CN111541638B - OFDM symbol synchronization algorithm based low-complexity implementation and synchronization updating method - Google Patents

OFDM symbol synchronization algorithm based low-complexity implementation and synchronization updating method Download PDF

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CN111541638B
CN111541638B CN202010645944.XA CN202010645944A CN111541638B CN 111541638 B CN111541638 B CN 111541638B CN 202010645944 A CN202010645944 A CN 202010645944A CN 111541638 B CN111541638 B CN 111541638B
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ofdm symbol
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CN111541638A (en
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朱江
胡登鹏
杨虎
高凯
杨军
朱立
王新建
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Hunan Guoke Ruicheng Electronic Technology Co ltd
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
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Abstract

The invention provides a low-complexity realization and synchronous updating method based on an OFDM symbol synchronization algorithm, which comprises a time delay calculation method based on an iterative OFDM signal time delay correlation function and a stable updating method based on a synchronous estimation result of OFDM symbol initial position estimation smoothing processing. In the calculation of the time delay, it is,
Figure 550384DEST_PATH_IMAGE001
the complex multiplications can be calculated simultaneously, as in the 1 complex multiplication,
Figure 520614DEST_PATH_IMAGE001
required for accumulation of complex multiplication values of individual samples
Figure 62453DEST_PATH_IMAGE001
1 addition with a delay of
Figure 764830DEST_PATH_IMAGE001
1 clock cycle, 2 addition delays of 2 clock cycles, the method will
Figure 392121DEST_PATH_IMAGE001
The 1 clock cycle is changed into 2 clock cycles, so that the algorithm time delay is greatly reduced. Due to influence of noise and the like, the position deviation value
Figure 621501DEST_PATH_IMAGE002
Is randomly varied and its distribution is related to the amplitude peak distribution of the delay correlation function. By iterative operation of pairs
Figure 549006DEST_PATH_IMAGE002
And carrying out low-pass filtering to realize smoothing processing, and controlling the speed of the change of the real position by using a coefficient.

Description

OFDM symbol synchronization algorithm based low-complexity implementation and synchronization updating method
Technical Field
The application relates to the technical field of wireless communication, in particular to a low-complexity realization and synchronization updating method based on an OFDM symbol synchronization algorithm, which is used for OFDM system non-data-assisted synchronization in wireless communication.
Background
Orthogonal Frequency Division Multiplexing (OFDM) is a special multi-carrier modulation technique, and has been widely used due to the advantages of being able to effectively resist multipath fading, high spectrum utilization, easy to implement, easy to combine with other multiple access methods, etc., it is a key technique of next generation mobile communication different from single carrier system, the OFDM system has a high requirement for synchronization technique, because the orthogonality between sub-carriers is destroyed due to the inter-symbol interference and inter-sub-carrier interference introduced by synchronization error, and the system performance is affected. Therefore, there is a need for synchronizing OFDM systems[1]。
The symbol timing synchronization is to obtain a correct starting point of each OFDM symbol in order to remove a cyclic prefix added in front of each OFDM symbol in order to resist channel multipath, thereby obtaining an OFDM frequency domain signal through FFT. When symbol timing synchronization is not ideal, inter-symbol interference (ISI) and inter-carrier interference (ICI) may be generated in the obtained OFDM frequency domain signal, thereby degrading the error rate performance of the OFDM system.
The OFDM system synchronization method can be mainly divided into a data-aided method and a non-data-aided method. The data-aided method is to design a pilot sequence with a special structure, and synchronize the system at the receiving end by using the special structure of the pilot signal, such as Schmidl algorithm using a training sequence[2]. In general, the method is simple and easy to implement. The non-data-aided rule isSince the systems are synchronized by extracting information from the signals themselves, most of these methods are complex and generally have less estimation accuracy than the former. However, the non-data-aided algorithm can effectively improve the spectrum efficiency, and only the non-data-aided algorithm can be used in the non-cooperative communication.
