CN116455460B - Low-frequency direct current component filtering method, demodulator and satellite communication equipment - Google Patents
Low-frequency direct current component filtering method, demodulator and satellite communication equipment Download PDFInfo
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Abstract
The invention relates to the technical field of communication, and provides a low-frequency direct-current component filtering method, a demodulator and satellite communication equipment. The analog signal processing module processes and samples the analog signal to obtain a digital signal; the zero frequency filtering module acquires an initial signal section from the digital signal and filters a zero frequency direct current component in the initial signal section to obtain a pending signal section; the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed; the digital signal processing module processes the signal section to be processed to obtain a target signal section; the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain new low-frequency parameters and feeds the new low-frequency parameters back to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameters. The frequency of the low-frequency direct current component is estimated and fed back to the low-frequency filtering module for filtering, and meanwhile, the direct current component in the signal is filtered by combining the zero-frequency filtering module, so that the demodulation effect is improved.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a low frequency direct current component filtering method, a demodulator, and a satellite communications device.
Background
In a satellite communication device, the demodulator is used for demodulating a signal received by an antenna, and the working procedure of the demodulator can be summarized simply as follows: firstly, processing an analog signal received by an antenna, then, sampling the processed analog signal to obtain a digital signal, and then, processing the digital signal to upload demodulated data to a user.
Since a direct current component is generated during sampling, the direct current component can interfere with the sampled digital signal, and the demodulation effect can be affected. Although the prior art can filter out the zero frequency direct current component, the low frequency direct current component can be generated due to the Doppler effect of satellite motion, and further how to filter out the low frequency direct current component is a critical problem.
Disclosure of Invention
Accordingly, the present invention is directed to a low frequency dc component filtering method, a demodulator and a satellite communication device.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
in order to achieve the above object, the technical scheme adopted by the embodiment of the invention is as follows:
in a first aspect, the present invention provides a low-frequency direct current component filtering method, applied to a demodulator, where the demodulator includes an analog signal processing module, a zero frequency filtering module, a low frequency filtering module, a digital signal processing module and a low frequency estimating module that are electrically connected in sequence, the low frequency estimating module is electrically connected with the low frequency filtering module, and the low-frequency direct current component filtering method includes:
the analog signal processing module processes the received analog signals and samples the processed analog signals to obtain digital signals;
the zero frequency filtering module acquires an initial signal section from the digital signal according to a preset signal length, and filters a zero frequency direct current component of the initial signal section to obtain a to-be-determined signal section;
the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed;
the digital signal processing module processes the signal segment to be processed to obtain a target signal segment;
and the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain a new low-frequency parameter, and feeds back the new low-frequency parameter to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameter.
In an optional implementation manner, the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed, which includes:
the low-frequency filtering module generates a compensation signal segment corresponding to the undetermined signal segment according to the current low-frequency parameter;
the low-frequency filtering module multiplies the compensation signal segment and the undetermined signal segment to convert a low-frequency direct current component of the undetermined signal segment into a zero-frequency direct current component;
and the low-frequency filtering module filters the zero-frequency direct current component of the signal section to be processed to obtain the signal section to be processed.
In an optional implementation manner, the low-frequency filtering module filters the zero-frequency direct current component of the signal section to be processed to obtain the signal section to be processed, and the method includes:
the low-frequency filtering module calculates the average value of the undetermined signal section to obtain a zero-frequency direct current component of the undetermined signal section, and subtracts the undetermined signal section from the zero-frequency direct current component of the undetermined signal section to obtain the signal section to be processed.
In an alternative embodiment, the digital signal processing module includes a frame capturing unit, a timing synchronization unit, and a frequency offset correction unit;
the digital signal processing module processes the signal segment to be processed to obtain a target signal segment, and the digital signal processing module comprises:
the frame capturing unit captures the frame header of the signal segment to be processed to obtain a captured signal segment;
the timing synchronization unit performs time difference correction on the captured signal segment to obtain a corrected signal segment;
and the frequency offset correction unit corrects the frequency offset of the corrected signal segment to obtain the target signal segment.
In an optional implementation manner, the low frequency estimation module performs low frequency estimation according to the target signal segment to obtain a new low frequency parameter, which includes:
the low-frequency estimation module acquires a pilot sequence from the target signal segment;
the low-frequency estimation module performs power calculation according to the pilot frequency sequence to obtain a plurality of noise powers; the change period of the plurality of noise powers is consistent with the change period of the low-frequency direct current component of the undetermined signal section;
and the low-frequency estimation module carries out frequency estimation according to the plurality of noise powers to obtain the new low-frequency parameters.
