CN111208538B - Method and device for demodulating text - Google Patents
Method and device for demodulating text Download PDFInfo
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- CN111208538B CN111208538B CN201811393126.4A CN201811393126A CN111208538B CN 111208538 B CN111208538 B CN 111208538B CN 201811393126 A CN201811393126 A CN 201811393126A CN 111208538 B CN111208538 B CN 111208538B
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- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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Abstract
The invention provides a method and a device for demodulating a telegraph text, wherein the method comprises the following steps: acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio, and storing the differential phase value and the maximum likelihood ratio into a Buffer; acquiring a first message of front M bits from the Buffer; when the first message does not pass the preset check, accumulating the M-bit message after the interval of the preset time and the first message to obtain a second message, and outputting the message of the second message; on the other hand, the reliability of the accumulated text judgment is improved through a probability statistical method of the maximum likelihood ratio, the sensitivity of text decoding is further improved, and the problem of inaccurate positioning caused by frequent errors of text demodulation in the related technology is solved.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for demodulating a text message.
Background
The GPS receiver is a device which obtains the transmission time of satellite signals, the position of the satellite in an ECEF (Earth-center-Earth-fixed coordinate system) coordinate system and the pseudo range between the satellite and the receiver by receiving DSSS (direct sequence spread Spectrum) spread spectrum ranging signals of a plurality of satellites (not less than 4 satellites) in the sky, continuously tracking the signals of the satellites, decoding the telegraph messages transmitted by the satellites, and resolving to obtain the coordinate values of the receiver in the ECEF. Under a normal outdoor open environment, a receiver needs about 6 seconds of time decoding TOW (time in week) after completing satellite capturing and tracking to complete signal frame synchronization acquisition and transmission time, then 18-30 seconds of time decoding satellite text information is needed, and TTFF (time to first fix) is generally more than 30 seconds.
In the aspect of technical implementation, a receiver of the pseudo-range earth surface receives and demodulates navigation message data modulated on a carrier signal through a capturing and tracking module. The total number of the set of navigation messages is 5 subframes, each subframe consumes 6s, and one frame consumes 30s in total, namely the set of navigation messages are broadcasted circularly in a period of 30 s. The 1 st, 2 nd and 3 rd sub-frames contain ephemeris information of precise orbit parameters, and the periods are the same; 4, 5 sub-frame contains the almanac information of the general orbit parameter, and the operation is repeated once in 12.5 minutes; the accurate position of the satellite at the current moment in the ECEF coordinate system can be calculated only after the 1 st, 2 nd and 3 rd sub-frames are correctly decoded, and the accurate position of the receiver can be further calculated.
Therefore, obtaining correct navigation message data is theoretically a key target of cold start of a receiver, the user position can be further calculated only by completing demodulation of the navigation message, and incomplete and wrong navigation messages cannot obtain accurate user positions and positioning fails.
The traditional receiver can directly use the demodulation result output by the tracking module for message decoding, or periodically accumulate the decoded message codes, so that the sensitivity of message demodulation can not be improved in principle, and under a complex environment, the situation of message decoding error or incomplete decoding still occurs at a high probability, so that accurate positioning information can not be acquired.
Aiming at the problem of inaccurate positioning caused by frequent errors of text demodulation in the related art, no effective solution exists at present.
Disclosure of Invention
The method and the device for demodulating the text can solve the problem of inaccurate positioning caused by frequent errors in text demodulation in the related art.
According to an embodiment of the present invention, there is provided a method of demodulating a text, including: acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio, and storing the differential phase value and the maximum likelihood ratio into a Buffer; acquiring a first message of front M bits from the Buffer, wherein M is an integer; and when the first message does not pass the preset verification, accumulating the M-bit messages after the preset time interval with the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, including the first message, and N is an integer greater than or equal to M.
