A Phase Modulation Depth Estimation and Correction System in PGC Demodulation

Abstract

The present application provides a phase modulation depth estimation and correction system in PGC demodulation, the system comprising: a digital interference signal is simultaneously connected to four multipliers; a reference signal generated by four direct digital frequency synthesizers is multiplied with the digital interference signal, and after low-pass filtering, the inversion module, the verification module, the subtractor, the multiplier and the inverse tangent module are processed, and the detection signal is output by the high-pass filter module. The advantages of the present application are: no additional auxiliary signal is needed, and the modulation depth can be estimated only by relying on the system noise; the estimation error is effectively avoided by introducing the verification module, and the accuracy of the modulation depth estimation is guaranteed; the digital interference signal of each frame is estimated, and the error caused by the modulation depth drift is corrected in real time to improve the signal detection accuracy.

Description

Technical Field

[0001] The present application belongs to the technical field of Phase Generated Carrier (PGC) demodulation, and in particular relates to a phase modulation depth estimation and correction system in PGC demodulation. Background Art

[0002] PGC demodulation technology has become one of the commonly used signal detection methods in fiber optic hydrophone systems due to its simple structure, resistance to low-frequency interference, and suppression of double Rayleigh scattering noise in optical fibers.

[0003] However, the demodulation process parameters of PGC demodulation technology, such as modulation depth, will drift with the changes in the environment, causing parameter detuning, resulting in distortion of the detection signal and affecting the detection performance of the system. Traditionally, the estimation method based on least squares ellipse fitting usually requires the addition of additional auxiliary signals and a large number of data points to ensure the accuracy of the estimation, which has a large amount of calculation and poor real-time performance. The estimation method based on Kalman filter ellipse fitting has high computational efficiency and good real-time performance, but it requires the statistical model of the signal and noise to be known in advance. In fact, the system model is often changing, which leads to the divergence of the Kalman filter and poor accuracy.

[0004] Therefore, in order to improve the accuracy of PGC demodulation detection signals and ensure the detection performance of the system, a system is urgently needed to accurately estimate and correct the system modulation depth in real time. Summary of the invention

[0005] The purpose of the present application is to overcome the defects of the modulation depth estimation method in the existing PGC demodulation technology, such as large amount of computation, poor real-time performance, or the need to know the statistical model of the signal and noise in advance.

[0006] In order to achieve the above objectives, the present application proposes a phase modulation depth estimation and correction system in PGC demodulation, the system comprising:

[0007] The digital interference signal is simultaneously connected to the input terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier;

[0008] The output terminals of the first direct digital frequency synthesizer, the second direct digital frequency synthesizer, the third direct digital frequency synthesizer and the fourth direct digital frequency synthesizer are connected to the input terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier respectively;

[0009] The output terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier are connected to the input terminals of the first low-pass filter, the second low-pass filter, the third low-pass filter and the fourth low-pass filter respectively;

[0010] The output end of the first low-pass filter is connected to the input end of the first inversion module and the input end of the subtractor respectively;

[0011] The output end of the third low-pass filter is connected to the input end of the first inversion module and the input end of the subtractor respectively;

[0012] The output end of the second low-pass filter is connected to the input end of the second inversion module and the input end of the inverse tangent module respectively;

[0013] The output of the fourth low-pass filter is connected to the input of the second inversion module;

[0014] The output end of the first inversion module and the output end of the second inversion module are both connected to the input end of the verification module;

[0015] The output end of the check module is connected to the input end of the sixth multiplier;

[0016] The output end of the sixth multiplier and the output end of the subtractor are both connected to the input end of the fifth multiplier; the sixth multiplier is a 0.25 times multiplier;

[0017] The output terminal of the fifth multiplier is connected to the input terminal of the inverse tangent module;

[0018] The output of the inverse tangent module is connected to the input of the high-pass filter module;

[0019] The output end of the high-pass filter module outputs a detection signal.

