CN108632185A - A kind of the AIS systems demodulation method and demodulating system of ship VDES systems - Google Patents

A kind of the AIS systems demodulation method and demodulating system of ship VDES systems Download PDF

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CN108632185A
CN108632185A CN201810462101.9A CN201810462101A CN108632185A CN 108632185 A CN108632185 A CN 108632185A CN 201810462101 A CN201810462101 A CN 201810462101A CN 108632185 A CN108632185 A CN 108632185A
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signal
ais
frequency
demodulation
phase
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CN108632185B (en
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武光辉
吴鹏程
李英飞
刘向楠
李晓亮
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Aerospace Long March Launch Vehicle Technology Co Ltd
Beijing Institute of Telemetry Technology
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Aerospace Long March Launch Vehicle Technology Co Ltd
Beijing Institute of Telemetry 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
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/36—Modulator circuits; Transmitter circuits
    • H04L27/362—Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated
    • H04L27/364—Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/38—Demodulator circuits; Receiver circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

The present invention relates to a kind of AIS systems demodulation method of ship VDES systems and demodulating systems, this method uses special signal detection, offset estimation and demodulation of frequency discriminator realize that signal demodulates, overcome the defect of the demodulation performance difference of traditional differential ference spiral, it is adapted to single/multiple time slot, data demodulation in the case of short frame/long frame signal etc. is arbitrary, the scope of application of data demodulation has been widened significantly, wherein according to training sequence feature in data frame structure, signal detection is carried out by counting adjacent symbol position situation of change, this method design is simple, it is easily achieved, and signal detecting result is accurate, with higher precision；It realizes that signal demodulates using demodulation of frequency discriminator, significantly improves Demodulation Systems performance；The carrier frequency that AIS receives signal can be quickly recovered from the frequency difference extracted in carrier wave phase demodulation error between local carrier signal and AIS reception signals using the principle of spectrum analysis, not only the capture period is short, but also accuracy is high.

Description

A kind of the AIS systems demodulation method and demodulating system of ship VDES systems
Technical field
The present invention relates to ships data exchange system modulation-demodulation technique field, more particularly to a kind of ship VDES systems AIS systems demodulation method and demodulating system, in the case of this method is suitable for single/multiple time slot, short frame/long frame signal etc. arbitrarily Data demodulation.
Background technology
M.1371-5 recommendation proposes the use in VHF Waterborne movable frequency ranges to 2 months 2014 International Telecommunication Union ITU-R The technical characteristic of the automatic recognition system (AIS) of time division multiple acess, and the communication technology characteristic of AIS systems has been made accordingly Regulation, but respective specified is not made to realization method, especially to arbitrary feelings such as single/multiple time slot, normal hair/bursts Realization method under condition, does not clearly state.
In existing AIS systems communication system, signal demodulating method uses 1bit/2bit differential ference spirals, this method Although realizing that simply demodulation performance is low, and practicability is not strong；Signal carrier frequency deviation estimating method is received using related operation come real Existing, this method needs are realized according to frame structure feature, cannot extensive use.
Invention content
It is an object of the invention to overcome the deficiencies of the prior art and provide a kind of AIS system solutions of ship VDES systems Tune method, this method are realized that signal demodulates using special signal detection, offset estimation and demodulation of frequency discriminator, are overcome traditional The defect of the demodulation performance difference of differential ference spiral, the number in the case of being adapted to single/multiple time slot, short frame/long frame signal etc. arbitrarily According to demodulation, the scope of application of data demodulation has been widened significantly.
Another object of the present invention is to provide a kind of AIS system demodulating systems of ship VDES systems.
What the above-mentioned purpose of the present invention was mainly achieved by following technical solution：
A kind of AIS system demodulation methods of ship VDES systems, include the following steps：
Signal is received to AIS and carries out sampling processing, by the local that the AIS Jing Guo sampling processing receives signal with frequency is fc Carrier signal with mutually with orthogonal mixing, phase demodulation error is obtained, further obtain local carrier signal and the AIS receives letter Frequency difference Δ f between number；
The AIS is received to the carrier signal after signal is compensated with frequency deviation to carry out, with phase and orthogonal mixing, obtaining same phase point The frequency of amount and quadrature component, the carrier signal after frequency deviation compensation is fc+ Δs f；
The in-phase component and quadrature component are subjected to low-pass filtering, remove radio-frequency component；
By after the low-pass filtering in-phase component and quadrature component carry out frequency discrimination processing, obtain demodulation of frequency discriminator result；
It is for statistical analysis to the adjacent symbol position variation of the demodulation of frequency discriminator result, realize signal detection；
To realizing that the data of signal detection are decoded and verify, the demodulation of AIS systems is completed.
