CN110166398B - Frequency offset OFDM transmission method - Google Patents

Frequency offset OFDM transmission method Download PDF

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CN110166398B
CN110166398B CN201910498396.XA CN201910498396A CN110166398B CN 110166398 B CN110166398 B CN 110166398B CN 201910498396 A CN201910498396 A CN 201910498396A CN 110166398 B CN110166398 B CN 110166398B
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CN110166398A (en
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沙学军
张宇思
王迦祺
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Harbin Hailnke Information Technology Co ltd
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Harbin Institute of Technology
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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
    • H04L27/2628—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators
    • 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
    • H04L27/2649—Demodulators
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Abstract

An OFDM transmission method of frequency offset belongs to the technical field of wireless communication. The invention solves the problem that the frequency spectrum efficiency of the traditional OFDM system can not be further improved due to the Nyquist orthogonal constraint. Firstly, 2 paths of orthogonal signals are generated for 2 users according to an OFDM system respectively, and the 2 paths of orthogonal signals are up-converted to different frequency positions and mixed to obtain non-orthogonal signals; then dividing the received signal into two paths for processing at a receiving end, respectively carrying out down-conversion on the two paths of signals to different frequencies to obtain signals to be processed of 2 users, carrying out time domain periodic extension on the signals to be processed to improve the frequency spectrum resolution, and filtering out required signal points by utilizing a comb filter; and finally, based on the balance and detection of the receiving end of the OFDM system, judging the processing result of each path of signal so as to obtain the original sending signal. The signal emitted by the radio frequency is a non-orthogonal signal, so that the aim of improving the frequency spectrum efficiency can be fulfilled. The invention can be applied to the technical field of wireless communication.

Description

Frequency offset OFDM transmission method
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a Frequency offset OFDM (orthogonal Frequency Division multiplexing) transmission method.
Background
With the development of 5G communication networks, the communication demand of users and the number of network access devices are increased dramatically, on one hand, the communication demand is increased greatly, on the other hand, the frequency resources are increasingly strained, and the development of communication systems needs to seek communication technologies with higher spectrum efficiency. In a scene with limited bandwidth, a transmission method with higher spectral efficiency can be utilized to meet the requirements of people on mobile communication as much as possible.
The conventional OFDM system is an orthogonal transmission system, and OFDM signals satisfy the nyquist orthogonality constraint in both time and frequency domains, but the orthogonal system is not an optimal strategy in terms of channel capacity and spectral efficiency. The frequency spectrum efficiency of the orthogonal system can be improved by sending a high-order modulation signal, however, the high-order modulation signal is sensitive to noise, and the nonlinear interference of a device can also cause great influence on the system performance; in addition, a filter bank can be designed to realize CP-free transmission and other modes to improve the spectrum efficiency of the orthogonal system, but the basic idea of the method is to eliminate the ICI influence, and the limitation of Nyquist orthogonal constraint on the spectrum efficiency is not broken through substantially.
Disclosure of Invention
The invention aims to solve the problem that the spectrum efficiency of the traditional OFDM system cannot be further improved due to the Nyquist orthogonality constraint, and provides a frequency-offset OFDM transmission method.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method of frequency-offset OFDM transmission, the method comprising the steps of:
step one, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate a source m1 of the 1 st user and a source m2 of the 2 nd user;
step two, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step three, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure BDA0002089379560000011
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step four, the signal tx of the step three is usedm1And signal txm2Mixing frequency to obtain a mixed signal tx, and transmitting the mixed signal tx to a channel through radio frequency of a transmitting end;
fifthly, after the mixed signal tx passes through a channel, the received signal of a receiving end is rx;
the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step six, the 1 st path signal rxm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure BDA0002089379560000021
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step seven, for the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point Discrete Fourier Transform (DFT) and comb filtering to obtain a frequency domain signal RKN,1-1；
Step eight, the frequency domain signal R is subjected toKN,1-1Performing KN point Inverse Discrete Fourier Transform (IDFT) to obtain a signal after the KN point inverse discrete Fourier transform, and then intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step nine, signal y1Sequentially carrying out N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step ten, for the signal r2Repeatedly executing the process from the step seven to the step nine to obtain an output signal Y2。
A frequency offset OFDM transmission method, the working process of the sending end of the method is:
step 1, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate an information source m1 of the 1 st user and an information source m2 of the 2 nd user;
step 2, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step 3, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure BDA0002089379560000022
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step 4, the signal tx in the step 3 is usedm1And signal txm2And performing frequency mixing to obtain a frequency-mixed signal tx, and transmitting the frequency-mixed signal tx to a channel through radio frequency of a transmitting end.
