OFDM-LFM (Orthogonal Frequency Division Multiplexing-Low Frequency Modulation) flux-inductance integrated signal waveform receiving method and equipment based on fractional Fourier transform

Abstract

The invention discloses an OFDM-LFM (Orthogonal Frequency Division Multiplexing-Local Frequency Modulation) integrated signal waveform receiving method and equipment based on fractional Fourier transform, LFM and OFDM are combined and improved, an OFDM-LFM integrated radar communication signal taking an orthogonal LFM signal as a subcarrier is adopted, and as the LFM subcarrier has larger Doppler tolerance, compared with a normal subcarrier, the OFDM-LFM integrated signal waveform receiving method and equipment based on fractional Fourier transform have higher Doppler tolerance, the radar communication signal can be received more accurately. The method not only can improve radar distance resolution and spectral efficiency, but also has a strong capability of avoiding Doppler effect, and can reliably transmit information, and when OFDM-LFM signals are received, in order to solve the problems of subcarrier frequency linear transformation, radar parameter extraction and the like, based on the sensitivity of fractional Fourier transform (FRFT) to LFM signals, the method can be used for solving the problems of subcarrier frequency linear transformation, radar parameter extraction and the like. According to the invention, the FRFT is used as the integrated signal receiver, the separation of the integrated signal communication receiver and the radar receiver is realized, and the system performance is improved while the complexity of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of synaesthesia integration, and in particular to an OFDM-LFM synaesthesia integration signal waveform receiving method and device based on fractional Fourier transform. Background Art

[0002] Next generation communication technologies such as Beyond 5G (B5G) and 6G have been identified as key enablers in many emerging fields. Among many visionary assumptions about B5G / 6G technology, an important direction is to integrate radar and communication into one system due to the overlap of radar and communication spectrum. It is foreseeable that the fusion of the two services in B5G / 6G technology is necessary, which has inspired the recent research on Integrated Interaesthesia Call Center (ISAC).

[0003] For the design of interawareness integration scheme, people have proposed many solutions to solve the key problems of signal sharing design in radar communication. When both radar and communication signals use linear frequency modulation (LFM) waveforms, they cannot meet the needs of transmitting large amounts of data. In recent years, orthogonal frequency division multiplexing (OFDM) has been introduced into the integration of radar and communication due to its advantages such as high spectrum efficiency, robustness against fading and multipath propagation effects. However, the integrated equipment has problems such as an increase in the number of system modules, requirements for the amount of collected data, linear transformation of subcarrier frequencies, and radar parameter extraction. Therefore, a new method and technology is urgently needed to solve the above problems. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides an OFDM-LFM synaesthesia integrated signal waveform receiving method and device based on fractional Fourier transform, LFM is combined with OFDM and improved, and an OFDM-LFM integrated radar communication signal with an orthogonal LFM signal as a subcarrier is adopted. Since the LFM subcarrier has a larger Doppler tolerance, compared with the sinusoidal subcarrier, the method can not only improve the radar distance resolution and spectrum efficiency, but also has a strong ability to avoid the Doppler effect, and can reliably transmit information. When receiving the OFDM-LFM signal, in order to solve the problems of subcarrier frequency linear transformation and radar parameter extraction, based on the sensitivity of fractional Fourier transform (FRFT) to the LFM signal, the present invention uses FRFT as an integrated signal receiver, which can demodulate the OFDM-LFM signal at the communication end while reducing the requirement for the amount of collected data at the radar end, thereby solving the problems mentioned in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: an OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform, comprising the following steps:

[0006] 1. Generate initial data information flow;

[0007] 2. Map the data information stream into QAM symbols;

[0008] 3. Convert the generated QAM symbols from serial data streams into parallel data streams, then modulate the parallel data into OFDM-LFM synaesthesia integrated signals through FRFT and save the FRFT order, add cyclic prefixes to the modulated symbols, and convert them into serial data;

[0009] 4. After the transmission signal is amplified, it is divided into two paths through a power divider. One path is the radar reference signal, and the other path is amplified by an amplifier and sent to free space by the transmitting antenna.

