CN106998237B - A kind of time-frequency synchronization method and device - Google Patents
A kind of time-frequency synchronization method and device Download PDFInfo
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Abstract
The embodiment of the present invention provides a kind of time-frequency synchronization method and device, this method comprises: carrying out thick synchronization process according to preset pilot frequency sequence and the conjugate sequence of the pilot frequency sequence to signal is received, determining and receive the corresponding thick sync bit of signal；According to thick sync bit, coarse frequency offset is carried out, Doppler shift estimator is obtained；According to thick sync bit and Doppler shift estimator, thin synchronization process is carried out；Wherein, the process of thin synchronization process includes: thick frequency deviation compensation, and determines the correlation for receiving signal；Final sync bit is determined according to the maximum related value in the correlation, it is compensated according to the final sync bit and thick frequency deviation as a result, the smart offset estimation of progress, determines essence offset estimation value；With the sum of smart offset estimation value and Doppler shift estimator, frequency deviation compensation is carried out, completes Frequency Synchronization.The embodiment of the present invention can realize the Time and Frequency Synchronization being suitable under biggish Doppler frequency shift environment, promote the precision of Time and Frequency Synchronization.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a time frequency synchronization method and a time frequency synchronization device.
Background
Time-frequency synchronization is an important link of communication, and mainly refers to performing time synchronization and frequency synchronization on received information in a communication process, wherein the time synchronization aims at finding the position of a frame header, and the frequency synchronization aims at eliminating frequency offset (frequency offset is caused by Doppler frequency shift and/or crystal oscillator drift) through frequency offset estimation. The realization of time-frequency synchronization can ensure the smooth processing of physical layer in the communication process, thereby effectively carrying out time-frequency synchronization and having important significance for a communication system.
Under the communication scene of high-speed movement such as high-speed railway, aviation, satellite communication, missile-borne communication and the like, the high-speed movement can bring large Doppler frequency shift (for example, in the missile-borne communication, the large relative speed between a missile and an aircraft can bring large Doppler frequency shift), and the time-frequency synchronization of received signals is realized under the large Doppler frequency shift environment (for short, large frequency offset environment), so that the method is a technical point which is currently realized time-frequency synchronization and is difficult to break through; for example, in a GMR-1 satellite mobile communication system, due to crystal frequency difference and relative motion, a receiving end needs to perform time synchronization on a received signal under the condition that a large doppler frequency shift exists, determine a timing synchronization position (e.g., determine a sampling time and a frame boundary), and simultaneously need to be able to estimate the size of a linear frequency offset to complete frequency synchronization of the received signal.
Disclosure of Invention
In view of this, embodiments of the present invention provide a time-frequency synchronization method and apparatus, so as to be suitable for implementing time-frequency synchronization in a larger doppler frequency shift environment, and improve the accuracy of time-frequency synchronization.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
a time-frequency synchronization method comprises the following steps:
according to a preset pilot frequency sequence and a conjugate sequence of the pilot frequency sequence, carrying out coarse synchronization processing on a received signal, and determining a coarse synchronization position corresponding to the received signal;
performing coarse frequency offset estimation according to the coarse synchronization position to obtain a Doppler frequency offset estimator;
performing fine synchronization processing according to the coarse synchronization position and the Doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: compensating coarse frequency offset and determining a correlation value of a received signal;
determining a final synchronous position according to the maximum correlation value in the correlation values, and performing fine frequency offset estimation according to the final synchronous position and a result after coarse frequency offset compensation to determine a fine frequency offset estimation value;
and determining the sum of the fine frequency offset estimation value and the Doppler frequency offset estimation quantity, and performing frequency offset compensation according to the determined sum to finish frequency synchronization.
Optionally, the performing coarse synchronization processing on the received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence, and determining a coarse synchronization position corresponding to the received signal includes:
respectively carrying out sliding correlation processing on a received signal by utilizing a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence and a second correlation power value corresponding to the received signal and the conjugate sequence;
for a received signal in a time slot, calculating the maximum peak position in a first correlation power value to obtain a first maximum peak position, and calculating the maximum peak position in a second correlation power value to obtain a second maximum peak position;
calculating the noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating the noise power corresponding to the second maximum peak position to obtain a second noise power;
calculating a synchronization mark according to the first noise power and the second noise power;
and if the synchronization mark is larger than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
Optionally, the determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position includes:
and rounding the mean value of the first maximum peak position and the second maximum peak position to determine the coarse synchronization position.
Optionally, the performing, according to the coarse synchronization position, coarse frequency offset estimation to obtain a doppler frequency offset estimator includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to carry out FFT frequency offset estimation;
and performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
Optionally, the result of the FFT frequency offset estimation includes: the peak value and the frequency point corresponding to the peak value of the FFT frequency offset estimation, and the peak value and the corresponding frequency point of the adjacent secondary peak;
performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a doppler frequency offset estimator, including:
establishing a quadratic interpolation polynomial to form a quadratic curve;
substituting the peak value and the frequency point corresponding to the peak value in the result of the FFT frequency deviation estimation, the peak value and the corresponding frequency point of the adjacent secondary peak into a secondary curve, and solving the parameter value of the secondary curve;
and calculating the maximum value of the quadratic curve and the corresponding frequency point according to the solved parameter value of the quadratic curve, and determining the calculated frequency point as the Doppler frequency offset estimator.
