CN118368181B - Nonlinear phase shift compensation method, communication chip and system based on OFDM - Google Patents
Nonlinear phase shift compensation method, communication chip and system based on OFDM Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2627—Modulators
- H04L27/2637—Modulators with direct modulation of individual subcarriers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2646—Arrangements specific to the transmitter only using feedback from receiver for adjusting OFDM transmission parameters, e.g. transmission timing or guard interval length
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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- H04L27/2669—Details of algorithms characterised by the domain of operation
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- H04L27/00—Modulated-carrier systems
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Abstract
The invention relates to the technical field of nonlinear phase shift, and discloses a nonlinear phase shift compensation method, a communication chip and a system based on OFDM, wherein the method comprises the following steps: acquiring a first actual phase response curve of a first IIR filter of a transmitting end, fitting the first actual phase response curve to obtain a first phase response fitting straight line, and obtaining first nonlinear phase offsets of different frequency signals according to the first actual phase response curve and the first phase response fitting straight line; performing reverse phase rotation on each subcarrier signal in the OFDM frequency domain signal according to the first nonlinear phase offset to obtain a compensated OFDM frequency domain signal; and converting the compensated OFDM frequency domain signal into an OFDM time domain signal, and transmitting the OFDM time domain signal to a channel after passing through a first IIR filter. The invention can ensure that the relative relation of the phases of the subcarriers of each frequency is not changed, and improves the signal quality of the transmitting end of the OFDM system.
Description
Technical Field
The invention relates to the technical field of nonlinear phase shift, in particular to a nonlinear phase shift compensation method, a communication chip and a system based on OFDM.
Background
In an orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) system, the signal is digitally filtered to reduce noise interference both before and after transmission and reception. Common digital filters are divided into two types, finite length unit impulse response (Finite Impulse Response, FIR) filters and infinite impulse response (Infinite Impulse Response, IIR) filters. Because the FIR filter occupies more design resources than the IIR filter when being realized by hardware, the IIR filter is more beneficial to reducing the area in the design with strict requirements on the chip area.
However, due to the inherent characteristics of the IIR filter, signals with different frequencies can generate nonlinear phase shift after passing through the IIR filter, which can adversely affect the signal quality of the OFDM system, for example, at a transmitting end of the signal, the introduction of the nonlinear phase shift phase can cause phase distortion, thereby affecting an error vector magnitude (error vector magnitude, EVM) index of the transmitted signal, so that the quality of the transmitted signal is not satisfied. Therefore, in order to ensure efficient transmission of OFDM system signals, it is desirable to address the impact of nonlinear phase shifts on signal quality.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to overcome the defects in the prior art, and provide the nonlinear phase shift compensation method, the communication chip and the system based on OFDM, which can ensure that the phase relative relation of subcarriers with different frequencies is not changed and improve the signal quality of a transmitting end of an OFDM system.
In order to solve the technical problems, the invention provides a nonlinear phase shift compensation method based on OFDM, which comprises the following steps:
acquiring a first actual phase response curve of a first IIR filter of a transmitting end, fitting the first actual phase response curve to obtain a first phase response fitting straight line, and obtaining first nonlinear phase offsets of different frequency signals according to the first actual phase response curve and the first phase response fitting straight line;
performing reverse phase rotation on each subcarrier signal in the OFDM frequency domain signal according to the first nonlinear phase offset to obtain a compensated OFDM frequency domain signal;
And converting the compensated OFDM frequency domain signal into an OFDM time domain signal, and transmitting the OFDM time domain signal to a channel after passing through the first IIR filter.
Further, the first nonlinear phase offset of the different frequency signals is obtained according to the first actual phase response curve and the first phase response fitting straight line, specifically: performing difference operation on the first actual phase response curve and the first phase response fitting straight line to obtain a first nonlinear phase offset of different frequency signals after the signals pass through a first IIR filter, wherein the first nonlinear phase offset is as follows:
，
In the method, in the process of the invention, Representing said first nonlinear phase shift of the kth signal frequency after passing through the first IIR filter,Representing the phase shift of the kth signal frequency on the first actual phase response curve,Representing the phase offset of the kth signal frequency on the first phase response fitting line.
Further, when the fitting of the first actual phase response curve obtains a first phase response fitting straight line, the first actual phase response curve is fitted into a linear straight line according to the frequency range of the subcarrier signal in the OFDM frequency domain signal, and the linear straight line is used as the first phase response fitting straight line.
