CN115037384B - A reconfigurable real-time underwater acoustic communication system and method - Google Patents

Abstract

The invention relates to a reconfigurable real-time underwater acoustic communication system and a method, comprising the following steps: the real-time system comprises a data preprocessing module and a data demodulation module; the data demodulation module demodulates according to the demodulation parameters; the FPGA circuit comprises a data modulation module, a frame synchronization module and a multipath related scaling estimation and resampling module; the data modulation module carries out multi-carrier modulation according to the modulation parameters; the multipath correlation scaling estimation and resampling module respectively analyzes the correlation of the data frame information and a plurality of preset Doppler frequency shift signals with different frequency shifts, and resamples the received signals based on the frequency shift parameters corresponding to the Doppler frequency shift signal with the largest correlation of the data frame information. The invention divides the system into reasonable functional modules, so that the quantity of the preset Doppler frequency shift signals in the multi-channel related scaling estimation and resampling module, the modulation parameters in the data modulation module and the demodulation parameters in the data demodulation module are not affected, and the system can be flexibly configured.

Description

A reconfigurable real-time underwater acoustic communication system and method

Technical Field

The present invention relates to the field of underwater acoustic communication, and in particular to a reconfigurable real-time underwater acoustic communication system and method.

Background technique

Early commercial underwater acoustic modem systems basically used serial link systems to provide remote data telemetry and remote control functions through underwater acoustic communications. Early modem systems were almost opaque to end users because their physical layer algorithms were hard-coded in the firmware, so the applications in the equipment were usually not configurable. Currently, they are not suitable for underwater acoustic communication research and applications, and the reconfiguration of modem systems is usually limited.

Reconfigurable software-defined adaptive underwater acoustic communication systems are the core components of underwater acoustic communication networks. With the widespread acceptance of the concept of software-defined radio and the in-depth development of related systems, the development direction of underwater acoustic communication systems is also software-defined open architecture, that is, reconfigurable or user-programmable modem systems. The research on reconfigurable underwater acoustic modem systems is mainly driven by the need for an adaptive platform whose characteristics (in terms of both physical layer schemes and network layer protocols) can be changed to adapt to different underwater acoustic communication scenarios.

The scientific research and application of underwater acoustic communication and network require a certain flexibility to cope with the complexity of underwater acoustic channels (such as multipath delay and Doppler effect). In recent years, due to the lack of standardization of underwater acoustic communication protocols, the interoperability and adaptability (i.e., the ability to switch protocols or parameter settings according to different environments or changing application requirements) between modem systems developed by different manufacturers are insufficient. At the same time, the reconfigurable or reprogrammable options of modem systems are usually limited, and any changes require a comprehensive understanding of the specific hardware and software architecture. Therefore, it is necessary to introduce an open architecture and adaptable underwater acoustic communication system, which will also promote the establishment and promotion of underwater acoustic communication standards. However, the parameter settings in existing systems or technologies are often coupled with each other and cannot be set flexibly, or modifying parameters requires modification or adjustment of the system structure or program. The parameters that need to be configured in the existing technology are often coupled with each other and cannot be flexibly configured.

Summary of the invention

The purpose of the present invention is to provide a reconfigurable real-time underwater acoustic communication system and method to solve the problem in the prior art that the parameters to be configured are coupled to each other and cannot be flexibly configured.

To achieve the above object, the present invention provides the following solutions:

A reconfigurable real-time underwater acoustic communication system, comprising: an underwater acoustic transceiver analog circuit, an FPGA circuit and a real-time system;

The underwater acoustic transceiver analog circuit includes an underwater acoustic analog output module and an underwater acoustic analog input module; wherein the underwater acoustic analog output module is used to transmit the modulation signal output by the modulation module to the underwater acoustic channel; the underwater acoustic analog input module is used to receive the underwater acoustic signal;

The real-time system includes a data preprocessing module and a data demodulation module; wherein the data preprocessing module is used to perform preprocessing operations on the digital signal to be transmitted; the data demodulation module is used to demodulate the resampled signal according to the demodulation parameters to obtain a demodulation result;

The FPGA circuit includes a data modulation module, a frame synchronization module, and a multi-channel correlation scaling estimation and resampling module; wherein the data modulation module is used to perform multi-carrier modulation on the pre-processed data according to the modulation parameters to obtain a modulated signal; the frame synchronization module is used to perform frame synchronization processing on the underwater acoustic signal received by the underwater acoustic simulation input module to obtain data frame information; the multi-channel correlation scaling estimation and resampling module is used to: perform correlation analysis on the data frame information with multiple preset Doppler frequency shift signals with different frequency shifts, and resample the received signal based on the frequency shift parameter corresponding to the Doppler frequency shift signal with the greatest correlation with the data frame information to obtain the resampled signal.