It is described that signal progress sampling processing is received to AIS in the AIS system demodulation methods of above-mentioned ship VDES systems, The local carrier signal that AIS Jing Guo sampling processing receives signal with frequency is fc with phase and orthogonal mixing, reflected Phase error, the specific method for further obtaining the frequency difference Δ f between local carrier signal and AIS reception signals include following step Suddenly：
(1.1), signal is received to AIS and carries out sampling processing, it is fc that the AIS Jing Guo sampling processing, which is received signal with frequency, Local carrier signal carry out with mutually and orthogonal mixing, output in-phase component I (t) and quadrature component Q (t)；
(1.2), the in-phase component I (t) and quadrature component Q (t) are subjected to low-pass filtering, remove radio-frequency component；
(1.3), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is subjected to phase demodulation processing, obtains phase demodulation mistake Difference
(1.4), judge that the AIS receives the energy of signal, if the energy is more than the threshold value of setting, obtained to described Phase demodulation errorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS connects Frequency difference Δ f between the collection of letters number, otherwise, without FFT operations.
In the AIS system demodulation methods of above-mentioned ship VDES systems, phase demodulation error in the step (1.3)Meter It is as follows to calculate formula：
In the AIS system demodulation methods of above-mentioned ship VDES systems, to the obtained phase demodulation in the step (1.4) ErrorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS receives signal Between frequency difference Δ f the specific method is as follows：
(1.4.1), to the phase demodulation errorM point FFT operations are done, export M operational data, wherein M is positive integer；
(1.4.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；
(1.4.3), the corresponding operational data of the peak-peak is found according to the peak-peak within the scope of 1~M/2 Location n calculates carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, and f is estimated accuracy, wherein：Fs is that AIS receives signal Sample rate.
In the AIS system demodulation methods of above-mentioned ship VDES systems, by the in-phase component and just after the low-pass filtering Component is handed over to carry out frequency discrimination processing, obtaining demodulation of frequency discriminator result, the specific method is as follows：
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q' (t) it is Q'(t) difference between two neighboring sampled point；I'(t), Q'(t) it is respectively after AIS receives signal and frequency deviation compensation Carrier signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
In the AIS system demodulation methods of above-mentioned ship VDES systems, the adjacent symbol of the demodulation of frequency discriminator result is accorded with The variation of number position is for statistical analysis, and realizing signal detection, the specific method is as follows：
(5.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the mirror are counted per 2N sampled point Frequency demodulation resultThe length of middle training sequence is L, and L is even number；N is that the AIS receives each data symbol in signal Interior sampled point number；
(5.2), continuous statistics L/2 times judges to complete letter if being consecutively detected L/2-1 sign bit occurs saltus step Number detection, enter step (5.3), otherwise, statistical result reset, return to step (5.1)；
(5.3), starting sample point of the sampled point as valid data of the subsequent time at signal detection moment is taken into, it is right Continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
In the AIS system demodulation methods of above-mentioned ship VDES systems, the data of described pair of realization signal detection solve Code and verification, completing the demodulation of AIS systems, the specific method is as follows：
(6.1), it is decoded to realizing that the data of signal detection carry out the reversed non-return-to-zero of bipolarity；
(6.2), the beginning flag and end mark in the reversed non-return-to-zero decoded data of bipolarity are found, and will be searched out In beginning flag and the complete data frame of end mark deposit memory；
(6.3), the complete data frame is read from memory and carries out CRC check, judges that the AIS receives data and is It is no correct.
In the AIS system demodulation methods of above-mentioned ship VDES systems, AIS reception signals are divided into two-way, wherein all the way Postponed, in addition carry out sampling processing all the way, by the local carrier that the AIS Jing Guo sampling processing receives signal with frequency is fc Signal with mutually with orthogonal mixing, phase demodulation error is obtained, further obtain between local carrier signal and AIS reception signals Frequency difference Δ f；AIS after delay is received to the carrier signal after signal is compensated with frequency deviation with phase and orthogonal mixing, obtain same The frequency of phase component and quadrature component, the carrier signal after frequency deviation compensation is fc+ Δs f.
A kind of AIS system demodulating systems of ship VDES systems, including frequency deviation estimating modules, frequency mixing module, low-pass filtering Module, demodulation of frequency discriminator module, signal detection module conciliate code check module, wherein：
Frequency deviation estimating modules：To AIS receive signal carry out sampling processing, by Jing Guo sampling processing AIS receive signal and The local carrier signal that frequency is fc with phase and orthogonal mixing, obtain phase demodulation error, further obtain local carrier signal And AIS receives the frequency difference Δ f between signal, and the frequency difference Δ f is exported to frequency mixing module；
Frequency mixing module：The frequency difference Δ f for receiving frequency deviation estimating modules output obtains the carrier signal after frequency deviation compensation, by institute It states AIS and receives the carrier signal progress after signal is compensated with frequency deviation with phase and orthogonal mixing, obtain in-phase component and quadrature component, The in-phase component and quadrature component are exported to low-pass filtering module, the frequency of the carrier signal after frequency deviation compensation is fc +Δf；
Low-pass filtering module：The in-phase component and quadrature component for receiving frequency mixing module output, by the in-phase component and just Hand over component to carry out low-pass filtering, remove radio-frequency component, and by after low-pass filtering in-phase component and quadrature component export to frequency discrimination Demodulation module；
Demodulation of frequency discriminator module：The in-phase component and quadrature component after the low-pass filtering of low-pass filtering module output are received, it will In-phase component and quadrature component after the low-pass filtering carry out frequency discrimination processing, obtain demodulation of frequency discriminator as a result, and exporting to signal Detection module；
Signal detection module：The demodulation of frequency discriminator of demodulation of frequency discriminator module output is received as a result, to the demodulation of frequency discriminator result Adjacent symbol position variation is for statistical analysis, realizes signal detection, and the data after signal detection are exported and give decoding school Test module；
Decode correction verification module：The data after the signal detection of signal detection module output are received, to realizing signal detection Data are decoded and verify, and complete the demodulation of AIS systems.
