the inverse of the correlation matrix:
R m (n)＝1/λ(R m (n-1)-K ml (n)U lm (n)R m (n-1))
updating a coefficient vector: w is a m (n+1)＝w m (n)+K ml (n)e l (n)
Wherein R is m Is the inverse of the correlation matrix of the signal estimate, I m Is to R m And (5) performing initialized identity matrixes.
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