Optionally, the preprocessing operation includes performing CRC encoding, FEC encoding and interleaving on the digital signal to be transmitted.

Optionally, the FPGA circuit further includes: a Rake module based on data sorting; the real-time system further includes: a data checking and sorting module;

The Rake module based on data sorting is used to: intercept and process the resampled signal based on a plurality of set parallel time windows, wherein the starting position of each time window is different;

The data demodulation module is used to demodulate the resampled signal after the interception processing according to the demodulation parameters to obtain a demodulation result;

The data checking and sorting module is used to obtain the bit error rate of each demodulation result through CRC checking, and sort out the demodulation result with the smallest bit error rate as the final digital signal.

Optionally, the multi-path correlation scaling estimation and resampling module comprises: a multi-path correlation scaling estimation unit and a resampling unit;

Wherein, the multi-path correlation scaling estimation unit is used to perform correlation analysis on the data frame information with multiple time scaling signals s[(1+Δ _i )nT _s ] respectively, and determine the time scaling coefficient (1+Δ) corresponding to the time scaling signal with the largest correlation as the optimal time scaling coefficient; wherein, the multiple time scaling signals are multiple Doppler frequency shift signals determined respectively according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler frequency shifts Δ, n is an integer, and T _s is a sampling period.

Optionally, the correlation analysis specifically includes:

The subcarrier signal in the orthogonal Chirp multiplexing of the data frame information is correlated with the time scaling signal and a modulus square operation is performed to obtain a correlation analysis result.

Optionally, the demodulation specifically includes: using an orthogonal Chirp signal for demodulation.

Optionally, the underwater acoustic simulation output module includes an analog conversion channel, a matching power amplifier and an underwater acoustic transducer connected in sequence. The underwater acoustic simulation input module includes a hydrophone, an amplifying and filtering circuit and an analog-to-digital conversion channel connected in sequence.

Optionally, a DMAFIFO module is also included; the DMAFIFO module is used to transmit data between the real-time system and the FPGA circuit.

The present invention also provides a reconfigurable real-time underwater acoustic communication method, comprising:

Acquiring received hydroacoustic signals;

Performing correlation analysis on the underwater acoustic signal and a plurality of preset Doppler frequency shift signals with different frequency shifts, and determining a frequency shift parameter corresponding to the Doppler frequency shift signal with the greatest correlation with the underwater acoustic signal;

Resampling the underwater acoustic signal according to the frequency shift parameter to obtain a resampled signal;

The resampled signal is demodulated.

Optionally, performing correlation analysis on the underwater acoustic signal and a plurality of preset Doppler frequency shift signals with different frequency shifts, and determining a frequency shift parameter corresponding to the Doppler frequency shift signal having the greatest correlation with the data frame information, specifically includes:

Performing correlation analysis on the underwater acoustic signal and a plurality of time scaling signals s[(1+Δ _i )nT _s ] respectively;

The time scaling coefficient (1+Δ) corresponding to the time scaling signal with the largest correlation is determined as the optimal time scaling coefficient; wherein the multiple time scaling signals are multiple Doppler frequency shift signals determined respectively according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler frequency shifts Δ, n is an integer, and _Ts is a sampling period.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The present invention provides a reconfigurable real-time underwater acoustic communication system and method, comprising: an underwater acoustic transceiver analog circuit, an FPGA circuit and a real-time system; the underwater acoustic transceiver analog circuit comprises an underwater acoustic analog output module and an underwater acoustic analog input module; wherein the underwater acoustic analog output module is used to transmit the modulated signal output by the modulation module to the underwater acoustic channel; the underwater acoustic analog input module is used to receive the underwater acoustic signal; the real-time system comprises a data preprocessing module and a data demodulation module; wherein the data preprocessing module is used to perform preprocessing operations on the digital signal to be transmitted; the data demodulation module is used to demodulate the resampled signal according to the demodulation parameter to obtain the demodulation result; the FPG Circuit A includes a data modulation module, a frame synchronization module, and a multi-channel correlation scaling estimation and resampling module; wherein the data modulation module is used to perform multi-carrier modulation on the pre-processed data according to the modulation parameters to obtain a modulation signal; the frame synchronization module is used to perform frame synchronization processing on the hydroacoustic signal received by the hydroacoustic simulation input module to obtain data frame information; the multi-channel correlation scaling estimation and resampling module is used to: respectively perform correlation analysis on the data frame information with a plurality of preset Doppler frequency shift signals with different frequency shifts, and resample the received signal based on the frequency shift parameter corresponding to the Doppler frequency shift signal with the greatest correlation with the data frame information to obtain the resampled signal. The present invention performs reasonable functional module division on the implementation of the system, so that the number of preset Doppler frequency shift signals in the multi-channel correlation scaling estimation and resampling module, the modulation parameters in the data modulation module, and the demodulation parameters in the data demodulation module are decoupled, and these parameters do not affect each other, thereby realizing flexible configuration of parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a structural diagram of a reconfigurable real-time underwater acoustic communication system provided in Example 1 of the present invention;