Optionally, the obtaining a differential phase value corresponding to a phase value of a message to be demodulated includes:
acquiring an integral value of the message to be demodulated, wherein the integral value comprises a pair of in-phase I value and quadrature Q value;
acquiring a phase value corresponding to the integral value according to the orthogonal Q value and the in-phase I value;
aiming at the output of a frequency locking loop FLL, acquiring the differential phase value according to the difference of the front phase value and the rear phase value; determining the phase value as the differential phase value for a Phase Locked Loop (PLL) output.
Optionally, the obtaining a maximum likelihood ratio value corresponding to a phase value of a message to be demodulated includes:
when the number of the differential phase values stored in the Buffer is larger than a threshold value, acquiring a standard deviation according to the phase values of 6 epochs;
acquiring a row number according to the absolute value of the current differential phase value, acquiring a column number according to the standard deviation, and inquiring a maximum likelihood table by using the row number and the column number to acquire a maximum likelihood ratio;
and assigning the polarities of the message values of the 6 epochs to the corresponding maximum likelihood ratios, wherein the phase change of the message values is determined according to the differential phase of each epoch, and the polarity of the message values is determined.
Optionally, before obtaining the first message with M bits before in the Buffer, the method further includes:
detecting whether the IODE of the current satellite age data event changes or not;
and emptying the cache Buffer when the age data event IODE changes.
Optionally, when the age data event IODE is not changed, the method further comprises:
performing parity check on the M-bit first text;
outputting the text word of the first text when the parity check is passed; and when the parity check is not passed, accumulating the M-bit text after the interval of preset time and the first text to obtain a second text, determining the polarity of the second text according to the accumulated value of the maximum likelihood ratio of the N-bit text, and outputting the text of the second text.
Optionally, the determining the polarity of the second message according to the accumulated value of the maximum likelihood ratio of the N-bit messages includes:
accumulating the maximum likelihood ratio of the N-bit message to obtain a phase-locked loop receiver PLLR;
when the PLLR is greater than 0, determining that the bit polarity of the second text is positive; and when the PLLR is less than 0, determining that the bit polarity of the second text is negative.
Optionally, after the obtaining a second message after accumulating the M-bit message separated by the preset time with the first message, the method further includes:
performing parity check on the second text;
when the second message does not pass the parity check, adding 1 to a counter, and executing a repeated accumulation process on the second message until the next output message passes the parity check, or the Buffer is cached when the counter exceeds a threshold value; and outputting the electric text of the second text when the second text passes the parity check.
According to another embodiment of the present invention, there is also provided a device for demodulating a text, including: the device comprises a first acquisition module, a second acquisition module and a Buffer, wherein the first acquisition module is used for acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio value, and storing the differential phase value and the maximum likelihood ratio value into the Buffer; a second obtaining module, configured to obtain a first message with M bits before in the Buffer, where M is an integer; and the output module is used for accumulating the M-bit messages after the interval of the preset time and the first messages to obtain second messages and outputting the messages of the second messages when the first messages do not pass the preset verification, wherein the polarity of the second messages is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, the N-bit messages comprise the first messages, and N is an integer greater than or equal to M.
According to another embodiment of the present invention, there is also provided a storage medium having a computer program stored therein, wherein the computer program is configured to perform the method of any one of the above embodiments when executed.
According to another embodiment of the present invention, there is also provided an electronic apparatus, including a memory and a processor, the memory having a computer program stored therein, the processor being configured to execute the computer program to perform the method of any one of the above embodiments.
The method, the device and the user equipment for demodulating the telegraph text acquire a differential phase value corresponding to a phase value of the telegraph text to be demodulated and a corresponding maximum likelihood ratio value, and store the differential phase value and the maximum likelihood ratio value into a Buffer; acquiring a first message of front M bits from the Buffer, wherein M is an integer; when the first message does not pass the preset verification, accumulating M-bit messages after the interval of the preset time and the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of N-bit messages, including the first message, N is an integer greater than or equal to M; on the other hand, the reliability of the accumulated text judgment is improved through a probability statistical method of the maximum likelihood ratio, the sensitivity of text decoding is further improved, and the problem of inaccurate positioning caused by frequent errors of text demodulation in the related technology is solved.
