A method for designing an integrated underwater detection and communication signal based on a ZC sequence OFDM

Abstract

The application relates to a ZC sequence-based OFDM underwater detection and communication integrated transmission signal design method, which comprises the following steps: a transmitting end carries out digital modulation processing on a to-be-transmitted OFDM signal to obtain a binary data sequence, carries out Hadamard product operation on the binary data sequence and a ZC sequence corresponding to the length of the binary data sequence to obtain a communication code word sequence; the communication code word sequence is subjected to OFDM modulation processing to obtain a ZC-OFDM integrated modulation signal, and the ZC-OFDM integrated modulation signal is transmitted into an underwater acoustic channel; a receiving end carries out OFDM demodulation processing on the ZC-OFDM integrated modulation signal obtained from the underwater acoustic channel, carries out element-by-element operation, removes the ZC sequence, and restores the binary data sequence. The application can make up for the deficiency of current OFDM signal application in the field of underwater detection and communication research, and can verify the feasibility of the application of the OFDM signal in the field of underwater detection and communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater target detection and underwater acoustic communication, and particularly relates to a design method of an OFDM underwater detection and communication integrated transmitting signal based on a ZC sequence. BACKGROUND

[0002] The development of marine economy has prompted countries around the world to increase the intensity of ocean exploration and development. In the process of deep sea exploration, due to the particularity of the deep sea environment, underwater platforms need to complete detection and communication. At present, underwater unmanned vehicles (UUV) clusters are mainly used to perform related tasks, so as to meet the high-intensity and multi-type task requirements of underwater platforms. In the process of underwater tasks, each UUV device in the UUV cluster needs to perceive the positions of other UUV devices around it and communicate with them, so that each UUV device needs to carry detection devices and communication devices.

[0003] In the existing underwater information system, the detection system and the communication system develop in parallel. The installation of detection devices and communication devices and various electronic devices working in parallel on the same underwater platform often causes serious spectrum congestion and interference, and the utilization rate of resources and space is very low. However, due to the many similarities between detection devices and communication devices in terms of working principles, system structures and the like, if the two can be organically integrated to construct a detection and communication integrated system with higher integration and comprehensiveness, the concealment of the system can be enhanced, the energy consumption can be reduced, and the cost can be reduced.

[0004] The working system of the detection and communication integrated system mainly includes four types: time-sharing system, frequency-division system, beam-division system, and simultaneous system. Among them, the detection and communication integrated system of the simultaneous system has the characteristics of high sharing degree, high spectrum and energy utilization rate, and is more suitable for underwater environments with narrow available frequency band, small array aperture, and slow underwater sound propagation speed. In the simultaneous system, the same signal waveform is used for detection and communication, which can realize the functions of detection and communication at the same time. At present, the underwater detection and communication system based on sonar is still in its infancy, and there are obvious differences between the waveforms used by the detection system and the communication system. The selection of the communication signal waveform is an important factor that determines the detection performance and communication performance of the detection and communication integrated system, but there are few research results in this regard, and there is also a lack of research on the feasibility of whether the selected communication signal can be used in the underwater detection and communication integrated system.

[0005] Therefore, it is necessary to propose a scheme to improve one or more problems in the above-mentioned related technical solutions.

[0006] It is to be understood that the information disclosed in the Background section is merely for the purpose of enhancing the understanding of the present application, and thus can include information that is not prior art to those skilled in the art. SUMMARY

[0007] The embodiment of the present application provides a kind of OFDM underwater detection communication integrated transmission signal design method based on ZC sequence, comprising the following steps:

[0008] The transmitting end carries out digital modulation processing to the OFDM signal to be transmitted, obtains binary data sequence, and carries out Hadamard product operation to the binary data sequence and the ZC sequence corresponding to the length of the binary data sequence, to obtain communication code word sequence;

[0009] The communication code word sequence is carried out OFDM modulation processing, and ZC-OFDM integrated modulation signal is obtained, and the ZC-OFDM integrated modulation signal is transmitted into underwater acoustic channel;

[0010] The receiving end carries out OFDM demodulation processing to the ZC-OFDM integrated modulation signal obtained from the underwater acoustic channel, and carries out element-by-element operation, removes the ZC sequence, and restores the binary data sequence;

[0011] Wherein, the OFDM modulation processing includes the conversion of series and parallel, inverse time-frequency conversion, parallel and series conversion, adding cyclic prefix and D / A conversion in turn;The OFDM demodulation processing includes A / D conversion, removing cyclic prefix, series and parallel conversion, time-frequency conversion and parallel and series conversion.