FIG2 is a schematic diagram of a multi-carrier modulation and demodulation process using orthogonal Chirp division multiplexing in Embodiment 1 of the present invention;

FIG3 is a schematic diagram of orthogonal Chirp division multiplexing of multi-channel subcarrier signals in Embodiment 1 of the present invention;

FIG4 is a schematic diagram of a signal processing process of a multi-path correlation scaling estimation and resampling module in Embodiment 1 of the present invention;

FIG5 is a transmission flow chart of a reconfigurable real-time underwater acoustic communication system in Embodiment 1 of the present invention;

FIG6 is a receiving flow chart of the reconfigurable real-time underwater acoustic communication system in Embodiment 1 of the present invention;

FIG7 is a schematic diagram of the BER/PER performance of the reconfigurable real-time underwater acoustic communication system in the Xiamen Port sea trial in Example 1 of the present invention.

Figure markings: A1-data preprocessing module; A2-data modulation module; A3-underwater acoustic simulation output module; B1-underwater acoustic simulation input module; B2-frame synchronization module; B3-multi-path correlation scaling estimation and resampling module; B4-Rake module based on data sorting; B5-data demodulation module; B6-data verification and sorting module.

Detailed ways

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

Reconfigurable modem systems allow users to modify certain communication parameters by issuing commands that are recognizable by the system firmware, such as dynamic adjustment of the bit rate and coding scheme of digital modulation in the physical layer. As the hardware and software of underwater acoustic modem systems are developed in academic research projects, the reprogrammable feature provides researchers with flexibility. Reprogrammable modem systems introduce the ability to freely replace major communication modules, such as complete modem schemes, signal processing algorithms, or network layer protocols. Reprogramming usually requires programming capabilities for different platforms, such as programming digital signal processors (DSPs) for physical layer signal processing schemes. Software-defined modem systems are a special case of reprogrammable modem systems, in which the entire transmitter and receiver functions of the system can be programmed by software. Open source or open architecture is one of the important development directions of underwater acoustic modem systems. Using open source or open architecture modem systems, users can refer to programming examples or templates to develop custom functions in the physical layer or network layer. Open architecture makes its architecture easier to understand and use by running software and algorithms on standard computing devices.

The purpose of the present invention is to provide a reconfigurable real-time underwater acoustic communication system and method to solve the problem in the prior art that the parameters to be configured are coupled to each other and cannot be flexibly configured.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1

The present invention provides a reconfigurable real-time underwater acoustic communication system. Referring to FIG1 , the system comprises:

Underwater acoustic transceiver analog circuits, FPGA circuits and real-time systems;

The underwater acoustic transceiver analog circuit includes an underwater acoustic analog output module A3 and an underwater acoustic analog input module B1; wherein the underwater acoustic analog output module A3 is used to transmit the modulation signal output by the modulation module to the underwater acoustic channel; the underwater acoustic analog input module B1 is used to receive the underwater acoustic signal;

In this embodiment, the underwater acoustic simulation output module A3 includes an analog conversion channel, a matching power amplifier and an underwater acoustic transducer connected in sequence. The underwater acoustic simulation input module B1 includes a hydrophone, an amplifying and filtering circuit and an analog-to-digital conversion channel connected in sequence.

The real-time system includes a data preprocessing module A1 and a data demodulation module B5; wherein the data preprocessing module A1 is used to perform preprocessing operations on the digital signal to be transmitted; and the data demodulation module B5 is used to demodulate the resampled signal according to the demodulation parameters to obtain a demodulation result.