Optionally, the performing fine synchronization processing according to the coarse synchronization position and the doppler frequency offset estimator includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position and a position set corresponding to the adjacent position;
performing coarse frequency offset compensation on each extracted received signal according to the Doppler frequency offset estimator; and for each group of correlation signals in the extracted receiving signals, performing segmented correlation on each group of correlation signals according to a set length and summing segmented correlation results to obtain correlation values of each group of correlation signals.
Optionally, the determining a final synchronization position according to a maximum correlation value of the correlation values includes:
selecting a maximum correlation value from correlation values of each group of correlation signals, and determining a position corresponding to the maximum correlation value in the position set as a final synchronous position of time;
and performing fine frequency offset estimation according to the final synchronization position and the result of the coarse frequency offset compensation, wherein the step of determining the fine frequency offset estimation value comprises the following steps:
and calling the front and rear sections of pilot frequency data after the coarse frequency offset compensation corresponding to the final synchronization position, and performing fine frequency offset estimation according to the called front and rear sections of pilot frequency data to obtain a fine frequency offset estimation value.
The embodiment of the present invention further provides a time frequency synchronization device, which includes:
the coarse synchronization processing module is used for performing coarse synchronization processing on the received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence and determining a coarse synchronization position corresponding to the received signal;
the coarse frequency offset estimation module is used for performing coarse frequency offset estimation according to the coarse synchronization position to obtain a Doppler frequency offset estimator;
the fine synchronization processing module is used for performing fine synchronization processing according to the coarse synchronization position and the Doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: compensating coarse frequency offset and determining a correlation value of a received signal;
the fine frequency offset estimation module is used for determining a final synchronous position according to the maximum correlation value in the correlation values, performing fine frequency offset estimation according to the final synchronous position and a result after coarse frequency offset compensation, and determining a fine frequency offset estimation value;
and the frequency offset compensation module is used for determining the sum of the fine frequency offset estimation value and the Doppler frequency offset estimation quantity, and performing frequency offset compensation according to the determined sum to complete frequency synchronization.
Optionally, the coarse synchronization processing module is configured to perform coarse synchronization processing on the received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence, and determine a coarse synchronization position corresponding to the received signal, and specifically includes:
respectively carrying out sliding correlation processing on a received signal by utilizing a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence and a second correlation power value corresponding to the received signal and the conjugate sequence;
for a received signal in a time slot, calculating the maximum peak position in a first correlation power value to obtain a first maximum peak position, and calculating the maximum peak position in a second correlation power value to obtain a second maximum peak position;
calculating the noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating the noise power corresponding to the second maximum peak position to obtain a second noise power;
calculating a synchronization mark according to the first noise power and the second noise power;
and if the synchronization mark is larger than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
Optionally, the coarse frequency offset estimation module is configured to perform coarse frequency offset estimation according to the coarse synchronization position to obtain a doppler frequency offset estimator, and specifically includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to carry out FFT frequency offset estimation;
and performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
Based on the technical scheme, when time-frequency synchronization is carried out, coarse synchronization is carried out firstly, and then fine synchronization is carried out, so that frequency offset compensation can be realized based on a fine frequency offset estimation value obtained by fine synchronization and a Doppler frequency offset estimation quantity obtained by coarse synchronization, time-frequency synchronization suitable for a large Doppler frequency offset environment is completed, and the precision of time-frequency synchronization is improved.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a flowchart of a time-frequency synchronization method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of synchronization using ZC sequences and their conjugate sequences;
FIG. 3 is a flow chart of a method of coarse synchronization processing;
FIG. 4 is a schematic diagram of a coarse synchronization process;
FIG. 5 is a flow chart of a method of coarse frequency offset estimation;
FIG. 6 is a flow chart of a method of fine synchronization processing;
FIG. 7 is a flowchart of a method of fine frequency offset estimation processing;
FIG. 8 is a graph comparing the probability of synchronization under AWGN channels;
FIG. 9 is a diagram illustrating a comparison of the root mean square error of the frequency offset estimation in the AWGN channel;
fig. 10 is a block diagram of a time-frequency synchronization apparatus according to an embodiment of the present invention.
Detailed Description
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.
Fig. 1 is a flowchart of a time-frequency synchronization method provided in an embodiment of the present invention, where the method is applicable to a receiving end of a communication system, and referring to fig. 1, the time-frequency synchronization method may include:
step S100, according to a preset pilot sequence and a conjugate sequence of the pilot sequence, performing coarse synchronization processing on a received signal, and determining a coarse synchronization position corresponding to the received signal.
In a larger doppler frequency shift environment, after a receiving end of a communication system receives a received signal, a preset pilot frequency sequence (set as p) can be adjustedi) And a conjugate sequence (set to p) of the pilot sequencei *) Thereby using the pilot sequence piAnd the conjugated sequence pi *Carrying out coarse synchronization processing on the received signals;
optionally, the coarse synchronization process may involve: sliding correlation processing, peak position determination, coarse synchronization position determination and the like.
