(19)
(11)EP 3 503 487 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.06.2020 Bulletin 2020/25

(21)Application number: 17852304.9

(22)Date of filing:  11.09.2017
(51)International Patent Classification (IPC): 
H04L 27/26(2006.01)
H04L 27/00(2006.01)
(86)International application number:
PCT/CN2017/101241
(87)International publication number:
WO 2018/054236 (29.03.2018 Gazette  2018/13)

(54)

METHOD AND DEVICE FOR OFDM SYSTEM SYNCHRONOUS TRACKING

VERFAHREN UND VORRICHTUNG ZUR SYNCHRONEN VERFOLGUNG EINES OFDM-SYSTEMS

DISPOSITIF ET PROCÉDÉ DESTINÉS AU SUIVI SYNCHRONE DE SYSTÈME OFDM


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 26.09.2016 CN 201610855133

(43)Date of publication of application:
26.06.2019 Bulletin 2019/26

(73)Proprietor: Allwinner Technology Co. Ltd.
Zhuhai, Guangdong 519000 (CN)

(72)Inventor:
  • ZHU, Jiajun
    Zhuhai Guangdong 519000 (CN)

(74)Representative: Wang, Bo 
Panovision IP Ebersberger Straße 3
85570 Markt Schwaben
85570 Markt Schwaben (DE)


(56)References cited: : 
CN-A- 103 248 596
CN-A- 106 453 187
US-B1- 9 137 083
CN-A- 104 052 707
US-A1- 2006 133 527
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD OF THE INVENTION



    [0001] The present invention relates to the field of communications technologies, specifically, to an OFDM system synchronization tracking method and apparatus, and in particular, to an OFDM system synchronization tracking method and apparatus based on the 802.11a/g/n/ac protocol.

    BACKGROUND OF THE INVENTION



    [0002] In the 802.11a/g/n/ac protocol, OFDM is an important modulation and demodulation technology which can greatly improve the data transmission rate. However, the OFDM is very sensitive to carrier frequency offset and timing offset. Existence of the frequency offset and the timing offset is likely to cause degraded demodulation performance of a receiver. The frequency offset is due to the carrier frequency deviation between a transmitter and a receiver. The frequency offset may destroy the orthogonality and phase rotation value of the OFDM, and results in serious degradation of demodulation performance of the receiver. Therefore, in a communication process, an OFDM training symbol is usually added to a frame header so that the receiver may estimate and eliminate the frequency offset. However, due to noise, for the initial frequency offset estimation of a frame header of a received frame, it is not ensured that the frequency offset is accurately estimated and completely eliminated, and the frequency offset value just can be controlled within a certain range. The residual frequency offset may continue to affect the demodulation performance of the receiver. Therefore, subsequent frequency offset tracking is very necessary. The timing offset is due to the crystal oscillator frequency difference between the transmitter and the receiver or Doppler frequency drift. The crystal oscillator frequency difference may cause phase drift of a sampling clock, causing the timing offset to vary over time. The timing offset is essentially inevitable for a system. The timing offset may cause subcarrier phase rotation of the OFDM, resulting in degradation of demodulation performance of the receiver. Therefore, after timing synchronization is performed on the frame header, timing offset tracking is also very necessary. In an 802.11a/g/n/ac OFDM system, the protocol stipulates that in each OFDM symbol, several pilots known by the receiver are inserted into an information subcarrier, so that a receiver may perform synchronization tracking operation. In the prior art, there are many synchronization tracking methods performed by using the pilots. However, under impact of noise, the accuracy of frequency offset value and timing offset value that are estimated by a limited quantity of pilots is quite limited, and the demodulation performance cannot be optimized. In addition, in the prior art, frequency offset value estimation and compensation are mostly performed in time domain, thus an inverse Fourier transformer is needed, and the complexity of circuit implementation is very high. Document US 2006/0133527 A1 discloses a method for estimation and compensation of residual frequency and time offset based on pilot subcarriers.

    SUMMARY OF THE INVENTION



    [0003] The present invention provides an OFDM system synchronization tracking method and apparatus, to overcome a defect that accuracy of frequency offset estimation and timing offset estimation is not high due to an OFDM system in the 802.11 protocol in the prior art using a pilot to perform synchronization tracking, and a defect of complex circuit due to frequency offset value estimation and compensation being performed in time domain.

    [0004] To resolve the foregoing technical problem, the following technical solutions are used in the present invention:
    An OFDM system synchronization tracking method includes steps of:

    A1. performing OFDM symbol segmentation on a received digital signal, sequentially performing a fast Fourier transform (FFT) on OFDM symbols obtained through the segmentation, transforming the OFDM symbols from time domain to frequency domain to obtain a frequency domain OFDM symbol sequence, and sequentially performing step A2 to step A5 on each frequency domain OFDM symbol in the frequency domain OFDM symbol sequence;

    A2. extracting information subcarrier symbols, pilot symbols, and a direct current (DC) subcarrier from a current frequency domain OFDM symbol, detecting and implementing a decision on the information subcarrier symbols, and generating a recovery information subcarrier symbol;

    A3. synthesizing the pilot symbols, the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol;

    A4. performing frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value; and

    A5. performing phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, setting the compensated frequency domain OFDM symbol to a current frequency domain OFDM symbol, and returning to the step A2.



