CN113904904B - Integer frequency offset estimation method, system, medium and equipment based on OFDM - Google Patents
Integer frequency offset estimation method, system, medium and equipment based on OFDM Download PDFInfo
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Abstract
The application relates to an integer frequency offset estimation method, a system, a medium and equipment based on OFDM, which comprises the following steps: carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data; performing conjugate operation on the preamble symbol and the preset preamble symbol; performing differential operation on the result of the conjugate operation; and carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset. The application can reduce the calculation complexity of the algorithm while ensuring the performance of the algorithm, and can be widely applied to the technical field of wireless communication.
Description
Technical Field
The present application relates to the field of wireless communications technologies, and in particular, to an integer frequency offset estimation method, system, medium, and device based on OFDM.
Background
Different from the traditional frequency division multiplexing system, the signal frequency band is divided into N mutually non-overlapping sub-channels for transmission, and the Orthogonal Frequency Division Multiplexing (OFDM) technology allows the sub-channel frequency spectrums to mutually overlap for parallel data transmission due to the mutual orthogonality among all sub-carriers during frequency division multiplexing, so that the frequency spectrum utilization rate can be improved to the greatest extent, and the frequency spectrum utilization rate has remarkable improvement effect on the aspects of resisting narrow-band impulse noise and multipath fading.
The Orthogonal Frequency Division Multiplexing (OFDM) technology has the characteristics of high spectrum utilization rate, strong anti-fading capability and the like, and has important application in a plurality of wireless communication fields. However, receiver synchronization errors, particularly frequency offset, have a significant impact on the performance of OFDM systems. For example, oscillator instability frequency mismatch, doppler shift, and complex channel environments of a transceiver system can introduce Carrier Frequency Offset (CFO) to an OFDM system, resulting in frequency offset of subcarrier frequencies. The performance of OFDM systems will drop dramatically because the frequency offset of the carrier frequency will destroy the orthogonality between the subcarriers. The carrier frequency offset consists of a Fractional Frequency Offset (FFO) and an Integer Frequency Offset (IFO). FFO causes inter-carrier interference (ICI), and IFO causes cyclic shift of subcarriers in the frequency domain, both of which affect the reliability of data processing at the receiving end. Implementation of OFDM receivers and transceivers requires a significant amount of hardware resources. If the IFO estimation module can use fewer resources, the resource utilization efficiency of the whole system is improved.
Disclosure of Invention
In view of the above problems, the present application aims to provide an integer frequency offset estimation method, system, medium and device based on OFDM, which can reduce the computational complexity of an algorithm while ensuring the performance of the algorithm.
In order to achieve the above purpose, the technical scheme adopted by one aspect of the application is as follows: an OFDM-based integer frequency offset estimation method, comprising: carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data; performing conjugate operation on the preamble symbol and the preset preamble symbol; performing differential operation on the result of the conjugate operation; and carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset.
Further, the OFDM signal preset with the preamble symbol is: setting a frequency domain value of a preamble symbol sequence for an original OFDM signal at a transmitter end; the preamble symbol sequence has a length of 2048, and the subcarrier used therein has a length of 1198.
Further, the preamble symbol for extracting the frequency domain data is:
R(k)＝P(k)H(k)+n
wherein P (k) is the preset preamble symbol of the transmitter, H (k) is the channel impulse response frequency domain expression, and n is the noise signal.
Further, the performing conjugate operation between the preamble symbol and the preset preamble symbol includes: and respectively judging by adopting a real part and an imaginary part, and carrying out complex multiplication on the preamble symbol and the preset preamble symbol to obtain an operation result.
Further, the performing a differential operation on the result of the conjugate operation includes: and according to the correlation of adjacent carriers, performing the difference operation of subtracting the previous term from the last term of the adjacent subcarriers to be used.
Further, the differential operation is:
M(k)＝{[P 2 (k-1)-P 2 (k)]H(k)}+[P(k-1) * -P(k) * ]n
wherein M (k) is the result of the differential operation, P (k) is the preset preamble symbol of the transmitter, and P (k) * Is the conjugation of P (k), H (k) is the channel impulse response frequency domain expression, and n is the noise signal; when P 2 (k) When constant, the term of the above formula {.cndot } is minimal.
