A spread spectrum based underwater acoustic backscatter communication system, method and apparatus

Abstract

The application discloses a kind of underwater acoustic backscattering communication systems, methods and devices based on spread spectrum, wherein system includes transmitting end, receiving end and multiple passive reflection labels;Multiple passive reflection labels send data in the following way: each passive reflection label uses unique PN sequence to encode data;Spectrum shift is performed, and OOK modulation is performed to realize the sending of data;The data sent by multiple passive reflection labels is received simultaneously by receiving end, and the following way is used to demodulate data: different frequency bands of data are separated by filter in receiving end;Energy detection demodulation is performed, and the data of each passive reflection label is decoded according to the unique PN sequence of the label.The application combines PN sequence and spread spectrum code division multiple access, realizes the simultaneous access of multiple passive backscattering labels, reduces direct link interference and multipath interference, improves spectrum utilization, improves the reliability of system, and can be widely applied in underwater acoustic communication field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of underwater acoustic communication, in particular to an underwater acoustic backscatter communication system, method and device based on spread spectrum. BACKGROUND

[0002] Underwater acoustic backscatter communication is a new underwater communication technology, which replaces the active generation of acoustic signals by backscattering existing acoustic signals, so it can enjoy the benefits of low power consumption, long time operation and other aspects brought by the Internet of Things. Because of its green and pollution-free characteristics, it can be widely used in ocean resource exploration, climate monitoring, species tracking and other fields.

[0003] However, the research on underwater acoustic backscatter communication system has just begun. The existing work focuses on single node (tag) communication scenarios, and multiple nodes (tags) cannot communicate simultaneously, which seriously limits the scalability to accommodate a large number of underwater Internet of Things devices in the future. How to eliminate direct link interference, multi-node interference, and multipath interference to improve the anti-interference ability of the system and realize simultaneous communication of a large number of nodes is a difficult problem to be solved.

[0004] Spread spectrum communication technology has strong anti-interference ability, can realize reliable transmission of information at low signal-to-noise ratio, and can resist intentional or unintentional interference. It also has the advantages of strong anti-narrowband interference, strong concealment of communication, and ability to realize code division multiple access. Therefore, spread spectrum technology is widely used in underwater acoustic communication, commonly used in long-range underwater acoustic communication, underwater military secure communication, etc. However, the existing underwater spread spectrum communication technology has high complexity and cannot be directly applied to underwater acoustic backscatter communication systems. SUMMARY

[0005] In order to at least partially solve one of the technical problems existing in the prior art, the purpose of the present application is to provide an underwater acoustic backscatter communication system, method and device based on spread spectrum.

[0006] The technical solution adopted by the present application is:

[0007] An underwater acoustic backscatter communication system based on spread spectrum, comprising a transmitting end, a receiving end and a plurality of passive reflection tags;

[0008] The plurality of passive reflection tags send data in the following way:

[0009] The plurality of passive reflection tags are grouped, every M passive reflection tags form a group, and there are N frequency bands in total;

[0010] Each passive reflection tag uses a unique PN sequence for data encoding;

[0011] The passive reflection tag performs spectrum shift and OOK modulation to realize data transmission;

[0012] The receiving end receives data transmitted by multiple passive reflection tags and demodulates the data in the following manner:

[0013] The receiving end separates data in different frequency bands through a filter;

[0014] The receiving end performs energy detection demodulation and decodes data of each passive reflection tag according to a unique PN sequence of the tag.

[0015] Further, the passive reflection tag is equipped with a transducer to collect energy.

[0016] Further, the signal generated by the transmitting end is a single-tone acoustic signal.

[0017] The single-tone acoustic signal is a continuous acoustic signal or a discontinuous acoustic signal, and the frequency of the single-tone acoustic signal is 10-100 kHz.

[0018] Further, the total number of the multiple passive reflection tags is M*N, and in any frequency band, M passive reflection tags use M PN sequences with a length of L, and the M PN sequences with the length of L in different frequency bands are the same.

[0019] Further, the PN sequence is used for direct sequence spread spectrum of the passive reflection tag, and in the M passive reflection tags in each frequency band, the PN sequence of each passive reflection tag is unique, and the passive reflection tags in different frequency bands can share the same PN sequence, wherein the PN sequence is an m sequence, a Gold sequence or a chaotic sequence.

[0020] Further, the passive reflection tag uses a square wave to perform spectrum shift on the single-tone acoustic signal generated by the transmitting end.