    [0005] According to embodiments of the present invention, the step A2 includes: implementing a maximum likelihood hard decision, and generating the recovery information subcarrier symbol.

    [0006] According to embodiments of the present invention, the step A4 includes: correcting the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value by using loop filters, and calculating a new frequency offset estimation phase rotation value and a new timing offset estimation phase rotation value after the correction.

    [0007] According to this embodiment of the present invention, the step A4 includes: the loop filters include a frequency offset loop filter and a timing offset loop filter, the frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value, and the timing offset loop filter is configured to correct the timing offset estimation phase rotation value.

    [0008] An OFDM system synchronization tracking apparatus includes a symbol timer, a fast Fourier transformer, a phase rotation compensator, an information subcarrier extractor, a channel estimator, a detector, a pilot subcarrier extractor, a subcarrier hard decider, an OFDM symbol synthesizer, a frequency offset and timing offset estimator, a frequency offset loop filter, a timing offset loop filter, and a phase rotation estimate calculator. The symbol timer, the fast Fourier transformer, the phase rotation compensator, the information subcarrier extractor, the detector, the subcarrier hard decider, the OFDM symbol synthesizer, the frequency offset and timing offset estimator, the frequency offset loop filter, and the phase rotation estimate calculator are sequentially connected. The phase rotation compensator, the channel estimator, and the detector are sequentially connected. The information subcarrier extractor, the pilot subcarrier extractor, and the OFDM symbol synthesizer are sequentially connected. The symbol timer is configured to perform OFDM symbol segmentation on a received digital signal, the fast Fourier transformer is configured to sequentially perform an FFT on OFDM symbols obtained through the segmentation, and transform the OFDM symbols from a time domain to a frequency domain to obtain a frequency domain OFDM symbol sequence. The channel estimator is configured to perform channel estimation according to a training sequence transparently transmitted by the phase rotation compensator, to obtain a channel estimate value. The information subcarrier extractor is configured to extract an information subcarrier symbol from a current frequency domain OFDM symbol. The pilot subcarrier extractor is configured to extract a pilot symbol and a DC subcarrier from the current frequency domain OFDM symbol. The detector is configured to detect the information subcarrier symbol. The subcarrier hard decider is configured to render a decision on the information subcarrier symbol and generate a recovery information subcarrier symbol. The OFDM symbol synthesizer is configured to synthesize the pilot symbol and the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol. The frequency offset and timing offset estimator is configured to perform frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value. The frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value. The timing offset loop filter is configured to correct the timing offset estimation phase rotation value. The phase rotation estimate calculator is configured to calculate the corresponding frequency offset estimation phase rotation value and the corresponding timing offset estimation phase rotation value. The phase rotation compensator is configured to perform phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, and the compensated frequency domain OFDM symbol is set to a current frequency domain OFDM symbol.

    [0009] According to embodiments of the present invention, the subcarrier hard decider implements a maximum likelihood hard decision, and generates the recovery information subcarrier symbol.

    [0010] The present invention has the following beneficial effects: a frequency offset phase rotation value and a timing offset phase rotation value of an OFDM symbol are estimated by combining information subcarrier hard decision feedback and a pilot subcarrier, thereby greatly improving estimation accuracy. In addition, phase rotation compensation is provided for a next OFDM symbol in frequency domain processing part, so that in an entire synchronization tracking process, not only tracking accuracy is improved, but also complexity of circuit timing implementation is reduced.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0011] The following specifically describes the present invention with reference to the accompanying drawings and in combination with examples, and advantages and implementations of the present invention will become more apparent. Content shown in the accompanying drawings is only used to explain and describe the present invention, but does not constitute any limitation on the present invention in any sense. In the accompanying drawings:

    FIG. 1 is a schematic diagram of subcarrier distribution of an 802.11a/g/n/ac OFDM symbol;

    FIG. 2 is a schematic diagram of an apparatus according to the present invention; and

    FIG. 3 is a schematic diagram of a loop filter according to the present invention.


    DETAILED DESCRIPTION



    [0012] As shown in FIG. 1, FIG. 2, and FIG. 3, an OFDM system synchronization tracking method according to the present invention includes steps of:

    A1. performing OFDM symbol segmentation on a received digital signal, sequentially performing a Fast Fourier transform (FFT) on OFDM symbols obtained through the division, transforming the OFDM symbols from time domain to frequency domain to obtain a frequency domain OFDM symbol sequence, and sequentially performing step A2 to step A5 on each frequency domain OFDM symbol in the frequency domain OFDM symbol sequence;

    A2. extracting information subcarrier symbols, pilot symbols, and a DC subcarrier from a current frequency domain OFDM symbol, detecting and implementing a decision on the information subcarrier symbols, and generating a recovery information subcarrier symbol;

    A3. synthesizing the pilot symbols, the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol;

    A4. performing frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value; and

    A5. performing phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, setting the compensated frequency domain OFDM symbol to a current frequency domain OFDM symbol, and returning to the step A2.



