CN108989261B - Timing synchronization method, device and related equipment of communication system - Google Patents
Timing synchronization method, device and related equipment of communication system Download PDFInfo
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
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- H—ELECTRICITY
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
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- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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- H04L27/2657—Carrier synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H04L2027/0026—Correction of carrier offset
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Abstract
The application discloses a timing synchronization method of a communication system, which comprises the steps of receiving a first signal sent by a communication transmitter; carrying out coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal; calling a leading time domain signal, and performing cross-correlation processing on a correction signal and the leading time domain signal to obtain a cross-correlation measurement set; clustering each cross-correlation measurement element in the cross-correlation measurement set by modifying an EM clustering algorithm to obtain a clustering result; determining a first coherence metric position in the clustering result as a fine timing synchronization position; performing timing synchronization according to the fine timing synchronization position; the timing synchronization method can accurately identify the correlation peak caused by channel multipath, and determine a more accurate timing position from the correlation peak, thereby further improving the timing precision of synchronization. The application also discloses a timing synchronization device, a timing synchronization system, a communication receiver and a computer readable storage medium of the communication system, which have the beneficial effects.
Description
Technical Field
The present application relates to the field of communications systems, and in particular, to a timing synchronization method for a communications system, and further relates to a timing synchronization apparatus, a timing synchronization system, a communications receiver, and a computer-readable storage medium for a communications system.
Background
OFDM (Orthogonal Frequency Division Multiplexing) is a very important transmission technology in the current wireless communication field, and is also a physical layer basic transmission technology of 5G. Timing synchronization is a necessary condition for maintaining orthogonality of the OFDM system, and inaccurate timing synchronization may introduce Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI), which may seriously degrade system performance.
Among the existing timing synchronization algorithms, the preamble sequence assisted synchronization algorithm has robustness and high efficiency, and thus has been widely applied to the OFDM system based on burst packet transmission. In a frequency selective channel environment, the optimal timing point should be the position where the data frame arrives through the first delay path of the channel. However, since the channel tap delay is random, the first path is not necessarily the arrival path with the largest instantaneous power, which poses a challenge to accurate timing.
Currently common preamble symbol based timing synchronization solutions can be broadly divided into two categories, autocorrelation based timing synchronization and cross-correlation based timing methods. The existing timing method based on the autocorrelation searches for a timing position by searching the maximum value of the autocorrelation measurement, and due to the existence of the cyclic prefix in the OFDM system, a classical autocorrelation algorithm is easily influenced by a measurement platform; in the prior art, most timing synchronization algorithms based on cross-correlation still improve timing accuracy by optimizing a training sequence structure, and still only can search a maximum value point of cross-correlation measurement as an initial position of a data frame. Therefore, no matter which technique in the prior art is adopted, the timing precision is limited, and the multipath channel is sensitive.
Therefore, how to accurately identify the correlation peak caused by channel multipath and determine a more accurate timing position from the correlation peak, thereby further improving the timing precision of synchronization is a problem to be solved by those skilled in the art.
Disclosure of Invention
The timing synchronization method can accurately identify the correlation peak caused by channel multipath, and determine a more accurate timing position from the correlation peak, thereby further improving the timing precision of synchronization; it is another object of the present application to provide a timing synchronization apparatus, a system, a communication receiver, and a computer-readable storage medium of a communication system, all of which have the above-mentioned advantages.
In order to solve the above technical problem, the present application provides a timing synchronization method of a communication system, where the timing synchronization method includes:
receiving a first signal sent by a communication transmitter;
carrying out coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
calling a leading time domain signal, and performing cross-correlation processing on the correction signal and the leading time domain signal to obtain a cross-correlation measurement set;
clustering each cross-correlation measurement element in the cross-correlation measurement set by modifying an EM clustering algorithm to obtain a clustering result;
and determining a first coherence metric position in the clustering result as a fine timing synchronization position so as to complete timing synchronization according to the fine timing synchronization position.
Preferably, the timing synchronization method of the communication system further includes:
the communication transmitter carries out inverse Fourier transform processing on a transmission signal to obtain a time domain signal;
inserting a cyclic prefix into the time domain signal to obtain the preamble time domain signal;
and transmitting the preamble time domain signal to a communication receiver through a channel.
Preferably, the performing coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal includes:
performing autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
determining a maximum autocorrelation metric element in the set of autocorrelation metrics;
taking the time corresponding to the maximum autocorrelation measurement element as a coarse timing synchronization position;
performing frequency offset estimation by using the coarse timing synchronization position to obtain carrier frequency offset;
and carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain the correction signal.
