CN114666030B - Hybrid underground signal encoding and decoding method - Google Patents
Hybrid underground signal encoding and decoding method Download PDFInfo
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- CN114666030B CN114666030B CN202210576694.8A CN202210576694A CN114666030B CN 114666030 B CN114666030 B CN 114666030B CN 202210576694 A CN202210576694 A CN 202210576694A CN 114666030 B CN114666030 B CN 114666030B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0016—Arrangements for synchronising receiver with transmitter correction of synchronization errors
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0054—Detection of the synchronisation error by features other than the received signal transition
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
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Abstract
The invention provides a hybrid downhole signal encoding and decoding method, which comprises the following steps: the underground transmitter adds a signal synchronization head at the front end of the modulated acquisition signal and transmits the acquisition signal to a ground receiver in an electromagnetic wave mode; the ground receiver calculates the cross correlation coefficient of the acquired signal and the preset code value of each type of synchronous head, and judges whether the acquired signal is a synchronous head or not based on the magnitude relation between the cross correlation coefficient and the threshold coefficient value of the corresponding type; if the synchronous head exists, determining a corresponding demodulation mode according to the type of the synchronous head and system setting parameters; and demodulating the acquired signal based on a demodulation mode. The invention distinguishes signal types by adding a synchronous head in front of information, identifies the type of the synchronous head and positions signals by setting a synchronous head detection area in a ground receiver and calculating cross correlation coefficients, and demodulates the acquired signals by selecting corresponding demodulation modes according to the type of the synchronous head, thereby giving consideration to both real-time performance and high precision of the signals.
Description
Technical Field
The invention relates to the field of communication, in particular to a hybrid underground signal encoding and decoding method.
Background
At present, the intelligent degree of the petroleum field in China is gradually improved, and a large amount of underground equipment is changed from a traditional wired communication mode to a wireless communication mode. At present, three types of underground wireless communication modes are mainstream, wherein electromagnetic wave communication is developed rapidly in recent years, and underground communication systems are developed by multiple companies based on electromagnetic waves. However, electromagnetic waves need to pass through a plurality of kilometers of stratum from the underground to the ground, and are affected by noise in the stratum and a complex series-parallel impedance network, so that distortion is very serious when signals are transmitted to the ground, the contents of the signals can be decoded only after filtering treatment, the impedance network has a complex structure, a transfer function of the impedance network is related to various factors such as an oil well structure and soil resistivity, the difficulty of signal filtering is increased, and a traditional filtering mode cannot be suitable for complex underground conditions.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a hybrid underground signal coding and decoding method, which comprises the following steps:
adding a signal synchronization head at the front end of the modulated acquisition signal by the underground transmitter, and transmitting the acquisition signal to a ground receiver in an electromagnetic wave mode;
the ground receiver calculates the cross-correlation coefficient of the acquired signal and the preset code value of each type of synchronous head, and judges whether the acquired signal in the identification area is the synchronous head or not based on the magnitude relation between the cross-correlation coefficient and the threshold coefficient value of the corresponding type;
if the synchronous head exists, determining a corresponding demodulation mode according to the type of the synchronous head and system setting parameters;
and demodulating the acquired signal based on the demodulation mode.
On the basis of the technical scheme, the invention can be improved as follows.
Optionally, the adding, by the downhole transmitter, a signal synchronization head to the front end of the modulated acquisition signal includes:
according to the type of the collected signals, a corresponding signal synchronization head is added at the front end of the collected signals by the underground transmitter, the signal synchronization head comprises a code value corresponding to the type of the collected signals, the type of the collected signals is an emergency type or a non-emergency type, and the length of the signal synchronization head of the emergency type is smaller than that of the signal synchronization head of the non-emergency type.
Optionally, the calculating, by the ground receiver, a cross-correlation coefficient of the preset code value between the acquired signal and each type of synchronization header, and determining whether the acquired signal currently in the identification area is a synchronization header based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of a corresponding type, includes:
the ground receiver calculates a first cross correlation coefficient between the acquired signal and a preset code value of an emergency type synchronous head and a second cross correlation coefficient between the acquired signal and a preset code value of a non-emergency type synchronous head;
when the first cross-correlation coefficient is less than an emergency threshold coefficient value, the acquisition signal is not a synchronization header; or, when the second cross-correlation coefficient is less than a non-emergency threshold coefficient value, the acquisition signal is not a synchronization header;
when the first cross-correlation coefficient is larger than an emergency threshold coefficient value, the acquired signal is a synchronous head, and the type of the acquired signal is an emergency type; or when the second cross-correlation coefficient is larger than a non-emergency threshold coefficient value, the acquisition signal is a synchronization header, and the type of the acquisition signal is a non-emergency type.
