CN114124197A - Satellite-borne AIS signal demodulation method - Google Patents

Satellite-borne AIS signal demodulation method Download PDF

Info

Publication number
CN114124197A
CN114124197A CN202111419397.4A CN202111419397A CN114124197A CN 114124197 A CN114124197 A CN 114124197A CN 202111419397 A CN202111419397 A CN 202111419397A CN 114124197 A CN114124197 A CN 114124197A
Authority
CN
China
Prior art keywords
signal
ais
frequency
baseband
sampling data
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
CN202111419397.4A
Other languages
Chinese (zh)
Inventor
曾祥华
王文博
张来云
张振华
廖鹏
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Changsha Xiandu Technology Co ltd
Original Assignee
Changsha Xiandu Technology Co ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Changsha Xiandu Technology Co ltd filed Critical Changsha Xiandu Technology Co ltd
Priority to CN202111419397.4A priority Critical patent/CN114124197A/en
Publication of CN114124197A publication Critical patent/CN114124197A/en
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • 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
    • H04L27/106—M-ary FSK
    • 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
    • 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
    • H04L27/16—Frequency regulation arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30—Services specially adapted for particular environments, situations or purposes
    • H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
    • H04W4/42—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for mass transport vehicles, e.g. buses, trains or aircraft
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

The invention provides a satellite borne AIS signal demodulation method, which comprises the following steps: performing band-pass sampling on the AIS intermediate frequency signal by an AD converter at a preset sampling rate, and then obtaining two paths of baseband sampling data of two frequency points after down-conversion and filtering extraction; performing frame header detection on the baseband sampling data, and extracting a complete AIS signal of a frame; carrying out frequency offset estimation and frequency offset compensation on the AIS signal through the code element information of the GMSK signal; completing timing synchronization of the AIS signals by the signal sampling data after frequency offset compensation is completed; and performing matched filtering on the AIS baseband signal after timing synchronization is completed, sampling at an integer code element moment to obtain an output signal, and performing Viterbi decoding on the output signal to obtain an original code element information sequence. The invention can demodulate the AIS signal, has less operation times and low operation complexity, and solves the technical problem of signal demodulation of the AIS signal with the defects of low signal-to-noise ratio, large signal dynamic range and the like in the prior art.