Drawings
FIG. 1 is a flow chart of a method for demodulating a message according to an embodiment of the present invention;
FIG. 2 is a navigation message structure diagram of a GPS message according to another embodiment of the present invention;
FIG. 3 is a block diagram of an apparatus for text decoding flow and raw maximum likelihood ratio acquisition according to another embodiment of the present invention;
FIG. 4 is a table diagram of maximum likelihood ratios for an 18 row, 9 column format used in accordance with another example of the present invention;
fig. 5 is a block diagram of an apparatus for text interface verification and maximum likelihood ratio accumulation according to another embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the present invention provides a method for demodulating a text, and fig. 1 is a flowchart of a method for demodulating a text according to an embodiment of the present invention, and as shown in fig. 1, the method includes:
s11, acquiring a differential phase value corresponding to the phase value of the message to be demodulated and a corresponding maximum likelihood ratio, and storing the differential phase value and the maximum likelihood ratio into a Buffer;
s12, obtaining a first message with M bits before in the Buffer, wherein M is an integer;
s13, when the first message does not pass the preset verification, accumulating the M-bit messages separated by the preset time with the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, the N-bit messages include the first message, and N is an integer greater than or equal to M.
Through the steps, a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio are obtained, and the differential phase value and the maximum likelihood ratio are stored in a Buffer; acquiring a first message of front M bits from the Buffer, wherein M is an integer; when the first message does not pass the preset verification, accumulating M-bit messages after the interval of the preset time and the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of N-bit messages, including the first message, N is an integer greater than or equal to M; on the other hand, the reliability of the accumulated text judgment is improved through a probability statistical method of the maximum likelihood ratio, the sensitivity of text decoding is further improved, and the problem of inaccurate positioning caused by frequent errors of text demodulation in the related technology is solved.
Optionally, acquiring a differential phase value corresponding to a phase value of a message to be demodulated includes: acquiring an integral value of the message to be demodulated, wherein the integral value comprises a pair of in-phase I value and quadrature Q value; acquiring a phase value corresponding to the integral value according to the orthogonal Q value and the in-phase I value; aiming at the output of a frequency locking loop FLL, acquiring the differential phase value according to the difference of the front phase value and the rear phase value; determining the phase value as the differential phase value for a Phase Locked Loop (PLL) output. The frequency locked loop FLL is also called carrier frequency tracking and the phase locked loop PLL is also carrier phase tracking. The cyclic accumulation of I, Q paths of integral values output by the tracking loop and the probability statistics theory are fully utilized to demodulate the message, the error rate of the message demodulation in a weak signal environment is reduced, and the sensitivity of the message demodulation is improved.
The calculation formula of the phase value may be: phase (k) ═ arctan (Q/I), k denotes the current epoch.
The differential Phase value may be calculated by delta (K) -Phase (K-1), where Phase (K) is the Phase value of the K-th epoch, and Phase (K-1) is the Phase value of the K-1 th epoch.
Optionally, obtaining a maximum likelihood ratio corresponding to a phase value of a message to be demodulated includes: when the number of the differential phase values stored in the Buffer is larger than a threshold value, acquiring a standard deviation according to the phase values of 6 epochs; acquiring a row number according to the absolute value of the current differential phase value, acquiring a column number according to the standard deviation, and inquiring a maximum likelihood table by using the row number and the column number to acquire a maximum likelihood ratio; and assigning the polarities of the message values of the 6 epochs to the corresponding maximum likelihood ratios, wherein the phase change of the message values is determined according to the differential phase of each epoch, and the polarity of the message values is determined.
