An OFDM-LFM integrated signal waveform receiving method and device based on fractional Fourier transform

Abstract

The application discloses an OFDM-LFM integrated signal waveform receiving method and equipment based on fractional Fourier transform, which combines and improves LFM and OFDM, adopts OFDM-LFM integrated radar communication signals taking orthogonal LFM signals as subcarriers, and has the advantages that, due to the large Doppler tolerance of the LFM subcarriers, compared with sinusoidal subcarriers, the method can not only improve radar range resolution and spectral efficiency, but also has strong ability to avoid Doppler effect, and can reliably transmit information; when receiving OFDM-LFM signals, in order to solve subcarrier frequency linear transformation and radar parameter extraction and other problems, based on the sensitivity of a fractional Fourier transform (FRFT) to LFM signals, the application uses the FRFT as an integrated signal receiver, realizes separation of an integrated signal communication receiver and a radar receiver, reduces the complexity of the system, and improves the system performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated sensing and communication, and in particular to an OFDM-LFM integrated sensing and communication signal waveform receiving method and device based on fractional Fourier transform. BACKGROUND

[0002] The next generation of communication technology (such as B5G (Beyond 5G) and 6G) has been regarded as a key driving factor in many emerging fields. Among many forward-looking assumptions for B5G / 6G technology, one important direction is to integrate radar and communication in one system due to radar and communication spectrum overlap, etc. It can be foreseen that it is necessary to integrate the two services in B5G / 6G technology, which has stimulated recent research on integrated sensing and communication (ISAC).

[0003] For the design of integrated sensing and communication scheme, many schemes have been proposed to solve the key problems of signal sharing design in radar communication. When radar and communication signals both use linear frequency modulation (LFM) waveforms, it cannot meet the demand of transmitting a large amount of data. In recent years, orthogonal frequency division multiplexing (OFDM) has been introduced into the integration of radar and communication due to its high spectral efficiency, robustness against fading and multipath propagation effects, etc. However, the integrated device has problems such as an increase in the number of system modules and a requirement for the amount of collected data, linear transformation of subcarrier frequency and radar parameter extraction, etc. Therefore, a new method and technology are needed to solve the above problems. SUMMARY

[0004] To solve the problems in the prior art, the present application provides an OFDM-LFM integrated sensing and communication signal waveform receiving method and device based on fractional Fourier transform, which combines and improves LFM and OFDM, uses OFDM-LFM integrated radar communication signals with orthogonal LFM signals as subcarriers. Since the LFM subcarriers have a large Doppler tolerance, compared with sinusoidal subcarriers, this method not only improves the radar range resolution and spectral efficiency, but also has strong ability to avoid Doppler effect, and can reliably transmit information. In order to solve the problems of subcarrier frequency linear transformation and radar parameter extraction, etc. in receiving OFDM-LFM signals, based on the sensitivity of LFM signals to fractional Fourier transform (FRFT), the present application uses FRFT as an integrated signal receiver, which can demodulate OFDM-LFM signals at the communication end while reducing the requirement for the amount of collected data at the radar end, solving the problems mentioned in the background technology.

[0005] To achieve the above purpose, the present application provides the following technical scheme: an OFDM-LFM integrated sensing and communication 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 a serial data stream into a parallel data stream, then modulate the parallel data into an OFDM-LFM integrated signal through FRFT and preserve the FRFT order, add a cyclic prefix 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 splitter. 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, it performs serial-to-parallel conversion and removes the cyclic prefix. The OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, thereby de-skewing the integrated signal and achieving signal separation at the communication end and the sensing end.

[0011] 6. In the radar receiver, the signal is reflected by the 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. 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 passing through a FRFT transformation 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 a p=1-order IDFRFT, it is considered as an IFFT, and the resulting signal 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 the OFDM signal modulation, the DFRFT transform is performed again The expression of the OFDM-LFM signal is as follows:

[0018]

[0019] Preferably, in step five, the DFRFT transform is performed according to the FRFT order in the transmitter when the signal is demodulated in the receiver in the communication, and the communication data can be obtained.