[0020] As an improvement of the above system, the workflow of the system includes:

[0021] Obtain the digital interference signal I(t) returned by the optical fiber hydrophone and subjected to power adjustment, photoelectric conversion and analog-to-digital conversion;

[0022] The first direct digital frequency synthesizer generates a first-order reference signal R1, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L1; the second direct digital frequency synthesizer generates a second-order reference signal R2, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L2; the third direct digital frequency synthesizer generates a third-order reference signal R3, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L3; the fourth direct digital frequency synthesizer generates a fourth-order reference signal R4, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L4; signals L1, L2, L3 and L4 are harmonic amplitude signals of various orders with detection signals;

[0023] Input the signals L1 and L3 into the inversion module to calculate the first estimated value C1 of the modulation depth; input the signals L2 and L4 into the inversion module to calculate the second estimated value C2 of the modulation depth;

[0024] Input the first estimated value C1 and the second estimated value C2 into the verification module to obtain the modulation depth estimated value C';

[0025] Subtract signal L1 from signal L3 and multiply it by 0.25 times of the estimated modulation depth C' to obtain signal L5. Perform an inverse tangent operation with signal L2 and then perform a high-pass filter to remove the initial phase φ o (t) Get the detection signal φ s (t).

[0026] As an improvement of the above system, the digital interference signal I(t) returned by the optical fiber hydrophone after power adjustment, photoelectric conversion and analog-to-digital conversion is obtained and expressed as:

[0027]

[0028] φ(t)=φ s (t)+φ o (t)

[0029] Among them, A is the DC amplitude, B is the AC amplitude, C is the modulation depth, ω c is the carrier angular frequency, is the carrier phase, t is the time, φ s (t) is the detection signal, φ o (t) is the initial phase.

[0030] As an improvement of the above system, the first-order reference signal R1 is expressed as:

[0031] The expression of the second-order reference signal R2 is:

[0032] The expression of the third-order reference signal R3 is:

[0033] The expression of the fourth-order reference signal R4 is:

[0034] Among them, ω c is the carrier angular frequency, is the carrier phase and t is the time.

[0035] As an improvement to the above system, the expressions of signals L1, L2, L3 and L4 are as follows:

[0036] L1=-BJ1(C)sinφ(t)

[0037] L2=-BJ2(C)cosφ(t)

[0038] L3=+BJ3(C)sinφ(t)

[0039] L4=+BJ4(C)sinφ(t)

[0040] Where B is the AC amplitude, C is the modulation depth, and J is k (C) is the kth order first kind Bessel function of C, k = 1, 2, 3, 4. As an improvement to the above system, the expressions of the first estimate C1 and the second estimate C2 are as follows:

[0041] C1=f -1 (J1(C) / J3(C))

[0042] C2=f -1 (J2(C) / J4(C))

[0043] Where C is the modulation depth, f -1 () is the inverse function operation, J k (C) is the kth order first kind Bessel function of C, k = 1, 2, 3, 4.

[0044] As an improvement of the above system, the inverse function operation establishes a mapping table between J1(C) / J3(C) and C, and obtains the first estimated value C1 of the modulation depth by looking up the mapping table; and establishes a mapping table between J2(C) / J4(C) and C, and obtains the first estimated value C2 of the modulation depth by looking up the mapping table.

[0045] As an improvement to the above system, the expression of the modulation depth estimation value C' is as follows:

[0046]

[0047] Among them, || represents the absolute value, δ is the verification threshold, and NaN represents an invalid value.

[0048] As an improvement to the above system, signal L5 and signal φ s (t) is expressed as follows:

[0049] L5=-BJ2(C)sinφ(t)

[0050]

[0051] Where HPF[] is a high-pass filter, arctan() is an inverse tangent operation, B is the AC amplitude, and J2(C) is the second-order first-kind Bessel function of C.

[0052] Compared with the prior art, the advantages of this application are:

[0053] 1. The system of the present application does not need to add additional auxiliary signals, and can estimate the modulation depth only by relying on system noise;

[0054] 2. The system of the present application effectively avoids estimation errors by introducing a verification module, thereby ensuring the accuracy of modulation depth estimation;

[0055] 3. The system of the present application estimates the digital interference signal of each frame and corrects it in real time to eliminate the error caused by modulation depth drift, thereby improving the signal detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Shown is a functional block diagram of the system of the present application;

[0057] Figure 2 The figure shows the result of simulation test data using the system of the present application.