Preferably, the performing cross-correlation processing on the correction signal and the preamble time-domain signal to obtain a cross-correlation metric set includes:
performing cross-correlation processing on the correction signal and the preamble time domain signal to obtain a complete cross-correlation measurement set;
determining a maximum cross-correlation metric element in the complete set of cross-correlation metrics;
and selecting an interval set with a preset length from the complete cross-correlation metric set according to the position of the maximum cross-correlation metric element to obtain the cross-correlation metric set.
Preferably, if the clustering result includes a coherent metric class and a non-coherent metric class, the determining a first coherent metric position in the clustering result as a fine timing synchronization position includes:
obtaining the coherence metric class in the clustering result;
and selecting a first measurement position in the coherence measurement class as the first coherence measurement position.
In order to solve the above technical problem, the present application further provides a timing synchronization apparatus of a communication system, where the timing synchronization apparatus includes:
the information receiving module is used for receiving a first signal sent by a communication transmitter;
the correction processing module is used for carrying out coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
the cross-correlation processing module is used for calling a preamble time domain signal and carrying out cross-correlation processing on the correction signal and the preamble time domain signal to obtain a cross-correlation measurement set;
the clustering processing module is used for clustering processing on each cross-correlation measurement element in the cross-correlation measurement set through a modified EM clustering algorithm to obtain a clustering result;
and the synchronous position determining module is used for determining a first coherent measurement position in the clustering result as a fine timing synchronous position so as to finish timing synchronization according to the fine timing synchronous position.
Preferably, the correction processing module includes:
the autocorrelation processing submodule is used for carrying out autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
a maximum autocorrelation metric element determining submodule for determining a maximum autocorrelation metric element in the set of autocorrelation metrics;
a coarse timing synchronization position determining submodule, configured to use a time corresponding to the maximum autocorrelation metric element as a coarse timing synchronization position;
the frequency offset estimation submodule is used for carrying out frequency offset estimation by utilizing the coarse timing synchronization position to obtain carrier frequency offset;
and the carrier frequency offset correction processing submodule is used for carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain the correction signal.
In order to solve the above technical problem, the present application further provides a communication receiver, including:
a memory for storing a computer program;
a processor for implementing the steps of the timing synchronization method of any of the above-mentioned communication systems when running said computer program.
In order to solve the above technical problem, the present application further provides a timing synchronization system of a communication system, where the timing synchronization system includes:
a communication receiver as described above;
a communication transmitter for transmitting a first signal to the communication receiver.
To solve the above technical problem, the present application further provides a computer-readable storage medium, having a computer program stored thereon, where the computer program, when executed by a processor, implements the steps of the timing synchronization method of any of the above communication systems.
The timing synchronization method of the communication system comprises the steps of receiving a first signal sent by a communication transmitter; carrying out coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal; calling a leading time domain signal, and performing cross-correlation processing on the correction signal and the leading time domain signal to obtain a cross-correlation measurement set; clustering each cross-correlation measurement element in the cross-correlation measurement set by modifying an EM clustering algorithm to obtain a clustering result; and determining a first coherence metric position in the clustering result as a fine timing synchronization position so as to complete timing synchronization according to the fine timing synchronization position.
Therefore, according to the technical scheme provided by the application, on the basis of finishing the cross-correlation processing on the received signal, namely the first signal, the clustering processing is performed on the received signal based on the fine timing synchronization algorithm for correcting EM (Expectation Maximization) clustering, namely, the correlation peak caused by channel multipath can be effectively identified in the OFDM system, and the first multipath correlation peak position is selected from the correlation peak, namely, the first coherence measurement position is used as the timing position, so that the timing synchronization of the communication system is realized, and the realization method has higher timing precision and can effectively avoid the problem that the traditional timing synchronization algorithm can only search the strongest path; meanwhile, the modified EM clustering algorithm is adopted for information processing, so that the influence of a channel on the timing accuracy can be reduced, the robust timing performance is realized under different channel conditions, and the stable timing performance can be obtained under the condition of a lower signal-to-noise ratio; in addition, the calculation complexity of the modified EM clustering algorithm is only influenced by the set range, the specific implementation process is simple, and the method has strong practicability.