[0021] The expression of the square wave is:

[0022]

[0023] The signal generated by the transmitting end is Sin(Ft), and the shifted spectrum is:

[0024] Sin(Ft)*Sin(Δft)=0.5(Cos(Ft-Δft)-cos(Ft+Δft))

[0025] Wherein, Δf is the frequency of the square wave, F is the frequency of the signal transmitted by the transmitting end, and t is time.

[0026] Further, the passive reflective tag controls its own impedance, and then controls the reflection coefficient Gamma to perform OOK amplitude modulation.

[0027] The expression of the reflection coefficient is:

[0028]

[0029] In the formula, Z L is the load impedance, Z S is the transducer impedance, is the conjugate of the transducer impedance.

[0030] Further, the filter used by the receiving end is a low-pass filter, a high-pass filter or a band-pass filter.

[0031] Another technical solution adopted by the present application is:

[0032] A multi-tag access method of a spread spectrum-based underwater acoustic backscatter communication system, comprising the following steps:

[0033] Grouping a plurality of passive reflective tags, wherein each group includes M passive reflective tags, and there are N frequency bands in total;

[0034] Each passive reflective tag uses a unique PN sequence to encode data, performs spectrum shifting and OOK modulation, and sends data to the receiving end;

[0035] After the receiving end receives the data sent by the plurality of passive reflective tags, the data of different frequency bands is separated by a filter;

[0036] The receiving end performs energy detection demodulation, and decodes the data of each passive reflective tag according to the unique PN sequence of the tag.

[0037] Another technical solution adopted by the present application is:

[0038] A multi-tag access device of a spread spectrum-based underwater acoustic backscatter communication system, comprising:

[0039] At least one processor;

[0040] At least one memory for storing at least one program;

[0041] When the at least one program is executed by the at least one processor, the at least one processor implements the above method.

[0042] The present application has the beneficial effects that: the present application combines PN sequence and spread spectrum code division multiple access, realizes simultaneous access of a plurality of passive backscatter tags, reduces direct link interference and multipath interference, improves spectrum utilization, and improves the reliability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following introduces the drawings of the related technical solutions in the embodiments of the present application or the prior art. It should be understood that the drawings in the following introduction are only for the convenience of clearly describing part of the embodiments of the technical solutions of the present application, and for those skilled in the art, other drawings can also be obtained without paying creative labor on the premise of the drawings.

[0044] Figure 1 is a structure diagram of a spread spectrum-based underwater acoustic backscattering communication system in the embodiments of the present application;

[0045] Figure 2 is a signal transmission schematic diagram of a passive reflection tag access system of a multi-user access method of a spread spectrum-based underwater acoustic backscattering communication system in the embodiments of the present application. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. For the step numbers in the following embodiments, they are only set for the convenience of description and explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0047] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0048] In the description of the present application, the meaning of several is one or more, and the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, and above, below, etc. are understood as including the number. If the first, second, etc. are described, they are only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or the sequence of the indicated technical features.

[0049] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solutions.

[0050] As Figure 1 shown, Figure 1 A structure diagram of a spread spectrum based underwater acoustic backscatter communication system, the system comprising an underwater acoustic transducer (i.e. a transmitting end), a hydrophone (i.e. a receiving end) and a plurality of passive backscatter tags. In order to realize simultaneous access of a plurality of passive backscatter tags, reduce direct link interference and multipath interference, improve spectrum utilization and improve the reliability of the system, the embodiment provides a spread spectrum based underwater acoustic backscatter communication system multi-tag access method, comprising the following steps:

[0051] (1) The passive reflection tag transmits data by the following steps:

[0052] S11, group the passive reflection tags, M passive reflection tags for a group, a total of N frequency bands;

[0053] S12, each passive reflection tag uses its own unique PN sequence for data encoding;

[0054] S13, the passive reflection tag performs spectrum shift and executes on / off (OOK) modulation to send its own data;

[0055] (2) The receiving end receives data from a plurality of passive reflection tags at the same time, and the receiving end demodulates the data by the following steps:

[0056] S21, the receiving end uses a filter to separate different frequency bands;

[0057] S22, the receiving end performs energy detection demodulation and uses the unique PN sequence of each passive reflection tag to decode the data of the tag

[0058] Further, as an optional implementation, the passive reflection tag is passive and is equipped with a transducer to collect energy.