    [0013] According to embodiments of the present invention, the step A2 includes: implementing a hard decision by using a maximum likelihood method, and generating the recovery information subcarrier symbol. The step A4 includes: correcting the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value by using loop filters, and calculating a new frequency offset estimation phase rotation value and a new timing offset estimation phase rotation value after the correction. The loop filters include a frequency offset loop filter and a timing offset loop filter. The frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value, and the timing offset loop filter is configured to correct the timing offset estimation phase rotation value.

    [0014] An OFDM system synchronization tracking apparatus according to the present invention includes a symbol timer, a fast Fourier transformer, a phase rotation compensator, an information subcarrier extractor, a channel estimator, a detector, a pilot subcarrier extractor, a subcarrier hard decider, an OFDM symbol synthesizer, a frequency offset and timing offset estimator, a frequency offset loop filter, a timing offset loop filter, and a phase rotation estimate calculator. The symbol timer, the fast Fourier transformer, the phase rotation compensator, the information subcarrier extractor, the detector, the subcarrier hard decider, the OFDM symbol synthesizer, the frequency offset and timing offset estimator, the frequency offset loop filter, and the phase rotation estimate calculator are sequentially connected. The phase rotation compensator, the channel estimator, and the detector are sequentially connected. The information subcarrier extractor, the pilot subcarrier extractor, and the OFDM symbol synthesizer are sequentially connected. The symbol timer is configured to perform OFDM symbol segmentation on a received digital signal. The fast Fourier transformer is configured to sequentially perform an FFT on OFDM symbols obtained through the segmentation, and transform the OFDM symbols from time domain to frequency domain to obtain a frequency domain OFDM symbol sequence. The channel estimator is configured to perform channel estimation according to a training sequence transparently transmitted by the phase rotation compensator, to obtain a channel estimate value. The information subcarrier extractor is configured to extract an information subcarrier symbol from a current frequency domain OFDM symbol. The pilot subcarrier extractor is configured to extract a pilot symbol and a DC subcarrier from the current frequency domain OFDM symbol. The detector is configured to detect the information subcarrier symbol. The subcarrier hard decider is configured to implement a decision on the information subcarrier symbol and generate a recovery information subcarrier symbol. The OFDM symbol synthesizer is configured to synthesize the pilot symbol and the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol. The frequency offset and timing offset estimator is configured to perform frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value. The frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value. The timing offset loop filter is configured to correct the timing offset estimation phase rotation value. The phase rotation estimate calculator is configured to calculate the corresponding frequency offset estimation phase rotation value and the corresponding timing offset estimation phase rotation value. The phase rotation compensator is configured to perform phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, and the compensated frequency domain OFDM symbol is set to a current frequency domain OFDM symbol. According to embodiments of the present invention, the subcarrier hard decider implements a maximum likelihood hard-decision, and generates the recovery information subcarrier symbol.

    [0015] The following describes the technical solutions of the present invention by using specific embodiments.

    [0016] A demodulation procedure of a receiver front end is as follows:
    1. 1. A received signal is sent to an analog to digital converter through an analog circuit, and is converted from an analog signal into a digital signal.
    2. 2. A down-sampler down-samples the digital signal output by the analog to digital converter. The sampling frequency is reduced to a frequency required for baseband demodulation.
    3. 3. Frequency offset compensation and symbol timing are used for initial synchronization. The frequency offset compensation reduces frequency offset effect of the received signal by using a frequency offset value estimated in a frame header training symbol. The symbol timer determines a windowing location of an FFT in each OFDM symbol in the frame header training symbol, that is, performs OFDM symbol segmentation on a series of received digital signals.
    4. 4. The fast Fourier transformer sequentially performs an FFT on each OFDM symbol obtained through the segmentation, and transforms the OFDM symbol from time domain to frequency domain.

    Synchronization tracking algorithm process:



    [0017] The following describes in detail how the synchronization tracking apparatus of the present invention operates in a demodulation process of a receiver and provides reliable synchronization tracking support for the receiver. In embodiments, it is assumed that an antenna mode is single-input single-output (SISO); the total quantity of tracked OFDM symbols is Y, and the total quantity of available subcarriers (information subcarrier, pilot subcarrier (pilot subcarrier), and DC subcarrier) is N + 1; and k represents an index of an available subcarrier of each OFDM symbol, and its representation range is



    [0018] An operating procedure of the apparatus is as follows:

    First step: Set an index y = 1. y represents an index of an OFDM symbol on which synchronization tracking is to be performed. y = 1 indicates that the OFDM symbol is a first OFDM symbol on which synchronization tracking is performed.