In order to eliminate the effect of multipath on the OFDM system, a cyclic prefix is usually added before each OFDM symbol. When the maximum delay of the channel is less than the cyclic prefix length, there will be a redundant cyclic prefix in the OFDM system. Therefore, the redundant cyclic prefix can be utilized for OFDM system synchronization. Beek et al in document [3] utilizes a maximum likelihood algorithm of cyclic prefixes to perform OFDM timing synchronization and decimal frequency offset synchronization, and has the advantages of small calculated amount, low redundancy and simple algorithm implementation. The algorithm is only suitable for Gaussian channels and flat fading channels, and under frequency selective fading channels, due to the influence of ISI, the cyclic prefix is influenced, so that the performance of the algorithm is reduced. Documents [4-7] propose an improved algorithm on the basis of the algorithm, improve a timing measurement function and a search mode, increase the use range of the OFDM symbol timing algorithm based on the cyclic prefix, and improve the performance of the algorithm.
The core of the algorithm is to obtain the starting position of the OFDM symbol by operating the cyclic prefix of the OFDM system. The mainly adopted operation processing method is delay correlation operation, because the cyclic prefix of the signal is the copy of the signal of the rear part of the OFDM symbol, each OFDM symbol in the correlation result has a peak value, and the position corresponding to the peak value is the initial position of the OFDM symbol. The timing of the OFDM symbol can be achieved by searching for the maximum value of the peak.
The cyclic prefix-based OFDM symbol synchronization algorithm is widely applied to OFDM systems without frame synchronization headers and non-data assistance, and when synchronization and result updating are realized, the problems of accurate result of algorithm realization, low resource consumption, low time delay and synchronization result updating stability need to be considered.
The main operation amount of the OFDM system symbol synchronization algorithm based on the cyclic prefix is in calculating the time delay correlation function part. The method analyzes the implementation process of the delay correlation function, discloses a low-complexity implementation method based on an FPGA, and has smaller delay.
In addition, for OFDM system timing synchronization, the main purpose is to determine the starting point of each OFDM, i.e. to determine the location where the cyclic prefix is removed. The cyclic prefix is used for resisting multipath interference, and only the position for removing the cyclic prefix is ensured to be the position without intersymbol interference. However, it should be noted that although there is no intersymbol interference in the OFDM symbol from which the cyclic prefix is removed, the signal obtained by FFT is not phase-rotated at the starting position of the original symbol, and needs to be removed by inserting known data. Typically, to reduce the loss of system resources, such known data is inserted into one symbol every multiple OFDM symbols. The removed cyclic prefix position of the OFDM symbol should be the same between these known data symbols and ensure that no inter-symbol interference is introduced at the next update. Therefore, how to make the parameter estimation value obtained by the synchronization algorithm be substituted into the system and make the result be stably updated is another problem to be considered. The patent discloses a stable, effective and low-complexity implementation method for updating a symbol timing synchronization estimation value by analyzing a parameter updating process.
Among them, references:
[1] non-data-assisted synchronization and PAPR suppression technology research in the hutenpeng OFDM system [ D ]. hunan: national defense science and technology university, 2010.
[2]Schmidl T M,Cox D C.Robust Frequency and Timing Synchronizationfor OFDM [J].IEEE Trans on Communications,1997,45(12):1613-1621.
[3]BeekJJ,SandellM,BorjessonP.ML Estimation of Time and FrequencyOffset in OFDM Systems[J].IEEETrans on Signal Processing,1997,45(7):1800-1805.
[4]MaShaodan, PanXinyue, YangGuanghua, etal. Blind SymbolSynchronization Based on CyclicPrefix for OFDM Systems [J].IEEE Trans onVehicular Technology, 2009, 58(4):1746-1751.
[5]LiWenxiu, YuanChaowei, ShenJie. A Reduced Symbol SynchronizationAlgorithm for OFDM Systems[C]//2010 International Conference onCommunications and Intelligence Information Security. Nanning:IEEE,2010:139-142.
[6]LiuXueyong, Pan Ke, Zuo Yong, etal. Blind Symbol Synchronizationfor OFDM Systems in Multipath Fading Channels [C]//2010 6thInternationalConferenceon Wireless Communications, Networking and Mobile Computing.Chengdu: IEEE, 2010: 1-4.
