CN112866163B - Method and system for estimating residual frequency offset of WiFi service - Google Patents

Method and system for estimating residual frequency offset of WiFi service Download PDF

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CN112866163B
CN112866163B CN202110012940.2A CN202110012940A CN112866163B CN 112866163 B CN112866163 B CN 112866163B CN 202110012940 A CN202110012940 A CN 202110012940A CN 112866163 B CN112866163 B CN 112866163B
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CN112866163A (en
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蒋芜
吴建兵
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Shenzhen Itest Technology Co ltd
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    • 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
    • H04L27/2657—Carrier synchronisation
    • H04L27/2659—Coarse or integer frequency offset determination and 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
    • H04L27/2657—Carrier synchronisation
    • H04L27/266—Fine or fractional frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase

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Abstract

The invention provides a method and a system for WiFi service residual frequency offset estimation, wherein the method for WiFi service residual frequency offset estimation comprises the following steps: step S1, coarse frequency offset estimation and compensation are realized through a short training sequence; step S2, the fine frequency offset estimation and compensation are realized through the long training sequence; step S3, estimating and compensating the residual frequency offset of the symbol cyclic prefix part; step S4, channel estimation is carried out on the received data after the residual frequency offset of the symbol cyclic prefix part is compensated; in step S5, intra-symbol phase difference compensation is performed on each data symbol until all data symbols have been processed. After the coarse frequency offset estimation compensation and the fine frequency offset estimation compensation are carried out, the residual frequency offset of the cyclic prefix part of the symbol is estimated and compensated, and phase difference compensation in the symbol is also carried out on each data symbol, so that the influence brought by the frequency offset is reduced to the minimum, and the accuracy and the stability of the test are effectively improved.

Description

Method and system for estimating residual frequency offset of WiFi service
Technical Field
The invention relates to a residual frequency offset estimation method, in particular to a method for estimating residual frequency offset of WiFi service, and a system adopting the method for estimating residual frequency offset of WiFi service.
Background
OFDM is a special multi-carrier transmission technique that can be considered either a modulation technique or a multiplexing technique. The OFDM parallels the high-rate information symbols into low-rate symbols, and then transmits the low-rate symbols on a plurality of orthogonal subcarriers in parallel, so that the influence caused by frequency selective fading of a broadband system can be reduced; by adding the cyclic prefix, the interference among all symbols can be effectively avoided. At the receiving end, the fading of the channel can be compensated only by using a simple frequency domain equalizer, so that the realization of the OFDM receiver becomes very simple.
In the Wi-Fi standard (802.11a/g/n/ac/ax) of IEEE802.11 based on OFDM communication, a preamble is inserted with a specific training sequence for completing synchronization, frequency offset estimation and channel estimation of a received signal, and in order to improve the range of frequency offset estimation, a short training sequence is designed for coarse frequency offset estimation. FIG. 2 is a time-frequency domain plot of a short training sequence of duration 0.8us repeated 10 times and a long training sequence of duration 3.2us repeated 2 times with a cyclic prefix of duration 0.8us for 802.11 a/g/n/ac/ax.
When a tester tests a DUT (object to be tested), due to errors in design of physical devices and circuits of the DUT, a Carrier Frequency Offset (Carrier Frequency Offset) exists in a signal sent by the DUT, and when the tester receives the signal sent by the DUT, Frequency Offset estimation and Frequency Offset compensation are required. The general frequency offset estimation strategy is to use a short training sequence to perform a coarse frequency offset estimation and compensation, and then use a long training sequence to perform a fine frequency offset estimation and compensation. However, this method has a premise that the frequency offset is basically unchanged on this receiving link, and actually, the frequency offset has a difference of several tens to several hundreds Hz at different times, which is generally called residual frequency offset, the residual frequency offset is gradually accumulated with the increase of the number of symbols, and when the corresponding phase offset after the residual frequency offset accumulation exceeds ± 2 pi, a phase inversion is induced to cause a reception failure.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for estimating the residual frequency offset of the WiFi service, which can minimize the influence caused by the frequency offset as much as possible, so as to achieve the purpose of improving the accuracy and stability of the signal performance of the device to be tested by a tester.