[0058] Figure ID:

[0059] A1: First Direct Digital Frequency Synthesizer A2: Second Direct Digital Frequency Synthesizer

[0060] A3: Third direct digital frequency synthesizer A4: Fourth direct digital frequency synthesizer

[0061] B1: First multiplier B2: Second multiplier

[0062] B3: The third multiplier B4: The fourth multiplier

[0063] B5: fifth multiplier B6: sixth multiplier

[0064] D1: First low-pass filter D2: Second low-pass filter

[0065] D3: The third low-pass filter D4: The fourth low-pass filter

[0066] E1: First inversion module E2: Second inversion module

[0067] F1: Check module G1: Subtractor

[0068] J1: Inverse tangent module K1: High pass filter module DETAILED DESCRIPTION

[0069] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0070] like Figure 1As shown, the phase modulation depth estimation and correction system in PGC demodulation provided by the present application has the following structure: the input ends of the first multiplier B1, the second multiplier B2, the third multiplier B3 and the fourth multiplier B4 are all connected to the digital interference signal I, and the output ends of the first direct digital frequency synthesizer A1, the second direct digital frequency synthesizer A2, the third direct digital frequency synthesizer A3 and the fourth direct digital frequency synthesizer A4 are respectively connected to the input ends of the first multiplier B1, the second multiplier B2, the third multiplier B3 and the fourth multiplier B4; the output end of the first multiplier B1 is respectively connected to the input end of the first inversion module E1 and the input end of the subtractor G1 through the first low-pass filter D1; the output end of the third multiplier B3 is respectively connected to the input end of the first inversion module E1 through the third low-pass filter D3 and the input end of the subtractor G1; the output end of the second multiplier B2 is connected to the input end of the second inversion module E2 and the input end of the inverse tangent module J1 respectively through the second low-pass filter D2; the output end of the fourth multiplier B4 is connected to the input end of the second inversion module E2 through the fourth low-pass filter D4; the output end of the first inversion module E1 and the output end of the second inversion module E2 are both connected to the input end of the verification module F1, the output end of the verification module F1 is connected to the input end of the multiplier B6, the output end of the multiplier B6 and the output end of the subtractor G1 are both connected to the input end of the fifth multiplier B4, and the output end of the fifth multiplier B5 is connected to the input end of the inverse tangent module J1; the output end of the inverse tangent module J1 is connected to the input end of the high-pass filter module K1, and the output end of the high-pass filter module K1 outputs the detection signal.

[0071] Preferably, multiplier B6 is a 0.25x multiplier.

[0072] The operation process of the phase modulation depth estimation and correction system in PGC demodulation is as follows:

[0073] S1: Obtain the digital interference signal I(t). The digital interference signal I(t) is the digital signal returned by the fiber optic hydrophone after power adjustment, photoelectric conversion and analog-to-digital conversion. Its expression is:

[0074]

[0075] φ(t)=φ s (t)+φ o (t)

[0076] Among them, A is the DC amplitude, B is the AC amplitude, C is the modulation depth, ω c is the carrier angular frequency, is the carrier phase, φ s (t) is the detection signal, φ o (t) is the initial phase, and t is the time.

[0077] S2: The first direct digital frequency synthesizer A1 generates a first-order reference signal The signal L1 is obtained by multiplying the digital interference signal I(t) and low-pass filtering. Meanwhile, the second direct digital frequency synthesizer A2 generates a second-order reference signal The signal L2 is obtained by multiplying the digital interference signal I(t) and low-pass filtering. Meanwhile, the third direct digital frequency synthesizer A3 generates a third-order reference signal The signal L3 is obtained by multiplying the digital interference signal I(t) and low-pass filtering. Meanwhile, the fourth direct digital frequency synthesizer A4 generates a fourth-order reference signal The signal L4 is obtained by multiplying the digital interference signal J(t) and low-pass filtering. Signals L1, L2, L3 and L4 are harmonic amplitude signals of various orders with detection signals, and the expressions are as follows:

[0078] L1=LPF[R1×I(t)]=-BJ1(C)sinφ(t)

[0079] L2=LPF[R2×I(t)]=-BJ2(C)cosφ(t)

[0080] L3=LPF(R3×I(t)]=+BJ3(C)sinφ(t)

[0081] L4=LPF[R4×I(t)]=+BJ4(C)sinφ(t)

[0082] Among them, LPF[] is low-pass filter, J k (C) is the kth order first kind Bessel function of C, k = 1, 2, 3, 4.