[7] OFDM system timing synchronization algorithm [ J ] utilizing cyclic prefix, scientific report of Western's university of electronics technology (Nature science edition), 2013,40(1): 141-one 147.
Disclosure of Invention
In order to solve the above problems, the present invention provides a low complexity implementation and synchronization update method based on an OFDM symbol synchronization algorithm, which includes the following steps:
a delay calculation method based on iterative OFDM signal delay correlation function;
the method is based on the stable updating method of the synchronous estimation result of the OFDM symbol initial position estimation smoothing processing.
The method for stably updating the synchronization estimation result based on the OFDM symbol initial position estimation smoothing processing comprises the following steps:
b1: is provided with
Figure 100002_DEST_PATH_IMAGE001
Is the length of the OFDM symbol and,
Figure DEST_PATH_IMAGE002
for the cyclic prefix length, due to the influence of multipath and noise, the position from which the cyclic prefix is removed needs to be shifted forward by a certain position from the true start time of the cyclic prefix, and the position can be shifted forward by half of the cyclic prefix length, that is, the cyclic prefix length
Figure 100002_DEST_PATH_IMAGE003
(ii) a Also, according to the properties of FFT, since the relative start time of each OFDM symbol with cyclic prefix removed is different in one frame of signal, the result after FFT is obtainedThe multiplied frequency components on the frequency domain signals of (a) are different; therefore, the realization of OFDM symbol synchronization needs to be carried out by combining a frame structure;
b2: combining the OFDM symbols with the frame structure, wherein the cyclic prefixes are removed;
b3: calculating the position deviation between the front OFDM symbol and the rear OFDM symbol; normally, the starting positions of the two front and back OFDM symbols should be the length of the OFDM symbol
Figure 148998DEST_PATH_IMAGE001
Adding a cyclic prefix
Figure DEST_PATH_IMAGE004
I.e. by
Figure 100002_DEST_PATH_IMAGE005
(ii) a When there is an error, the positional deviation between the front and rear OFDM symbols is
Figure DEST_PATH_IMAGE006
Wherein
Figure 100002_DEST_PATH_IMAGE007
Estimating a subscript for a starting position of the nth symbol; wherein n is an integer;
b4: position deviation to OFDM symbol
Figure DEST_PATH_IMAGE008
Performing smoothing to obtain the position deviation
Figure 256019DEST_PATH_IMAGE008
The mean value estimated value of the OFDM symbol is used as a deviation value adopted when the cyclic prefix position of the OFDM symbol is removed; when removing the cyclic prefix, the synchronization result is to be updated stably according to the position deviation estimated each time, that is, the deviation is processed to keep the position deviation within a small range, so that the phase rotation introduced into the OFDM symbol when removing the cyclic prefix can be effectively removed by inserting the known data. Assume multiple OF apartWhen a DM symbol is inserted into a known data symbol, the positions of the removed cyclic prefixes of the OFDM symbols between the known data symbols are the same, that is, the position offset value is not updated, and the position offset value between the positions is accumulated to the next known data symbol, which is needed to ensure that no inter-symbol interference is introduced into each OFDM symbol from which the cyclic prefix is removed; the position deviation value is influenced by factors such as multipath and noise
Figure 504598DEST_PATH_IMAGE008
Is randomly varied and its distribution is related to the amplitude peak distribution of the delay correlation function. When the noise is a gaussian noise, the noise is,
Figure 493283DEST_PATH_IMAGE008
also obeys a gaussian distribution with the true position as the mean, so that the position deviation of each OFDM symbol can be obtained
Figure 776496DEST_PATH_IMAGE008
Performing smoothing to obtain the position deviation
Figure 864538DEST_PATH_IMAGE008
The mean estimate value of (a) is used as the offset value used when the cyclic prefix position of the OFDM symbol is removed.