Optionally, the ground receiver includes a signal buffer, the signal buffer includes a first synchronization header detection area and a second synchronization header detection area, and the length of the signal buffer satisfies the following condition:
and when the signal synchronization head of the acquired signal enters the second synchronization head detection area, the whole acquired signal should completely enter the signal buffer area.
Optionally, the calculating, by the ground receiver, a cross-correlation coefficient of the preset code value between the acquired signal and each type of synchronization header, and determining whether the acquired signal currently in the identification area is a synchronization header based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of a corresponding type, includes:
after a first synchronous head detection area of a signal cache area of a ground receiver receives an acquisition signal, judging whether the acquisition signal is a synchronous head or not, and if not, waiting for detecting a next section of acquisition signal;
if the acquired signal is judged to be an emergency type signal, demodulating the acquired signal in real time based on a real-time demodulation mode;
and if the acquired signal is judged to be a non-emergency type signal, entering a second synchronous head detection area for detection, and demodulating the acquired signal based on a delay demodulation mode when the second synchronous head detection area detects the acquired signal to be the non-emergency type signal again.
Optionally, the formula for calculating the cross-correlation coefficient between the acquired signal and the preset code value of each type of synchronization head is as follows:
wherein
In order to acquire the signal(s),
a preset code value for each type of sync header, N is the length of the acquired signal,
the value range of (1) is 0-1.
Optionally, the emergency threshold coefficient value and the non-emergency threshold coefficient value are calculated as follows:
the downhole transmitter sends a known correction code to a surface receiver, and the surface receiver calculates a third cross-correlation coefficient between the received correction code and the original known correction code;
determining the emergency threshold coefficient value and the non-emergency threshold coefficient value based on the third cross-correlation coefficient, wherein the emergency threshold coefficient value is less than the non-emergency threshold coefficient value.
Optionally, the determining, according to the type of the synchronization header and the system setting parameter, a corresponding demodulation manner includes:
if the type of the synchronous head is an emergency type, determining that the demodulation mode is a real-time demodulation mode: performing real-time filtering by adopting Butterworth or Chebyshev low-pass filtering to obtain a real-time acquisition signal;
if the type of the synchronization head is a non-emergency type, determining that the demodulation mode is a delay demodulation mode: waiting for the signal acquisition to be finished, and obtaining a high-precision delay signal by using an ideal low-pass filter;
if the system is set to a hybrid filtering demodulation mode, a Butterworth or Chebyshev filter is used for obtaining a real-time acquisition signal, and after the real-time acquisition signal is received, an ideal low-pass filter is used for obtaining a high-precision signal to replace the previously obtained real-time acquisition signal.
Optionally, the method further includes:
the ground receiver calculates the phase-frequency correspondence and amplitude-frequency response of the formation impedance network at the moment according to the received correction codes;
correspondingly, demodulating the collected signal based on the demodulation mode includes:
and carrying out phase compensation and amplitude compensation on the acquired signals based on the demodulation mode.
The invention provides a hybrid underground signal coding and decoding method, which is characterized in that a synchronous head is added at the front part of information to distinguish signal types, a synchronous head detection area is arranged on a ground receiver, cross-correlation coefficients are calculated to identify the synchronous head types and position signals, a corresponding demodulation mode is selected according to the synchronous head types to demodulate collected signals, and the real-time performance and the high precision of the signals are considered.
Drawings
FIG. 1 is a flow chart of a hybrid downhole signal encoding and decoding method provided by the present invention;
FIG. 2 is a schematic diagram of a signal buffer;
FIG. 3 is a schematic overall flow chart of a hybrid downhole signal encoding and decoding method.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Example one
A hybrid downhole encoding and decoding method, see fig. 1, the method essentially comprising the steps of:
and S1, adding a signal synchronization head at the front end of the modulated acquisition signal by the underground transmitter, and sending the acquisition signal to a surface receiver in an electromagnetic wave mode.