And step S110, performing coarse frequency offset estimation according to the coarse synchronization position to obtain a Doppler frequency offset estimator.
Alternatively, the coarse frequency offset estimation process may involve FFT frequency offset estimation, and parabolic interpolation processing, etc.
Step S120, fine synchronization processing is carried out according to the coarse synchronization position and the Doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: coarse frequency offset compensation, and determining the correlation value of the received signal.
Step S130, determining a final synchronization position according to the maximum correlation value in the correlation values, and performing fine frequency offset estimation according to the final synchronization position and a result after coarse frequency offset compensation to determine a fine frequency offset estimation value.
And S140, determining the sum of the fine frequency offset estimation value and the Doppler frequency offset estimator, and performing frequency offset compensation according to the determined sum to complete frequency synchronization.
It can be seen that, in the embodiment of the present invention, when performing time-frequency synchronization, coarse synchronization is performed first (as shown in step S100 to step S110), and then fine synchronization is performed (as shown in step S120), so that frequency offset compensation can be implemented based on a fine frequency offset estimation value obtained by the fine synchronization and a doppler frequency offset estimation value obtained by the coarse synchronization, and time-frequency synchronization applicable to a larger doppler frequency shift environment is completed, thereby improving the accuracy of the time-frequency synchronization.
When time-frequency synchronization is performed, the coarse synchronization is performed first, and then the fine synchronization is performed, which are considered as follows:
if the bilinear FM signal with specific frequency modulation can be equivalent to the summation of the ZC sequence and the conjugate sequence thereof, the invention uses the ZC sequence and the conjugate sequence thereof to complete the synchronization function; the structure is shown in FIG. 2;
the expression of the ZC sequence may be as follows:
wherein u is a root sequence number of the ZC sequence. The impact of frequency offset on the correlation of ZC sequences is now analyzed. Suppose the signal sampling rate is fsFrequency deviation of fdThe first point of the sequence introduces a phase change of 0,the nth point phase change is:
after adding the frequency offset, the sequence is:
it can be known that whenTime-of-flight, i.e. frequency offset causes a shift of the sequence, resulting in a shift of the correlation peak of the received sequence, the shiftThe number of points is n-k.
It can be seen that when the two sequence indexes satisfy the following formula, adding frequency offset causes sequence shift, resulting in a pseudo correlation peak.
Wherein
Assuming that k is n-x, and x is the number of sequence shift points, solving the above equation can obtain:
when in useSatisfy the requirement ofTime, i.e., the sequence is shifted exactly x points exactly for the sequence repetition, an
Thus, it can be seen thatAnd the time synchronization is less influenced, and the position of the correlation peak is shifted by x ≈ 0 at the time.
That is, the frequency offset satisfiesThe peak position does not shift. When in useI.e., frequency offset satisfiesTime, peak position shiftAnd moving the x point. Take u-1 as an example, when the frequency offset is fromTo the direction ofWhen changed, the detection peak will move from the shifted x point to x + 1.
Similarly, for the conjugate d of a ZC sequenceu,n *＝d-u,n. When in useI.e., frequency offset satisfiesThe peak position is shifted by-x points. Take u-1 as an example, when the frequency offset is fromTo the direction ofWhen changed, the detection peak will move from the shifted-x point to-x-1.
It can be known that the influence of the large frequency offset on the two training sequences is opposite. And averaging the peak positions of the two signals, thereby completing timing synchronization under large frequency offset. And when the frequency offset is atAndin between, there may be a deviation from the ideal synchronization position due to averaging of the peak positions due to the influence of noise.
Therefore, the invention carries out the fine synchronization after finishing the coarse synchronization based on the principle. When u is 1, the coarse synchronization position may have a deviation of one sample point from the ideal synchronization position. When the root sequence number of the ZC sequence used is another value, the deviation is different.
When fine synchronization is performed, the root sequence number of the used ZC sequence and whether the root sequence number is generated in a frequency domain or a time domain are required to be combined for adjustment.
The principle of the invention for completing timing synchronization under large frequency deviation is briefly analyzed, and the principle is essentially consistent with the principle of a bilinear frequency modulation signal time domain synchronization algorithm for resisting large frequency deviation. The invention mainly improves the timing synchronization precision and the frequency offset estimation, so that the timing synchronization position is accurate and the frequency offset estimation precision is higher.
It should be noted that the contents of the bilinear fm signal time domain synchronization algorithm for resisting the large frequency offset are mainly as follows:
if GMR-1 uses a dual-chirp format (dual-chirp format) in the FCCH for time-frequency synchronization, the dual chirp is a real signal whose energy normalized baseband signal expression is:
wherein,
t is the duration of the bilinear frequency modulation signal, and T is more than or equal to 0 and less than or equal to T.
