CN116418644B

CN116418644B - ISAC method, equipment and network based on orthogonal multi-carrier FSCM signal

Info

Publication number: CN116418644B
Application number: CN202310315897.6A
Authority: CN
Inventors: 李烁; 胡宏耀; 李自蹊; 周定岳; 陈立; 刘定泉
Original assignee: Changsha University of Science and Technology
Current assignee: Changsha University of Science and Technology
Priority date: 2023-03-29
Filing date: 2023-03-29
Publication date: 2025-09-09
Anticipated expiration: 2043-03-29
Also published as: CN116418644A

Abstract

The present invention discloses an ISAC method, device, and network based on orthogonal multi-carrier FSCM signals. For any ISAC device in the ISAC network, the following steps are implemented: (1) frequency-shift chirp modulation is performed on the communication symbols of a data stream to generate and transmit an orthogonal multi-carrier FSCM signal; (2) echo signals reflected from each target in a multi-target scenario are received and processed to achieve real-time detection of the target; the echo signals reflected from the targets are orthogonal multi-carrier FSCM signals; and (3) orthogonal multi-carrier FSCM signals transmitted by other ISAC devices in the ISAC network are received, and the received signals are demultiplexed and demodulated to achieve communication between the ISAC devices. The present invention achieves the integration of communication and perception without sacrificing communication and perception performance.

Description

ISAC method, equipment and network based on orthogonal multi-carrier FSCM signal

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to an ISAC method, equipment and a network based on orthogonal multi-carrier FSCM signals.

Background

As the number of wireless communication devices has shown an explosive growth trend, the demand for wireless spectrum by the global communication industry is becoming increasingly stringent. This makes it even more urgent to explore additional spectrum resources. To alleviate this contradiction, in future B5G and 6G scenarios, the communication system will explore the feasibility of co-existence with other electronic devices in the same frequency band.

The conventional multiplexing method separates communication and radar sensing, such as (1) a design centered on radar (2) a design centered on communication. Radar-centric designs are intended to implement communication functions in radar systems, typically embedding information into FMCW radar signals. However, the communication symbol rate of an FMCW signal corresponds to its Chirp rate, which is typically an order of magnitude lower than the symbol rate achieved by a dedicated communication system having the same bandwidth. Many communication-centric designs use IEEE 802.11 signals, and IEEE 802.11 compliant OFDM signals are also used to implement sensing functions in a vehicle network, but the randomness of the communication data results in a higher peak-to-average power ratio and random autocorrelation characteristics, which reduces the sensing accuracy of the system. Exploring communication and perception in higher frequency bands, such as millimeter wave bands, can make hardware devices expensive to manufacture, and their perceived distance can be reduced due to wavelength effects.

Disclosure of Invention

The invention provides an ISAC method, equipment and a network based on orthogonal multi-carrier FSCM signals, which realize communication and perception integration on the premise of not losing communication and perception performances.

In order to achieve the technical purpose, the invention adopts the following technical scheme:

An ISAC method based on orthogonal multi-carrier FSCM signals for any ISAC device in an ISAC network:

(1) Performing frequency shift chirp modulation on communication symbols of the data stream to generate orthogonal multi-carrier FSCM signals and transmitting the signals;

(2) Receiving and processing echo signals reflected by each target in a multi-target scene to realize real-time detection of the target, wherein the echo signals reflected by the targets are orthogonal multi-carrier FSCM signals,

(3) Orthogonal multi-carrier FSCM signals transmitted by other ISAC devices in an ISAC network are received, and the received signals are demultiplexed and demodulated to achieve communication between ISAC devices.

Further, in frequency-shifting chirp modulation of the communication symbols, different spreading factors are used for modulation in each channel of the transmitter.

Further, the method for modulating by adopting different spreading factors comprises the following steps:

Adding a carrier frequency offset f _offset,f_offset to the subcarrier FSCM signal is given by the following definition:

Wherein, B is the bandwidth, SF is a spreading factor, i.e., the number of modulation bits per communication symbol, t _s is the period time per communication symbol, S is the communication symbol;

In the folding time As a boundary, a communication symbol S is expressed as two parts, expressed by the following formula:

Wherein k is the slope of the frequency variation, x _T (t) is the transmitting end FSCM signal obtained by embedding the communication symbol S;

The discrete form of the FSCM signal obtained by sampling the xT (t) of the embedded communication symbol S is represented by the following formula:

where N is the sampling sequence, f _s is the sampling frequency, a single bandwidth is used, N ₁＝{0,...,n_fold-1},N₂＝{n_fold,...,2^SF -1, and N _fold＝t_fold·f_s.