A module (206) for calculating the standard deviation of the current Buffer, which takes the phase values of the close 6 epochs in the Buffer and calculates the standard deviation curStd value after the current differential phase updates the Buffer; calculating the formula:
average Phase avePhase ═ (Phase1+. + Phase 6)/6;
std＝sqrt(((Phase1-avg)^2+..+(Phase6-avg)^2)/6)；
the current standard deviation currstd ═ (std + last Buffer standard deviation lastStd)/2.
Optionally, before acquiring the first message of the previous M bits from the Buffer, detecting whether the current age of the satellite data event IODE changes; and emptying the cache Buffer when the age data event IODE changes.
Optionally, when the age data event IODE is not changed, performing parity check on the M-bit first text; outputting the text word of the first text when the parity check is passed; and when the parity check is not passed, accumulating the M-bit text after the interval of preset time and the first text to obtain a second text, determining the polarity of the second text according to the accumulated value of the maximum likelihood ratio of the N-bit text, and outputting the text of the second text.
Optionally, determining the polarity of the second message according to the accumulated value of the maximum likelihood ratio of the N-bit messages includes: accumulating the maximum likelihood ratio of the N-bit message to obtain a phase-locked loop receiver PLLR; when the PLLR is greater than 0, determining that the bit polarity of the second text is positive; and when the PLLR is less than 0, determining that the bit polarity of the second text is negative.
Optionally, after accumulating the M-bit text after the interval of the preset time and the first text to obtain a second text, performing parity check on the second text; when the second message does not pass the parity check, adding 1 to a counter, and executing a repeated accumulation process on the second message until the next output message passes the parity check, or the Buffer is cached when the counter exceeds a threshold value; and outputting the electric text of the second text when the second text passes the parity check.
The following description will be made in conjunction with another embodiment of the present invention.
In the related art, a receiver generally only uses information which is output by a tracking module and is stripped of a carrier and a spread spectrum code for extracting a message, so that the error rate is very low in an environment with a strong signal, and the decoding is simple and effective.
Another method in the related art is to accumulate the demodulated text for 30s periods, in an attempt to improve the sensitivity of text decoding by decoding the accumulated data. However, errors of the demodulated text are already accumulated in the result, so that the demodulated text is accumulated, and the error bits also influence the final accumulation result, so that the text decoding capability is not improved.
The traditional satellite navigation receiver has a simpler demodulation process for the message, and the integration result which is directly output by a tracking module and stripped of a signal carrier and a pseudo-random code is directly used for judging the positive polarity and the negative polarity of the navigation message. The method basically has no error code under the condition of stronger signal power, but when the satellite signals are weak, such as urban canyons and the like, the error rate index is increased along with the reduction of the signal-to-noise ratio, and the electronic characters cannot be correctly decoded or the decoding of the electronic characters is wrong under most conditions, so that the positioning failure or the error is huge.
In another embodiment of the present invention, the original I, Q value output by the tracking module is used for text judgment, and the accumulated result with the maximum likelihood ratio is output as the accumulated text value through a probability statistical method. On one hand, the signal energy of tracking output is improved through accumulation, and the signal to noise ratio is improved; on the other hand, the reliability of the accumulated text judgment is improved through a probability statistics method, and the sensitivity of text decoding is further improved.
Another embodiment of the present invention is to provide a high-sensitivity navigation message demodulation algorithm, which fully utilizes the I, Q integral values output by the tracking loop to perform message demodulation according to the theory of cyclic accumulation and probability statistics, so as to reduce the error rate of message demodulation in a weak signal environment and improve the sensitivity of message demodulation.