The timing synchronization device, the timing synchronization system, the communication receiver and the computer readable storage medium of the communication system provided by the present application all have the above beneficial effects, and are not described herein again.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present application, 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 illustrating a timing synchronization method of a communication system according to the present application;
fig. 2 is a schematic flowchart of a synchronization preamble processing method according to the present application;
fig. 3 is a schematic flow chart of a coarse synchronization and frequency offset correction processing method according to the present application;
fig. 4 is a schematic flow chart of a signal cross-correlation processing method provided in the present application;
fig. 5 is a flow chart of a method for timing synchronization in a communication system provided by the present application;
fig. 6 is a schematic structural diagram of a timing synchronization apparatus of a communication system provided in the present application;
fig. 7 is a schematic structural diagram of a communication receiver provided in the present application;
fig. 8 is a schematic structural diagram of a timing synchronization system of a communication system provided in the present application.
Detailed Description
The core of the application is to provide a timing synchronization method of a communication system, which can accurately identify the correlation peak caused by channel multipath and determine a more accurate timing position from the correlation peak, thereby further improving the timing precision of synchronization; another core of the present application is to provide a timing synchronization apparatus, a system, a communication receiver, and a computer-readable storage medium of a communication system, all having the above-mentioned advantages.
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all 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 application.
In the prior art, both the self-correlation timing synchronization technology and the cross-correlation timing synchronization technology have the limitations of limited timing precision and sensitivity to multipath channels. Therefore, in order to solve the above problems, the present application provides a timing synchronization method in a communication system, which can accurately identify correlation peaks caused by channel multipath, and determine a more accurate timing position from the correlation peaks, thereby effectively improving the timing accuracy of synchronization.
Referring to fig. 1, fig. 1 is a flowchart illustrating a timing synchronization method of a communication system according to the present application, where the timing synchronization method includes:
s100: receiving a first signal sent by a communication transmitter;
specifically, information transmission in a communication system can be generally realized through a channel, and the information transmission party can be divided into a communication transmitter and a communication receiver. For example, in a single-antenna OFDM (Orthogonal Frequency Division Multiplexing) system, which includes a single-antenna communication transmitter and a single-antenna communication receiver, when information transmission is required, a signal to be transmitted can be transmitted to the communication receiver through a channel by the communication transmitter. The signal to be transmitted is a signal which is sent by a communication transmitter and is not transmitted through a channel, and the first signal is a signal which is obtained after the signal to be transmitted is transmitted through the channel and is received by a communication receiver.
Certainly, the single-antenna OFDM system is only a relatively common communication system provided by the present application, and is not unique, and the technical solution provided by the present application may also be extended to other typical communication systems such as TDS-OFDM, CDMA system, and the like.
Further, in order to facilitate the implementation of the timing synchronization function in the subsequent communication receiver, the communication transmitter may also perform preprocessing on the signal to be transmitted before sending the signal, so as to please refer to fig. 2 as a preferred embodiment, fig. 2 is a schematic flow diagram of a method for preprocessing a sent signal provided in the present application, and the timing synchronization method of the communication system may further include:
s101: the communication transmitter carries out inverse Fourier transform processing on the transmitted signal to obtain a time domain signal;
s102: inserting a cyclic prefix into the time domain signal to obtain a preamble time domain signal;
s103: the preamble time domain signal is transmitted to the communication receiver through the channel.
Specifically, the transmission signal in S101 is the signal to be transmitted, and generally belongs to a frequency domain signal, so that the communication receiver may perform IFFT (Inverse Fast Fourier Transform) processing on the signal to be transmitted first, so as to realize conversion from the frequency domain signal to a time domain signal; further, a cyclic prefix may be inserted into the obtained time domain signal to combat inter-symbol interference, and a preamble time domain signal is obtained; the time domain preamble signal may then be transmitted over a channel to a communication receiver. Therefore, preprocessing and transmission of the signal to be transmitted are realized.
S200: carrying out coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
specifically, after receiving the first signal, the communication receiver may perform carrier frequency offset correction processing on the first signal to obtain a corresponding correction signal. Of course, as to the specific process of the correction processing, reference may be made to any one of the prior arts, and the present application is not particularly limited.
As a preferred embodiment, please refer to fig. 3, where fig. 3 is a flowchart illustrating a signal correction processing method provided in the present application, where the performing coarse synchronization and carrier frequency offset correction processing on the first signal to obtain the corrected signal includes:
s201: performing autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
s202: determining a maximum autocorrelation metric element in the set of autocorrelation metrics;
s203: taking the time corresponding to the maximum autocorrelation measurement element as a coarse timing synchronization position;
s204: carrying out frequency offset estimation by using the coarse timing synchronization position to obtain carrier frequency offset;
s205: and carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain a correction signal.