In the AIS system demodulating systems of above-mentioned ship VDES systems, the frequency deviation estimating modules to AIS receive signal into Row sampling processing carries out the local carrier signal that the AIS Jing Guo sampling processing receives signal with frequency is fc with mutually and orthogonal Mixing, obtains phase demodulation error, further obtains local carrier signal and AIS receives the specific method of the frequency difference Δ f between signal Include the following steps：
(1.1), signal is received to AIS and carries out sampling processing, it is fc that the AIS Jing Guo sampling processing, which is received signal with frequency, Local carrier signal carry out with mutually and orthogonal mixing, output in-phase component I (t) and quadrature component Q (t)；
(1.2), the in-phase component I (t) and quadrature component Q (t) are subjected to low-pass filtering, remove radio-frequency component；
(1.3), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is subjected to phase demodulation processing, obtains phase demodulation mistake Difference
(1.4), judge that the AIS receives the energy of signal, if the energy is more than the threshold value of setting, obtained to described Phase demodulation errorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS connects Frequency difference Δ f between the collection of letters number, otherwise, without FFT operations.
In the AIS system demodulating systems of above-mentioned ship VDES systems, phase demodulation error in the step (1.3)Meter It is as follows to calculate formula：
To the obtained phase demodulation error in the step (1.4)Carry out FFT operations, and to FFT operation results into Row analysis, obtaining the frequency difference Δ f that local carrier signal and the AIS receive between signal, the specific method is as follows：
(1.4.1), to the phase demodulation errorM point FFT operations are done, M operational data is exported, wherein M is just whole Number；
(1.4.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；
(1.4.3), the corresponding operational data of the peak-peak is found according to the peak-peak within the scope of 1~M/2 Location n calculates carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, and f is estimated accuracy, wherein：Fs is that AIS receives signal Sample rate.
In the AIS system demodulating systems of above-mentioned ship VDES systems, the demodulation of frequency discriminator module receives low-pass filtering mould Block output low-pass filtering after in-phase component and quadrature component, by after the low-pass filtering in-phase component and quadrature component into The processing of row frequency discrimination, obtaining demodulation of frequency discriminator result, the specific method is as follows：
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q' (t) it is Q'(t) difference between two neighboring sampled point；I'(t), Q'(t) it is respectively after AIS receives signal and frequency deviation compensation Carrier signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
In the AIS system demodulating systems of above-mentioned ship VDES systems, the signal detection module receives demodulation of frequency discriminator mould The demodulation of frequency discriminator of block output to the adjacent symbol position of the demodulation of frequency discriminator result as a result, change for statistical analysis, realization The specific method is as follows for signal detection：
(5.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the mirror are counted per 2N sampled point Frequency demodulation resultThe length of middle training sequence is L, and L is even number；N is that the AIS receives each data symbol in signal Interior sampled point number；
(5.2), continuous statistics L/2 times judges to complete letter if being consecutively detected L/2-1 sign bit occurs saltus step Number detection, enter step (5.3), otherwise, statistical result reset, return to step (5.1)；
(5.3), starting sample point of the sampled point as valid data of the subsequent time at signal detection moment is taken into, it is right Continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
In the AIS system demodulating systems of above-mentioned ship VDES systems, the decoding correction verification module receives signal detection mould Data after the signal detection of block output complete the demodulation of AIS systems to realizing that the data of signal detection are decoded and verify The specific method is as follows：
(6.1), it is decoded to realizing that the data of signal detection carry out the reversed non-return-to-zero of bipolarity；
(6.2), the beginning flag and end mark in the reversed non-return-to-zero decoded data of bipolarity are found, and will be searched out In beginning flag and the complete data frame of end mark deposit memory；
(6.3), the complete data frame is read from memory and carries out CRC check, judges that the AIS receives data and is It is no correct.
The present invention has the advantages that compared with prior art：
(1), AIS systems demodulation method of the present invention is realized using special signal detection, offset estimation and demodulation of frequency discriminator Signal demodulates, and overcomes the defect of the demodulation performance difference of traditional differential ference spiral, is adapted to single/multiple time slot, short frame/long frame Data demodulation in the case of signal etc. is arbitrary, has widened the scope of application of data demodulation significantly.
(2), the present invention is according to training sequence feature in data frame structure, by counting adjacent symbol position situation of change Carry out signal detection (preamble detecting), this method design is simple, it is easy to accomplish, and signal detecting result is accurate, have compared with High precision.
(3), the present invention realizes that signal demodulates using demodulation of frequency discriminator, significantly improves Demodulation Systems performance.