[0010] 5. After the communication antenna receives the signal, the signal is converted from serial to parallel and the cyclic prefix is ​​removed. The OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, thereby achieving de-skewing of the integrated signal and separation of the signal at the communication end and the sensing end.

[0011] 6. In the radar receiver, the signal is reflected by the sensing target and then received by the receiving antenna;

[0012] 7. The received signal is amplified and mixed with the reference signal through a mixer to obtain a de-skewed signal. The de-skewed signal is subjected to FFT processing to obtain the distance information of the detected object. The de-skewed signal is subjected to order search using FRFT to obtain the speed information of the detected object.

[0013] Preferably, in OFDM-LFM modulation and demodulation, the multiplication and addition operations when the data stream is modulated into an OFDM signal are equivalent to IFFT transformation, and are equivalent to FFT operations during demodulation, and the OFDM skewing and deskewing process is achieved by mixing with the LFM signal; due to the additivity of FRFT, the data stream can achieve the effect that can only be achieved by IFFT and mixing with the LFM signal in the traditional method after being transformed by a FRFT of a reasonable order, thereby obtaining an OFDM-LFM signal.

[0014] Preferably, when modulating the OFDM-LFM signal, the two steps of IFFT and LFM signal mixing are integrated, according to The relationship between the angle, order and slope is obtained, and the order p of IDFRFT is decomposed into When the data to be modulated is subjected to p=1-order IDFRFT, it is regarded as an IFFT, and the signal obtained is:

[0015]

[0016] Where t(0≤t≤LT p ) is the duration of the signal, T pis the duration of a symbol, L = 0, 1, 2, ..., ∞, q = 0, 1, 2, ..., N-1, D L Respectively represent the data information carried by the Lth symbol on the qth subcarrier, f q is the frequency of the qth subcarrier;

[0017] After completing OFDM signal modulation, The expression of the OFDM-LFM signal is:

[0018]

[0019] Preferably, in step five, in the receiver during communication, a DFRFT transformation is performed according to the FRFT order in the transmitter during signal demodulation to obtain communication data.

[0020] Preferably, in step seven, the received signal is amplified and then mixed with the reference signal by a mixer to obtain a de-skewed signal. After obtaining a single echo signal, an FFT is completed in the fast time dimension to obtain a range spectrum, and the echo signal is subjected to order detection to obtain the target speed value. Compared with the traditional solution of receiving multiple echoes and performing speed checks in the slow time dimension, the present invention reduces the requirement on the number of echoes.

[0021] On the other hand, to achieve the above purpose, the present invention also provides the following technical solutions: an OFDM-LFM synaesthesia integrated signal waveform receiving device based on fractional Fourier transform, wherein the device implements the OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform when in operation. The present invention realizes the functions of the communication module and radar module of the entire OFDM-LFM synaesthesia integrated system based on FRFT technology.

[0022] The beneficial effects of the present invention are as follows: the present invention proposes a receiver design based on FRFT for an OFDM-LFM synaesthesia integrated signal receiving system, and realizes the separation of an integrated signal communication receiver and a radar receiver by using fractional-order Fourier transform as an OFDM-LFM synaesthesia integrated signal receiver, which not only reduces the number of system modules when modulating and demodulating OFDM-LFM signals in a communication module, but also reduces the requirement for the amount of collected data in a radar module. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flowchart of the OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform;

[0024] Figure 2 It is a time-frequency diagram of OFDM-LFM signal;

[0025] Figure 3 It is the power spectrum density diagram of the OFDM-LFM transmitter;

[0026] Figure 4 It is the time-frequency diagram of the power spectrum of the OFDM-LFM transmitter;

[0027] Figure 5 The figure is a comparison of the bit error rates of OFDM signals based on FFT modulation and OFDM-LFM signals based on FRFT modulation using 4QAM and 16QAM respectively;

