CN117424784B - OFDM system channel estimation method based on leading and pilot frequency - Google Patents
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Abstract
The invention discloses an OFDM system channel estimation method based on a preamble and a pilot frequency, which comprises the following steps: constructing a two-dimensional pilot pattern; channel estimation is carried out based on the preamble, and channel frequency response of sub-carriers corresponding to the preamble symbols is obtainedThe method comprises the steps of carrying out a first treatment on the surface of the Channel estimation based on pilot frequency to obtain channel frequency response of data sub-carrierThe method comprises the steps of carrying out a first treatment on the surface of the According to channel frequency responseAnd channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method comprises the steps of carrying out a first treatment on the surface of the According to channel frequency responseAnd carrying out equalization processing on the received frequency domain data Y and sending the frequency domain data Y into a demodulation module. The invention improves the DFT algorithm by utilizing the preamble and the pilot frequency symbol, and simultaneously carries out double channel estimation by the known pilot frequency and the known preamble sequence, not only carries out channel estimation by inserting the pilot frequency subcarrier, but also carries out channel estimation by using the preamble known sequence in the data subcarrier, thereby greatly enhancing the channel estimation performance and effectively and accurately completing the channel estimation of the OFDM system in a severe environment.
Description
Technical Field
The invention relates to the field of communication, in particular to an OFDM system channel estimation method based on a preamble and a pilot frequency.
Background
Orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) is a special scheme for data transmission using multiple carriers, which is designed with FFT and IFFT as cores, and has extremely wide application in practical engineering. The channel estimation and equalization technology is a key technology in the OFDM system, and in order that the OFDM system can adapt to various complex channel environments, only the accurate channel estimation is performed at the receiving end of the system to obtain the frequency response of the channel where the current system is positioned, the channel equalization can be performed correctly, so that correct user data can be demodulated. Otherwise, if the channel estimation is inaccurate in the communication process, the system will work abnormally, resulting in data loss, so that the channel estimation and equalization technology of the data link system is extremely important, and by adopting the reliable and accurate channel estimation and equalization technology, the Doppler shift resistance and multipath resistance of the system can be improved, and the data can be correctly transmitted in different channel environments.
In an OFDM system, a mature technology of channel estimation adopts LS, DFT or MMSE algorithm, which is mainly applied to three pilot patterns of block, comb and diamond, and channel estimation is carried out through an inserted known pilot sequence, however, according to the specificity of the OFDM system, different pilot patterns and channel estimation methods are required to be designed in different channel environments. At present, when facing a more complex and severe channel environment, the conventional channel estimation method cannot meet the system performance requirement.
Disclosure of Invention
The invention mainly aims to provide an OFDM system channel estimation method based on a preamble and a pilot frequency, and aims to solve the technical problem that the conventional channel estimation method cannot meet the system performance requirement when facing a complex and severe channel environment.
In order to achieve the above object, the present invention provides a method for estimating an OFDM system channel based on a preamble and a pilot, the method comprising:
s1: constructing a two-dimensional pilot pattern; wherein the two-dimensional pilot pattern comprises data subcarriers and pilot subcarriers inserted into the data subcarriers;
s2: channel estimation is carried out based on the preamble, and channel frequency response of sub-carriers corresponding to the preamble symbols is obtained；
S3: channel estimation based on pilot frequency to obtain channel frequency response of data sub-carrier；
S4: according to the channel frequency responseAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency response；
S5: according to the channel frequency responseAnd carrying out equalization processing on the received frequency domain data Y, and sending an equalization processing result to a demodulation module.
Optionally, in the step S1, a two-dimensional pilot pattern is constructed, specifically: every 4 OFDM symbols are divided into one period, and 1 pilot subcarrier is inserted at 1 data subcarrier interval in the 4 th OFDM symbol.