Description

Satellite-borne AIS signal demodulation method
Technical Field
The invention relates to the technical field of radio communication, in particular to a satellite-borne AIS signal demodulation method applied to a signal receiver.
Background
In order to realize supervision of ships in a large area and avoid safety accidents of the ships, the AIS communication system is gradually widely used. The AIS communication system mainly comprises a shore-based system and a satellite-borne AIS system based on low-earth orbit satellites. The shore-based system cannot observe and track ships far away from the land, and the low-orbit satellite-based satellite-borne AIS system can realize the observation and tracking of ocean-going ships, and is a future development trend.
The coverage area of the satellite-borne AIS system can reach more than 1000km, and navigation data can be exchanged between ships or between the ships and the base station, so that the purposes of improving the navigation safety of the ships and strengthening monitoring of personnel on marine events, such as coastal guard protection, search and rescue, safety management and the like, are achieved. However, the satellite-borne AIS system performs communication in a complex space environment with doppler effect, faraday deflection, and the like, so that the received AIS signals have the defects of low signal-to-noise ratio, serious co-channel interference, mutual interference of multiple signals, large dynamic range of signals, and the like. Therefore, how to perform optimal signal demodulation on the AIS signal in the signal receiver is a problem to be solved.
The conventional AIS signal demodulation algorithm is a sequence estimation algorithm, which is a symbol sequence estimation algorithm capable of adaptively tracking channel parameters, and uses kalman filtering to track the channel parameters to demodulate signals.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a satellite-borne AIS signal demodulation method which can demodulate AIS signals, has less operation times and low operation complexity and solves the technical problems of signal demodulation of the AIS signals with the defects of low signal-to-noise ratio, serious co-channel interference, mutual interference of multiple signals, large dynamic range of signals and the like in the prior art.
The technical scheme of the invention is as follows:
a satellite-borne AIS signal demodulation method comprises the following steps:
performing band-pass sampling on the AIS intermediate-frequency signal by an AD converter at a preset sampling rate, performing down-conversion, filtering and m-time sample extraction, and outputting two paths of AIS baseband signals to obtain two paths of baseband sampling data of two frequency points;
performing frame header detection on the baseband sampling data, and extracting a complete AIS signal of a frame;
carrying out frequency offset estimation and frequency offset compensation on the AIS signal through the code element information of the GMSK signal;
correlating and matching the signal sampling data after completing the frequency offset compensation with a local sampling sequence generated by a fixed sequence of an AIS signal frame header, determining the maximum value of the correlation as the starting position of the frame header, and completing the timing synchronization of the AIS signal;
and performing matched filtering on the AIS baseband signal after timing synchronization is completed, sampling at integer symbol time to obtain an output signal x (n), and performing Viterbi decoding on the output signal x (n) to obtain an original symbol information sequence a (n).
Further, the down-conversion, filtering and N times of sample extraction comprises the following steps:
the AIS signal is used as a dual-channel broadband signal and is subjected to down-conversion to a baseband in an integral mode, two-stage CIC filtering processing is carried out, samples are extracted according to a sampling rate which is 25 times that of the AIS signal, and the AIS complex signal containing two frequency points of AIS1 and AIS2 is output;
the method comprises the steps of carrying out down-conversion processing on AIS complex signals of two frequency points of AIS1 and AIS2, carrying out FIR filtering and carrying out sample extraction according to a sampling rate which is 5 times, and obtaining two paths of baseband sampling data of the two frequency points.
Further, frame header detection is performed on the baseband sampling data, and a complete frame of AIS signal is extracted, specifically including the following steps:
inputting baseband sampling data into a frequency discriminator, processing the 192-point sampling data of the frame header through the frequency discriminator, wherein the processing expression is phi (n) ═ I (n) Q (n-1) -Q (n) I (n-1), and obtaining signal waveform information of the frame header part of the signal;
according to the signal waveform information, performing sliding DFT operation on 192-point sampling data of a signal frame header part, confirming that the k-th frequency point is a DFT peak point of the frame header signal and calculating to obtain a sliding DFT value of the k-th frequency point, wherein the sliding DFT calculation formula of the k-th frequency point is
Figure BDA0003376308330000021
0<＝k<N；
Calculating DFT average values, wherein the DFT average values are the DFT values of M frequency points on the left side of the frequency point k where the peak value is located and the DFT values of M frequency points on the right side;
judging whether the ratio of the sliding DFT value of the kth frequency point to the DFT average value continuously exceeds a threshold value for L times, if so, confirming that the frame header part is detected and extracting signal sampling data of a whole frame for storage; wherein, the calculation expression of the threshold value is as follows:
Figure BDA0003376308330000022
further, the frequency offset estimation and frequency down offset compensation are carried out on the AIS signal through the code element information of the GMSK signal, and the method comprises the following steps:
calculating the kth code element information of the GMSK signal, wherein the kth code element expression of the GMSK signal is
Figure BDA0003376308330000031
kTi<t≤(k+1)TiWherein a iskIs a original symbol, ak∈{-1,1}，
Figure BDA0003376308330000032
Is the initial phase of the start time of the kth symbol, fcIs the carrier frequency, TiFor symbol width, corresponding symbol rate fs＝1/Ti；
According to GMSKK-th code element information of the signal, K-point fast Fourier transform is carried out on GMSK signal sampled by N times of the code element, and f is obtainedc±fiTwo spectral line information;
accumulating two spectrum spectral line peak values by windowing a GMSK signal frequency domain, determining the maximum value of a fast Fourier transform spectral line as an AIS signal frequency offset value, and performing frequency compensation on the signal sampling data of the whole frame subjected to frame header detection; wherein, the impact function expression of the frequency domain window is:
Figure BDA0003376308330000033
L＝fi/(fsand/K) +1, wherein K is the number of fast Fourier transform points and fs is the sampling rate.
Further, performing matched filtering on the timing synchronized AIS baseband signal and sampling at an integer symbol time to obtain an output signal x (n), performing viterbi decoding on the output signal x (n) to obtain an original symbol information sequence a (n), including:
performing matched filtering on the signal sampling data after timing synchronization is completed through a matched filter, and outputting a signal x (n) at an integer code element moment, wherein the expression of the matched filtering is as follows:
Figure BDA0003376308330000034
wherein wnApproximately white noise, theta is the initial phase, which is a fixed constant, glAs shown in the following formula:
Figure BDA0003376308330000035
wnapproximately white noise;
using Viterbi decoding to make optimum path search for output signal x (n) to obtain x (n) minimum sequence { bnThen according to { b }nThe symbol information sequence a is easily obtainednAnd f, wherein the functional expression of the Viterbi decoding is as follows:
Figure BDA0003376308330000036
according to the satellite-borne AIS signal demodulation method, AIS baseband sampling data are obtained after band-pass sampling, down-conversion, filtering and sample extraction are carried out on AIS intermediate-frequency signals, and then frame header detection, fast Fourier transform, frequency compensation and timing synchronization are carried out on the AIS baseband sampling data; and finally, performing matched filtering and Viterbi decoding on the AIS baseband signal with the timing synchronization completed to obtain an original symbol sequence, thereby completing AIS signal demodulation.
The invention has the beneficial effects that:
1. the AIS signal demodulation method of the invention ensures low complexity, and has excellent system demodulation performance, sensitivity superior to-100 dBm and instantaneous dynamic range superior to 60 dB.