To this end, the present invention provides a method for estimating residual frequency offset of WiFi service, which includes the following steps:
step S1, the coarse frequency offset estimation and compensation are realized through the short training sequence;
step S2, the fine frequency offset estimation and compensation are realized through the long training sequence;
step S3, estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
step S4, channel estimation is carried out on the received data after the residual frequency offset of the symbol cyclic prefix part is compensated;
in step S5, intra-symbol phase difference compensation is performed on each data symbol until all data symbols have been processed.
The invention is further improved in that in the step S3, the formula is adopted
Figure BDA0002885674190000021
Estimating the residual frequency offset of the cyclic prefix part of the symbol to obtain the residual frequency offset f of the cyclic prefix part of the symbolGIThen, compensating the received signal, wherein M is the total number of data symbols, i is the cyclic variable of the data symbols, fsym,iIs the residual frequency offset of the ith data symbol.
The invention is further improved in that in the step S3, the formula is adopted
Figure BDA0002885674190000022
Compensating the received signal, wherein y3(t) is a received signal after estimating and compensating for residual frequency offset of a cyclic prefix portion of a symbol, y2And (t) is a received signal after the fine frequency offset estimation and compensation are realized, j is an imaginary number unit, and t is a sampling point serial number.
In a further improvement of the present invention, in the step S5, the formula is used
Figure BDA0002885674190000023
Figure BDA0002885674190000024
Performing intra-symbol phase difference compensation on each data symbol, wherein,
Figure BDA0002885674190000025
a frequency-domain value compensated for intra-symbol phase difference for the ith data symbol,
Figure BDA0002885674190000026
frequency-domain value, Phdiff, before intra-symbol phase difference compensation for the ith data symbolsym,iIs the average value of the phase differences.
The invention is further improved in that in the step S5, the formula is adopted
Figure BDA0002885674190000027
Figure BDA0002885674190000028
Calculating the frequency domain value of the ith data symbol before phase difference compensation in the symbol
Figure BDA0002885674190000029
Wherein, Y (f)sym,i) And (3) the ideal frequency domain value of the ith data symbol, wherein N is the number of Fourier transform points of the OFDM system, and Fs is the sampling rate.
In a further improvement of the present invention, in the step S5, an average value of a plurality of pilot phase differences is calculated according to the phase difference between the received signal carrier and the ideal carrier on the pilot subcarrier, so as to obtain a phase difference average value Phdiffsym,i。
In a further improvement of the present invention, in the step S1, the step is implemented by a formula
Figure BDA0002885674190000031
Coarse frequency offset compensation, wherein y1(t) is the received signal after coarse frequency offset estimation and compensation, y (t) is the received signal, j is the imaginary unit, fstsAnd t is a sampling point serial number.
The invention is further improved in that, in the step S2, the formula is used to implement
Figure BDA0002885674190000032
Fine frequency offset compensation, wherein y2(t) to achieve a fine frequency offset estimate and compensated received signal, fltsIs the fine frequency offset estimation value.
In a further improvement of the present invention, the frequency offsets of the streams of each data symbol are respectively calculated in the steps S1, S2 and S3, and then averaged, so as to compensate the averaged frequency offsets on the streams of each data symbol.
The invention also provides a system for estimating the residual frequency offset of the WiFi service, which adopts the method for estimating the residual frequency offset of the WiFi service and comprises the following steps:
the coarse frequency offset estimation compensation module is used for realizing coarse frequency offset estimation and compensation through a short training sequence;
the fine frequency offset estimation compensation module is used for realizing fine frequency offset estimation and compensation through a long training sequence;
the residual frequency offset estimation compensation module of the symbol cyclic prefix is used for estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
the channel estimation module is used for carrying out channel estimation on the received data after the residual frequency offset of the cyclic prefix part of the symbol is compensated;
and the intra-symbol phase difference compensation module is used for performing intra-symbol phase difference compensation on each data symbol until all the data symbols are processed.
