Iot dft precoding fbmc carrier synchronization and channel estimation method

Abstract

The application discloses an Internet of Things DFT precoding FBMC carrier synchronization and channel estimation method, and relates to the technical field of wireless communication. The method comprises the following steps: obtaining FBMC symbol data to be transmitted, and constructing three continuous training sequence symbols; placing the three continuous training sequence symbols together with other data symbols which have completed conjugate symmetric mapping, and obtaining corresponding time-domain sending signals after data mapping, DFT precoding, FBMC-OQAM system FFT, IFFT subcarrier modulation and polyphase filtering; at the receiving end, after polyphase filtering and IFFT subcarrier demodulation of the receiving signal, receiving data signals are obtained, and the data on the 0th, 2nd, 4th, M-1th and the like subcarriers in the second training sequence symbol are used as pilot points to perform channel estimation. The method can simultaneously realize carrier synchronization and channel estimation, and has a low peak-to-average ratio.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication, in particular to a DFT precoding FBMC carrier synchronization and channel estimation method for Internet of Things. BACKGROUND

[0002] In recent years, the filter bank multi-carrier with offset quadrature amplitude modulation (FBMC-OQAM) system based on offset quadrature amplitude modulation has potential application advantages in the face of the integration of massive Internet of Things asynchronous user scenarios due to its extremely low out-of-band radiation performance and the ability to relax the synchronization between users.

[0003] In the Internet of Things transmission, the power consumption of the communication system is an important factor. In order to facilitate low-power transmission, a new DFT precoding FBMC-OQAM system based on data mapping has been proposed in recent years on the basis of the traditional FBMC-OQAM system to reduce the peak-to-average ratio of the transmitted signal, improve the efficiency of the power amplifier, and realize low-power transmission. In the DFT precoding FBMC-OQAM system based on data mapping, how to realize efficient carrier frequency offset and channel estimation is an important problem for the application of the FBMC system.

[0004] In the FBMC-OQAM system, due to the superposition effect of the symbol, it is difficult to construct a synchronization sequence. In addition, as an real orthogonal system, the FBMC-OQAM has inherent imaginary interference between data, which will cause interference at the pilot point when using the pilot for channel estimation, thereby affecting the channel estimation. In addition, in wireless communication, the carrier frequency offset will cause serious inter-carrier interference, and the accuracy of channel estimation is directly related to the demodulation performance of the system. SUMMARY

[0005] To solve the above problems, the present application provides a DFT precoding FBMC carrier synchronization and channel estimation method for Internet of Things, which designs a training sequence with low peak-to-average ratio, and realizes carrier synchronization and channel estimation with the help of the training sequence.

[0006] A DFT precoding FBMC carrier synchronization and channel estimation method for Internet of Things, comprising the following steps:

[0007] Obtain the FBMC symbol data to be transmitted, and construct three continuous training sequence symbols, the data sequence structures of the three continuous training sequence symbols are respectively represented as:

[0008]

[0009] Wherein, j n, j n+1 , j n+2 is a phase factor term required for OQAM modulation, n is a symbol sequence number, z(k) is the first M / 4 sequence values of a CAZAC sequence with a length of M / 2-1, w(k) is a weighting coefficient sequence, when k = 1, 2,..., M / 4-1, the value is the reciprocal value of the corresponding filter signal value, and M is the number of subcarriers of the FBMC system;

[0010] Three continuously placed training sequence symbols are obtained together with other data symbols which have completed conjugate symmetric mapping, after data mapping, DFT precoding, FFT, IFFT subcarrier modulation, polyphase filtering of the FBMC-OQAM system, and corresponding sending signals in the time domain are obtained;

[0011] At the receiving end, after polyphase filtering and IFFT subcarrier demodulation of the received signal, the received data signal is obtained, and the data on the 0th, 2nd, 4th,..., M-1th subcarriers in the second training sequence symbol are used as pilot points for channel estimation.