[0083] S3: Input the signals L1 and L3 into the inversion module to calculate the first estimated value C1 of the modulation depth; at the same time, input the signals L2 and L4 into the inversion module to calculate the second estimated value C2 of the modulation depth. The expressions of C1 and C2 are as follows:

[0084] C1=f -1 (-L1 / L3) = f -1 (J1(C) / J3(C))

[0085] C2=f -1 (-L2 / L4) = f -1 (J2(C) / J4(C))

[0086] Among them, f -1 () is the inverse function operation.

[0087] Preferably, within the range of C∈(0,6.38], J1(C) / J3(C) and J2(C) / J4(C) are both monotonic functions of the modulation depth C. Therefore, a mapping table between J1(C) / J3(C) and C can be established, and the first estimated value C1 of the modulation depth can be quickly obtained through the lookup table. A mapping table between J2(C) / J4(C) and C can be established, and the second estimated value C2 of the modulation depth can be quickly obtained through the lookup table.

[0088] S4: Input the first estimated value C1 and the second estimated value C2 into the verification module F1 to obtain the modulation depth estimated value C', which is expressed as follows:

[0089]

[0090] Among them, || represents the absolute value, δ is the verification threshold, and NaN represents an invalid value.

[0091] When φ(t) is near mπ, m=0, ±1, ±2…, sinφ(t) approaches 0. At this time, signals L1 and L3 are greatly affected by system noise, and the first estimated value C1 obtained in step S3 has a large error.

[0092] When φ(t) is near nπ / 2, n=±1,±3,±5…, cosφ(t) approaches 0. At this time, signals L2 and L4 are greatly affected by system noise, and the second estimated value C2 obtained in step S3 has a large error.

[0093] Therefore, by introducing the verification module F1, estimation errors can be effectively avoided, thereby ensuring the accuracy of modulation depth estimation.

[0094] S5: Subtract the signal L1 in step S2 from the signal L3 and multiply it by 0.25 times the modulation depth estimation value C' obtained in step S4 to obtain the signal L5. Perform an inverse tangent operation on the signal L2 in step S2 and then perform a high-pass filter to remove the initial phase φ o (t) Get the detection signal φ s (t), signal L5 and signal φ s (t) is expressed as follows:

[0095] L5=(L1-L3)×0.25V=-BJ2(C)sinφ(t)

[0096]

[0097] Among them, HPF[] is high-pass filtering, and arctan() is the inverse tangent operation.

[0098] At this point, the estimation and correction of the modulation depth in PGC demodulation are realized, and an accurate detection signal φ is obtained. s (t).