Compared with the prior art, the invention has the beneficial effects that: after the coarse frequency offset estimation compensation and the fine frequency offset estimation compensation are carried out, the residual frequency offset of the cyclic prefix part of the symbol is estimated and compensated, on the basis, when the data symbols are processed, phase difference compensation in the symbols is carried out on each data symbol, and through the combined use of multiple estimation and compensation modes and the like, the influence brought by the frequency offset is reduced to the minimum, the accuracy and the stability of the signal performance of the device to be tested by the tester are effectively improved, and the high-performance requirement of the residual frequency offset estimation of the WiFi service is met.
Drawings
FIG. 1 is a schematic workflow diagram of one embodiment of the present invention;
FIG. 2 is a time-frequency domain diagram of a training sequence;
FIG. 3 is a diagram illustrating simulation of residual frequency offset causing symbol phase inversion resulting in analysis failure;
FIG. 4 is a schematic diagram of a True MIMO test networking mode;
FIG. 5 is a schematic diagram of a Compette MIMO test networking mode;
FIG. 6 is a simulation diagram illustrating a normal analysis performed according to an embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
As shown in fig. 1, this example provides a method for estimating residual frequency offset of WiFi service, which includes the following steps:
step S1, the coarse frequency offset estimation and compensation are realized through the short training sequence;
step S2, the fine frequency offset estimation and compensation are realized through the long training sequence;
step S3, estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
step S4, channel estimation is carried out on the received data after the residual frequency offset of the symbol cyclic prefix part is compensated;
in step S5, intra-symbol phase difference compensation is performed on each data symbol until all data symbols have been processed.
The purpose of this example is to eliminate as much as possible the adverse effect of residual frequency offset on the received signal. Fig. 3 shows a simulation case of reception failure caused by residual frequency offset, in fig. 3, the EVM of the symbol in the 940 th symbol causes blurring of the whole constellation point due to phase inversion, and finally, the signal analysis fails.
The OFDM technology is to transmit signals on a plurality of overlapped sub-channels, and in order to receive correctly, orthogonality between sub-carriers must be guaranteed, but because doppler shift and receiving and transmitting frequency mixer crystal oscillator are different, there is often a certain carrier frequency deviation, orthogonality between sub-carriers is affected, and the influence of the deviated carrier frequency on phase is also additive. In order to guarantee the performance of OFDM, carrier frequency synchronization, i.e., frequency offset estimation and compensation, must be performed.
Assuming that a signal at a transmitting end is x (t), t is a sampling point number, only the influence of frequency deviation of delta f exists from the transmitting end to a receiving end through an ideal channel, and the received signal is y (t) ═ x (t) × ej2πΔftIf the interval duration delta t is a group of repeated data, the sampling rate is Fs, N is the number of interval sampling points, which is also called the number of Fourier transform points of the OFDM system; n ═ Fs Δ t, then x (t + N) ═ x (t) ej2πΔfΔt。
Figure BDA0002885674190000041
Figure BDA0002885674190000042
Then the frequency offset can be determined
Figure BDA0002885674190000043
Where the superscript H is the complex conjugate.
Since the arctan operation value range is (-pi), the frequency deviation estimation range
Figure BDA0002885674190000044
The preamble begins with a short midamble of duration 0.8us (microseconds) and repeated 10 times, then the frequency offset estimation range of the short midamble is
Figure BDA0002885674190000051
The long training sequence is a sequence of duration 3.2us and repeated 2 times, and therefore has a frequency offset estimation range of
Figure BDA0002885674190000052
It is assumed that time synchronization has been completed before frequency offset estimation.