Further, each subcarrier signal in the OFDM frequency domain signal is reverse phase rotated according to the first nonlinear phase offset, specifically, each subcarrier signal is multiplied by a complex index of the first nonlinear phase offset to perform reverse phase rotation.
Further, the multiplying each subcarrier signal by the complex exponent of the first nonlinear phase offset to perform reverse phase rotation is specifically:
the subcarrier signals in the OFDM frequency domain signal are as follows:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal, t representing time,Representing the amplitude of the kth subcarrier signal, j representing the imaginary unit,The frequency of the kth subcarrier signal is represented, e being a natural constant;
and according to the first nonlinear phase offset, performing reverse phase rotation on the subcarrier signal, specifically:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal in the compensated OFDM frequency domain signal,Representing said first nonlinear phase offset of the kth signal frequency after passing through the first IIR filter.
Further, the method further comprises:
receiving the OFDM time domain signal transmitted through the channel;
Performing homodromous phase rotation on the local preamble sub-carrier according to the second nonlinear phase offset to obtain a processed local preamble sub-carrier; the second nonlinear phase offset is obtained according to a second actual phase response curve of a second IIR filter of the receiving end;
and carrying out frame synchronization on the OFDM time domain signal processed by the second IIR filter according to the processed local preamble subcarrier.
Further, the local preamble subcarrier is subjected to the same-direction phase rotation according to the second nonlinear phase offset, and specifically, the local preamble subcarrier is multiplied by a complex index of the second nonlinear phase offset to perform the same-direction phase rotation.
Further, the multiplying the local preamble subcarrier by the complex exponent of the second nonlinear phase offset to perform homodromous phase rotation is specifically:
，
In the method, in the process of the invention, Representing the complex version of the kth local preamble subcarrier after processing, t represents time,Representing the amplitude of the kth local preamble subcarrier, j represents the imaginary unit,Representing the frequency of the kth local preamble subcarrier,And e is a natural constant, and represents the second nonlinear phase offset of the kth signal frequency after passing through a second IIR filter.
The invention also provides a communication chip based on the nonlinear phase shift compensation of OFDM, and the communication chip realizes the nonlinear phase shift compensation method based on OFDM.
The invention also provides a system for nonlinear phase shift compensation based on OFDM, which uses the communication chip for nonlinear phase shift compensation based on OFDM.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
According to the invention, the phase compensation is performed in advance by carrying out reverse phase rotation on the subcarriers in the OFDM frequency domain signal at the transmitting end so as to offset nonlinear phase offset introduced by the IIR filter at the transmitting end, so that the relative relationship of the phases of the subcarriers at all frequencies is not changed, the signal EVM quality at the transmitting end of the OFDM system is improved, and the reliability of communication is ensured.
Drawings
In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings, in which:
fig. 1 is a process schematic of a signal processing flow in the present invention.
Fig. 2 is a flowchart of a nonlinear phase shift compensation method based on OFDM according to a first embodiment of the present invention.
Fig. 3 is a flowchart of a nonlinear phase shift compensation method based on OFDM in a second embodiment of the present invention.
Fig. 4 is a diagram illustrating an example of a linear fit of the nonlinear phase response of an IIR filter in an embodiment of the present invention.