Further, each ISAC device transmits and receives signals using MIMO antennas, and each ISAC device is provided with a plurality of transmitting antennas and a plurality of receiving antennas, each corresponding to a plurality of different spreading factors.

Further, the processing of the echo signal comprises demultiplexing the received orthogonal multi-carrier FSCM signal, and the specific demultiplexing comprises:

Let the received orthogonal multi-carrier FSCM signal be expressed as:

Y=A(θ)x+v

Where v is additive zero-mean time white noise with covariance R _z;

Firstly, generating a corresponding reference signal g _i (t) in each channel of a receiver according to a corresponding spreading factor SF, wherein the reference signal is in the form of an FSCM signal with a carrier frequency offset f _offset of 0;

Then, in each channel, the received orthogonal multi-carrier FSCM signal Y (t) is multiplied by the conjugate of the reference signal g _i (t), and the FSCM subcarrier x _R,i (t) corresponding to each channel is extracted:

the covariance matrix of the extracted sub-carriers of the received signals is expressed as:

Wherein R _Y,i and R _N represent covariance matrices of the received signal and the noise signal, respectively;

Assuming that the noise signal is continuous, performing feature decomposition on the covariance matrix R to obtain M feature values of R arranged in descending order, and deforming R into the following formula:

Where Λ _S is a diagonal matrix of K eigenvalues η ₁,η₂,η₃,...,η_K of matrix R, Y _S is a signal subspace of K corresponding eigenvectors, Λ _n is a diagonal matrix of M-K eigenvalues, and Y _n is a subspace of M-K eigenvalues.

Further, the processing of the echo signal further includes performing target detection by using the obtained subcarriers, specifically:

Firstly, selecting an FSCM subcarrier with the largest spreading factor SF corresponding to a channel, setting the sampling frequency f _s to be equal to the bandwidth B corresponding to the spreading factor SF of the channel, namely, f _s =B, and sampling to obtain an FSCM discrete signal as follows:

Wherein, the Is the maximum spreading factor the FSCM discrete signal within the SF _max channel, phi represents the phase of the received FSCM discrete signal Y _i [ N ], k is the slope of the frequency variation, N is the sample sequence, N ₁＝{0,...,n_fold-1},N₂＝{n_fold,...,2^SF -1, N is the union of N ₁ and N ₂, and N _fold＝t_fold·f_s,f_s is the sample frequency, t _fold is the folding time of the FSCM symbol representation in two parts,B is the bandwidth of the optical fiber,S is the communication symbol in the data stream, n' is the delay of the signal at discrete times;

the FSCM subcarrier is then mixed using a standard chirp signal of the same slope, resulting in an intermediate frequency signal f _IF (t):

Wherein, T n represents the standard chirp signal of slope k ₀, represents conjugate operation, and intermediate frequency f _IF＝-k₀ n' is the phase of intermediate frequency signal obtained by mixing the received signal with the reference signal;

And finally, adopting a CZT algorithm to process f _IF (t) to finish the estimation of the distance and the speed of the target, and adopting a MUSIC algorithm and a spectral peak searching method to estimate the arrival angle, wherein the expression is as follows:

Where θ _MUSIC represents the estimated angle of arrival, a (θ) represents the transmit receive matrix, which is the product of the transmit steering matrix and the transpose of the receive steering matrix.

Further, the received signals are demultiplexed and demodulated, wherein the demodulation is to demodulate the FSCM sub-carriers in each channel respectively, specifically based on the principle of coherent demodulation, a down-chirp signal with the same spreading factor value as that in the modulated signals is used as a reference signal for demodulation, and the demodulation operation in the ith channel is as follows:

Wherein, the Representing a conjugate version of the discrete reference signal x _ref,i n, the communication symbol S corresponds to the maximum sequence number after the FFT operation.

An ISAC device based on an orthogonal multi-carrier FSCM signal, comprising a transmitter and a receiver;

The transmitter carries out frequency shift chirp modulation on communication symbols of the data stream, generates orthogonal multi-carrier FSCM signals and transmits the signals;

The receiver receives and processes the echo signals reflected by each target in the multi-target scene to realize real-time detection of the targets, wherein the echo signals reflected by the targets are orthogonal multi-carrier FSCM signals,

The receiver also receives orthogonal multi-carrier FSCM signals transmitted by other ISAC devices in the ISAC network, and demultiplexes and demodulates the received signals to enable communication between the ISAC devices.