[0059] Further, as an optional implementation, the signal generated by the transmitting end is a single tone acoustic signal, which can be a continuous acoustic signal or a discontinuous acoustic signal, and the frequency is 10Khz-100KHz.

[0060] Further, as an optional implementation, in step S11, M passive reflection tags for a group, a total of N frequency bands, then the total number of passive reflection tags is M*N, in any frequency band, M passive reflection tags use M PN sequences with a length of L, and the M PN sequences with a length of L in different frequency bands are the same.

[0061] Further, as an optional implementation, the PN sequence in step S12 is used for direct sequence spread spectrum by the passive reflecting tag. In each frequency band, the PN sequence of each passive reflecting tag is unique, and the passive reflecting tags in different frequency bands can share the same PN sequence. The PN sequence can be an m-sequence, a Gold sequence, or a chaotic sequence.

[0062] Further, as an optional implementation, in step S13, the passive reflecting tag uses a square wave to perform spectrum shifting on the single-tone acoustic signal generated by the transmitting end. The square wave can be approximated as a sine wave Sin(Δft), and the signal generated by the transmitting end is Sin(Ft). The shifted spectrum is Sin(Ft)*Sin(Δft)=0.5(Cos(Ft-Δft)-cos(Ft+Δft)).

[0063] Further, as an optional implementation, in step S13, the passive reflecting tag performs on / off (OOK) amplitude modulation by controlling its own impedance and thus controlling the reflection coefficient . The Z L is the load impedance, and the Z S is the transducer impedance.

[0064] Further, as an optional implementation, in step S21, the filter used by the receiving end can be a low-pass filter, a high-pass filter, or a band-pass filter.

[0065] Further, as an optional implementation, in step S22, the receiving end uses the unique PN sequence of each passive reflecting tag for despreading.

[0066] The above system and method will be explained in detail below in combination with the accompanying drawings and specific embodiments.

[0067] Consider a passive acoustic backscattering communication network including one hydrophone, one underwater acoustic transducer, and four passive backscattering tags. The underwater acoustic transducer transmits a sine wave acoustic signal with a frequency of F=50Khz and a power of P. The hydrophone collects the acoustic signal and performs offline processing in MATLAB. Tag A and tag B share a frequency band and shift the sine wave transmitted by the transducer by Δf1=10Khz. The PN sequence of tag A is [1 0 1 1 0], and the PN sequence of tag B is [1 1 0 0 1]. Tag C and tag D share a frequency band and shift the sine wave transmitted by the transducer by Δf2=20Khz. The PN sequence of tag C is [10 1 1 0], which is the same as that of tag A, and the PN sequence of tag D is [1 1 0 0 1], which is the same as that of tag B. Assuming that the four passive reflecting tags transmit data simultaneously, the operation steps of the method applied to the above passive acoustic backscattering communication system are as follows:

[0068] S11. Labels A and B form a group, occupying a frequency band of 40kHz (F-Δf1); labels C and D form a group, occupying a frequency band of 30kHz (F-Δf2).

[0069] S12. The PN sequence for tags A and C is [1 0 1 1 0], which means encoding 1 as [1 0 1 1 0] and 0 as [0 1 0 0 1]. The PN sequence for tags B and D is [1 1 0 0 1], which means encoding 1 as [1 1 0 0 1] and 0 as [0 0 1 1 0]. The PN sequence can be chosen from various options, such as an m-sequence, a Gold sequence, or a chaotic sequence.

[0070] S13, such as Figure 2 As shown, the passive backscatter tag uses a square wave to move the 50kHz sine wave emitted by the underwater acoustic transducer. Specifically, for each tag, the microcontroller generates a square wave with a preset fixed frequency Δf to control the opening and closing of the switching component, as expressed by the square wave expression. It can be seen that a square wave can be approximated as a sine wave with a frequency of Δf. Multiplication in the time domain is equivalent to convolution in the frequency domain. Therefore, the frequency spectrum can be shifted by multiplying the square wave with the single-tone signal generated by the transducer. When the square wave controls the switching component to be in the open or closed state, the signal reflector sends binary data '1'. When the square wave is completely turned off, the signal reflector sends binary data '0'. For example, if the transducer emits a signal with a frequency of F, and a square wave with a preset fixed frequency of Δf controls the opening and closing of the switching component, the frequency of the amplified source signal becomes the frequency F-Δf. Thus, the hydrophone can separate the source signal and the backscattered signal in the frequency domain and demodulate them, effectively reducing direct link interference.