[0012] In an exemplary embodiment of the present application, the transmitting end carries out digital modulation processing to the OFDM signal to be transmitted to obtain binary data sequence, and the step includes:

[0013] The digital modulation processing is quadrature amplitude modulation, and the quadrature amplitude modulation includes symbol mapping phase and carrier modulation phase;

[0014] In the symbol mapping phase, the OFDM signal to be transmitted is divided into a plurality of modulation symbols, and each modulation symbol corresponds to an amplitude and phase combination;

[0015] In the carrier modulation phase, the OFDM signal to be transmitted is mapped to the corresponding modulation symbol in the form of bit stream, to obtain the binary data sequence.

[0016] In an exemplary embodiment of the present application, the expression of the ZC sequence is:

[0017]

[0018] Wherein, Zμ (n) represents the ZC sequence, μ represents the sequence number of the physical root sequence of the ZC sequence, and n represents the nth symbol of the ZC sequence under the corresponding physical root sequence, n∈{1,2,...,N}. z}, N z N represents the length of the ZC sequence. z It can be an odd number or a prime number, and j represents the imaginary unit.

[0019] In an exemplary embodiment of this application, the expression of the communication codeword sequence is:

[0020]

[0021] in, Representing the matrix form of the communication codeword sequence, This represents the binary data sequence allocated to the i-th modulation symbol and the k-th subcarrier after serial-to-parallel conversion. This indicates the (M-1)th row and the Nth row. zo The binary data in column -1, where ⊙ represents the Hadamard product operation. Representing the matrix form of the ZC sequence, This indicates the (M-1)th row and the Nth row. zo ZC data in column -1.

[0022] In an exemplary embodiment of this application, the expression of the ZC-OFDM integrated modulation signal is:

[0023]

[0024] Among them, S t (t) represents the ZC-OFDM integrated modulation signal after adding the cyclic prefix, h window Let M represent the window function, i represent the number of modulation symbols, t represent the transmission time of the OFDM signal to be transmitted, and N represent the number of modulation symbols. zo T represents the number of subcarriers, k represents the k-th subcarrier, and T sym T represents the effective duration of the subcarrier. sym =T0+T cp T0 represents the duration of the ZC-OFDM integrated modulation signal, T cp f represents the length of the time-domain signal after adding the cyclic prefix. c This indicates the initial frequency of the subcarrier.

[0025] In an exemplary embodiment of this application, the window function is a raised cosine window function, and the expression of the window function is:

[0026]

[0027] wherein h window denotes a window function, and β denotes a roll-off factor.

[0028] In an example embodiment of the present application, in the symbol mapping stage, a guard interval is added between each of the modulation symbols, and the guard interval is added in the form of a cyclic prefix, and the length of each of the guard intervals is 2-4 times the root mean square of the delay spread.

[0029] In an example embodiment of the present application, after the receiving end obtains the ZC-OFDM integrated modulation signal, the receiving end also needs to evaluate the detection performance and the communication performance of the ZC-OFDM integrated modulation signal, including: removing the cyclic prefix and performing the serial-to-parallel conversion processing on the ZC-OFDM integrated modulation signal received by the receiving end, to recover the baseband form of the OFDM signal to be transmitted, and then evaluating the detection performance and the communication performance.

[0030] In an example embodiment of the present application, the detection performance is evaluated by using a blurring function;

[0031] The expression of the time-domain form of the ZC-OFDM integrated modulation signal is:

[0032]

[0033] wherein S(t) denotes the time-domain form of the ZC-OFDM integrated modulation signal, Δf z denotes the interval of the subcarriers in the ZC-OFDM integrated modulation signal, Δf z = 1 / T sym ;

[0034] The expression of the blurring function is:

[0035]

[0036] wherein χ denotes the blurring function, u(t) denotes the OFDM signal to be transmitted at the transmission time t, * denotes a conjugate, u * denotes the conjugate of the OFDM signal to be transmitted, Γ denotes a time delay, f d denotes a Doppler shift, χ auto denotes the autocorrelation component of each of the subcarriers in the blurring function, χ cross denotes the cross-correlation component between each of the subcarriers in the blurring function, P1(t) denotes the P1th communication code word sequence at the transmission time t, denotes the conjugate of the P2th communication code word sequence, k1 denotes the k1th subcarrier, and k2 denotes the k2th subcarrier.