2. The satellite-borne AIS signal demodulation method can still achieve 98% of unpacking rate under the condition of low signal-to-noise ratio, the demodulation error rate is less than 5E-5, and the satellite-borne AIS signal demodulation method has strong adaptability and reliability under the condition of low signal-to-noise ratio.
3. When the satellite-borne AIS signal demodulation method is used for mixing various AIS signals or other types of signals, for example, when the frequency difference between the AIS signals and interference AIS signals is 0-8kHz, the satellite-borne AIS signal demodulation method has strong extraction capability for the strong AIS signals, and meanwhile, the AIS signals or other types of signals with weak signals can be filtered through filtering preprocessing, so that the satellite-borne AIS signal demodulation method has strong anti-interference capability.
4. Compared with the traditional algorithm, the satellite-borne AIS signal demodulation method has the advantages of less operation times and low operation complexity.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a flowchart of an AIS signal demodulation method according to an embodiment of the present invention;
FIG. 2 is a flow chart of a down-conversion, filtering and decimation method according to an embodiment of the present invention;
fig. 3 is a flowchart of a frame header detection method according to an embodiment of the present invention;
FIG. 4 is a waveform diagram of a frame header portion of an AIS signal after frequency discrimination according to an embodiment of the present invention;
FIG. 5 is a graph of a spectrum obtained by fast Fourier transform according to an embodiment of the present invention;
FIG. 6 is a frequency domain windowed spectrogram, in accordance with an embodiment of the present invention;
fig. 7 is a flowchart of viterbi demodulation according to an embodiment of the invention.
Detailed Description
The embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways as defined and covered by the claims.
As shown in fig. 1, a satellite-borne AIS signal demodulation method includes the following steps:
step S01, performing band-pass sampling on the AIS intermediate frequency signal at a preset sampling rate through an AD converter, performing down-conversion, filtering and 125-time sample extraction, and outputting two paths of AIS baseband signals to obtain two paths of baseband sampling data of two frequency points;
s02, performing frame header detection on the baseband sampling data, and extracting a complete AIS signal of a frame;
s03, carrying out frequency offset estimation and frequency offset compensation on the AIS signal through the code element information of the GMSK signal;
s04, correlating and matching the signal sampling data subjected to frequency offset compensation with a local sampling sequence generated by a fixed sequence of an AIS signal frame header, determining the maximum value of correlation as the starting position of the frame header, and completing timing synchronization of the AIS signal;
and S05, performing matched filtering on the AIS baseband signal which is subjected to timing synchronization and sampling at the integer code element moment to obtain an output signal x (n), and performing Viterbi decoding on the output signal x (n) to obtain an original code element information sequence a (n).
Preferably, in step S01, the down-converting, filtering and N times of sample decimation includes the following steps:
and S101, integrally down-converting the AIS signal serving as a dual-channel broadband signal to a baseband, carrying out two-stage CIC filtering processing and sample extraction according to a 25-time sampling rate, and outputting an AIS complex signal containing two frequency points of AIS1 and AIS 2.
And S102, performing down-conversion treatment on AIS complex signals of two frequency points of AIS1 and AIS2, performing FIR filtering and sample extraction according to a sampling rate of 5 times to obtain two paths of baseband sampling data of the two frequency points.
As shown in fig. 2, s (n) is an AIS real signal sampled at 2.8MHz intermediate frequency 9.6MHz, and the signal bit width is 14 bit; step S101 is a first-stage down-conversion, filtering and extraction step; the AIS signal is integrally converted into a baseband through frequency conversion by the first-stage down conversion as a dual-channel broadband signal, and filtering and 25-time extraction are carried out; the first-stage down-conversion local carrier is 2.8MHz, the local orthogonal carrier sequence is a periodic signal, and the period is 24 sampling values; the quantization bit number of the first-stage local carrier is 9 bits, the gain is 2^8, and the input is 14 bits of real signals, so the first-stage down-conversion calculation process adopts 22 bits of bit width.