The FPGA circuit includes a data modulation module A2, a frame synchronization module B2 and a multi-channel correlation scaling estimation and resampling module B3; wherein the data modulation module A2 is used to perform multi-carrier modulation on the pre-processed data according to the modulation parameters to obtain a modulated signal; the frame synchronization module B2 is used to perform frame synchronization processing on the underwater acoustic signal received by the underwater acoustic simulation input module B1 to obtain data frame information; the multi-channel correlation scaling estimation and resampling module B3 is used to: perform correlation analysis on the data frame information with multiple preset Doppler frequency shift signals with different frequency shifts, and resample the received signal based on the frequency shift parameter corresponding to the Doppler frequency shift signal with the greatest correlation with the data frame information to obtain the resampled signal.

The preprocessing in the data preprocessing module A1 and the data checking and sorting module B6; operations include CRC encoding, FEC encoding and interleaving of the digital signal to be transmitted.

In this embodiment, a cyclic redundancy check (CRC) is inserted into the binary data of the digital signal to be transmitted before forward error correction (FEC) coding. The CRC overhead is very small, and 16 bits are usually sufficient (i.e., CRC-16). The CRC code is then interleaved with the matrix in the data frame after forward error correction coding. Considering the balance between complexity and error correction performance, the forward error correction coding is selected as a convolutional code.

The data modulation module A2 uses an orthogonal Chirp signal to perform multi-carrier modulation on the pre-processed data to obtain a modulated signal.

The multi-carrier modulation process of orthogonal Chirp signals is shown in (a) of FIG2 , where ψ _n (t) represents a set of mutually orthogonal Chirp signals:

Where n is the serial number of the Chirp signal, the period of the Chirp signal is set to T, and N is the number of Chirp signals in the group. The kth symbol of binary information modulated by Quadrature Phase ShiftKeying (QPSK) is x(k), and the signal modulated by the multi-carrier of the orthogonal Chirp signal is s(t), as shown in the following formula:

The underwater acoustic simulation input module B1 receives the underwater acoustic signal, and obtains the data frame information after the frame synchronization processing of the frame synchronization module B2. The beginning of each frame of the data frame information is a leading sequence composed of two hyperbolic frequency modulation (HFM) signals (upward sweep frequency and downward sweep frequency). The HFM signal has Doppler invariance and can be used for accurate frame synchronization in communication. The guard interval of the preamble sequence is _TG in length. After the guard interval of the preamble sequence is a known pilot symbol sequence, which is mainly used for channel estimation. After the pilot sequence is the communication data block for transmitting information. The duration of the data block is T. A cyclic prefix is inserted between adjacent data blocks. The cyclic prefix is the guard interval between data blocks. Its duration _TCP is generally set to be greater than the delay spread of the channel (due to the reflection of the sea surface, seabed and obstacles and the heterogeneity of the ocean, the delay spread of the shallow water acoustic channel is relatively large, which may reach tens or even hundreds of milliseconds. The delay spread τ of the impulse response of a typical shallow water acoustic channel is about 80ms). However, an excessively long guard interval between data blocks will obviously significantly increase the duration of the data frame, thereby reducing the communication rate of multi-carrier underwater acoustic communication.

The multi-path correlation scaling estimation and resampling module B3 of this embodiment includes: a multi-path correlation scaling estimation unit and a resampling unit; wherein the multi-path correlation scaling estimation unit is used to perform correlation analysis on the data frame information and multiple time scaling signals s[(1+Δ _i )nT _s ] respectively, and determine the time scaling coefficient (1+Δ) corresponding to the time scaling signal with the largest correlation as the optimal time scaling coefficient; wherein the multiple time scaling signals are multiple Doppler frequency shift signals respectively determined according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler frequency shifts Δ, n is an integer, and T _s is a sampling period. Specifically:

The multi-channel correlation scaling estimation and resampling module B3 can effectively reduce the influence of Doppler frequency shift in the underwater acoustic channel. As shown in FIG4 : the subcarrier signal in the orthogonal Chirp multiplexing of the above data frame information is correlated with each time scaling signal s[(1+Δ _i )nT _s ] stored in the FPGA, and the modulus square operation is performed. By finding the branch with the largest energy spectrum peak as the best estimate of the time scaling coefficient (1+Δ), the received signal is resampled once according to the best estimated time scaling coefficient, and the Doppler frequency shift suppressed broadband received signal s′[nT _s ] can be obtained, wherein the Doppler frequency shift Δ is defined as the ratio of the relative speed between the transmitting end and the receiving end to the underwater acoustic propagation speed. The multi-channel subcarrier signal in the orthogonal Chirp multiplexing is shown in FIG3 , and the last (N-1) subcarrier signal is used as the correlation signal, which is conducive to real-time tracking of the intra-frame changes of the Doppler frequency shift and eliminating the rapidly changing Doppler frequency shift in units of data blocks.

