CN110113276B - OFDM frequency offset estimation method, system and device based on IEEE802.11 - Google Patents
OFDM frequency offset estimation method, system and device based on IEEE802.11 Download PDFInfo
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- CN110113276B CN110113276B CN201810099899.5A CN201810099899A CN110113276B CN 110113276 B CN110113276 B CN 110113276B CN 201810099899 A CN201810099899 A CN 201810099899A CN 110113276 B CN110113276 B CN 110113276B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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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
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
- H04L2027/0026—Correction of carrier offset
Abstract
The invention discloses an OFDM frequency offset estimation method, a system and a device based on IEEE 802.11. The method comprises the following steps: performing front-back autocorrelation operation on two identical long training sequences in a Preamble of a received signal on a time domain to obtain a first carrier frequency offset estimation value; performing time domain carrier frequency offset compensation on the Signal according to the first carrier frequency offset estimation value; converting the compensated Signal from a time domain Signal into a frequency domain Signal; analyzing the Signal of the frequency domain to obtain a frequency domain reference Signal; performing local correlation operation on the frequency domain reference Signal and the Signal of the frequency domain to obtain a second carrier frequency offset estimation value; and performing time domain carrier frequency offset compensation on Payload according to the first carrier frequency offset estimation value and the second carrier frequency offset estimation value. Combining the time domain carrier frequency offset estimation of the Preamble and the frequency domain carrier frequency offset estimation of the Signal, and finally obtaining more accurate time domain carrier frequency offset estimation compensation in Payload; the method has the advantages of high accuracy, low complexity and strong real-time performance.
Description
Technical Field
The present invention relates to the field of communications technologies, and in particular, to an OFDM frequency offset estimation method, system, and apparatus based on IEEE 802.11.
Background
IEEE802.11 is a communication protocol based on OFDM (orthogonal frequency division multiplexing) technology. This technique improves throughput by transmitting multiple subcarriers simultaneously. Each subcarrier carries different information. Since the subcarriers are orthogonal, there is no mutual interference. OFDM techniques are very sensitive to Carrier Frequency Offset (CFO), however, because the carrier frequency offset not only introduces phase rotation to the subcarrier information, but also destroys orthogonality between subcarriers, allowing subcarriers to interfere with each other (ICI).
Therefore, the OFDM receiver needs to have effective carrier frequency offset estimation and compensation.
For IEEE802.11 protocol, the prior art basically performs carrier frequency offset estimation through a Preamble training sequence (STF or LTF), or performs iterative tracking through some characteristics in the data receiving process. However, these methods have problems of low accuracy, high complexity, and poor real-time performance.
A frequency offset estimation method and device (application number: 201111049869.1) of OFDM communication system remodulates the feedback information obtained by analysis in frequency domain and converts it to time domain, and carries out local correlation operation in time domain. The local correlation in the time domain avoids the noise introduced by ICI interference, resulting in higher accuracy, but introduces greater complexity.
A carrier frequency offset estimation method (application number: 201610147118.6) suitable for MIMO-OFDM system uses autocorrelation of N STFs (short training sequences) on a Preamble to perform rough frequency offset estimation, and then uses autocorrelation of two LTFs (long training sequences) to obtain accurate carrier frequency offset estimation. Finally, the accurate carrier frequency offset estimation value is used for compensating to subsequent Signal and Payload parts, and the demodulation performance of the parts is guaranteed. The autocorrelation of the two LTFs provides a limited accuracy in the frequency offset estimation and, therefore, there is a certain loss in reception performance. Some methods are to perform iterative estimation by using some information of subsequent Payload, and in the iterative process, the performance is gradually improved along with the time, but the method does not have real-time performance, and the front part in the Payload cannot be guaranteed in time.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an OFDM frequency offset estimation method, system and device based on IEEE802.11, the method, system or device completes local correlation operation in the frequency domain, and the frequency domain local correlation of the Signal part is utilized to improve the accuracy of frequency offset estimation, thereby solving the problems of low accuracy, high complexity and poor real-time performance of the existing carrier frequency offset estimation method.