Further, the ISAC device is configured to implement an ISAC method based on an orthogonal multi-carrier FSCM signal according to any one of the above embodiments.

An ISAC network based on an orthogonal multi-carrier FSCM signal comprising a number of ISAC devices based on an orthogonal multi-carrier FSCM signal as claimed in any one of the preceding claims.

Advantageous effects

The invention provides a brand-new communication perception integrated method, equipment and a network, which realize high-precision perception of environmental targets, communicate among different equipment, and do not lose any performance of communication and perception. Wherein, the

(1) A low sampling rate method is proposed, i.e. the sampling frequency is set equal to the bandwidth B corresponding to the SF of the channel, i.e. f _s =b, and the FSCM signal can be simplified mathematically to a standard chirp signal and carries the communication symbol S. The operation eliminates the problem of false alarm when FSCM signals are directly mixed for sensing, reduces the calculation complexity and improves the sensing precision of the system.

(2) By applying fractional Fourier transform and under the premise of ensuring the sensing precision of the system, the communication rate is greatly improved by constructing an orthogonal multi-carrier FSCM signal.

(3) By combining with the MIMO technology and utilizing the orthogonal FSCM signal, the system reliability and the capacity of resisting multipath fading are improved by a fractional Fourier domain multiplexing mode under the condition of not improving the antenna radiation power, and the antenna pattern design of the system is more flexible.

Drawings

FIG. 1 is a communication awareness integrated network;

fig. 2FSCM signal is directly mixed with reference signal in time domain and time-frequency domain;

FIG. 3 illustrates a comparison of target detection results before and after eliminating false alarm problems;

fig. 4 time-frequency domain of an orthogonal multi-carrier FSCM signal.

Fig. 5 orthogonal multi-carrier FSCM signal frame format;

The signal reception model of the array antenna of fig. 6;

FIG. 7is an ISAC device orthogonal multi-carrier FSCM signal demultiplexing process;

FIG. 8ISAC device-object awareness process;

fig. 9ISAC device two frequency shift chirp demodulation process;

fig. 10 perception results of orthogonal four-carrier FSCM signals;

FIG. 11 illustrates communication error rates of orthogonal four-carrier FSCM signals under different signal-to-noise conditions;

Detailed Description

The following describes in detail the embodiments of the present invention, which are developed based on the technical solution of the present invention, and provide detailed embodiments and specific operation procedures, and further explain the technical solution of the present invention.

Example 1

The present embodiment provides an ISAC method based on orthogonal multi-carrier FSCM signals, which is applied to a communication and sensing integrated network as shown in fig. 1, for any ISAC device in the ISAC network:

Example 2

The embodiment provides an ISAC device based on an orthogonal multi-carrier FSCM signal, which comprises a transmitter and a receiver;

Example 3

This embodiment provides an ISAC network based on orthogonal multi-carrier FSCM signals, comprising the ISAC device described in embodiment 2 above.

The ISAC device in any of the above embodiments may be improved over an existing communication device or radar device, where the required carrier frequency is 915MHz, the maximum bandwidth is 51.2MHz, two transmit antennas and two receive antennas are each used, the orthogonal multi-carrier FSCM signal defines a scan time of 20us, and the spreading factor of each channel may be {4,5,6,7,8,9,10,11,12}. As shown in the ISAC network scene in FIG. 1, the ISAC network scene comprises a plurality of object targets and two ISAC devices, each ISAC device can be used as a transmitting end or a receiving end, and the communication and perception dual functions can be realized.