Resampling principle: Assume that s(t) and r(t) are the transmitted signal and the received signal respectively. Sampling the transmitted signal with discrete time can obtain s[nTs], where n is an integer and _Ts is the sampling period. At this time, the received signal r[ _nTs ] can be expressed as:

r[nT _s ]＝s[(1+Δ)nT _s ]

Where the Doppler frequency shift is Δ, the conversion rate during resampling should be 1\(1+Δ), and resampling can be performed using the following formula to eliminate the fixed Doppler frequency shift Δ:

The resampled signal can be obtained through the above steps. The FPGA circuit also includes: a Rake module based on data sorting. The Rake module based on data sorting is used to: intercept and process the resampled signal based on a set plurality of parallel time windows, wherein the starting position of each time window is different. The data demodulation module is used to demodulate the intercepted resampled signal according to the demodulation parameters to obtain a demodulation result. The resampled signal includes a plurality of communication data blocks, and the communication data blocks contain target communication information. The resampled signal is intercepted and processed using a set plurality of parallel time windows to obtain signals under a plurality of time windows, and the signal under each time window is demodulated to obtain a demodulation result.

The Rake module B4 based on data sorting is used to reduce the influence of multipath delay spread of the underwater acoustic channel of the resampled signal. Specifically, it includes:

It is obvious that the multipath delay spread of shallow water acoustic channels will cause inter-block interference (IBI) and inter-carrier interference (ICI). ICI can be eliminated by selecting an appropriate analysis time window, but the delay information of multipath arrival must be clearly known. The exact delay of each path in the multipath is usually unclear in the actual underwater acoustic communication environment. Therefore, because the multipath delay (τ ₁ ...τ _i ) and the corresponding attenuation coefficient (α ₁ ...α _i ) are unknown, it is necessary to design multiple parallel analysis time windows (Rake modules) for demodulation. The number of parallel analysis time windows in the system is set to K < 64.

The data demodulation module B5 demodulates the resampled signal after the above-mentioned interception processing according to the demodulation parameters to obtain the demodulation result corresponding to each time window, specifically:

Since ψ _n (t) are mutually orthogonal, the information x(m) can be easily extracted through a matched filter, as shown in the multi-carrier demodulation process of the orthogonal Chirp signal in (b) of Figure 2:

The modulated signal is transmitted to the underwater acoustic channel through the underwater acoustic simulation output module A3.

On the basis of mutual decoupling of functional modules, in order to meet the requirements of reconfiguration (to cope with the complexity of the underwater acoustic channel), as shown in Figure 1, the important parameters in the system can be flexibly configured, mainly including: the underwater acoustic orthogonal Chirp multiplexing modulation and demodulation parameters in the data modulation module A2 and the data demodulation module B5 are reconfigurable (including parameters such as the number of subcarriers, CP ratio, and protection interval); the number of multi-path correlation scaling estimation branches and the number of Rake receiving branches based on data sorting in the multi-path correlation scaling estimation and resampling module B3 and the Rake module based on data sorting B4 are reconfigurable.

The real-time system also includes: a data checking and sorting module; the data checking and sorting module is used to obtain the bit error rate of each demodulation result through CRC checking, and sort out the demodulation result with the smallest bit error rate as the final digital signal.

Furthermore, the data checking and sorting module B6 is used to obtain the bit error rate of the demodulation result corresponding to each time window through CRC checking, and sort out the demodulation result with the smallest bit error rate as the final digital signal.

The demodulation results of parallel multiplexing are checked for errors in the output data through CRC check, and the best error-free branch is selected through data sorting to obtain the final binary information.

In order to meet the real-time requirements, since there is a large amount of data exchange between the multi-channel correlation scaling estimation and resampling module B3, the data sorting-based Rake module B4 and the data demodulation module B5, DMAFIFO (Direct Memory Access, First In First Out) is used for fast data transmission between the FPGA and the real-time system. As shown in Figures 1 and 4, DMAFIFO transmission can constitute a fast processing structure between the FPGA and the real-time system to reduce CPU overhead and speed up data processing.