In an alternative embodiment, the low frequency estimation module performs power calculation according to the pilot sequence to obtain a plurality of noise powers, including:
the low-frequency estimation module sequentially slides according to a preset window length, and a plurality of pilot groups are obtained from the pilot sequence, wherein each pilot group comprises the same number of pilot values;
the low-frequency estimation module calculates the average value after accumulating all pilot frequency values in each pilot frequency group to obtain a first value, and calculates the square of the first value to obtain the signal power of the pilot frequency group to obtain the signal power of each pilot frequency group;
the low-frequency estimation module calculates the square of each pilot frequency value in each pilot frequency group, then accumulates the squares to obtain a second value, calculates the average value of the second values to obtain the total power of the pilot frequency groups, and obtains the total power of each pilot frequency group;
and the low-frequency estimation module calculates the difference value between the total power of each pilot frequency group and the signal power to obtain the plurality of noise powers.
In an optional implementation manner, the low frequency estimation module performs frequency estimation according to the plurality of noise powers to obtain the new low frequency parameter, including:
the low-frequency estimation module calculates the average value of the plurality of noise powers to obtain power of Gaussian white noise, and calculates the difference value of each noise power and the power of Gaussian white noise to obtain each target power;
the low-frequency estimation module performs fast Fourier transform according to all target power and preset transform points to obtain frequency parameters;
the low-frequency estimation module carries out frequency estimation according to a preset formula and the frequency parameter, the preset conversion point number and the preset pilot frequency rate to obtain the new low-frequency parameter;
the preset formula is as follows:
；
wherein ,representing new low frequency parameters; />Representing a preset pilot rate; />Representing a frequency parameter; />Representing the preset conversion point number.
In an optional embodiment, the demodulator further includes a frame decoding module electrically connected to the digital signal processing module, and the low-frequency direct current component filtering method further includes:
and the de-framing and decoding module de-frames and decodes the target signal segment to obtain a demodulated signal segment.
In a second aspect, the present invention provides a demodulator for implementing the low frequency dc component filtering method according to any one of the foregoing embodiments.
In a third aspect, the present invention provides a satellite communication device comprising a demodulator according to the previous embodiments.
According to the low-frequency direct current component filtering method, the demodulator and the satellite communication equipment, the analog signal processing module processes the received analog signals and samples the processed analog signals to obtain digital signals; the zero frequency filtering module acquires an initial signal section from the digital signal according to a preset signal length, and filters a zero frequency direct current component of the initial signal section to obtain a to-be-determined signal section; the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed; the digital signal processing module processes the signal section to be processed to obtain a target signal section; the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain new low-frequency parameters, and feeds the new low-frequency parameters back to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameters. The low-frequency direct current component is subjected to frequency estimation through the low-frequency estimation module and fed back to the low-frequency filtering module to filter the low-frequency direct current component, and meanwhile, the zero-frequency filtering module is combined to filter the zero-frequency direct current component, so that the direct current component in the digital signal is filtered, the influence caused by the direct current component is effectively avoided, and the demodulation effect is improved.
In order to make the above objects, features and advantages of the present invention more comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows one of schematic structural diagrams of a demodulator according to an embodiment of the present invention;
fig. 2 shows one of flow diagrams of a low-frequency dc component filtering method according to an embodiment of the present invention;
FIG. 3 is a second flowchart illustrating a low frequency DC component filtering method according to an embodiment of the present invention;
FIG. 4 shows a second schematic diagram of a demodulator according to an embodiment of the present invention;
fig. 5 shows a third flow chart of a low-frequency dc component filtering method according to an embodiment of the present invention;
FIG. 6 shows a third schematic diagram of a demodulator according to an embodiment of the present invention;
fig. 7 shows an exemplary constellation diagram without dc components;
fig. 8 shows an exemplary constellation diagram with a dc component;
fig. 9 shows an exemplary diagram of a constellation for filtering out zero frequency dc components using the prior art;
fig. 10 shows an exemplary constellation diagram of a low-frequency dc component filtering method according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present invention.
It is noted that relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
In a satellite communication device, the demodulator is used for demodulating a signal received by an antenna, and the working procedure of the demodulator can be summarized simply as follows: firstly, processing an analog signal received by an antenna, then, sampling the processed analog signal to obtain a digital signal, and then, processing the digital signal to upload demodulated data to a user. Due to hardware adjustment or the like, a direct current component is generated in the process of converting the processed analog signal into a digital signal, which may interfere with the sampled digital signal.