In the experimental scene, the ISAC equipment firstly transmits orthogonal multi-carrier FSCM signals and processes echo signals of targets in the scene to realize real-time detection of the targets. The second ISAC device receives the orthogonal multi-carrier FSCM signal, demultiplexes and demodulates the signal to enable communication between the ISAC devices. Specifically:

step one, constructing orthogonal multi-carrier MIMO-FSCM waveform and frame format

Frequency Shift Chirp Modulation (FSCM) is a long range, low power consumption communication modulation technique based on a chirp signal in which the communication symbols S are encoded in a constant slope (CHIRP RATE) chirp signal by means of a frequency offset. In FSCM techniques, the symbol S is embedded in the chirp waveform by adding a carrier frequency offset (carrier frequency offset) f _offset,f_offset to the waveform, given by the following definition:

In the folding time As a boundary, an FSCM symbol can be represented in two parts, expressed as:

Wherein bandwidth B is

SF is a spreading factor, i.e., the number of modulation bits per symbol, and is typically {4,5,6,7,8,9,10,11}. f _offset is the carrier frequency, k is the slope of the frequency change, and the FSCM signal discrete form is shown as follows:

Where N is the sampling sequence, f _s is the sampling frequency, N ₁＝{0,…,v_fold-1},N₂＝{n_fold,…,2^sF -1, and N _fold＝t_fold·f_s. Compared with the traditional sine modulation mode, the FSCM signal with the spread spectrum and frequency hopping properties not only inherits the excellent characteristics of the chirp signal, but also has better anti-interception performance. The dual-function requirements of communication and perception can be achieved simultaneously, and thus can be used as the basic waveform of an ISAC system, but the communication rate of the waveform only corresponds to the chirp rate of the waveform, and is usually an order of magnitude lower than the symbol rate achieved by a communication system under the same bandwidth.

Because of the discontinuous phase of the FSCM signal, mixing the FSCM signal directly with the reference signal presents high frequency components, and is subject to false alarm problems, and the Carrier Frequency Offset (CFO) of the FSCM waveform is determined by the communication symbol, with randomness. Therefore, it is difficult to set appropriate filter parameters since the frequency range of the interference is not known. To solve this problem, by establishing and analyzing the FSCM signal model, when a complex baseband structure is adopted and the sampling frequency is lower than the nyquist (the nyquist is usually 2 times of bandwidth, and the bandwidth is 1 time in the present embodiment), the mathematical model of the FSCM can be simplified to Chirp, and the interference caused by the frequency discontinuity is eliminated. In fig. 2, the FSCM signal is directly mixed with the reference signal to form a time domain and a time-frequency domain, which can be seen that a period of high-frequency components are included in the signal, and fig. 3 is a comparison of target detection results before and after the false alarm problem is eliminated.

However, although the autocorrelation and spectral characteristics of the FSCM signal are good, the communication efficiency is low. The communication efficiency of the system can be improved by introducing the idea of OFDM multi-carrier multiplexing. However, the multicarrier technique requires subcarriers to be orthogonal to each other, so the core problem of FSCM multicarrier is how to select the appropriate orthogonal basis and construct orthogonal subcarriers. To cope with this problem, the key of FSCM orthogonal multi-carrier communication is that the subcarriers do not interfere with each other, so that it is necessary to construct FSCM subcarrier signals orthogonal to each other. The orthogonality of the FSCM waveforms in the time-frequency domain is demonstrated using a fractional fourier transform (FrFT) followed by constructing an FSCM orthogonality basis to create a set of orthogonal multi-carrier FSCM signals. Fig. 4 is a time-frequency domain image of an orthogonal multi-carrier FSCM signal.

FrFT can be seen as the rotation of a vector by any angle in the time-frequency domain. The different N frequency modulated chirp signals can be seen as a chirp base signal rotated N angles in the a-u plane. The definition of the h-order fractional fourier transform (FrFT) of the signal x (t) is as follows:

Wherein F ^h is the operation operator of FrFT, and the rotation angle of the signal in the time-frequency domain K _h (t, u) is the transform kernel of the FrFT, defined as:

The fractional Fourier transform can analyze and process signals in a fractional Fourier transform domain between a time domain and a frequency domain, and breaks through the limitation of the traditional Fourier analysis.

The FSCM signals with different slopes are obtained through the fractional Fourier transform structure, and then autocorrelation is carried out on any two FSCM signals with different slopes, so that the result is as follows:

Wherein, psi _p (t) and psi _q (t) represent FSCM signals with any two different slopes, Representing the conjugate of the signal ψ _q (t), it can be seen that the FSCM signals of different slopes are orthogonal to each other in the time-frequency domain.

In the method provided by the invention, firstly, an ISAC device generates an FSCM orthogonal subcarrier group in each channel of a transmitter by frequency shift chirp modulation, and the pulse time is 20us due to different spreading factors in each channel, according to the formula:

therefore, the slopes k of the FSCM subcarriers generated by the channels are different and mutually orthogonal.