In order to achieve the purpose, the technical scheme of the invention is as follows:
an OFDM frequency offset estimation method based on IEEE802.11 comprises the following steps: performing front-back autocorrelation operation on two identical long training sequences in a Preamble of a received signal on a time domain to obtain a first carrier frequency offset estimation value; carrying out time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value; converting the compensated Signal from a time domain Signal into a frequency domain Signal; analyzing the Signal of the frequency domain, and modulating the analyzed information again to obtain a frequency domain reference Signal; performing local correlation operation on the frequency domain reference Signal and the Signal of the frequency domain to obtain a second carrier frequency offset estimation value; and performing time domain carrier frequency offset compensation on Payload of the received signal according to the first carrier frequency offset estimation value and the second carrier frequency offset estimation value.
Further, the formula for performing the front-back autocorrelation operation on two identical long training sequences in the Preamble of the received signal in the time domain is as follows:
where N is the length of the long training sequence, yLTF1And yLTF2Respectively, a first long training sequence and a second long training sequence in the Preamble, (.)*Represents a conjugation;
wherein f issIs the sample rate of the received signal.
Further, the formula for performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value is as follows:
wherein the content of the first and second substances,in order to compensate the time domain Signal after the compensation,for compensated white Gaussian noise, foIs the actual carrier frequency offset value.
Further, the formula for converting the compensated Signal from the time domain Signal to the frequency domain Signal is as follows:
wherein the content of the first and second substances,for the converted frequency domain Signal, L is the distance between OFDM symbols; f. ofΔThe carrier frequency deviation value after compensation.
Further, the formula for performing local correlation operation on the frequency domain reference Signal and the frequency domain Signal is as follows:
wherein the content of the first and second substances,in order to convert the frequency domain Signal,is the frequency domain reference signal;
an OFDM frequency offset estimation system based on IEEE802.11 comprises a first frequency offset estimation unit, a Signal frequency offset compensation unit, a Fourier transform unit, a frequency domain reference Signal acquisition unit, a second frequency offset estimation unit and a Payload frequency offset compensation unit.
The first frequency offset estimation unit is used for performing front-back autocorrelation operation on two identical long training sequences in a Preamble of a received signal in a time domain to obtain a first carrier frequency offset estimation value.
And the Signal frequency offset compensation unit is used for performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value.
And the Fourier transform unit is used for converting the compensated Signal from a time domain Signal into a frequency domain Signal.
The frequency domain reference Signal acquisition unit is used for analyzing the Signal of the frequency domain and remodulating the analyzed information to obtain the frequency domain reference Signal.
And the second frequency offset estimation unit is used for carrying out local correlation operation on the frequency domain reference Signal and the frequency domain Signal to obtain a second carrier frequency offset estimation value.
And the Payload frequency offset compensation unit is used for performing time domain carrier frequency offset compensation on Payload of the received signal according to the first carrier frequency offset estimation value and the second carrier frequency offset estimation value.
Further, the formula of performing a pre-autocorrelation and post-autocorrelation operation on two identical long training sequences in the Preamble of the received signal by the first frequency offset estimation unit on the time domain is as follows:
where N is the length of the long training sequence, yLTF1And yLTF2Respectively, a first long training sequence and a second long training sequence in the Preamble, (.)*Representing conjugation.
wherein f issIs the sample rate of the received signal.
Further, the formula of the Signal frequency offset compensation unit performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value is as follows:
wherein the content of the first and second substances,in order to compensate the time domain Signal after the compensation,for compensated white Gaussian noise, foIs the actual carrier frequency offset value.
Further, the formula for the fourier transform unit to convert the compensated Signal from the time domain Signal to the frequency domain Signal is as follows:
wherein the content of the first and second substances,for the converted frequency domain Signal, L is the distance between OFDM symbols; f. ofΔThe carrier frequency deviation value after compensation.
The frequency domain reference Signal obtaining unit performs local correlation operation on the frequency domain reference Signal and the frequency domain Signal according to the following formula:
an IEEE 802.11-based OFDM frequency offset estimation apparatus, comprising a memory, a processor and a computer program stored on the memory and executable on the processor; the computer program, when executed by the processor, implements the steps of any of the methods described above.