The present invention performs reasonable functional module division for the implementation of the system, so that the system modules are completely decoupled and the parameters that need to be configured in each module do not affect each other. Therefore, the parameters in each module of the present application can be flexibly configured.

In order to meet the requirements of functional module decoupling and real-time performance, the system adopts an open architecture of ARM plus reconfigurable FPGA. It can be seen from the flowcharts of the transmitter in Figure 5 and the receiver in Figure 6 that the core functions of the system are mainly run in the FPGA or the real-time system (Linux RT). Functional decoupling and real-time performance require reasonable functional division of the system implementation (as shown in Figure 1): A1, B5 and B6 modules are run in the real-time system (Linux RT), mainly completing CRC encoding and verification, FEC encoding and decoding, interleaving and deinterleaving, and final data selection. Since the multi-channel correlation scaling estimation and resampling module B3 and the data sorting-based Rake module B4 adopt an exhaustive search method, there are a large number of requirements for efficient parallel operation and calculation (CPU-based processing cannot meet real-time requirements), the two core modules B3 and B4 with parallel characteristics and the A2 module are mainly run in the FPGA. The parallel characteristics of the FPGA greatly reduce the time of data processing. At the same time, the modules run in the FPGA in the form of soft cores, which is conducive to convenient and real-time adjustment of the number of multi-channel correlation scaling estimation branches and the number of Rake receiving branches based on data sorting.

Based on the reasonable functional module division of the system, it can be seen that the A2 and B6 modules responsible for the modulation/demodulation part and the two core modules B3 and B4 are completely run in software (B3 and B4 run in the form of soft cores on FPGA). This design makes the system modules completely decoupled. This decoupling separation is very helpful for the flexibility of the modem and the verification and testing of the hardware (A3 and B1 modules). For example, the system can even be used to send/receive modulated signals from different systems, and can also be used to demodulate signals sent from different systems (for example, the same hardware can be used to verify the performance of the OFDM modulation scheme and compare it with the system implementation of the JANUS standard modulation). Secondly, by decoupling the functional modules, the important parameters are decoupled from each other, thus providing a system with flexible and adjustable parameters. By adjusting different communication parameters, it can provide users with the possibility of better adapting to different underwater acoustic channel scenarios, and easily adapt to the changing underwater acoustic channel conditions and variable transmission and reception distances.

FIG7 shows the BER (biterror rate) and PER (packet error rate) performance of the configurable real-time underwater acoustic communication system of the present application in the sea trial experiment of Xiamen Port. It can be seen from the results of FIG7 that the PR-DP-Rake OCDM has a strong channel adaptability through parameter reconfiguration, and its performance is better than that of the PR-DP-Rake OFDM; the system performance will be affected by the dual expansion characteristics of the shallow water acoustic channel. For the PR-DP-Rake OCDM system, the performance curve trends of BER and PER are basically the same. When the signal-to-noise ratio is less than 4.5dB, the system BER is higher than 10 ^-2 ; when the SNR is greater than 7.9dB, the system bit error rate is 0. It can be seen that the PR-DP-Rake OCDM system with reasonable parameter configuration has good anti-Doppler and anti-multipath performance.

Through the above steps, this application has the following effects:

(1) This application completely decouples the important modules of the system through reasonable division of functional modules and soft-core operation, so that the important parameters in multiple modules can be flexibly configured to cope with the variability and complexity of underwater acoustic channels in underwater acoustic communications, and easily adapt to the changing underwater acoustic channel conditions and variable transmission and reception distances. At the same time, the decoupling and separation of system functional modules and the reconfigurable parameters are very helpful for the flexibility of the modem and the verification and testing of communication performance, which is conducive to the development, verification and implementation of underwater acoustic communication algorithm modules.

(2) This application adopts an open architecture of ARM plus a reconfigurable FPGA, uses DMAFIFO transmission between the FPGA and the real-time system, and constructs a fast processing structure between the FPGA and the real-time system to meet the real-time requirements.

(3) The reconfigurable real-time underwater acoustic communication system of the present application has the dual characteristics of anti-Doppler and anti-multipath, and can effectively reduce the bit error rate of underwater acoustic communication. The multi-path correlation scaling estimation and resampling module B3 in the system searches for the best estimate of the time scaling coefficient through the multi-path correlation estimation algorithm, thereby effectively suppressing the Doppler frequency shift of the broadband underwater acoustic signal; the data sorting-based Rake module B4 in the system analyzes and processes the data blocks of the orthogonal Chirp signal through multiple parallel analysis time windows to find the best analysis time window to eliminate the inter-carrier interference caused by multipath delay.