Another embodiment of the invention is divided into 2 stages: the first stage, solving phase difference and maximum likelihood ratio; second stage, text extraction and maximum likelihood ratio accumulation decoding;
fig. 3 is a block diagram of a device for decoding a text message and obtaining an original maximum likelihood ratio according to another embodiment of the present invention, as shown in fig. 3, the device includes a tracking module 301, a phase detection module 302, a phase difference processing module 303, a phase difference storage module 304, a Buffer whether sufficient module 305, a current Buffer standard deviation calculating module 306, a maximum likelihood table look-up module 307, and a table look-up value storing Buffer module 308, and the specific functions of each module are as follows:
first, the tracking module (301) outputs a pair of integral values (in-phase I, (quadrature) Q) every 20ms, and fig. 2 is a navigation message structure diagram of a GPS message according to another embodiment of the present invention, and as shown in fig. 2, the structure diagram of the navigation message is described by the GPS message, and each message bit occupies 20 ms. The phase value of the current integral value can be calculated by a phase detection module (302), and the calculation formula is as follows: phase (k) arctan (Q/I), k representing the current epoch;
the phase difference processing module (303) performs phase difference decoding on the output of the frequency-locked loop (carrier frequency tracking) FLL, so that the phase difference before and after the phase difference is needed to be solved, a receiver using the phase-locked loop (carrier phase tracking) PLL does not need to perform difference decoding, and the value output by the module 302 is the actual phase value of the telegraph text. Formula for phase difference processing: delta (k) -Phase (k-1);
the phase difference storage module (304) stores the difference phase output by the module 303 into a corresponding Buffer for subsequent calculation of the maximum likelihood ratio of the difference phase; meanwhile, according to a differential demodulation principle, the phase change between the current telegraph text Bit (K) and the previous telegraph text Bit (K-1) is judged through the current differential phase, and if the current differential phase is about 180 degrees, the K epoch and the K-1 epoch telegraph text are turned over; if the current differential phase is near 0 degree, the k epoch is consistent with the k-1 epoch telegraph text, and therefore the telegraph text value of the current epoch is output;
a Buffer enough module (305) judges whether more than 6 differential phases are stored in the current Buffer, and the 6 differential phases are used for calculating the standard deviation of the smooth differential phases subsequently; if the number of the currently stored buffers is less than 6, continuing to store the buffers, and jumping to a 301 module; if the number of the stored differential phases is not less than 6, switching to a subsequent calculation module 306;
a module (306) for calculating the standard deviation of the current Buffer, which takes the phase values of the close 6 epochs in the Buffer and calculates the standard deviation curStd value after the current differential phase updates the Buffer; the calculation formula is as follows:
avePhase＝(Phase1+..+Phase6)/6；
std＝sqrt(((Phase1-avg)^2+..+(Phase6-avg)^2)/6)；
curStd＝(std+lastStd)/2；
a table look-up maximum likelihood table (307) module, which respectively calculates the row number and the column number of the table according to the absolute value abs (Delta (k)) of the current differential phase value and the curStd value calculated by the 306 module; wherein the row number is: the rows 1-18 correspond to the normalized phase value respectively, and the row number index can be obtained by calculating the value of abs (Delta (k)) to be closest to the phase value represented by which corresponding row number; column number: 1-9, representing normalized maximum standard deviation values, fig. 4 is a table diagram of maximum likelihood ratios in an 18 row, 9 column format used in accordance with another embodiment of the present invention;
the table-look-up value is stored in a Buffer module 308, the corresponding maximum likelihood ratio value can be taken out by obtaining the index value of the table look-up through 307, and then the maximum likelihood ratio value is given according to the polarity (positive/negative) of the telegraph text value output by 304 and then stored in the Buffer.
With the 301 to 308 modules, 2 outputs can be obtained: differential decoding output and maximum likelihood ratio values;
and in the second stage, the telegram is decoded and checked.
Fig. 5 is a structural diagram of an apparatus for text interface verification and maximum likelihood ratio accumulation according to another embodiment of the present invention, as shown in fig. 5, the apparatus includes a soft bit text input module 501, an IODE detection module 502, a text extraction module 503, a parity detection module 504, a parity determination module 505, a text extraction module 506, a parity determination module 507, a current text storage module 508, a text re-decision failure processing module 509, a current text output module 510, a failure frequency determination module 511, and a Buffer clearing module 512, and specific functions of each module are as follows:
differential decoding obtained from the previous step enters a soft bit text input (501) module, if the age data event IODE is known to have changed at present, the previously stored Buffer is cleared, the text has changed at the moment, the previously stored Buffer is not available any more, and otherwise, the use is continued.