The invention has the beneficial effects that:
the invention utilizes the autocorrelation operation of two LTFs of the Preamble part to obtain a more accurate carrier frequency offset estimation value, and compensates the carrier frequency offset estimation value to the subsequent Signal part in the time domain; converting the time-domain compensated Signal to a frequency domain for demodulation and analyzing information; the obtained information can be assumed as accurate information and is remodulated and fed back, and local correlation estimation is carried out in a frequency domain to obtain a more accurate carrier frequency offset value; by combining the time domain carrier frequency offset estimation in the Preamble and the frequency domain carrier frequency offset estimation in the Signal, more accurate time domain carrier frequency offset estimation compensation can be obtained in time in the Payload part finally; the method has the advantages of high accuracy, low complexity and strong real-time performance.
Drawings
FIG. 1 shows a physical layer Legacy frame format of the IEEE802.11a/g protocol.
Fig. 2 shows the physical layer HT-GF frame format of the ieee802.11n protocol.
Fig. 3 shows the physical layer HT-MM frame format of the ieee802.11n protocol.
Fig. 4 is a flowchart illustrating an OFDM frequency offset estimation method based on IEEE802.11 according to the present invention.
Fig. 5 is a diagram of a simulation result of carrier frequency offset estimation according to the present invention.
Detailed Description
The invention is further illustrated below with reference to the figures and examples.
IEEE802.11 is a communication protocol for WLANs under which both the transmitting and receiving parties can effectively communicate. Since the protocol content to which the present invention relates is only the physical layer communication frame format, its physical layer frame format is first briefly stated.
As shown in fig. 1 to 3, 3 physical layer frame formats of ieee802.11a/g/n are listed, respectively, and these frame formats are based on the OFDM modulation technique. Basically, the frame format is divided into three major parts: preamble, Signal, Payload. Ieee802.11a, ieee802.11g, and ieee802.11n are 3 standard protocols that have been further developed based on IEEE 802.11.
(1) Preamble: this part does not carry any information and the content is well-defined by the protocol and used for frame synchronization, i.e. frame detection, reception timing, power adjustment, Carrier Frequency Offset (CFO) estimation, etc.
(2) Signal: carrying characteristic information of the frame such as bandwidth, length, modulation format, etc. The characteristic information has high robustness and noise immunity and is a prerequisite for correctly receiving information. Therefore, the information is generally difficult to interfere with to make errors.
(3) Payload: carrying the transmission content.
Example 1:
as shown in fig. 4, an OFDM frequency offset estimation method based on IEEE802.11 includes the following steps:
s1: performing front-back autocorrelation operation on two identical Long Training Sequences (LTFs) in a Preamble of a received signal on a time domain to obtain a first carrier frequency offset estimation value
S2: according to the first carrier frequency deviation estimated valueAnd performing time domain carrier frequency offset compensation on the Signal of the received Signal.
S3: and converting the compensated Signal from a time domain Signal into a frequency domain Signal.
S4: analyzing the Signal of the frequency domain, and re-modulating the analyzed information to obtain a frequency domain reference Signal
S5: reference signal of frequency domainCarrying out local correlation operation with the Signal of the frequency domain to obtain a second carrier frequency offset estimation value
S6: according to the first carrier frequency deviation estimated valueAnd a second carrier frequency offset estimateAnd carrying out time domain carrier frequency offset compensation on Payload of the received signal.
The invention utilizes the autocorrelation operation of two LTFs of the Preamble part to obtain a more accurate carrier frequency offset estimation value, and compensates the carrier frequency offset estimation value to the subsequent Signal part in the time domain; converting the time-domain compensated Signal to a frequency domain for demodulation and analyzing information; the obtained information can be assumed as accurate information and the feedback is remodulated, and local correlation estimation is carried out in a frequency domain to obtain a more accurate carrier frequency offset value. And finally, more accurate time domain carrier frequency offset estimation compensation can be obtained in time in the Payload part by combining the time domain carrier frequency offset estimation in the Preamble and the frequency domain carrier frequency offset estimation in the Signal. The method has the advantages of high accuracy, low complexity and strong real-time performance.
Specifically, in step S1, the formula for performing the pre-post autocorrelation operation on the time domain is:where N is the length of the LTF, yLTF1And yLTF2First and second LTF, (. DEG) within the Preamble, respectively*Is conjugated.