For example, assume that the processed analog signal isAccording to the time interval->Sampling is carried out, and the sampled digital signal is +.>, wherein Representing the sampled digital signal, < >>Digital signal representing the actual need, < >>Representing the dc component.
If the DC component isZero frequency, then it can be considered unchanged for a period of time, thenI.e. the dc component is a constant value. The prior art therefore uses the characteristic that the zero frequency dc component is a constant value to filter the sampled digital signal to filter the dc component.
But due to the Doppler effect of satellite motion, a low frequency DC component is also generated, and the DC component becomes available, wherein />Representing the amplitude of the zero frequency direct current component, +.>Representing the amplitude of the low frequency direct current component, +.>Representing the frequency of the low frequency dc component. Although the amplitude of the dc component is small compared to the amplitude of the digital signal actually required, the dc component may cause a decrease in the output signal-to-noise ratio of the demodulator, thereby affecting demodulation efficiency. Therefore, the embodiment of the invention provides a low-frequency direct current component filtering method to solve the problems.
Referring to fig. 1, a schematic structural diagram of a demodulator according to an embodiment of the present invention includes an analog signal processing module, a zero frequency filtering module, a low frequency filtering module, a digital signal processing module, and a low frequency estimating module electrically connected in sequence, where the low frequency estimating module is further electrically connected to the low frequency filtering module. The low frequency dc component filtering method according to the embodiment of the present invention will be described below with the demodulator shown in fig. 1 as an execution body.
Referring to fig. 2, fig. 2 is a flow chart of a low-frequency dc component filtering method according to an embodiment of the invention.
Step S202, an analog signal processing module processes a received analog signal and samples the processed analog signal to obtain a digital signal;
in this embodiment, the analog signal processing module may include a spectrum shifting unit, an analog filtering unit, and an analog-to-digital conversion unit. The spectrum shifting unit and the analog filtering unit are used for processing analog signals, and the analog-to-digital conversion unit is used for converting the analog signals into digital signals.
For example, after receiving an analog signal, the analog signal processing module performs spectrum shifting on the received analog signal by the spectrum shifting unit to obtain a shifted analog signal; the analog filtering unit filters the moved analog signals to obtain filtered analog signals; the analog-to-digital conversion unit samples the filtered analog signal according to a preset time interval to convert the filtered analog signal into a digital signal.
Step S204, a zero frequency filtering module acquires an initial signal section from a digital signal according to a preset signal length, and filters a zero frequency direct current component of the initial signal section to obtain a pending signal section;
the preset signal length can be understood as a preset processing length of the zero frequency filtering module, that is, how long the zero frequency filtering module processes the digital signal each time, and if the preset signal length is N, N is a positive integer, the length of the digital signal processed by the zero frequency filtering module each time is N.
In this embodiment, the zero frequency filtering module obtains an initial signal segment from the digital signal output by the analog signal processing module every time, and the length of the initial signal segment is a preset signal length. As described above, the initial signal segment includes the digital signal and the dc component that are actually needed, and the zero frequency dc component in the dc component is a constant value, and the zero frequency filtering module may be used to filter the zero frequency dc component therein, so as to obtain the filtered initial signal segment that is the pending signal segment.
It will be appreciated that the zero frequency filtering module will obtain a plurality of initial signal segments from the digital signal output from the analog signal processing module, but each initial signal segment is processed in a similar manner, and for brevity, the embodiment of the present invention will be described by taking one initial signal segment as an example. Similarly, each of the following modules is described by taking a signal segment as an example.
Step S206, the low-frequency filtering module filters the low-frequency direct current component of the undetermined signal section according to the current low-frequency parameters to obtain the signal section to be processed;
step S208, the digital signal processing module processes the signal segment to be processed to obtain a target signal segment;
step S210, the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain new low-frequency parameters, and feeds the new low-frequency parameters back to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameters;
it can be understood that, since the signal segment output by the zero frequency filtering module is a set signal length, the subsequent low frequency filtering module, digital signal processing module and low frequency estimating module all process the signal segment of the signal length.
In this embodiment, after the low-frequency filtering module obtains the undetermined signal segment output by the zero-frequency filtering module, the undetermined signal segment is filtered according to the current low-frequency parameter, so as to filter the low-frequency direct current component therein, and then the undetermined signal segment is obtained. The current low frequency parameter may be understood as the low frequency parameter that was fed back to the low frequency filter module before the low frequency estimation module. The low-frequency parameter refers to the frequency of the low-frequency direct current component estimated by the low-frequency estimation module based on the signal segment output by the digital signal processing module.