The sub-carriers of each channel are then superimposed in the transmitter by an adder and transmitted. Fig. 5 depicts a constructed form of an orthogonal multi-carrier FSCM signal frame format in the time-frequency domain, comprising three parts, a preamble, a header, and a payload, wherein the preamble comprises three parts, a variable preamble, a synchronization word, and a frequency synchronization.

In the past research, it has been found that the MIMO technology can improve the degree of freedom of system design, and the antenna pattern design is more flexible, so as to better realize target distance, speed, angle estimation, etc. under low signal-to-noise ratio. Meanwhile, the MIMO technology can also improve the channel capacity limit, the system communication rate and the reliability can be improved, and the MIMO radar model and the MIMO communication model have more common points in mathematical expression. Therefore, in order to further enhance the sensing and communication performance of the ISAC system, the preferred embodiment of the present invention further enhances the dual-function performance of communication and sensing by utilizing the MIMO antennas in the current communication device and radar sensing device. The method of transmitting and receiving orthogonal multi-carrier FSCM signals using MIMO antennas is simply referred to as MIMO-FSCM method.

In the MIMO-FSCM method, data streams of all branch channels are modulated by FSCM and then transmitted through corresponding antennas, and are overlapped on each antenna in a two-carrier mode, and then transmitted through the MIMO antennas, namely the corresponding FSCM signal spreading factors on each antenna are {3/4}, {5/6}, {7/8}, and {9/10}. In this way, the eight-carrier FSCM sensing communication integration can be realized on four antennas, and the transmission signals among the antennas are mutually orthogonal, so that the dual-function performance is not greatly affected.

It is assumed that each array element transmits mutually orthogonal signals x as shown in the following equation:

Where x _i(n),i∈{1,2,...,N_t is the signal in the ith transmit antenna, N _t is the number of transmit antennas, then the echo signal at the target at azimuth angle θ ₀ is:

In the above-mentioned method, the step of, Let Kronecher be the product, ζ=e _s η be the amplitude of each array element received signal after passing through the matched filter, η be the transmission loss of the signal, v be the received noise vector of dimension N _tN_r, and N _r be the number of receiving antennas. α _T(θ₀) and α _R(θ₀) are respectively a transmission steering vector and a reception steering vector of the MIMO radar, and the specific forms are:

Wherein, the AndThe phase difference in space between each transmitting array element and between receiving array elements is represented, λ is the wavelength, d _T is the spacing between the transmitting antenna array elements, d _R is the spacing between the receiving antenna array elements, and then the N _tN_r -dimensional equivalent guide matrix of the MIMO array is:

That is, the output of the transmit and receive beam of the MIMO-FSCM aware communication integrated system is that y=a ^Hx+v,(·)^H represents the conjugate transpose of the vector.

Step two, demultiplexing orthogonal multi-carrier MIMO-FSCM signals by ISAC device one and device two receivers

The signal reception model of the array antenna is shown in fig. 6. A set of uniform linear arrays of 4 antenna elements is used to receive the signal.

After the ISAC device receives the orthogonal multi-carrier FSCM signal in the channel on the MIMO antennas, the form is as follows:

Y=A(θ)x+v

Where v is additive zero mean time white noise with covariance R _z, and then the FSCM orthogonal multi-carrier signal is demultiplexed using the FrFT method. The method is specifically operated by generating a corresponding reference signal g _i (t) in each channel of the receiver according to a corresponding SF, wherein the reference signal is in the form of an FSCM signal with carrier frequency offset f _offset of 0 and same slope as the sub-carrier. The received orthogonal multi-carrier FSCM signal Y (t) is then multiplied by the conjugate of the reference signal g _i (t) within each channel:

the FSCM subcarrier corresponding to the channel SF can be extracted, and the flow is shown in fig. 7.

The extracted subcarrier signals are evaluated with covariance matrices to demonstrate the interference immunity of the received signals, wherein the covariance matrices of the extracted received signal subcarriers can be expressed as:

And R _N represents covariance matrices of the received subcarrier signal and the noise signal, respectively. Assuming that the noise signal is continuous, the covariance matrix R is subjected to feature decomposition, so that M feature values of R arranged in descending order can be obtained, and R can be deformed into the following formula:

Λ _S in the above equation is a diagonal matrix composed of K eigenvalues η ₁,η₂,η₃,...,η_K of the matrix R, and Y _S is a signal subspace composed of K corresponding eigenvectors. Λ _n is a diagonal matrix of M-K eigenvalues, _Y n is a subspace of eigenvectors corresponding to M-K eigenvalues.

