CN106603117A - Method for measuring underwater propagation delay - Google Patents

Abstract

The invention relates to a method for measuring underwater propagation delay, aiming at overcoming low reliability and high measurement errors of traditional methods for measuring the propagation delay of voice signals in a non-responsive manner. According to the invention, the method combines the advantages of wideband hyperbolic frequency modulation, namely anti-Doppler effects, high time resolution and excellent anti-noise properties of direct spread spectrum modulation of m sequence, can effectively counter the influence of channel Doppler effects and noise, and acquire reliable measuring properties with a low processing complexity. According to the invention, the method has high measuring precision, strong anti-underwater acoustic channel capability, low processing complexity and excellent reliability. Due to aforementioned reasons, according to the invention, the method can be applied to the field of underwater acoustic navigation, positioning and underwater acoustic communication.

Description

A Method for Measuring Propagation Delay Underwater

technical field

The invention relates to the fields of underwater acoustic navigation, positioning and underwater acoustic communication, in particular to a method for underwater measurement of propagation time delay.

Background technique

With the development of marine resources and the needs of national defense construction, underwater AUV (Autonomous Underwater Vehicle, autonomous underwater vehicle)/UUV (Unmanned Underwater Vehicle, unmanned underwater vehicle) navigation, underwater salvage positioning, underwater Application scenarios such as docking guidance have an increasingly urgent demand for broadcast multi-user (similar to GPS) underwater navigation and positioning. Non-responsive measurement of acoustic signal propagation delay is the basis for realizing broadcast multi-user underwater navigation and positioning functions. Although the traditional non-responsive method of measuring the propagation delay of acoustic signals also uses broadband signals with large bandwidth-time products (such as linear frequency modulation and hyperbolic frequency modulation signals), it is difficult to obtain a sound signal in water with strong Doppler effect and large background noise interference. Under acoustic channel conditions, there are disadvantages of low reliability and high delay measurement error.

Contents of the invention

In order to solve the deficiencies in the prior art, the present invention aims to provide a method for non-responsive underwater measurement of acoustic signal propagation time delay. Combining the advantages of high and m-sequence direct spread spectrum modulation with good anti-noise performance, this method can effectively resist the influence of channel Doppler effect and noise, and obtain reliable measurement performance with low processing complexity.

In order to achieve the above object, the present invention mainly provides the following technical solutions: a method for underwater measurement of propagation delay, which includes the following steps: first, at the signal transmitting end: 11) obtaining the current local synchronous clock time stamp information at the signal transmitting end T _{tx 0} ; 12) According to T _{tx 0} and delaying the fixed time t _d to obtain the time stamp information T _tx = T _{tx 0} +t _d of the time stamp of the transmitted signal, perform m-sequence direct spread spectrum modulation for T _tx , and combine the composite The hyperbolic FM signal generates the transmission signal T _xSignal ; 13) the signal transmitting end utilizes the local synchronous clock pulse signal to reach the transition edge of the T _tx moment to trigger the T _xSignal emission; secondly, at the signal receiving end: 21) according to the characteristics of the composite hyperbolic FM signal Estimate the signal arrival time and Doppler coefficient; 22) Perform m-sequence direct spread spectrum data demodulation on the message data signal, obtain the time stamp information T _tx of the time synchronization clock of the transmitted signal, and calculate the transmitted signal according to the length of the received message data Time length T _signal ; 23) when the receiving end of the signal obtains the time stamp information T _tx of the clock synchronization clock at the time of transmitting the signal, the local synchronization time stamp information T _rx , the local timer reading T' _rx and the arrival start time T _buffer of the transmission signal, And calculate the final estimated value of propagation delay Δt according to the following formula:

Δt=T _rx +T' _rx -(T _signal +T _buffer )-T _tx .

In the step 12), the synchronous clock time stamp information of the m-sequence direct spread spectrum modulation is composed of frame header data cyclic prefix, frame header data, message data and message data CRC checksum.