Example 2

The present invention provides a reconfigurable real-time underwater acoustic communication method, the method comprising:

Acquiring received hydroacoustic signals;

Performing correlation analysis on the underwater acoustic signal and a plurality of preset Doppler frequency shift signals with different frequency shifts, and determining a frequency shift parameter corresponding to the Doppler frequency shift signal with the greatest correlation with the underwater acoustic signal;

Resampling the underwater acoustic signal according to the frequency shift parameter to obtain a resampled signal;

The resampled signal is demodulated.

The step of performing correlation analysis on the underwater acoustic signal and a plurality of preset Doppler frequency shift signals with different frequency shifts, and determining a frequency shift parameter corresponding to the Doppler frequency shift signal having the greatest correlation with the data frame information, specifically includes:

Performing correlation analysis on the underwater acoustic signal and a plurality of time scaling signals s[(1+Δ _i )nT _s ] respectively;

The time scaling coefficient (1+Δ) corresponding to the time scaling signal with the largest correlation is determined as the optimal time scaling coefficient; wherein the multiple time scaling signals are multiple Doppler frequency shift signals determined respectively according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler frequency shifts Δ, n is an integer, and _Ts is a sampling period.

specifically:

The multi-path correlation scaling estimation and resampling module can effectively reduce the influence of Doppler frequency shift in the underwater acoustic channel. The subcarrier signals in the orthogonal Chirp multiplexing of the above data frame information are correlated with the respective time scaling signals s[(1+Δ _i )nT _s ] stored in the FPGA and the modulus square operation is performed. By finding the branch with the largest energy spectrum peak as the best estimate of the time scaling coefficient (1+Δ), the received signal is resampled once according to the best estimated time scaling coefficient, and the Doppler frequency shift suppressed broadband received signal s′[nT _s ] can be obtained, wherein the Doppler frequency shift Δ is defined as the ratio of the relative speed between the transmitting end and the receiving end to the underwater acoustic propagation speed.

Resampling principle: Assume that s(t) and r(t) are the transmitted signal and the received signal respectively. Sampling the transmitted signal with discrete time can obtain s[nTs], where n is an integer and _Ts is the sampling period. At this time, the received signal r[ _nTs ] can be expressed as:

r[nT _s ]＝s[(1+Δ)nT _s ]

Where the Doppler frequency shift is Δ, the conversion rate during resampling should be 1\(1+Δ), and resampling can be performed using the following formula to eliminate the fixed Doppler frequency shift Δ:

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (8)

1. A reconfigurable real-time underwater acoustic communication system, comprising: the system comprises an underwater sound receiving and transmitting analog circuit, an FPGA circuit and a real-time system;

the underwater sound receiving and transmitting analog circuit comprises an underwater sound analog output module and an underwater sound analog input module; the underwater sound analog output module is used for transmitting the modulation signal output by the modulation module to an underwater sound channel; the underwater sound analog input module is used for receiving underwater sound signals;

the real-time system comprises a data preprocessing module and a data demodulation module; the data preprocessing module is used for preprocessing a digital signal to be transmitted; the data demodulation module is used for demodulating the resampled signal according to the demodulation parameters to obtain a demodulation result;

the FPGA circuit comprises a data modulation module, a frame synchronization module and a multipath related scaling estimation and resampling module;

the data modulation module is connected with the data preprocessing module; the underwater sound simulation output module is connected with the data modulation module; the frame synchronization module is connected with the underwater sound simulation input module; the multipath correlated scaling estimation and resampling module is connected with the frame synchronization module;

the data modulation module is used for carrying out multi-carrier modulation on the preprocessed data according to the modulation parameters to obtain a modulation signal; the frame synchronization module is used for performing frame synchronization processing on the underwater sound signals received by the underwater sound analog input module to obtain data frame information; the multipath correlated scaling estimation and resampling module is used for: carrying out correlation analysis on the data frame information and a plurality of preset Doppler frequency shift signals with different frequency shifts respectively, and resampling a received signal based on a frequency shift parameter corresponding to the Doppler frequency shift signal with the largest correlation with the data frame information to obtain a resampled signal, wherein the method specifically comprises the following steps:

respectively combining the data frame information with a plurality of time scaling signals s [ (1+delta) _i )nT _s ]Performing correlation analysis, and determining a time scaling coefficient (1+delta) corresponding to the time scaling signal with the maximum correlation as an optimal time scaling coefficient; wherein the plurality of time scaling signals are a plurality of Doppler shift signals respectively determined according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler shifts delta, n is an integer, T _s Is the sampling period;

the subcarrier signals in the orthogonal Chirp division multiplexing of the data frame information are respectively stored with each time scaling signal s [ (1+delta) correspondingly stored in the FPGA _i )nT _s ]Performing correlation and modulo square operation, searching the branch with the maximum energy spectrum peak as the optimal estimation (1+delta) of the time scaling factor, and performing single resampling on the received signal according to the time scaling factor of the optimal estimation to obtain a broadband received signal s' [ nT ] with Doppler frequency shift inhibition _s ]。

2. The reconfigurable real-time underwater acoustic communication system of claim 1, wherein the preprocessing operation comprises CRC encoding, FEC encoding, and interleaving of the digital signal to be transmitted.

3. The reconfigurable real-time underwater acoustic communication system of claim 2, wherein the FPGA circuit further comprises: a Rake module based on data sorting; the real-time system further comprises: a data checking and sorting module; the Rake module based on data sorting is connected with the multipath related scaling estimation and resampling module; the data checksum sorting module is connected with the data demodulation module;

the Rake module based on data sorting is used for: intercepting the resampled signal based on a plurality of set parallel time windows, wherein the starting positions of the time windows are different;

the data demodulation module is used for demodulating the resampled signal after interception processing according to the demodulation parameters to obtain a demodulation result;

the data checksum sorting module is used for obtaining the error rate of each demodulation result through CRC check, and sorting out the demodulation result with the minimum error rate as a final digital signal.

4. The reconfigurable real-time underwater acoustic communication system of claim 1, wherein said multicarrier modulation is in particular: performing multi-carrier modulation by adopting an orthogonal Chirp signal; the correlation analysis specifically comprises:

and carrying out correlation and modular square operation on the subcarrier signals in the orthogonal Chirp division multiplexing of the data frame information and the time scaling signals to obtain a correlation analysis result.

5. The reconfigurable real-time underwater acoustic communication system of claim 1, wherein the demodulating is specifically: demodulation is performed using an orthogonal Chirp signal.

6. The reconfigurable real-time underwater acoustic communication system of claim 1, wherein the underwater acoustic analog output module comprises an analog conversion channel, a matching power amplifier and an underwater acoustic transducer which are connected in sequence; the underwater sound analog input module comprises a hydrophone, an amplifying and filtering circuit and an analog-to-digital conversion channel which are sequentially connected.

7. A reconfigurable real-time underwater acoustic communication system according to claim 3, further comprising a DMAFIFO module; the DMAPFO module is used for transmitting data between the real-time system and the FPGA circuit; the DMAPFO module is connected with the Rake module based on data sorting and the data demodulation module.

8. A reconfigurable real-time underwater acoustic communication method based on the reconfigurable real-time underwater acoustic communication system of claim 1, comprising:

acquiring a received underwater sound signal;

performing frame synchronization processing on the received underwater sound signals to obtain data frame information;

carrying out correlation analysis on the data frame information and a plurality of preset Doppler frequency shift signals with different frequency shifts, and determining frequency shift parameters corresponding to the Doppler frequency shift signal with the largest correlation of the data frame information; resampling the underwater sound signal according to the frequency shift parameter to obtain a resampled signal, which specifically comprises:

respectively combining the data frame information with a plurality of time scaling signals s [ (1+delta) _i )nT _s ]Performing correlation analysis, and determining a time scaling coefficient (1+delta) corresponding to the time scaling signal with the maximum correlation as an optimal time scaling coefficient; wherein the plurality of time scaling signals are a plurality of Doppler shift signals respectively determined according to different time scaling coefficients, the different time scaling coefficients are determined by different Doppler shifts delta, n is an integer, T _s Is the sampling period;

the subcarrier signals in the orthogonal Chirp division multiplexing of the data frame information are respectively stored with each time scaling signal s [ (1+delta) correspondingly stored in the FPGA _i )nT _s ]Performing correlation and modulo square operation, searching the branch with the maximum energy spectrum peak as the optimal estimation (1+delta) of the time scaling factor, and performing single resampling on the received signal according to the time scaling factor of the optimal estimation to obtain a broadband received signal s' [ nT ] with Doppler frequency shift inhibition _s ]；

Demodulating the resampled signal.