The filtering extraction of the first stage adopts a 2-stage CIC filter to carry out 25 times of extraction, the CIC filtering process adopts 31bit width, the data is quantized into 16 bits after the 25 times of filtering extraction is finished, and the data rate is converted into 384 KHz; the signals extracted by the first-stage down-conversion filtering comprise AIS1 and AIS2 frequency point signals, wherein the center frequency points are-25 KHz and 25KHz respectively; the embodiment of the invention adopts two-stage filtering extraction, occupies less resources, and solves the problems that the FIR order required by conventional filtering is very large, nearly 300 orders are required in prediction, and the occupied resources are huge.
Step S102 is a second-stage down-conversion, filtering and extraction step, wherein the second-stage down-conversion input is complex signals of AIS1 and AIS2, the local carrier frequencies are 25KHz and-25 KHz respectively, the second-stage frequency conversion is used for respectively carrying out AIS1 and AIS2 complex lower edge frequencies to baseband signals, then filtering and 5-time extraction are carried out, and data quantization is 16 bits after filtering is finished.
Preferably, frame header detection is performed on the baseband sampling data to extract a complete frame of AIS signals, and frame header detection can only judge whether signals exist or not and cannot judge an accurate frame header position, as shown in fig. 3, the method specifically includes the following steps:
step S201, inputting the baseband sampling data into a frequency discriminator, processing the 192-point sampling data of the frame header through the frequency discriminator, wherein the processing expression is phi (n) ═ I (n) Q (n-1) -Q (n) I (n-1), and obtaining the signal waveform information of the frame header part of the signal.
The 192 sampling point data of the frame head is processed through a frequency discriminator, the data is a sinusoidal signal with the period being 4 times of the symbol rate, the frequency is 9.6e3/4, and the corresponding 192 sampling points comprise 6 complete sinusoidal wave periods; as shown in fig. 4, a is a waveform diagram of a frame header portion after the frequency discrimination of the noiseless AIS signal, and b is a waveform diagram of a frame header portion after the frequency discrimination of the AIS signal with the signal-to-noise ratio of 7 dB.
Step S202, according to the signal waveform information, 192-point sampling data of a signal frame header part is subjected to sliding DFT operation, the k-th frequency point is confirmed to be a DFT peak point of the frame header signal, the sliding DFT value of the k-th frequency point is obtained through calculation, and the sliding DFT calculation formula of the k-th frequency point is
Figure BDA0003376308330000061
0<＝k<N。
In step S202, the value of k is 6, that is, the FFT operation is performed on the received 192 point data, and obviously, if the data is the frame header data, the FFT peak is the 6 th point (the start number is 0); when the frame header signal exists, the DFT peak point is Xn(6)。
S203, calculating a DFT average value, wherein the DFT average value is the average value of DFT values of M frequency points on the left side and M frequency points on the right side of a frequency point k where a peak value is located; in this example, k has a value of 6 and M has a value of 4.
S204, judging whether the ratio of the sliding DFT value of the kth frequency point to the DFT average value continuously exceeds a threshold value for L times, if so, confirming that the frame header part is detected and extracting signal sampling data of a whole frame for storage; in this embodiment, when there is a frame header signal, the DFT peak point is Xn(6) The threshold is taken as 20, and the DFT value X of the peak point and the left and right 4 frequency points thereof is calculatedn(2:10), frame header detection and gating can be realized by judging the ratio of the peak value to the mean value of 4 DFT values around the peak value pointThe limit calculation formula is as follows:
Figure BDA0003376308330000062
if the threshold is crossed for 3 times continuously, the frame header is considered to be detected, and at the moment, the whole frame of data is sent to the rear end in advance for demodulation processing; the data of a whole frame is 256 bits, and 2048 sampling point data are totally obtained.