In step S1, the coarse frequency offset estimation uses a short training sequence, y (t) ═ x (t) × ej2πΔftThe duration of the short training sequence repetition interval Δ t is 0.8us, the sampling point N is Δ t Fs,
Figure BDA0002885674190000053
Figure BDA0002885674190000054
wherein n issts,iIs the starting position of the ith short training sequence signal, Rsts,iComputing an intermediate variable of frequency offset, y (t + n), for the ith short training sequencests,i) For receiving signals y (t) at t + nsts,iThe value of time, y (t + N + N)sts,i) For receiving signals y (t) at t + N + Nsts,iThe value of the time is marked with H to solve complex conjugation; then
Figure BDA0002885674190000055
Short training sequence has 10 repeats, Rsts,iIt is possible to construct 9 of the number,
Figure BDA0002885674190000056
Figure BDA0002885674190000057
i is a loop variable.
Calculating to obtain a coarse frequency offset estimation value fstsThen, the method is realized by a formula
Figure BDA0002885674190000058
Coarse frequency offset compensation, wherein y1(t) is the received signal after coarse frequency offset estimation and compensation, y (t) is the received signal, j is the imaginary unit, fstsAnd t is a sampling point serial number.
In step S2, the fine frequency offset estimation uses a long training sequence, where the long training sequence repetition interval duration Δ t is 3.2us, the sample point N is Δ t × Fs,
Figure BDA0002885674190000059
wherein n isltsIs the starting position of the long training sequence signal, y1(t+nlts) For receiving a signal y1(t) at t + nltsValue of time, y1(t+N+nlts) For receiving a signal y1(t) at t + N + NltsA value of a time of day; then
Figure BDA00028856741900000510
Calculating to fine frequency offset estimation value fltsThen, the method is realized by a formula
Figure BDA00028856741900000511
Fine frequency offset compensation, wherein y2(t) to achieve a fine frequency offset estimate and compensated received signal, fltsIs the fine frequency offset estimate.
In this example, step S3 is used to implement residual frequency offset estimation and compensation, and steps S1 and S2 are frequency offsets calculated based on the training sequence, and because the channel has time-varying property, the residual frequency offset on subsequent symbols is not the sameSimilarly, to obtain a better received signal, statistical residual frequency offset estimation and compensation are required. Each data symbol has a cyclic prefix associated with the data, the length of the cyclic prefix is 0.8us at 11a/g, two types of cyclic prefixes are respectively 0.4us and 0.8us at 11N and 11ac, three types of cyclic prefixes are respectively 0.8us, 1.6us and 3.2us at 11ax, the cyclic prefixes are collectively referred to as duration delta t1, and duration sampling point N is1Δ t1 Fs. The interval duration is 3.2us at 11a/g, 11N and 11ac, 12.8us at 11ax, collectively denoted as duration Δ t2, and the sample duration N2Δ t2 × Fs. Assume that the received signal has M data symbols.
Figure BDA0002885674190000061
Wherein n issym,iIs the starting position of the ith data symbol, then
Figure BDA0002885674190000062
Rsym,iCalculating an intermediate amount of frequency offset, y, for the ith data symbol2(t+nsym,i) For receiving a signal y2(t) at t + nsym,iValue of time, y2(t+N2+nsym,i) For receiving a signal y2(t) at t + N2+nsym,iThe value of the time of day.
In step S3 in this example, the formula is used
Figure BDA0002885674190000063
Estimating the residual frequency offset of the cyclic prefix part of the symbol to obtain the residual frequency offset f of the cyclic prefix part of the symbolGIThen, compensating the received signal, wherein M is the total number of data symbols, i is the cyclic variable of the data symbols, fsym,iIs the residual frequency offset of the ith data symbol.
In step S3 in this example, the formula is used
Figure BDA0002885674190000064
Compensating the received signal, wherein y3(t) is the received signal after estimation and compensation of the residual frequency offset of the cyclic prefix portion of the symbol, y2(t) to achieve fine frequency offset estimation and compensationIn the received signal, j is an imaginary unit, and t is a sampling point serial number.