By way of example, the downhole transmitter adds a signal synchronization head to the front end of the modulated acquisition signal, and the method comprises the following steps: according to the type of the collected signals, a corresponding signal synchronization head is added at the front end of the collected signals by the underground transmitter, the signal synchronization head comprises a code value corresponding to the type of the collected signals, the type of the collected signals is an emergency type or a non-emergency type, and the length of the signal synchronization head of the emergency type is smaller than that of the signal synchronization head of the non-emergency type.
It can be understood that the downhole transmitter may be a downhole sensor, and the downhole sensor modulates the data acquired by the downhole sensor in a frequency modulation or amplitude modulation manner, and then transmits the signal to the ground in an electromagnetic wave manner after adding a signal synchronization head to the front end of the modulated acquired signal.
The signal synchronization head comprises a code value capable of representing the type of the acquired signal, wherein the corresponding relation between the code value and the type of the signal is shown in the following table 1.
TABLE 1 correspondence table of coding values and signal types
According to table 1, for example, when the signal collected by the sensor is a non-emergency type signal, the encoding values such as 000, 001, and 010 may be set in the synchronization head, if the signal collected by the downhole sensor is an air pressure signal and is an emergency signal, the encoding value 00 may be set in the synchronization head, and after the encoding value is set in the synchronization head at the front end of the collected signal, the collected signal is sent to the ground.
The underground transmitter adds a corresponding synchronization head according to the signal type, adds an emergency signal synchronization head when the signal is an emergency signal, and adds a non-emergency signal synchronization head when the signal is a non-emergency signal. The emergency signal synchronization header should be shorter than the non-emergency signal synchronization header to increase the demodulation speed of the emergency signal. The length of the signal synchronization head can be self-defined, and can contain information or be only used for positioning the signal position without any meaning, preferably, in order to improve the calculation efficiency of the system, the length of the signal synchronization head should be as short as possible on the premise of ensuring that the synchronization head plays its corresponding role. Specifically, in this embodiment, the emergency signal synchronization header takes 2 bits, and the non-emergency signal synchronization header takes 3 bits, and the code value table is shown in table 1 above.
And S2, the ground receiver calculates the cross correlation coefficient of the acquired signal and the preset code value of each type of synchronous head, and judges whether the acquired signal in the identification area is the synchronous head or not based on the magnitude relation between the cross correlation coefficient and the threshold coefficient value of the corresponding type.
And S3, if the synchronization header exists, determining a corresponding demodulation mode according to the type of the synchronization header and the system setting parameters.
It can be understood that, after receiving the collected signal, the ground receiver calculates a cross-correlation coefficient between the collected signal and preset code values of different types of synchronization heads, and determines whether the collected signal currently in the identification area is a synchronization head and the type of the collected signal, that is, whether the collected signal is an emergency type signal or a non-emergency type signal, based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of a corresponding type.
As an embodiment, the formula for calculating the cross-correlation coefficient between the acquired signal and the preset code value of each type of synchronization head is as follows:
wherein
In order to acquire the signal(s),
a preset code value for each type of sync header, N is the length of the acquired signal,
the value range of (1) is 0-1.
As an embodiment, the ground receiver calculates a cross-correlation coefficient of a preset code value of the acquired signal and each type of synchronization header, and determines whether the acquired signal currently in the identification area is a synchronization header based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of the corresponding type, including: the ground receiver calculates a first cross-correlation coefficient between the acquired signal and a preset code value of an emergency type synchronous head and a second cross-correlation coefficient between the acquired signal and a preset code value of a non-emergency type synchronous head; when the first cross-correlation coefficient is less than the emergency threshold coefficient value, the acquired signal is not a synchronization header; or when the second cross correlation coefficient is smaller than a non-emergency threshold coefficient value, the acquired signal is not a synchronous head; when the first cross-correlation coefficient is larger than the emergency threshold coefficient value, the acquired signal is a synchronous head, and the type of the acquired signal is an emergency type; or when the second cross-correlation coefficient is larger than the non-emergency threshold coefficient value, the acquired signal is a synchronous head, and the type of the acquired signal is a non-emergency type.