Further, the performing a minimum search on the cumulative sum of the results of the differential operation includes: and taking absolute values from the differential operation results, then carrying out accumulated summation, carrying out minimum value search on the differential operation results, and obtaining corresponding correct integer frequency offset values when the minimum values are obtained.
On the other hand, the technical scheme adopted by the application is as follows: an OFDM-based integer frequency offset estimation method, comprising: the preprocessing module performs fractional frequency offset estimation and compensation on the OFDM signal which is received by the receiver and is preset with the preamble symbol, performs FFT (fast Fourier transform) to obtain frequency domain data, and extracts the preamble symbol of the frequency domain data; the conjugate operation module carries out conjugate operation on the preamble symbol and the preset preamble symbol; the difference operation module is used for carrying out difference operation on the conjugate operation result; and the accumulation and summation module is used for carrying out minimum value search on the accumulation and summation of the differential operation result to obtain a minimum value, and the integer frequency offset corresponding to the minimum value is used as feedback output to obtain the correct integer frequency offset.
On the other hand, the technical scheme adopted by the application is as follows: a computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by a computing device, cause the computing device to perform any of the methods described above.
On the other hand, the technical scheme adopted by the application is as follows: a computing apparatus, comprising: one or more processors, memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods described above.
Due to the adoption of the technical scheme, the application has the following advantages:
1. the application utilizes the similarity degree between adjacent subcarriers to estimate the IFO, and the square operation is replaced by the absolute value operation in the calculation process, thereby effectively reducing the calculation complexity and saving the hardware realization resources in the actual application process.
2. The application is based on OFDM technology, adopts FPGA implementation method of signal integer frequency offset estimation at the receiving end, and carries out integer frequency offset estimation by the accumulation summation module through the conjugate operation register module and the differential summation module, thereby solving the problem of overlarge processing resource consumption in FPGA when realizing integer frequency offset time sharing.
The application can be widely applied to the technical field of OFDM communication.
Drawings
FIG. 1 is a schematic overall flow chart of an estimation method according to an embodiment of the application;
FIG. 2 is a diagram of an OFDM physical layer frame structure in an embodiment of the application;
fig. 3 is a schematic diagram of a signal processing flow of an OFDM receiver according to an embodiment of the present application;
fig. 4 is a schematic diagram of an integer frequency offset estimation system for OFDM in an embodiment of the application;
FIG. 5 is a schematic diagram of a computing device in an embodiment of the application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present application. It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the application, fall within the scope of protection of the application.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Assuming that the transmission signal is x (n), the OFDM baseband model of the passband signal y (n) is:
where x (n) is signal data output after the transmitting end performs IFFT on the multicarrier quadrature modulation data. y (n) is the signal data of the transmitted signal arriving at the receiver through the channel with frequency selective fading characteristics, w (n) is the noise in the channel, and the noise type is AWGN. h (l) is the Channel Impulse Response (CIR). N is the number of FFT points. ζ is the normalized frequency offset part, which consists of CFO and IFO, k representing the sequence number of the subcarrier.
OFDM systems are very sensitive to synchronization bias, in particular frequency bias, which in turn is divided into fractional frequency bias and integer frequency bias, referred to as Fractional Frequency Offset (FFO) and Integer Frequency Offset (IFO), respectively, with respect to subcarrier spacing. Wherein the fractional frequency offset causes inter-subcarrier interference (ICI); the integer frequency offset does not cause inter-subcarrier interference but causes cyclic shifts of the received data symbols such that the error rate of the demodulated information symbols increases. And the FFO is eliminated by compensating the signal y (n) after the signal passes through the channel, so that the interference among subcarriers can be effectively avoided, then IFO frequency offset estimation is carried out, compensation is carried out according to the estimated frequency offset value, the error rate of the demodulation signal can be effectively reduced, and the transmission reliability is improved.