Step S4 is used to realize channel estimation after compensation of residual frequency offset fGIThen, an LS mode is used for channel estimation, 11a/g uses a long training sequence lts, 11n uses HT-LTF, 11ac uses VHT-LTF, and 11ax uses HE-LTF; this process is the same as the existing MIMO approach to estimate each channel state and is not discussed.
In this example, step S5 is used to realize intra-symbol frequency offset estimation and compensation, and step S3 only statistically processes residual frequency offset of the data as a whole, and actually residual frequency offset still exists in each symbol. The residual frequency offset within each symbol is processed and may be tracked using pilots. In this example, after the compensation in step S3, n is usedsym,iDenotes the starting position of the ith symbol, and has a residual frequency offset of fsym,i，
Figure BDA0002885674190000065
y3(t+nsym,i) For receiving a signal y3(t) at t + nsym,iThe value of time, y (t + n)sym,i) For receiving signals y (t) at t + nsym,iThe value of the time of day.
If y (t + n)sym,i) The ideal value of the frequency domain of (c) is represented as Y (f)sym,i) According to the Fourier transform characteristic, then at the residual frequency offset fsym,iThe frequency domain affected by the data compensated by the steps S1, S2 and S3 is shown as
Figure BDA0002885674190000066
Figure BDA0002885674190000067
Counting; i.e. by the formula
Figure BDA0002885674190000068
Calculating the frequency domain value of the ith data symbol before phase difference compensation in the symbol
Figure BDA0002885674190000071
Wherein, Y (f)sym,i) Number of iAnd (3) obtaining the ideal frequency domain value of the data symbol, wherein N is the number of Fourier transform points of the OFDM system, and Fs is the sampling rate.
Then through the formula
Figure BDA0002885674190000072
Performing intra-symbol phase difference compensation for each data symbol, wherein,
Figure BDA0002885674190000073
a frequency-domain value compensated for intra-symbol phase difference for the ith data symbol,
Figure BDA0002885674190000074
frequency-domain value, Phdiff, before intra-symbol phase difference compensation for the ith data symbolsym,iIs the average value of the phase differences.
In step S5, preferably, the average of the multiple pilot phase differences is calculated by using the phase difference between the received signal carrier on the pilot subcarrier and the ideal carrier to obtain the phase difference average Phdiffsym,i(ii) a Then, phase difference compensation in the symbol is carried out; finally, the frequency domain value after the phase difference compensation in the symbol is carried out through the ith data symbol is optimized
Figure BDA0002885674190000075
To complete demodulation, decoding and calculation of EVM.
This example processes each data symbol of the received data one by one until all data symbols have been analyzed.
After step S5 is completed, i.e., after the residual frequency offset estimation and correlation compensation are completed in the previous step, the remaining process flow of the present example is performed according to the normal receiver operation flow. Fig. 6 is an analysis result corresponding to the data in fig. 3, where the method and system for estimating residual frequency offset of WiFi service in this example are applied, as shown in fig. 6, phase inversion is solved, and performance is greatly improved.
When the present example is applied to the Composite MIMO test, only the step S4 channel estimation module needs to estimate each channel state according to the MIMO method, and the rest steps are completely the same.
Preferably, in the present example, the frequency offsets of the streams of each data symbol are respectively calculated in step S1, step S2 and step S3, and then frequency offset averages are obtained to compensate the frequency offset averages on the streams of each data symbol. In this example, step S4 needs to estimate each channel state in a MIMO manner, and step S5 performs separate processing on each stream.
The present embodiment also provides a system for estimating WiFi service residual frequency offset, which employs the method for estimating WiFi service residual frequency offset as described above, and includes:
the coarse frequency offset estimation compensation module is used for realizing coarse frequency offset estimation and compensation through a short training sequence;
the fine frequency offset estimation compensation module is used for realizing fine frequency offset estimation and compensation through a long training sequence;
the residual frequency offset estimation compensation module of the symbol cyclic prefix is used for estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
the channel estimation module is used for carrying out channel estimation on the received data after the residual frequency offset of the cyclic prefix part of the symbol is compensated;
and the intra-symbol phase difference compensation module is used for performing intra-symbol phase difference compensation on each data symbol until all the data symbols are processed.