The digital signal processing module processes the signal segment to be processed output by the low-frequency filtering module after obtaining the signal segment to be processed, so as to obtain a target signal segment, and transmits the target signal to the low-frequency estimating module; the low-frequency estimation module estimates the frequency of the low-frequency direct current component according to the target signal segment to obtain a new low-frequency parameter, and feeds the new low-frequency parameter back to the low-frequency filtering module; and then the low-frequency filtering module obtains new low-frequency parameters, and performs low-frequency direct current component filtering on the signal segment output by the zero-frequency filtering module according to the new low-frequency parameters, namely the low-frequency filtering module updates the low-frequency parameters according to the frequency estimated by the low-frequency estimating module, and performs filtering according to the updated low-frequency parameters.
It can be understood that in the embodiment of the invention, the low-frequency estimation module is used for carrying out frequency estimation on the low-frequency direct current component to obtain the low-frequency parameter and feeding the low-frequency parameter back to the low-frequency filtering module, the low-frequency filtering module is used for carrying out low-frequency direct current component filtering according to the low-frequency parameter, namely, the low-frequency filtering module and the low-frequency estimation module are used for updating the low-frequency parameter in a feedback iteration mode so as to filter the low-frequency direct current component and filter the zero-frequency direct current component by combining with the zero-frequency filtering module, thereby filtering the direct current component in the sampled digital signal, effectively avoiding the influence caused by the direct current component and improving the demodulation effect.
Based on the steps, the analog signal processing module processes the received analog signal and samples the processed analog signal to obtain a digital signal; the zero frequency filtering module acquires an initial signal section from the digital signal according to a preset signal length, and filters a zero frequency direct current component of the initial signal section to obtain a to-be-determined signal section; the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed; the digital signal processing module processes the signal section to be processed to obtain a target signal section; the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain new low-frequency parameters, and feeds the new low-frequency parameters back to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameters. The low-frequency direct current component is subjected to frequency estimation through the low-frequency estimation module and fed back to the low-frequency filtering module to filter the low-frequency direct current component, and meanwhile, the zero-frequency filtering module is combined to filter the zero-frequency direct current component, so that the direct current component in the digital signal is filtered, the influence caused by the direct current component is effectively avoided, and the demodulation effect is improved.
Alternatively, for the step S206, a possible implementation manner is provided in the embodiment of the present invention, please refer to fig. 3.
Step S206-1, the low-frequency filtering module generates a compensation signal segment corresponding to the undetermined signal segment according to the current low-frequency parameters;
step S206-3, the low-frequency filtering module multiplies the compensating signal segment with the undetermined signal segment to convert the low-frequency direct current component of the undetermined signal segment into a zero-frequency direct current component;
in step S206-5, the low frequency filtering module filters the zero frequency DC component of the signal segment to be determined to obtain the signal segment to be processed.
It can be understood that the current low-frequency parameter refers to the frequency of the low-frequency direct current component estimated by the low-frequency estimation module based on the previous signal segment output by the digital signal processing module, and the low-frequency estimation module and the low-frequency filtering module are adopted for feedback iteration based on the embodiment of the invention, so that the current low-frequency parameter can be considered as the frequency of the low-frequency direct current component of the signal segment to be determined.
In this embodiment, the low-frequency filtering module may use DDS (Direct Digital Frequency Synthesis ) technology to synthesize a digital signal according to the current low-frequency parameter to obtain the compensation signal segment. Assume that the low frequency dc component in the pending signal segment is, in accordance with the previous exampleThe compensation signal segment is +>I.e. the frequency of the compensation signal segment is opposite to the frequency of the low frequency dc component in the pending signal segment.
Then the low-frequency filtering module multiplies the compensation signal section and the undetermined signal section, namely, the frequency of the low-frequency direct current component in the undetermined signal section is shifted to zero frequency, and the low-frequency direct current component of the undetermined signal section is converted into the zero-frequency direct current component; and finally, the low-frequency filtering module filters the zero-frequency direct current component of the signal section to be determined to obtain the signal section to be processed.
It may be understood that, the low-frequency filtering module in the embodiment of the present invention generates a compensation signal segment with a frequency opposite to that of the low-frequency dc component in the signal segment to be determined based on the low-frequency parameter fed back by the low-frequency estimating module, and shifts the frequency of the low-frequency dc component in the signal segment to be determined to zero frequency by using the compensation signal segment, so as to convert the low-frequency dc component into the zero-frequency dc component and then filter the zero-frequency dc component, thereby filtering the low-frequency dc component.