The received signal y (n) has, in addition to noise, a carrier frequency offset, expressed as:
wherein x (n) is a useful signal; z (n) is white Gaussian noise,. sigma2Is the power;causing phase rotation for carrier frequency offset estimation; f. ofoIs the carrier frequency offset value; f. ofsIs the sample rate of the received signal.
Therefore, the pre-post autocorrelation estimation of the Preamble can be expressed as:
wherein the content of the first and second substances,is white noise after autocorrelation and follows Gaussian distribution, and the power is 2 NxXLTF1|2σ2;xLTF1=xLTF2。
By obtaining the angle θ (angle) (g) for g, the angle can be obtainedThus, a first carrier frequency offset estimation value is obtained
First carrier frequency offset estimation valueIs the actual carrier frequency offset foSince it is impossible to accurately obtain the actual carrier frequency offset value foSo there is also a residual value f of carrier frequency offsetΔ。
The accuracy of the carrier frequency offset estimation can be generally expressed by the signal-to-noise ratio after autocorrelation, and the expression is as follows:
specifically, in step S2, the formula for time-domain carrier frequency offset compensation on Signal is as follows:
wherein the content of the first and second substances,the compensated time domain Signal part is obtained; z is a radical ofsig(n) andfor compensating Gaussian white noise before and after, the power is sigma2;fΔThe compensated carrier frequency offset residual value is obtained.
Obtaining a first carrier frequency offset estimation value by utilizing LTF time domain autocorrelation operationWhen the Signal of the received Signal is compensated in the time domain, the noise introduced by ICI (inter-carrier interference) can be basically ignored when the Signal is converted from the time domain to the frequency domain, and the demodulation performance of the Signal is improved.
Specifically, in step S3, Fast Fourier Transform (FFT) is performed on the compensated Signal, and the Signal is converted from the time domain to the frequency domain, which is a necessary step for demodulating OFDM. The formula is as follows:
wherein the content of the first and second substances,is an FFT frequency point sequence;represented as a time-domain compensated frequency domain Signal; zsig(k) Expressed as frequency domain white Gaussian noise, with a power of
wherein the content of the first and second substances,is Gaussian white noise (including frequency domain noise and ICI-induced noise) and has power ofL is the distance from the previous OFDM symbol (L is more than or equal to N).
Specifically, in step S4, for the frequency domainAnd demodulating and analyzing the information to obtain bit information of a Signal part of the sending end, and feeding back the information. Demodulation may select hard decisions, or channel decoding. The feedback is more accurate after the channel decoding is adopted, because the channel decoding has an error correction function and needs a certain time delay; while the hard decision feedback is directly passed throughThe most likely bit information is found without considering delay. The two feedback performances are slightly different through experiments.
Then, the feedback information is remodulated by the same processing as the sending end, and the frequency domain reference signal is obtainedFrequency domain reference signalIs estimated according to the received signal, not necessarily the signal X actually modulated by the receiving endsig(k) Are completely consistent.
Specifically, in step S5, the frequency domain reference signal is transmittedReceived signal in frequency domainCarrying out local correlation operation, wherein the formula is as follows:
assuming an estimated frequency domain reference signalIs completely correct, thenThe local correlation result can be expressed as:
finally, the angle is calculated by the angle of GThus, a second carrier frequency offset estimation value is obtained
The modulation format of Signal is BPSK with the highest robustness, and the channel coding is 1/2 code rate with the highest robustness, so the demodulation performance of Signal is much higher than that of payload, and errors are difficult to make. Therefore, Signal information can basically be assumed to be correct, and it is a very reliable way to use its feedback as carrier frequency offset estimation. Feedback modulating the information analyzed by Signal, modulating the obtainedReceived signal in frequency domainThe local correlation is performed, and the performance gain improvement is higher than the performance gain of the self-correlation before and after the time domain.
After local correlation, assuming N ═ L, the signal-to-noise ratio is expressed as:
in contrast, it can be seen that the signal-to-noise ratio of the local correlation is a 3dB higher gain than the autocorrelation.
Specifically, in step S6, the final time domain carrier frequency offset compensation value for Payload is
As shown in fig. 5, which is a simulation result diagram of carrier frequency offset estimation according to the present invention, the frequency offset estimation error is CDF, and the channel environment is AWGN (SNR ═ 1.5 dB). The solid line is the result of the LTF autocorrelation estimation before and after use alone, with a 10% error greater than 11 KHz. The dotted line is the result obtained by adding Signal frequency domain local correlation estimation, and the error of 10% of the frequency offset estimation of the invention is more than 4 KHz. Obviously, the invention has excellent performance.