    Second step: The phase rotation compensator performs phase compensation on a yth OFDM symbol output by the fast Fourier transformer, that is, corrects a phase rotation error caused by frequency offset and timing offset. A correction algorithm of the phase rotation compensator is expressed as:



    [0019] In the equation: (1) Ry(k) represents a kth subcarrier of the yth received OFDM symbol output by the fast Fourier transformer. (2) e-jθ̂y(k) is a phase rotation compensation value of the kth subcarrier of the yth OFDM symbol. (3) y(k) is the kth subcarrier of the yth OFDM symbol after phase rotation compensation.

    [0020] The equation (1) may be further expressed as:



    [0021] In the equation: (1) H(k) represents channel estimation information of the kth subcarrier. (2) Sy(k) represents the kth subcarrier of the yth sent OFDM symbol. (3) ey(k) represents a phase rotation value of the kth subcarrier of the yth OFDM symbol. (4) θy(k) = ay + k·by, where ay and by respectively represent a frequency offset phase rotation value and a timing offset phase rotation value. (5) Zy(k) represents white Gaussian noise of the kth subcarrier.

    [0022] When y = 1, θ̂1(k) = 0. Therefore, the first tracked OFDM symbol has no phase rotation compensation.

    [0023] Third step: After the detector detects an information subcarrier of the yth OFDM symbol, the detected information subcarrier y(k) is to be sent to the subcarrier hard decider for a maximum likelihood hard decision. Currently, there are many types of detection methods in the industry, and different communication modes have their own detection methods. Herein, because the communication mode in the example is SISO, a detection method is LS detection, that is:



    [0024] The maximum likelihood hard decision algorithm is expressed as

    where Sl represents a subcarrier symbol that may be sent at a transmitting terminal, and ξ is a set of all symbols that may be sent. A recovered

    represents a kth subcarrier symbol (only an information subcarrier) of a yth recovered OFDM symbol.

    [0025] It is assumed that all symbols that may be sent are the following four symbols:



    [0026] Then, distance calculations are separately performed, by using y(k), for the four symbols that may be sent in the set ξ:



    [0027] After that, Sl corresponding to the smallest distance of dy,l(k) is selected as maximum likelihood decision value of y(k). Finally, a recovered

    is obtained.

    [0028] Fourth step: The pilot subcarrier generator generates an original pilot subcarrier of the yth OFDM. The OFDM symbol synthesizer combines an information subcarrier on which a hard decision has been implemented and the generated pilot subcarrier, and a yth original OFDM symbol

    (which includes an information subcarrier, a pilot subcarrier, and a DC subcarrier) is reconstructed.

    [0029] Fifth step: The frequency offset and timing offset estimator performs frequency offset and timing offset phase rotation value estimation based on the reconstructed yth original OFDM symbol

    , channel estimation information H(k) of the channel estimator, and y(k) output by the phase rotation compensator. An estimation algorithm used herein is as follows:





    [0030] In the foregoing equation (5) and equation (6): (1) ay and by respectively represent a frequency offset phase rotation amount and a timing offset phase rotation amount. (2) imag{·} represents obtaining an imaginary part of a value. (3) [·]* represents a complex conjugate of the value.

    [0031] Sixth step: A frequency offset phase rotation estimate value and a timing offset phase rotation estimate value are respectively sent to respective loop filters for correction. The structure and the parameters of the loop filter may be determined according to actual requirements. Herein, a parameter Kp of a second-order loop filter is set to 0.25, and Ki is set to 0.125.

    [0032] Seventh step: The frequency offset phase rotation estimate value and the timing offset phase rotation estimate value corrected by the loop filters are sent to the phase rotation estimate calculator to calculate a phase rotation estimate value of the kth subcarrier. A calculation manner is expressed as

    where

    represents the phase rotation estimate value.

    [0033] Eighth step: The phase rotation estimate value

    of the kth subcarrier and phase rotation estimate values of the kth subcarrier of previous y-1 OFDM symbols are accumulated to obtain θ̂y+1(k), that is,

    Then, θ̂y+1(k) is sent to the phase rotation compensator and a phase rotation compensation value in exponential form is generated through table lookup, that is, e-jθ̂y+1(k). Next, Phase rotation compensation is to be performed on a (y +1)th received OFDM symbol Ry+1(k).

    [0034] Ninth step: Set index y = y + 1. If y ≤ Y, return to the second step; otherwise, end the process.

    [0035] The foregoing descriptions are merely preferably feasible embodiments of the present invention, and are not intended to limit the scope of the present invention.