Optionally, for the step S206-5, a possible implementation manner is provided in the embodiment of the present invention, namely: the low-frequency filtering module calculates the average value of the signal section to be determined to obtain the zero-frequency direct-current component of the signal section to be determined, and subtracts the zero-frequency direct-current component of the signal section to be determined from the signal section to be processed.
In this embodiment, as known from the foregoing description, the amplitude of the zero-frequency dc component in the pending signal segment is a constant value, and the average value of the amplitude of the ac component in the pending signal segment is 0, so the low-frequency filtering module may calculate the average value of the pending signal segment first, that is, obtain the zero-frequency dc component in the pending signal segment, and then subtract the zero-frequency dc component from the pending signal segment, so as to filter the zero-frequency dc component, and obtain the filtered pending signal segment, that is, the signal segment to be processed.
Optionally, another structural schematic diagram of the demodulator is provided in the embodiment of the invention. Referring to fig. 4, the analog signal processing module includes a spectrum shifting unit, an analog filtering unit, and an analog-to-digital conversion unit electrically connected in sequence; the digital signal processing module comprises a frame capturing unit, a timing synchronization unit and a frequency offset correction unit which are electrically connected in sequence, and further for the step S208, a possible implementation manner is provided in the embodiment of the invention.
Step S208-1, a frame capturing unit captures a frame header of a signal segment to be processed to obtain a captured signal segment;
step S208-3, the timing synchronization unit carries out time difference correction on the captured signal segment to obtain a corrected signal segment;
and step S208-5, the frequency offset correction unit corrects the frequency offset of the corrected signal segment to obtain a target signal segment.
In this embodiment, after the digital signal processing module obtains the signal segment to be processed output by the low-frequency filtering module, the frame capturing unit captures a frame header of the signal segment to be processed, so as to obtain a captured signal segment; the timing synchronization unit carries out time difference correction on the captured signal segment to obtain a corrected signal segment; and the frequency offset correction unit corrects the frequency offset of the corrected signal segment to obtain a target signal segment.
It can be understood that, in the embodiment of the invention, the zero frequency filtering module and the low frequency filtering module for filtering the direct current component are arranged between the analog signal processing module and the digital signal processing module, so that after the demodulator converts the analog signal into the digital signal, the direct current component in the converted digital signal is directly filtered, and the digital signal processing module is convenient for capturing the frame header, correcting the time difference and correcting the frequency offset of the digital signal without the direct current component interference, thereby improving the processing effect of the digital signal.
Alternatively, for the above step S210, a possible implementation manner is provided in the embodiment of the present invention, please refer to fig. 5.
Step S210-1, a low frequency estimation module acquires a pilot sequence from a target signal segment;
step S210-3, the low frequency estimation module performs power calculation according to the pilot frequency sequence to obtain a plurality of noise powers; the change period of the plurality of noise powers is consistent with the change period of the low-frequency direct current component of the undetermined signal section;
in step S210-5, the low frequency estimation module performs frequency estimation according to the plurality of noise powers to obtain new low frequency parameters.
For easy understanding, the working principle of the frequency offset correction unit will be described before describing the above steps S210-1 to S210-5.
The frequency offset correction unit measures frequency offset through pilot frequency in the signal and compensates the frequency offset to realize frequency offset correction. The pilot is a known symbol that is inserted into the signal by the transmitting end every a fixed period of time. The two parties agree on the known symbols to be fixed values after normalization processing, namely agree on correct pilot values.
The frequency offset correction unit measures the frequency offset of the signal by using the frequency offset between the received pilot value and the correct pilot value. Assuming a correct pilot value of 1, the received pilot value isThen there is a low frequency after samplingThe pilot value in the digital signal of the DC component is, wherein />Representing the frequency offset of the signal, < >>Indicating pilot rate +.>Representing the initial gaussian white noise.
After being processed by the timing synchronization unit and the frequency offset correction unit, the frequency offset of the signal is corrected and compensated, and the pilot frequency value becomes, wherein />Representing the residual gaussian white noise after compensation,representing the low frequency dc component remaining after compensation. It can be seen that the received pilot value differs from the correct pilot value, i.e. 1>These two parts directly affect the signal-to-noise ratio and therefore embodiments of the present invention consider gaussian white noise and low frequency dc components together as noise.