A frequency offset OFDM transmission method, the working process of the receiving end of the method is:
step 1), the received signal of the receiving end is rx, and the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step 2), the 1 st path signal rx is processedm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure BDA0002089379560000031
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step 3), to the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point Discrete Fourier Transform (DFT) and comb filtering to obtain a frequency domain signal RKN,1-1；
Step 4) for the frequency domain signal RKN,1-1Performing KN point Inverse Discrete Fourier Transform (IDFT) to obtain a signal after the KN point inverse discrete Fourier transform, and then intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step 5), signal y1Sequentially pass throughPerforming N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step 6) for the signal r2Repeatedly executing the processes from step 3) to step 5) to obtain an output signal Y2。
The invention has the beneficial effects that: the invention has proposed the OFDM transmission method of a frequency deviation, the invention first generates 2 routes of orthogonal signals to 2 users according to OFDM system separately, 2 routes of orthogonal signals are through the different frequency positions of up-conversion and carry on the mixing, get the non-orthogonal signal; then dividing the received signal into two paths for processing at a receiving end, respectively carrying out down-conversion on the two paths of signals to different frequencies to obtain signals to be processed of 2 users, carrying out time domain periodic extension on the signals to be processed to improve the frequency spectrum resolution, and filtering out required signal points by utilizing a comb filter; and finally, based on the balance and detection of the receiving end of the OFDM system, judging the processing result of each path of signal so as to obtain the original sending signal. The signal emitted by the radio frequency is a non-orthogonal signal, and for the OFDM transmission method of frequency offset of two users, 1 time more signal can be transmitted than the traditional OFDM transmission method, so that the purpose of improving the frequency spectrum efficiency is achieved.
Drawings
Fig. 1 is a block diagram of a transmitting end of a frequency offset OFDM transmission method of the present invention;
FIG. 2 is a block diagram of a receiving end of a frequency offset OFDM transmission method of the present invention;
fig. 3 is a schematic diagram of the frequency spectrum of the signal transmitted by the user 1 according to the present invention;
fig. 4 is a schematic diagram of the frequency spectrum of the signal transmitted by the user 2 of the present invention;
FIG. 5 is a schematic diagram of the frequency spectrum of the mixed signal transmission signal of the present invention;
wherein: the solid line is the user 1 spectrum and the dashed line is the user 2 spectrum.
Detailed Description
The first embodiment is as follows: as shown in fig. 1 and fig. 2, the method for OFDM transmission with frequency offset according to this embodiment includes the following steps:
step one, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate a source m1 of the 1 st user and a source m2 of the 2 nd user;
step two, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step three, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure BDA0002089379560000041
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step four, the signal tx of the step three is usedm1And signal txm2Mixing frequency to obtain a mixed signal tx, and transmitting the mixed signal tx to a channel through radio frequency of a transmitting end;
fifthly, after the mixed signal tx passes through a channel, the received signal of a receiving end is rx;
the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step six, the 1 st path signal rxm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure BDA0002089379560000042
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step seven, for the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point Discrete Fourier Transform (DFT) and comb filtering to obtain a frequency domain signal RKN,1-1；
Step eight, the frequency domain signal R is subjected toKN,1-1Performing KN point Inverse Discrete Fourier Transform (IDFT) to obtain a signal after the KN point inverse discrete Fourier transform, and then intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step nine, signal y1Sequentially carrying out N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step ten, for the signal r2Repeatedly executing the process from the step seven to the step nine to obtain an output signal Y2。
In consideration of the limitations of the orthogonal system in terms of channel capacity and spectral efficiency, the present invention provides a frequency offset OFDM transmission method, which simultaneously transmits a plurality of user signals (in this embodiment, the number of user signals is 2) in the same frequency and time resource, and the signals transmitted by radio frequency are non-orthogonal signals, so as to achieve the purpose of improving spectral efficiency.