    Claims

    1. An OFDM system synchronization tracking method, comprising steps of:

    A1. performing OFDM symbol segmentation on a received digital signal, sequentially performing a fast Fourier transform, FFT, on OFDM symbols obtained through the segmentation, transforming the OFDM symbols from time domain to frequency domain to obtain a frequency domain OFDM symbol sequence, and sequentially performing step A2 to step A5 on each frequency domain OFDM symbol in the frequency domain OFDM symbol sequence;

    A2. extracting an information subcarrier symbol, pilot symbols, and a direct current, DC, subcarrier from a current frequency domain OFDM symbol, detecting and implementing a decision on the information subcarrier symbol, and generating a recovery information subcarrier symbol;

    A3. synthesizing the pilot symbols, the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol;

    A4. performing frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value; and

    A5. performing phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, setting the compensated frequency domain OFDM symbol to a current frequency domain OFDM symbol, and returning to the step A2.


     
    2. The OFDM system synchronization tracking method according to claim 1, wherein the step A2 comprises: implementing a hard decision by using a maximum likelihood method, and generating the recovery information subcarrier symbol.
     
    3. The OFDM system synchronization tracking method according to claim 2, wherein the step A4 comprises: correcting the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value by using loop filters, and calculating a new frequency offset estimation phase rotation value and a new timing offset estimation phase rotation value after the correction.
     
    4. The OFDM system synchronization tracking method according to claim 3, wherein the step A4 comprises: the loop filters comprise a frequency offset loop filter and a timing offset loop filter, the frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value, and the timing offset loop filter is configured to correct the timing offset estimation phase rotation value.
     
    5. An OFDM system synchronization tracking apparatus, comprising a symbol timer, a fast Fourier transformer, a phase rotation compensator, an information subcarrier extractor, a channel estimator, a detector, a pilot subcarrier extractor, a subcarrier hard decider, an OFDM symbol synthesizer, a frequency offset and timing offset estimator, a frequency offset loop filter, a timing offset loop filter, and a phase rotation estimate calculator, wherein the symbol timer, the fast Fourier transformer, the phase rotation compensator, the information subcarrier extractor, the detector, the subcarrier hard decider, the OFDM symbol synthesizer, the frequency offset and timing offset estimator, the frequency offset loop filter, and the phase rotation estimate calculator are sequentially connected; the phase rotation compensator, the channel estimator, and the detector are sequentially connected; the information subcarrier extractor, the pilot subcarrier extractor, and the OFDM symbol synthesizer are sequentially connected; the symbol timer is configured to perform OFDM symbol segmentation on a received digital signal; the fast Fourier transformer is configured to sequentially perform a fast Fourier transform, FFT, on OFDM symbols obtained through the segmentation, and transform the OFDM symbols from time domain to frequency domain to obtain a frequency domain OFDM symbol sequence; the channel estimator is configured to perform channel estimation according to a training sequence transparently transmitted, to obtain a channel estimate value; the information subcarrier extractor is configured to extract an information subcarrier symbol from a current frequency domain OFDM symbol; the pilot subcarrier extractor is configured to extract a pilot symbol and a direct current, DC, subcarrier from the current frequency domain OFDM symbol, the detector is configured to detect the information subcarrier symbol; the subcarrier hard decider is configured to implement a decision on the information subcarrier symbol and generate a recovery information subcarrier symbol; the OFDM symbol synthesizer is configured to synthesize the pilot symbol and the DC subcarrier in the current OFDM symbol and the recovery information subcarrier symbol into a recovery OFDM symbol; the frequency offset and timing offset estimator is configured to perform frequency offset estimation and timing offset estimation on the recovery OFDM symbol, to obtain a corresponding frequency offset estimation phase rotation value and a corresponding timing offset estimation phase rotation value; the frequency offset loop filter is configured to correct the frequency offset estimation phase rotation value; the timing offset loop filter is configured to correct the timing offset estimation phase rotation value; the phase rotation estimate calculator is configured to calculate the corresponding frequency offset estimation phase rotation value and the corresponding timing offset estimation phase rotation value; and the phase rotation compensator is configured to perform phase compensation on a next frequency domain OFDM symbol in the frequency domain OFDM symbol sequence by using the frequency offset estimation phase rotation value and the timing offset estimation phase rotation value, and the compensated frequency domain OFDM symbol is set to a current frequency domain OFDM symbol.
     
    6. The OFDM system synchronization tracking apparatus according to claim 5, wherein the subcarrier hard decider implements a maximum likelihood hard decision, and generates the recovery information subcarrier symbol.
     


    Ansprüche

    1. OFDM-System-Synchronisationsverfolgungsverfahren, umfassend Schritte zum:

    A1. Durchführen von OFDM-Symbolsegmentierung an einem empfangenen digitalen Signal, sequenzielles Durchführen einer Fast-Fourier-Transformation, FFT, an OFDM-Symbolen, die durch die Segmentierung erhalten werden, Transformieren der OFDM-Symbole von Zeitdomäne zu Frequenzdomäne, um eine Frequenzdomänen-OFDM-Symbolsequenz zu erhalten, und sequenzielles Durchführen von Schritt A2 bis Schritt A5 an jedem Frequenzdomänen-OFDM-Symbol in der Frequenzdomänen-OFDM-Symbolsequenz;