And any one real signal can be represented in the form of the sum of two conjugate complex signals, i.e.:
s(t)＝su(t)+sd(t)
wherein,
here, the component signal s is referred tou(t) is an up-chirp waveform whose instantaneous frequency increases from-KT/2 to KT/2 over time; component signal sd(t) is a down-chirp waveform whose instantaneous frequency decreases from KT/2 to-KT/2 over time; the absolute value of the rate of change of the two component signal frequencies is the same. The bandwidth of the bilinear chirp signal is therefore B-KT.
Optionally, in the embodiment of the present invention, the coarse synchronization processing performed in step S100 shown in fig. 1 may be as shown in fig. 3, and includes:
step S200, performing sliding correlation processing on the received signal respectively by using a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence, and a second correlation power value corresponding to the received signal and the conjugate sequence.
In a larger doppler frequency shift environment, after a receiving end of a communication system receives a received signal, a preset pilot frequency sequence (set as p) can be adjustedi) And a conjugate sequence (set to p) of the pilot sequencei *) So that the pilot sequence p can be utilizediPerforming sliding correlation processing on the received signal to obtain the received signal and a pilot frequency sequence piCorresponding first correlation power value (set to σ 1)j) And using said conjugated sequence pi *Performing sliding correlation processing on the received signal to obtain the received signal and a conjugate sequence pi *Corresponding second power value (set to σ 2)j)。
Optionally, a pilot sequence piThe length of N can be selectedpA ZC (Zadoff-Chu) sequence of (1); ZC sequences have very good autocorrelation and very low cross-correlationThis capability can be used to generate a synchronization signal as a correlated conveyance of time and frequency.
The following formula implementation that may be adopted in the embodiments of the present invention is exemplified by a time-domain ZC sequence with a sequence number of 1.
Alternatively, an alternative expression formula for performing the sliding correlation process may be as follows:
wherein N ispIs the length of the pilot sequence (.)*The representation is conjugate, |, represents modulus, i represents the numeric value of the pilot sequence length, and j represents the number of sliding points during sliding correlation.
Step S210, for the received signal in a time slot, calculating a maximum peak position in the first correlation power value to obtain a first maximum peak position, and calculating a maximum peak position in the second correlation power value to obtain a second maximum peak position.
Optionally, for a correlation value (received signal) in one timeslot, the embodiment of the present invention may determine a maximum peak position in a first correlation power value corresponding to each received signal to obtain a first maximum peak position (set to pos1), and determine a maximum peak position in a second correlation power value corresponding to each received signal to obtain a second maximum peak position (set to pos 2);
alternatively, pos1 and pos2 can be calculated by the following formulas;
step S220, calculating a noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating a noise power corresponding to the second maximum peak position to obtain a second noise power.
Alternatively, taking the first noise power calculation corresponding to the first maximum peak position pos1 as an example, the first noise power may be set to δpos1(ii) a Optionally, deltapos1The calculation of (c) can be achieved by the following formula:
wherein N iswinThe length of the unilateral window used for noise calculation can be determined according to the length of the pilot frequency sequence; as can be seen from the above formula, pos1 corresponds to the first noise power δpos1Can be calculated by calculating the left and right N of pos1winNoise power corresponding to each position is obtained, and then the average noise power is taken as the noise power corresponding to pos 1;
optionally, the second noise power (which may be set to δ) corresponding to the second maximum peak position pos2pos2) Can be calculated from the above-mentioned deltapos1The same applies to the calculation of (1).
And step S230, calculating a synchronization mark according to the first noise power and the second noise power.
Optionally, the synchronization flag may be set as a flag, and the calculation of the synchronization flag may be implemented by the following formula:
step S240, if the synchronization flag is greater than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
Optionally, the preset threshold may be set to 10Th/10If flag > 10Th/10If so, judging bit synchronization, and calculating a coarse synchronization position subsequently; alternatively, Th may be considered as a threshold value, and the threshold value Th may be a dB value, which may be obtained through simulation.
Optionally, the coarse synchronization position pos may be set to be determined by rounding the average of the first maximum peak position pos1 and the second maximum peak position pos 2; alternatively, the coarse synchronization position pos may be calculated by the following formula:
wherein [ ·]Indicating a rounding process.
Optionally, steps S200 to S240 may be regarded as an embodiment of the present invention, and a preset pilot sequence and a conjugate sequence of the pilot sequence are used to perform coarse synchronization processing, so as to determine an optional implementation form of a coarse synchronization position corresponding to a received signal.
Alternatively, the procedure of the coarse synchronization process may be as shown in fig. 4; in the example shown in fig. 4, to increase the operation speed, the time domain sliding correlation algorithm may be performed based on FFT, so that the received data is divided into a plurality of windows win _ num, and the window length is set so that the received signal length is an integral multiple of the window length.
Optionally, in the embodiment of the present invention, the coarse frequency offset estimation process performed in step S110 shown in fig. 1 may be as shown in fig. 5, and includes:
step S300, extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to perform FFT frequency offset estimation.
After the coarse synchronization position pos is obtained, N can be taken out according to the coarse synchronization position pospThe received signal (set to rp 0) corresponding to a pointi) Receiving signal rp0iWith a conjugated sequence pi *After multiplication, an FFT (fast Fourier transform) frequency offset estimate is made.