Optionally, in the step S2, channel estimation is performed based on the preamble to obtain a channel frequency response of the subcarrier corresponding to the preamble symbolThe method specifically comprises the following steps:
s21: after FFT conversion is carried out on the received preamble, the protection sub-carrier and the DC sub-carrier are removed to obtain the effective frequency domain dataCorresponding frequency domain data to knownDividing to obtain channel frequency response corresponding to effective sub-carrier of preambleObtaining；
S22: for a pair ofSymmetrically expanding the number of subcarriers to N to obtainAnd then symmetrically expandingAnd (3) performing inverse Fourier transform to obtain:；
s23: for a pair ofIntercepting and threshold judgment are carried out;
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
s24: for a pair ofPerforming Fourier transform to obtain；
S25: removing the data of the second step expansion bit to obtain the channel frequency response of the subcarrier corresponding to the leading symbol。
Optionally, in the step S3, channel estimation is performed based on the pilot frequency to obtain a channel frequency response of the data subcarrierThe method comprises the following steps:
s31: taking pilot frequency sequence of OFDM symbol after FFT conversionWith corresponding known pilot frequency domain dataDividing to obtain channel frequency response corresponding to pilot frequency sub-carrierObtaining；
S32: for a pair ofPerforming linear interpolation, and obtaining channel frequency response of data subcarrier position by channel frequency response interpolation of pilot subcarrier position to obtain effective data，Channel frequency response corresponding to the effective sub-carrier;
s33: for a pair ofSymmetrically expanding the number of subcarriers to N to obtainFor symmetrically expandedPerforming inverse Fourier transform to obtain；
S34: for a pair ofAnd (3) intercepting and threshold judgment:
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,for the valid subcarrier frequency domain data sequence after the guard and DC subcarriers are currently removed,n is the number of sub-carriers,is the length of the cyclic prefix;
s35: for a pair ofPerforming Fourier transform to obtain；
S36: after the data of the third step expansion bit is removed, the channel frequency response of the pilot frequency and the data subcarrier is obtainedThen fromExtracting the corresponding values of the data sub-carrier positions to form the channel frequency response of the data sub-carrier。
Optionally, in the step S4, according to the channel frequency responseAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method specifically comprises the following steps:
s41: for the channel frequency response corresponding to the effective sub-carrier in the three OFDM symbols after the preamble, the channel frequency response of the preamble sequenceAnd channel frequency response of the fourth OFDM symbolAnd (5) carrying out linear interpolation on a frequency axis.
Optionally, in the step S4, according to the channel frequency responseAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method specifically comprises the following steps:
s42: from the fifth OFDM, the channel frequency response corresponding to the effective sub-carrier in the OFDM symbol without pilot frequency is obtained by linear interpolation on the frequency axis from the channel frequency response calculated by the front and rear OFDM symbols containing pilot frequency.
Optionally, in the step S5, the equalization processing result specifically includes:
；
wherein,for the interpolated channel frequency response, Y is the received frequency domain data,is the result of the equalization process.
The invention has the beneficial effects that: the method for estimating the OFDM system channel based on the preamble and the pilot frequency comprises the following steps: s1: constructing a two-dimensional pilot pattern; wherein the two-dimensional pilot pattern comprises data subcarriers and pilot subcarriers inserted into the data subcarriers; s2: channel estimation is carried out based on the preamble, and a channel of sub-carrier corresponding to the preamble symbol is obtainedFrequency responseThe method comprises the steps of carrying out a first treatment on the surface of the S3: channel estimation based on pilot frequency to obtain channel frequency response of data sub-carrierThe method comprises the steps of carrying out a first treatment on the surface of the S4: according to the channel frequency responseAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method comprises the steps of carrying out a first treatment on the surface of the S5: according to the channel frequency responseAnd carrying out equalization processing on the received frequency domain data Y, and sending an equalization processing result to a demodulation module. The invention utilizes the leading and pilot frequency symbols to improve the DFT algorithm, and simultaneously carries out double channel estimation through the known pilot frequency and the known leading sequence, not only carries out channel estimation through inserting the pilot frequency sub-carrier, but also carries out channel estimation through using the leading known sequence in the data sub-carrier; the method is suitable for the OFDM system with the two-dimensional pilot frequency pattern, greatly enhances the channel estimation performance, and experiments prove that the method can effectively and accurately finish the channel estimation of the OFDM system in a severe environment.