Example 2:
an OFDM frequency offset estimation system based on IEEE802.11 comprises a first frequency offset estimation unit, a Signal frequency offset compensation unit, a Fourier transform unit, a frequency domain reference Signal acquisition unit, a second frequency offset estimation unit and a Payload frequency offset compensation unit.
A first frequency offset estimation unit, configured to perform a pre-and-post autocorrelation operation on two identical long training sequences in a Preamble of a received signal in a time domain to obtain a first carrier frequency offset estimation value
A Signal frequency offset compensation unit for estimating the frequency offset according to the first carrier frequency offsetAnd performing time domain carrier frequency offset compensation on the Signal of the received Signal.
And the Fourier transform unit is used for converting the compensated Signal from a time domain Signal into a frequency domain Signal.
A frequency domain reference Signal obtaining unit, configured to analyze the Signal in the frequency domain, and remodulate the analyzed information to obtain a frequency domain reference Signal
A second frequency offset estimation unit for estimating the frequency domain reference signalCarrying out local correlation operation with the Signal of the frequency domain to obtain a second carrier frequency offset estimation value
A Payload frequency offset compensation unit for estimating the first carrier frequency offsetAnd a second carrier frequency offset estimateAnd carrying out time domain carrier frequency offset compensation on Payload of the received signal.
The invention utilizes the autocorrelation operation of two LTFs of the Preamble to obtain a more accurate carrier frequency offset estimation value, and compensates the carrier frequency offset estimation value to a subsequent Signal part in a time domain; converting the time-domain compensated Signal to a frequency domain for demodulation and analyzing information; the obtained information can be assumed as accurate information and the feedback is remodulated, and local correlation estimation is carried out in a frequency domain to obtain a more accurate carrier frequency offset value. And finally, more accurate time domain carrier frequency offset estimation compensation can be obtained in time in the Payload part by combining the time domain carrier frequency offset estimation in the Preamble and the frequency domain carrier frequency offset estimation in the Signal. The method has the advantages of high accuracy, low complexity and strong real-time performance.
Specifically, the formula of the first frequency offset estimation unit performing the pre-and post-autocorrelation operation on the time domain is as follows:where N is the length of the LTF, yLTF1And yLTF2First and second LTF, (. DEG) within the Preamble, respectively*Is conjugated.
The received signal y (n) has, in addition to noise, a carrier frequency offset, expressed as:
wherein x (n) is a useful signal; z (n) is white Gaussian noise,. sigma2Is the power;causing phase rotation for carrier frequency offset estimation; f. ofoIs the carrier frequency offset value; f. ofsIs the sample rate of the received signal.
Therefore, the pre-post autocorrelation estimation of the Preamble can be expressed as:
wherein the content of the first and second substances,is white noise after autocorrelation and follows Gaussian distribution, and the power is 2 NxXLTF1|2σ2;xLTF1=xLTF2。
By obtaining the angle θ (angle) (g) for g, the angle can be obtainedThus, a first carrier frequency offset estimation value is obtained
First carrier frequency offset estimation valueIs the actual carrier frequency offset foSince it is impossible to accurately obtain the actual carrier frequency offset value foSo there is also a residual value f of carrier frequency offsetΔ。
The accuracy of the carrier frequency offset estimation can be generally expressed by the signal-to-noise ratio after autocorrelation, and the expression is as follows:
specifically, the formula of the Signal frequency offset compensation unit performing time domain carrier frequency offset compensation on the Signal is as follows:
wherein the content of the first and second substances,the compensated time domain Signal part is obtained; z is a radical ofsig(n) andfor compensating Gaussian white noise before and after, the power is sigma2;fΔThe compensated carrier frequency offset residual value is obtained.
Obtaining a first carrier frequency offset estimation value by utilizing LTF time domain autocorrelation operationWhen the Signal of the received Signal is compensated in the time domain, the noise introduced by ICI (inter-carrier interference) can be basically ignored when the Signal is converted from the time domain to the frequency domain, and the demodulation performance of the Signal is improved.