And S310, performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
Optionally, the result of the FFT frequency offset estimation may be: the peak value and the frequency point corresponding to the peak value of the FFT frequency offset estimation, and the peak value and the corresponding frequency point of the adjacent secondary peak;
the peak value and the frequency point corresponding to the peak value of the FFT frequency offset estimation can be set as (z)d，fd) Where d is the position of the peak, fdFor corresponding frequency points, zdIs the peak value; the peak value and corresponding frequency point of two secondary peaks adjacent to the estimated peak value are (z)d-1，fd-1) And (z)d+1，fd+1)；
Then, according to the peak value and the frequency point corresponding to the peak value in the result of the FFT frequency offset estimation, and the peak value and the corresponding frequency point of the adjacent secondary peak, parabolic interpolation processing may be performed, and the process of the parabolic interpolation processing may be:
establishing a quadratic interpolation polynomial to form a quadratic curve z; a is0f2+a1f+a2
Substituting the peak value and the frequency point corresponding to the peak value in the result of the FFT frequency deviation estimation, the peak value and the corresponding frequency point of the adjacent secondary peak into a quadratic curve z, and solving the parameter value a of the quadratic curve z0、a1、a2；
Correspondingly, according to the solved parameter value a of the quadratic curve z0、a1、a2The maximum value of the quadratic curve z and the corresponding frequency point can be calculatedThereby obtaining a more approximate Doppler frequency offset estimator
Alternatively to this, the first and second parts may,the calculation process of (a) can be expressed by the following formula:
where Δ f is the frequency resolution.
Optionally, steps S300 to S310 may be regarded as an optional implementation manner of performing coarse frequency offset estimation according to the coarse synchronization position to obtain the doppler frequency offset estimator.
Optionally, in the embodiment of the present invention, the fine synchronization processing procedure performed in step S120 shown in fig. 1 may be as shown in fig. 6, and includes:
step S400, according to the coarse synchronization position and the position set corresponding to the adjacent position, extracting the receiving signal corresponding to the length point of the pilot frequency sequence.
Optionally, after the coarse synchronization position Pos is obtained, a position set corresponding to the coarse synchronization position Pos and an adjacent position of the Pos, such as the Pos, may be usedtemp＝[Pos-1,Pos,Pos+1]Wherein postempRepresenting the set of locations; thereby aggregating Pos according to locationtemp＝[Pos-1,Pos,Pos+1]Can take out the corresponding NpReceived signal Rp0 of pointjiAnd Rp1ji。
Step S410, performing coarse frequency offset compensation on each extracted received signal according to the Doppler frequency offset estimator; and for each group of correlation signals in the extracted receiving signals, performing segmented correlation on each group of correlation signals according to a set length and summing segmented correlation results to obtain correlation values of each group of correlation signals.
Alternatively, the correlation value may be considered as a possible fine synchronization position.
Optionally, aggregating Pos according to locationtemp＝[Pos-1,Pos,Pos+1]Take out the corresponding NpReceived signal Rp0 of pointjiAnd Rp1jiThe estimate may then be based on the Doppler frequency offsetRespectively to Rp0jiAnd Rp1jiPerforming coarse frequency offset compensation; alternatively, the implementation formula may be as follows:
meanwhile, for each group of relevant signals of the received signals, the embodiment of the invention can respectively carry out segment correlation on each group of relevant signals according to the set length and calculate the sum of segment correlation results to obtain the correlation value of each group of relevant signals;
alternatively, the correlation value of the jth group of correlation signals may be set as RRjJ may be 1, 2, 3; then the correlation value RR of the jth group of correlation signalsjThe alternative calculation formula of (c) can be as follows:
wherein N iswIn order to set the length, the length of the pilot sequence and the maximum frequency offset possible by the system can be combined for setting, and an optimal length is obtained through simulation.
Optionally, steps S400 to S410 may be regarded as an optional implementation manner of performing fine synchronization processing according to the coarse synchronization position and the doppler frequency offset estimator; optionally, the fine synchronization processing procedure includes: coarse frequency offset compensation, and determining the correlation value of the received signal.
Optionally, in the embodiment of the present invention, the fine frequency offset estimation processing procedure performed in step S130 shown in fig. 1 may be as shown in fig. 7, and includes:
step S500, selecting a maximum correlation value from the correlation values of the correlation signals of each group, and determining a position corresponding to the maximum correlation value in the position set as a final synchronization position of time.
After the correlation values of each group of correlation signals are obtained, the maximum value of the correlation signals can be judged to obtain the maximum correlation value, and the position value corresponding to the maximum correlation value in the position set postemp is the accurate final synchronous position Posfinal。
Step S510, retrieving the former and latter pilot data after the coarse frequency offset compensation corresponding to the final synchronization position, and performing fine frequency offset estimation according to the retrieved former and latter pilot data to obtain a fine frequency offset estimation value.