    A2. Extrahieren eines Informationssubträgersymbols, von Leitsymbolen und eines Gleichstrom-, DC-, Subträgers von einem aktuellen Frequenzdomänen-OFDM-Symbol, Erfassen und Implementieren einer Entscheidung über das Informationssubträgersymbol und Erzeugen eines Wiederherstellungsinformationssubträgersymbols;

    A3. Synthetisieren der Leitsymbole, des DC-Subträgers in dem aktuellen OFDM-Symbol und des Wiederherstellungsinformationssubträgersymbols in ein Wiederherstellungs-OFDM-Symbol;

    A4. Durchführen von Frequenzversatzschätzung und Zeitversatzschätzung an dem Wiederherstellungs-OFDM-Symbol, um einen entsprechenden Frequenzversatzschätzungsphasenrotationswert und einen entsprechenden Zeitversatzschätzungsphasenrotationswert zu erhalten; und

    A5. Durchführen von Phasenkompensation an einem nächsten Frequenzdomänen-OFDM-Symbol in der Frequenzdomänen-OFDM-Symbolsequenz unter Verwendung des Frequenzversatzschätzungsphasenrotationswerts und des Zeitversatzschätzungsphasenrotationswerts, Einstellen des kompensierten Frequenzdomänen-OFDM-Symbols auf ein aktuelles Frequenzdomänen-OFDM-Symbol und Zurückkehren zu dem Schritt A2.


     
    2. OFDM-Systemsynchronisationsverfolgungsverfahren nach Anspruch 1, wobei der Schritt A2 umfasst: Implementieren einer harten Entscheidung unter Verwendung eines Verfahrens der höchsten Wahrscheinlichkeit und Erzeugen des Wiederherstellungsinformationssubträgersymbols.
     
    3. OFDM-Systemsynchronisationsverfolgungsverfahren nach Anspruch 2, wobei der Schritt A4 umfasst: Korrigieren des Frequenzversatzschätzungsphasenrotationswerts und des Zeitversatzschätzungsphasenrotationswerts unter Verwendung von Schleifenfiltern und Berechnen eines neuen Frequenzversatzschätzungsphasenrotationswerts und eines neuen Zeitversatzschätzungsphasenrotationswerts nach der Korrektur.
     
    4. OFDM-Systemsynchronisationsverfolgungsverfahren nach Anspruch 3, wobei der Schritt A4 umfasst: die Schleifenfilter umfassen ein Frequenzversatzschleifendfilter und ein Zeitversatzschleifenfilter, das Frequenzversatzschleifenfilter ist konfiguriert, den Frequenzversatzschätzungsphasenrotationswert zu korrigieren und das Zeitversatzschleifenfilter ist konfiguriert, den Zeitversatzschätzungsphasenrotationswert zu korrigieren.
     
    5. OFDM-Systemsynchronisationsverfolgungseinrichtung, umfassend einen Symbolzeitgeber, einen Fast-Fourier-Transformator, einen Phasenrotationskompensator, einen Informationssubträgerextrahierer, einen Kanalschätzer, einen Detektor, einen Leitsubträgerextrahierer, einen harten Subträgerentscheider, einen OFDM-Symbolsynthesizer, einen Frequenzversatz- und Zeitversatzschätzer, ein Frequenzversatzschleifenfilter, ein Zeitversatzschleifenfilter und einen Phasenrotationsschätzungsrechner, wobei der Symbolzeitgeber, der Fast-Fourier-Transformator, der Phasenrotationskompensator, der Informationssubträgerextrahierer, der Detektor, der harte Subträgerentscheider, der OFDM-Symbolsynthesizer, der Frequenzversatz- und Zeitversatzschätzer, das Frequenzversatzschleifenfilter und der Phasenrotationsschätzungsrechner aufeinanderfolgend verbunden sind; der Phasenrotationskompensator, der Kanalschätzer und der Detektor aufeinanderfolgend verbunden sind; der Informationssubträgerextrahierer, der Leitsubträgerextrahierer und der OFDM-Symbolsynthesizer aufeinanderfolgend verbunden sind; der Symbolzeitgeber konfiguriert ist, OFDM-Symbolsegmentierung an einem empfangenen digitalen Signal durchzuführen; der Fast-Fourier-Transformator konfiguriert ist, aufeinanderfolgend eine Fast-Fourier-Transformation, FFT, an OFDM-Symbolen durchzuführen, die durch die Segmentierung erhalten werden, und die OFDM-Symbole von Zeitdomäne zu Frequenzdomäne zu transformieren, um eine Frequenzdomänen-OFDM-Symbolsequenz zu erhalten; der Kanalschätzer konfiguriert ist, Kanalschätzung gemäß einer Lernsequenz durchzuführen, die transparent übertragen wird, um einen Kanalschätzungswert zu erhalten; der Informationssubträgerextrahierer konfiguriert ist, ein Informationssubträgersymbol von einem aktuellen Frequenzdomänen-OFDM-Symbol zu extrahieren; der Leitsubträgerextrahierer konfiguriert ist, ein Leitsymbol und einen Gleichstrom-, DC-, Subträger von dem aktuellen Frequenzdomänen-OFDM-Symbol zu extrahieren, der Detektor konfiguriert ist, das Informationssubträgersymbol zu erfassen; der harte Subträgerentscheider konfiguriert ist, eine Entscheidung über das Informationssubträgersymbol zu implementieren und ein Wiederherstellungsinformationssubträgersymbol zu erzeugen; der OFDM-Symbolsynthesizer konfiguriert ist, das Leitsymbol und den DC-Subträger in dem aktuellen OFDM-Symbol und das Wiederherstellungsinformationssubträgersymbol in ein Wiederherstellungs-OFDM-Symbol zu synthetisieren; der Frequenzversatz- und Zeitversatzschätzer konfiguriert ist, Frequenzversatzschätzung und Zeitversatzschätzung an dem Wiederherstellungs-OFDM-Symbol durchzuführen, um einen entsprechenden Frequenzversatzschätzungsphasenrotationswert und einen entsprechenden Zeitversatzschätzungsphasenrotationswert zu erhalten; das Frequenzversatzschleifenfilter konfiguriert ist, den Frequenzversatzschätzungsphasenrotationswert zu korrigieren; das Zeitversatzschleifenfilter konfiguriert ist, den Zeitversatzschätzungsphasenrotationswert zu korrigieren; der Phasenrotationsschätzungsrechner konfiguriert ist, den entsprechenden Frequenzversatzschätzungsphasenrotationswert und den entsprechenden Zeitversatzschätzungsphasenrotationswert zu berechnen; und der Phasenrotationskompensator konfiguriert ist, Phasenkompensation an einem nächsten Frequenzdomänen-OFDM-Symbol in der Frequenzdomänen-OFDM-Symbolsequenz unter Verwendung des Frequenzversatzschätzungsphasenrotationswerts und des Zeitversatzschätzungsphasenrotationswerts durchzuführen, und das kompensierte Frequenzdomänen-OFDM-Symbol auf ein aktuelles Frequenzdomänen-OFDM-Symbol eingestellt ist.
     