As shown in fig. 3 to 5, the specific generation process of the mixing signal is as follows:
the rf end transmit signal tx may be regarded as 2N-point OFDM signals, and the 2N-point OFDM signals respectively experience different subcarrier frequency offsets (i.e. respectively experience 0 hz and 0 hz)
Figure BDA0002089379560000051
Frequency offset) and then converted to a center frequency f0The above.
When the bandwidth is fixed, the number of subcarriers is large enough and the subcarrier spacing is small, at this time, the bandwidth of the non-orthogonal multiuser signal in the invention
Figure BDA0002089379560000052
Wherein f is0For user 1 to up-convert the center frequency, Δ f is the subcarrier frequency spacing.
Compared with the traditional OFDM system, the invention sacrifices the subcarrier spacing and obtains higher spectrum efficiency on the premise of not increasing additional frequency band and time resource.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the specific process of the second step is as follows:
the information source m1 of the 1 st user obtains a modulated signal x corresponding to the 1 st user through serial/parallel conversion and N-point inverse discrete Fourier transformm1The signal source m2 of the 2 nd user is subjected to serial/parallel conversion and N-point inverse discrete Fourier transform to obtain a modulated signal x corresponding to the 2 nd userm2。
In the seventh step and the ninth step, DFT is performed on the time domain discrete signal x (N) to obtain a frequency domain discrete signal x (k), and a mathematical expression of the N-point DFT is as follows:
Figure BDA0002089379560000053
in the second step and the eighth step, IDFT is performed on the frequency domain discrete signal x (k) to obtain a time domain discrete signal x (N), and the expression of the N-point IDFT is as follows:
Figure BDA0002089379560000054
the specific process of performing IDFT on the signal in step two and step eight is as follows:
Figure BDA0002089379560000055
Figure BDA0002089379560000056
the third concrete implementation mode: the second embodiment is different from the first embodiment in that: the pair signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1The specific process comprises the following steps:
Figure BDA0002089379560000061
for a signal r with a number of sampling points N1After K times period extension, a signal [ r ] with length KN can be obtained]KN,1；
Wherein: [ r ] of]KN,1(n) the representative signal [ r ]]KN,1The nth point, n is 1,2, …, KN, r1(n-kN) represents the pair r1(n) right shifting kN, i.e. right shifting to a position K cycles later, K being 0,11(n) the representative signal r1The nth point.
The fourth concrete implementation mode: the third difference between the present embodiment and the specific embodiment is that: the time domain signal [ r]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1The specific process comprises the following steps:
for two-user mixing signals, comb filter Hcomb，1In the frequency domain form:
Figure BDA0002089379560000062
wherein i is an intermediate variable, i is 0,1, …, N-1, f represents a frequency domain independent variable, Δ f is an OFDM signal subcarrier interval in hertz, and δ (f-i Δ f) represents an impulse function;
Figure BDA0002089379560000063
f is an argument, and is chosen because the formula is a frequency domain expression, similar to the function f (x) x, where x is an argument and x has no specific meaning.
Comb filter Hcomb，1The discrete form of the frequency domain is:
Figure BDA0002089379560000064
then the frequency domain signal RKN,1-1The mathematical expression of (a) is:
RKN,1-1＝DFT[[r]KN,1]·Hcomb,1。
RKN,1-1is the user 1 signal resulting from the path 1 signal, which is interfered by user 2, for user 2,
RKN,2-1＝DFT[[r]KN,2]·Hcomb,1
RKN,2-1is the user 2 signal with user 1 interference resulting from the 2 nd signal.