It can be understood that, according to table 1 above, the signals are mainly divided into two types, an emergency type and a non-emergency type, and according to table 1 above, there are four synchronization header preset code values of the emergency type and four synchronization header preset code values of the non-emergency type. Then, the ground receiver calculates cross-correlation coefficients of the acquired signals and each preset code value corresponding to the emergency type, four first cross-correlation coefficients are obtained through calculation, the magnitude relation between each first cross-correlation coefficient and the emergency threshold coefficient value is compared, if the four first cross-correlation coefficients are all smaller than the emergency threshold coefficient value, the acquired signals are not synchronous heads, and next section of signals need to be detected; if one of the first cross correlation coefficients is greater than the emergency threshold coefficient value, the acquisition signal is a synchronization header and the acquisition signal type is an emergency type.
Similarly, the ground receiver calculates cross-correlation coefficients of the acquired signals and each preset code value corresponding to the non-emergency type, four second cross-correlation coefficients are obtained through calculation, the magnitude relation between each second cross-correlation coefficient and the non-emergency threshold coefficient value is compared, if the four second cross-correlation coefficients are all smaller than the non-emergency threshold coefficient value, the acquired signals are not synchronous heads, and the next section of signals need to be detected; if one of the second cross correlation coefficients is greater than the non-emergency threshold coefficient value, the acquisition signal is a sync header and the acquisition signal type is a non-emergency type.
Wherein the emergency threshold coefficient value and the non-emergency threshold coefficient value are calculated by: the downhole transmitter sends a known correction code to a surface receiver, and the surface receiver calculates a third cross-correlation coefficient between the received correction code and the original known correction code; determining the emergency threshold coefficient value and the non-emergency threshold coefficient value based on the third cross-correlation coefficient, wherein the emergency threshold coefficient value is less than the non-emergency threshold coefficient value.
It will be appreciated that the threshold coefficient value should be calculated from the received results of the calibration code, the degree of signal attenuation is related to the well structure and the soil resistivity, and the signal will have phase and amplitude variations during transmission. The downhole transmitter transmits a known calibration code prior to transmission of the signal, and the surface receiver receives the code and calculates the calibration of the received code and the original transmissionThe cross-correlation coefficients being encoded to calculate threshold coefficients for the current use, including an urgent threshold coefficient value and a non-urgent threshold coefficient value, and in particular, in this embodiment, the urgent threshold coefficient value
Taking a value of 0.7, a non-emergency threshold coefficient
0.9 is taken.
Wherein, as the embodiment, including the signal buffer zone in the ground receiver, the signal buffer zone includes first synchronization head detection area and second synchronization head detection area, and the length in signal buffer zone satisfies the following condition: and when the signal synchronization head of the acquired signal enters the second synchronization head detection area, the whole acquired signal should completely enter the signal buffer area. Preferably, the signal buffer length should be set aside with a margin in case that the above condition is satisfied, so as to prevent data loss caused by signal truncation.
It can be understood that, after the ground receiver receives the collected signal, the collected signal is stored in the signal buffer area, and the synchronous head detection area of the signal buffer area detects the collected signal.
As an embodiment, the ground receiver calculates a cross-correlation coefficient of a preset code value of each type of synchronization header and a collected signal, and determines whether the collected signal currently in an identification area is a synchronization header based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of a corresponding type, including: after a first synchronous head detection area of a signal cache area of a ground receiver receives an acquisition signal, judging whether the acquisition signal is a synchronous head or not, and if not, waiting for detecting a next section of acquisition signal; if the acquired signal is judged to be an emergency type signal, demodulating the acquired signal in real time based on a real-time demodulation mode; and if the acquired signal is judged to be a non-emergency type signal, entering a second synchronous head detection area for detection, and demodulating the acquired signal based on a delay demodulation mode when the second synchronous head detection area detects the acquired signal to be the non-emergency type signal again.
It can be understood that the signal buffer of the terrestrial receiver includes a first synchronization header detection area and a second synchronization header detection area, and performs second synchronization header detection on the received acquisition signal. Specifically, when the first synchronous head detection area detects that the acquired signal is not a synchronous head, waiting for the detection of the next section of signal; if the first synchronous head detection area detects that the collected signals are emergency type signals, immediately demodulating the collected signals in a real-time demodulation mode; if the first synchronous head detection area detects that the collected signals are non-emergency type signals, waiting for a period of time, carrying out second synchronous head detection, and if the collected signals are detected again and still are non-emergency type signals, demodulating the collected signals in a delay demodulation mode.