    6. OFDM-Systemsynchronisationsverfolgungseinrichtung nach Anspruch 5, wobei der harte Subträgerentscheider eine harte Entscheidung einer maximalen Wahrscheinlichkeit implementiert und das Wiederherstellungsinformationssubträgersymbol erzeugt.
     


    Revendications

    1. Procédé de suivi de synchronisation de système OFDM, comprenant les étapes consistant à :

    A1. effectuer une segmentation de symbole OFDM sur un signal numérique reçu, effectuer séquentiellement une transformée de Fourier rapide, FFT, sur des symboles OFDM obtenus par la segmentation, transformer les symboles OFDM de domaine temporel en domaine fréquentiel pour obtenir une séquence de symboles OFDM de domaine fréquentiel, et effectuer séquentiellement l'étape A2 à l'étape A5 sur chaque symbole OFDM de domaine fréquentiel dans la séquence de symboles OFDM de domaine fréquentiel ;

    A2. extraire un symbole de sous-porteuse d'informations, des symboles pilotes, et une sous-porteuse de courant continu, CC, depuis un symbole OFDM de domaine fréquentiel actuel, détecter et mettre en œuvre une décision sur le symbole de sous-porteuse d'informations, et générer un symbole de sous-porteuse d'informations de récupération ;

    A3. synthétiser les symboles pilotes, la sous-porteuse CC dans le symbole OFDM actuel et le symbole de sous-porteuse d'informations de récupération dans un symbole OFDM de récupération ;

    A4. effectuer une estimation de décalage de fréquence et une estimation de décalage de temps sur le symbole OFDM de récupération, pour obtenir une valeur de rotation de phase d'estimation de décalage de fréquence correspondante et une valeur de rotation de phase d'estimation de décalage de temps correspondante ; et

    A5. effectuer une compensation de phase sur un symbole OFDM de domaine fréquentiel suivant dans la séquence de symboles OFDM de domaine fréquentiel en utilisant la valeur de rotation de phase d'estimation de décalage de fréquence et la valeur de rotation de phase d'estimation de décalage de temps, définir le symbole OFDM de domaine fréquentiel compensé sur un symbole OFDM de domaine fréquentiel actuel, et revenir à l'étape A2.


     
    2. Procédé de suivi de synchronisation de système OFDM selon la revendication 1, dans lequel l'étape A2 comprend les étapes consistant à : mettre en œuvre une décision difficile en utilisant un procédé de vraisemblance maximale, et générer le symbole de sous-porteuse d'informations de récupération.
     
    3. Procédé de suivi de synchronisation de système OFDM selon la revendication 2, dans lequel l'étape A4 comprend les étapes consistant à : corriger la valeur de rotation de phase d'estimation de décalage de fréquence et la valeur de rotation de phase d'estimation de décalage de temps en utilisant des filtres de boucle, et calculer une nouvelle valeur de rotation de phase d'estimation de décalage de fréquence et une nouvelle valeur de rotation de phase d'estimation de décalage de temps après la correction.
     