[0037] In an example embodiment of the present application, the communication performance is evaluated by using the bit error rate, and the expression of the bit error rate is:

[0038]

[0039] The expression of the ZC sequence is removed as:

[0040]

[0041] wherein, represents element-wise division, represents the communication code word data of the M-1th row and the N-1th column, zo represents the ZC data of the M-1th row and the N-1th column. zo

[0042] Advantages:

[0043] (1) The present application synchronously processes the communication information carried by the OFDM signal to be transmitted by using the characteristics of the Zadoff-Chu sequence, i.e., the ZC sequence, so that the OFDM signal to be transmitted has good communication performance and detection performance at the same time. The ZC-OFDM integrated modulation signal is subjected to OFDM demodulation processing and element-wise operation, the ZC sequence is removed, and the binary data sequence is restored. The present application makes up for the lack of research results of the application of the OFDM signal in the field of underwater integrated signal detection and communication.

[0044] (2) The present application removes the cyclic prefix of the ZC-OFDM integrated modulation signal received by the receiving end and performs serial-parallel conversion processing to restore the baseband form of the OFDM signal to be transmitted, and then evaluates the detection performance and the communication performance, so as to verify the feasibility of the application of the OFDM signal in the field of underwater integrated signal detection and communication. BRIEF DESCRIPTION OF DRAWINGS

[0045] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the principles of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0046] Figure 1 FIG. 1 shows a schematic diagram of the steps of the design method of the OFDM underwater detection and communication integrated transmission signal based on the ZC sequence in an example embodiment of the present application;

[0047] Figure 2 ​​A flowchart illustrating the integrated OFDM underwater detection and communication transmission signal design method based on ZC sequence in an exemplary embodiment of this application is shown.

[0048] Figure 3a This diagram illustrates the simulation performance analysis of the ambiguity function of an OFDM signal in an exemplary embodiment simulation experiment of this application.

[0049] Figure 3b This diagram illustrates the simulation performance analysis of the ambiguity function of the ZC-OFDM integrated modulation signal in an exemplary embodiment of this application.

[0050] Figure 4a A schematic diagram of the distance ambiguity function of the OFDM signal in a simulation experiment of an exemplary embodiment of this application is shown.

[0051] Figure 4b A schematic diagram of the distance ambiguity function of the ZC-OFDM integrated modulation signal in a simulation experiment of an exemplary embodiment of this application is shown.

[0052] Figure 5a A schematic diagram of the velocity ambiguity function of the OFDM signal in a simulation experiment of an exemplary embodiment of this application is shown.

[0053] Figure 5b A schematic diagram of the velocity ambiguity function of the ZC-OFDM integrated modulation signal in a simulation experiment of an exemplary embodiment of this application is shown.

[0054] Figure 6 The diagram illustrates the constellation of the ZC-OFDM integrated modulation signal acquired by the receiver under a 10dB signal-to-noise ratio in a simulation experiment of an exemplary embodiment of this application.

[0055] Figure 7 The diagram shows a comparison of the communication performance of OFDM signals and ZC-OFDM integrated modulation signals when 16QAM modulation is applied to them respectively under a 10dB signal-to-noise ratio in a simulation experiment of an exemplary embodiment of this application. Detailed Implementation

[0056] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0057] Moreover, the accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application. In the drawings:

[0058] The present example embodiment provides a ZC sequence-based OFDM underwater detection and communication integrated transmission signal design method, which can include the following steps: Figure 1 The present example embodiment provides a ZC sequence-based OFDM underwater detection and communication integrated transmission signal design method, which can include the following steps:

[0059] Step S101: The transmitting end performs digital modulation processing on the OFDM signal to be transmitted, obtains a binary data sequence, and performs Hadamard product operation on the binary data sequence and a ZC sequence corresponding to the length of the binary data sequence, to obtain a communication code word sequence.

[0060] Step S102: The communication code word sequence is subjected to OFDM modulation processing to obtain a ZC-OFDM integrated modulation signal, and the ZC-OFDM integrated modulation signal is transmitted into an underwater acoustic channel.