The smoothing is performed by applying a plurality of position deviations
Figure 475779DEST_PATH_IMAGE008
Averaging, or pairing by iterative operations
Figure 143521DEST_PATH_IMAGE008
Low-pass filtering is carried out; the iterative operation expression is as follows:
Figure DEST_PATH_IMAGE009
whereinαThe smaller the value of the ordinal number multiplied in iterative operation, the slower the updating, the smoother the output, and the less sensitive to the change of data, so that the method is suitable for the real position changeSlow conditions; and otherwise, the faster the updating is, the faster the real position change is, the condition that the real position change is fast is suitable for.
As a further improvement of the above scheme:
the invention also discloses a delay calculation method of the OFDM signal delay correlation function based on iteration, which comprises the following steps:
a1: in an OFDM system, a transmitting terminal maps information bits into a modulation pattern required by a QPSK system through a constellation, then distributes information data to useful subcarriers through subcarrier distribution, and obtains an OFDM baseband signal after Inverse Fast Fourier Transform (IFFT) and cyclic prefix addition;
a2: at a receiving end, an OFDM system firstly carries out sampling through an analog-to-digital converter; then, the signals are converted to a baseband through orthogonal down-conversion; then, after cyclic prefix, FFT and de-mapping are carried out, information bits are obtained;
a3: after the calculation of the delay correlation function is completed according to the calculation of the information bits, the initial position of the OFDM symbol can be determined by searching the subscript of the maximum value in the OFDM symbol, and the estimation of the initial position of the OFDM symbol is completed.
Further, the method comprises the following steps of; the starting position of the OFDM symbol is obtained by the following method:
let the received signal be r (N), N be the number of sub-carriers,
Figure 874716DEST_PATH_IMAGE002
for cyclic prefix length, delay M, correlation length
Figure 710823DEST_PATH_IMAGE002
The delay correlation function of (a) can be expressed as:
Figure DEST_PATH_IMAGE010
then
Figure DEST_PATH_IMAGE011
The mold (A) is as follows:
Figure DEST_PATH_IMAGE012
therefore, the temperature of the molten metal is controlled,
Figure DEST_PATH_IMAGE013
the maximum value within one OFDM symbol is:
Figure DEST_PATH_IMAGE014
subscript corresponding to the maximum value
Figure DEST_PATH_IMAGE015
The initial position of the OFDM symbol is obtained; wherein n is an integer, k is 0 to
Figure 606098DEST_PATH_IMAGE002
Is an integer of (1).
It can be seen that the main amount of computation in the implementation of the algorithm is in computing the sliding correlation part of the delay correlation function. Calculating the delay as M correlation length as
Figure 188782DEST_PATH_IMAGE002
According to the expression, when the data updates a sampling point, the time delay related function should be carried out
Figure 181009DEST_PATH_IMAGE002
The number of times of complex multiplication calculation,
Figure 204329DEST_PATH_IMAGE002
1 complex addition and before storage
Figure DEST_PATH_IMAGE016
Signal sample data. The calculated delay is mainly calculated
Figure 259004DEST_PATH_IMAGE002
The delay caused by the second complex multiplication.
Through the calculation formula of the observation function, the nth calculation is the result of sliding on the n-1 st calculation result, and can be expressed as:
Figure DEST_PATH_IMAGE017
wherein
Figure DEST_PATH_IMAGE018
Is composed of
Figure DEST_PATH_IMAGE019
Time delay
Figure 330865DEST_PATH_IMAGE004
As a result of (1), therefore, can be reduced to
Figure 817079DEST_PATH_IMAGE004
The multiplication result of the sub-signals is stored and numbered, when the nth calculation is carried out, the related accumulated value of the (n-1) th time is firstly read out, the current signal sample point and the time delay are added
Figure DEST_PATH_IMAGE020
By multiplying the complex conjugate of the signal sample by the product of the complex conjugate of the signal sample, subtracting
Figure DEST_PATH_IMAGE021
And multiplying the complex conjugate of the sampling points of the order by a calculated value to obtain the nth sliding correlation result.
