CN111935047A - FM signal demodulation method and system with low signal-to-noise ratio loss - Google Patents

FM signal demodulation method and system with low signal-to-noise ratio loss Download PDF

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CN111935047A
CN111935047A CN202010623257.8A CN202010623257A CN111935047A CN 111935047 A CN111935047 A CN 111935047A CN 202010623257 A CN202010623257 A CN 202010623257A CN 111935047 A CN111935047 A CN 111935047A
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CN111935047B (en
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王健欢
张宗攀
雷静
杨克元
韩小娟
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Xian Institute of Space Radio Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H04L27/142—Compensating direct current components occurring during the demodulation and which are caused by mistuning
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
    • H04L27/14—Demodulator circuits; Receiver circuits
    • H04L27/144—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements
    • H04L27/148—Demodulator circuits; Receiver circuits with demodulation using spectral properties of the received signal, e.g. by using frequency selective- or frequency sensitive elements using filters, including PLL-type filters

Abstract

The invention relates to an FM signal demodulation method and system with low signal-to-noise ratio loss, which comprises the following steps: (1) carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed; (2) carrying out quadrature down-conversion and low-pass filtering by using a local carrier, moving a frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, filtering high-frequency components through a low-pass filter, and suppressing out-of-band noise; (3) performing first CIC filtering on the results of the orthogonal down-conversion and the low-pass filtering to realize accumulated speed reduction; (4) carrying out digital frequency discrimination on the result after the first CIC filtering to obtain carrier Doppler frequency offset; (5) taking the carrier frequency offset obtained by digital frequency discrimination as compensation quantity, and performing orthogonal down-conversion and low-pass filtering again to realize carrier Doppler elimination; (6) performing second CIC filtering on the signal subjected to the quadrature down-conversion and low-pass filtering; (7) and carrying out digital frequency discrimination on the result of the second CIC filtering to obtain modulation signal information and realize the demodulation of the FM signal.

Description

FM signal demodulation method and system with low signal-to-noise ratio loss
Technical Field
The invention belongs to the field of communication, and relates to compensation of carrier Doppler frequency offset of an FM modulation signal and demodulation of the modulation signal.
Background
Digital frequency discrimination is a key technology in a PCM/PSK/FM modulation signal demodulation system, and the performance of the digital frequency discrimination directly determines the demodulation capability of the frequency modulation system under a threshold level.
In the conventional FM signal demodulation method, by means of a digital frequency discrimination principle, an arc tangent operation is performed to obtain phase information of a received signal, and then a first order differential operation is performed to obtain frequency information of the received signal, that is, modulation data information, wherein doppler residual frequency offset is expressed as a direct current component. The method is characterized in that an approximate substitution relation is utilized, but the approximate substitution precondition is that the sampling rate before frequency discrimination needs to meet 12 times of the sampling relation, the bandwidth of a signal after sampling is large, and the in-band signal-to-noise ratio is reduced.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method and the system for demodulating the FM signal with low signal-to-noise ratio loss overcome the requirement of a traditional digital frequency discrimination mode on the sampling relation of 12 times before frequency discrimination, and can realize the demodulation of the frequency-modulated signal with low signal-to-noise ratio under the condition of meeting the Nyquist sampling theorem.
The technical scheme adopted by the invention is as follows:
a FM signal demodulation method with low signal-to-noise ratio loss comprises the following steps:
(1) carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed;
(2) carrying out quadrature down-conversion and low-pass filtering on the frequency modulation signal, moving the frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, and filtering out high-frequency components and inhibiting out-of-band noise through a low-pass filter;
(3) performing first CIC filtering on the results of the orthogonal down-conversion and the low-pass filtering to realize accumulated speed reduction;
(4) performing digital frequency discrimination on the result obtained after the first CIC filtering, and accumulating the result obtained by the digital frequency discrimination to obtain a direct current component, namely carrier frequency offset;
(5) taking the carrier frequency offset as a compensation quantity, and performing orthogonal down-conversion and low-pass filtering again to realize Doppler elimination;
(6) performing second CIC filtering on the signal subjected to the quadrature down-conversion and low-pass filtering in the step (5);
(7) and carrying out digital frequency discrimination on the result of the second CIC filtering to obtain modulation signal information and realize the demodulation of the FM signal.