According to the multi-dimensional frequency offset estimation and compensation, a tester acquires signals and carries out down-conversion processing on the signals into baseband signals, and after the synchronization process is completed, a short training sequence is firstly used for short duration in a time domain, so that the characteristic of a larger frequency offset range can be estimated, and coarse frequency offset estimation and compensation are carried out; and then, the duration of the long training sequence is consistent with the length of the symbol in the time domain, and the fine frequency offset estimation and compensation are carried out. Because each symbol has a section of guard interval (cyclic prefix) for preventing intersymbol interference, the cyclic prefix is the copy of a symbol time domain signal, so that the cyclic prefix can be used for estimating residual frequency offset, the cyclic prefixes of all symbols can estimate a statistical residual frequency offset to compensate the frequency offset, and the adverse factor of overlarge residual frequency offset after frequency offset compensation based on a training sequence can be avoided.
And then, performing channel estimation in an LS mode, wherein 11a/g uses a long training sequence lts, 11n uses HT-LTF, 11ac uses VHT-LTF, and 11ax uses HE-LTF. When processing data symbol i, estimating residual frequency offset from frequency domain by using pilot frequency phase and actual phase difference of data symbol i, and compensating the phase difference for data carrier. The frequency offset estimation and compensation methods are combined for use, so that the influence caused by frequency offset can be minimized, and the accuracy and stability of the DUT signal performance tested by the tester are improved.
In an application scenario, the present example is not limited to use in only a single signal generator and single signal analyzer mode. The principle of MIMO (multiple input multiple output) technology is that signals are simultaneously transmitted and received through multiple antennas at a transmitting end and a receiving end, thereby improving the quality of service obtained by each user. In modern wireless communication systems, the combination of OFDM (orthogonal frequency division multiplexing) technology and MIMO (composite MIMO) technology greatly improves the capacity of the system. The standards of IEEE802.11n, IEEE802.11ac and IEEE802.11ax promoted by the Wi-Fi alliance adopt the two technologies. For a Device Under Test (DUT) supporting MIMO, because each data stream carries different information, multiple RF ports of a tester are required to test signals of multiple radio frequency transmitting antenna ports of the DUT. The testing method of one RF port for one analyzer is known in the industry as True MIMO testing, and Composite MIMO is organized as shown in fig. 4. In order to reduce the cost of MIMO testing, the tester also supports a Composite MIMO testing method, where the Composite MIMO is networked as shown in fig. 5, and multiple signals are combined into one path through the power splitter and input to the tester, and the tester only needs one radio frequency receiving link. The example is equally applicable to both True and Composite MIMO test scenarios.
In summary, after the coarse frequency offset estimation compensation and the fine frequency offset estimation compensation are performed, the residual frequency offset of the cyclic prefix portion of the symbol is estimated and compensated, on this basis, when the data symbols are processed, phase difference compensation in the symbol is performed on each data symbol, and by using multiple estimation and compensation modes in a combined manner, the influence caused by the frequency offset is reduced to the minimum, the accuracy and stability of the signal performance of the device to be tested by the tester are effectively improved, and the high-performance requirement of the residual frequency offset estimation of the WiFi service is met.