[0028] Figure 6 is the distance spectrum of the perception side;

[0029] Figure 7 It is the speed order diagram of the perception side. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] See also Figure 1-Figure 7 The present invention provides a technical solution: an OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform, which can overcome certain or some defects of the prior art. Figure 1 As shown, the method comprises the following steps:

[0032] 1. Generate initial data information flow;

[0033] 2. Map the data stream into QAM symbols;

[0034] 3. After converting the generated QAM symbols from serial data streams into parallel data streams, the parallel data is modulated into OFDM-LFM synaesthesia integrated signals through FRFT and the FRFT order is saved. The modulated symbols are added with cyclic prefixes and converted into serial data;

[0035] 4. After the transmission signal is amplified, it is divided into two paths through a power divider. One path is the radar reference signal, and the other path is amplified by an amplifier and sent to free space by the transmitting antenna.

[0036] 5. After the communication antenna receives the signal, the signal is converted from serial to parallel and the cyclic prefix is ​​removed. The OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, thereby realizing the de-skewing processing of the integrated signal and achieving the function of separating the signal at the communication end and the sensing end;

[0037] 6. In the radar receiver, the signal is reflected by the sensing target and then received by the receiving antenna;

[0038] 7. The received signal is amplified and mixed with the reference signal through a mixer to obtain a de-skewed signal. The distance information of the detected object can be obtained by performing FFT processing on the de-skewed signal. The speed information of the detected object can be obtained by performing order search on the de-skewed signal using FRFT.

[0039] Furthermore, in OFDM-LFM modulation and demodulation, the multiplication and addition operations when the data stream is modulated into an OFDM signal can be equivalent to IFFT transformation, and can be equivalent to FFT operation during demodulation. The OFDM skewing and deskewing process can be achieved by mixing with the LFM signal. Although the subcarrier spacing of OFDM and OFDM-LFM signals is constant, the subcarrier frequency of the OFDM-LFM signal changes linearly. Due to the additivity of FRFT, the data stream can achieve the effect that can only be achieved by IFFT and mixing with the LFM signal in the traditional method after being transformed by a reasonable order of FRFT, thereby obtaining an OFDM-LFM signal.

[0040] Furthermore, in step five, in the receiver during communication, a DFRFT transformation is performed according to the FRFT order in the transmitter during signal demodulation to obtain communication data.

[0041] Furthermore, in step seven, the traditional solution completes an FFT in the fast time dimension after obtaining the de-skewed signal to obtain the distance spectrum, and completes an FFT in the slow time dimension after collecting multiple echoes to obtain the speed spectrum by sensing the initial phase difference of each echo signal. In the present invention, in the radar receiver, the received signal is amplified and mixed with a reference signal by a mixer to obtain a de-skewed signal, and after obtaining a single echo signal, an FFT is completed in the fast time dimension to obtain the distance spectrum. Then, the echo signal is subjected to FRFT order detection to obtain the target speed value. Compared with the traditional solution of receiving multiple echoes and performing speed checks in the slow time dimension, the present invention reduces the requirements for the number of echoes.

[0042] A device for receiving OFDM-LFM synaesthesia integrated signal waveform based on fractional Fourier transform, which implements the OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform when the device is running. The present invention realizes the functions of the communication module and radar module of the entire OFDM-LFM synaesthesia integrated system based on FRFT technology.

[0043] FRFT

[0044] As a generalization of the standard Fourier transform, FRFT can be viewed as a counterclockwise rotation of the signal around the origin in the time-frequency plane. If the Fourier transform of a signal can be viewed as a π / 2 counterclockwise rotation from the time axis to the frequency axis, that is, the u axis, then FRFT can also be viewed as a counterclockwise rotation of an angle α from the time axis to the u axis.