Further, the expression of the analog FM modulation signal is:
Figure BDA0002563803590000021
where A is the amplitude of the FM modulation signal, ωcIs the carrier center angle frequency, t is time,
Figure BDA0002563803590000022
in order to modulate the phase of the signal,
Figure BDA0002563803590000023
kffor frequency-modulated sensitivity, AmFor modulating the amplitude, omega, of the signalmIn order to modulate the angular frequency of the signal,
Figure BDA0002563803590000024
a fixed phase difference between the input signal and the local signal due to non-synchronization is taken into account.
Further, the digitally sampled frequency modulated signal is:
Figure BDA0002563803590000025
wherein f iscIs the carrier center frequency and n is the time after digital sampling.
Further, the step (2) performs quadrature down-conversion and low-pass filtering on the frequency-modulated signal, and the obtained result is:
Figure BDA0002563803590000026
Figure BDA0002563803590000027
wherein S isI(n) is the quadrature down-converted and low-pass filtered I-path output signal, SQ(n) is Q-path output signal after quadrature down-conversion and low-pass filtering, cos (2 pi f)cn) is the I local signal of quadrature down-conversion, sin (2 π f)cn) is the quadrature down-converted Q local signal.
Further, the step (3) performs first CIC filtering on the I path result and the Q path result after the quadrature down-conversion and the low-pass filtering, respectively, to realize cumulative speed reduction, specifically:
Figure BDA0002563803590000035
Figure BDA0002563803590000031
wherein S isI1(n) is the output result of the first CIC filtering of the I path, SQ1And (N) is an output result of Q paths after the first CIC filtering, and N is the accumulated point number of the first CIC filtering.
Further, in the step (4), digital frequency discrimination is performed on the result after the first CIC filtering, and the result obtained by the digital frequency discrimination is accumulated to obtain a dc component therein, which specifically is:
(6.1) performing arc tangent operation on output results of the I path and the Q path after the first CIC filtering according to the following formula to obtain phase information of the FM modulation signal:
Figure BDA0002563803590000032
wherein the content of the first and second substances,
Figure BDA0002563803590000033
phase information of the FM modulation signal;
(6.2) phase information on FM modulated Signal
Figure BDA0002563803590000034
Carrying out first-order differential operation to obtain a modulation signal with frequency offset, wherein the calculation process is as follows:
Figure BDA0002563803590000041
wherein the content of the first and second substances,
Figure BDA0002563803590000042
in order to demodulate the modulated signal with the frequency offset,
Figure BDA0002563803590000043
in order to modulate the signal, the signal is modulated,
Figure BDA0002563803590000044
Figure BDA0002563803590000045
in order to modulate the frequency offset of the signal,
Figure BDA0002563803590000046
S′Q1(n) is SQ1(n) as a result of the first order differential operation,
Figure BDA0002563803590000047
SQ1(n) is the value of the current time, SQ1(n-1) is the value of the previous moment, Delta T is the time difference between the current moment and the previous moment, SI′1(n) is SI1(n) as a result of the first order differential operation,
Figure BDA0002563803590000048
SI1(n) is the value of the current time, SI1(n-1) is the value of the previous moment;
(6.3) modulated Signal with frequency offset
Figure BDA0002563803590000049
Obtained by accumulating time duration DeltaT
Figure BDA00025638035900000410
The direct-current component of the signal, i.e. carrier frequency offset
Figure BDA00025638035900000411
Further, taking the carrier frequency offset in the step (5) as a compensation quantity, and performing orthogonal down-conversion and low-pass filtering again to realize doppler elimination, specifically:
Figure BDA00025638035900000412
Figure BDA00025638035900000413
wherein S isI11(n) is the I-path output signal after orthogonal down-conversion and low-pass filtering after compensating carrier frequency offset, SQ11And (n) is the Q path output signal after quadrature down-conversion and low-pass filtering after compensating carrier frequency offset.