The application provides an integer frequency offset estimation method, a system, a medium and equipment based on OFDM, which comprises the following steps: an integer frequency offset estimation module is arranged in an OFDM receiver synchronization module, wherein the integer frequency offset estimation module comprises a conjugate operation module, a differential operation module and an accumulation and summation module. The conjugate operation module stores the real part and imaginary part data of the locally known preamble symbol, and performs operation with the real part and imaginary part of the serially entered signal, and the specific operation mode is shown in the following specific embodiment. The output obtained by the conjugate operation module enters the differential operation module of the OFDM receiver, the length of one data symbol is 2048, the used subcarrier is 1198, and the differential operation of subtracting the previous term from the subsequent term is carried out on the used adjacent subcarrier. The result obtained by the differential operation enters an accumulation and summation module, the accumulation and summation module of the receiver obtains the absolute value of the data obtained by the differential operation and then carries out minimum value search, and when the minimum value appears, the corresponding correct integer frequency offset value is obtained. Therefore, the application can reduce the calculation complexity of the algorithm while ensuring the performance of the algorithm.
In one embodiment of the present application, as shown in fig. 1, an integer frequency offset estimation method based on OFDM is provided, where this embodiment is applied to a terminal for illustration, it is understood that the method may also be applied to a server, and may also be applied to a system including a terminal and a server, and implemented through interaction between the terminal and the server. In this embodiment, the method includes the steps of:
1) Carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data;
when the method is used, a preamble symbol in a frame of OFDM signal received by a receiver is known information in advance, the receiver performs symbol timing synchronization on the received frame of OFDM signal, performs fractional frequency offset estimation and compensation, and performs FFT conversion to obtain an OFDM signal of frequency domain data;
2) Performing conjugate operation on the preamble symbol and a preset preamble symbol;
3) Performing differential operation on the conjugate operation result;
4) And carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset.
In this embodiment, the OFDM signal physical layer frame structure is shown in fig. 2, in which preamble symbol 1 and preamble symbol 2 are used for synchronization and channel estimation, each occupying 1 OFDM symbol. The Data field carries a Data message. The present embodiment performs integer frequency offset estimation based on two preamble symbols of the physical layer frame structure. The method comprises the following steps: after receiving frame data, the two leading symbols are used for timing synchronization, after finding out the frame head, OFDM signal data is subjected to FFO estimation and compensation, after FFT, the first symbol is taken for integer frequency offset estimation.
When in use, as shown in fig. 3, the receiving end antenna receives the OFDM signal and performs time synchronization, frequency offset estimation and compensation, cyclic prefix removal, and correct decoding after steps such as FFT and channel equalization. The step of frequency offset estimation and compensation includes extracting the preamble symbol shown in fig. 2, performing IFO estimation, obtaining the frequency offset value, feeding back, and performing subsequent receiver operation until the OFDM receiver demodulates correctly.
In this embodiment, the time domain sampling data of the OFDM preamble symbol is y (t), and in order to estimate the integer frequency offset IFO, the FFO-compensated OFDM preamble symbol needs to be correlated with the original OFDM preamble symbol. In order to achieve the purpose, the receiving end extracts y (t), performs Fourier transform on y (t) to obtain frequency domain data, and performs correlation calculation according to the frequency domain data to obtain an estimated value of IFO.
In the above step 1), the OFDM signal in which the preamble symbol is preset is: setting a frequency domain value of a preamble symbol sequence for an original OFDM signal at a transmitter end; the preamble symbol sequence length is 2048, and the subcarrier length used is 1198.
The method comprises the following steps: setting the frequency domain values of the preamble symbol sequence as follows: 0-j,0+j,1, -1, obviously, the modular value of each value is 1, the length of the preamble symbol sequence is 2048, and the real part and the imaginary part are respectively registered in a local storage; from the OFDM baseband model, equation (1), xi is the normalized frequency offset part, which consists of FFO and IFO, denoted FFO as ε, respectively 0 ，IFOε 1 The preamble symbol is denoted as x (n) at the transmitting end, and the receiving end signal y (n) has the following expression:
after FFO compensation, epsilon is eliminated 0 Thereafter, only IFO ε is left 1 Has the following expression
Wherein the meaning of the parameters is consistent with the formula (1).