The module for extracting the telegraph text (503) extracts the front 30 bits of the input telegraph text according to the sequence, and enters the parity check judgment module (505), if the current word can pass the parity check, the first round check of the telegraph text is passed, and the telegraph text can enter the back check logic; otherwise, the error bit exists in the current electric text obtained by differential decoding or the current 30 bits are not an electric text, the maximum likelihood ratio accumulation judgment module (505) is entered;
as can be known from fig. 1, each set of text has 1500 bits, where 900 bits of the 1 st, 2 nd, and 3 rd subframes are played cyclically every 30 seconds, that is, every 30 seconds of data in the Buffer in the first stage can be accumulated, so as to ensure that the 1 st, 2 nd, and 3 th subframes are enhanced by accumulation, which is convenient for text decoding, and the structural rule of this text is the theoretical basis of the subsequent accumulation logic;
the 505 module accumulates the maximum likelihood ratio values of adjacent 1500 bits to obtain a phase-locked loop receiver llr (phase-locked loop receiver), and then performs the accumulated text judgment according to the following logic:
if pLLR >0, the output bit polarity is positive;
if pLLR <0, the output bit polarity is negative;
a group of telegrams are output again by the method and sent to the telegram character extracting module (506);
the format of the formed 30-bit electric characters is subjected to a parity check judgment (507) module, if the check is passed, the current electric characters are kept (508), then the current electric characters are output (510), and the electric character extraction work is finished; if the verification fails, entering a Buffer error judgment module;
adding one to the count value every time the failure count is over a certain threshold (509), when the failure count is over a certain threshold, indicating that a larger accumulated error exists in the current Buffer, and the Buffer value needs to be cleared, namely entering a 512 module;
the embodiment of the invention also provides a device for demodulating the telegraph text, which comprises:
the device comprises a first acquisition module, a second acquisition module and a Buffer, wherein the first acquisition module is used for acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio value, and storing the differential phase value and the maximum likelihood ratio value into the Buffer;
a second obtaining module, configured to obtain a first message with M bits before in the Buffer, where M is an integer;
and the output module is used for accumulating the M-bit messages after the interval of the preset time and the first messages to obtain second messages and outputting the messages of the second messages when the first messages do not pass the preset verification, wherein the polarity of the second messages is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, the N-bit messages comprise the first messages, and N is an integer greater than or equal to M.
Acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio value through the device, and storing the differential phase value and the maximum likelihood ratio value into a Buffer; acquiring a first message of front M bits from the Buffer, wherein M is an integer; when the first message does not pass the preset verification, accumulating M-bit messages after the interval of the preset time and the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of N-bit messages, including the first message, N is an integer greater than or equal to M; on the other hand, the reliability of the accumulated text judgment is improved through a probability statistical method of the maximum likelihood ratio, the sensitivity of text decoding is further improved, and the problem of inaccurate positioning caused by frequent errors of text demodulation in the related technology is solved.
The apparatus of this embodiment may be configured to implement the technical solutions of the above method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
According to another embodiment of the present invention, there is also provided a storage medium having a computer program stored therein, wherein the computer program is configured to perform the method of any one of the above embodiments when executed.
According to another embodiment of the present invention, there is also provided an electronic apparatus, including a memory and a processor, the memory having a computer program stored therein, the processor being configured to execute the computer program to perform the method of any one of the above embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A method for demodulating a text, comprising:
acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio, and storing the differential phase value and the maximum likelihood ratio into a Buffer;
acquiring a first message of front M bits from the Buffer, wherein M is an integer;
and when the first message does not pass the preset verification, accumulating the M-bit messages after the preset time interval with the first message to obtain a second message, and outputting the message of the second message, wherein the polarity of the second message is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, including the first message, and N is an integer greater than or equal to M.