The ISAC equipment firstly carries out high-precision estimation on a target in a radar channel;

after extracting the subcarrier, the ISAC equipment selects the FSCM subcarrier with the largest channel corresponding to SF And (5) performing sensing processing. Because the FSCM signal has the problem of discontinuous phase, the direct adoption of a radar processing algorithm to mix the FSCM with a reference signal can lead to the false alarm problem. To solve this problem, the method sets the sampling frequency f _s to be equal to the bandwidth B corresponding to the SF of the channel, i.e., f _s =b, and the FSCM discrete signal can be simplified as follows:

Thus, the FSCM signal can be mathematically reduced to a standard chirp signal and carries the communication symbol S. The operation can eliminate the false alarm problem caused by direct mixing of FSCM signals and improve the perception precision of the system. The FSCM subcarrier is then mixed using a standard chirp signal of the same slope, resulting in an intermediate frequency signal f _IF (t):

Where T ^* n represents the conjugate of the slope of the standard chirp signal and the intermediate frequency f _IF = -k0n ', n' is the delay of the signal in discrete time. And finally, adopting a CZT algorithm to process f _IF (t) (refer to 'spectral analysis comparison of ZFFT and Chirp-Z transformation refinement and band selection' published by Ding Kang et al), and then carrying out high-precision estimation on the distance speed of the target. And estimating an arrival angle by using a MUSIC algorithm (refer to "DOA estimation performance of correction MUSIC algorithm on related signal sources" published by He Zishu et al) and a spectral peak search method (i.e. finding a peak value in a frequency spectrum after CZT refinement treatment, which is a frequency value of a corresponding target), wherein the expression is as follows:

Fig. 8 is a flow chart of processing a target echo by a device.

The method adopts a low sampling rate mode, can reduce the operation time of the system, improves the operation speed, and eliminates the false alarm problem caused by the discontinuous FSCM phase. Meanwhile, as the FSCM signal bandwidth with the largest SF is higher, the high accuracy of target distance sensing is ensured.

And step four, the ISAC equipment II demodulates the FSCM sub-carrier in the communication channel to restore the communication information.

The fourth step and the third step are respectively developed in two different devices, and the step sequence is not sequential.

And step two, after the subcarrier demultiplexing operation of the step two, the ISAC equipment obtains FSCM subcarriers corresponding to SF in each channel. The FSCM is then demodulated in each channel. The demodulation process is based on the concept of coherent demodulation, using a down-chirp signal having the same value as the SF of the modulated signal as a reference signal for demodulation, whose (CF 0) is 0, and the specific flow is shown in fig. 9. The demodulation operation in the i-th channel is as follows:

Wherein the method comprises the steps of Representing a conjugate version of the discrete reference signal x _ref n, the communication symbol S corresponds to the maximum sequence number after the FFT operation, and the particular flow is shown in fig. 9. This algorithm has lower computational complexity than incoherent demodulation.

The invention provides an ISAC method, equipment and a network based on orthogonal multi-carrier FSCM signals, which solve the problem of current spectrum congestion, realize remote sensing, adopt a multi-carrier communication scheme and ensure communication reliability.

Simulation experiments were performed using Zedboard software radio, the parameters are shown in table 1:

Table 1 simulation experiment parameters

The invention adopts a low sampling rate method, eliminates the problem of false alarm when FSCM signals are directly mixed, and reduces the calculation complexity. Fig. 10 shows the sensing result of the orthogonal four-carrier FSCM signal, and the sensing error can be as low as 10cm when the highest spreading factor is 10.

The invention applies fractional Fourier transform, provides an orthogonal multi-carrier MIMO-FSCM signal group, greatly improves the communication rate and has higher communication reliability. When the spreading factor is {3/4,5/6,7/8,9/10}, the communication rate of the orthogonal multi-carrier MIMO-FSCM signal group can reach 89.2Mbps, and as the spreading factor is increased, the communication rate is multiplied, and when the signal-to-noise ratio is 0dB, the error rate can reach 10 ^-4. Fig. 11 shows the communication error rate of the orthogonal four-carrier FSCM signal under different signal-to-noise ratios.