The method needs to be as follows
Figure 683404DEST_PATH_IMAGE002
The calculation results of the subsamples are stored, and 2 times of complex multiplication and 2 times of complex addition are used for replacing
Figure 756533DEST_PATH_IMAGE002
The sum of the secondary complex multiplications
Figure 38610DEST_PATH_IMAGE002
Figure 38610DEST_PATH_IMAGE002
1 time of complex addition, thereby greatly reducing the operation amount of algorithm implementation. In the calculation of the time delay, it is,
Figure 130063DEST_PATH_IMAGE002
the complex multiplications can be calculated simultaneously, as in the 1 complex multiplication,
Figure 370551DEST_PATH_IMAGE002
required for accumulation of complex multiplication values of individual samples
Figure 166862DEST_PATH_IMAGE002
Figure 166862DEST_PATH_IMAGE002
1 addition with a delay of
Figure 518209DEST_PATH_IMAGE002
1 clock cycle, 2 addition delays of 2 clock cycles, the method will
Figure 464168DEST_PATH_IMAGE002
The 1 clock cycle is changed into 2 clock cycles, so that the algorithm time delay is greatly reduced.
Compared with the prior art, the invention has the following advantages;
1. the invention only needs to be connected with
Figure 875558DEST_PATH_IMAGE002
The calculation results of the subsamples are stored, and 2 times of complex multiplication and 2 times of complex addition are used for replacing
Figure 657700DEST_PATH_IMAGE002
The sum of the secondary complex multiplications
Figure 547159DEST_PATH_IMAGE002
Figure 547159DEST_PATH_IMAGE002
1 time of complex addition, thereby greatly reducing the operation amount of algorithm implementation.
2. In the calculation of the time delay, it is,
Figure 613204DEST_PATH_IMAGE002
the complex multiplications can be calculated simultaneously, as in the 1 complex multiplication,
Figure 195495DEST_PATH_IMAGE002
required for accumulation of complex multiplication values of individual samples
Figure 963469DEST_PATH_IMAGE002
Figure 963469DEST_PATH_IMAGE002
1 addition with a delay of
Figure 656618DEST_PATH_IMAGE002
1 clock cycle, 2 addition delays of 2 clock cycles, the method will
Figure 983694DEST_PATH_IMAGE002
The 1 clock cycle is changed into 2 clock cycles, so that the algorithm time delay is greatly reduced.
3. Due to influence of noise and the like, the position deviation value
Figure 861520DEST_PATH_IMAGE008
Is randomly varied and its distribution is related to the amplitude peak distribution of the delay correlation function. By positional deviation for each OFDM symbol
Figure 742889DEST_PATH_IMAGE008
Performing smoothing to obtain the position deviation
Figure 115095DEST_PATH_IMAGE008
The mean value estimated value is used as a deviation value adopted when the cyclic prefix position of the OFDM symbol is removed, and iterative operation is carried out on the deviation value
Figure 765520DEST_PATH_IMAGE008
And carrying out low-pass filtering to realize smoothing processing, and controlling the speed of the change of the real position by using a coefficient.
Drawings
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 some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a normalized delay correlation function of a received signalThe simulation results, where N =512,
Figure 548668DEST_PATH_IMAGE002
=128，M=512。
fig. 2 shows a data frame structure when the system performs data transmission.
Fig. 3 is a processing flow of OFDM symbol synchronization at the receiving end.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
A low-complexity realization and synchronous updating method based on an OFDM symbol synchronization algorithm comprises the following steps:
a delay calculation method of an OFDM signal delay correlation function based on iteration comprises the following steps:
a1: the transmitting terminal maps the information bits into modulation patterns required by a QPSK system through a constellation, then distributes information data to useful subcarriers through subcarrier distribution, and obtains OFDM baseband signals after IFFT and adding cyclic prefix;
a2: at a receiving end, an OFDM system firstly carries out sampling through an analog-to-digital converter; then, the signals are converted to a baseband through orthogonal down-conversion; then, after cyclic prefix, FFT and de-mapping are carried out, information bits are obtained;
a3: after the delay correlation function calculation is completed according to the information bit calculation, the initial position of the OFDM symbol can be determined by searching the subscript of the maximum value in the OFDM symbol, and the estimation of the initial position of the OFDM symbol is completed.