2. The method of claim 1, wherein obtaining a differential phase value corresponding to a phase value of a message to be demodulated comprises:
acquiring an integral value of the message to be demodulated, wherein the integral value comprises a pair of in-phase I value and quadrature Q value;
acquiring a phase value corresponding to the integral value according to the orthogonal Q value and the in-phase I value;
aiming at the output of a frequency locking loop FLL, acquiring the differential phase value according to the difference of the front phase value and the rear phase value; determining the phase value as the differential phase value for a Phase Locked Loop (PLL) output.
3. The method of claim 2, wherein obtaining the maximum likelihood ratio value corresponding to the phase value of the message to be demodulated comprises:
when the number of the differential phase values stored in the Buffer is larger than a threshold value, acquiring a standard deviation according to the phase values of 6 epochs;
acquiring a row number according to the absolute value of the current differential phase value, acquiring a column number according to the standard deviation, and inquiring a maximum likelihood table by using the row number and the column number to acquire a maximum likelihood ratio;
and assigning the polarities of the message values of the 6 epochs to the corresponding maximum likelihood ratios, wherein the phase change of the message values is determined according to the differential phase of each epoch, and the polarity of the message values is determined.
4. The method of claim 1, wherein before the first message of the first M bits is obtained in the Buffer, the method further comprises:
detecting whether the IODE of the current satellite age data event changes or not;
and emptying the cache Buffer when the age data event IODE changes.
5. The method of claim 4, wherein when the age of satellite data event IODE is unchanged, the method further comprises:
performing parity check on the M-bit first text;
outputting the text word of the first text when the parity check is passed; and when the parity check is not passed, accumulating the M-bit text after the interval of preset time and the first text to obtain a second text, determining the polarity of the second text according to the accumulated value of the maximum likelihood ratio of the N-bit text, and outputting the text of the second text.
6. The method of claim 1, wherein determining the polarity of the second message from the accumulated value of the maximum likelihood ratios of the N-bit messages comprises:
accumulating the maximum likelihood ratio of the N-bit message to obtain a phase-locked loop receiver PLLR;
when the PLLR is greater than 0, determining that the bit polarity of the second text is positive; and when the PLLR is less than 0, determining that the bit polarity of the second text is negative.
7. The method according to claim 1, wherein after the adding the M-bit message separated by the preset time to the first message to obtain a second message, the method further comprises:
performing parity check on the second text;
when the second message does not pass the parity check, adding 1 to a counter, and executing a repeated accumulation process on the second message until the next output message passes the parity check, or the Buffer is cached when the counter exceeds a threshold value; and outputting the electric text of the second text when the second text passes the parity check.
8. An apparatus for demodulating a text, comprising:
the device comprises a first acquisition module, a second acquisition module and a Buffer, wherein the first acquisition module is used for acquiring a differential phase value corresponding to a phase value of a message to be demodulated and a corresponding maximum likelihood ratio value, and storing the differential phase value and the maximum likelihood ratio value into the Buffer;
a second obtaining module, configured to obtain a first message with M bits before in the Buffer, where M is an integer;
and the output module is used for accumulating the M-bit messages after the interval of the preset time and the first messages to obtain second messages and outputting the messages of the second messages when the first messages do not pass the preset verification, wherein the polarity of the second messages is determined according to the accumulated value of the maximum likelihood ratio of the N-bit messages, the N-bit messages comprise the first messages, and N is an integer greater than or equal to M.
9. A storage medium, in which a computer program is stored, wherein the computer program is arranged to perform the method of any of claims 1 to 7 when executed.
10. An electronic device comprising a memory and a processor, wherein the memory has stored therein a computer program, and wherein the processor is arranged to execute the computer program to perform the method of any of claims 1 to 7.
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