(4), the present invention utilizes the principle of spectrum analysis, extracts local carrier signal from carrier wave phase demodulation error and AIS connects Frequency difference between the collection of letters number, can quickly recover the carrier frequency that AIS receives signal, and it is short but also accurate not only to capture the period Degree is high.
(5), FFT operations are realized using IP kernel in fpga chip in the present invention, and consuming hardware resource is few, and accuracy is high, The defect that can effectively overcome the prior art to be limited by hardware platform, reduces cost.
Description of the drawings
Fig. 1 is the functional block diagram of the AIS system demodulation methods of ship VDES systems of the present invention.
Fig. 2 is the specific implementation block diagram of the AIS system demodulation methods of ship VDES systems of the present invention.
Fig. 3 is the structural schematic diagram of the AIS system demodulating systems of the ship VDES systems of the present invention.
Specific implementation mode
The present invention is described in further detail with specific example below in conjunction with the accompanying drawings：
The functional block diagram of implementation method is demodulated for the AIS systems of ship VDES systems as shown in Figure 1, Fig. 2 show ship The specific implementation block diagram of the AIS system demodulation methods of VDES systems.The AIS systems demodulation of the ship VDES systems of the present invention is realized Method specifically includes the following steps：
(1), signal is received to AIS with analog-digital converter (ADC) and carries out sampling processing, there is N number of adopt in each data symbol Sampling point.
(2), the AIS Jing Guo sampling processing signal is received to carry out with phase and orthogonal mixing, output with local carrier signal In-phase component I (t) and quadrature component Q (t)；Wherein, local carrier signal frequency is fc.
(3), in-phase component I (t) and quadrature component Q (t) is subjected to low-pass filtering, removes radio-frequency component.
(4), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is passed through into phase-shift discriminator, carries out phase demodulation Processing, obtains phase demodulation errorWherein phase demodulation errorCalculation formula it is as follows：
(5), judge that AIS receives the energy of signal, if the energy is more than the threshold value of setting, to the obtained phase demodulation ErrorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS receives signal Between frequency difference Δ f, otherwise, without FFT operations.
In the embodiment of the present invention, the energy of sampled data is as the threshold value of setting, i.e. noise when no AIS is received signal Energy as setting threshold value.
Local carrier signal is obtained in the embodiment of the present invention and the AIS receives the specific side of the frequency difference Δ f between signal Method is as follows：
(5.1), to the phase demodulation errorM point FFT operations are done, export M operational data, wherein M is positive integer, M For 2 n times power；FFT operations use IPcore in fpga chip to realize.
(5.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；Detect model It encloses for 1~M/2 operational data.
(5.3), the corresponding operational data of peak-peak institute within the scope of 1~M/2 is found according to the peak-peak The position n at place calculates carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, represents which operational data；F is estimated accuracy, wherein：Fs is the sample rate that AIS receives signal.
(6), the AIS after delay is received to the carrier signal after signal is compensated with frequency deviation to carry out with phase and orthogonal mixing, it is defeated Go out in-phase component I'(t) and quadrature component Q'(t)；Wherein, the frequency of the carrier signal after frequency deviation compensation is fc+ Δs f.
(7), by in-phase component I'(t) and quadrature component Q'(t) low pass (FIR) filtering is carried out, remove radio-frequency component；
(8), the in-phase component I'(t after filtering FIR) and quadrature component Q'(t) frequency discrimination carried out by frequency discriminator Processing, obtains demodulation of frequency discriminator result
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q' (t) it is Q'(t) difference between two neighboring sampled point；I'(t), Q'(t) it is respectively after AIS receives signal and frequency deviation compensation Carrier signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
(9), according to training sequence feature in data frame structure, to demodulation of frequency discriminator resultAdjacent symbol position become It is for statistical analysis to change situation, realizes signal detection (preamble detecting), the specific method is as follows：
(9.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the mirror are counted per 2N sampled point Frequency demodulation resultThe length of middle training sequence is L, and L is even number；N is that the AIS is received in signal each Sampled point number in data symbol.For example, in the embodiment of the present inventionTraining sequence is in frame structure 110011001100110011001100, totally 24 bit.
(9.2), continuous statistics L/2 times judges to complete letter if being consecutively detected L/2-1 sign bit occurs saltus step Number detection, enter step (9.3), otherwise, statistical result reset, return to step (9.1).
(9.3), starting sample point of the sampled point as valid data of the subsequent time at signal detection moment is taken into, it is right Continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
(10), the reversed non-return-to-zero of bipolarity (NRZI) is carried out to the data for completing preamble detecting in step (9.3) to decode；
(11), the beginning flag and end mark in NRZI decoded datas are found, and beginning flag and knot will be searched out The complete data frame of bundle flag is sequentially stored into memory Ram；
(12), complete data frame is read from memory Ram and carries out CRC check, judges whether demodulation is correct, if CRC Verification is correct, then shows that demodulation is correct, while exporting the binary data after demodulation, otherwise shows to demodulate mistake.