S4, demodulating the collected signal based on the demodulation mode.
As an embodiment, determining a corresponding demodulation mode according to the type of the synchronization header and the system setting parameters includes: if the type of the synchronous head is an emergency type, determining that the demodulation mode is a real-time demodulation mode: performing real-time filtering by adopting Butterworth or Chebyshev low-pass filtering to obtain a real-time acquisition signal; if the type of the synchronous head is a non-emergency type, determining that the demodulation mode is a delay demodulation mode: waiting for the signal acquisition to be finished, and obtaining a high-precision delay signal by using an ideal low-pass filter; if the system is set to a hybrid filtering demodulation mode, a Butterworth or Chebyshev filter is used for obtaining a real-time acquisition signal, and after the real-time acquisition signal is received, an ideal low-pass filter is used for obtaining a high-precision signal to replace the previously obtained real-time acquisition signal.
It can be understood that whether the collected signal is an emergency signal or a non-emergency signal is detected, and if the collected signal is an emergency signal, a real-time demodulation mode is adopted for demodulation; if the signal is a non-emergency signal, a delay demodulation mode is adopted for demodulation. However, if the system is set to be mixed and filtered, the acquired signal is demodulated according to the filtering demodulation mode set by the system whether the acquired signal is an emergency signal or a non-emergency signal.
It should be noted that, the ground receiver calculates the phase-frequency correspondence and amplitude-frequency response of the formation impedance network at this time according to the received correction code; and in the subsequent demodulation process, carrying out phase compensation and amplitude compensation on the acquired signals.
Example two
A hybrid downhole signal encoding and decoding method, referring to fig. 3, the main process of the method comprises: the underground transmitter sends a collected signal containing a signal synchronization head to a ground receiver, the ground receiver calculates cross-correlation coefficients between the collected signal and preset code values of each type of synchronization head after receiving the collected signal, and determines whether the collected signal is a synchronization head and the type of the collected signal according to the magnitude relation between the cross-correlation coefficients and the threshold coefficient values. And demodulating the acquired signals by adopting a corresponding signal demodulation mode according to the type of the acquired signals.
The invention provides a hybrid underground signal coding and decoding method, which determines the attenuation amplitude of a formation impedance network through a correction code and determines a threshold coefficient of a signal according to the attenuation amplitude, calculates the amplitude-frequency response and the phase-frequency response of the formation impedance network by comparing the received correction code with an original code, and performs amplitude compensation and phase compensation on the received signal. The signal types are distinguished by adding a synchronous head at the front part of the information, the synchronous head is identified and the signal is positioned by setting a synchronous head detection area at a ground receiver and calculating a cross-correlation coefficient, and finally, the real-time performance and the high precision of the signal are considered by setting a buffer area.
It should be noted that, in the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to relevant descriptions of other embodiments for parts that are not described in detail in a certain embodiment.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (9)
1. A hybrid downhole signal encoding and decoding method, comprising:
adding a signal synchronization head at the front end of the modulated acquisition signal by the underground transmitter, and transmitting the acquisition signal to a ground receiver in an electromagnetic wave mode;
the ground receiver calculates the cross-correlation coefficient of the acquired signal and the preset code value of each type of synchronous head, and judges whether the acquired signal in the identification area is the synchronous head or not based on the magnitude relation between the cross-correlation coefficient and the threshold coefficient value of the corresponding type;
if the synchronous head exists, determining a corresponding demodulation mode according to the type of the synchronous head and system setting parameters;
and demodulating the acquired signal based on the demodulation mode.
2. The hybrid downhole signal encoding and decoding method of claim 1, wherein the downhole transmitter adds a signal synchronization head to a front end of the modulated acquisition signal, comprising:
according to the type of the acquired signal, a corresponding signal synchronization head is added to the front end of the acquired signal by an underground transmitter, the signal synchronization head comprises a code value corresponding to the type of the acquired signal, the type of the acquired signal is an emergency type or a non-emergency type, and the length of the signal synchronization head of the emergency type is smaller than that of the signal synchronization head of the non-emergency type.