The fifth concrete implementation mode: as shown in fig. 1, a transmitting end of the method for OFDM transmission with frequency offset according to this embodiment operates as follows:
step 1, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate an information source m1 of the 1 st user and an information source m2 of the 2 nd user;
step 2, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step 3, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure BDA0002089379560000071
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step 4, the signal tx in the step 3 is usedm1And signal txm2And performing frequency mixing to obtain a frequency-mixed signal tx, and transmitting the frequency-mixed signal tx to a channel through radio frequency of a transmitting end.
In consideration of the limitations of the orthogonal system in terms of channel capacity and spectral efficiency, the present invention provides a frequency offset OFDM transmission method, which simultaneously transmits a plurality of user signals (in this embodiment, the number of user signals is 2) in the same frequency and time resource, and the signals transmitted by radio frequency are non-orthogonal signals, so as to achieve the purpose of improving spectral efficiency.
As shown in fig. 3 to 5, the specific generation process of the mixing signal is as follows:
the rf end transmit signal tx may be regarded as 2N-point OFDM signals, and the 2N-point OFDM signals respectively experience different subcarrier frequency offsets (i.e. respectively experience 0 hz and 0 hz)
Figure BDA0002089379560000072
Frequency offset) and then converted to a center frequency f0The above.
When the bandwidth is fixed, the number of subcarriers is large enough and the subcarrier spacing is small, at this time, the bandwidth of the non-orthogonal multiuser signal in the invention
Figure BDA0002089379560000073
Wherein f is0For user 1 to up-convert the center frequency, Δ f is the subcarrier frequency spacing.
Compared with the traditional OFDM system, the invention sacrifices the subcarrier spacing and obtains higher spectrum efficiency on the premise of not increasing additional frequency band and time resource.
The sixth specific implementation mode: the fifth embodiment is different from the fifth embodiment in that: the specific process of the step 2 is as follows:
the information source m1 of the 1 st user obtains a modulated signal x corresponding to the 1 st user through serial/parallel conversion and N-point inverse discrete Fourier transformm1The signal source m2 of the 2 nd user is subjected to serial/parallel conversion and N-point inverse discrete Fourier transform to obtain a modulated signal x corresponding to the 2 nd userm2。
For example, the specific process of performing IDFT on the K-point frequency domain discrete signal x (K) to obtain the time domain discrete signal x (n) is as follows:
Figure BDA0002089379560000081
the process of IDFT for m1 is:
Figure BDA0002089379560000082
the seventh embodiment: as shown in fig. 2, in the OFDM transmission method with frequency offset according to this embodiment, a receiving end of the method operates as follows:
step 1), the received signal of the receiving end is rx, and the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step 2), the 1 st path signal rx is processedm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure BDA0002089379560000083
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step 3), to the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1；
Step 4) for the frequency domain signal RKN,1-1Performing KN point inverse discrete Fourier transform to obtain a signal after the KN point inverse discrete Fourier transform, and intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step 5), signal y1Sequentially carrying out N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step 6) for the signal r2Repeatedly executing the processes from step 3) to step 5) to obtain an output signal Y2。
The specific implementation mode is eight: the seventh embodiment is different from the seventh embodiment in that: the pair signal r1Is carried out by K timesTime domain cycle extension to obtain time domain signal [ r ] with extended time domain cycle]KN,1The specific process comprises the following steps:
Figure BDA0002089379560000084
wherein: [ r ] of]KN,1(n) the representative signal [ r ]]KN,1The nth point, n is 1,2, …, KN, r1(n-kN) represents the pair r1(n) right shifting kN, K-1, r, 0,11(n) the representative signal r1The nth point.
The period extension in the time domain is equivalent to an increase in the resolution in the frequency domain.