In the step 1), the mathematical expression of the receiving end after performing fourier transform on y (n) is:
Y(k)＝FFT[y(t)] (4)
i.e. the frequency domain of the Y (t) signal obtained at the receiving end is denoted Y (k), where k is the subcarrier number.
In the formula (4), FFT (·) represents fourier transform; y (k) is a signal on the kth subcarrier of the OFDM symbol.
The Y (k) signal is symbol timing synchronized with the FFO compensated preamble symbol signal, denoted as R (k).
R(k)＝P(k)H(k)+n
Where P (k) is a preset preamble symbol of the transmitter, H (k) is a channel impulse response frequency domain expression, and n is a noise signal. After FFO compensation of the received signal, only the IFO value ε is left 0 。
In the step 2), the conjugate operation is performed on the preamble symbol and the preset preamble symbol, specifically: and respectively judging by adopting a real part and an imaginary part, and carrying out complex multiplication on the preamble symbol and a preset preamble symbol to obtain an operation result.
In the present embodiment, R (k) is conjugated with the locally stored preamble symbol data P (k). From the complex algorithm and the preamble symbol configuration, the result of complex multiplication of the signal entering the conjugate operation module and the preamble symbol can be denoted as T (k).
T(k)＝R(k)P(k) * (6)
Has the following components
T(k)＝R(k)P(k) * ＝P 2 (k)H(k)+P(k) * n (7)
Because of the specificity of the preamble symbol, the operation such as a multiplier is not directly used when the preamble symbol is implemented in the FPGA, and the adopted method is to judge the real part and the imaginary part respectively.
In the step 3), the result of the conjugate operation is subjected to differential operation, specifically: and according to the correlation of adjacent carriers, performing the difference operation of subtracting the previous term from the last term of the adjacent subcarriers to be used.
Wherein, the differential operation is:
M(k)＝T(k-1)-T(k) (8)
since the channel response is slowly varying, it is thus possible to:
M(k)＝{[P 2 (k-1)-P 2 (k)]H(k)}+[P(k-1) * -P(k) * ]n (9)
wherein M (k) is the result of the differential operation, P (k) is the preset preamble symbol of the transmitter, and P (k) * Is the conjugation of P (k), H (k) is the channel impulse response frequency domain expression, and n is the noise signal; when the preamble symbols are aligned, the value of the preamble symbol set in advance can be known that, when P 2 (k) When constant, the term of the above formula {.cndot } is minimal.
In the step 4), the minimum value searching is performed by accumulating and summing the results of the differential operation, including:
and taking absolute values from the differential operation results, carrying out accumulated summation, carrying out minimum value search on the differential operation results, and obtaining corresponding correct integer frequency offset values when the minimum values are obtained.
Since the conventional method is to first find the modulus value of the signal on each subcarrier from the signal sequence M (k) obtained above, and then cumulatively sum the modulus values of the signals on all subcarriers, the multiplication operation in the FPGA consumes a lot of resources. In this embodiment, the absolute value operation is replaced by square operation, and the simulation proves that the performance is feasible, and the multiplication operation is reduced to save resources. The following formula (10) is a square modular value expression in the conventional method, and the formula (11) is an absolute value expression, and is a method proposed and used in the application.
N is the number of FFT points, minimum value searching is carried out on the basis of the formula (9), and when the minimum value appears, the corresponding correct integer frequency offset value is obtained. The formula is as follows:
as can be seen from equation (12), k is the ideal subcarrier position when the preamble symbols are aligned. The estimated integer frequency offset can be obtained by multiple times of calculation through a method (12)And is marked as an integer frequency offset nsc.
In summary, the application aims to reduce the influence of channel impulse response on the subsequent operation steps by differential operation on adjacent subcarriers in the OFDM preamble symbol, and can effectively reduce the calculation complexity and reduce the FPGA resource use by combining the accumulated summation operation. In the process of obtaining integer frequency offset by correlation operation, absolute value summation operation is adopted to replace square summation operation in the accumulation summation stage, and simulation proves that the method is feasible, and the absolute value summation can greatly reduce the calculated amount and save resources.