[0012] Further, the three continuously placed training sequence symbols are superimposed into a special time domain conjugate symmetric CAZAC sequence with a length of M / 2 in the time domain sending signal, and carrier synchronization detection is performed using the special time domain conjugate symmetric CAZAC sequence, specifically including the following steps:

[0013] The three training symbol sequences are represented as z' except for the phase factor j n , j n+1 , j n+2 , and the rest is represented by z', the first half and the second half of z' are the same, and there is a conjugate symmetric relationship inside, the first half or the second half of z' is represented by u and u # , two sequence vectors with a length of M / 4, wherein u # is a specific conjugate symmetric sequence of u;

[0014] At the receiver end, a local sequence u' = [- (u # ) * , u * ] is constructed, wherein the superscript * is the conjugate, the received special time domain conjugate symmetric CAZAC sequence is taken as two continuous parts with a length of M / 4, and the two part sequences are respectively correlated with the corresponding parts of the local sequence except for the first value to obtain a correlation result;

[0015] The correlation result of the first part sequence is conjugated and multiplied by the correlation result of the second part sequence to obtain a frequency offset metric function;

[0016] A fractional frequency offset estimate is obtained according to the frequency offset metric function, and carrier frequency offset compensation is performed using the frequency offset estimate value to complete fractional carrier frequency synchronization.

[0017] Further, the frequency offset metric function is expressed as:

[0018]

[0019] wherein, l represents the sample sequence number, r(l) is the sample value of the received signal, u'(l) is the sequence value of the local sequence, v is the frequency offset, Δl is the starting position of the sample number of the special time domain sequence, and F is the subcarrier spacing;

[0020] At this time, the estimated value of the frequency offset v is The phase of the frequency offset metric function J(v) is obtained by solving:

[0021]

[0022] wherein, angle() is the phase taking operation.

[0023] Further, in the second training sequence symbol, the data on the 0th, 2nd, 4th, …, M-1th subcarriers are used as pilot points for channel estimation, which is expressed as:

[0024]

[0025] wherein, is the channel coefficient of the mth subcarrier position in the second training symbol of the symbol, b m,n is the pilot data value of the mth subcarrier position, which is the Fourier transform result sequence of the sequence c2 / j n+1 is the mth value of the Fourier transform result sequence of the sequence c2 / j m，n is the filtered frequency domain signal value corresponding to the pilot signal point received, j m is the phase factor.

[0026] Further, the w(k) is a weighting coefficient sequence, when k=1, 2, …, M / 4-1, the value is the reciprocal value of the corresponding filter signal value weighted superposition, which is expressed as:

[0027]

[0028] wherein, p1, p2, … p 4K is the sequence block divided according to the length M / 4 of the prototype filter signal, and K is the overlap factor.

[0029] Further, the z(k) is a ZC sequence with a length of M / 4-1, which is expressed as:

[0030]

[0031] wherein, o is the root number, and Nc is the sequence length.

[0032] Further, the data mapping DFT precoding FBMC-OQAM system signal transmission process from the sending end to the receiving end includes the following steps:

[0033] Grouping the original signal to be transmitted, serial-parallel conversion, conjugate symmetric mapping, inserting a special training sequence, DFT precoding, and obtaining a real-imaginary alternating data sequence;

[0034] IFFT conversion, polyphase filtering, and outputting a baseband transmission signal to the channel after frequency modulation;

[0035] The received signal from the channel is polyphase filtered, subcarrier demodulated by FFT, equalized and OQAM demodulated to obtain real data;

[0036] After adding a phase factor, IFFT conversion, demapping and serial-parallel conversion operations are performed on the real data, and the output data is obtained.