The step 12) includes the following steps: 121) Delaying the obtained T _{tx 0} for a fixed time t _d to obtain the time stamp information T _tx = T _{tx 0} +t _d of the transmitted signal time synchronization clock; 122) performing m on the T _tx information Sequence direct spread spectrum modulation to form synchronous clock time stamp information, wherein, the synchronous clock time stamp information of m-sequence direct spread spectrum modulation consists of frame header data cyclic prefix, frame header data, message data and message data CRC checksum ; 123) Combining the synchronous clock timestamp information with the composite hyperbolic FM signal to generate a transmitting signal T _xSignal at the transmitting end.

The compound hyperbolic FM signal in the step 123) is formed by the linear superposition of hyperbolic FM signals of 2 different parameters:

S(t)＝S ₁ (t)+S ₂ (t)

in, is the lower limit frequency of one of the hyperbolic FM signals, is the upper limit frequency of the hyperbolic FM signal, is the lower limit frequency of another hyperbolic FM signal, is the upper limit frequency of the hyperbolic FM signal, and T is the duration of a single hyperbolic FM signal.

The step 21) includes the following steps: 211) the receiving end samples the received analog signal according to a certain sampling rate f _s , and uses S ₁ (t) and S ₂ (t) to perform copy related processing on the received signal, respectively Obtain the absolute value of its correlation function |C ₁ (τ)| and |C ₂ (τ)|; 212) compare the maximum value of |C ₁ (τ)| and |C ₂ (τ)| with the threshold, if are not greater than the threshold, then return to step 211); if all exceed the threshold, it is judged that there may be a signal arrival, and proceed to step 213); 213) calculate according to the sampling rate f _s : when |C ₁ (τ)| is The time t ₁ corresponding to the maximum value in the receiving buffer and the corresponding time t ₂ in the receiving buffer when |C ₂ (τ)| τ:

214) According to get

D and τ, carry out m-sequence direct spread spectrum data demodulation to frame head data, check whether the frame head data is the expected frame head data, if not, then return to step 211), if so, then determine that the signal arrives at the time confirmation, turn over to Step 22).

In said step 22), m-sequence direct spread spectrum data demodulation is carried out at the message data signal to obtain a complete frame of message data, the message data including message data CRC checksum, using message data CRC check check and carry out CRC check on the received message data, if the check is wrong, then return to 211) in step 21); if the check is correct, then obtain the complete transmitter synchronous clock time stamp information T _tx , and according to the received The message data length is calculated to transmit the signal time length T _signal , and then go to step 23).

In the step 23), obtain the local synchronous time stamp information T _rx and the local timer reading T' _rx when the signal receiving end obtains the synchronous clock time stamp information T _tx at the time of transmitting the signal, and record that the received signal is cached at time The data length Len recorded after τ is calculated according to the sampling rate f _s and the arrival start time T _buffer of the transmitted signal corresponding to this length: And calculate the final propagation delay estimation value Δt according to the following formula: Δt=T _rx +T' _rx -(T _signal +T _buffer )-T _tx .

Due to the adoption of the above technical solutions, the present invention has the following advantages: the present invention uses the signal transmitting end to transmit signals according to certain rules and signal forms, and the signal receiving end processes the received signals according to certain steps, thereby obtaining the estimation of the propagation time delay of the acoustic signal, In the process, both the signal transmitting end and the signal receiving end use a global synchronous clock, and the receiving end additionally uses a local timer with a timing accuracy below the millisecond level, and makes the timer's operating cycle fully synchronized with the global synchronous clock. Because the present invention adopts the above technology, it makes full use of the advantages of wideband hyperbolic FM signal anti-Doppler effect, high time resolution, and m-sequence direct spread spectrum modulation with good anti-noise performance, and can effectively resist the Doppler effect of underwater acoustic channel And the influence of noise, adapt to various complex underwater acoustic channel conditions, and realize reliable acoustic signal propagation delay estimation. The method of the invention has low processing complexity and high reliability. In view of the above reasons, the present invention can be directly applied to fields such as broadcast type multi-user underwater precise navigation and positioning, and underwater acoustic communication.