In one embodiment of the present application, as shown in fig. 4, there is provided an OFDM-based integer frequency offset estimation system, comprising:
the preprocessing module performs fractional frequency offset estimation and compensation on the OFDM signal which is received by the receiver and is preset with the preamble symbol, performs FFT (fast Fourier transform) to obtain frequency domain data, and extracts the preamble symbol of the frequency domain data;
the conjugate operation module carries out conjugate operation on the preamble symbol and a preset preamble symbol;
the difference operation module is used for carrying out difference operation on the conjugate operation result;
and the accumulation and summation module is used for carrying out minimum value search on the accumulation and summation of the differential operation result to obtain a minimum value, and the integer frequency offset corresponding to the minimum value is used as feedback output to obtain the correct integer frequency offset.
In summary, at a receiving end of an OFDM system, the application firstly carries out fractional frequency offset estimation and compensation on received OFDM signals, carries out FFT (fast Fourier transform) on the signals subjected to the fractional frequency offset compensation to obtain frequency domain data, and extracts leading symbols in the signals; carrying out integer frequency offset estimation through correlation operation, and carrying out conjugate operation and registration of data in a conjugate operation module; the data obtained by the conjugate operation module is sent to the differential operation module to carry out differential operation on the data; and the data obtained by the differential operation enter an accumulation summation module to perform minimum value search to obtain a minimum value, and the correct integer frequency offset nsc is fed back and output according to the minimum value.
The system provided in this embodiment is used to execute the above method embodiments, and specific flow and details refer to the above embodiments, which are not described herein.
As shown in fig. 5, a schematic structural diagram of a computing device provided in an embodiment of the present application, where the computing device may be a terminal, and may include: a processor (processor), a communication interface (Communications Interface), a memory (memory), a display screen, and an input device. The processor, the communication interface and the memory complete communication with each other through a communication bus. The processor is configured to provide computing and control capabilities. The memory comprises a non-volatile storage medium and an internal memory, wherein the non-volatile storage medium stores an operating system and a computer program, and the computer program is executed by a processor to realize an integer frequency offset estimation method; the internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The communication interface is used for carrying out wired or wireless communication with an external terminal, and the wireless mode can be realized through WIFI, a manager network, NFC (near field communication) or other technologies. The display screen can be a liquid crystal display screen or an electronic ink display screen, the input device can be a touch layer covered on the display screen, can also be a key, a track ball or a touch pad arranged on the shell of the computing equipment, and can also be an external keyboard, a touch pad or a mouse and the like. The processor may call logic instructions in memory to perform the following method:
carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data; performing conjugate operation on the preamble symbol and a preset preamble symbol; performing differential operation on the conjugate operation result; and carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset.
Further, the logic instructions in the memory described above may be implemented in the form of software functional units and stored in a computer-readable storage medium when sold or used as a stand-alone product. Based on this understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
It will be appreciated by those skilled in the art that the architecture shown in fig. 5 is merely a block diagram of some of the architecture relevant to the present inventive arrangements and is not limiting of the computing devices to which the present inventive arrangements may be applied, and that a particular computing device may include more or fewer components than shown, or may combine some of the components, or have a different arrangement of components.
In one embodiment of the present application, there is provided a computer program product comprising a computer program stored on a non-transitory computer readable storage medium, the computer program comprising program instructions which, when executed by a computer, are capable of performing the methods provided by the method embodiments described above, for example comprising: carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data; performing conjugate operation on the preamble symbol and a preset preamble symbol; performing differential operation on the conjugate operation result; and carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset.
In one embodiment of the present application, there is provided a non-transitory computer-readable storage medium storing server instructions that cause a computer to perform the methods provided by the above embodiments, for example, including: carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data; performing conjugate operation on the preamble symbol and a preset preamble symbol; performing differential operation on the conjugate operation result; and carrying out minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking the integer frequency offset corresponding to the minimum value as feedback output to obtain the correct integer frequency offset.