[0037] Further, the conjugate symmetric mapping includes the following steps:

[0038] For any nth group of original data represented by vector x n , the group of original data x n is mapped to the nth group of data sequence represented by vector b n ;

[0039] The nth group of original data x n is mapped to the nth group of data sequence b n satisfying a specific conjugate symmetric characteristic according to the following formula:

[0040]

[0041] Wherein, n is a non-negative integer; x n (k) represents the kth data in the nth group of original data x n ; b n (k) represents the kth data in the nth group of data sequence b n ; the superscript * represents the conjugate value; is a real part operation; is an imaginary part operation.

[0042] The present application provides an Internet of Things DFT precoding FBMC carrier synchronization and channel estimation method, which has the following advantages:

[0043] The present application inserts the special training sequence into the signal conjugate symmetry mapping after or before the signal conjugate symmetry mapping of the FBMC-OQAM system sending end, and the special training sequence is used for channel estimation, and the time domain signal characteristics of the special training sequence are used to estimate and correct the carrier frequency offset. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The flow chart of the channel estimation method of the Internet of Things DFT precoding FBMC system in the embodiment of the present application is shown.

[0045] Figure 2 The flow chart of the carrier synchronization method of the Internet of Things DFT precoding FBMC system in the embodiment of the present application is shown.

[0046] Figure 3 The architecture diagram of the data mapping DFT precoding FBMC-OQAM system in the embodiment of the present application is shown.

[0047] Figure 4 The data sequence example diagram satisfying the specific conjugate symmetry characteristics in the embodiment of the present application is shown.

[0048] Figure 5 The signal segmentation schematic diagram of the prototype filter in the embodiment of the present application is shown.

[0049] Figure 6 The schematic diagram of the transmitting signal composition in the embodiment of the present application is shown.

[0050] Figure 7 The schematic diagram of the construction process of the FBMC signal in the embodiment of the present application is shown.

[0051] Figure 8 The schematic diagram of the inherent imaginary part interference of the FBMC-OQAM modulation in the embodiment of the present application is shown.

[0052] Figure 9 The root mean square error performance evaluation schematic diagram of the carrier estimation in the embodiment of the present application is shown.

[0053] Figure 10 The bit error rate performance schematic diagram of the channel estimation in the embodiment of the present application is shown. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0055] Aiming at the novel data mapping DFT precoding FBMC-OQAM system, the present invention proposes an Internet of Things DFT precoding FBMC carrier synchronization and channel estimation method, which can complete the carrier frequency offset estimation and channel estimation functions while having low complexity.

[0056] The data mapping DFT precoding FBMC-OQAM system architecture is shown in the figure below: Figure 3 As shown, specifically including:

[0057] The data-mapped DFT precoding FBMC-OQAM system transmitter includes a preprocessing module and a transmitting module. The preprocessing module is used to preprocess the original pre-transmitted data to obtain real and imaginary alternating pre-transmitted data that meets the real orthogonality requirements of the FBMC-OQAM system. The transmitting module is used to send the pre-processed pre-transmitted data from the transmitting end. The preprocessing module includes: a pre-serial-to-parallel conversion module 21, a conjugate symmetry module 22, a pre-FFT module 23, a pre-IFFT module 24, and a pre-polyphase filtering module 25.

[0058] The pre-serial-to-parallel conversion module 21 is used to group the pre-transmitted original data and perform serial-to-parallel conversion on each group of original data. In one embodiment, the length of each group of original data is set to M / 2, where M is the number of subcarriers in the FBMC-OQAM system, M=2 L , L is a natural number greater than 2.

[0059] The conjugate symmetry module 22 is used to map each set of original data after serial-to-parallel conversion into a data sequence that satisfies a specific conjugate symmetry property. n Indicates that the original data x n The nth group of data sequences mapped is represented by vector b n Indicates; the nth group of original data x n According to the following formula, it is mapped to the nth group of data sequence b that meets the specific conjugate symmetry characteristics. n :

[0060]

[0061] Among them, the value range of n is a non-negative integer; x n (k) represents the nth group of original data x n The kth data in b n (k) represents the nth group of data sequence b n The kth data in Figure 4 shown.