For Gaussian white noise, the power of each frequency is equal and is irrelevant to time, so that the noise power of the pilot frequency only changes along with the change of the low-frequency direct current component, namely the change period of the noise power is consistent with the change period of the low-frequency direct current component. Therefore, the embodiment of the invention estimates the frequency of the low-frequency direct current component based on the change period of the noise power.
In this embodiment, after obtaining the target signal segment output by the frequency offset correction unit, the low frequency estimation module obtains a plurality of pilot values from the target signal segment to obtain a pilot sequence, performs power calculation according to the pilot sequence to obtain a plurality of noise powers, performs frequency estimation according to the plurality of noise powers to obtain a new low frequency parameter, and feeds back the new low frequency parameter to the low frequency filtering module to enable the low frequency filtering module to filter according to the new low frequency parameter.
Optionally, for the step S210-3 described above, one possible implementation is provided by the embodiments of the present invention.
Step S210-3-1, a low frequency estimation module slides sequentially according to a preset window length, a plurality of pilot groups are obtained from a pilot sequence, and each pilot group comprises the same number of pilot values;
step S210-3-3, for each pilot frequency group, the low frequency estimation module adds up all pilot frequency values in the pilot frequency group, calculates a mean value to obtain a first value, and calculates the square of the first value to obtain the signal power of the pilot frequency group to obtain the signal power of each pilot frequency group;
step S210-3-5, for each pilot frequency group, the low frequency estimation module calculates the square of each pilot frequency value in the pilot frequency group, then accumulates to obtain a second value, calculates the average value of the second value to obtain the total power of the pilot frequency group, and obtains the total power of each pilot frequency group;
in step S210-3-7, the low frequency estimation module calculates the difference between the total power of each pilot group and the signal power to obtain a plurality of noise powers.
In this embodiment, the low frequency estimation module slides in the pilot sequence in sequence according to a preset window length, and takes all pilot values in each window as one pilot group, that is, a plurality of pilot groups are obtained, and the total number of pilot values in each pilot group is the same.
It will be appreciated that the low frequency estimation module processes each pilot set in a similar manner, and for brevity, one pilot set will be described as an example.
The low frequency estimation module is used for respectively calculating the total power and the signal power of the pilot frequency group based on a plurality of pilot frequency values in the pilot frequency group, and then subtracting the signal power from the total power to obtain a difference value which is the noise power of the pilot frequency group.
The process of calculating the signal power of the pilot group by the low frequency estimation module is as follows: all pilot values in the pilot group are accumulated, then the average value is calculated based on the accumulated sum and the total number of the pilot values in the pilot group to obtain a first value, and then the square of the first value is calculated to obtain the signal power of the pilot group. It can be understood that, because the calculation mode of accumulating and then averaging is adopted, the noise in the pilot frequency group cannot be counted, so that the power obtained after square calculation is the power of the signal.
The process of calculating the total power of the pilot group by the low frequency estimation module is as follows: separately calculating the square of each pilot frequency value in the pilot frequency group, and accumulating the squares of each pilot frequency value in the pilot frequency group to obtain a second numerical value; and calculating the average value based on the second numerical value and the total number of pilot values in the pilot group to obtain the total power of the pilot group. It can be understood that, since the calculation mode of squaring and then averaging is adopted, the noise in the pilot frequency group is also counted, so that the obtained power is the sum of the power of the signal and the noise, namely the total power.
In a similar manner as described above, the total power and the signal power of each pilot group can be obtained, and then the difference between the total power and the signal power of each pilot group is calculated to obtain the noise power of each pilot group, so that a plurality of noise powers can be obtained based on a plurality of pilot groups.
Optionally, for the step S210-5 described above, one possible implementation is provided by the embodiments of the present invention.
Step S210-5-1, calculating the average value of a plurality of noise powers by the low-frequency estimation module to obtain the power of Gaussian white noise, and calculating the difference value of each noise power and the power of Gaussian white noise to obtain each target power;
s210-5-3, performing fast Fourier transform by the low-frequency estimation module according to all target power and preset transform points to obtain frequency parameters;
step S210-5-5, the low frequency estimation module carries out frequency estimation according to a preset formula and according to the frequency parameter, the preset conversion point number and the preset pilot frequency sequence rate to obtain a new low frequency parameter;
the preset formula is:
；
wherein ,representing new low frequency parameters; />Representing a preset pilot rate; />Representing a frequency parameter; />Representing the preset conversion point number.
In this embodiment, since the power of the gaussian white noise is a constant value, the low frequency estimation module calculates the average value of the plurality of noise powers to obtain the power of the gaussian white noise, and then subtracts the power of the gaussian white noise from each noise power to obtain each target power. It can be understood that subtracting the average value of the noise power, that is, shifting the noise power to the periphery of the amplitude of 0, then the frequency of the low-frequency direct current component in the undetermined signal segment can be estimated according to the change period of the target power.