[0045] From the perspective of linear integral transformation, the FRFT expression of the signal x(t) defined in the t domain can be obtained as:

[0046]

[0047] In the formula, K p (u,t)=A p exp[jπ(u 2 Cotα-2utcscα+t 2 cotα)], called the kernel function of FRFT p≠2n, where n is an integer.

[0048] After substitution, the common FRFT expression can be obtained:

[0049]

[0050] Here, an improved DFRFT algorithm is selected. This algorithm satisfies both orthogonality and reversibility, while maintaining the same computational complexity as the algorithm proposed by Ozakatas. The final discrete mathematical expression of DFRFT is:

[0051] X p =F p x (3)

[0052] where F p is the N-dimensional discrete FRFT matrix, whose components are given by:

[0053]

[0054] in

[0055]

[0056] I N×N and J N×N are the N-dimensional unit matrix and the exchange matrix respectively. m,n=0,1,...,N-1, Δu is the time interval. To ensure the reversibility of the algorithm, there is an additional constraint relationship between Δu and Δt:

[0057]

[0058] FRFT Order

[0059] For a single tone signal f(t) = exp(j2πf c t) Doing fractional Fourier transform gives:

[0060]

[0061] It can be seen that after the FRFT transformation, the single tone signal will become an LFM signal with a chirp rate of tanα. Therefore, the relationship between the order and the slope can be obtained:

[0062]

[0063] Simulation and Results

[0064] Since the FRFT order is additive, the IFFT and mixing with the LFM signal can be combined when modulating the OFDM-LFM signal. That is, according to the relationship between the angle, order and slope obtained by equation (7), the IDFRFT order p is decomposed into When the data to be modulated is subjected to p=1-order IDFRFT, it can be regarded as an IFFT, so the signal can be obtained:

[0065]

[0066] Where t(0≤t≤LT p ) is the duration of the signal, T p is the duration of a symbol, L = 0, 1, 2, ..., ∞, q = 0, 1, 2, ..., N-1, D L Respectively represent the data information carried by the Lth symbol on the qth subcarrier, f q is the frequency of the qth subcarrier.

[0067] After completing OFDM signal modulation, Order IDFRFT transform, such as Figure 2 As shown, we can get:

[0068]

[0069] The expression of OFDM-LFM signal is:

[0070]

[0071] By comparing (9) and (10), it can be seen that the OFDM-LFM signal modulated by the present invention differs from the standard form only in the carrier and the initial phase. After a slight correction, quantitative analysis of all functions of the OFDM-LFM signal during reception can be achieved.

[0072] The key parameters of the transmitted OFDM-LFM signal are shown in Table 1.

[0073] Table 1 OFDM-LFM transmission signal parameters

[0074]

[0075] The power spectrum density diagram and time-frequency diagram of the OFDM-LFM transmitter are as follows Figure 3 and Figure 4 shown.

[0076] A. Communication module receiver

[0077] In order to realize the wireless communication function, the signal is modulated through a white noise signal, and the signal is demodulated by DFRFT at the receiving end in reverse order. The bit error rate of the OFDM signal and the OFDM-LFM signal based on FRFT modulation are compared using 4QAM and 16QAM respectively. The OFDM signal is modulated using IFFT, and other parameters remain unchanged. The results are as follows: Figure 5 shown.

[0078] As can be seen in the figure, whether 4QAM modulation or 16QAM modulation is used, in the white noise channel, the bit error rate curves of the two signals used for comparison fit well. Therefore, the OFDM-LFM waveform modulated by the present invention does not deteriorate the communication quality compared with the traditional OFDM waveform under the same conditions.

[0079] B. Radar module receiver

[0080] In order to demonstrate the radar function, a target object with a distance of 2m from the transmitter and a speed of 5m / s is preset. Then the reflected signal received through the white noise channel is mixed with the initial signal. The result is as follows Figure 6 shown.

[0081] Then, the received signal is amplified and mixed with the reference signal to realize the radar de-chirping process. The measured distance result is the difference between the target test and the cable test r0 = 2.06m, which is 3% compared with the preset distance of 2m, which is basically the same as the preset result.