Drawings
Fig. 1 is a flow chart of an OFDM system channel estimation method based on a preamble and a pilot frequency according to the present invention;
FIG. 2 is a schematic diagram of a two-dimensional pilot pattern according to the present invention;
FIG. 3 is a schematic diagram of a preamble structure according to the present invention;
fig. 4 is a schematic diagram of a channel estimation procedure based on a preamble and a pilot according to the present invention;
FIG. 5 is a diagram showing the demodulation performance index when the frequency offset is 0.01 times the subcarrier spacing according to the present invention;
fig. 6 is a schematic diagram of demodulation performance index when the frequency offset is 0.05 times of subcarrier spacing according to the present invention.
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The embodiment of the invention provides an OFDM system channel estimation method based on a preamble and a pilot frequency, and referring to fig. 1, fig. 1 is a flow diagram of an embodiment of the OFDM system channel estimation method based on the preamble and the pilot frequency.
In this embodiment, an OFDM system channel estimation method based on a preamble and a pilot frequency includes:
s1: constructing a two-dimensional pilot pattern; wherein the two-dimensional pilot pattern comprises data subcarriers and pilot subcarriers inserted into the data subcarriers;
s2: channel estimation is carried out based on the preamble, and channel frequency response of sub-carriers corresponding to the preamble symbols is obtained；
S3: channel estimation based on pilot frequency to obtain channel frequency response of data sub-carrier；
S4: according to the channel frequency responseAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency response；
S5: according to the channel frequency responseAnd carrying out equalization processing on the received frequency domain data Y, and sending an equalization processing result to a demodulation module.
In a preferred embodiment, in the step S1, a two-dimensional pilot pattern is constructed, specifically: every 4 OFDM symbols are divided into one period, and 1 pilot subcarrier is inserted at 1 data subcarrier interval in the 4 th OFDM symbol.
In a preferred embodiment, in the step S2, channel estimation is performed based on the preamble, and a channel frequency response of the subcarrier corresponding to the preamble symbol is obtainedThe method specifically comprises the following steps:
s21: after FFT conversion is carried out on the received preamble, the protection sub-carrier and the DC sub-carrier are removed to obtain the effective frequency domain dataCorresponding frequency domain data to knownDividing to obtain channel frequency response corresponding to effective sub-carrier of preambleObtaining；
S22: for a pair ofSymmetrically expanding the number of subcarriers to N to obtainAnd then symmetrically expandingAnd (3) performing inverse Fourier transform to obtain:；
s23: for a pair ofIntercepting and threshold judgment are carried out;
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
s24: for a pair ofPerforming Fourier transform to obtain；
S25: removing the data of the second step expansion bit to obtain the channel frequency response of the subcarrier corresponding to the leading symbol。
In a preferred embodiment, in the step S3, channel estimation is performed based on pilot frequency to obtain channel frequency response of data subcarriersThe method comprises the following steps:
s31: taking pilot frequency sequence of OFDM symbol after FFT conversionWith corresponding known pilot frequency domain dataDividing to obtain channel frequency response corresponding to pilot frequency sub-carrierObtaining；
S32: for a pair ofPerforming linear interpolation, and obtaining channel frequency response of data subcarrier position by channel frequency response interpolation of pilot subcarrier position to obtain effective data，Channel frequency response corresponding to the effective sub-carrier;
s33: for a pair ofSymmetrically expanding the number of subcarriers to N to obtainFor symmetrically expandedPerforming inverse Fourier transform to obtain；
S34: for a pair ofAnd (3) intercepting and threshold judgment:
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,for the valid subcarrier frequency domain data sequence after the guard and DC subcarriers are currently removed,n is the number of sub-carriers,is the length of the cyclic prefix;
s35: for a pair ofPerforming Fourier transform to obtain；
S36: after the data of the third step expansion bit is removed, the channel frequency response of the pilot frequency and the data subcarrier is obtainedThen fromExtracting the corresponding values of the data sub-carrier positions to form the channel frequency response of the data sub-carrier。
In a preferred embodiment, in S4, the frequency response is based on the channelAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method specifically comprises the following steps: s41: for the channel frequency response corresponding to the effective sub-carrier in the three OFDM symbols after the preamble, the channel frequency response of the preamble sequenceAnd channel frequency response of the fourth OFDM symbolAnd (5) carrying out linear interpolation on a frequency axis.