Specifically, the step S200 may be a coarse timing synchronization processing procedure of the signal, so that the present application provides a more specific correction processing method, that is, the correction processing method is implemented by an autocorrelation timing synchronization technique. Firstly, a communication receiver carries out autocorrelation processing on a received first signal to obtain a plurality of autocorrelation measurement elements to form an autocorrelation measurement set; further, determining the autocorrelation measurement element with the largest value in the autocorrelation measurement set, obtaining the maximum autocorrelation measurement element, and taking the time corresponding to the maximum autocorrelation measurement element as a coarse timing synchronization position; further, frequency offset estimation is carried out based on the coarse synchronization position to obtain corresponding carrier frequency offset, so that carrier frequency offset correction processing can be carried out on the first signal based on the carrier frequency offset to obtain a final correction signal, and carrier frequency offset in a communication system is approximately and completely compensated.
S300: calling a preamble time domain signal, and performing cross-correlation processing on the correction signal and the preamble time domain signal to obtain a cross-correlation measurement set;
specifically, the step aims to implement the cross-correlation processing of the signals based on the cross-correlation timing synchronization technology, the communication receiver calls a preamble time domain signal pre-stored in the communication receiver, and performs the cross-correlation processing on the correction signal obtained in S200 and the preamble time domain signal, and similar to the self-correlation processing process, a plurality of cross-correlation metric elements are obtained to form the cross-correlation metric set.
As a preferred embodiment, please refer to fig. 4, fig. 4 is a flowchart illustrating a signal cross-correlation processing method provided in the present application, where the cross-correlation processing the correction signal and the preamble time-domain signal to obtain a cross-correlation metric set includes:
s301: performing cross-correlation processing on the correction signal and the preamble time domain signal to obtain a complete cross-correlation measurement set;
s302: determining a maximum cross-correlation metric element in the complete cross-correlation metric set;
s303: and selecting an interval set with a preset length from the complete cross-correlation measurement set according to the position of the maximum cross-correlation measurement element to obtain a cross-correlation measurement set.
Specifically, the present application provides a more specific implementation manner for performing cross-correlation processing on signals, after performing cross-correlation processing on a correction signal and a preamble time domain signal, a plurality of cross-correlation metric elements are obtained, all cross-correlation metric elements form a complete cross-correlation metric set, that is, the complete cross-correlation metric set, and a cross-correlation metric element with a maximum value, that is, the maximum cross-correlation metric element, is determined in the complete cross-correlation metric set; further, according to the position of the maximum cross-correlation metric element, that is, the position corresponding to the strongest path, an interval set with a predetermined length is selected, and the interval set is an adjacent interval set of the maximum cross-correlation metric element, so that the cross-correlation metric set can be obtained. The preset length can be set according to actual requirements, and the preset length is not limited in the application.
S400: clustering each cross-correlation measurement element in the cross-correlation measurement set by modifying an EM clustering algorithm to obtain a clustering result;
s500: and determining a first coherence metric position in the clustering result as a fine timing synchronization position so as to complete timing synchronization according to the fine timing synchronization position.
Specifically, after the cross-correlation measurement set is obtained, a modified EM clustering algorithm may be called to perform clustering processing on each cross-correlation measurement element in the cross-correlation measurement set to obtain a corresponding clustering result, so that a first coherence measurement position may be determined in the clustering result as a fine timing synchronization position in the communication system. Furthermore, the timing synchronization of the communication system can be realized according to the obtained fine timing synchronization position, and the realization of the timing synchronization has higher precision.
Preferably, the clustering result may include a coherent metric class and a non-coherent metric class, and the determining a first coherent metric position in the clustering result as the fine timing synchronization position may include: obtaining a coherence metric class from the clustering result; and selecting a first measurement position in the coherence measurement class as a first coherence measurement position.
Specifically, after clustering processing is performed on each cross-correlation metric element in the cross-correlation metric set, the obtained clustering result may include a coherence metric class and a non-coherence metric class; further, a first measurement position can be selected from the coherence measurement class, and the first coherence measurement position, that is, the fine timing synchronization position, is obtained.