[0082] Continue to search for the order of the de-skewing signal, and the result is as follows: Figure 7 shown.

[0083] The order corresponding to the speed of 5 m / s is 4.24e-8. Here, the speed corresponding to the search order obtained by performing FRFT on the de-skewed signal is 5.304 m / s, with an error of 6%, which is basically the same as the preset result.

[0084] Since the channel currently used is a white noise channel, there is a slight error in the simulation results. When the white noise of the channel is removed, the error of the system is close to 0%.

[0085] The present invention realizes the separation of the integrated signal communication receiver and the radar receiver by using fractional Fourier transform as the OFDM-LFM synaesthesia integrated signal receiver, which not only reduces the number of system modules when modulating and demodulating OFDM-LFM signals in the communication module, but also reduces the requirement for the amount of collected data in the radar module.

[0086] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for receiving OFDM-LFM synaesthesia integrated signal waveform based on fractional Fourier transform, characterized in that: The steps include:

1. Generate initial data information flow; 2. Map the data information stream into QAM symbols; 3. Convert the generated QAM symbols from serial data streams into parallel data streams, then modulate the parallel data into OFDM-LFM synaesthesia integrated signals through FRFT and save the FRFT order, add cyclic prefixes to the modulated symbols, and convert them into serial data; 4. After the transmission signal is amplified, it is divided into two paths through a power divider. One path is the radar reference signal, and the other path is amplified by an amplifier and sent to free space by the transmitting antenna.

5. After the communication antenna receives the signal, the signal is converted from serial to parallel and the cyclic prefix is ​​removed. The OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, thereby achieving de-skewing of the integrated signal and separation of the signal at the communication end and the sensing end.

6. In the radar receiver, the signal is reflected by the sensing target and then received by the receiving antenna; 7. The received signal is amplified and mixed with the reference signal through a mixer to obtain a de-skewed signal. The de-skewed signal is subjected to FFT processing to obtain the distance information of the detected object. The de-skewed signal is subjected to order search using FRFT to obtain the speed information of the detected object.

2. The OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform according to claim 1, characterized in that: In OFDM-LFM modulation and demodulation, the multiplication and addition operations when the data stream is modulated into an OFDM signal are equivalent to IFFT transformation, and are equivalent to FFT operations during demodulation. The OFDM skewing and deskewing process is achieved by mixing with the LFM signal. Due to the additivity of FRFT, the OFDM-LFM signal can be obtained after the data stream is transformed by a FRFT of a reasonable order.

3. The OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform according to claim 1, characterized in that: When modulating OFDM-LFM signals, the two steps of IFFT and LFM signal mixing are integrated. The relationship between the angle, order and slope is obtained, and the order p of IDFRFT is decomposed into When the data to be modulated is subjected to p=1-order IDFRFT, it is regarded as an IFFT, and the signal obtained is: Where t(0≤t≤LT p ) is the duration of the signal, T p is the duration of a symbol, L = 0, 1, 2, ..., ∞, q = 0, 1, 2, ..., N-1, D L Respectively represent the data information carried by the Lth symbol on the qth subcarrier, f q is the frequency of the qth subcarrier; After completing OFDM signal modulation, The expression of the OFDM-LFM signal is:

4. The OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform according to claim 1, characterized in that: In step seven, the received signal is amplified and mixed with the reference signal through a mixer to obtain a de-skewed signal. After obtaining a single echo signal, an FFT is completed in the fast time dimension to obtain the range spectrum. The order detection is performed on the echo signal to obtain the target speed value.

5. An OFDM-LFM synaesthesia integrated signal waveform receiving device based on fractional Fourier transform, characterized in that: When the device is running, the OFDM-LFM synaesthesia integrated signal waveform receiving method based on fractional Fourier transform as described in any one of claims 1 to 4 is implemented.

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