Description of drawings

Fig. 1 is a schematic diagram of the overall process of the present invention;

Fig. 2 is the transmission signal format in the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As shown in Figure 1, a kind of method of underwater measurement propagation time delay of the present invention, it comprises the following steps:

First, on the signaling end:

11) Obtain the current local synchronous clock timestamp information T _{tx 0} at the signal transmitting end;

12) According to T _{tx 0} and the delayed fixed time t _d , obtain the time stamp information T _tx = T _tx0 +t _d of the time stamp of the synchronous clock at the time of transmitting the signal, perform m-sequence direct spread spectrum modulation on T _tx , and combine the compound hyperbolic FM signal to generate Transmitting signal T _xSignal ; the selection of the above t _d should ensure that the transmitting system has enough time to complete the transmitting signal and preparation of transmitting equipment, which is determined according to the actual system implementation and experience;

Step 12) comprises the following steps:

121) Delay the obtained T _{tx 0} for a fixed time t _d to obtain the time stamp information of the transmitted signal time synchronization clock T _tx =T _{tx 0} +t _d ;

122) Perform m-sequence direct spread spectrum modulation on T _tx information to form synchronous clock timestamp information, wherein the synchronous clock timestamp information of m-sequence direct spread spectrum modulation consists of frame header data cyclic prefix, frame header data, message data and Message data CRC checksum composition;

123) As shown in Figure 2, the synchronous clock timestamp information is combined with the composite hyperbolic FM signal to generate the transmitting terminal transmission signal T _xSignal ;

Wherein, the composite hyperbolic FM signal is formed by the linear superposition of hyperbolic FM signals with two different parameters (parameters are determined according to the available bandwidth of the specific signal transmission and receiving system, and belong to constants known to those skilled in the art, so they will not be described in detail again). become:

S(t)＝S ₁ (t)+S ₂ (t)

in, is the lower limit frequency of one of the hyperbolic FM signals, is the upper limit frequency of the hyperbolic FM signal, is the lower limit frequency of another hyperbolic FM signal, is the upper limit frequency of the hyperbolic FM signal, and T is the duration of a single hyperbolic FM signal.

13) The transmitting end uses the local synchronous clock pulse signal to reach the transition edge (up or down transition) at the T _tx time to trigger the T _xSignal transmission, so as to ensure that the T _xSignal transmission time is the accurate T _tx time;

Second, at the signal receiving end:

21) Carry out signal arrival time and Doppler coefficient estimation according to compound hyperbolic FM signal feature, it comprises the following steps:

211) The receiving end samples the received analog signal according to a certain sampling rate f _s (the selection of the sampling rate is usually determined according to the experience of those skilled in the art, and will not be described in detail here), using S ₁ (t) and S ₂ (t) perform copy correlation processing on the received signal (correlation processing is a common method for those skilled in the art, so it will not be described in detail), and the absolute values of their correlation functions |C ₁ (τ)| and |C ₂ (τ)|;

212) Compare the maximum value of |C ₁ (τ)| and |C ₂ (τ)| with the threshold, if they are not greater than the threshold, return to 211), if both exceed the threshold, it is judged that there may be signal arrival , turn to 213), the above-mentioned threshold is determined according to the signal-to-noise ratio, usually according to the experience of those skilled in the art, and will not be described in detail here;

213) Calculate according to the sampling rate f _s : when |C ₁ (τ)| is the maximum value, the corresponding time t ₁ in the receiving buffer and when |C ₂ (τ)| is the maximum value, the corresponding time in the receiving buffer t ₂ (according to the sampling rate f _s to calculate |C ₁ (τ)| and |C ₂ (τ)| is a method commonly used by those skilled in the art, so it will not be described in detail), the relative Doppler coefficient D is calculated using the following formula and the channel arrival time estimate τ:

214) According to D and τ obtained in 213), carry out m-sequence direct spread spectrum data demodulation to the frame header data, and check whether the frame header data is the expected frame header data (determine the specific situation according to the frame header data value and analyze it specifically), if No, then return to 211), if so, then determine that the signal reaches the moment confirmation, and proceed to 22);

22) Carry out m-sequence direct spread spectrum data demodulation to the message data signal, and obtain the synchronous clock time stamp information T _tx of the transmitted signal moment;

Perform m-sequence direct spread spectrum data demodulation on the message data signal to obtain a complete frame of message data, which includes the CRC checksum of the message data, and use the CRC checksum of the message data to check the received message The data is checked by CRC, and if the check is wrong, return to 211) in step 21); if the check is correct, the complete synchronous clock timestamp information T _tx of the transmitter is obtained, and the transmit signal is calculated according to the length of the received message data Time length T _signal , go to step 23).