[0062] The pre-FFT module 23 is used to perform DFT precoding on each group of mapped data sequences to obtain real and imaginary alternating pre-transmission data that meets the real orthogonality requirement of the FBMC-OQAM system.

[0063] The pre-IFFT module 24 is used for IFFT conversion of the DFT precoded data sequence, i.e. subcarrier modulation of the FBMC-OQAM system.

[0064] The pre-multiphase filtering module 25 is used for multiphase filtering of the subcarrier modulated data sequence signal and outputting a baseband transmission signal, which is modulated by a carrier frequency by a intermediate frequency and radio frequency processing unit and then transmitted to the channel 26.

[0065] The receiving end of the FBMC-OQAM system comprises a receiving module and a post-processing module; the receiving module is used for multiphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation of the received baseband signal to obtain real data; the post-processing module is used for adding a phase factor, IFFT conversion, demapping and serial-parallel conversion to the real data obtained by the receiving module, and then outputting the data as the output data of the FBMC-OQAM system. The receiving module comprises a post-multiphase filtering module 31, a post-FFT module 32 and a demodulation output module 33; the post-multiphase filtering module 31, the post-FFT module 32 and the demodulation output module 33 are respectively used for multiphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation of the signal received from the channel 26.

[0066] Based on the above system, the present application proposes an Internet of Things DFT precoding FBMC carrier synchronization and channel estimation method, a special training sequence is constructed by conjugate symmetry, the special training sequence is inserted into the signal conjugate symmetry mapping of the transmitting end of the FBMC-OQAM system before or after the signal conjugate symmetry mapping, and three conjugate symmetry transmitting sequences are used to form a synchronization sequence for signal estimation, and the frequency domain characteristics of the special training sequence are used to estimate and correct the carrier frequency offset.

[0067] The specific process is shown in Figure 1 The method comprises the following steps:

[0068] S1, obtaining an FBMC signal to be transmitted.

[0069] As shown in Figure 7 In the mapped DFT precoding FBMC system, the final transmission signal is copied from the mapped data, multiplied point by point with the prototype filter after being copied to the same length as the prototype filter, and then a FBMC symbol signal is generated. Different symbols before and after are offset and superimposed to obtain the final transmission signal.

[0070] S2, using the transmission signal construction process to design a synchronization sequence; three consecutive training sequence symbols are constructed, assuming that the training sequence symbol sequence numbers are: n, n+1, n+2, and the data sequence structures of the three consecutive training sequence symbols are respectively represented as:

[0071]

[0072] wherein M is the number of subcarriers of the FBMC system, generally assumed to be even; the value 1 in the sequence can be any real value, in particular the first 1 and the third 1 can take values of any complex number and its conjugate, respectively; z(k) is the first M / 4 part of a CAZAC sequence of length M / 2-1, which can be a ZC sequence:

[0073]

[0074] wherein o is the root index and Nc is the sequence length.

[0075] w(k) is a weighting coefficient sequence, when k = 1, 2,..., M / 4-1, it takes the value of the reciprocal of the corresponding filter signal value weighted and superimposed:

[0076]

[0077] wherein p1, p2,..., p 4K are the sequence blocks of the prototype filter signal divided according to the length M / 4, and K is the overlap factor.

[0078] The three training sequences have the same sequence form if the influence of the phase factor j n is not considered, which is denoted as z', the first half and the second half of z' are the same, and there is a conjugate symmetry relationship inside, z' can be expressed as u and u # , which are two sequence vectors of length M / 4.

[0079] The data sequence is respectively pre-encoded by DFT (the front FFT module) to obtain the pre-transmission data arranged in real and imaginary alternation to meet the real orthogonal requirement of the FBMC-OQAM system, and after IFFT subcarrier modulation and polyphase filtering, the transmission signal sequence is obtained; wherein the training sequence is superimposed as a sequence of length M / 2 after DFT pre-encoding, IFFT subcarrier modulation and polyphase filtering, which is u # , the analysis process is shown in Figure 5 , 6 .