Optionally, the precise final synchronization position PosfinalCorrespondingly, the front and back sections of pilot frequency data after coarse frequency offset compensation are respectively marked as x1(n)，x2(n) can be represented by1(n) multiplication with its conjugate sequence, x2(n) multiplying with its conjugate sequence, then:
alternatively, the fine frequency offset estimate may be expressed as follows:
thus, the fine frequency offset estimation valueThis can be obtained by the following formula:
it can be seen that the frequency offset estimation range isWherein T issFor the sampling interval, Δ φ is the carrier phase offset, NdThe interval between the front and back training sequences. By adjusting NdThe frequency offset estimation range may be adjusted to achieve the required frequency offset estimation accuracy.
Optionally, received data RP0 may also be used in order to extend the frequency offset estimation rangeiAnd RP1iThe respective front and rear parts are subjected to differential frequency offset estimation. Meanwhile, the accuracy of frequency offset estimation can be adjusted by adjusting the length of the training sequence.
Optionally, steps S500 to S510 may be regarded as an optional implementation manner of performing fine frequency offset estimation according to a maximum correlation value in the correlation values and a result after coarse frequency offset compensation, and determining a fine frequency offset estimation value.
Setting random frequency offset-12 kHz and selecting AWGN as a channel through simulation. The dual-chirp sequence used by the original algorithm is 1024 points, and the simulation is carried out by taking the time-domain synchronization algorithm as an example. The invention uses 512 ZC sequence with root sequence number 1 and conjugate thereof in simulation, so that the overhead of the two methods is consistent. When the synchronous position does not deviate from the ideal position, the synchronization is considered to be successful; otherwise, the synchronization is considered to fail. The simulation can be as shown in fig. 8 and fig. 9, where fig. 8 is a comparison of synchronization probability under AWGN channel, and fig. 9 is a comparison of root mean square error of frequency offset estimation under AWGN channel; therefore, the time-frequency synchronization method used in the embodiment of the invention solves the problem of timing synchronization precision in a large frequency offset environment, and obviously improves the frequency offset estimation precision.
The embodiment of the invention also provides a time frequency synchronization device, and the time frequency synchronization device described below can be correspondingly referred to the content of the time frequency synchronization method described above.
Fig. 10 is a block diagram of a time frequency synchronization apparatus according to an embodiment of the present invention, where the time frequency synchronization apparatus is applicable to a receiving end, and referring to fig. 10, the time frequency synchronization apparatus may include:
a coarse synchronization processing module 100, configured to perform coarse synchronization processing on a received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence, and determine a coarse synchronization position corresponding to the received signal;
a coarse frequency offset estimation module 200, configured to perform coarse frequency offset estimation according to the coarse synchronization position to obtain a doppler frequency offset estimator;
a fine synchronization processing module 300, configured to perform fine synchronization processing according to the coarse synchronization position and the doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: compensating coarse frequency offset and determining a correlation value of a received signal;
a fine frequency offset estimation module 400, configured to determine a final synchronization position according to a maximum correlation value of the correlation values, perform fine frequency offset estimation according to the final synchronization position and a result after coarse frequency offset compensation, and determine a fine frequency offset estimation value;
and a frequency offset compensation module 500, configured to determine a sum of the fine frequency offset estimation value and the doppler frequency offset estimator, perform frequency offset compensation according to the determined sum, and complete frequency synchronization.
Optionally, the coarse synchronization processing module 100 is configured to perform coarse synchronization processing on the received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence, and determine a coarse synchronization position corresponding to the received signal, and specifically includes:
respectively carrying out sliding correlation processing on a received signal by utilizing a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence and a second correlation power value corresponding to the received signal and the conjugate sequence;
for a received signal in a time slot, calculating the maximum peak position in a first correlation power value to obtain a first maximum peak position, and calculating the maximum peak position in a second correlation power value to obtain a second maximum peak position;
calculating the noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating the noise power corresponding to the second maximum peak position to obtain a second noise power;
calculating a synchronization mark according to the first noise power and the second noise power;
and if the synchronization mark is larger than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
Optionally, the coarse synchronization processing module 100 is configured to determine a coarse synchronization position according to the first maximum peak position and the second maximum peak position, and specifically includes:
and rounding the mean value of the first maximum peak position and the second maximum peak position to determine the coarse synchronization position.
Optionally, the coarse frequency offset estimation module 200 is configured to perform coarse frequency offset estimation according to the coarse synchronization position to obtain a doppler frequency offset estimator, and specifically includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to carry out FFT frequency offset estimation;
and performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
Optionally, the result of the FFT frequency offset estimation includes: the peak value and the frequency point corresponding to the peak value of the FFT frequency offset estimation, and the peak value and the corresponding frequency point of the adjacent secondary peak;
correspondingly, the coarse frequency offset estimation module 200 is configured to perform parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a doppler frequency offset estimator, and specifically includes:
establishing a quadratic interpolation polynomial to form a quadratic curve;
substituting the peak value and the frequency point corresponding to the peak value in the result of the FFT frequency deviation estimation, the peak value and the corresponding frequency point of the adjacent secondary peak into a secondary curve, and solving the parameter value of the secondary curve;
and calculating the maximum value of the quadratic curve and the corresponding frequency point according to the solved parameter value of the quadratic curve, and determining the calculated frequency point as the Doppler frequency offset estimator.