According to the timing synchronization method of the communication system, on the basis of finishing cross-correlation processing on a received signal, namely the first signal, clustering processing is carried out on the received signal based on a fine timing synchronization algorithm for correcting EM (Expectation Maximization) clustering, namely a correlation peak caused by channel multipath can be effectively identified in an OFDM (orthogonal frequency division multiplexing) system, and a first channel multipath correlation peak position is selected from the correlation peaks, namely the first coherence measurement position is used as a timing position, so that timing synchronization of the communication system is realized, the realization method has high timing accuracy, and the problem that only the strongest path can be found by a traditional timing synchronization algorithm can be effectively avoided; meanwhile, the modified EM clustering algorithm is adopted for information processing, so that the influence of a channel on the timing accuracy can be reduced, the robust timing performance is realized under different channel conditions, and the stable timing performance can be obtained under the condition of a lower signal-to-noise ratio; in addition, the calculation complexity of the modified EM clustering algorithm is only influenced by the set range, the specific implementation process is simple, and the method has strong practicability.
On the basis of the above embodiments, the present embodiment takes an OFDM communication system as an example, and provides a more specific implementation manner.
In OFDM communication system, communication transmitter can adopt IFFT algorithm of N point operation to convert transmitted frequency domain signal into time domain signal, and set useful subcarrier number as Nuse(ii) a Further, a cyclic prefix is inserted, the length of which is set to LCPThen the single OFDM symbol length is Ns＝N+LCPAnd the length of a preamble symbol of a frame in the OFDM system is an OFDM symbol length. Therefore, assuming that the frequency domain signal of the kth subcarrier of the symbol transmitted by the communication transmitter is x (k), the time domain signal x (n) obtained after the above processing is:
wherein exp (.) represents an exponential operation,
k is 0 to NuseAn integer between-1 and N is 0 to N + LCPAn integer in between.
Further, because the channel environment between the communication transmitter and the communication receiver in the OFDM system is a frequency selective multipath fading channel, the maximum multipath delay length of the channel is L, and it is assumed that the channel impulse response coefficient on the L-th multipath is h (L), where L is an integer between 0 and L-1. Then, after the time domain signal x (n) passes through the channel, gaussian white noise w (n) is superimposed; meanwhile, due to mismatch of transmission delay, transmission and reception crystal oscillators introduced by a channel, a received signal at a communication receiver has symbol timing deviation θ and carrier frequency offset Δ F, and after normalization processing is performed on the carrier frequency offset Δ F with respect to a subcarrier interval F of an OFDM system, normalized carrier frequency offset ∈ ═ Δ F/F can be obtained, so that the first signal, i.e., a received signal r (n) of the communication receiver, is:
thereby, signal transmission between the communication transmitter and the communication receiver is realized.
Based on the above signal transmission process, please refer to fig. 5, and fig. 5 is a flowchart of a timing synchronization method in a communication system according to the present application.
Step one, a signal transmission process between a communication transmitter and a communication receiver:
first, a frequency domain signal to be transmitted is denoted as X ═ X0 X1 … XN-1]TWherein X is at even number of subcarriers2q＝zqThen z isqCan be expressed as:
where κ is an arbitrary coprime to N/2. The frequency domain signal at odd subcarriers is set to zero.
Further, converting the frequency domain signal into a time domain signal, and inserting the time domain signal with a length LCPGenerating a cyclic prefix of length NsPreamble time domain signal S:
S＝[Acp A A]；
wherein A represents a time domain random sequence with the length of N/2, ACPIs expressed as length LCPThe cyclic prefix of (c); i.e. the preamble time domain signal S is formed by a length LCPCyclic prefix of (A)CPAnd two time domain random sequences A with the length of N/2 and the same value.
Step two, the coarse synchronization process of the communication receiver to the received signal:
firstly, assuming that a received signal corresponding to a preamble time domain signal S after channel transmission is r (n), the received signal r (n) is utilized to perform autocorrelation processing to calculate and obtain an autocorrelation metric function m (d):
where, | represents an absolute value operation, (-)*Indicating a conjugate operation.
Further, the time T at which the autocorrelation measurement function M (d) takes the maximum value is searchedCAs a coarse timing synchronization position; and using the coarse timing synchronization position TC to perform frequency offset estimation to obtain a carrier frequency offset estimation value
Wherein, angle { } represents the phase taking operation.
Further, carrier frequency offset estimation is utilized
Carrying out carrier frequency offset correction processing on the received signal r (n) to obtain a correction signal
Wherein, let epsilon ∈ (-1,1), thereby, the system carrier frequency offset can be approximately and completely compensated.