Specifically, AIS reception signals are divided into two-way in the embodiment of the present invention, wherein being postponed all the way, in addition all the way Sampling processing is carried out, the local carrier signal that the AIS Jing Guo sampling processing receives signal with frequency is fc is carried out with mutually and just Mixing is handed over, phase demodulation error is obtained, further obtains the frequency difference Δ f between local carrier signal and AIS reception signals；After postponing AIS receive the carrier signal after the compensation of signal and frequency deviation and carry out, with phase and orthogonal mixing, obtaining in-phase component and quadrature component, The frequency of carrier signal after the compensation of its frequency deviation is fc+ Δs f.It can be postponed using FIFO, as shown in Figure 2.
It is illustrated in figure 3 the structural schematic diagram of the AIS system demodulating systems of the ship VDES systems of the present invention, it can by figure Know, the AIS system demodulating systems of ship VDES systems of the present invention include frequency deviation estimating modules, frequency mixing module, low-pass filtering module, Demodulation of frequency discriminator module, signal detection module conciliate code check module.
Frequency deviation estimating modules, to AIS receive signal carry out sampling processing, by Jing Guo sampling processing AIS receive signal and The local carrier signal that frequency is fc with phase and orthogonal mixing, obtain phase demodulation error, further obtain local carrier signal And AIS receives the frequency difference Δ f between signal, and the frequency difference Δ f is exported to frequency mixing module.
Frequency mixing module receives the frequency difference Δ f of frequency deviation estimating modules output, the carrier signal after frequency deviation compensation is obtained, by institute It states AIS and receives the carrier signal progress after signal is compensated with frequency deviation with phase and orthogonal mixing, obtain in-phase component and quadrature component, The in-phase component and quadrature component are exported to low-pass filtering module, the frequency of the carrier signal after frequency deviation compensation is fc +Δf。
Low-pass filtering module receives the in-phase component and quadrature component of frequency mixing module output, by the in-phase component and just Hand over component to carry out low-pass filtering, remove radio-frequency component, and by after low-pass filtering in-phase component and quadrature component export to frequency discrimination Demodulation module.
Demodulation of frequency discriminator module receives in-phase component and quadrature component after the low-pass filtering of low-pass filtering module output, will In-phase component and quadrature component after the low-pass filtering carry out frequency discrimination processing, obtain demodulation of frequency discriminator as a result, and exporting to signal Detection module.
Signal detection module receives the demodulation of frequency discriminator of demodulation of frequency discriminator module output as a result, to the demodulation of frequency discriminator result Adjacent symbol position variation is for statistical analysis, realizes signal detection, and the data after signal detection are exported and give decoding school Test module.
Correction verification module is decoded, the data after the signal detection of signal detection module output are received, to realizing signal detection Data are decoded and verify, and complete the demodulation of AIS systems.
Specifically, in the embodiment of the present invention, frequency deviation estimating modules receive signal to AIS and carry out sampling processing, will pass through and adopt The local carrier signal that the AIS that sample is handled receives signal with frequency is fc carries out, with phase and orthogonal mixing, obtaining phase demodulation error, into The specific method that one step obtains the frequency difference Δ f between local carrier signal and AIS reception signals includes the following steps：
(1.1), signal is received to AIS and carries out sampling processing, it is fc that the AIS Jing Guo sampling processing, which is received signal with frequency, Local carrier signal carry out with mutually and orthogonal mixing, output in-phase component I (t) and quadrature component Q (t)；
(1.2), the in-phase component I (t) and quadrature component Q (t) are subjected to low-pass filtering, remove radio-frequency component；
(1.3), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is subjected to phase demodulation processing, obtains phase demodulation mistake DifferencePhase demodulation errorCalculation formula it is as follows：
(1.4), judge that the AIS receives the energy of signal, if the energy is more than the threshold value of setting, obtained to described Phase demodulation errorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS connects Frequency difference Δ f between the collection of letters number, otherwise, without FFT operations.
Local carrier signal is obtained in the embodiment of the present invention and the AIS receives the specific side of the frequency difference Δ f between signal Method is as follows：
(1.4.1), to the phase demodulation errorM point FFT operations are done, M operational data is exported, wherein M is positive integer, The n times power that M is 2；FFT operations use IPcore in fpga chip to realize.
(1.4.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；Detection Ranging from 1~M/2 operational data.
(1.4.3), the corresponding operational data of the peak-peak is found according to the peak-peak within the scope of 1~M/2 Location n calculates carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, and f is estimated accuracy, wherein：Fs is that AIS receives signal Sample rate.