Optionally, the fine synchronization processing module 300 is configured to perform fine synchronization processing according to the coarse synchronization position and the doppler frequency offset estimator, and specifically includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position and a position set corresponding to the adjacent position;
performing coarse frequency offset compensation on each extracted received signal according to the Doppler frequency offset estimator; and for each group of correlation signals in the extracted receiving signals, performing segmented correlation on each group of correlation signals according to a set length and summing segmented correlation results to obtain correlation values of each group of correlation signals.
Optionally, the fine frequency offset estimation module 400 is configured to determine a final synchronization position according to a maximum correlation value in the correlation values, and specifically includes:
selecting a maximum correlation value from correlation values of each group of correlation signals, and determining a position corresponding to the maximum correlation value in the position set as a final synchronous position of time;
correspondingly, the fine frequency offset estimation module 400 is configured to perform fine frequency offset estimation according to the final synchronization position and the result after the coarse frequency offset compensation, and determine a fine frequency offset estimation value, which specifically includes:
and calling the front and rear sections of pilot frequency data after the coarse frequency offset compensation corresponding to the final synchronization position, and performing fine frequency offset estimation according to the called front and rear sections of pilot frequency data to obtain a fine frequency offset estimation value.
The time frequency synchronization device provided by the embodiment of the invention can realize time frequency synchronization under a larger Doppler frequency shift environment, and improve the accuracy of the time frequency synchronization.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. A time-frequency synchronization method is characterized by comprising the following steps:
according to a preset pilot frequency sequence and a conjugate sequence of the pilot frequency sequence, carrying out coarse synchronization processing on a received signal, and determining a coarse synchronization position corresponding to the received signal;
performing coarse frequency offset estimation according to the coarse synchronization position to obtain a Doppler frequency offset estimator;
performing fine synchronization processing according to the coarse synchronization position and the Doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: compensating coarse frequency offset and determining a correlation value of a received signal;
determining a final synchronous position according to the maximum correlation value in the correlation values, and performing fine frequency offset estimation according to the final synchronous position and a result after coarse frequency offset compensation to determine a fine frequency offset estimation value;
determining the sum of the fine frequency offset estimation value and the Doppler frequency offset estimator, and performing frequency offset compensation according to the determined sum to complete frequency synchronization;
the coarse synchronization processing of the received signal according to the preset pilot sequence and the conjugate sequence of the pilot sequence, and determining the coarse synchronization position corresponding to the received signal includes:
respectively carrying out sliding correlation processing on a received signal by utilizing a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence and a second correlation power value corresponding to the received signal and the conjugate sequence;
for a received signal in a time slot, calculating the maximum peak position in a first correlation power value to obtain a first maximum peak position, and calculating the maximum peak position in a second correlation power value to obtain a second maximum peak position;
calculating the noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating the noise power corresponding to the second maximum peak position to obtain a second noise power;
calculating a synchronization mark according to the first noise power and the second noise power;
and if the synchronization mark is larger than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
2. The time-frequency synchronization method according to claim 1, wherein the determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position comprises:
and rounding the mean value of the first maximum peak position and the second maximum peak position to determine the coarse synchronization position.
3. The time-frequency synchronization method according to claim 1, wherein the performing a coarse frequency offset estimation according to the coarse synchronization position to obtain a doppler frequency offset estimator comprises:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to carry out FFT frequency offset estimation;
and performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
4. The time-frequency synchronization method of claim 3, wherein the result of the FFT frequency offset estimation comprises: the peak value and the frequency point corresponding to the peak value of the FFT frequency offset estimation, and the peak value and the corresponding frequency point of the adjacent secondary peak;
performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a doppler frequency offset estimator, including:
establishing a quadratic interpolation polynomial to form a quadratic curve;
substituting the peak value and the frequency point corresponding to the peak value in the result of the FFT frequency deviation estimation, the peak value and the corresponding frequency point of the adjacent secondary peak into a secondary curve, and solving the parameter value of the secondary curve;
and calculating the maximum value of the quadratic curve and the corresponding frequency point according to the solved parameter value of the quadratic curve, and determining the calculated frequency point as the Doppler frequency offset estimator.
5. The time-frequency synchronization method of claim 3, wherein the performing fine synchronization based on the coarse synchronization position and the Doppler frequency offset estimate comprises:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position and a position set corresponding to the adjacent position;
performing coarse frequency offset compensation on each extracted received signal according to the Doppler frequency offset estimator; and for each group of correlation signals in the extracted receiving signals, performing segmented correlation on each group of correlation signals according to a set length and summing segmented correlation results to obtain correlation values of each group of correlation signals.
6. The time-frequency synchronization method according to claim 5, wherein the determining a final synchronization position according to a maximum correlation value of the correlation values comprises:
selecting a maximum correlation value from correlation values of each group of correlation signals, and determining a position corresponding to the maximum correlation value in the position set as a final synchronous position of time;
and performing fine frequency offset estimation according to the final synchronization position and the result of the coarse frequency offset compensation, wherein the step of determining the fine frequency offset estimation value comprises the following steps:
and calling the front and rear sections of pilot frequency data after the coarse frequency offset compensation corresponding to the final synchronization position, and performing fine frequency offset estimation according to the called front and rear sections of pilot frequency data to obtain a fine frequency offset estimation value.