Step three, the cross-correlation processing process of the communication receiver to the correction signal:
firstly, the correction signal is utilized
Performing cross-correlation processing with locally stored preamble time domain signal S to obtain cross-correlation measurement function Pc(q)：
Wherein, S (n) represents the nth sample point of the leading time domain signal, and q takes the value of Tc-N/2 to TcAn integer between + N/2;
further, the value of q ∈ [ T ]c-N/2,Tc+N/2]Inner search cross-correlation metric Pc(q) maximum value, and the corresponding time is denoted as Ts：
Ts＝argmaxq(|Pc(q)|)；
Wherein argmaxq(. cndot.) denotes taking the q value such that the function in parentheses takes the maximum value.
Further, based on the above TsSelecting a neighboring interval set of the maximum cross-correlation peak with the length of U at any moment to obtain a cross-correlation measurement set
Wherein the related metrics are set
Including U cross-correlation metric elements.
Step four, the communication receiver carries out clustering processing on the cross-correlation measurement elements:
in particular, the set of correlation metrics
Respective cross-correlation metric elements P inc(q), which can be classified as having a large variance
Gaussian coherence measure and smaller variance
Is classified into two types, and
when q ∈ { theta, theta +1, …, theta + L-1}, Pc(q) is a gaussian coherence measure with larger variance, and otherwise a gaussian non-coherence measure with smaller variance.
In the clustering process, firstly, initialization processing is carried out, the initial value of the EM clustering algorithm is set, and the correlation measurement set is calculated
Energy value | P of all cross-correlation metric elements inc(q)|2And taking the maximum energy value as a large variance
Initial value of (2)
Taking the minimum energy value as a small variance
Initial value of (2)
Wherein, ()0Representing the preset value before the EM clustering algorithm starts to run. Assuming that the cross-correlation measure takes large variance
Is initialized to (P)0)0Then take the small variance
Is initialized to (P)1)01-a/U, wherein (P)0)0When a is 1-2, the EM clustering algorithm can obtain a value under medium fading channel conditionsRobust system performance.
Further, iteration processing is carried out, and in the ith iteration process, a correlation metric set is calculated
Of each cross-correlation metric element Pc(q) two corresponding posterior probabilities (ω)0(q))iAnd (ω)1(q))iWherein, theiRepresents the ith iteration process, (omega)0(q))iMeasure P for cross-correlationc(q) compliance with large variance
Posterior probability of zero mean gaussian distribution (ω)1(q))iMeasure P for cross-correlationc(q) compliance with small variance
Posterior probability of zero mean gaussian distribution:
(ω1(q))i＝1-(ω0(q))i；
further, in the ith iteration process, the large variance is processed
Sum of small variance
Updating:
then during the ith iteration the two prior probability values (P)0)iAnd (P)1)iRespectively as follows:
(P1)i＝1-(P0)i；
wherein min {. cndot } represents the minimum value in parentheses.
Further, calculating a log-likelihood ratio in the ith iteration:
wherein log (·) represents a natural logarithm operation; when | LLR(i)-LLR(i-1)And when the |, is less than or equal to 0.001, finishing correcting the EM clustering algorithm, otherwise, setting i to i +1, and continuing to perform iterative processing.
Step five, timing synchronization process of the communication receiver:
assuming that the modified EM clustering algorithm obtains convergence after I iterations, at this time, the correlation metric set can be aggregated by the following formula
Calculating the clustering results of all the cross-correlation measurement elements:
wherein, C (q) represents the clustering result of the q-th cross-correlation metric element; arg maxi{. denotes taking i such that the brace function takes the maximum value, and i is 0, 1. Further, C (q) is 0qThe moment T corresponding to the minimum valueBThe fine timing synchronization position is used as a timing synchronization position of the communication system.
According to the timing synchronization method of the communication system, on the basis of completing autocorrelation processing on a received signal, namely the first signal, clustering processing is performed on the received signal based on a fine timing synchronization algorithm for correcting EM (Expectation Maximization) clustering, namely, a correlation peak caused by channel multipath can be effectively identified in an OFDM (orthogonal frequency division multiplexing) system, and a first channel multipath correlation peak position is selected from the correlation peak, namely, the first coherence measurement position is used as a timing position, so that timing synchronization of the communication system is realized, the realization method has high timing accuracy, and the problem that only the strongest path can be found by a traditional timing synchronization algorithm can be effectively avoided; meanwhile, the modified EM clustering algorithm is adopted for information processing, so that the influence of a channel on the timing accuracy can be reduced, the robust timing performance is realized under different channel conditions, and the stable timing performance can be obtained under the condition of a lower signal-to-noise ratio; in addition, the calculation complexity of the modified EM clustering algorithm is only influenced by the set range, the specific implementation process is simple, and the method has strong practicability.