Fig. 5 is an exemplary graph of IIR filter phase and amplitude response in an embodiment of the invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
Example 1
At the transmitting end of the OFDM system, the bit stream signal to be transmitted is converted into a time domain signal after being coded, modulated and IFFT transformed, and then is transmitted into a channel through the analog front end after up-sampling and filtering processing of the digital front end. In this embodiment, an IIR filter of 0-6 mhz is taken as an example of a low-pass filter, as shown in fig. 5, the amplitude response of subcarrier signals with different frequencies is 0dB after passing through the IIR filter, but the phase response has obvious nonlinear offset, so that the relative phase relationship of each frequency component is changed, and the quality of the EVM index of the transmitting end is seriously affected. It should be noted that the EVM index refers to a measure of a gap between an actual transmission signal and a theoretical transmission signal, and is an important parameter for measuring signal quality, and the nonlinear offset may destroy orthogonality of the OFDM signal, resulting in increased interference between subcarriers, resulting in an increased EVM value (a larger EVM value indicates poor signal quality), and possibly causing a receiving end to fail to demodulate the signal correctly when serious. Thus, referring to fig. 2, the present embodiment discloses a nonlinear phase shift compensation method based on OFDM, which includes the following steps:
S1: at a transmitting end of the OFDM system, a first nonlinear phase offset introduced by a first IIR filter is calculated. Acquiring an actual phase response curve of a first IIR filter, fitting the first actual phase response curve to obtain a first phase response fitting straight line, and obtaining first nonlinear phase offsets of different frequency signals according to the first actual phase response curve and the first phase response fitting straight line;
S1-1: after the design of the IIR filter is completed, the phase response curve of the filter for signals with different frequencies can be analyzed according to the parameters such as the frequency, the bandwidth, the order and the like of the IIR filter. In order to compensate for nonlinear phase offset introduced by the IIR filters, in this embodiment, a linearization fit is performed on a first phase response curve of a first IIR filter at the transmitting end. Optionally, when the first actual phase response curve is fitted to obtain a first phase response fitting straight line, the first actual phase response curve may be fitted to a linear straight line according to a frequency range of a subcarrier signal in the OFDM frequency domain signal, and the linear straight line is used as the first phase response fitting straight line, so that a more accurate nonlinear offset may be obtained, and a compensation effect may be improved. The fitting method can also be linear regression, polynomial fitting and other methods. For example, as shown in fig. 4, the frequency range of the subcarrier of the OFDM is 0MHz-6MHz, the phase response points of the 0MHz frequency point and the 6MHz frequency point are connected into a straight line, a linear phase response straight line is fitted, the fitted linear phase response straight line can be various, the slope of the straight line is different, the delay time of each frequency signal passing through the IIR filter is affected, but the relative phase relation among each frequency signal is not changed.
S1-2: obtaining a first nonlinear phase offset of different frequency signals according to a first actual phase response curve and a first phase response fitting straight line, specifically:
Performing difference operation on the first actual phase response curve and the first phase response fitting straight line of the first IIR filter to obtain a first nonlinear phase offset of different frequency signals after the signals pass through the first IIR filter, wherein the first nonlinear phase offset is as follows:
，
In the method, in the process of the invention, Representing said first nonlinear phase shift of the kth signal frequency after passing through the first IIR filter,Representing the phase shift of the kth signal frequency on the first actual phase response curve,Representing the phase offset of the kth signal frequency on the first phase response fitting line. The first IIR filter in this embodiment may be a low pass filter of 0-6 MHz.
S2: and multiplying each subcarrier signal in the OFDM frequency domain signal by the complex index of the first nonlinear phase offset to perform reverse phase rotation after modulating the subcarrier signal and before performing IFFT, so as to obtain a compensated OFDM frequency domain signal, and the compensated OFDM frequency domain signal is used for compensating the nonlinear phase offset introduced by the first IIR filter in the subsequent step.
S2-1: the subcarrier signals in the OFDM frequency domain signal are:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal, t representing time,Representing the amplitude of the kth subcarrier signal, j representing the imaginary unit,The frequency of the kth subcarrier signal is represented, e being a natural constant.
S2-2: and according to the first nonlinear phase offset, performing reverse phase rotation on the subcarrier signal which is modulated and not subjected to IFFT so as to pre-compensate nonlinear phase offset introduced by a subsequent first IIR filter, namely:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal in the compensated OFDM frequency domain signal,Representing said first nonlinear phase offset of the kth signal frequency after passing through the first IIR filter.
S3: the compensated subcarrier signal is converted into a time domain signal using an inverse fast fourier transform (INVERSE FAST Fourier Transform, IFFT), processed by a first IIR filter, and transmitted into a channel. The nonlinear phase offset introduced by the first IIR filter and the phase quantity during pre-compensation are mutually offset, so that the linear phase offset is ensured, the linear phase offset can ensure that the relative phase relation of subcarriers with different frequencies in the signal is not changed, and the EVM index quality of the transmitted signal is improved.