7. A time-frequency synchronization device, comprising:
the coarse synchronization processing module is used for performing coarse synchronization processing on the received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence and determining a coarse synchronization position corresponding to the received signal;
the coarse frequency offset estimation module is used for performing coarse frequency offset estimation according to the coarse synchronization position to obtain a Doppler frequency offset estimator;
the fine synchronization processing module is used for performing fine synchronization processing according to the coarse synchronization position and the Doppler frequency offset estimator; wherein, the fine synchronization processing process comprises: compensating coarse frequency offset and determining a correlation value of a received signal;
the fine frequency offset estimation module is used for determining a final synchronous position according to the maximum correlation value in the correlation values, performing fine frequency offset estimation according to the final synchronous position and a result after coarse frequency offset compensation, and determining a fine frequency offset estimation value;
the frequency offset compensation module is used for determining the sum of the fine frequency offset estimation value and the Doppler frequency offset estimator, and performing frequency offset compensation according to the determined sum to complete frequency synchronization;
the coarse synchronization processing module is configured to perform coarse synchronization processing on a received signal according to a preset pilot sequence and a conjugate sequence of the pilot sequence, and determine a coarse synchronization position corresponding to the received signal, and specifically includes:
respectively carrying out sliding correlation processing on a received signal by utilizing a preset pilot sequence and a conjugate sequence of the pilot sequence to obtain a first correlation power value corresponding to the received signal and the pilot sequence and a second correlation power value corresponding to the received signal and the conjugate sequence;
for a received signal in a time slot, calculating the maximum peak position in a first correlation power value to obtain a first maximum peak position, and calculating the maximum peak position in a second correlation power value to obtain a second maximum peak position;
calculating the noise power corresponding to the first maximum peak position to obtain a first noise power, and calculating the noise power corresponding to the second maximum peak position to obtain a second noise power;
calculating a synchronization mark according to the first noise power and the second noise power;
and if the synchronization mark is larger than a preset threshold, determining a coarse synchronization position according to the first maximum peak position and the second maximum peak position.
8. The time-frequency synchronization device according to claim 7, wherein the coarse frequency offset estimation module is configured to perform coarse frequency offset estimation according to the coarse synchronization position to obtain a doppler frequency offset estimator, and specifically includes:
extracting a receiving signal corresponding to the length point of the pilot frequency sequence according to the coarse synchronization position, and multiplying the extracted receiving signal by the conjugate sequence to carry out FFT frequency offset estimation;
and performing parabolic interpolation processing according to the FFT frequency offset estimation result to obtain a Doppler frequency offset estimator.
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| CN108123788B (en) * | 2017-12-18 | 2020-11-06 | 中国电子科技集团公司第五十四研究所 | Fast synchronization device based on blind separation iterative reconstruction and suitable for scattering communication |
| CN108924073B (en) * | 2018-06-28 | 2019-08-20 | 中国科学院声学研究所 | A kind of quick self-adapted Doppler estimation synchronous based on pseudo-random sequence |
| CN110113285B (en) * | 2019-05-05 | 2021-06-11 | 东南大学 | OFDM system closed-loop time-frequency synchronization method and device |
| CN110311722B (en) * | 2019-06-24 | 2021-08-06 | 四川九洲电器集团有限责任公司 | Satellite transponder local oscillation frequency calibration test method |
| CN112152677B (en) * | 2019-06-28 | 2021-11-16 | 清华大学 | Space-based opportunistic signal Doppler frequency estimation method, device, equipment and medium |
| CN110601718B (en) * | 2019-09-05 | 2022-11-04 | 珠海市杰理科技股份有限公司 | Spread spectrum communication capturing method, device and system |
| CN110995630B (en) * | 2019-10-22 | 2022-08-09 | 北京全路通信信号研究设计院集团有限公司 | Frequency offset correction method of narrow-band communication system suitable for mixed running of multi-level trains |
| CN111181890B (en) * | 2019-12-31 | 2022-12-30 | 北京华力创通科技股份有限公司 | Method and device for synchronizing signals and server |
| CN111431827B (en) * | 2020-05-07 | 2023-03-07 | 中国人民解放军63921部队 | FFT-based step-by-step progressive high-precision frequency estimation method |
| JP2023544660A (en) * | 2020-08-05 | 2023-10-25 | 中興通訊股▲ふん▼有限公司 | Method for time information indication |
| CN114079606B (en) * | 2020-08-17 | 2023-10-24 | 海能达通信股份有限公司 | Air interface time alignment method and device and electronic equipment |
| CN114553387B (en) * | 2022-01-26 | 2023-03-21 | 小唐科技(上海)股份有限公司 | Method and device for judging validity of received signal |
| CN115333715B (en) * | 2022-08-12 | 2024-03-29 | 上海金卓科技有限公司 | Synchronization method, device, communication equipment and medium of narrowband communication system |
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