[0099] In the simulation experiment, the modulation depth is set as a random variable to generate a digital interference signal I(t), the verification threshold δ=0.005, the simulation time is 100 seconds, and the modulation depth is estimated according to the method proposed in the present invention. The results are as follows: Figure 2 As shown. Figure 2 The upper figure is the actual C value, the middle figure is the estimated C value, and the lower figure is the estimated error, that is, the difference between the estimated C value and the actual C value. It can be seen that the estimated C value follows the change of the actual C value in real time, and the estimation error does not exceed 0.005rad, realizing the real-time and high-precision estimation of the modulation depth in PGC demodulation without relying on additional auxiliary signals.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. A phase modulation depth estimation and correction system in PGC demodulation, characterized in that: The system comprises: The digital interference signal is simultaneously connected to the input terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier; The output terminals of the first direct digital frequency synthesizer, the second direct digital frequency synthesizer, the third direct digital frequency synthesizer and the fourth direct digital frequency synthesizer are connected to the input terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier respectively; The output terminals of the first multiplier, the second multiplier, the third multiplier and the fourth multiplier are connected to the input terminals of the first low-pass filter, the second low-pass filter, the third low-pass filter and the fourth low-pass filter respectively; The output end of the first low-pass filter is connected to the input end of the first inversion module and the input end of the subtractor respectively; The output end of the third low-pass filter is connected to the input end of the first inversion module and the input end of the subtractor respectively; The output end of the second low-pass filter is connected to the input end of the second inversion module and the input end of the inverse tangent module respectively; The output of the fourth low-pass filter is connected to the input of the second inversion module; The output end of the first inversion module and the output end of the second inversion module are both connected to the input end of the verification module; The output end of the check module is connected to the input end of the sixth multiplier; The output end of the sixth multiplier and the output end of the subtractor are both connected to the input end of the fifth multiplier; the sixth multiplier is a 0.25 times multiplier; The output terminal of the fifth multiplier is connected to the input terminal of the inverse tangent module; The output of the inverse tangent module is connected to the input of the high-pass filter module; The output end of the high-pass filter module outputs a detection signal; The workflow of the system includes: Obtain the digital interference signal I(t) returned by the optical fiber hydrophone and subjected to power adjustment, photoelectric conversion and analog-to-digital conversion; The first direct digital frequency synthesizer generates a first-order reference signal R1, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L1; the second direct digital frequency synthesizer generates a second-order reference signal R2, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L2; the third direct digital frequency synthesizer generates a third-order reference signal R3, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L3; the fourth direct digital frequency synthesizer generates a fourth-order reference signal R4, which is multiplied by the digital interference signal I(t) and low-pass filtered to obtain a signal L4; signals L1, L2, L3 and L4 are harmonic amplitude signals of various orders with detection signals; Input the signals L1 and L3 into the first inversion module to calculate the first estimated value C1 of the modulation depth; input the signals L2 and L4 into the second inversion module to calculate the second estimated value C2 of the modulation depth; Input the first estimated value C1 and the second estimated value C2 into the verification module to obtain the modulation depth estimated value C'; Subtract signal L1 from signal L3 and multiply it by 0.25 times of the estimated modulation depth C' to obtain signal L5. Perform an inverse tangent operation with signal L2 and then perform a high-pass filter to remove the initial phase φ o (t) Get the detection signal φ s (t).

2. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: The digital interference signal I(t) returned by the optical fiber hydrophone after power adjustment, photoelectric conversion and analog-to-digital conversion is obtained and expressed as: φ(t)=φ s (t)+φ o (t) Among them, A is the DC amplitude, B is the AC amplitude, C is the modulation depth, ω c is the carrier angular frequency, is the carrier phase, t is the time, φ s (t) is the detection signal, φ o (t) is the initial phase.

3. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: The expression of the first-order reference signal R1 is: The expression of the second-order reference signal R2 is: The expression of the third-order reference signal R3 is: The expression of the fourth-order reference signal R4 is: Among them, ω c is the carrier angular frequency, is the carrier phase and t is the time.

4. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: The expressions of signals L1, L2, L3 and L4 are as follows: L1=-BJ1(C)sinφ(t) L2=-BJ2(C)sinφ(t) L3=+BJ3(C)sinφ(t) L4=+BJ4(C)sinφ(t) Where B is the AC amplitude, C is the modulation depth, and J is k (C) is the kth order first kind Bessel function of C, k = 1, 2, 3, 4; t is time.

5. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: The expressions for the first estimate C1 and the second estimate C2 are as follows: C1=f -1 (J1(C) / J3(C)) C2=f- 1 (J2(C) / J4(C)) Where C is the modulation depth, f -1 () is the inverse function operation, J k (C) is the kth order first kind Bessel function of C, k = 1, 2, 3, 4.

6. The phase modulation depth estimation and correction system in PGC demodulation according to claim 5, characterized in that: The inverse function operation is performed by establishing a mapping table between J1(C) / J3(C) and C, and obtaining the first estimated value C1 of the modulation depth by looking up the mapping table; and by establishing a mapping table between J2(C) / J4(C) and C, and obtaining the first estimated value C2 of the modulation depth by looking up the mapping table.

7. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: The expression of the modulation depth estimate C' is as follows: Among them, || represents the absolute value, δ is the verification threshold, and NaN represents an invalid value.

8. The phase modulation depth estimation and correction system in PGC demodulation according to claim 1, characterized in that: Signal L5 and signal φ s (t) is expressed as follows: L5=-BJ2(C)sinφ(t) Where HPF[] is a high-pass filter, arctan() is an inverse tangent operation, B is the AC amplitude, and J2(C) is the second-order first-kind Bessel function of C.

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