[0080] For the DFT precoding FBMC system, the training data is subjected to DFT precoding, IDFT subcarrier modulation and polyphase filtering operation to obtain the transmission signal. Since DFT precoding and IDFT subcarrier modulation are a pair of inverse transformations, when polyphase filtering is performed, the data of each training symbol is equivalent to being copied K times (K is an overlap factor), and then multiplied point by point with the prototype filter signal, that is, a single FBMC symbol transmission signal is obtained, and finally a plurality of FBMCs are superimposed by one symbol period to obtain the final transmission signal s(t). For convenience of representation, the prototype filter sequence is segmented, and the segmentation length is M / 4, as shown in the following formula. Figure 5 According to the above process, since the filter energy is mainly concentrated in the middle six blocks, the superposition effect of other segments is ignored, then Figure 6 The transmission signal sequence in the middle red dashed line part corresponds to the part of u, which can be represented as (assuming the sequence number k = 1, 2,..., M / 4-1 in this part of the sequence):

[0081]

[0082] Similarly, the part corresponding to u # is represented as:

[0083]

[0084] In the above formula, the last step is derived from the symmetry of the filter signal, as shown in the following formula. Figure 6

[0085] S3, carrier synchronization detection: three continuous training sequence symbols are superimposed into a special time domain conjugate symmetric CAZAC sequence with a length of M / 2 in the time domain transmission signal, and carrier synchronization detection is performed using the special time domain conjugate symmetric CAZAC sequence, which specifically includes the following steps:

[0086] The three training symbol sequences are represented by z' except for the front phase factors j n , j n+1 , j n+2 , the front half and the rear half of z' are the same, and there is a conjugate symmetric relationship inside, and the front half or the rear half of z' can be represented by u and u # Two length M / 4 sequence vectors are represented by u # , which is a specific conjugate symmetric sequence of u.

[0087] At the receiver end, a local sequence u' = [- (u # ) * , u * ​, where the superscript * is to take the conjugate, the received special time-domain conjugate symmetric CAZAC sequence is divided into two parts with a length of M / 4, and the correlation operation is performed between the two parts of the sequence and the corresponding part of the local sequence except the first value to obtain the correlation result.

[0088] The correlation result of the first part of the sequence is conjugated and multiplied by the correlation result of the second part of the sequence to obtain a frequency offset metric function; a decimal multiple frequency offset estimate is obtained according to the frequency offset metric function, and carrier frequency offset compensation is performed using the frequency offset estimate value to complete the decimal multiple carrier frequency synchronization.

[0089] The frequency offset metric function is represented as:

[0090]

[0091] Wherein, l represents the sequence number of the sampling sequence, r(l) is the sampling value of the received signal, u'(l) is the sequence value of the local sequence, v is the frequency offset, Δl is the starting position of the sampling number of the special time-domain sequence, and F is the subcarrier spacing.

[0092] At this time, the estimation value of the frequency offset v is The phase of the frequency offset metric function J(v) is obtained by solving:

[0093]

[0094] Wherein, angle() is a phase operation.

[0095] MATLAB numerical simulation is performed on the carrier estimation method of the training sequence in the application, the system frequency offset is set to 0.5 times the subcarrier spacing, and the root mean square error (RMSE) performance of the carrier estimation is as shown in Figure 9 , and good estimation performance is achieved.

[0096] S4, after the transmitted signal passes through the channel to reach the receiver, the received signal r(t) is subjected to receiving filtering, IFFT subcarrier demodulation and other operations, and the received data symbol y m，n :

[0097]

[0098] Wherein, x m,n is the real data corresponding to the transmitting end, is the channel coefficient of the point, and the second term in the above formula is the imaginary part interference from the surrounding data signals, and the third term is the noise.