[0061] Step S103: The receiving end performs OFDM demodulation processing on the ZC-OFDM integrated modulation signal obtained from the underwater acoustic channel, and performs element-by-element operation to remove the ZC sequence and restore the binary data sequence.

[0062] The OFDM modulation processing includes serial-parallel conversion, inverse time-frequency conversion, parallel-serial conversion, cyclic prefix addition, and D / A conversion in sequence; and the OFDM demodulation processing includes A / D conversion, cyclic prefix removal, serial-parallel conversion, time-frequency conversion, and parallel-serial conversion.

[0063] The present example embodiment provides a ZC sequence-based OFDM underwater detection and communication integrated transmission signal design method, which has at least the following beneficial effects:

[0064] (1) The present application uses the characteristics of the Zadoff-Chu sequence, i.e., the ZC sequence, to synchronize the communication information carried by the OFDM signal to be transmitted, so that the OFDM signal to be transmitted has good communication performance and detection performance at the same time; and the ZC-OFDM integrated modulation signal is subjected to OFDM demodulation processing, and element-by-element operation is performed to remove the ZC sequence and restore the binary data sequence. The present application makes up for the lack of research results on the application of OFDM signals in the field of underwater integrated signal detection and communication;

[0065] (2) The application removes the cyclic prefix of the ZC-OFDM integrated modulation signal received by the receiving end, and performs serial-parallel conversion processing to restore the baseband form of the OFDM signal to be transmitted, and then evaluates the detection performance and communication performance, so that the feasibility of the application of the OFDM signal in the field of underwater integrated signal detection and communication can be verified.

[0066] The working system of the detection and communication integrated system mainly includes four types: time-sharing system, frequency-sharing system, beam-sharing system and simultaneous system. Among them, the simultaneous system has the characteristics of high sharing degree, high spectrum and energy utilization rate, and is more suitable for underwater environment with narrow available frequency band, small array aperture and slow underwater sound propagation speed. In the simultaneous system, the same signal waveform is used for detection and communication, which can realize the functions of detection and communication at the same time.

[0067] At present, the research on underwater detection and communication integrated system based on sonar is still in its infancy, and there is a significant difference between the waveforms used for detection and communication. When detecting, the detection subsystem requires a large average power and a large time-bandwidth product of the transmitted signal, which can be accurately copied at the receiving end, so as to ensure the processing gain brought by matched filtering, and then improve the signal detection ability and parameter resolution ability. When communicating, the communication subsystem requires the transmitted signal to carry as much changing information as possible, and the bandwidth utilization rate should be high. Therefore, it can be seen that the selection of the communication signal waveform has an important influence on the detection performance and communication performance of the detection and communication integrated system, and the research results in this field are relatively scarce.

[0068] In view of the above problems, the application provides an OFDM underwater detection and communication integrated transmission signal design method based on ZC sequence. The application utilizes the constant amplitude characteristics, good correlation characteristics and Fourier invariant characteristics of the Zadoff-Chu sequence (ZC sequence), processes the communication information carried by the OFDM signal by using the ZC sequence, so as to make the OFDM signal have good correlation performance, and thus make the OFDM signal have good communication performance and detection performance at the same time.

[0069] In step S101 of the embodiment, the transmitting end performs digital modulation processing on the OFDM signal to be transmitted to obtain a binary data sequence, and performs Hadamard product operation on the binary data sequence and the ZC sequence corresponding to the length of the binary data sequence to obtain a communication code word sequence.

[0070] The digital modulation process is preferably Quadrature Amplitude Modulation (QAM), which is a digital modulation method that modulates the amplitude and phase of a signal as two independent parameters. The QAM modulation process mainly includes two stages: symbol mapping stage and carrier modulation stage.

[0071] In the symbol mapping stage, the to-be-transmitted OFDM signal is divided into multiple different modulation symbols, each of which corresponds to a specific amplitude and phase combination. In this stage, the symbol of the to-be-transmitted OFDM signal can be represented as: k (t) = A k cos(ω c t + θ k ), where e k (t) represents the symbol of the to-be-transmitted OFDM signal, A k represents the amplitude of the to-be-transmitted OFDM signal, ω c represents the frequency of the to-be-transmitted OFDM signal, θ k represents the phase of the to-be-transmitted OFDM signal, and t represents the transmission time of the to-be-transmitted OFDM signal.