In a preferred embodiment, in S4, the frequency response is based on the channelAnd the channel frequency responseLinear interpolation on frequency axis to obtain channel frequency responseThe method specifically comprises the following steps: s42: from the fifth OFDM, the channel frequency response corresponding to the effective sub-carrier in the OFDM symbol without pilot frequency is obtained by linear interpolation on the frequency axis from the channel frequency response calculated by the front and rear OFDM symbols containing pilot frequency.
In a preferred embodiment, in the step S5, the equalization processing result is specifically:the method comprises the steps of carrying out a first treatment on the surface of the Wherein,for the interpolated channel frequency response, Y is the received frequency domain data,is the result of the equalization process.
For a clearer explanation of the present application, specific examples of the present application in practical applications are provided below.
1. For pilot pattern and preamble design:
the present embodiment designs that every four OFDM symbols are one period, the first three symbols do not need to be inserted with pilot frequency, and in the fourth OFDM symbol, 1 data subcarrier is separated by inserting a pilot frequency, and it should be noted that the first and last effective subcarriers in the fourth symbol must be pilot frequency subcarriers, and the pilot frequency inserting structure is shown in fig. 2. The square pilot pattern is an improvement on the block pilot pattern and the comb pilot pattern, and pilot is inserted at the same or different intervals in the two directions of the frequency domain and the time domain, because pilot distribution is scattered, and compared with the block pilot structure and the comb pilot, the square pilot structure has higher resource utilization rate.
In addition, as shown in fig. 3, in the design of the data preamble sequence of the system of this embodiment, CP is a cyclic prefix, N is the OFDM symbol length, and is also the number of subcarriers; the preamble is transmitted in data subcarriers, the first OFDM symbol contains a cyclic prefix and the second OFDM symbol has no cyclic prefix.
2. Implementation principle for OFDM channel estimation based on preamble and pilot frequency:
LS is the most basic channel estimation algorithm, and the estimation value of LSCalculated as follows:
；
where X is the transmitted known vector, Y is the received corresponding vector,channel frequency response for the estimated corresponding subcarrier locations. However, since the accuracy is susceptible to noise, van De Beek et al propose a Discrete Fourier Transform (DFT) based estimation algorithm that corrects the estimate of the channel frequency response based on the LS algorithm by attenuating noise outside the maximum multipath delay spread.
The channel estimation method of the OFDM system in this embodiment is improved on the basis of the DFT noise reduction algorithm, and the channel estimation is performed based on the preamble and the pilot frequency, where the preamble also belongs to the known symbol data, and is transmitted in the data subcarriers, and the main flow is shown in fig. 4.
As shown in fig. 4, the main workflow is as follows:
scheme 1: channel estimation based on preambles
(1) LS channel estimation: after FFT conversion is carried out on the received preamble, the protection sub-carrier and the DC sub-carrier are removed to obtain the effective frequency domain dataCorresponding frequency domain data to knownDividing to obtain channel frequency response corresponding to effective sub-carrier of preamble：
(2) For a pair ofSymmetrically expanding the number of subcarriers to N to obtainAnd then symmetrically expandingAnd (3) performing inverse Fourier transform to obtain:
(3) For a pair ofAnd (3) intercepting and threshold judgment:
intercepting:；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
(4) For a pair ofPerforming Fourier transform to obtain；
(5) Removing the data of the second step expansion bit to obtain the channel frequency response of the subcarrier corresponding to the leading symbol。
Scheme 2: channel estimation based on pilot
(1) LS channel estimation: after OFDM symbol is FFT transformed, the pilot sequence is taken outWith corresponding known pilot frequency domain dataDividing to obtain channel frequency response corresponding to pilot frequency sub-carrierObtaining
(2) For a pair ofPerforming linear interpolation, and obtaining channel frequency response of data subcarrier position by channel frequency response interpolation of pilot subcarrier position to obtain effective data，The channel frequency response corresponding to the effective sub-carrier.
(3) For a pair ofSymmetrically expanding the number of subcarriers to N to obtainFor symmetrically expandedAnd performing inverse Fourier transform, namely:
(4) For a pair ofAnd (3) intercepting and threshold judgment:
intercepting:；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix.