The foregoing embodiment provides a computer readable storage medium, which has similar principles and technical effects to those of the foregoing method embodiment, and will not be described herein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims (7)
1. An integer frequency offset estimation method based on OFDM, which is characterized by comprising the following steps:
carrying out fractional frequency offset estimation and compensation on an OFDM signal which is received by a receiver and is preset with a preamble symbol, carrying out FFT (fast Fourier transform) to obtain frequency domain data, and extracting the preamble symbol of the frequency domain data;
performing conjugate operation on the preamble symbol and the preset preamble symbol;
performing differential operation on the result of the conjugate operation;
performing minimum value search on the accumulated sum of the differential operation results to obtain a minimum value, and taking integer frequency offset corresponding to the minimum value as feedback output to obtain correct integer frequency offset;
the OFDM signal with the preset preamble symbol is: setting a frequency domain value of a preamble symbol sequence for an original OFDM signal at a transmitter end; the preamble symbol sequence length is 2048, and the subcarrier length used is 1198;
the preamble symbol for extracting the frequency domain data is:
R(k)＝P(k)H(k)+n
wherein P (k) is the preset preamble symbol of the transmitter, H (k) is a channel impulse response frequency domain expression, and n is a noise signal;
the performing conjugate operation on the preamble symbol and the preset preamble symbol includes:
and respectively judging by adopting a real part and an imaginary part, and carrying out complex multiplication on the preamble symbol and the preset preamble symbol to obtain an operation result.
2. The integer frequency offset estimation method of claim 1 wherein said performing a differential operation on the result of said conjugate operation comprises:
and according to the correlation of adjacent carriers, performing the difference operation of subtracting the previous term from the last term of the adjacent subcarriers to be used.
3. The integer frequency offset estimation method of claim 2 wherein said differential operation is:
M(k)＝{[P 2 (k-1)-P 2 (k)]H(k)}+[P(k-1) * -P(k) * ]n
wherein M (k) is the result of the differential operation, P (k) is the preset preamble symbol of the transmitter, and P (k) * Is the conjugation of P (k), H (k) is the channel impulse response frequency domain expression, and n is the noise signal; when P 2 (k) When constant, the term of the above formula {.cndot } is minimal.
4. The integer frequency offset estimation method of claim 1 wherein said performing a minimum search of said accumulated sums of results of said differential operations comprises:
and taking absolute values from the differential operation results, then carrying out accumulated summation, carrying out minimum value search on the differential operation results, and obtaining corresponding correct integer frequency offset values when the minimum values are obtained.
5. An integer frequency offset estimation method based on OFDM, which is characterized by comprising the following steps:
the preprocessing module performs fractional frequency offset estimation and compensation on the OFDM signal which is received by the receiver and is preset with the preamble symbol, performs FFT (fast Fourier transform) to obtain frequency domain data, and extracts the preamble symbol of the frequency domain data;
the conjugate operation module carries out conjugate operation on the preamble symbol and the preset preamble symbol;
the difference operation module is used for carrying out difference operation on the conjugate operation result;
the accumulation and summation module is used for carrying out minimum value search on the accumulation and summation of the differential operation result to obtain a minimum value, and the integer frequency offset corresponding to the minimum value is used as feedback output to obtain a correct integer frequency offset;
the OFDM signal with the preset preamble symbol is: setting a frequency domain value of a preamble symbol sequence for an original OFDM signal at a transmitter end; the preamble symbol sequence length is 2048, and the subcarrier length used is 1198;
the preamble symbol for extracting the frequency domain data is:
R(k)＝P(k)H(k)+n
wherein P (k) is the preset preamble symbol of the transmitter, H (k) is a channel impulse response frequency domain expression, and n is a noise signal;
the performing conjugate operation on the preamble symbol and the preset preamble symbol includes:
and respectively judging by adopting a real part and an imaginary part, and carrying out complex multiplication on the preamble symbol and the preset preamble symbol to obtain an operation result.
6. A computer readable storage medium storing one or more programs, wherein the one or more programs comprise instructions, which when executed by a computing device, cause the computing device to perform any of the methods of claims 1-4.
7. A computing device, comprising: one or more processors, memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods of claims 1-4.
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