23) Obtain the local synchronization time stamp information T _rx , the local timer reading T' _rx and the arrival start time T _buffer of the transmission signal when the signal receiving end obtains the synchronization clock time stamp information T _tx of the transmission signal time, and calculate according to the following formula Obtain the final propagation delay estimation value Δt: Δt=T _rx +T' _rx -(T _signal +T _buffer )-T _tx , the specific process is as follows:

Obtain the time stamp information T _tx of the synchronized clock at the receiving end of the signal at the time of obtaining the transmitted signal

, the local synchronization time stamp information T _rx , the local timer reading T' _rx , and record the data length Len recorded after the received signal cache at this moment after time τ, and calculate the corresponding length of the transmitted signal arrival start according to the sampling rate f _s Time T _buffer :

Calculate the final propagation delay estimate Δt according to the following formula:

Δt＝T _rx +T' _rx -(T _signal +T _buffer )-T _tx (4)

Example 1

First, on the signaling end:

11) Obtain the current local synchronous clock timestamp information T _{tx 0} at the signal transmitting end;

12) According to T _{tx 0} and the delayed fixed time t _d , obtain the synchronous clock time stamp information T _tx = T _{tx 0} +t _d of the transmitted signal, perform m-sequence direct spread spectrum modulation for T _tx , and combine the composite hyperbolic FM signal Generate the transmission signal; the selection of the above t _d should ensure that the transmission system has enough time to complete the transmission signal and the preparation of the transmission equipment, which is determined according to the actual system implementation and experience;

121) Delay the obtained T _{tx 0} for a fixed time t _d to obtain the time stamp information of the transmitted signal time synchronization clock T _tx =T _{tx 0} +t _d ;

In this embodiment, t _d is set to 2 seconds. The selection of t _d should ensure that the transmitting system has enough time to complete the work of transmitting signals and preparing the transmitting equipment, which is determined according to actual system implementation and experience.

122) Perform m-sequence direct spread spectrum modulation on T _tx information to form synchronous clock timestamp information, wherein the synchronous clock timestamp information of m-sequence direct spread spectrum modulation consists of frame header data cyclic prefix, frame header data, message data and Message data CRC checksum composition;

In this embodiment, the m-sequence direct spread spectrum modulation adopts the 7th-order m-sequence, and the generator polynomial is: x ⁷ +x ³ +1; the center frequency of the modulated carrier is 10 kHz, and the single chip time is 0.6 ms, and the chip shaping filter adopts Square wave shaping cascaded 8k-12kHz bandpass filter;

The frame header data cyclic prefix time length is selected as 50ms. The frame header data adopts 1 byte, and the data content is 0xff; the CRC check adopts 8-bit CRC check, and the generating polynomial is: x ⁸ +x ⁵ +x ⁴ +1;

Considering that if the actual sending and receiving distance between two points is less than 5400km, the synchronous clock timestamp information at the transmitting end only needs to include "minute" and "second" information. Therefore, the synchronous clock timestamp information only contains 2 bytes of payload data, One byte is used to represent "minute" information, and one byte is used to represent "second" information;

The synchronization clock time stamp information of the whole m-sequence direct spread spectrum modulation contains 4 bytes of data in total, and the duration is 354.8ms.

The entire transmit signal duration:

T _signal ＝354.8+125＝479.8ms

123) As shown in Figure 2, the synchronous clock timestamp information is combined with the composite hyperbolic FM signal to generate the transmitting terminal transmission signal T _xSignal ;

Wherein, the composite hyperbolic FM signal is formed by the linear superposition of hyperbolic FM signals with two different parameters (parameters are determined according to the available bandwidth of the specific signal transmission and receiving system, and belong to constants known to those skilled in the art, so they will not be described in detail again). become:

S(t)＝S ₁ (t)+S ₂ (t)

in, is the lower limit frequency of one of the hyperbolic FM signals, is the upper limit frequency of the hyperbolic FM signal, is the lower limit frequency of another hyperbolic FM signal, is the upper limit frequency of the hyperbolic FM signal, and T is the duration of a single hyperbolic FM signal.