Threshold judgment:；
in the above-mentioned method, the step of,for the active subcarrier frequency domain data sequence (OFDM symbol containing pilot) after the guard and DC subcarriers are currently removed,n is the number of sub-carriers,is the length of the cyclic prefix.
(5) For a pair ofPerforming Fourier transform to obtain。
(6) After the data of the third step expansion bit is removed, the channel frequency response of the pilot frequency and the data subcarrier is obtainedThen fromExtracting the corresponding values of the data sub-carrier positions to form the channel frequency response of the data sub-carrier。
Scheme 3: linear interpolation on frequency axis
(1) First case: channel frequency response corresponding to effective sub-carrier in three OFDM symbols after preamble, channel frequency response of preamble sequenceAnd channel frequency response of the fourth OFDM symbolAnd (5) carrying out linear interpolation on a frequency axis.
(2) Other: according to the pilot pattern, since the system has one period for every four OFDM symbols, the last OFDM symbol of the four OFDM symbols contains pilot, so from the fifth OFDM, the channel frequency response corresponding to the effective subcarrier in the OFDM symbol without pilot can be obtained by linear interpolation on the frequency axis from the channel frequency response calculated by the two OFDM symbols containing pilot.
Scheme 4: equalization
Assuming that the channel frequency response obtained after interpolation isThe received frequency domain data is Y, and then equalization processing is carried out,obtained byAnd after being combined, the signals are sent to a demodulation module.
3. For simulation results:
in the multipath and white gaussian noise channel, when the frequency offset is set to be 0.01 times and 0.05 times of subcarrier spacing, the demodulation performance index of the channel estimation method adopting the embodiment is shown in fig. 5 and fig. 6.
As shown in fig. 5 and fig. 6, after the pre-stage frequency offset estimation, the channel estimation method still has a certain residual frequency offset resistance, and compared with the traditional channel estimation method, the channel estimation method has the performance which is closer to ideal estimation, and can meet the demands of an OFDM communication system in a worse channel environment.
Therefore, the channel estimation method provided by the embodiment is suitable for an OFDM communication system working under a more complex and severe channel environment, the square pilot frequency pattern is designed and adopted, the pilot frequency channel estimation is combined with the pilot frequency channel estimation, meanwhile, the DFT algorithm is improved, double channel estimation is carried out through the known pilot frequency and the known pilot sequence, the channel estimation is carried out through inserting pilot frequency sub-carriers, the channel estimation is carried out through the known pilot frequency sequence in the data sub-carriers, compared with the conventional method for carrying out the channel estimation through only inserting the pilot frequency, the performance of the method is closer to that of ideal estimation, the accuracy of the estimation can still be guaranteed in the severe environment, the engineering application value is higher, and experiments prove that the channel estimation method of the OFDM system can complete reliable channel estimation in the severe environment, and the demodulation performance of the post-stage of a receiver is guaranteed.
It is appreciated that in the description herein, reference to the terms "one embodiment," "another embodiment," "other embodiments," or "first through nth embodiments," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or system. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or system that comprises the element.
The foregoing embodiment numbers of the present invention are merely for the purpose of description, and do not represent the advantages or disadvantages of the embodiments.
The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather is intended to cover any equivalents of the structures or equivalent processes disclosed herein or in the alternative, which may be employed directly or indirectly in other related arts.