The low-frequency estimation module performs fast Fourier transform according to all target power and preset transform points to obtain a frequency spectrum, determines the position of the maximum spectral line in the frequency spectrum to obtain a frequency parameter, and then calculates according to a preset formula to calculate the frequency parameterAnd the preset conversion point +.>Will calculate the ratio to the preset pilot rate +.>And obtaining the new low-frequency parameters.
Optionally, an embodiment of the present invention further provides a schematic structural diagram of a demodulator, referring to fig. 6, where the demodulator further includes a frame decoding module electrically connected to the digital signal processing module, and further after the step S210, the following steps may be further performed, that is: in step S212, the de-framing and decoding module de-frames and decodes the target signal segment to obtain a demodulated signal segment.
In this embodiment, after obtaining the target signal segment output by the frequency offset correction unit, the frame decoding module decodes and decodes the target signal segment to obtain a demodulated signal segment, so as to obtain a demodulated signal based on a plurality of demodulated signal segments.
In order to better embody the effects of the present invention, the prior art and the present invention will be compared with one example. For example, assume that the transmitting end modulates a signal by adopting a QPSK (Quadrature Phase Shift Keying ) mode, the rate of the signal is 2MHz, the input signal to noise ratio is 30dB, the amplitude of the signal is 128, the amplitudes of the zero frequency direct current component and the low frequency direct current component are both 4, the frequency of the low frequency direct current component is 40Hz, and the number of constellation points received by the receiving end is 2500.
Please refer to fig. 7, which shows a constellation diagram obtained by demodulating the received signal at the receiving end under the ideal condition of no dc component, and the output signal-to-noise ratio is 29.6dB. Please refer to fig. 8, which is a constellation diagram obtained by demodulating a received signal by a receiving end under the condition of actually having a dc component (including a zero frequency dc component and a low frequency dc component), and the output signal-to-noise ratio is 22dB.
Please refer to fig. 9, which is a constellation diagram obtained by demodulating a received signal and filtering out a zero frequency dc component by a receiving end according to the prior art, and the output signal-to-noise ratio is 24.5dB. Please refer to fig. 10, which is a constellation diagram obtained by demodulating a received signal by a receiving end and filtering out a zero-frequency direct current component and a low-frequency direct current component by the method provided by the embodiment of the present invention, wherein the output signal-to-noise ratio is 29dB.
As can be seen from fig. 7 and 8, the dc component causes the constellation points to separate and reduces the output signal to noise ratio, i.e. affects the demodulation effect.
As can be seen from fig. 8 and 9, after the zero-frequency direct current component is filtered by adopting the prior art, although the output signal-to-noise ratio is improved and the situation of constellation point separation is improved to a certain extent, the demodulation effect is improved to a smaller extent because the low-frequency direct current component is not filtered.
As can be seen from fig. 9 and 10, the present invention can filter not only the zero frequency dc component but also the low frequency dc component, and can achieve the effect of almost completely eliminating the influence of the dc component. Compared with the prior art, the output signal-to-noise ratio of the invention is improved by 4.5dB, the constellation point separation condition is obviously improved, and the demodulation effect is greatly improved.
The embodiment of the invention also provides a demodulator for realizing the low-frequency direct current component filtering method provided by the embodiment of the invention.
The embodiment of the invention also provides satellite communication equipment which comprises the demodulator provided by the embodiment of the invention.