To solve the above problem, please refer to fig. 6, fig. 6 is a schematic structural diagram of a timing synchronization apparatus of a communication system provided in the present application, where the timing synchronization apparatus may include:
the information receiving module 10 is used for receiving a first signal sent by a communication transmitter;
a correction processing module 20, configured to perform coarse synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
a cross-correlation processing module 30, configured to invoke the preamble time domain signal, and perform cross-correlation processing on the correction signal and the preamble time domain signal to obtain a cross-correlation metric set;
the clustering processing module 40 is used for clustering each cross-correlation metric element in the cross-correlation metric set by modifying the EM clustering algorithm to obtain a clustering result;
a synchronization position determining module 50, configured to determine a first coherence metric position in the clustering result as a fine timing synchronization position, so as to complete timing synchronization according to the fine timing synchronization position.
As a preferred embodiment, the correction processing module 20 may include:
the autocorrelation processing submodule is used for carrying out autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
a maximum autocorrelation measurement element determining submodule for determining a maximum autocorrelation measurement element in the set of autocorrelation measurements;
the coarse timing synchronization position determining submodule is used for taking the time corresponding to the maximum autocorrelation measurement element as a coarse timing synchronization position;
the frequency offset estimation submodule is used for carrying out frequency offset estimation by utilizing the coarse timing synchronization position to obtain carrier frequency offset;
and the carrier frequency offset correction processing submodule is used for carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain a correction signal.
As a preferred embodiment, the cross-correlation processing module 30 may include:
the cross-correlation processing submodule is used for carrying out cross-correlation processing on the correction signal and the preamble time domain signal to obtain a complete cross-correlation measurement set;
a maximum cross-correlation metric element determining submodule for determining a maximum cross-correlation metric element in the complete cross-correlation metric set;
and the cross-correlation measurement set acquisition submodule is used for selecting an interval set with a preset length in the complete cross-correlation measurement set according to the position of the maximum cross-correlation measurement element to obtain the cross-correlation measurement set.
As a preferred embodiment, the synchronization position determining module 50 may include:
a coherence measure class obtaining submodule for obtaining a coherence measure class from the clustering result;
and the first coherence metric position selection submodule is used for selecting a first metric position in the coherence metric class as a first coherence metric position.
For the introduction of the apparatus provided in the present application, please refer to the above method embodiments, which are not described herein again.
To solve the above technical problem, please refer to fig. 7, where fig. 7 is a schematic structural diagram of a communication receiver provided in the present application, and the communication receiver may include:
a memory 101 for storing a computer program;
a processor 102 for implementing the steps of the timing synchronization method of any of the above-described communication systems when running a computer program.
For the introduction of the communication receiver provided in the present application, please refer to the above method embodiment, which is not described herein again.
To solve the above problem, please refer to fig. 8, where fig. 8 is a schematic structural diagram of a timing synchronization system of a communication system provided in the present application, and the timing synchronization system may include:
a communication transmitter 100 for transmitting the first signal to a communication receiver 200;
the communication receiver 200 described in the previous embodiment;
as a preferred embodiment, the communication transmitter 100 is specifically configured to perform inverse fourier transform processing on a transmission signal to obtain a time-domain signal; inserting a cyclic prefix into the time domain signal to obtain a preamble time domain signal; the preamble time domain signal is transmitted to a receiver through a channel.
For the introduction of the system provided by the present application, please refer to the above method embodiment, which is not described herein again.
To solve the above problem, the present application further provides a computer-readable storage medium, on which a computer program is stored, and the computer program, when executed by a processor, can implement the steps of timing synchronization of any of the above communication systems.
The computer-readable storage medium may include: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
For the introduction of the computer-readable storage medium provided in the present application, please refer to the above method embodiments, which are not described herein again.
The embodiments are described in a progressive manner in the specification, 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 application.
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 timing synchronization method, apparatus, system, communication receiver, and computer readable storage medium of the communication system provided by the present application are described in detail above. The principles and embodiments of the present application are explained herein using specific examples, which are provided only to help understand the method and the core idea of the present application. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and these improvements and modifications also fall into the elements of the protection scope of the claims of the present application.