Claims (5)
1. A method for channel estimation in an OFDM system based on a preamble and a pilot, the method comprising:
s1: constructing a two-dimensional pilot pattern; wherein the two-dimensional pilot pattern comprises data subcarriers and pilot subcarriers inserted into the data subcarriers; in the step S1, a two-dimensional pilot pattern is constructed, which specifically includes: dividing each 4 OFDM symbols into a period, and inserting 1 pilot frequency subcarrier into 1 data subcarrier at intervals in the 4 th OFDM symbol;
s2: channel estimation is carried out based on the preamble, and a preamble symbol corresponding sub-is obtainedChannel frequency response of carrierThe method comprises the steps of carrying out a first treatment on the surface of the In the step S2, channel estimation is performed based on the preamble, and the channel frequency response +.>The method specifically comprises the following steps:
s21: after FFT conversion is carried out on the received preamble, the protection sub-carrier and the DC sub-carrier are removed to obtain the effective frequency domain dataFrequency domain data corresponding to the known +.>Dividing to obtain channel frequency response corresponding to effective sub-carrier of preamble +.>Obtain->；
S22: for a pair ofSymmetrically expanding the left and right of the number of subcarriers to N to obtain +.>Symmetrically expanding +.>And (3) performing inverse Fourier transform to obtain: />；
S23: intercepting and threshold judging hls 1;
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
s24: for a pair ofFourier transforming to obtain hls3=fft (Hls 3, N);
s25: removing the data of the second step expansion bit to obtain the channel frequency response of the subcarrier corresponding to the leading symbol；
S3: channel estimation based on pilot frequency to obtain channel frequency response of data sub-carrier；
S4: according to the channel frequency responseAnd said channel frequency response +.>Linear interpolation is performed on the frequency axis to obtain the channel frequency response +.>；
S5: according to the channel frequency responseAnd carrying out equalization processing on the received frequency domain data Y, and sending an equalization processing result to a demodulation module.
2. The method for channel estimation of OFDM system based on preamble and pilot according to claim 1, wherein in said step S3, channel estimation is performed based on pilot to obtain channel frequency response of data sub-carrierThe method comprises the following steps:
s31: taking pilot frequency sequence of OFDM symbol after FFT conversionCorresponding known pilot frequency domain data +.>Dividing to obtain channel frequency response corresponding to pilot frequency sub-carrier>Obtain->；
S32: for a pair ofPerforming linear interpolation, and obtaining channel frequency response of data sub-carrier position by channel frequency response interpolation of pilot sub-carrier position to obtain effective data +.>，/>Channel frequency response corresponding to the effective sub-carrier;
s33: for a pair ofSymmetrically expanding the left and right of the number of subcarriers to N to obtain +.>For symmetrical expansion +.>Performing inverse Fourier transform to obtain ∈K>；
S34: for a pair ofAnd (3) intercepting and threshold judgment:
the intercepting step specifically comprises the following steps:
；
in the above-mentioned method, the step of,n is the number of sub-carriers,is the length of the cyclic prefix;
the threshold judgment step specifically comprises the following steps:
；
in the above-mentioned method, the step of,for the valid subcarrier frequency domain data sequence after the guard and DC subcarriers are currently removed,n is the number of sub-carriers,is the length of the cyclic prefix;
s35: for a pair ofFourier transforming->；
S36: after the data of the third step expansion bit is removed, the channel frequency response of the pilot frequency and the data subcarrier is obtainedThen from->Extracting the corresponding value of the data sub-carrier position to form the channel frequency response of the data sub-carrier>。
3. The method for channel estimation in an OFDM system based on preamble and pilot according to claim 2, wherein in S4, the channel frequency response is based on the channel frequency responseAnd said channel frequency response +.>Linear interpolation is performed on the frequency axis to obtain the channel frequency response +.>The method specifically comprises the following steps:
s41: for the channel frequency response corresponding to the effective sub-carrier in the three OFDM symbols after the preamble, the channel frequency response of the preamble sequenceAnd channel frequency response of the fourth OFDM symbol +.>And (5) carrying out linear interpolation on a frequency axis.
4. The method for channel estimation in OFDM system based on preamble and pilot as recited in claim 3, wherein in said S4, according to said channel frequency responseAnd said channel frequency response +.>Linear interpolation is performed on the frequency axis to obtain the channel frequency response +.>The method specifically comprises the following steps:
s42: from the fifth OFDM, the channel frequency response corresponding to the effective sub-carrier in the OFDM symbol without pilot frequency is obtained by linear interpolation on the frequency axis from the channel frequency response calculated by the front and rear OFDM symbols containing pilot frequency.
5. The method for estimating the channel of the OFDM system based on the preamble and the pilot according to claim 4, wherein in the step S5, the equalization result is specifically:
；
wherein,for the interpolated channel frequency response, +.>For the received frequency domain data, < > a->Is the result of the equalization process.
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