Specifically, the fourier transform unit performs Fast Fourier Transform (FFT) on the compensated Signal, and converts the Signal from the time domain to the frequency domain, which is a necessary step for demodulating OFDM. The formula is as follows:
wherein the content of the first and second substances,is an FFT frequency point sequence;represented as a time-domain compensated frequency domain Signal; zsig(k) Expressed as frequency domain white Gaussian noise, with a power of
wherein the content of the first and second substances,is Gaussian white noise (including frequency domain noise and ICI-induced noise) and has power ofL is the distance from the previous OFDM symbol (L is more than or equal to N).
Specifically, the frequency domain reference signal acquisition unit is for the frequency domainAnd demodulating and analyzing the information to obtain bit information of a Signal part of the sending end, and feeding back the information. Demodulation may select hard decisions, or channel decoding. The feedback is more accurate after the channel decoding is adopted, because the channel decoding has an error correction function and needs a certain time delay; while the hard decision feedback is directly passed throughThe most likely bit information is found without considering delay. The two feedback performances are slightly different through experiments.
Then, the feedback information is remodulated by the same processing as the sending end, and the frequency domain reference signal is obtainedFrequency domain reference signalIs estimated according to the received signal, not necessarily the signal X actually modulated by the receiving endsig(k) Are completely consistent.
Specifically, the second frequency offset estimation unit is used for estimating a frequency domain reference signalReceived signal in frequency domainCarrying out local correlation operation, wherein the formula is as follows:
assuming an estimated frequency domain reference signalIs completely correct, thenThe local correlation result can be expressed as:
finally, the angle is calculated by the angle of GThus, a second carrier frequency offset estimation value is obtained
The modulation format of Signal is BPSK with the highest robustness, and the channel coding is 1/2 code rate with the highest robustness, so the demodulation performance of Signal is much higher than that of payload, and errors are difficult to make. Therefore, Signal information can basically be assumed to be correct, and it is a very reliable way to use its feedback as carrier frequency offset estimation. Feedback modulating the information analyzed by Signal, modulating the obtainedReceived signal in frequency domainThe local correlation is performed, and the performance gain improvement is higher than the performance gain of the self-correlation before and after the time domain.
After local correlation, assuming N ═ L, the signal-to-noise ratio is expressed as:
in contrast, it can be seen that the signal-to-noise ratio of the local correlation is a 3dB higher gain than the autocorrelation.
Specifically, the final time domain carrier frequency offset compensation value of Payload by the Payload frequency offset compensation unit is
Example 3:
the embodiment provides an OFDM frequency offset estimation apparatus based on IEEE802.11, including: a memory, a processor and a computer program stored on the memory and executable on the processor, the computer program, when executed by the processor, implementing the steps S1-S6 of the method of embodiment 1.
What has been described above is only a preferred embodiment of the present invention, and the present invention is not limited to the above examples. It is to be understood that other modifications and variations directly derivable or suggested by those skilled in the art without departing from the basic concept of the present invention are to be considered as included within the scope of the present invention.
Claims (10)
1. An OFDM frequency offset estimation method based on IEEE802.11 is characterized in that:
the method comprises the following steps:
performing front-back autocorrelation operation on two identical long training sequences in a Preamble of a received signal on a time domain to obtain a first carrier frequency offset estimation value;
carrying out time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value;
converting the compensated Signal from a time domain Signal into a frequency domain Signal;
analyzing the Signal of the frequency domain, and modulating the analyzed information again to obtain a frequency domain reference Signal;
performing local correlation operation on the frequency domain reference Signal and the Signal of the frequency domain to obtain a second carrier frequency offset estimation value;
and performing time domain carrier frequency offset compensation on Payload of the received signal according to the first carrier frequency offset estimation value and the second carrier frequency offset estimation value.
2. The method of estimating OFDM frequency offset based on IEEE802.11, according to claim 1, wherein:
the formula for performing the front and back autocorrelation operation on two identical long training sequences in the Preamble of the received signal on the time domain is as follows:
where N is the length of the long training sequence, yLTF1And yLTF2Respectively, a first long training sequence and a second long training sequence in the Preamble, (.)*Represents a conjugation;
the first carrier frequency offset estimation value is:
wherein f issIs the sample rate of the received signal.