Claims (9)
1. A method for timing synchronization in a communication system, comprising:
receiving a first signal sent by a communication transmitter;
carrying out coarse timing synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
calling a leading time domain signal, and performing cross-correlation processing on the correction signal and the leading time domain signal to obtain a cross-correlation measurement set;
clustering each cross-correlation measurement element in the cross-correlation measurement set by modifying an EM clustering algorithm to obtain a clustering result;
determining a first coherence measurement position in the clustering result as a fine timing synchronization position so as to complete timing synchronization according to the fine timing synchronization position;
wherein the invoking the preamble time domain signal comprises:
calling the preamble time domain signal from the communication transmitter; and the communication transmitter performs inverse Fourier transform processing on the transmitted signal to obtain a time domain signal, and inserts a cyclic prefix into the time domain signal to obtain the preamble time domain signal.
2. The timing synchronization method of claim 1, wherein the performing coarse timing synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal comprises:
performing autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
determining a maximum autocorrelation metric element in the set of autocorrelation metrics;
taking the time corresponding to the maximum autocorrelation measurement element as a coarse timing synchronization position;
performing frequency offset estimation by using the coarse timing synchronization position to obtain carrier frequency offset;
and carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain the correction signal.
3. The timing synchronization method of claim 2, wherein the cross-correlating the correction signal with the preamble time domain signal to obtain a set of cross-correlation metrics comprises:
performing cross-correlation processing on the correction signal and the preamble time domain signal to obtain a complete cross-correlation measurement set;
determining a maximum cross-correlation metric element in the complete set of cross-correlation metrics;
and selecting an interval set with a preset length from the complete cross-correlation metric set according to the position of the maximum cross-correlation metric element to obtain the cross-correlation metric set.
4. The timing synchronization method of claim 1, wherein the clustering result includes a coherent metric class and a non-coherent metric class, and determining a first coherent metric position in the clustering result as a fine timing synchronization position comprises:
obtaining the coherence metric class in the clustering result;
and selecting a first measurement position in the coherence measurement class as the first coherence measurement position.
5. A timing synchronization apparatus for a communication system, comprising:
the information receiving module is used for receiving a first signal sent by a communication transmitter;
the correction processing module is used for carrying out coarse timing synchronization and carrier frequency offset correction processing on the first signal to obtain a correction signal;
the cross-correlation processing module is used for calling a preamble time domain signal and carrying out cross-correlation processing on the correction signal and the preamble time domain signal to obtain a cross-correlation measurement set;
the clustering processing module is used for clustering processing on each cross-correlation measurement element in the cross-correlation measurement set through a modified EM clustering algorithm to obtain a clustering result;
a synchronous position determining module, configured to determine a first coherence metric position in the clustering result, as a fine timing synchronous position, so as to complete timing synchronization according to the fine timing synchronous position;
wherein the cross-correlation processing module is specifically configured to invoke the preamble time domain signal from the communication transmitter; and the communication transmitter performs inverse Fourier transform processing on the transmitted signal to obtain a time domain signal, and inserts a cyclic prefix into the time domain signal to obtain the preamble time domain signal.
6. The timing synchronization apparatus of claim 5, wherein the correction processing module comprises:
the autocorrelation processing submodule is used for carrying out autocorrelation processing on the first signal to obtain an autocorrelation measurement set;
a maximum autocorrelation metric element determining submodule for determining a maximum autocorrelation metric element in the set of autocorrelation metrics;
a coarse timing synchronization position determining submodule, configured to use a time corresponding to the maximum autocorrelation metric element as a coarse timing synchronization position;
the frequency offset estimation submodule is used for carrying out frequency offset estimation by utilizing the coarse timing synchronization position to obtain carrier frequency offset;
and the carrier frequency offset correction processing submodule is used for carrying out carrier frequency offset correction processing on the first signal by utilizing the carrier frequency offset to obtain the correction signal.
7. A communication receiver, comprising:
a memory for storing a computer program;
processor for implementing the steps of the timing synchronization method of the communication system according to any of claims 1 to 4 when running said computer program.
8. A computer-readable storage medium, characterized in that a computer program is stored on the computer-readable storage medium, which computer program, when being executed by a processor, carries out the steps of the timing synchronization method of a communication system according to any one of claims 1 to 4.
9. A timing synchronization system of a communication system, comprising the communication receiver of claim 7;
a communication transmitter for transmitting a first signal to the communication receiver.
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