Preferably, the frequency offset estimation and frequency down offset compensation are performed on the AIS signal through symbol information of the GMSK signal, including the steps of:
step S301, k code element information of the GMSK signal is calculated, and the k code element expression of the GMSK signal is
Figure BDA0003376308330000063
kTi<t≤(k+1)TiWherein a iskIs a original symbol, ak∈{-1,1}，
Figure BDA0003376308330000064
Is the initial phase of the start time of the kth symbol, fcIs the carrier frequency, TiFor symbol width, corresponding symbol rate fs9.6 GHz; in this example, when akWhen the signal frequency is f ═ 1c-fiAndwhen a iskWhen the signal frequency is equal to 1, the signal frequency is fc+fi/4。
Step S302, according to the kth code element information of the GMSK signal, K-point fast Fourier transform is carried out on the GMSK signal sampled by the N times of the symbols, and f is obtainedc±fiThe two spectral line information, as shown in fig. 5; in this embodiment, N takes the value of 8, and K takes the value of 2048.
Step S303, accumulating two spectrum spectral line peak values by windowing a GMSK signal frequency domain, determining the maximum value of a fast Fourier transform spectral line as an AIS signal frequency offset value, and performing frequency compensation on the signal sampling data of the whole frame after frame header detection is completed; wherein, the impact function expression of the frequency domain window is:
Figure BDA0003376308330000071
L＝fi/(fsk) +1, where K is the number of fast fourier transform points and fs is the sampling rate; the frequency domain windowed spectrum is shown in figure 6.
Preferably, the method for obtaining the timing synchronization AIS baseband signal includes performing matched filtering on the timing synchronization AIS baseband signal, sampling at an integer symbol time to obtain an output signal x (n), performing viterbi decoding on the output signal x (n) to obtain an original symbol information sequence a (n), and includes:
step S401, performing matched filtering on the signal sampling data after timing synchronization is completed through a matched filter, and outputting a signal x (n) at an integer code element moment, wherein the expression of the matched filtering is as follows:
Figure BDA0003376308330000072
wherein wnApproximately white noise, theta is the initial phase, which is a fixed constant, glAs shown in the following formula:
Figure BDA0003376308330000073
wnapproximately white noise.
S402, using Viterbi decoding to search the optimal path of output signal x (n) to obtain the minimum sequence { b: (n) }nThen according to { b }nThe symbol information sequence a is easily obtainednAnd f, wherein the functional expression of the Viterbi decoding is as follows:
Figure BDA0003376308330000074
in the prior art, the maximum likelihood estimation is generally adopted to obtain the sequence b with the minimum expressionnGet symbol sequence { a }n}; the AIS signal has 256 bits, that is, N is 256, and if the maximum likelihood estimation method is adopted, the calculation amount is huge, and in this embodiment, the optimal path search is performed on the output signal x (N) by adopting viterbi decoding, so that the complexity of maximum likelihood estimation can be greatly reduced; after simulation, the Viterbi algorithm is adopted, when the memory depth is 6 bits,the symbol error rate of 5e-5 can be realized at the signal-to-noise ratio of 10dB, which is superior to the index requirement of the conventional technology.
According to the satellite-borne AIS signal demodulation method, AIS baseband sampling data are obtained after band-pass sampling, down-conversion, filtering and sample extraction are carried out on AIS intermediate-frequency signals, and then frame header detection, fast Fourier transform, frequency compensation and timing synchronization are carried out on the AIS baseband sampling data; finally, the AIS baseband signal which is completed with timing synchronization is subjected to matched filtering and Viterbi decoding to obtain an original symbol sequence, so that the aim of AIS signal demodulation is fulfilled, the AIS baseband signal has stronger adaptability and reliability under the condition of low signal-to-noise ratio and stronger anti-interference capability, and the technical problem of signal demodulation aiming at the AIS signal with the defects of low signal-to-noise ratio, serious co-channel interference, multi-signal mutual interference, large signal dynamic range and the like in the prior art is solved.