Example two
The embodiment discloses another nonlinear phase shift compensation method based on OFDM, at the receiving end of an OFDM system, after signals are received by an analog front end and then subjected to downsampling and filtering processing of a digital front end, the same IIR filter at the same place can also cause nonlinear offset of subcarriers with different frequencies, so that waveforms of time domain signals are changed, such as peak offset or signal strength reduction, frame synchronization correlation peaks of leading time domain signals are inconsistent with expected results, and frame synchronization failure or error synchronization can occur. In order to ensure that the leading time domain signals can be correctly synchronized, the local leading subcarriers of the receiving end of the OFDM system can be multiplied by complex indexes of nonlinear phase offset corresponding to an IIR filter of the receiving end in the frequency domain in advance to perform homodromous phase rotation, and then the complex indexes are converted into the leading time domain signals of the time domain through IFFT. At this time, the correlation peak detection can be realized by the leading time domain signal in the received signal and the local leading signal after rotation, so that the subsequent data processing is convenient. As shown in fig. 1 and 3, the method specifically comprises the following steps:
S1: at a transmitting end of the OFDM system, a first nonlinear phase offset introduced by a first IIR filter is calculated. Acquiring an actual phase response curve of a first IIR filter, fitting the first actual phase response curve to obtain a first phase response fitting straight line, and obtaining first nonlinear phase offsets of different frequency signals according to the first actual phase response curve and the first phase response fitting straight line;
S1-1: after the design of the IIR filter is completed, the phase response curve of the filter for signals with different frequencies can be analyzed according to the parameters such as the frequency, the bandwidth, the order and the like of the IIR filter. In order to compensate for nonlinear phase offset introduced by the IIR filters, in this embodiment, a linearization fit is performed on a first phase response curve of a first IIR filter at the transmitting end. Optionally, when the first actual phase response curve is fitted to obtain a first phase response fitting straight line, the first actual phase response curve may be fitted to a linear straight line according to a frequency range of a subcarrier signal in the OFDM frequency domain signal, and the linear straight line is used as the first phase response fitting straight line, so that a more accurate nonlinear offset may be obtained, and a compensation effect may be improved. The fitting method can also be linear regression, polynomial fitting and other methods. For example, as shown in fig. 4, the frequency range of the subcarrier of the OFDM is 0MHz-6MHz, the phase response points of the 0MHz frequency point and the 6MHz frequency point are connected into a straight line, a linear phase response straight line is fitted, the fitted linear phase response straight line can be various, the slope of the straight line is different, the delay time of each frequency signal passing through the IIR filter is affected, but the relative phase relation among each frequency signal is not changed.
S1-2: obtaining a first nonlinear phase offset of different frequency signals according to a first actual phase response curve and a first phase response fitting straight line, specifically:
Performing difference operation on the first actual phase response curve and the first phase response fitting straight line of the first IIR filter to obtain a first nonlinear phase offset of different frequency signals after the signals pass through the first IIR filter, wherein the first nonlinear phase offset is as follows:
，
In the method, in the process of the invention, Representing said first nonlinear phase shift of the kth signal frequency after passing through the first IIR filter,Representing the phase shift of the kth signal frequency on the first actual phase response curve,Representing the phase offset of the kth signal frequency on the first phase response fitting line. The first IIR filter in this embodiment may be a low pass filter of 0-6 MHz.
S2: and multiplying each subcarrier signal in the OFDM frequency domain signal by the complex index of the first nonlinear phase offset to perform reverse phase rotation after modulating the subcarrier signal and before performing IFFT, so as to obtain a compensated OFDM frequency domain signal, and the compensated OFDM frequency domain signal is used for compensating the nonlinear phase offset introduced by the first IIR filter in the subsequent step.
S2-1: the subcarrier signals in the OFDM frequency domain signal are:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal, t representing time,Representing the amplitude of the kth subcarrier signal, j representing the imaginary unit,The frequency of the kth subcarrier signal is represented, e being a natural constant.
S2-2: and according to the first nonlinear phase offset, performing reverse phase rotation on the subcarrier signal which is modulated and not subjected to IFFT so as to pre-compensate nonlinear phase offset introduced by a subsequent first IIR filter, namely:
，
In the method, in the process of the invention, Representing the complex version of the kth subcarrier signal in the compensated OFDM frequency domain signal,Representing said first nonlinear phase offset of the kth signal frequency after passing through the first IIR filter.
S3: the compensated subcarrier signal is converted into a time domain signal using an inverse fast fourier transform (INVERSE FAST Fourier Transform, IFFT), processed by a first IIR filter, and transmitted into a channel. The nonlinear phase offset introduced by the first IIR filter and the phase quantity during pre-compensation are mutually offset, so that the linear phase offset is ensured, the linear phase offset can ensure that the relative phase relation of subcarriers with different frequencies in the signal is not changed, and the EVM index quality of the transmitted signal is improved.
S4: at a receiving end of the OFDM system, an OFDM time domain signal transmitted through a channel is received, after IIR filtering and before frame synchronization are carried out on the received OFDM time domain signal, the local preamble sub-carrier is subjected to homodromous phase rotation according to a second nonlinear phase offset in a frequency domain to obtain a processed local preamble sub-carrier, and then the processed local preamble sub-carrier is converted into a local preamble time domain signal through IFFT.