The above embodiments are preferred embodiments of the present application, and various changes or modifications may be made thereto by those skilled in the art, which should be construed as falling within the scope of the present application as claimed herein, without departing from the general inventive concept.

Term interpretation:

ISAC-communication and awareness integration refers to a method of integrating a communication device and an awareness device into the same system and seeking trade-offs and gains from each other between them. In ISAC systems, both communication and perception functions are no longer considered separate goals, but are designed together for reciprocity and reciprocity, so ISACs can greatly improve spectrum and energy efficiency while reducing hardware and signal costs.

FMCW radar, frequency modulated continuous wave radar (FMCW RADAR), refers to continuous wave radar that emits frequencies modulated by a particular signal, such as weather radar. The frequency modulation continuous wave radar obtains the distance information of the target by comparing the difference method between the echo signal frequency at any moment and the frequency of the transmitting signal at the moment, and the distance is proportional to the frequency difference of the echo signal frequency and the frequency of the transmitting signal at the moment. The radial velocity and distance of the target can be obtained by processing the measured frequency difference between the two. Compared with other range and speed measuring radars, the frequency modulation continuous wave radar has simpler structure. The FMCW radar has the advantages of relatively abundant technical experience, relatively low required transmitting power peak value, easy modulation, low cost and simple signal processing.

Chirp-a Chirp (LFM) signal is a modulated signal whose frequency varies linearly with time, and is also called a Chirp (Chirp) signal. The LFM technology is widely applied to radar and sonar technologies, and can be used for increasing the radio frequency pulse width, increasing the communication distance and increasing the average transmitting power, and simultaneously, maintaining enough signal spectrum width without reducing the distance resolution of the radar.

FSCM frequency-shifted Chirp modulation (FSCM), which is a modulation scheme in which information is encoded in a Chirp signal of constant slope (CHIRP RATE) by means of a frequency offset. FSCM (frequency-shift keying) signals are a long-distance and low-power-consumption technology based on chirp signals and are widely applied to Internet of things communication. Compared with the traditional sine modulation mode, the FSCM signal with the spread spectrum and frequency hopping properties not only inherits the excellent characteristics of the Chirp signal, but also has better anti-interception performance.

LoRa Long Range Radio (Long Range Radio) is a low-power-consumption local area network wireless standard, and is characterized by further propagation distance under the same power consumption condition. Because of the characteristics of remote, low power consumption, safe data transmission and the like, the method is widely applied to the Internet of things, public or private networks.

The FrFT is fractional Fourier transform, namely, signals are rotated by different angles on a time frequency domain through fractional transform operators, so that the range of signal processing is widened.

MIMO: multiple input multiple output antennas.

Claims

1. An ISAC method based on orthogonal multi-carrier FSCM signals, characterized in that for any ISAC device in an ISAC network:

(1) Perform frequency shift chirp modulation on the communication symbols of the data stream to generate an orthogonal multi-carrier FSCM signal and transmit it;

When frequency-shift chirp modulation is performed on communication symbols, different spreading factors are used for modulation in each channel of the transmitter;

(2) Receive and process the echo signals reflected by each target in a multi-target scenario to achieve real-time detection of the target; the echo signals reflected by the target are orthogonal multi-carrier FSCM signals.

(3) Receive orthogonal multi-carrier FSCM signals transmitted by other ISAC devices in the ISAC network, and demultiplex and demodulate the received signals to achieve communication between ISAC devices.

2. The ISAC method according to claim 1, wherein the method of using different spreading factors for modulation is:

Add a carrier frequency offset f _offset to the subcarrier FSCM signal, f _offset is given by the following definition:

Where B is the bandwidth, SF is the spreading factor, that is, the number of modulation bits for each communication symbol, _ts is the cycle time of each communication symbol, and S is the communication symbol;

Folding time As the dividing line, a communication symbol S is represented as two parts, which can be expressed as follows:

Where k is the slope of frequency change; x _T (t) is the transmitter FSCM signal obtained by embedding the communication symbol S;

The discrete form of the FSCM signal obtained by sampling the x _T (t) embedded in the communication symbol S is shown as follows:

Where n is the sampling sequence, _fs is the sampling frequency, and single bandwidth is adopted; _N1 = {0,…, _nfold -1}, _N2 = { _nfold ,…, ^2SF -1}, and _nfold = _tfold · _fs .