[0072] In the carrier modulation stage, the to-be-transmitted OFDM signal is mapped to the corresponding modulation symbol in the form of a bit stream, obtaining a binary data sequence. In this process, the symbol of the to-be-transmitted OFDM signal can be represented as:

[0073] e k (t) = X k cosω c t + Y k sinω c t

[0074] s.t. X k = A k cosθ k , Y k = -A k sinθ k

[0075] where s.t. represents constraint.

[0076] The binary data sequence and the ZC sequence corresponding to the length of the binary data sequence are subjected to Hadamard product operation to obtain a communication code word sequence. Here, the ZC sequence is uniformly distributed to each subcarrier of the to-be-transmitted OFDM signal by this method.

[0077] Here, the expression of the ZC sequence is:

[0078]

[0079] wherein, Z μ (n) represents a ZC sequence, μ represents a sequence number of a physical root sequence of the ZC sequence, n represents the n th symbol of the ZC sequence under the corresponding physical root sequence, n∈{1, 2, …, N z}, Nz represents the length of the ZC sequence, Nz is an odd number or a prime number, and j represents an imaginary unit.

[0080] The expression of the communication code word sequence is:

[0081]

[0082] wherein, represents the matrix form of the communication code word sequence, represents the matrix form of the binary data sequence allocated to the i th modulation symbol and the k th subcarrier after the serial-parallel conversion, represents the binary data of the M-1 th row and the N zo -1 th column, and represents the Hadamard product operation, represents the matrix form of the ZC sequence, represents the ZC data of the M-1 th row and the N zo -1 th column.

[0083] In step S102 of the embodiment, as shown in the figure, Figure 2 the communication code word sequence is subjected to OFDM modulation processing before being transmitted, that is, the communication code word sequence is subjected to serial-parallel conversion, inverse time-frequency conversion, parallel-serial conversion, cyclic prefix addition, and D / A conversion in sequence, to obtain a ZC-OFDM integrated modulation signal. Then, the ZC-OFDM integrated modulation signal is transmitted into the underwater acoustic channel.

[0084] Further, when the serial-parallel conversion is performed, the code word sequence on each modulation symbol needs to be subjected to serial-parallel conversion processing, so that the ZC sequence can be uniformly allocated to each subcarrier of the OFDM signal to be transmitted.

[0085] Further, in the embodiment, the inverse time-frequency conversion is preferably an inverse fast Fourier transform, to obtain the information of the time domain signal. After the inverse time-frequency conversion, the obtained information of the time domain signal needs to be subjected to parallel-serial conversion, cyclic prefix addition, and D / A conversion in sequence.

[0086] Further, in the process of adding the cyclic prefix, the last part of the obtained information of the time domain signal is copied and filled into the protection interval at the front end of each time domain signal as the cyclic prefix, and then superimposed and transmitted.

[0087] Here, the expression of the complex envelope of the ZC-OFDM integrated modulation signal with a finite symbol length is defined as:

[0088]

[0089] where S(t) represents the ZC-OFDM integrated modulation signal without adding a cyclic prefix, h window (·) represents a window function, M represents the number of modulation symbols, i represents the i-th modulation symbol, t represents the transmission time of the OFDM signal to be transmitted, N o represents the number of subcarriers without adding a cyclic prefix, k represents the k-th subcarrier, Δf represents the interval of the subcarriers in the ZC-OFDM integrated signal without adding a cyclic prefix, T0represents the duration of the ZC-OFDM integrated modulation signal, f c represents the initial frequency of the subcarriers.

[0090] In a specific application, since the time delay spread of the acoustic wave in the shallow sea is in the order of tens of milliseconds, a guard interval (GI) needs to be added between each modulation symbol of the OFDM signal, and the guard interval is added in the form of a cyclic prefix (CP) in the symbol mapping stage, and the length of the guard interval is 2-4 times the root mean square of the time delay spread. After adding the cyclic prefix, the ZC-OFDM integrated modulation signal is obtained, and the expression is:

[0091]

[0092] where S t (t) represents the ZC-OFDM integrated modulation signal after adding a cyclic prefix, h window represents a window function, M represents the number of modulation symbols, i represents the i-th modulation symbol, t represents the transmission time of the OFDM signal to be transmitted, N zo represents the number of subcarriers, k represents the k-th subcarrier, k = (k1, k2,..., k n ), T sym represents the effective duration of the subcarriers, T sym = T0+ T cp , T0represents the duration of the ZC-OFDM integrated modulation signal, T cp represents the length of the time domain signal after adding a cyclic prefix, f c represents the initial frequency of the subcarriers.