Specifically, in the embodiment of the present invention, after demodulation of frequency discriminator module receives the low-pass filtering of low-pass filtering module output In-phase component and quadrature component, by after the low-pass filtering in-phase component and quadrature component carry out frequency discrimination processing, obtain frequency discrimination The specific method is as follows for demodulation result：
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q' (t) it is Q'(t) difference between two neighboring sampled point；I'(t), Q'(t) it is respectively after AIS receives signal and frequency deviation compensation Carrier signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
Specifically, in the embodiment of the present invention, signal detection module receive demodulation of frequency discriminator module output demodulation of frequency discriminator as a result, It is for statistical analysis to the adjacent symbol position variation of the demodulation of frequency discriminator result, realize the specific method of signal detection such as Under：
(2.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the mirror are counted per 2N sampled point Frequency demodulation resultThe length of middle training sequence is L, and L is even number；N is that the AIS receives each data symbol in signal Interior sampled point number；
(2.2), continuous statistics L/2 times judges to complete letter if being consecutively detected L/2-1 sign bit occurs saltus step Number detection, enter step (2.3), otherwise, statistical result reset, return to step (2.1)；
(2.3), starting sample point of the sampled point as valid data of the subsequent time at signal detection moment is taken into, it is right Continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
Specifically, in the embodiment of the present invention, after decoding correction verification module receives the signal detection of signal detection module output Data, to realizing that the data of signal detection are decoded and verify, completing the demodulation of AIS systems, the specific method is as follows：
(3.1), it is decoded to realizing that the data of signal detection carry out the reversed non-return-to-zero of bipolarity；
(3.2), the beginning flag and end mark in the reversed non-return-to-zero decoded data of bipolarity are found, and will be searched out In beginning flag and the complete data frame of end mark deposit memory；
(3.3), the complete data frame is read from memory and carries out CRC check, judges that the AIS receives data and is It is no correct.
Embodiment：
In the present embodiment, the data transfer rate Rb=9.6kbps of the AIS systems of ship VDES systems, frame length 928bit, number It is 0X7E, end-of-data mark 0X7E, local carrier frequency fc=6.4MHz according to beginning flag, FIR filter exponent number is 16 Rank, FFT operations points M=4096, CRC bit number is 16.
Signal is received to AIS with ADC and carries out sampling processing, sample rate fc=153.6kHz has 16 in each data symbol A sampled point (i.e. N=16), the local carrier signal that the AIS after over-sampling receives signal with frequency is 6.4MHz carry out same phase After orthogonal mixing low-pass filtering, in-phase component I (t) and quadrature component Q (t) and phase demodulation error are obtainedIt is rightIt does 4096 point FFT operations, and peak-peak detection is carried out to 1~2048 operation result, the Maximum value is detected at 1428 points, is obtained carrier wave frequency deviation Δ f=1428*153.6kHz/4096=53.55kHz, is further obtained Reception signal(-) carrier frequency is 6.45355MHz.
By the AIS after FIFO postpones receive local carrier signal that signal and frequency are 6.45355MHz into Row obtains in-phase component I'(t with mutually and after orthogonal mixing low-pass filtering) and quadrature component Q'(t), and to this progress frequency discrimination Demodulation, the signal after being demodulatedAccording toTraining sequence in frame structure The characteristics of (110011001100110011001100, totally 24 bit, i.e. L=24), judgesAdjacent symbol in signal Position situation of change, every 32 sampled points count a sign bit saltus step situation, until continuously there are 11 saltus steps, indicate to find Frame head (training sequence), to completing preamble detectingSignal carries out integral output successively by 16 sampled points.
NRZI decodings are carried out again, find beginning flag (0X7E)/end mark (0X7E), CRC check, you can recover original The binary data source of beginning.
The above, a specific implementation mode only of the invention, but scope of protection of the present invention is not limited thereto, appoints What those familiar with the art in the technical scope disclosed by the present invention, the change or replacement that can be readily occurred in, all It is covered by the protection scope of the present invention.
The content that description in the present invention is not described in detail belongs to the known technology of professional and technical personnel in the field.

Claims (14)

1. a kind of AIS system demodulation methods of ship VDES systems, it is characterised in that：Include the following steps：
Signal is received to AIS and carries out sampling processing, by the local carrier that the AIS Jing Guo sampling processing receives signal with frequency is fc Signal carries out, with mutually and orthogonal mixing, obtaining phase demodulation error, further obtain local carrier signal and the AIS receive signal it Between frequency difference Δ f；
By the AIS receive the carrier signal after the compensation of signal and frequency deviation carry out with mutually and orthogonal mixing, obtain in-phase component with The frequency of quadrature component, the carrier signal after frequency deviation compensation is fc+ Δs f；
The in-phase component and quadrature component are subjected to low-pass filtering, remove radio-frequency component；
By after the low-pass filtering in-phase component and quadrature component carry out frequency discrimination processing, obtain demodulation of frequency discriminator result；
It is for statistical analysis to the adjacent symbol position variation of the demodulation of frequency discriminator result, realize signal detection；
To realizing that the data of signal detection are decoded and verify, the demodulation of AIS systems is completed.
2. the AIS system demodulation methods of ship VDES systems according to claim 1, it is characterised in that：It is described that AIS is connect The collection of letters number carries out a sampling processing, and it is same for the local carrier signal progress of fc with frequency that the AIS Jing Guo sampling processing is received signal Mutually with orthogonal mixing, phase demodulation error is obtained, further obtains the frequency difference Δ f's between local carrier signal and AIS reception signals Specific method includes the following steps：
(1.1), signal is received to AIS and carries out sampling processing, by the sheet that the AIS Jing Guo sampling processing receives signal with frequency is fc Ground carrier signal is carried out with phase and orthogonal mixing, output in-phase component I (t) and quadrature component Q (t)；
(1.2), the in-phase component I (t) and quadrature component Q (t) are subjected to low-pass filtering, remove radio-frequency component；
(1.3), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is subjected to phase demodulation processing, obtains phase demodulation error
(1.4), judge that the AIS receives the energy of signal, if the energy is more than the threshold value of setting, to the obtained mirror Phase errorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS receives letter Frequency difference Δ f between number, otherwise, without FFT operations.