The specific implementation method nine: the eighth embodiment is different from the eighth embodiment in that: the time domain signal [ r]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1The specific process comprises the following steps:
for two-user mixing signals, comb filter Hcomb，1In the frequency domain form:
Figure BDA0002089379560000091
wherein i is an intermediate variable, i is 0,1, …, N-1, f represents a frequency domain independent variable, Δ f is an OFDM signal subcarrier interval in hertz, and δ (f-i Δ f) represents an impulse function;
Figure BDA0002089379560000092
comb filter Hcomb，1The discrete form of the frequency domain is:
Figure BDA0002089379560000093
then the frequency domain signal RKN,1-1The mathematical expression of (a) is:
RKN,1-1＝DFT[[r]KN,1]·Hcomb,1。
RKN,1-1is the user 1 signal resulting from the path 1 signal, which is interfered by user 2, for user 2,
RKN,2-1＝DFT[[r]KN,2]·Hcomb,1。
the above-described calculation examples of the present invention are merely to explain the calculation model and the calculation flow of the present invention in detail, and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that other variations and modifications of the present invention can be made based on the above description, and it is not intended to be exhaustive or to limit the invention to the precise form disclosed, and all such modifications and variations are possible and contemplated as falling within the scope of the invention.

Claims (9)

1. A method of frequency-offset OFDM transmission, the method comprising the steps of:
step one, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate a source m1 of the 1 st user and a source m2 of the 2 nd user;
step two, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step three, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure FDA0003147316560000011
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step four, the signal tx of the step three is usedm1And signal txm2Mixing is carried outFrequency, obtaining a frequency-mixed signal tx, and transmitting the frequency-mixed signal tx to a channel through radio frequency of a transmitting end;
fifthly, after the mixed signal tx passes through a channel, the received signal of a receiving end is rx;
the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step six, the 1 st path signal rxm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure FDA0003147316560000012
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step seven, for the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1，RKN,1-1The signal is a user 1 signal which is obtained by the 1 st path signal and is interfered by a user 2;
step eight, the frequency domain signal R is subjected toKN,1-1Performing KN point inverse discrete Fourier transform to obtain a signal after the KN point inverse discrete Fourier transform, and intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step nine, signal y1Sequentially carrying out N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step ten, for the signal r2Repeatedly executing the process from the step seven to the step nine to obtain an output signal Y2。
2. The method according to claim 1, wherein the specific process of the second step is as follows:
information of the 1 st userThe source m1 obtains a modulated signal x corresponding to the 1 st user through serial/parallel conversion and N-point inverse discrete Fourier transformm1The signal source m2 of the 2 nd user is subjected to serial/parallel conversion and N-point inverse discrete Fourier transform to obtain a modulated signal x corresponding to the 2 nd userm2。
3. A method of frequency-offset OFDM transmission as claimed in claim 2, wherein said pair of signals r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1The specific process comprises the following steps:
Figure FDA0003147316560000021
wherein: [ r ] of]KN,1(n) the representative signal [ r ]]KN,1The nth point, n is 1,2, …, KN, r1(n-kN) represents the pair r1(n) right shifting kN, K-0, 11(n) the representative signal r1The nth point.
4. A method of frequency-shifted OFDM transmission as claimed in claim 3, wherein said time domain signal [ r [ ] is]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1The specific process comprises the following steps:
comb filter Hcomb，1In the frequency domain form:
Figure FDA0003147316560000022
wherein i is an intermediate variable, i is 0,1, …, N-1, f represents a frequency domain independent variable, Δ f is an OFDM signal subcarrier interval in hertz, and δ (f-i Δ f) represents an impulse function;
Figure FDA0003147316560000023
comb filter Hcomb，1The discrete form of the frequency domain is:
Figure FDA0003147316560000024
then the frequency domain signal RKN,1-1The mathematical expression of (a) is:
RKN,1-1＝DFT[[r]KN,1]·Hcomb,1。
5. an OFDM transmission method with frequency offset is characterized in that a transmitting end of the method operates as follows:
step 1, respectively generating binary bit streams of a 1 st user and a 2 nd user, wherein the binary bit stream of each user is coded and constellation mapped to generate an information source m1 of the 1 st user and an information source m2 of the 2 nd user;
step 2, respectively modulating the information source m1 of the 1 st user and the information source m2 of the 2 nd user into N OFDM subcarriers to obtain a modulated signal x corresponding to the 1 st userm1Modulated signal x corresponding to the 2 nd userm2；
Step 3, xm1Up-conversion to frequency f obtained by parallel/serial conversion and digital/analogue conversion0Signal tx ofm1，xm2Up-conversion to frequency obtained by parallel/serial conversion and digital/analogue conversion
Figure FDA0003147316560000031
Signal tx ofm2(ii) a Wherein: f. of0Up-converting the central frequency for the 1 st user, wherein delta f is the subcarrier frequency interval;
step 4, the signal tx in the step 3 is usedm1And signal txm2And performing frequency mixing to obtain a frequency-mixed signal tx, and transmitting the frequency-mixed signal tx to a channel through radio frequency of a transmitting end.