S4-1: and acquiring a second nonlinear phase offset according to a second IIR filter of the receiving end of the OFDM system. The receiving end of the OFDM system is also provided with an IIR filter for carrying out IIR filtering on the received OFDM signals. The method for calculating the second nonlinear phase offset is the same as the method for calculating the first nonlinear offset in step S1, and specifically is obtained according to the second actual phase response curve of the second IIR filter. The second IIR filter at the receiving end may be the same as or different from the first IIR filter at the transmitting end, and the first IIR filter and the second IIR filter in this embodiment are the same. When the IIR filters at the transmitting end and the receiving end are the same, the first nonlinear phase offset and the second nonlinear phase offset are the same and only need to be calculated once.
And according to the second nonlinear phase offset, performing homodromous phase rotation on the local preamble subcarrier in the frequency domain to compensate nonlinear phase offset introduced by a second IIR filter at the receiving end. Specifically, multiplying each local preamble subcarrier by a complex index of a second nonlinear phase offset to perform homodromous phase rotation, and obtaining the processed local preamble subcarrier as follows:
，
In the method, in the process of the invention, Representing the complex version of the kth local preamble subcarrier after processing, t represents time,Representing the amplitude of the kth local pilot subcarrier, j represents the imaginary unit,Representing the frequency of the kth local preamble subcarrier,Representing said second nonlinear phase offset of the kth signal frequency after passing through a second IIR filter.
S4-2: the processed local preamble sub-carriers are converted into local preamble time domain signals by IFFT.
S5: and performing frame synchronization on the local preamble time domain signal and the OFDM time domain signal processed by the second IIR filter.
When the frame synchronization is carried out on the time domain signal, the local preamble sub-carrier wave has carried out the homodromous phase rotation to compensate the nonlinear phase offset introduced by the second IIR filter of the receiving end, so that the success of the detection of the correlation peak of the local preamble signal and the received preamble signal can be ensured.
In this embodiment, at a transmitting end of an OFDM system, first, phase compensation is performed in advance by performing reverse phase rotation on subcarriers in an OFDM frequency domain signal, then, the compensated OFDM frequency domain signal is converted into an OFDM time domain signal through IFFT, and finally, the OFDM time domain signal is transmitted to a channel after passing through a first IIR filter; nonlinear phase offset introduced by a first IIR filter of a transmitting end can be counteracted, and the relative relation of phases of subcarrier signals of all frequencies is not changed, so that the signal EVM quality of the transmitting end of an OFDM system is improved, and the reliability of communication is ensured. Further, at a receiving end of the OFDM system, the OFDM time domain signal transmitted by the channel is received through a second IIR filter of the receiving end, then the local preamble sub-carrier is subjected to the same-direction phase rotation, and finally the frame synchronization is performed; nonlinear phase offset of a second IIR filter of the receiving end to the leading carrier signal can be counteracted, and correlation peak detection of frame synchronization of the receiving end is guaranteed, so that effective data signals can be successfully received.
Example III
The embodiment discloses a communication chip based on OFDM nonlinear phase shift compensation, which realizes the OFDM nonlinear phase shift compensation method in the first embodiment or the second embodiment.
Example IV
The embodiment discloses a nonlinear phase shift compensation system based on OFDM, which uses the communication chip based on the nonlinear phase shift compensation of the OFDM in the third embodiment.
The invention carries out phase compensation in advance by carrying out reverse phase rotation on the subcarriers before IFFT so as to offset nonlinear phase offset introduced by an IIR filter of a transmitting end, ensures that the phase relative relation of subcarriers with different frequencies is not changed, can greatly improve the signal EVM quality of the transmitting end of an OFDM system and ensures the reliability of communication.