3. A hybrid downhole signal encoding and decoding method according to claim 1 or 2, wherein the surface receiver calculates a cross-correlation coefficient of the collected signal with a preset code value of each type of sync head, and determines whether the collected signal currently in the identification area is a sync head based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of the corresponding type, including:
the ground receiver calculates a first cross-correlation coefficient between the acquired signal and a preset code value of an emergency type synchronous head and a second cross-correlation coefficient between the acquired signal and a preset code value of a non-emergency type synchronous head;
when the first cross-correlation coefficient is less than an emergency threshold coefficient value, the acquisition signal is not a synchronization header; or, when the second cross-correlation coefficient is less than a non-emergency threshold coefficient value, the acquisition signal is not a synchronization header;
when the first cross-correlation coefficient is larger than an emergency threshold coefficient value, the acquired signal is a synchronous head, and the type of the acquired signal is an emergency type; or when the second cross-correlation coefficient is larger than a non-emergency threshold coefficient value, the acquisition signal is a synchronization header, and the type of the acquisition signal is a non-emergency type.
4. The hybrid downhole signal encoding and decoding method of claim 3, wherein the surface receiver comprises a signal buffer, the signal buffer comprises a first sync header detection area and a second sync header detection area, and the length of the signal buffer satisfies the following condition:
and when the signal synchronization head of the acquired signal enters the second synchronization head detection area, the whole acquired signal should completely enter the signal buffer area.
5. The hybrid downhole signal encoding and decoding method of claim 4, wherein the surface receiver calculates a cross-correlation coefficient between the collected signal and a preset code value of each type of sync head, and determines whether the collected signal currently in an identification area is a sync head based on a magnitude relationship between the cross-correlation coefficient and a threshold coefficient value of a corresponding type, comprising:
after a first synchronous head detection area of a signal cache area of a ground receiver receives an acquisition signal, judging whether the acquisition signal is a synchronous head or not, and waiting for detecting a next section of acquisition signal if the acquisition signal is not the synchronous head;
if the acquired signal is judged to be an emergency type signal, demodulating the acquired signal in real time based on a real-time demodulation mode;
and if the acquired signal is judged to be a non-emergency type signal, entering a second synchronous head detection area for detection, and demodulating the acquired signal based on a delay demodulation mode when the second synchronous head detection area detects the acquired signal to be the non-emergency type signal again.
6. A hybrid downhole signal encoding and decoding method according to claim 1, wherein the cross-correlation coefficient of the acquired signal with the preset code value for each type of sync head is calculated by the formula:
wherein
In order to acquire the signal(s),
for each type of synchronisationA preset code value of the head, N is the length of the acquired signal,
the value range of (1) is 0-1.
7. A hybrid downhole signal encoding and decoding method according to claim 3, wherein the emergency threshold coefficient value and the non-emergency threshold coefficient value are calculated by:
the downhole transmitter sends a known correction code to a surface receiver, and the surface receiver calculates a third cross-correlation coefficient between the received correction code and the original known correction code;
determining the emergency threshold coefficient value and the non-emergency threshold coefficient value based on the third cross-correlation coefficient, wherein the emergency threshold coefficient value is less than the non-emergency threshold coefficient value.
8. The hybrid downhole signal encoding and decoding method according to claim 1 or 5, wherein the determining the corresponding demodulation mode according to the type of the synchronization head and the system setting parameter comprises:
if the type of the synchronous head is an emergency type, determining that the demodulation mode is a real-time demodulation mode: performing real-time filtering by adopting Butterworth or Chebyshev low-pass filtering to obtain a real-time acquisition signal;
if the type of the synchronization head is a non-emergency type, determining that the demodulation mode is a delay demodulation mode: waiting for the signal acquisition to be finished, and obtaining a high-precision delay signal by using an ideal low-pass filter;
if the system is set to a hybrid filtering demodulation mode, a Butterworth or Chebyshev filter is used for obtaining a real-time acquisition signal, and after the real-time acquisition signal is received, an ideal low-pass filter is used for obtaining a high-precision signal to replace the previously obtained real-time acquisition signal.
9. The hybrid downhole signal encoding and decoding method of claim 7, further comprising:
the ground receiver calculates the phase-frequency correspondence and amplitude-frequency response of the formation impedance network at the moment according to the received correction codes;
correspondingly, demodulating the collected signal based on the demodulation mode includes:
and carrying out phase compensation and amplitude compensation on the acquired signals based on the demodulation mode.
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