[0093] Further, after generating the ZC-OFDM integrated modulation signal, in order to reduce the spectral sidelobes of the window function, the embodiment preferably uses a raised cosine window function as the window function, and the expression of the window function is:

[0094]

[0095] wherein h window denotes a window function, and β denotes a roll-off factor.

[0096] Finally, the obtained ZC-OFDM integrated modulation signal is transmitted to the underwater acoustic channel through the sonar transducer. During the propagation of the ZC-OFDM integrated modulation signal in the underwater acoustic channel, on the one hand, the ZC-OFDM integrated modulation signal is received by the sonar transducers of other transmitting signals, and the information interaction between the sonars is realized through analysis and decoding; on the other hand, the ZC-OFDM integrated modulation signal reflected by the target in the underwater acoustic channel is absorbed by the sonar itself and other sonars, and through signal processing such as beam forming and target detection, the purpose of joint detection between sonars is realized. Therefore, the obtained ZC-OFDM integrated modulation signal has both detection and communication functions.

[0097] In step S103 of the embodiment, the ZC-OFDM integrated modulation signal is obtained by Figure 2 It can be seen that the receiving end needs to obtain the ZC-OFDM integrated modulation signal from the underwater acoustic channel, and perform OFDM demodulation processing on the ZC-OFDM integrated modulation signal, that is, sequentially performing A / D conversion, removing the cyclic prefix, serial-parallel conversion, time-frequency conversion and parallel-serial conversion on the ZC-OFDM integrated modulation signal. It can be seen that the OFDM demodulation processing is the inverse process of the OFDM modulation processing.

[0098] Further, in the embodiment, after the ZC-OFDM integrated modulation signal is obtained at the receiving end, the detection performance and the communication performance of the ZC-OFDM integrated modulation signal need to be evaluated

[0099] Further, after the ZC-OFDM integrated modulation signal received by the receiving end is removed of the cyclic prefix and subjected to serial-parallel conversion processing, the baseband form of the to-be-transmitted OFDM signal is restored, and then the detection performance and the communication performance of the to-be-transmitted OFDM signal are evaluated.

[0100] Further, in the evaluation of the detection performance, the ambiguity function is used, which is an important tool for analyzing the detection performance of a signal.

[0101] Here, the expression of the time domain form of the ZC-OFDM integrated modulation signal is:

[0102]

[0103] wherein S(t) denotes the time domain form of the ZC-OFDM integrated modulation signal, Δf zΔf represents the interval of the sub-carriers in the ZC-OFDM integrated modulation signal z = 1 / T sym .

[0104] The expression of the ambiguity function is:

[0105]

[0106] Wherein, χ represents the ambiguity function, u(t) represents the to-be-transmitted OFDM signal at the transmission time t, * represents the conjugate, u * represents the conjugate of the to-be-transmitted OFDM signal, Γ represents the time delay, f d represents the Doppler shift, χ auto represents the autocorrelation component of each sub-carrier in the ambiguity function, χ cross represents the cross-correlation component between each sub-carrier in the ambiguity function, P1(t) represents the P1th communication code word sequence at the transmission time t, represents the conjugate of the P2th communication code word sequence, k1 represents the k1th sub-carrier, and k2 represents the k2th sub-carrier.

[0107] Further, when evaluating the communication performance, the concept of bit error rate is utilized. The bit error rate is an important indicator for measuring the accuracy of underwater acoustic signal transmission. The expression of the bit error rate is:

[0108]

[0109] Further, before decoding and mapping, element-by-element operation is required, and in this embodiment, element-by-element division is preferred, so as to remove the ZC sequence and restore the binary data sequence.

[0110] The expression for removing the ZC sequence is:

[0111]

[0112] Wherein, represents element-by-element division, represents the communication code word data of the M-1th row and the N zo -1th column, represents the ZC data of the M-1th row and the N zo -1th column.

[0113] In order to verify the effect of the detection performance and the communication performance of the OFDM underwater detection communication integrated transmission signal design method based on the ZC sequence proposed in the present application, the following simulation experiment is performed.