Further, for signals with different frequencies, nonlinear phase offset is generated after the signals pass through an IIR filter at a receiving end, and when the receiving end of the signals synchronizes the OFDM symbols, the leading time domain signals may cause peak reduction due to the nonlinear phase offset, so that a situation that frames cannot be synchronized occurs. The invention also carries out the phase rotation in the same direction through the local leading subcarrier of the receiving end, thereby ensuring that the correlation peak of the local leading time domain signal and the leading time domain signal received after passing through the IIR filter is consistent with the expected value when the receiving end is synchronous, and further ensuring the accuracy of the frame synchronization.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present invention will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (9)
1. A method of non-linear phase shift compensation based on OFDM, the method comprising:
acquiring a first actual phase response curve of a first IIR filter of a transmitting end, fitting the first actual phase response curve to obtain a first phase response fitting straight line, and obtaining first nonlinear phase offsets of different frequency signals according to the first actual phase response curve and the first phase response fitting straight line;
performing reverse phase rotation on each subcarrier signal in the OFDM frequency domain signal according to the first nonlinear phase offset to obtain a compensated OFDM frequency domain signal;
Converting the compensated OFDM frequency domain signal into an OFDM time domain signal, and transmitting the OFDM time domain signal to a channel after passing through the first IIR filter;
the method further comprises the steps of:
receiving the OFDM time domain signal transmitted through the channel;
Performing homodromous phase rotation on the local preamble sub-carrier according to the second nonlinear phase offset to obtain a processed local preamble sub-carrier; the second nonlinear phase offset is obtained according to a second actual phase response curve of a second IIR filter of the receiving end;
and carrying out frame synchronization on the OFDM time domain signal processed by the second IIR filter according to the processed local preamble subcarrier.
2. The OFDM-based nonlinear phase shift compensation method according to claim 1, wherein: the first nonlinear phase offset of the different frequency signals is obtained according to the first actual phase response curve and the first phase response fitting straight line, specifically: performing difference operation on the first actual phase response curve and the first phase response fitting straight line to obtain a first nonlinear phase offset of different frequency signals after the signals pass through a first IIR filter, wherein the first nonlinear phase offset is as follows:
In the method, in the process of the invention, Representing the first nonlinear phase shift of the kth signal frequency after passing through the first IIR filter, θ act,k representing the phase shift of the kth signal frequency on the first actual phase response curve, and θ fit,k representing the phase shift of the kth signal frequency on the first phase response fitting line.
3. The OFDM-based nonlinear phase shift compensation method according to claim 1, wherein: when the fitting of the first actual phase response curve obtains a first phase response fitting straight line, the first actual phase response curve is fitted into a linear straight line according to the frequency range of the subcarrier signal in the OFDM frequency domain signal, and the linear straight line is used as the first phase response fitting straight line.
4. The OFDM-based nonlinear phase shift compensation method according to claim 1, wherein: and carrying out reverse phase rotation on each subcarrier signal in the OFDM frequency domain signal according to the first nonlinear phase offset, and particularly multiplying each subcarrier signal by a complex index of the first nonlinear phase offset to carry out reverse phase rotation.
5. The method for compensating for nonlinear phase shift based on OFDM according to claim 4, wherein: the multiplying each subcarrier signal by the complex index of the first nonlinear phase offset to perform reverse phase rotation is specifically:
the subcarrier signals in the OFDM frequency domain signal are as follows:
Where x k (t) represents a complex form of the kth subcarrier signal, t represents time, d k represents an amplitude of the kth subcarrier signal, j represents an imaginary unit, f k represents a frequency of the kth subcarrier signal, and e is a natural constant;
and according to the first nonlinear phase offset, performing reverse phase rotation on the subcarrier signal, specifically:
Where x k (t)' represents the complex form of the kth subcarrier signal in the compensated OFDM frequency domain signal, Representing said first nonlinear phase offset of the kth signal frequency after passing through the first IIR filter.
6. The OFDM-based nonlinear phase shift compensation method according to claim 1, wherein: and performing homodromous phase rotation on the local preamble subcarrier according to the second nonlinear phase offset, specifically, multiplying the local preamble subcarrier by a complex index of the second nonlinear phase offset to perform homodromous phase rotation.
7. The method for OFDM-based nonlinear phase shift compensation according to claim 6, wherein: the complex index of the local preamble subcarrier multiplied by the second nonlinear phase offset is used for performing homodromous phase rotation, specifically:
Where y k (t) represents the complex version of the kth local preamble subcarrier after processing, t represents time, d k 'represents the amplitude of the kth local preamble subcarrier, j represents the imaginary unit, f k' represents the frequency of the kth local preamble subcarrier, And e is a natural constant, and represents the second nonlinear phase offset of the kth signal frequency after passing through a second IIR filter.
8. The utility model provides a communication chip based on nonlinear phase shift compensation of OFDM which characterized in that: the communication chip implements the non-linear phase shift compensation method based on OFDM according to any one of claims 1-7.
9. A system for non-linear phase shift compensation based on OFDM, characterized by: the system for non-linear phase shift compensation based on OFDM uses the communication chip for non-linear phase shift compensation based on OFDM according to claim 8.
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