Further, the method comprises the following steps of; the starting position of the OFDM symbol is obtained by the following method:
let the received signal be
Figure DEST_PATH_IMAGE022
，
Figure DEST_PATH_IMAGE023
Is the number of sub-carriers,
Figure 220128DEST_PATH_IMAGE002
is the cyclic prefix length, delayed by
Figure DEST_PATH_IMAGE024
Correlation length of
Figure 582976DEST_PATH_IMAGE002
The delay correlation function of (a) can be expressed as:
Figure 228852DEST_PATH_IMAGE010
then
Figure 58268DEST_PATH_IMAGE011
The mold (A) is as follows:
Figure 38862DEST_PATH_IMAGE012
therefore, the temperature of the molten metal is controlled,
Figure 877505DEST_PATH_IMAGE013
the maximum value within one OFDM symbol is:
Figure 610844DEST_PATH_IMAGE014
subscript corresponding to the maximum value
Figure 876740DEST_PATH_IMAGE015
The initial position of the OFDM symbol is obtained; wherein n is an integer, k is 0 to
Figure 79051DEST_PATH_IMAGE002
Is an integer of (1).
Further, the method comprises the following steps of; the number N of subcarriers of the OFDM system is 512, and the length of a cyclic prefix
Figure 721385DEST_PATH_IMAGE002
Is 128, OFDM symbol length N +
Figure 997646DEST_PATH_IMAGE002
The baseband modulation pattern is QPSK, 640. The data frame structure is shown in fig. 2, each data frame is composed of a header of one symbol and data of 15 symbols, and the total number of the data frames is 16 OFDM symbols. The frame header is a start symbol of a frame of data, and is used for performing frame start synchronization, channel estimation, transmission of system parameter setting information, and the like.
Further, the method comprises the following steps of; at a receiving end, no sampling frequency deviation is set, preprocessing is firstly carried out, and sampling is carried out according to a sampling point of each subcarrier after orthogonal down-conversion and low-pass filtering. The OFDM symbol synchronization adopts a non-data assisted synchronization algorithm based on a cyclic prefix, and a processing flow for performing OFDM symbol synchronization is shown in fig. 3. The delay M of the delay correlation function is 512 and the correlation length is 128. Setting the length of a delay correlation calculation signal memory to be 640, calculating a delay correlation function once when updating a sampling point, then obtaining a module of a newly obtained delay correlation function, comparing the module with a module value obtained previously, if the module value is larger than the stored temporary maximum value, updating the temporary maximum value to a current value, and recording a position subscript, otherwise, not updating. And when one OFDM symbol length 640 is compared, recording the temporary maximum value as the maximum value of the symbol, clearing the temporary maximum value, wherein the recorded position index is the initial position estimation value of the symbol, the difference between the position where the cyclic prefix is removed from the previous frame data is a position estimation error, and obtaining the position where the cyclic prefix is removed from the next frame after smoothing.
A method for stably updating a synchronization estimation result based on the estimation smoothing of an OFDM symbol starting position comprises the following steps:
b1: let N be the length of an OFDM symbol,
Figure 309809DEST_PATH_IMAGE002
for cyclic prefix length, one half of the cyclic prefix is removed due to multipath and noise effects, i.e.
Figure 874783DEST_PATH_IMAGE002
/2；
B2: combining the OFDM symbols with the frame structure, wherein the cyclic prefixes are removed;
b3: calculating the position deviation between the front OFDM symbol and the rear OFDM symbol, wherein the position deviation is
Figure DEST_PATH_IMAGE025
Wherein InEstimating a subscript for a starting position of the nth symbol; wherein n is an integer;
b4: position deviation to OFDM symbol
Figure DEST_PATH_IMAGE026
Performing smoothing to obtain the position deviation
Figure 494376DEST_PATH_IMAGE026
The average value of the estimated value is used as the deviation value used when the OFDM symbol removes the cyclic prefix position update, and the smoothing process is carried out by the deviation of a plurality of positions
Figure 828406DEST_PATH_IMAGE026
Averaging, or pairing by iterative operations
Figure 560738DEST_PATH_IMAGE026
Low-pass filtering is carried out; the iterative operation expression is as follows:
Figure DEST_PATH_IMAGE027
whereinαThe ordinal number of the product in iterative operation is smaller in value, slower in updating, smoother in output, less sensitive to the change of data, and suitable for the condition that the change of a real position is slower; and otherwise, the faster the updating is, the faster the real position change is, the condition that the real position change is fast is suitable for. The smoothing being iterativeIn a manner of takingα=1/16, the estimated value obtained from the previous symbol is multiplied by 15, added to the current position error, and then the obtained value is divided by 16 by right shifting by 4 bits, to obtain the position estimated value of the current symbol.