[0114] Parameter setting

[0115] In the simulation experiment, the number of subcarriers of the signal is set to 512, the number of modulation symbols is set to 4, and the length of the cyclic prefix is set to 128. The root sequence number μ of the selected ZC sequence is 1, the sequence length is 201, and the roll-off coefficient of the raised cosine window is 1 / 32.

[0116] First, as shown in Figure 3a and 3b , the ambiguity function of the OFDM signal and the ambiguity function of the ZC-OFDM integrated modulation signal obtained by the present application are simulated respectively.

[0117] As can be seen from Figure 3a and 3b , the ambiguity function of the ZC-OFDM integrated modulation signal presents a clear "graph pin" shape. Since in the simulation, the QAM code word sequence transmitted by the modulation symbol is all randomly generated, there is still some randomness in the modulation of the QAM code word sequence. This is reflected in the image of the ambiguity function of the signal, which is a relatively low peak sidelobe diffused on the entire function base. By comparing with the ambiguity function of the OFDM signal containing multiple modulation symbols, it can be seen that the ambiguity function of the ZC-OFDM integrated modulation signal shows that the ambiguity volume of the ZC-OFDM integrated modulation signal is mainly concentrated on the main peak of the "graph pin", only a small part exists on the relatively low sidelobe, which shows that the signal echo of the ZC-OFDM integrated modulation signal is relatively concentrated when matched filtering, which is conducive to the detection of the target.

[0118] Secondly, in the simulation experiment, here, the zero Doppler frequency profile and the zero time delay profile of the image of the ambiguity function of the OFDM signal and the ambiguity function of the ZC-OFDM integrated modulation signal obtained by the present application are obtained respectively, and the range ambiguity function image and the velocity ambiguity function image of the two signals are obtained.

[0119] As can be seen from Figure 4a and Figure 4b , in the range ambiguity function images of the two signals, the sidelobes of the range ambiguity function of the OFDM signal fluctuate more. Since the data is randomly generated in the simulation process, the form of the sidelobes also changes constantly, which shows that the correlation performance of the OFDM signal is crossed. The ZC-OFDM integrated modulation signal has only a few sidelobes, which are mainly concentrated around the main lobe, and the main lobe is relatively narrow, so the ZC-OFDM integrated modulation signal can be obtained. It has high range resolution.

[0120] Similarly, as can be seen from Figure 5a and Figure 5bAs can be seen, the velocity ambiguity function image of the OFDM signal exhibits more pronounced sidelobe fluctuations, which significantly impacts its detection performance. Using OFDM as an integrated signal for detection will result in poor differentiation of different target echo signals, leading to ambiguity or uncertainty and lower accuracy. In contrast, the velocity ambiguity function image of the ZC-OFDM integrated modulation signal shows fewer sidelobes and a slightly wider main lobe, indicating that this ZC-OFDM integrated modulation signal is insensitive to changes in the velocity of the detected target and is a Doppler-tolerant signal.

[0121] Finally, this simulation experiment performed demodulation of the ZC-OFDM integrated modulation signal under a signal-to-noise ratio of 10dB, such as... Figure 6 and Figure 7 As shown, due to the introduction of the ZC sequence into the OFDM signal, and the Fourier invariance of the ZC sequence, the communication bit information carried by the ZC-OFDM integrated modulation signal can be successfully demodulated and demapped at the receiving end, while maintaining the original OFDM signal's communication performance. Therefore, the ZC-OFDM integrated modulation signal obtained through this application can simultaneously possess both detection and communication performance.

[0122] It should be noted that: Figure 3b , Figure 4b and Figure 5b The ZC-OFDM signal mentioned refers to the ZC-OFDM integrated modulation signal. Figure 7 The ZC-OFDM mentioned here also refers to the ZC-OFDM integrated modulation signal.

[0123] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0124] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0125] The above description is only specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present application, and these modifications or replacements shall be covered within the protection scope of the present application.

[0126] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the application being indicated by the following claims.