Claims (5)

1. A satellite-borne AIS signal demodulation method is characterized by comprising the following steps:
performing band-pass sampling on the AIS intermediate-frequency signal by an AD converter at a preset sampling rate, performing down-conversion, filtering and m-time sample extraction, and outputting two paths of AIS baseband signals to obtain two paths of baseband sampling data of two frequency points;
performing frame header detection on the baseband sampling data, and extracting a complete AIS signal of a frame;
carrying out frequency offset estimation and frequency offset compensation on the AIS signal through the code element information of the GMSK signal;
correlating and matching the signal sampling data after completing the frequency offset compensation with a local sampling sequence generated by a fixed sequence of an AIS signal frame header, determining the maximum value of the correlation as the starting position of the frame header, and completing the timing synchronization of the AIS signal;
and performing matched filtering on the AIS baseband signal after timing synchronization is completed, sampling at integer symbol time to obtain an output signal x (n), and performing Viterbi decoding on the output signal x (n) to obtain an original symbol information sequence a (n).
2. The method for demodulating the satellite-borne AIS signal according to claim 1, wherein the down-conversion, filtering and N times sample extraction comprises the following steps:
the AIS signal is used as a dual-channel broadband signal and is subjected to down-conversion to a baseband in an integral mode, two-stage CIC filtering processing is carried out, samples are extracted according to a sampling rate which is 25 times that of the AIS signal, and the AIS complex signal containing two frequency points of AIS1 and AIS2 is output;
the method comprises the steps of carrying out down-conversion processing on AIS complex signals of two frequency points of AIS1 and AIS2, carrying out FIR filtering and carrying out sample extraction according to a sampling rate which is 5 times, and obtaining two paths of baseband sampling data of the two frequency points.
3. The method for demodulating a satellite-borne AIS signal according to claim 1, wherein the method for performing frame header detection on the baseband sampling data to extract a complete frame of AIS signal specifically comprises the following steps:
inputting baseband sampling data into a frequency discriminator, processing the 192-point sampling data of the frame header through the frequency discriminator, wherein the processing expression is phi (n) ═ I (n) Q (n-1) -Q (n) I (n-1), and obtaining signal waveform information of the frame header part of the signal;
according to the signal waveform information, performing sliding DFT operation on 192-point sampling data of a signal frame header part, confirming that the k-th frequency point is a DFT peak point of the frame header signal and calculating to obtain a sliding DFT value of the k-th frequency point, wherein the sliding DFT calculation formula of the k-th frequency point is
Figure FDA0003376308320000011
Calculating DFT average values, wherein the DFT average values are the DFT values of M frequency points on the left side of the frequency point k where the peak value is located and the DFT values of M frequency points on the right side;
judging whether the ratio of the sliding DFT value of the kth frequency point to the DFT average value continuously exceeds a threshold value for L times, if so, confirming that the frame header part is detected and extracting signal sampling data of a whole frame for storage; wherein, the calculation expression of the threshold value is as follows:
Figure FDA0003376308320000021
4. the method for demodulating a satellite-borne AIS signal according to claim 1, wherein the AIS signal is frequency offset estimated and frequency down offset compensated by symbol information of GMSK signal, comprising the steps of:
calculating the kth code element information of the GMSK signal, wherein the kth code element expression of the GMSK signal is
Figure FDA0003376308320000022
Wherein a iskIs a original symbol, ak∈{-1,1}，
Figure FDA0003376308320000023
Is the initial phase of the start time of the kth symbol, fcIs the carrier frequency, TiFor symbol width, corresponding symbol rate fs＝1/Ti；
According to the kth code element information of the GMSK signal, performing K-point fast Fourier transform on the GMSK signal sampled by N times of symbols to obtain the result that f is fc±fiTwo spectral line information;
accumulating two spectrum spectral line peak values by windowing a GMSK signal frequency domain, determining the maximum value of a fast Fourier transform spectral line as an AIS signal frequency offset value, and performing frequency compensation on the signal sampling data of the whole frame subjected to frame header detection; wherein, the impact function expression of the frequency domain window is:
Figure FDA0003376308320000024
wherein K is the number of fast Fourier transform points and fs is the sampling rate.
5. The demodulation method for the satellite-borne AIS signal according to claim 1, wherein the timing synchronized AIS baseband signal is matched filtered and sampled at integer symbol time to obtain an output signal x (n), and the output signal x (n) is viterbi decoded to obtain an original symbol information sequence a (n), comprising:
performing matched filtering on the signal sampling data after timing synchronization is completed through a matched filter, and outputting a signal x (n) at an integer code element moment, wherein the expression of the matched filtering is as follows:
Figure FDA0003376308320000025
wherein wnApproximately white noise, theta is the initial phase, which is a fixed constant, glAs shown in the following formula:
Figure FDA0003376308320000026
wnapproximately white noise;
using Viterbi decoding to make optimum path search for output signal x (n) to obtain x (n) minimum sequence { bnThen according to { b }nThe symbol information sequence a is easily obtainednAnd f, wherein the functional expression of the Viterbi decoding is as follows:
Figure FDA0003376308320000027
CN202111419397.4A 2021-11-26 2021-11-26 Satellite-borne AIS signal demodulation method Withdrawn CN114124197A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202111419397.4A CN114124197A (en) 2021-11-26 2021-11-26 Satellite-borne AIS signal demodulation method