6. The method according to claim 5, wherein the specific process of step 2 is as follows:
the information source m1 of the 1 st user obtains a modulated signal x corresponding to the 1 st user through serial/parallel conversion and N-point inverse discrete Fourier transformm1The signal source m2 of the 2 nd user is subjected to serial/parallel conversion and N-point inverse discrete Fourier transform to obtain a modulated signal x corresponding to the 2 nd userm2。
7. An OFDM transmission method with frequency offset is characterized in that the working process of the receiving end of the method is as follows:
step 1), the received signal of the receiving end is rx, and the received signal rx is divided into 2 paths for processing, wherein: the 1 st path signal is rxm1The 2 nd signal is rxm2；
Step 2), the 1 st path signal rx is processedm1Down conversion f0From Hertz to baseband, obtaining a down-converted signal r corresponding to the 1 st path signal1The 2 nd path signal rxm2Down conversion
Figure FDA0003147316560000032
From Hertz to baseband, obtaining a down-converted signal r corresponding to the 2 nd path signal2；
Step 3), to the signal r1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1(ii) a Time domain signal r]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1，RKN,1-1The signal is a user 1 signal which is obtained by the 1 st path signal and is interfered by a user 2;
step 4) for the frequency domain signal RKN,1-1Performing KN point inverse discrete Fourier transform to obtain a signal after the KN point inverse discrete Fourier transform, and intercepting the front N points of the obtained signal after the KN point inverse discrete Fourier transform to obtain an intercepted time domain signal y1；
Step 5), signal y1Sequentially carrying out N-point discrete Fourier transform, nonlinear detection, constellation demapping and decoding to obtain an output signal Y1；
Step 6) forSignal r2Repeatedly executing the processes from step 3) to step 5) to obtain an output signal Y2。
8. The method of claim 7, wherein the pair of signals r is transmitted in a frequency-shifted OFDM transmission system1Carrying out K time domain period prolongation to obtain a time domain signal [ r ] after the time domain period prolongation]KN,1The specific process comprises the following steps:
Figure FDA0003147316560000041
wherein: [ r ] of]KN,1(n) the representative signal [ r ]]KN,1The nth point, n is 1,2, …, KN, r1(n-kN) represents the pair r1(n) right shifting kN, K-1, r, 0,11(n) the representative signal r1The nth point.
9. The method of claim 8, wherein the time domain signal [ r ] is transmitted in a frequency-shifted OFDM manner]KN,1Sequentially carrying out KN point discrete Fourier transform and comb filtering to obtain a frequency domain signal RKN,1-1The specific process comprises the following steps:
comb filter Hcomb，1In the frequency domain form:
Figure FDA0003147316560000042
wherein i is an intermediate variable, i is 0,1, …, N-1, f represents a frequency domain independent variable, Δ f is an OFDM signal subcarrier interval in hertz, and δ (f-i Δ f) represents an impulse function;
Figure FDA0003147316560000043
comb filter Hcomb，1The discrete form of the frequency domain is:
Figure FDA0003147316560000051
then the frequency domain signal RKN,1-1The mathematical expression of (a) is:
RKN,1-1＝DFT[[r]KN,1]·Hcomb,1。
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