Further, performing second CIC filtering on the signal subjected to quadrature down-conversion and low-pass filtering in the step (6), specifically:
Figure BDA00025638035900000414
Figure BDA00025638035900000415
wherein S isI22(n) is the output result of the second CIC filtering of the I path, SQ22(n) is the output result of Q-path second CIC filtering, M is the accumulated point number of the second CIC filtering and M>N。
Further, performing digital frequency discrimination on the result obtained after the second CIC filtering in the step (7), wherein the process of the digital frequency discrimination is the same as that in the step (4), and the result obtained after the digital frequency discrimination is as follows:
Figure BDA0002563803590000051
wherein the content of the first and second substances,
Figure BDA0002563803590000052
for the final FM demodulated output, m (n) is the demodulated modulated data.
Further, the present invention also provides an FM signal demodulation system, including:
a sampling module: carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed;
a down-conversion and filtering module: carrying out quadrature down-conversion and low-pass filtering on the frequency modulation signal, moving the frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, and filtering out high-frequency components and inhibiting out-of-band noise through a low-pass filter;
and a CIC filtering module: CIC filtering is carried out on the results after the orthogonal down-conversion and the low-pass filtering, and accumulated speed reduction is realized;
the digital frequency discrimination module: performing digital frequency discrimination on the result after CIC filtering, and accumulating the result obtained by the digital frequency discrimination to obtain a direct current component, namely carrier frequency offset; taking the carrier frequency offset as a compensation quantity, performing orthogonal down-conversion and low-pass filtering again to realize Doppler elimination, and then performing CIC filtering again; and carrying out digital frequency discrimination on the result of the second CIC filtering to obtain modulation signal information and realize the demodulation of the FM signal.
Compared with the prior art, the invention has the advantages that:
(1) the invention realizes the demodulation of FM modulation signals through the arc tangent operation and the first order differential operation to obtain carrier Doppler information and modulation data information, and the engineering is easy to realize.
(2) The invention does not adopt approximation in the implementation process, and compared with a cross product frequency discrimination algorithm, the invention has no requirement of 12 times of sampling relation on the sampling rate before digital frequency discrimination, realizes distortion-free demodulation under the condition of meeting the Nyquist sampling theorem, and reduces the signal-to-noise ratio requirement of the signal before digital frequency discrimination.
(3) Compared with a cross product frequency discrimination algorithm, the method can improve the error code performance by 1dB by using the arc tangent frequency discrimination algorithm under the condition of low signal to noise ratio.
(4) The FM modulation signal demodulation method provided by the invention can adaptively modify the accumulation coefficient of the CIC filter according to different application scenes and indexes, and obtain the carrier Doppler compensation through digital frequency discrimination to complete the demodulation of the FM modulation signal.
Drawings
FIG. 1 is a schematic diagram of the method of the present invention.
FIG. 2 is a simulation diagram of the frequency discrimination result of the cross product frequency discrimination according to the present invention.
FIG. 3 is a comparison chart of the bit error rate test data of the method of the present invention and the cross product frequency discrimination method.
Detailed Description
As shown in fig. 1, which is a schematic diagram of the method of the present invention, the method for demodulating an FM signal with low snr loss according to the present invention mainly comprises the following steps:
(1) carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed;
the analog FM modulated signal expression is:
Figure BDA0002563803590000061
where A is the amplitude of the FM modulation signal, ωcIs the carrier center angle frequency, t is time,
Figure BDA0002563803590000062
in order to modulate the phase of the signal,
Figure BDA0002563803590000063
kffor frequency-modulated sensitivity, AmFor modulating the amplitude, omega, of the signalmIn order to modulate the angular frequency of the signal,
Figure BDA0002563803590000064
a fixed phase difference between the input signal and the local signal due to non-synchronization is taken into account.