After the frame head position is determined through frame synchronization in the frequency domain, the position of the next frame without the cyclic prefix is updated at the frame head. The phase rotation introduced by the OFDM symbol start position advance will be removed together when channel parameter correction is performed.
The foregoing is only a preferred embodiment of the present invention and is not intended to limit the invention in any way. Although the invention has been described with reference to preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present invention, or modify equivalent embodiments to equivalent variations, without departing from the scope of the invention, using the teachings disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.

Claims (2)

1. The method is characterized in that the method is based on OFDM symbol synchronization algorithm low complexity realization and synchronous updating; the method comprises a delay calculation method based on an iterative OFDM signal delay correlation function and a stable updating method based on a synchronous estimation result of OFDM symbol initial position estimation smoothing processing;
the method for stably updating the synchronization estimation result based on the OFDM symbol initial position estimation smoothing processing comprises the following steps:
b1: let N be the length of an OFDM symbol,
Figure DEST_PATH_IMAGE001
for cyclic prefix length, one half of the cyclic prefix is removed due to multipath and noise effects, i.e.
Figure 893185DEST_PATH_IMAGE002
；
B2: removing the cyclic prefix of the OFDM symbol by combining a frame structure;
b3: calculating the position deviation between the front OFDM symbol and the rear OFDM symbol, wherein the position deviation is as follows:
Figure DEST_PATH_IMAGE003
wherein
Figure 471977DEST_PATH_IMAGE004
Estimating a subscript for a starting position of the nth symbol; wherein n is a natural number;
b4: position deviation to OFDM symbol
Figure DEST_PATH_IMAGE005
Performing smoothing to obtain the position deviation
Figure 48452DEST_PATH_IMAGE005
As the deviation value used in the cyclic prefix position updating of the OFDM symbol, and the smoothing process is performed by correcting the deviation values of a plurality of positions
Figure 771557DEST_PATH_IMAGE005
Averaging, or pairing by iterative operations
Figure 789192DEST_PATH_IMAGE005
Low-pass filtering is carried out; the iterative operation expression is as follows:
Figure 939550DEST_PATH_IMAGE006
wherein
Figure DEST_PATH_IMAGE007
The ordinal number of multiplication in iterative operation is smaller in value, slower in updating, smoother in output and less sensitive to data change, and is suitable for true operationA case where the real position changes slowly; and otherwise, the faster the updating is, the faster the real position change is, the condition that the real position change is fast is suitable for.
2. The OFDM symbol synchronization algorithm based low complexity implementation and synchronization update method of claim 1, wherein; the delay calculation method of the OFDM signal delay correlation function based on iteration comprises the following steps:
a1: at a transmitting end, mapping information bits into a modulation pattern required by a QPSK system through a constellation, then distributing information data to useful subcarriers through subcarrier distribution, and obtaining an OFDM baseband signal after IFFT and adding a cyclic prefix;
a2: at a receiving end, an OFDM system firstly carries out sampling through an analog-to-digital converter; then, the signals are converted to a baseband through orthogonal down-conversion; then, after cyclic prefix, FFT and de-mapping are carried out, information bits are obtained;
a3: after the calculation of the delay correlation function is completed according to the calculation of the information bits, the initial position of the OFDM symbol can be determined by searching the subscript of the maximum value in the OFDM symbol, and the estimation of the initial position of the OFDM symbol is completed.
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