[0020] Preferably, in step seven, the received signal is mixed with a reference signal through a mixer after amplification to obtain a dechirped signal, and the order detection is performed on the echo signal when the distance spectrum is obtained by performing the FFT on the echo signal in the fast time dimension, and the target speed value can be obtained. Compared with the traditional scheme of receiving multiple echoes and performing the speed check in the slow time dimension, the number of echoes required by the present application is reduced.

[0021] In addition, to achieve the above object, the present application also provides the following technical scheme: an OFDM-LFM communication and sensing integrated signal waveform receiving device based on a fractional Fourier transform, which realizes the OFDM-LFM communication and sensing integrated signal waveform receiving method based on the fractional Fourier transform when in operation. The present application realizes the functions of the communication module and the radar module of the entire OFDM-LFM communication and sensing integrated system based on the FRFT technology.

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

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

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

[0025] Figure 3 Power spectrum density diagram for OFDM-LFM transmitter end;

[0026] Figure 4 Power spectrum time-frequency diagram for OFDM-LFM transmitter end;

[0027] Figure 5 Bit error rate comparison diagram for FFT modulation based OFDM signal and FRFT modulation based OFDM-LFM signal using 4QAM and 16QAM respectively;

[0028] Figure 6 Distance spectrum diagram for sensing side;

[0029] Figure 7 Velocity order diagram for sensing side. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be apparently and completely described below with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those of ordinary skill in the art without any creative work belong to the protection scope of the present application.

[0031] Please refer to Figures 1-7 , the present application provides a kind of technical solutions: a kind of OFDM-LFM integrated sensing signal waveform receiving method based on fractional fourier transform, it can overcome certain or some defects of prior art. As Figure 1 Shown, the method comprises the following steps:

[0032] I. generating initial data information stream;

[0033] II. mapping data stream into QAM symbol;

[0034] III. after the generated QAM symbol is converted from serial data stream into parallel data stream, parallel data is modulated into OFDM-LFM integrated sensing signal by FRFT and FRFT order is saved. After modulated symbol is added to cyclic prefix, it is converted into serial data;

[0035] IV. after signal amplification, it is divided into two ways by power divider, one way is radar reference signal, another way is amplified by amplifier and sent to free space by transmitting antenna;

[0036] V. After receiving the signal by the communication antenna, the signal is converted from serial to parallel, the cyclic prefix is removed, and the OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, so as to realize the desloping of the integrated signal, and achieve the separation of the signal at the communication end and the sensing end;

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

[0038] VII. After the received signal is amplified, the desloped signal is obtained by mixing the signal with a reference signal through a mixer, and the distance information of the detected object can be obtained by performing FFT on the desloped signal. The speed information of the detected object can be obtained by searching the order of the FRFT on the desloped signal.

[0039] Further, in the 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 the demodulation can be equivalent to FFT operation. The OFDM desloping process can be realized by mixing the signal with an LFM signal. Although the subcarrier spacing of the OFDM and OFDM-LFM signals is unchanged, the subcarrier frequency of the OFDM-LFM signal is linearly changed. Since the FRFT is additive, the data stream can be transformed by a reasonable order of FRFT to realize the effect that can be realized only by IFFT and mixing with an LFM signal in the traditional method, so as to obtain the OFDM-LFM signal.

[0040] Further, in step V, in the communication receiver, the communication data can be obtained by performing DFRFT transformation according to the order of the FRFT in the transmitter when the signal is demodulated.

[0041] Further, in step VII, in the traditional scheme, the distance spectrum can be obtained by performing FFT in the fast time dimension after obtaining the desloped signal, and the velocity spectrum can be obtained by performing FFT in the slow time dimension after collecting multiple echoes and sensing the initial phase difference of each echo signal. In the present application, in the radar receiver, the desloped signal is obtained by mixing the received signal with a reference signal through a mixer after the received signal is amplified, and the distance spectrum can be obtained by performing FFT in the fast time dimension after obtaining a single echo signal. The target speed value can be obtained by performing FRFT order detection on the echo signal. Compared with the traditional scheme of receiving multiple echoes and performing velocity detection in the slow time dimension, the present application reduces the requirement for the number of echoes.