The digitally sampled frequency modulated signal is:
Figure BDA0002563803590000065
wherein f iscIs the carrier center frequency and n is the time after digital sampling.
(2) Carrying out quadrature down-conversion and low-pass filtering on the frequency modulation signal obtained in the step (1), moving the frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, filtering high-frequency components through a low-pass filter, and suppressing out-of-band noise;
the result after the first down-conversion and the low-pass filtering is:
Figure BDA0002563803590000071
Figure BDA0002563803590000072
wherein S isI(n) is the quadrature down-converted and low-pass filtered I-path output signal, SQ(n) is Q-path output signal after quadrature down-conversion and low-pass filtering, cos (2 pi f)cn) is the I local signal of quadrature down-conversion, sin (2 π f)cn) is the quadrature down-converted Q local signal.
(3) Performing first CIC filtering on the results of the orthogonal down-conversion and the low-pass filtering obtained in the step (2) to realize accumulated speed reduction;
the result after the first CIC filtering is:
Figure BDA0002563803590000073
Figure BDA0002563803590000074
wherein S isI1(n) is the output result of the first CIC filtering of the I path, SQ1And (N) is an output result of Q paths after the first CIC filtering, and N is the accumulated point number of the first CIC filtering.
(4) Performing arc tangent operation on the result obtained after the first CIC filtering in the step (3) according to the following formula to obtain phase information of the FM modulation signal;
Figure BDA0002563803590000081
wherein the content of the first and second substances,
Figure BDA0002563803590000082
phase information of the FM modulation signal;
(5) the phase information of the FM modulation signal obtained in the step (4)
Figure BDA0002563803590000083
Carrying out first-order differential operation to obtain a modulation signal with frequency offset, wherein the calculation process is as follows:
Figure BDA0002563803590000084
wherein the content of the first and second substances,
Figure BDA0002563803590000085
in order to demodulate the modulated signal with the frequency offset,
Figure BDA0002563803590000086
in order to modulate the signal, the signal is modulated,
Figure BDA0002563803590000087
Figure BDA0002563803590000088
in order to modulate the frequency offset of the signal,
Figure BDA0002563803590000089
S′Q1(n) is SQ1(n) as a result of the first order differential operation,
Figure BDA00025638035900000810
SQ1(n) is the value of the current time, SQ1(n-1) is the value of the previous moment, Delta T is the time difference between the current moment and the previous moment, SI′1(n) is SI1(n) as a result of the first order differential operation,
Figure BDA00025638035900000811
SI1(n) is the value of the current time, SI1(n-1) is the value of the previous moment;
(6) for the modulation signal with frequency deviation obtained in the step (5)
Figure BDA00025638035900000812
Obtained by accumulating time duration DeltaT
Figure BDA00025638035900000813
The direct-current component of the signal, i.e. carrier frequency offset
Figure BDA00025638035900000814
Since the delta T is not considered during frequency discrimination, the real size of the direct current component needs to be calculated when the direct current component is obtained for Doppler correction; therefore, the frequency discriminated result needs to be accumulated according to the accumulated time length Δ T to obtain the true doppler angular frequency, and then the true doppler frequency is obtained by dividing the doppler angular frequency by 2 pi.
(7) The carrier frequency deviation obtained in the step (6)
Figure BDA00025638035900000815
As a compensation amount, quadrature down-conversion and low-pass filtering are performed again,realizing Doppler elimination;
the result after the second down-conversion and low-pass filtering is:
Figure BDA0002563803590000091
Figure BDA0002563803590000092
wherein S isI11(n) is the I-path output signal after orthogonal down-conversion and low-pass filtering after compensating carrier frequency offset, SQ11And (n) is the Q path output signal after quadrature down-conversion and low-pass filtering after compensating carrier frequency offset.