The foregoing is a further detailed description of the invention in connection with specific preferred embodiments and it is not intended to limit the invention to the specific embodiments described. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (9)

1. A method for estimating residual frequency offset of WiFi service is characterized by comprising the following steps:
step S1, coarse frequency offset estimation and compensation are realized through a short training sequence;
step S2, the fine frequency offset estimation and compensation are realized through the long training sequence;
step S3, estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
step S4, channel estimation is carried out on the received data after the residual frequency offset of the symbol cyclic prefix part is compensated;
step S5, performing intra-symbol phase difference compensation on each data symbol until all data symbols are processed;
in the step S5, the formula is used
Figure FDA0003640405730000011
Calculating the frequency domain value of the ith data symbol before phase difference compensation in the symbol
Figure FDA0003640405730000012
Wherein, Y (f)sym,i) The ideal value of the frequency domain of the ith data symbol, wherein N is the number of Fourier transform points of the OFDM system, and Fs is the sampling rate; f. ofsym,iIs the residual frequency offset of the ith data symbol.
2. According to claim 1The method for estimating the residual frequency offset of the WiFi service is characterized in that, in step S3, the residual frequency offset is estimated according to a formula
Figure FDA0003640405730000013
Estimating the residual frequency deviation of the cyclic prefix part of the symbol to obtain the residual frequency deviation f of the cyclic prefix part of the symbolGIThen, compensating the received signal, wherein M is the total number of data symbols, i is the cyclic variable of the data symbols, fsym,iIs the residual frequency offset of the ith data symbol.
3. The method for WiFi service residual frequency offset estimation according to claim 2, wherein in the step S3, it is represented by the formula
Figure FDA0003640405730000014
Compensating the received signal, wherein y3(t) is the received signal after estimation and compensation of the residual frequency offset of the cyclic prefix portion of the symbol, y2And (t) is a received signal after the fine frequency offset estimation and compensation are realized, j is an imaginary number unit, and t is a sampling point serial number.
4. Method for residual frequency offset estimation of WiFi services according to claim 2 or 3, characterized in that in said step S5, the data is obtained according to the formula
Figure FDA0003640405730000015
Performing intra-symbol phase difference compensation on each data symbol, wherein,
Figure FDA0003640405730000016
a frequency-domain value compensated for intra-symbol phase difference for the ith data symbol,
Figure FDA0003640405730000017
frequency-domain value, Phdiff, before intra-symbol phase difference compensation for the ith data symbolsym,iIs the average value of the phase differences.
5. The method of claim 4, wherein in step S5, the average of the plurality of pilot phase differences is calculated according to the phase differences between the received signal carriers and the ideal carriers on the pilot subcarriers to obtain a phase difference average Phdiffsym,i。
6. Method for estimating residual frequency offset of WiFi service according to any one of claims 1-3, wherein in step S1, the method is implemented by formula
Figure FDA0003640405730000021
Coarse frequency offset compensation, wherein y1(t) is the received signal after coarse frequency offset estimation and compensation, y (t) is the received signal, j is the imaginary unit, fstsAnd t is a sampling point serial number.
7. The method for residual frequency offset estimation of WiFi services according to claim 6, wherein in said step S2, the implementation is performed according to the formula
Figure FDA0003640405730000022
Fine frequency offset compensation, wherein y2(t) to achieve a fine frequency offset estimate and compensated received signal, fltsIs the fine frequency offset estimation value.
8. The method of any of claims 1 to 3, wherein the step S1, the step S2 and the step S3 are respectively to calculate the frequency offset of each stream of data symbols, and then to average the frequency offsets, so as to compensate the average frequency offset on each stream of data symbols.
9. A system for WiFi service residual frequency offset estimation, characterized in that, the method for WiFi service residual frequency offset estimation according to any of claims 1 to 8 is adopted, and includes:
the coarse frequency offset estimation compensation module is used for realizing coarse frequency offset estimation and compensation through a short training sequence;
the fine frequency offset estimation compensation module is used for realizing fine frequency offset estimation and compensation through a long training sequence;
the residual frequency offset estimation compensation module of the symbol cyclic prefix is used for estimating and compensating the residual frequency offset of the symbol cyclic prefix part;
the channel estimation module is used for carrying out channel estimation on the received data after the residual frequency offset of the cyclic prefix part of the symbol is compensated;
and the intra-symbol phase difference compensation module is used for performing intra-symbol phase difference compensation on each data symbol until all the data symbols are processed.
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