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202111419397.4A CN114124197A (en) 2021-11-26 2021-11-26 Satellite-borne AIS signal demodulation method

Publications (1)

Publication Number Publication Date
CN114124197A true CN114124197A (en) 2022-03-01

Family

ID=80369702

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202111419397.4A Withdrawn CN114124197A (en) 2021-11-26 2021-11-26 Satellite-borne AIS signal demodulation method

Country Status (1)

Country Link
CN (1) CN114124197A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115347979A (en) * 2022-08-08 2022-11-15 新诺北斗航科信息技术（厦门）股份有限公司 Method, device and storage medium for identifying AIS frame header data

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010288077A (en) * 2009-06-11 2010-12-24 Nippon Hoso Kyokai <Nhk> Device for receiving multicarrier modulated signal
CN105763498A (en) * 2016-04-08 2016-07-13 南京理工大学 All-digital receiving method for satellite-borne AIS
CN110011724A (en) * 2019-04-18 2019-07-12 上海航天测控通信研究所 A kind of method of reseptance of ship automatic identification system, receiver and telecommunication satellite
CN110636021A (en) * 2019-09-24 2019-12-31 苏州市江海通讯发展实业有限公司 Large frequency offset correction method for GMSK demodulator under AIS system
CN111147406A (en) * 2019-12-06 2020-05-12 上海航天电子有限公司 ASM system demodulation method based on constant false alarm signal detection and frequency offset correction

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010288077A (en) * 2009-06-11 2010-12-24 Nippon Hoso Kyokai <Nhk> Device for receiving multicarrier modulated signal
CN105763498A (en) * 2016-04-08 2016-07-13 南京理工大学 All-digital receiving method for satellite-borne AIS
CN110011724A (en) * 2019-04-18 2019-07-12 上海航天测控通信研究所 A kind of method of reseptance of ship automatic identification system, receiver and telecommunication satellite
CN110636021A (en) * 2019-09-24 2019-12-31 苏州市江海通讯发展实业有限公司 Large frequency offset correction method for GMSK demodulator under AIS system
CN111147406A (en) * 2019-12-06 2020-05-12 上海航天电子有限公司 ASM system demodulation method based on constant false alarm signal detection and frequency offset correction

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115347979A (en) * 2022-08-08 2022-11-15 新诺北斗航科信息技术（厦门）股份有限公司 Method, device and storage medium for identifying AIS frame header data
CN115347979B (en) * 2022-08-08 2023-09-01 新诺北斗航科信息技术（厦门）股份有限公司 Method, device and storage medium for identifying AIS frame header data

Similar Documents

Publication Publication Date Title
CN105763498B (en) A kind of digital method of reseptance of spaceborne AIS
EP3128707B1 (en) Co-channel spatial separation using matched doppler filtering
CN101674270B (en) Identification method of low signal-to-noise ratio phase-shift keying modulating signal
US20030063596A1 (en) Methods and apparatus for canceling co-channel interference in a receiving system using spatio-temporal whitening
US6876645B1 (en) Delay and channel estimation for multi-carrier CDMA system
US20070297541A1 (en) Signal Detector Using Matched Filter For Training Signal Detection
CN103117965B (en) A kind of spaceborne ais signal timing frequency deviation combined estimation method and realize system
CN112511477A (en) Hybrid satellite communication modulation identification method and system based on constellation diagram and deep learning
CN110011724B (en) Receiving method of ship automatic identification system, receiver and communication satellite
US10848357B2 (en) Method for estimating parameters of signals contained in a frequency band
CN110933007B (en) Device and method for eliminating interference aiming at OFDM broadband signal
CN114124197A (en) Satellite-borne AIS signal demodulation method
CN106972895B (en) Underwater acoustic preamble signal detection method based on accumulated correlation coefficient under sparse channel
CN116647311B (en) Unmanned aerial vehicle communication signal processing method, system and equipment based on blind source separation
CN110113273B (en) Time-frequency overlapping signal blind separation method based on frequency spectrum symmetry
US20050254593A1 (en) Doppler aided detection, processing and demodulation of multiple signals
CN115047501B (en) Satellite navigation authorization signal estimation method suitable for BOC modulation
US7978796B2 (en) Recovering symbols in a communication receiver
AU2023234893A1 (en) Delay-doppler domain channel estimation and frame synchronization
Meng et al. Frequency offset estimation in the intermediate frequency for satellite-based AIS signals
CN112565127B (en) Measurement and control signal modulation identification method based on residual error network and frequency domain graph
CN112865882A (en) Anti-frequency-deviation DMR interphone signal rapid identification method
CN113949612A (en) Burst signal capturing method and system in helicopter and satellite communication
CN107947810B (en) Digital domain interference elimination method of full-duplex constant amplitude modulation system
WO1993022854A1 (en) Radio communication modem for receiving and estimating a transmitted symbol

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
WW01 Invention patent application withdrawn after publication
WW01 Invention patent application withdrawn after publication

Application publication date: 20220301