(8) Performing second CIC filtering on the signal obtained in the step (7) after the second quadrature down-conversion and the low-pass filtering;
the result after the second CIC filtering is:
Figure BDA0002563803590000093
Figure BDA0002563803590000094
wherein S isI22(n) is the output result of the second CIC filtering of the I path, SQ22(n) is the output result of Q-path second CIC filtering, M is the accumulated point number of the second CIC filtering and M>N。
(9) And (4) carrying out digital frequency discrimination on the result obtained by the second CIC filtering in the step (8) to obtain modulation signal information, and realizing the demodulation of the FM signal.
The process of digital frequency discrimination is the same as the steps (4) to (5), and the result obtained after digital frequency discrimination is as follows:
Figure BDA0002563803590000095
wherein the content of the first and second substances,
Figure BDA0002563803590000096
for the final FM demodulated output, m (n) is the demodulated modulated data.
Example (b):
the frequency discrimination mode of the invention only needs to perform arc tangent operation on the I path signal and the Q path signal after the CIC filter finishes speed reduction, and phase information and modulation data information of a received signal can be obtained through first order differential operation, and the frequency discrimination mode is easy to realize in engineering. In addition, the method of the invention does not adopt approximation in the realization process, so that the sampling rate before digital frequency discrimination does not have the requirement of 12 times of sampling relation, distortion-free demodulation is realized under the condition of meeting the Nyquist sampling theorem, and the signal-to-noise ratio requirement before digital frequency discrimination is reduced.
FIG. 2 is a simulation diagram of the frequency discrimination result of the cross product frequency discrimination according to the present invention. It can be seen from the figure that under the same test conditions, when the sampling rate before frequency discrimination satisfies the 2.5-fold relationship, the cross-product frequency discrimination result in fig. 2 has severe distortion, while the arctan frequency discrimination result can demodulate a complete single-carrier signal.
FIG. 3 is a comparison chart of the bit error rate test data of the method of the present invention and the cross product frequency discrimination method. As can be seen from fig. 3, under the condition of low snr, compared with the cross product frequency discrimination algorithm, the arctangent frequency discrimination algorithm of the present invention can improve the error code performance by 1 dB.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.

Claims (10)

1. An FM signal demodulation method with low signal-to-noise ratio loss is characterized by comprising the following steps:
(1) carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed;
(2) carrying out quadrature down-conversion and low-pass filtering on the frequency modulation signal, moving the frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, and filtering out high-frequency components and inhibiting out-of-band noise through a low-pass filter;
(3) performing first CIC filtering on the results of the orthogonal down-conversion and the low-pass filtering to realize accumulated speed reduction;
(4) performing digital frequency discrimination on the result obtained after the first CIC filtering, and accumulating the result obtained by the digital frequency discrimination to obtain a direct current component, namely carrier frequency offset;
(5) taking the carrier frequency offset as a compensation quantity, and performing orthogonal down-conversion and low-pass filtering again to realize Doppler elimination;
(6) performing second CIC filtering on the signal subjected to the quadrature down-conversion and low-pass filtering in the step (5);
(7) and carrying out digital frequency discrimination on the result of the second CIC filtering to obtain modulation signal information and realize the demodulation of the FM signal.
2. The method of claim 1, wherein the FM signal demodulation with low SNR loss comprises: the analog FM modulated signal expression is:
Figure FDA0002563803580000011
where A is the amplitude of the FM modulation signal, ωcIs the carrier center angle frequency, t is time,
Figure FDA0002563803580000012
in order to modulate the phase of the signal,
Figure FDA0002563803580000013
kffor frequency-modulated sensitivity, AmFor modulating the amplitude, omega, of the signalmIn order to modulate the angular frequency of the signal,
Figure FDA0002563803580000014
a fixed phase difference between the input signal and the local signal due to non-synchronization is taken into account.