[0071] If the tag wants to send a '1', it uses a square wave to control the state of the switch for a certain symbol time; otherwise, the tag remains silent and does nothing. Specifically, there are two layers of modulation to achieve communication on the tag. The first layer is spectral shifting by transmitting a square wave at a frequency of Δf. The other is on / off (OOK) modulation to enable the tag to transmit its own data. In this modulation, the Δf square wave acts as the carrier wave, with its presence for a specific duration representing a binary 1 and its absence for the same duration representing a binary 0.

[0072] S21. After the hydrophone collects the reflected signals from each tag, it uses a filter to separate the signals of each frequency band. In this example, the center frequencies of the two frequency bands are 40kHz and 30kHz, so bandpass filters with center frequencies of 40kHz and 30kHz can be used respectively.

[0073] S22, after separating each frequency band, then in each frequency band, using the PN sequence corresponding to each tag to decode, using the PN sequence of each tag to perform cross-correlation with the received sequence.If the correlation of the PN sequence representing '1' is higher than that of the PN sequence representing '0', the chip is decoded as '1', and vice versa.

[0074] In summary, the present application has at least the following advantages and beneficial effects relative to the prior art:

[0075] (1), the present application provides a kind of based on spread spectrum underwater acoustic backscattering communication multi-tag access method, adopt this mechanism, the encoding data of each passive reflection tag contains the unique PN sequence of corresponding passive reflection tag itself, so that receiver can distinguish the encoding data sent by different passive reflection tags according to different PN sequence when decoding received encoding data, realize the simultaneous transmission of multiple nodes in the underwater acoustic reflection communication system containing multiple passive reflection tags using code division multiple access.

[0076] (2), the present application proposes to use frequency shift mechanism in underwater acoustic backscattering communication system, realize frequency division multiplexing, combined with spread spectrum code division multiple access, further improve the access number of node, reduce the length and number of required PN sequence, improve frequency band utilization, and eliminate direct link interference and inter-node interference.

[0077] The embodiment also provides a kind of multi-tag access device of underwater acoustic backscattering communication system based on spread spectrum, comprising:

[0078] At least one processor;

[0079] At least one memory for storing at least one program;

[0080] When the at least one program is executed by the at least one processor, the at least one processor implements the above method.

[0081] A kind of multi-tag access device of underwater acoustic backscattering communication system based on spread spectrum of the embodiment can execute the multi-tag access method of underwater acoustic backscattering communication system based on spread spectrum provided in the method embodiment of the present application, can execute the implementation steps of any combination of method embodiment, possess the corresponding function and beneficial effects of the method.

[0082] In some alternative embodiments, the function / operations mentioned in the block diagrams can not occur in the order mentioned in the operational illustrations. For example, depending on the involved function / operation, two blocks shown in succession can in fact be executed substantially concurrently or the blocks can sometimes be executed in reverse order, depending upon the functionality / operations involved. Furthermore, embodiments presented and described in the flowcharts are only examples of implementing the present application. Alternative embodiments are possible where functions described as portions of independent operations are implemented as a combined operation or functions described as a combined operation are implemented as separate operations. The flowcharts can also represent code segments when executed that provide the processes described and / or illustrated therein. Alternatively, the flowcharts can also represent program steps in a procedural, object-oriented, or other programming language object- oriented programming language.

[0083] Furthermore, although the present application is described in the context of functional modules, it is understood that one or more of the functions and / or features described can be integrated in a single physical device and / or software module, or one or more functions and / or features can be implemented in separate physical devices or software modules. It is also understood that detailed discussion of the actual implementation of each module is unnecessary to an understanding of the present application. Rather, the actual implementation is within the routine skill of engineers familiar with the properties, functions and internal relationships of the various functional modules disclosed herein. Accordingly, the present application is not limited to purely hardware implementations, but also encompasses software implementations, including object-oriented programming language implementations. It is also understood that the particular concepts disclosed are merely illustrative and not intended to limit the scope of the present application, which is defined by the appended claims and their equivalents.

[0084] If the functions are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or the part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk or an optical disk, and various media that can store program codes.

[0085] The logic and / or steps represented in the flow diagrams or otherwise described herein, for example, can be embodied in non-transitory computer- readable media, executed by an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions, or in conjunction with which the instructions can be executed. In the context of this specification, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium.

[0086] More specific examples (a non-exhaustive list) of the computer-readable medium include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can also be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, for example, via optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and stored in a computer memory.