3. The ISAC method according to claim 1, wherein each ISAC device transmits and receives signals using a MIMO antenna, and each ISAC device is provided with multiple transmitting antennas and multiple receiving antennas, each antenna corresponding to multiple different spreading factors.

4. The ISAC method according to claim 1 , wherein processing the echo signal comprises demultiplexing the received orthogonal multi-carrier FSCM signal; wherein the demultiplexing of the received orthogonal multi-carrier FSCM signal comprises:

Assume that the received orthogonal multi-carrier FSCM signal is expressed as:

Y＝A(θ)X+v

where v is additive zero-mean temporal white noise with covariance R _z ;

First, a corresponding reference signal g _i (t) is generated in each channel of the receiver according to the corresponding spreading factor SF. The reference signal is in the form of an FSCM signal with a carrier frequency offset f _offset of 0.

Then, in each channel, the received orthogonal multi-carrier FSCM signal Y(t) is multiplied by the conjugate of the reference signal g _i (t) to extract the FSCM subcarrier x _R,i (t) corresponding to each channel:

5. The ISAC method according to claim 4, wherein processing the echo signal further comprises performing target detection using the obtained subcarriers, specifically:

First, select the FSCM subcarrier with the largest spreading factor SF corresponding to the channel, and set the sampling frequency _fs to be equal to the bandwidth B corresponding to the spreading factor SF of the channel, that is, _fs = B. Then the FSCM discrete signal obtained by sampling is:

Where _xRi [n] is the FSCM discrete signal corresponding to each channel, φ represents the phase of the received FSCM discrete signal _Yi [n], k is the slope of the frequency change, n is the sampling sequence, _N1 = {0,…, _nfold -1}, _N2 = { _nfold ,…, ^2SF -1}, N is the union of _N1 and _N2 , and _nfoId = _tfoId · _fs , _fs is the sampling frequency, _tfold is the folding time of the FSCM symbol representation into two parts, B is the bandwidth, S is the communication symbol in the data stream; n' is the delay of the signal in discrete time;

Then, a standard chirp signal with the same slope is mixed with the FSCM subcarrier to obtain the intermediate frequency signal f _IF (t):

Where, T[n] represents the slope k _0, which is the standard chirp signal, * represents the conjugate operation, the intermediate frequency f _IF = -k ₀ n';φ' is the phase of the intermediate frequency signal obtained by mixing the received signal with the reference signal;

Finally, the CZT algorithm is used to process f _IF (t) to complete the estimation of the target's distance and speed; and the MUSIC algorithm and spectrum peak search method are also used to estimate the arrival angle, which is expressed as follows:

Where θ _MUSIC represents the estimated angle of arrival, A(θ) represents the transmit-receive matrix, which is the product of the transposed transmit steering matrix and the receive steering matrix. Λ _n is a diagonal matrix consisting of the last MK eigenvalues of the covariance matrix R of the received signal subcarriers, arranged in descending order.

6. The ISAC method according to claim 4, wherein the received signal is demultiplexed and demodulated, wherein the demodulation is performed on the FSCM subcarriers in each channel respectively, based on the principle of coherent demodulation, using a down-chirp signal with the same spreading factor value as the modulated signal as a reference signal for demodulation; the demodulation operation in the i-th channel is as follows:

in, Represents the conjugate form of the discrete reference signal x _ref,i [n], and the communication symbol S corresponds to the maximum value sequence number after the FFT operation.

7. An ISAC device based on orthogonal multi-carrier FSCM signals, comprising a transmitter and a receiver;

The transmitter performs frequency shift chirp modulation on the communication symbols of the data stream to generate an orthogonal multi-carrier FSCM signal and transmits it;

The receiver receives and processes the echo signals reflected by each target in a multi-target scene to achieve real-time detection of the target; wherein the echo signals reflected by the target are orthogonal multi-carrier FSCM signals,

The receiver also receives orthogonal multi-carrier FSCM signals transmitted by other ISAC devices in the ISAC network, and demultiplexes and demodulates the received signals to achieve communication between ISAC devices.

8. The ISAC device according to claim 7, characterized in that it is used to implement the ISAC method according to any one of claims 2 to 6.

9. An ISAC network system based on orthogonal multi-carrier FSCM signals, characterized by comprising a plurality of ISAC devices based on orthogonal multi-carrier FSCM signals according to any one of claims 7-8.