In the several embodiments provided in the present invention, it should be understood that the disclosed method may be implemented in other manners. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
In addition, functional modules in the embodiments of the present invention may be integrated together to form a single part, or each module may exist alone, or two or more modules may be integrated to form a single part.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. The low-frequency direct current component filtering method is characterized by being applied to a demodulator, wherein the demodulator comprises an analog signal processing module, a zero frequency filtering module, a low-frequency filtering module, a digital signal processing module and a low-frequency estimating module which are electrically connected in sequence, the low-frequency estimating module is electrically connected with the low-frequency filtering module, and the low-frequency direct current component filtering method comprises the following steps:
the analog signal processing module processes the received analog signals and samples the processed analog signals to obtain digital signals; the digital signal comprises a direct current component, the direct current component being expressed as:
；
wherein ,representing the direct current component, +.>Representing the amplitude of the zero frequency direct current component, +.>Representing the amplitude of the low frequency direct current component, +.>Frequency representing low frequency dc component, +.>Time interval representing sampling, +.>；
The zero frequency filtering module acquires an initial signal section from the digital signal according to a preset signal length, and filters a zero frequency direct current component of the initial signal section to obtain a to-be-determined signal section;
the low-frequency filtering module filters the low-frequency direct current component of the signal section to be processed according to the current low-frequency parameter to obtain the signal section to be processed;
the digital signal processing module processes the signal segment to be processed to obtain a target signal segment;
the low-frequency estimation module carries out low-frequency estimation according to the target signal segment to obtain a new low-frequency parameter, and feeds the new low-frequency parameter back to the low-frequency filtering module so that the low-frequency filtering module filters according to the new low-frequency parameter;
the low frequency estimation module performs low frequency estimation according to the target signal segment to obtain new low frequency parameters, including:
the low-frequency estimation module acquires a pilot sequence from the target signal segment;
the low-frequency estimation module sequentially slides according to a preset window length, and a plurality of pilot groups are obtained from the pilot sequence, wherein each pilot group comprises the same number of pilot values;
the low-frequency estimation module calculates the average value after accumulating all pilot frequency values in each pilot frequency group to obtain a first value, and calculates the square of the first value to obtain the signal power of the pilot frequency group to obtain the signal power of each pilot frequency group;
the low-frequency estimation module calculates the square of each pilot frequency value in each pilot frequency group, then accumulates the squares to obtain a second value, calculates the average value of the second values to obtain the total power of the pilot frequency groups, and obtains the total power of each pilot frequency group;
the low-frequency estimation module calculates the difference value between the total power of each pilot frequency group and the signal power to obtain a plurality of noise powers; the change period of the plurality of noise powers is consistent with the change period of the low-frequency direct current component of the undetermined signal section;
the low-frequency estimation module calculates the average value of the plurality of noise powers to obtain power of Gaussian white noise, and calculates the difference value of each noise power and the power of Gaussian white noise to obtain each target power;
the low-frequency estimation module performs fast Fourier transform according to all target power and preset transform points to obtain a frequency spectrum, and determines the position of the maximum spectral line in the frequency spectrum to obtain a frequency parameter;
the low-frequency estimation module carries out frequency estimation according to a preset formula and the frequency parameter, the preset conversion point number and the preset pilot frequency rate to obtain the new low-frequency parameter;
the preset formula is as follows:
；
wherein , representing new low frequency parameters; />Representing a preset pilot rate; />Representing a frequency parameter; />Representing the preset conversion point number.
2. The method for filtering low-frequency dc components according to claim 1, wherein the filtering the low-frequency dc components of the pending signal segment by the low-frequency filtering module according to the current low-frequency parameter to obtain the pending signal segment includes:
the low-frequency filtering module generates a compensation signal segment corresponding to the undetermined signal segment according to the current low-frequency parameter;
the low-frequency filtering module multiplies the compensation signal segment and the undetermined signal segment to convert a low-frequency direct current component of the undetermined signal segment into a zero-frequency direct current component;
and the low-frequency filtering module filters the zero-frequency direct current component of the signal section to be processed to obtain the signal section to be processed.
3. The method for filtering a low-frequency direct current component according to claim 2, wherein the low-frequency filtering module filters a zero-frequency direct current component of the signal segment to be processed to obtain the signal segment to be processed, and the method comprises the following steps:
the low-frequency filtering module calculates the average value of the undetermined signal section to obtain a zero-frequency direct current component of the undetermined signal section, and subtracts the undetermined signal section from the zero-frequency direct current component of the undetermined signal section to obtain the signal section to be processed.
4. The method according to claim 1, wherein the digital signal processing module includes a frame capturing unit, a timing synchronization unit, and a frequency offset correction unit;
the digital signal processing module processes the signal segment to be processed to obtain a target signal segment, and the digital signal processing module comprises:
the frame capturing unit captures the frame header of the signal segment to be processed to obtain a captured signal segment;
the timing synchronization unit performs time difference correction on the captured signal segment to obtain a corrected signal segment;
and the frequency offset correction unit corrects the frequency offset of the corrected signal segment to obtain the target signal segment.
5. The method of claim 1, wherein the demodulator further comprises a de-framing decoding module electrically connected to the digital signal processing module, the method further comprising:
and the de-framing and decoding module de-frames and decodes the target signal segment to obtain a demodulated signal segment.
6. A demodulator for implementing the low frequency direct current component filtering method of any one of claims 1 to 5.
7. A satellite communication device comprising the demodulator of claim 6.
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