[0087] It should be understood that aspects of the application can be implemented in hardware, software, firmware or combinations thereof. In the above described embodiments, the various steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and in another embodiment, any of the following technologies, known in the art, or combinations thereof, can be used: discrete logic circuitry having logic gates for implementing logic functions upon an application of data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), and so forth.

[0088] In the above description of the present specification, reference has been made to descriptive terms such as "one embodiment," "another embodiment," "some embodiments," or the like, which can describe a specific feature, structure, material or characteristic in connection with an embodiment or example. The describing use of these terms in the above specification is not necessarily intended to refer to the same embodiment or example, unless otherwise indicated. Moreover, description of a particular feature, structure, material or characteristic in connection with an embodiment or example is not intended to imply that such feature, structure, material or characteristic is required in all embodiments or examples. Thus, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0089] While the embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary and are not to be taken as limiting the scope of the application. The scope of the application is defined by the claims and their equivalents.

[0090] The above is the specific description of the preferred embodiment of the application, but the application is not limited to the above-mentioned embodiments, and those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the application, and these equivalent modifications or replacements are all included in the scope defined by the claims of the application.

Claims

1. A spread spectrum based underwater acoustic backscatter communication system, characterized by, The passive reflection tag comprises a transmitting end, a receiving end and a plurality of passive reflection tags. The plurality of passive reflection tags send data in the following manner: The plurality of passive reflection tags are grouped, and every M passive reflection tags form a group, and there are N frequency bands in total; Each passive reflection tag uses a unique PN sequence to encode data; The PN sequence is used for direct sequence spread spectrum of the passive reflection tag, and the PN sequence of each passive reflection tag is unique in M passive reflection tags in each frequency band, and the passive reflection tags in different frequency bands can share the same PN sequence, wherein the PN sequence is an m sequence, a Gold sequence or a chaotic sequence; The passive reflection tag performs frequency spectrum shift and OOK modulation to realize data transmission; The receiving end receives data sent by the plurality of passive reflection tags at the same time, and demodulates the data in the following manner: The receiving end separates data of different frequency bands through a filter; The receiving end performs energy detection demodulation and decodes data of each passive reflection tag according to a unique PN sequence of the passive reflection tag; The signal generated by the transmitting end is a single-tone sound signal, the frequency of the single-tone sound signal is 10Khz-100KHz, and the passive reflection tag uses a square wave to perform frequency spectrum shift on the single-tone sound signal generated by the transmitting end; The expression of the square wave is as follows: The signal generated at the transmitting end is ; the frequency spectrum after the shift is: wherein is the frequency of the square wave, is the frequency of the transmitted signal at the transmitting end, t is time; The passive reflective tag controls its own impedance, and in turn, controls the reflection coefficient to perform OOK amplitude modulation; The expression of the reflection coefficient is as follows: wherein is the load impedance, is the transducer impedance, is the conjugate of the transducer impedance.

2. A spread spectrum based underwater acoustic backscatter communication system as claimed in claim 1, wherein, The passive reflection tag is provided with a transducer to collect energy.

3. A spread spectrum based underwater acoustic backscatter communication system as claimed in claim 1, wherein, The total number of the plurality of passive reflective tags is M N, in any frequency band, M passive reflective tags use M PN sequences with length L, and the M PN sequences with length L in different frequency bands are the same.

4. A spread spectrum based underwater acoustic backscatter communication system as claimed in claim 1, wherein, The filter used by the receiving end is a low-pass filter, a high-pass filter or a band-pass filter.

5. A multi-tag access method for a spread spectrum based underwater acoustic backscatter communication system, applied to the system of any one of claims 1-4, characterized in that, The method comprises the following steps: The plurality of passive reflection tags are grouped, and every group comprises M passive reflection tags, and there are N frequency bands in total; Each passive reflection tag uses a unique PN sequence to encode data, performs frequency spectrum shift and OOK modulation, and sends data to the receiving end; After the receiving end receives data sent by the plurality of passive reflection tags, the receiving end separates data of different frequency bands through a filter; The receiving end performs energy detection demodulation and decodes data of each passive reflection tag according to a unique PN sequence of the passive reflection tag.

6. A multi-tag access apparatus for a spread spectrum based underwater acoustic backscatter communication system, characterized by The method comprises the following steps: at least one processor; at least one memory for storing at least one program; when the at least one program is executed by the at least one processor, the at least one processor implements the method of claim 5.

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