3. the AIS system demodulation methods of ship VDES systems according to claim 2, it is characterised in that：The step (1.3) phase demodulation error inCalculation formula it is as follows：
4. the AIS system demodulation methods of ship VDES systems according to claim 2, it is characterised in that：The step (1.4) to the obtained phase demodulation error inFFT operations are carried out, and FFT operation results are analyzed, obtain local load Wave signal and the AIS receive the frequency difference Δ f between signal, and the specific method is as follows：
(1.4.1), to the phase demodulation errorM point FFT operations are done, export M operational data, wherein M is positive integer；
(1.4.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；
(1.4.3), that the corresponding operational data of the peak-peak is found according to the peak-peak is residing within the scope of 1~M/2 Position n, calculate carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, and f is estimated accuracy, wherein：Fs is that AIS receives adopting for signal Sample rate.
5. the AIS system demodulation methods of ship VDES systems according to claim 1, it is characterised in that：By the low pass Filtered in-phase component and quadrature component carry out frequency discrimination processing, and obtaining demodulation of frequency discriminator result, the specific method is as follows：
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q'(t) be Q'(t) the difference between two neighboring sampled point；I'(t), Q'(t) it is respectively that AIS receives signal and the carrier wave after frequency deviation compensation Signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
6. the AIS system demodulation methods of ship VDES systems according to claim 1, it is characterised in that：To the frequency discrimination The adjacent symbol position variation of demodulation result is for statistical analysis, and realizing signal detection, the specific method is as follows：
(5.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the frequency discrimination solution are counted per 2N sampled point Adjust resultThe length of middle training sequence is L, and L is even number；N is that the AIS is received in signal in each data symbol Sampled point number；
(5.2), continuous statistics L/2 times judges to complete signal inspection if being consecutively detected L/2-1 sign bit occurs saltus step It surveys, enters step (5.3), otherwise, statistical result is reset, return to step (5.1)；
(5.3), starting sample point of the sampled point as valid data for taking into the subsequent time at signal detection moment, to continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
7. the AIS system demodulation methods of ship VDES systems according to claim 1, it is characterised in that：Described pair of realization The data of signal detection are decoded and verify, and completing the demodulation of AIS systems, the specific method is as follows：
(6.1), it is decoded to realizing that the data of signal detection carry out the reversed non-return-to-zero of bipolarity；
(6.2), the beginning flag and end mark in the reversed non-return-to-zero decoded data of bipolarity are found, and starting will be searched out In mark and the complete data frame of end mark deposit memory；
(6.3), the complete data frame is read from memory and carries out CRC check, judges whether just the AIS receives data Really.
8. the AIS system demodulation methods of ship VDES systems according to claim 1, it is characterised in that：AIS is received and is believed Number it is divided into two-way, wherein being postponed all the way, in addition carries out sampling processing all the way, the AIS Jing Guo sampling processing is received into signal It carries out, with phase and orthogonal mixing, obtaining phase demodulation error with the local carrier signal that frequency is fc, further obtains local carrier letter Number AIS receive signal between frequency difference Δ f；AIS after delay is received signal to carry out with the carrier signal after frequency deviation compensation With phase and orthogonal mixing, in-phase component and quadrature component are obtained, the frequency of the carrier signal after frequency deviation compensation is fc+ Δs f.
9. a kind of AIS system demodulating systems of ship VDES systems, it is characterised in that：Including frequency deviation estimating modules, frequency mixing module, Low-pass filtering module, demodulation of frequency discriminator module, signal detection module conciliate code check module, wherein：
Frequency deviation estimating modules：Signal is received to AIS and carries out sampling processing, the AIS Jing Guo sampling processing is received into signal and frequency For the local carrier signal of fc with phase and orthogonal mixing, obtain phase demodulation error, further obtain local carrier signal and AIS The frequency difference Δ f between signal is received, the frequency difference Δ f is exported to frequency mixing module；
Frequency mixing module：The frequency difference Δ f for receiving frequency deviation estimating modules output obtains the carrier signal after frequency deviation compensation, by the AIS The carrier signal after signal is compensated with frequency deviation is received to carry out, with phase and orthogonal mixing, in-phase component and quadrature component being obtained, by institute It states in-phase component and quadrature component is exported to low-pass filtering module, the frequency of the carrier signal after frequency deviation compensation is fc+ Δs f；
Low-pass filtering module：The in-phase component and quadrature component for receiving frequency mixing module output, by the in-phase component and orthogonal point Amount carries out low-pass filtering, removes radio-frequency component, and by after low-pass filtering in-phase component and quadrature component export to demodulation of frequency discriminator Module；
Demodulation of frequency discriminator module：The in-phase component and quadrature component after the low-pass filtering of low-pass filtering module output are received, it will be described In-phase component and quadrature component after low-pass filtering carry out frequency discrimination processing, obtain demodulation of frequency discriminator as a result, and exporting to signal detection Module；
Signal detection module：The demodulation of frequency discriminator of demodulation of frequency discriminator module output is received as a result, to the adjacent of the demodulation of frequency discriminator result The variation of symbol position is for statistical analysis, realizes signal detection, and the data after signal detection are exported and give decoding calibration mode Block；
Decode correction verification module：The data after the signal detection of signal detection module output are received, to realizing the data of signal detection It is decoded and verifies, complete the demodulation of AIS systems.