[0042] An OFDM-LFM all-in-one signal waveform receiving device based on fractional Fourier transform, which realizes the OFDM-LFM all-in-one signal waveform receiving method based on fractional Fourier transform when in operation.

[0043] FRFT

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

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

[0046]

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

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

[0049]

[0050] Here, an improved DFRFT algorithm is selected. The algorithm meets the orthogonality and reversibility, and at the same time, maintains the same computational complexity as the algorithm proposed by Ozakatas. Finally, the discrete mathematical expression of DFRFT is obtained as follows:

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

[0052] Where F p is an N-dimensional discrete FRFT matrix, and its components are obtained as follows:

[0053]

[0054] Where

[0055]

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

[0057]

[0058] FRFT order

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

[0060]

[0061] It can be seen that after the FRFT transform, the single-tone signal becomes an LFM signal with a chirp rate of tanα. Therefore, the relationship between order and 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 formula (7), the IDFRFT order p is decomposed into When the data to be modulated is subjected to a 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 Represents 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] As can be seen from the comparison of (9) and (10), the OFDM-LFM signal modulated by the application and the standard form only differ in the carrier and initial phase, and after slight modification, the quantitative analysis of the full function of the OFDM-LFM signal at the receiving time can be realized.

[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 OFDM-LFM transmission end power spectrum density diagram and time-frequency diagram are shown in Figure 3 and Figure 4 .

[0076] A. Communication module receiver

[0077] In order to realize the wireless communication function, after the signal is modulated, it passes through the white noise signal, and at the receiving end, the DFRFT is used to demodulate the signal with the inverse order, and the 4QAM and 16QAM are used respectively to compare the bit error rate of the OFDM signal and the OFDM-LFM signal based on the FRFT modulation, wherein the OFDM signal uses the IFFT modulation, and other parameters remain unchanged, and the result is shown in Figure 5 .

[0078] As can be seen from the figure, whether using 4QAM modulation or 16QAM modulation, in the white noise channel, the bit error rate curve fitting of the two signals for comparison is good. Therefore, the OFDM-LFM waveform modulated by the application does not appear to deteriorate the communication quality under the same conditions compared with the traditional OFDM waveform.

[0079] B. Radar module receiver

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

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

[0082] The order search is continued on the de-chirped signal, and the result is shown in Figure 7 .

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

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

[0085] The application uses the fractional Fourier transform as an OFDM-LFM integrated signal receiver, realizes the separation of the integrated signal communication receiver and the radar receiver, reduces the system module number when modulating and demodulating the OFDM-LFM signal in the communication module, and reduces the requirement for the collected data amount in the radar module.

[0086] Although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements for part of the technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for receiving OFDM-LFM synaesthesia integrated signal waveform based on fractional-order 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 a serial data stream into a parallel data stream, then modulate the parallel data into an OFDM-LFM integrated signal through FRFT and preserve the FRFT order, add a cyclic prefix to the modulated symbols, and convert them into serial data; 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 p1 of IDFRFT is decomposed into When performing a first-order IDFRFT on the data to be modulated, it is regarded as an IFFT, and the resulting signal 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 Represents 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, do Order IDFRFT transformation; the expression of the OFDM-LFM signal is:

4. After the transmission signal is amplified, it is divided into two paths through a power splitter. 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, it performs serial-to-parallel conversion and removes the cyclic prefix. The OFDM-LFM received signal is demodulated according to the order of the FRFT at the transmitting end, thereby de-skewing the integrated signal and achieving signal separation at the communication end and the sensing end.

6. In the radar receiver, the signal is reflected by the 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 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 echo signal is then subjected to order detection to obtain the target speed value.

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