    4. Procédé de suivi de synchronisation de système OFDM selon la revendication 3, dans lequel l'étape A4 comprend : les filtres de boucle comprennent un filtre de boucle de décalage de fréquence et un filtre de boucle de décalage de temps, le filtre de boucle de décalage de fréquence est configuré pour corriger la valeur de rotation de phase d'estimation de décalage de fréquence, et le filtre de boucle de décalage de temps est configuré pour corriger la valeur de rotation de phase d'estimation de décalage de temps.
     
    5. Appareil de suivi de synchronisation de système OFDM, comprenant un minuteur de symbole, un transformateur de Fourier rapide, un compensateur de rotation de phase, un extracteur de sous-porteuse d'informations, un estimateur de canal, un détecteur, un extracteur de sous-porteuse pilote, un décideur difficile de sous-porteuse, un synthétiseur de symbole OFDM, un estimateur de décalage de fréquence et de décalage de temps, un filtre de boucle de décalage de fréquence, un filtre de boucle de décalage de temps, et un calculateur d'estimation de rotation de phase, dans lequel le minuteur de symbole, le transformateur de Fourier rapide, le compensateur de rotation de phase, l'extracteur de sous-porteuse d'informations, le détecteur, le décideur difficile de sous-porteuse, le synthétiseur de symbole OFDM, l'estimateur de décalage de fréquence et de décalage de temps, le filtre de boucle de décalage de fréquence, et le calculateur d'estimation de rotation de phase sont raccordés séquentiellement ; le compensateur de rotation de phase, l'estimateur de canal, et le détecteur sont raccordés séquentiellement ; l'extracteur de sous-porteuse d'informations, l'extracteur de sous-porteuse pilote, et le synthétiseur de symbole OFDM sont raccordés séquentiellement ; le minuteur de symbole est configuré pour effectuer une segmentation de symbole OFDM sur un signal numérique reçu ; le transformateur de Fourier rapide est configuré pour effectuer séquentiellement une transformée de Fourier rapide, FFT, sur des symboles OFDM obtenus par la segmentation, et transformer les symboles OFDM de domaine temporel en domaine fréquentiel pour obtenir une séquence de symboles OFDM de domaine fréquentiel ; l'estimateur de canal est configuré pour effectuer une estimation de canal selon une séquence d'entraînement transmise de manière transparente, pour obtenir une valeur d'estimation de canal ; l'extracteur de sous-porteuse d'informations est configuré pour extraire un symbole de sous-porteuse d'informations depuis un symbole OFDM de domaine fréquentiel actuel ; l'extracteur de sous-porteuse pilote est configuré pour extraire un symbole pilote et une sous-porteuse de courant continu, CC, depuis le symbole OFDM de domaine fréquentiel actuel, le détecteur est configuré pour détecter le symbole de sous-porteuse d'informations ; le décideur difficile de sous-porteuse est configuré pour mettre en œuvre une décision sur le symbole de sous-porteuse d'informations et générer un symbole de sous-porteuse d'informations de récupération ; le synthétiseur de symbole OFDM est configuré pour synthétiser le symbole pilote et la sous-porteuse CC dans le symbole OFDM actuel et le symbole de sous-porteuse d'informations de récupération dans un symbole OFDM de récupération ; l'estimateur de décalage de fréquence et de décalage de temps est configuré pour effectuer une estimation de décalage de fréquence et une estimation de décalage de temps sur le symbole OFDM de récupération, pour obtenir une valeur de rotation de phase d'estimation de décalage de fréquence correspondante et une valeur de rotation de phase d'estimation de décalage de temps correspondante; le filtre de boucle de décalage de fréquence est configuré pour corriger la valeur de rotation de phase d'estimation de décalage de fréquence ; le filtre de boucle de décalage de temps est configuré pour corriger la valeur de rotation de phase d'estimation de décalage de temps ; le calculateur d'estimation de rotation de phase est configuré pour calculer la valeur de rotation de phase d'estimation de décalage de fréquence correspondante et la valeur de rotation de phase d'estimation de décalage de temps correspondante ; et le compensateur de rotation de phase est configuré pour effectuer une compensation de phase sur un symbole OFDM de domaine fréquentiel suivant dans la séquence de symboles OFDM de domaine fréquentiel en utilisant la valeur de rotation de phase d'estimation de décalage de fréquence et la valeur de rotation de phase d'estimation de décalage de temps, et le symbole OFDM de domaine fréquentiel compensé est défini sur un symbole OFDM de domaine fréquentiel actuel.
     
    6. Appareil de suivi de synchronisation de système OFDM selon la revendication 5, dans lequel le décideur difficile de sous-porteuse met en œuvre une décision difficile de vraisemblance maximale, et génère le symbole de sous-porteuse d'informations de récupération.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description