3. The method of estimating OFDM frequency offset based on IEEE802.11, according to claim 2, wherein:
the formula for performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value is as follows:
4. The method of estimating OFDM frequency offset based on IEEE802.11, according to claim 1, wherein:
the formula for converting the compensated Signal from the time domain Signal to the frequency domain Signal is as follows:
5. The method of estimating OFDM frequency offset based on IEEE802.11, according to claim 1, wherein:
the formula for performing local correlation operation on the frequency domain reference Signal and the frequency domain Signal is as follows:
wherein the content of the first and second substances,in order to convert the frequency domain Signal,is the frequency domain reference signal;
6. an OFDM frequency offset estimation system based on IEEE802.11 is characterized in that:
the device comprises a first frequency offset estimation unit, a Signal frequency offset compensation unit, a Fourier transform unit, a frequency domain reference Signal acquisition unit, a second frequency offset estimation unit and a Payload frequency offset compensation unit;
the first frequency offset estimation unit is used for carrying out front-back autocorrelation operation on two identical long training sequences in a Preamble of a received signal on a time domain to obtain a first carrier frequency offset estimation value;
the Signal frequency offset compensation unit is used for performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value;
the Fourier transformation unit is used for converting the compensated Signal from a time domain Signal into a frequency domain Signal;
the frequency domain reference Signal acquisition unit is used for analyzing the Signal of the frequency domain and remodulating the analyzed information to obtain a frequency domain reference Signal;
the second frequency offset estimation unit is used for performing local correlation operation on the frequency domain reference Signal and the Signal of the frequency domain to obtain a second carrier frequency offset estimation value;
and the Payload frequency offset compensation unit is used for performing time domain carrier frequency offset compensation on Payload of the received signal according to the first carrier frequency offset estimation value and the second carrier frequency offset estimation value.
7. The IEEE802.11 based OFDM frequency offset estimation system of claim 6, wherein:
the formula of the first frequency offset estimation unit performing the front and back autocorrelation operation on two identical long training sequences in the Preamble of the received signal in the time domain is as follows:
where N is the length of the long training sequence, yLTF1And yLTF2Respectively, a first long training sequence and a second long training sequence in the Preamble, (.)*Represents a conjugation;
wherein f issIs the sample rate of the received signal.
8. The IEEE802.11 based OFDM frequency offset estimation system of claim 7, wherein:
the formula of the Signal frequency offset compensation unit for performing time domain carrier frequency offset compensation on the Signal of the received Signal according to the first carrier frequency offset estimation value is as follows:
9. The IEEE802.11 based OFDM frequency offset estimation system of claim 6, wherein:
the formula for converting the compensated Signal from the time domain Signal to the frequency domain Signal by the Fourier transform unit is as follows:
wherein the content of the first and second substances,for the converted frequency domain Signal, L is the distance between OFDM symbols; f. ofΔThe carrier frequency deviation value after compensation is obtained;
the frequency domain reference Signal obtaining unit performs local correlation operation on the frequency domain reference Signal and the frequency domain Signal according to the following formula:
wherein the content of the first and second substances,is that it isA frequency domain reference signal;
10. an OFDM frequency offset estimation device based on IEEE802.11 is characterized in that:
comprising a memory, a processor, and a computer program stored on the memory and executable on the processor; the computer program, when executed by the processor, implementing the steps of the method of any one of claims 1 to 5.
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CN112751797B (en) * | 2020-12-29 | 2023-11-03 | 厦门城市职业学院(厦门开放大学) | OFDMA uplink carrier frequency offset blind estimation method |
CN112866160B (en) * | 2020-12-30 | 2023-09-01 | 中电科思仪科技(安徽)有限公司 | Method and device for analyzing high-order modulation OFDMA-WLAN signal under large bandwidth |
CN112929311B (en) * | 2021-01-26 | 2023-01-03 | 白盒子(上海)微电子科技有限公司 | High-precision frequency offset estimation method for multi-user multiplexing of control channel |
CN113271279B (en) * | 2021-05-14 | 2022-07-05 | 成都爱瑞无线科技有限公司 | High-precision detection method for random access channel of narrow-band Internet of things |
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