10. the AIS system demodulating systems of ship VDES systems according to claim 9, it is characterised in that：The frequency deviation is estimated It counts module and signal progress sampling processing is received to AIS, the AIS Jing Guo sampling processing is received into the local load that signal is fc with frequency Wave signal with mutually with orthogonal mixing, phase demodulation error is obtained, further obtain between local carrier signal and AIS reception signals The specific method of frequency difference Δ f include the following steps：
(1.1), signal is received to AIS and carries out sampling processing, by the sheet that the AIS Jing Guo sampling processing receives signal with frequency is fc Ground carrier signal is carried out with phase and orthogonal mixing, output in-phase component I (t) and quadrature component Q (t)；
(1.2), the in-phase component I (t) and quadrature component Q (t) are subjected to low-pass filtering, remove radio-frequency component；
(1.3), in-phase component I (t) and the quadrature component Q (t) after low-pass filtering is subjected to phase demodulation processing, obtains phase demodulation error
(1.4), judge that the AIS receives the energy of signal, if the energy is more than the threshold value of setting, to the obtained mirror Phase errorFFT operations are carried out, and FFT operation results are analyzed, local carrier signal is obtained and the AIS receives letter Frequency difference Δ f between number, otherwise, without FFT operations.
11. the AIS system demodulating systems of ship VDES systems according to claim 10, it is characterised in that：The step (1.3) phase demodulation error inCalculation formula it is as follows：
To the obtained phase demodulation error in the step (1.4)FFT operations are carried out, and FFT operation results are divided Analysis, obtaining the frequency difference Δ f that local carrier signal and the AIS receive between signal, the specific method is as follows：
(1.4.1), to the phase demodulation errorM point FFT operations are done, export M operational data, wherein M is positive integer；
(1.4.2), peak-peak detection is carried out to M operational data of the output, until finding peak-peak；
(1.4.3), that the corresponding operational data of the peak-peak is found according to the peak-peak is residing within the scope of 1~M/2 Position n, calculate carrier beat Δ f：
Δ f=n × f
Wherein：N is some value within the scope of 1~M/2, and f is estimated accuracy, wherein：Fs is that AIS receives adopting for signal Sample rate.
12. the AIS system demodulating systems of ship VDES systems according to claim 9, it is characterised in that：The frequency discrimination solution Mode transfer block receives the in-phase component and quadrature component after the low-pass filtering of low-pass filtering module output, after the low-pass filtering In-phase component and quadrature component carry out frequency discrimination processing, and obtaining demodulation of frequency discriminator result, the specific method is as follows：
Wherein：It is demodulation of frequency discriminator as a result, Δ I'(t) be I'(t) difference between two neighboring sampled point, Δ Q'(t) be Q'(t) the difference between two neighboring sampled point；I'(t), Q'(t) it is respectively that AIS receives signal and the carrier wave after frequency deviation compensation Signal carries out with phase and orthogonal mixing and carries out low-pass filtering, obtained in-phase component and quadrature component.
13. the AIS system demodulating systems of ship VDES systems according to claim 9, it is characterised in that：The signal inspection It surveys module and receives the demodulation of frequency discriminator of demodulation of frequency discriminator module output as a result, the adjacent symbol position to the demodulation of frequency discriminator result becomes Change for statistical analysis, realizing signal detection, the specific method is as follows：
(5.1), according to demodulation of frequency discriminator resultA sign bit saltus step situation, the frequency discrimination solution are counted per 2N sampled point Adjust resultThe length of middle training sequence is L, and L is even number；N is that the AIS is received in signal in each data symbol Sampled point number；
(5.2), continuous statistics L/2 times judges to complete signal inspection if being consecutively detected L/2-1 sign bit occurs saltus step It surveys, enters step (5.3), otherwise, statistical result is reset, return to step (5.1)；
(5.3), starting sample point of the sampled point as valid data for taking into the subsequent time at signal detection moment, to continuous N number of sampled point carries out integral and is exported as a valid data, and so on, export a frame valid data.
14. the AIS system demodulating systems of ship VDES systems according to claim 9, it is characterised in that：The decoding school It tests module and receives the data after the signal detection of signal detection module output, to realizing that the data of signal detection are decoded and school It tests, completing the demodulation of AIS systems, the specific method is as follows：
(6.1), it is decoded to realizing that the data of signal detection carry out the reversed non-return-to-zero of bipolarity；
(6.2), the beginning flag and end mark in the reversed non-return-to-zero decoded data of bipolarity are found, and starting will be searched out In mark and the complete data frame of end mark deposit memory；
(6.3), the complete data frame is read from memory and carries out CRC check, judges whether just the AIS receives data Really.
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