[0099] According to the system principle of FBMC-OQAM, the imaginary part interference has a symmetric characteristic, as shown in Figure 8The training sequence designed by the application forms the data arrangement shown in Table 1 in time-frequency domain after DFT pre-coding:

[0100] Table 1 data arrangement

[0101] n-th symbol (training symbol 1) n+1 -th symbol (training symbol 2) n+2 -th symbol (training symbol 3) j n b 0，n ]]> j n+1 b 0，n ]]> j n+2 b 0，n =-j n b 0，n ]]> 0 0 0 j n b 2，n ]]> j n+1 b 2，n ]]> j n+2 b 2，n =-j n b 2，n ]]> 0 0 0 … … … j n b m，n ]]> j n+1 b m，n ]]> j n+2 b m，n =-j n b m，n ]]> … … … 0 0 0 j n b M-1，n ]]> j n+1 b M-1，n ]]> j n+2 b M-1，n =-j n b M-1，n ]]>

[0102] According to the arrangement relationship of the data in Table 1 and the symmetrical relationship of the imaginary part interference, it can be seen that the imaginary part interference superposition is approximately 0 at the position of the non-zero data points in the second training symbol, and therefore these data points can be used as pilots for direct channel estimation. 0，n , 0, b 2，n , 0, …, b m，n , 0, …, 0, b M-1，n The sequence is the DFT operation result of the training sequence c2 after removing the j n+1 factor.

[0103] At this time, the channel coefficient can be directly estimated by using the pilot points in the second training symbol, i.e.

[0104]

[0105] wherein, is the channel coefficient at the mth subcarrier position of the symbol, b m,n is the data value at the mth subcarrier position, which is the mth value of the Fourier transform result sequence of the sequence c2 / j n+1 , y m,n is the filtered frequency domain signal value corresponding to the pilot signal point received, j m is a phase factor.

[0106] MATLAB numerical simulation is performed on the channel estimation method of the training sequence in the application, and the bit error rate performance is shown in Figure 10 , and good estimation performance is achieved.

[0107] The above description is only the preferred specific implementation of the application, but the protection scope of the application is not limited to this. Any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the application within the technical range disclosed by the application, and all of them should be covered in the protection scope of the application.

Claims

1. A DFT precoding FBMC carrier synchronization and channel estimation method for the Internet of Things, characterized in that: The following steps are involved: The FBMC symbol data to be transmitted is obtained and conjugate symmetric mapping is performed, and three consecutive training sequence symbols are constructed at the same time. The data sequence structures of the three consecutive training sequence symbols are respectively expressed as follows: Among them, j n 、j n+1 、j n+2 is the phase factor term required for OQAM modulation, n is the symbol number, z(k) is the first M / 4 sequence values ​​of the CAZAC sequence with a length of M / 2-1, w(k) is a weighted coefficient sequence, when k = 1, 2, ..., M / 4-1, the value is the reciprocal value of the weighted superposition of the corresponding filter signal value, M is the number of subcarriers in the FBMC system, M = 2 L , L is a natural number greater than 2; The three consecutive training sequence symbols together with other data symbols that have completed conjugate symmetric mapping are subjected to the pre-FFT, IFFT subcarrier modulation, and polyphase filtering of the data mapping DFT precoding FBMC-OQAM system to obtain the corresponding transmission signal in the time domain; At the receiving end, the received signal is subjected to polyphase filtering and IFFT subcarrier demodulation to obtain the received data signal. In the second training sequence symbol, the data on the 0th, 2nd, 4th, ..., M-2th subcarriers are used as pilot points for channel estimation. The three consecutive training sequence symbols are superimposed in the time domain transmission signal to form a special time domain conjugate symmetric CAZAC sequence with a length of M / 2. The special time domain conjugate symmetric CAZAC sequence is used to perform carrier synchronization detection, specifically including the following steps: The three consecutive training sequence symbols are divided by the phase factor j n 、j n+1 、j n+2 The rest is represented by z'. The first and second halves of z' are the same and have a conjugate symmetry relationship inside. The first or second half of z' is represented by u and u. # Two length M / 4 sequence vectors are represented, where u # is a specific conjugate symmetric sequence of u; At the receiver, a local sequence u'=[-(u # ) * ,u * ], where the superscript * represents conjugation, taking two consecutive parts of length M / 4 from the received special time-domain conjugate symmetric CAZAC sequence, and performing correlation operations on the two parts of the sequence except the first value with the corresponding part of the local sequence to obtain correlation results; The frequency deviation measurement function is obtained by conjugating the correlation result of the first part of the sequence and multiplying it with the correlation result of the second part of the sequence; A fractional frequency offset estimate is obtained according to a frequency offset measurement function, and the frequency offset estimate is used to perform carrier frequency offset compensation to achieve fractional carrier frequency synchronization.

2. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 1, characterized in that: The frequency deviation metric function is expressed as: Wherein, l represents the sampling sequence number, r(l) is the sampling value of the received signal, u'(l) is the sequence value of the local sequence, v is the frequency offset, Δl is the starting position of the sampling sequence number of the special time-domain conjugate symmetric CAZAC sequence, and F is the subcarrier spacing; At this time, the estimated value of the frequency deviation v is By obtaining the phase of the frequency deviation metric function J(v), we can obtain: Among them, angle() is the phase operation.

3. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 1, characterized in that: In the second training sequence symbol, the data on the 0th, 2nd, 4th, ..., M-2th subcarriers are used as pilot points for channel estimation, which is expressed as: in, is the channel coefficient of the mth subcarrier position in the second training sequence symbol, b m,n is the pilot data value at the mth subcarrier position, which is the sequence c2 / j n+1 The mth value of the Fourier transform result sequence, y m,n is the filtered frequency domain signal value received corresponding to the pilot signal point, j m is the phase factor.

4. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 1, characterized in that: The w(k) is a weighted coefficient sequence. When k=1, 2, ..., M / 4-1, the value is the inverse value of the weighted superposition of the corresponding filter signal values, which is expressed as: Among them, p1, p2, ... p 4K is a sequence block of the prototype filter signal divided into length M / 4, and K is the overlap factor.

5. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 1, characterized in that: The z(k) is a ZC sequence of length M / 4-1, which is expressed as: Among them, o is the root sequence number and Nc is the sequence length.

6. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 1, characterized in that: The signal transmission process from the transmitting end to the receiving end of the data mapping DFT precoding FBMC-OQAM system includes the following steps: The original signal to be transmitted is grouped, converted into serial-to-parallel, conjugate-symmetrically mapped, a special training sequence is inserted, and DFT precoding is performed to obtain a data sequence in which real and virtual data are alternately arranged. Perform IFFT conversion and polyphase filtering on the data sequence and output the baseband transmission signal, which is then sent to the channel after carrier frequency modulation; The signal received from the channel is subjected to polyphase filtering, FFT subcarrier demodulation, equalization and OQAM demodulation to obtain real data; After adding phase factors, IFFT conversion, demapping, and serial-to-parallel conversion operations to the real data, the data is output.

7. The method for DFT precoding FBMC carrier synchronization and channel estimation for the Internet of Things according to claim 6, characterized in that: The conjugate symmetric mapping comprises the following steps: For any nth set of original data, use vector x n Indicates that the original data x n The nth group of data sequences mapped is represented by vector b n express; The nth group of original data x n According to the following formula, it is mapped to the nth group of data sequence b that meets the specific conjugate symmetry characteristics. n : Among them, the value range of n is non-negative integer; x n (k) represents the nth group of original data x n The kth data in b n (k) represents the nth group of data sequence b n The kth data in ; the superscript * represents the conjugate value; is the real part operation; To take the imaginary part operation.

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