3. The method of claim 2, wherein the FM signal demodulation with low SNR loss comprises: the digitally sampled frequency modulated signal is:
Figure FDA0002563803580000021
wherein f iscIs the carrier center frequency and n is the time after digital sampling.
4. A method of demodulating an FM signal having a low loss of signal to noise ratio as claimed in claim 3, wherein: performing quadrature down-conversion and low-pass filtering on the frequency-modulated signal in the step (2), and obtaining a result that:
Figure FDA0002563803580000022
Figure FDA0002563803580000023
wherein S isI(n) is the quadrature down-converted and low-pass filtered I-path output signal, SQ(n) is Q-path output signal after quadrature down-conversion and low-pass filtering, cos (2 pi f)cn) is the I local signal of quadrature down-conversion, sin (2 π f)cn) is the quadrature down-converted Q local signal.
5. The method of claim 4, wherein the FM signal demodulation with low SNR loss comprises: the step (3) performs first CIC filtering on the I path and Q path results after the quadrature down-conversion and the low-pass filtering respectively to realize cumulative speed reduction, specifically:
Figure FDA0002563803580000024
Figure FDA0002563803580000025
wherein S isI1(n) is the output result of the first CIC filtering of the I path, SQ1And (N) is an output result of Q paths after the first CIC filtering, and N is the accumulated point number of the first CIC filtering.
6. The method of claim 5, wherein the FM signal demodulation with low SNR loss comprises: the step (4) performs digital frequency discrimination on the result after the first CIC filtering, and accumulates the result obtained by the digital frequency discrimination to obtain a direct current component therein, which specifically includes:
(6.1) performing arc tangent operation on output results of the I path and the Q path after the first CIC filtering according to the following formula to obtain phase information of the FM modulation signal:
Figure FDA0002563803580000031
wherein the content of the first and second substances,
Figure FDA0002563803580000032
phase information of the FM modulation signal;
(6.2) phase information on FM modulated Signal
Figure FDA0002563803580000033
Carrying out first-order differential operation to obtain a modulation signal with frequency offset, wherein the calculation process is as follows:
Figure FDA0002563803580000034
wherein the content of the first and second substances,
Figure FDA0002563803580000035
in order to demodulate the modulated signal with the frequency offset,
Figure FDA0002563803580000036
in order to modulate the signal, the signal is modulated,
Figure FDA0002563803580000037
Figure FDA0002563803580000038
in order to modulate the frequency offset of the signal,
Figure FDA0002563803580000039
S′Q1(n) is SQ1(n) as a result of the first order differential operation,
Figure FDA00025638035800000310
SQ1(n) is the value of the current time, SQ1(n-1) is a value of a previous moment, and delta T is a time difference S 'between the current moment and the previous moment'I1(n) is SI1(n) as a result of the first order differential operation,
Figure FDA00025638035800000311
SI1(n) is the value of the current time, SI1(n-1) is the value of the previous moment;
(6.3) modulated Signal with frequency offset
Figure FDA00025638035800000312
Obtained by accumulating time duration DeltaT
Figure FDA00025638035800000313
The direct-current component of the signal, i.e. carrier frequency offset
Figure FDA00025638035800000314
7. The method of claim 6, wherein the FM signal demodulation with low SNR loss comprises: and (5) taking the carrier frequency offset as a compensation quantity, and performing orthogonal down-conversion and low-pass filtering again to realize Doppler elimination, specifically:
Figure FDA0002563803580000041
Figure FDA0002563803580000042
wherein S isI11(n) is the I-path output signal after orthogonal down-conversion and low-pass filtering after compensating carrier frequency offset, SQ11And (n) is the Q path output signal after quadrature down-conversion and low-pass filtering after compensating carrier frequency offset.