Claims

1. A method based on sequential The underwater detection and communication integrated transmission signal design method is characterized by, Includes the following steps: The launcher is ready to launch. The signal undergoes digital modulation processing to obtain a binary data sequence, and the binary data sequence, along with a length corresponding to the binary data sequence, is then processed. The sequence is subjected to the Hadamard product operation to obtain the communication codeword sequence; The The expression for the sequence is: （1） in, express sequence, express The physical root sequence number of the sequence. Represents the corresponding physical root sequence The first of the sequence A symbol, , express The length of the sequence, It is an odd number or a prime number. Represents the imaginary unit; The expression for the communication codeword sequence is: （2） in, Representing the matrix form of the communication codeword sequence, This indicates that after serial-to-parallel conversion, the data is assigned to the first... The modulation symbol, the first Binary data sequence on each subcarrier , Indicates the first Okay, number The binary data of the column, This represents the Hadamard product operation. Representing the matrix form of the ZC sequence, , Indicates the first Okay, number Columns data; Perform on the communication codeword sequence Modulation processing, to obtain Integrated modulation signal, and the The integrated modulated signal is transmitted into the underwater acoustic channel; The The expression for the integrated modulation signal is: （3） in, Indicates the result after adding the loop prefix Integrated modulation signal, Represents the window function. Indicates the number of modulation symbols, Indicates the first One modulation symbol, Indicates that it is ready to launch. The time of signal transmission, Indicates the number of subcarriers. Indicates the first Subcarriers, Indicates the effective duration of the subcarrier. , express The duration of the integrated modulation signal, This indicates the length of the time-domain signal after adding the cyclic prefix. Indicates the initial frequency of the subcarrier; The window function is a raised cosine window function, and its expression is: in, Represents the window function. Indicates the roll-off factor; The receiving end obtains the underwater acoustic channel with the Integrated modulation signal Demodulation processing, followed by element-wise operations to remove the... The sequence is used to reconstruct the binary data sequence. Among them, the Modulation processing includes sequential serial-to-parallel conversion, inverse time-frequency conversion, parallel-to-serial conversion, and the addition of a cyclic prefix. Conversion; the Demodulation processing includes Conversion, removal of cyclic prefix, serial-to-parallel conversion, time-frequency conversion, and parallel-to-serial conversion.

2. Based on claim 1 sequential The underwater detection and communication integrated transmission signal design method is characterized by, The steps of the transmitting end performing digital modulation processing on the OFDM signal to be transmitted to obtain a binary data sequence include: The digital modulation process is orthogonal amplitude modulation, which includes a symbol mapping stage and a carrier modulation stage; In the symbol mapping stage, the OFDM signal to be transmitted is divided into multiple modulation symbols, each of which corresponds to an amplitude and phase combination; During the carrier modulation stage, the OFDM signal to be transmitted is mapped onto the corresponding modulation symbol in the form of a bit stream to obtain the binary data sequence.

3. Based on claim 2 sequential The underwater detection and communication integrated transmission signal design method is characterized by, In the symbol mapping stage, guard intervals need to be added between each modulation symbol. The guard intervals are added by adding the cyclic prefix, and the length of each guard interval is 2 to 4 times the root mean square of the delay spread.

4. Based on claim 3 sequential The underwater detection and communication integrated transmission signal design method is characterized by, The receiving end acquires the After integrating the modulation signal, it is also necessary to further process the above. The detection and communication performance of the integrated modulation signal are evaluated separately, including: the performance of the signal received by the receiver. The integrated modulation signal undergoes cyclic prefix removal and serial-to-parallel conversion to recover the baseband form of the OFDM signal to be transmitted, and then the detection performance and communication performance are evaluated respectively.

5. Based on claim 4 sequential The underwater detection and communication integrated transmission signal design method is characterized by, The detection performance is evaluated using a fuzzy function; The The time-domain expression of the integrated modulation signal is: （5） in, express The time-domain form of the integrated modulation signal. express The spacing between subcarriers in an integrated modulation signal. ; The expression for the fuzzy function is: （6） in, Represents a fuzzy function. Indicates launch time The OFDM signal to be transmitted at that time Indicates conjugate. This represents the conjugate of the OFDM signal to be transmitted. Indicates time delay. Indicates Doppler frequency shift, This represents the autocorrelation component of each subcarrier in the ambiguity function. This represents the cross-correlation component between each subcarrier in the ambiguity function. Indicates launch time The first time A sequence of communication codewords, Indicates the first The conjugate of a communication codeword sequence, Indicates the first Subcarriers, Indicates the first Subcarriers.

6. Based on claim 4 sequential The underwater detection and communication integrated transmission signal design method is characterized by, The communication performance is evaluated using the bit error rate, which is expressed as: （7） Remove the The expression for the sequence is: in, This indicates element-wise division. Indicates the first Okay, number The communication codeword data of the column, Indicates the first Okay, number Columns data.

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