In this embodiment, the parameters are selected as follows:

13) The transmitting end uses the local synchronous clock pulse signal to reach the transition edge (upward or downward transition) at the T _tx time to trigger the T _xSignal transmission to ensure that the T _xSignal transmission time is the exact T _tx time;

Second, at the signal receiving end:

21) Carry out signal arrival time and Doppler coefficient estimation according to compound hyperbolic FM signal feature, it comprises the following steps:

211) The receiving end samples the received analog signal according to a certain sampling rate f _s (the selection of the sampling rate is usually determined according to the experience of those skilled in the art, and will not be described in detail here), using S ₁ (t) and S ₂ (t) perform copy correlation processing on the received signal (correlation processing is a common method for those skilled in the art, so it will not be described in detail), and the absolute values of their correlation functions |C ₁ (τ)| and |C ₂ (τ)|;

212) Compare the maximum value of |C ₁ (τ)| and |C ₂ (τ)| with the threshold, if they are not greater than the threshold, return to 211), if both exceed the threshold, it is judged that there may be signal arrival , turn to 213), the above-mentioned threshold is determined according to the signal-to-noise ratio, usually according to the experience of those skilled in the art, and will not be described in detail here;

213) Calculated according to the sampling rate f _s : when |C ₁ (τ)| is the maximum value in the receive buffer for

The corresponding time t ₁ and the corresponding time t ₂ in the receiving buffer when |C ₂ (τ)| is the maximum value, (according to

Calculation of |C ₁ (τ)| and |C ₂ (τ)| with sampling rate f _s is a method commonly used by those skilled in the art, so it is no longer

Detailed description) The relative Doppler coefficient D and the channel arrival time estimate τ are calculated using the following formula.

in,

214) According to D and τ obtained in 213), carry out Gold soft spread spectrum data demodulation to the frame header data, and check whether the frame header data is the expected frame header data 0xff (determine the specific situation according to the data value for specific analysis), if not, Then return to 211), if so, then determine that the signal reaches the moment confirmation, and proceed to 22);

22) Perform m-sequence direct spread spectrum data demodulation on the message data signal, and obtain the time stamp information T _tx of the synchronous clock time of the transmitted signal:

Perform m-sequence direct spread spectrum data demodulation on the message data signal to obtain a complete frame of message data, which includes message data CRC checksum;

Use message data CRC checksum to carry out CRC checksum to the received message data, if checksum is not 0, then return step 21) in 211);

If the checksum is 0, obtain the complete synchronous clock time stamp information T _tx of the transmitter, and calculate the time length of the transmitted signal T _signal according to the data length of the received message, and then go to step 23).

23) Obtain the local synchronization time stamp information T _rx and the local timer reading T' _rx when the signal receiving end obtains the synchronization clock time stamp information T _tx at the time of transmitting the signal, and record the data that the received signal is cached after time τ at this time Length Len, according to the sampling rate f _s

Calculate the arrival start time T _buffer of the transmitted signal corresponding to this length:

Calculate the final propagation delay estimate Δt according to the following formula:

Δt＝T _rx +T' _rx -(T _signal +T _buffer )-T _tx (4)

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present invention, and should be included in the scope of the present invention. within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (7)