8. The method of claim 7, wherein the FM signal demodulation with low SNR loss comprises: performing second CIC filtering on the signal subjected to the quadrature down-conversion and the low-pass filtering in the step (6), specifically:
Figure FDA0002563803580000043
Figure FDA0002563803580000044
wherein S isI22(n) is the output result of the second CIC filtering of the I path, SQ22(n) is the output result of Q-path second CIC filtering, M is the accumulated point number of the second CIC filtering and M>N。
9. The method of claim 8, wherein the FM signal demodulation with low SNR loss comprises: and (4) performing digital frequency discrimination on the result obtained after the second CIC filtering in the step (7), wherein the process of the digital frequency discrimination is the same as that in the step (4), and the result obtained after the digital frequency discrimination is as follows:
Figure FDA0002563803580000045
wherein the content of the first and second substances,
Figure FDA0002563803580000046
for the final FM demodulated output, m (n) is the demodulated modulated data.
10. An FM signal demodulation system realized based on the FM signal demodulation method with low signal-to-noise ratio loss of any one of claims 1-9, characterized by comprising:
a sampling module: carrying out digital sampling on the analog FM modulation signal to generate a frequency modulation signal to be processed;
a down-conversion and filtering module: carrying out quadrature down-conversion and low-pass filtering on the frequency modulation signal, moving the frequency modulation signal to zero intermediate frequency through the quadrature down-conversion, and filtering out high-frequency components and inhibiting out-of-band noise through a low-pass filter;
and a CIC filtering module: CIC filtering is carried out on the results after the orthogonal down-conversion and the low-pass filtering, and accumulated speed reduction is realized;
the digital frequency discrimination module: performing digital frequency discrimination on the result after CIC filtering, and accumulating the result obtained by the digital frequency discrimination to obtain a direct current component, namely carrier frequency offset; taking the carrier frequency offset as a compensation quantity, performing orthogonal down-conversion and low-pass filtering again to realize Doppler elimination, and then performing CIC filtering again; and carrying out digital frequency discrimination on the result of the second CIC filtering to obtain modulation signal information and realize the demodulation of the FM signal.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113672541A (en) * 2021-07-13 2021-11-19 中国人民解放军战略支援部队航天工程大学 PCM/FM telemetering signal incoherent demodulation implementation method based on GPU

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6091765A (en) * 1997-11-03 2000-07-18 Harris Corporation Reconfigurable radio system architecture
CN102694563A (en) * 2012-06-21 2012-09-26 山东神戎电子股份有限公司 Digital demodulation down-conversion system and method for acoustical signals
CN103973620A (en) * 2014-04-24 2014-08-06 中国电子科技集团公司第四十一研究所 Full-digital FM/AM signal demodulation and analysis method
CN209462366U (en) * 2019-02-18 2019-10-01 西安汉华防务电子科技有限公司 A kind of telemetering digital if receiver

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6091765A (en) * 1997-11-03 2000-07-18 Harris Corporation Reconfigurable radio system architecture
CN102694563A (en) * 2012-06-21 2012-09-26 山东神戎电子股份有限公司 Digital demodulation down-conversion system and method for acoustical signals
CN103973620A (en) * 2014-04-24 2014-08-06 中国电子科技集团公司第四十一研究所 Full-digital FM/AM signal demodulation and analysis method
CN209462366U (en) * 2019-02-18 2019-10-01 西安汉华防务电子科技有限公司 A kind of telemetering digital if receiver

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
JIANHUAN WANG: "Soft-output MIMO detector for MMSE receiver with channel estimation error", 《2016 IEEE/CIC INTERNATIONAL CONFERENCE ON COMMUNICATIONS IN CHINA (ICCC WORKSHOPS)》 *
唐然等: "带通采样星载AIS非相干接收机的FPGA实现", 《电子技术应用》 *
方勉等: "一种数字无线收发系统设计", 《电子设计工程》 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113672541A (en) * 2021-07-13 2021-11-19 中国人民解放军战略支援部队航天工程大学 PCM/FM telemetering signal incoherent demodulation implementation method based on GPU

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