1. A method for underwater measurement of propagation delay, comprising the following steps: First, on the signaling end: 11) Obtain the current local synchronous clock timestamp information T _tx0 at the signal transmitting end; 12) According to T _tx0 and the delayed fixed time t _d , obtain the synchronous clock time stamp information T _tx = T _tx0 + t _d of the transmitted signal time, perform m-sequence direct spread spectrum modulation on T _tx , and combine the composite hyperbolic FM signal to generate transmission signal _TxSignal ; 13) The signal transmitting end uses the local synchronous clock pulse signal to reach the transition edge at T _tx time to trigger T _xSignal transmission; Second, at the signal receiving end: 21) Estimate the signal arrival time and Doppler coefficient according to the characteristics of the composite hyperbolic FM signal; 22) Perform m-sequence direct spread spectrum data demodulation on the message data signal to obtain the time stamp information T _tx of the synchronous clock at the time of transmitting the signal, and calculate the time length of the transmitting signal T _signal according to the length of the received message data; 23) Obtain the local synchronization time stamp information T _rx , the local timer reading T′ _rx , and the arrival start time T _buffer of the transmission signal when the signal receiving end obtains the synchronization clock time stamp information T _tx of the transmission signal time, and calculate according to the following formula The final propagation delay estimation value Δt is obtained: Δt=T _rx +T′ _rx -(T _signal +T _buffer )-T _tx . 2. the method for a kind of underwater measurement propagation time delay according to claim 1 is characterized in that: in described step 12), the synchronous clock timestamp information of m sequence direct spread spectrum modulation is by frame head data cyclic prefix, Frame header data, message data, and message data CRC checksum. 3. a kind of method for measuring propagation time delay underwater according to claim 2, is characterized in that: described step 12) comprises the following steps: 121) Delay the obtained T _tx0 for a fixed time t _d to obtain the time stamp information of the transmitted signal time synchronization clock T _tx =T _tx0 +t _d ; 122) Perform m-sequence direct spread spectrum modulation on T _tx information to form synchronous clock timestamp information, wherein the synchronous clock timestamp information of m-sequence direct spread spectrum modulation consists of frame header data cyclic prefix, frame header data, message data and Message data CRC checksum composition; 123) Combining the synchronous clock time stamp information with the complex hyperbolic FM signal to generate a transmitting signal T _xSignal at the transmitting end. 4. the method for a kind of underwater measurement propagation time delay according to claim 3, is characterized in that: the complex hyperbolic FM signal in described step 123), it is linearly superimposed by the hyperbolic FM signal of 2 different parameters into: S(t)＝S ₁ (t)+S ₂ (t) in, is the lower limit frequency of one of the hyperbolic FM signals, is the upper limit frequency of the hyperbolic FM signal, is the lower limit frequency of another hyperbolic FM signal, is the upper limit frequency of the hyperbolic FM signal, and T is the duration of a single hyperbolic FM signal. 5. a kind of method for measuring propagation time delay underwater according to claim 4, is characterized in that: described step 21) comprises the following steps: 211) The receiving end samples the received analog signal according to a certain sampling rate f _s , uses S ₁ (t) and S ₂ (t) to perform copy correlation processing on the received signal, and obtains the absolute value of the correlation function |C ₁ (τ)| and |C ₂ (τ)|; 212) Compare the maximum values of |C ₁ (τ)| and |C ₂ (τ)| with the threshold, if they are not greater than the threshold, return to step 211); Signal arrival, proceed to step 213); 213) Calculate according to the sampling rate f _s : when |C ₁ (τ)| is the maximum value, the corresponding time t ₁ in the receiving buffer and when |C ₂ (τ)| is the maximum value, the corresponding time in the receiving buffer t ₂ , use the following formulas to calculate the relative Doppler coefficient D and the channel arrival time estimate τ: $\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; =</span>\frac{\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$ $\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}$ 214) According to the obtained D and τ, the m-sequence direct spread spectrum data demodulation is carried out to the frame header data, and whether the frame header data is the expected frame header data, if not, then return to step 211), if so, then it is judged that the signal reaches Time confirmation, go to step 22). 6. the method for a kind of underwater measurement propagation time delay according to claim 5, is characterized in that: in described step 22), carry out m sequence direct spread spectrum data demodulation at message data signal, obtain complete one Frame message data, the message data includes the message data CRC checksum, use the message data CRC checksum to carry out the CRC checksum to the received message data, if the check is wrong, then return to 211 in step 21) ); if the verification is correct, obtain the complete synchronous clock time stamp information T _tx of the transmitter, and calculate the time length of the transmitted signal T _signal according to the data length of the received message, and then go to step 23). 7. The method for underwater measurement of propagation time delay according to claim 6, characterized in that: in the step 23), the local time stamp information T tx of the signal receiving end when obtaining the time synchronization clock time stamp information T _tx of the transmitted signal is obtained. Synchronize the time stamp information T _rx and the local timer reading T′ _rx , and record the data length Len recorded after the received signal is buffered after time τ at this moment, and calculate the arrival start time T _buffer of the transmitted signal corresponding to this length according to the sampling rate f _s : And calculate the final propagation delay estimation value Δt according to the following formula: Δt=T _rx +T′ _rx -(T _signal +T _buffer )-T _tx .