WO2011058527A1 - Procédé et appareil pour traiter des signaux de sonar - Google Patents

Procédé et appareil pour traiter des signaux de sonar Download PDF

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Publication number
WO2011058527A1
WO2011058527A1 PCT/IB2010/055168 IB2010055168W WO2011058527A1 WO 2011058527 A1 WO2011058527 A1 WO 2011058527A1 IB 2010055168 W IB2010055168 W IB 2010055168W WO 2011058527 A1 WO2011058527 A1 WO 2011058527A1
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Prior art keywords
code
phase component
correlation function
quadrature
signals
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PCT/IB2010/055168
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English (en)
Inventor
Eduard Germ
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Nordic Sonar Ou
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Publication of WO2011058527A1 publication Critical patent/WO2011058527A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/42—Simultaneous measurement of distance and other co-ordinates
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/93—Sonar systems specially adapted for specific applications for anti-collision purposes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/523—Details of pulse systems
    • G01S7/526—Receivers
    • G01S7/527—Extracting wanted echo signals
    • G01S7/5273—Extracting wanted echo signals using digital techniques

Definitions

  • the present invention relates generally to sonars, and more specifically to processing of sonar signals.
  • forward-looking sonars provide a real-time 2D image of underwater objects and the bottom ahead up to several hundred meters forward of the vessels bow. Forward looking sonars are applicable for navigation in shallow and hazardous waters, hydrographic survey, dredging, rescue operations, diving assistance, underwater security, bottom searches in dim conditions, for example.
  • Active sonar uses a sound transmitter and a receiver. Active sonar creates a sound signal, typically a pulse of sound, often called a "ping", and then listens for reflections (echo) of the pulse. This pulse of sound is generally created electronically using a signal generator, power amplifier and electro- acoustic transducer/array. The transducer is generally mounted in the bow or stem of a vessel, facing to the direction to be scanned. To measure the distance to an object, the time from transmission of a pulse to reception (i.e. a round trip time) is measured and converted into a range by knowing the speed of sound.
  • a sound signal typically a pulse of sound, often called a "ping”
  • echo reflections
  • an array of hydrophones may be used for measuring the relative amplitude in beams formed through a process called beamforming.
  • the target signal (if present) together with noise is then passed through various forms of signal processing, which for simple sonars may be just energy measurement.
  • the pulse may be at constant frequency or a chirp of changing frequency (to allow pulse compression on reception).
  • Simple sonars generally use the former technique with a filter wide enough to cover possible Doppler changes due to target movement, while more complex ones generally include the latter tech- nique.
  • Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This spatial selectivity is achieved by using adaptive or fixed receive and/or transmit beam patterns. The improvement compared with an omnidirectional reception/transmission is known as the receive/transmit gain (or loss).
  • An object of the present invention is to provide a method and an apparatus for real-time processing of sonar signals more efficiently such that less computation capacity is required.
  • the object of the invention is achieved with an apparatus and method according to the appended independent claims. Embodiments of the invention are disclosed in the dependent claims
  • An aspect of the present invention is an apparatus for processing sonar signals, comprising
  • an array of transducers adapted to receive a sounding signal and to provide a plurality of received analogue sounding signals, the received sounding signal being of a predetermined frequency and phase-coded according to a predetermined code consisting of code elements, whereby each code element is defined by N consecutive periods of said sounding signal, wherein N is an integer greater than 1 ,
  • a digitizer adapted to digitize the received analogue sounding signals provided by the array of transducers into a plurality of received digital sounding signals
  • beamforming means for forming from said plurality of received digital sounding signals a plurality of beamformed signals corresponding different azimuth angles
  • An another aspect of the invention is a method for processing sonar signals, comprising
  • a correlation function is computed separately for each individual copy of the code, i.e. the process is divided into number of steps, which is equal to the number of data points (signal periods) per code element.
  • the results are combined (aligned) and the moving average filter is applied resulting in an overall correlation function.
  • This kind of processing instead of computing correlation function straightforwardly, approach allows to obtain more efficient computation, i.e. less arithmetic operations have to be performed in order to obtain the final result. As result less computation capacity is needed for real-time processing.
  • the gain in efficiency is increasing as the number N of data points (signal periods) per code ele- ments increases.
  • the efficiency of the calculation can be further enhanced and the need for computing power further decrease by means of reducing the number of samples per a sounding signal period in each of said plurality of beamformed signals.
  • the number of samples per a sounding signal period in each of said plurality of beamformed signals is reduced by selecting every k sample, wherein k is an integer greater than 1 , and generating for generating, for each of said plurality of beamformed signals, said quadrature phase component and said in-phase component based on the selected samples.
  • the quadrature phase component Q and the in-phase component / is generated for each of the plurality of beamformed signals based on two selected quadrature phase component samples c/ ? and q 2 , and two selected in-phase component samples and i 2 , respectively, as follows:
  • the accuracy of the range measurement is further enhanced by using filter for suppressing side-lobes occurring in correlation functions of binary codes.
  • side-lobe suppression filtering is applied, separately for the quadrature phase component and the in- phase component, one or more of the following correlation functions:
  • the side-lobe filtering comprises performing a convolution operation of a filter function and the respective correlation function to be filtered.
  • the predetermined code comprises a binary code from the following group: Barker code, M-code, V- code, Barker-on-Barker code, and any combination thereof.
  • a novel manipulation of Barker codes, M-codes and/or V-codes is used in order to decrease the sensibility of the object detection to the Doppler effect.
  • Figures 1A, 1 B and 1 C schematically illustrate a typical use of a forward-looking sonar
  • Figure 2 is a block diagram of an exemplary sonar system
  • Figure 3 illustrates a sine wave signal coded using binary Barker 13 code
  • Figure 4 illustrates in more detail the first code element (three signal periods) for the signal shown in Figure 3;
  • Figures 5 and 6 illustrate a quadrature part and an in-phase part, respectively, of decoded sounding signal shown in Figure 3;
  • Figures 7(a), 7(b), 7(c), 7(d) and 7(e) illustrate correlation functions after different processing steps, when side-lobe suppression filter is not applied;
  • Figures 8(a), 8(b), 8(c), 8(d) and 8(e) illustrates correlation functions after different processing steps, when side-lobe suppression filter is applied;
  • Figures 9(a) and 9(b) illustrate the modulus of quadrature components of correlation function, when there is no side-lobe suppression filtering applied and when the filtering is applied, respectively;
  • Figure 10 a flow diagram illustrating an exemplary data processing according to the present invention
  • Figure 1 1 illustrates a quadrature part of a decoded sounding signal, when the sounding signal is phase-coded using B 3 xB 3 code;
  • Figures 12(a) and 12(b) illustrate correlation functions of the inner code of B 3 xB 3i when the side-lobe suppression filter not is applied and when the side-lobe suppression filter is applied, respectively;
  • Figures 12(c) and 12(d) illustrate correlation functions of the outer code of B 3 xB 3, when the side-lobe suppression filter not is applied and when the side-lobe suppression filter is applied, respectively;
  • Figure 12(e) illustrates the correlation function of the outer code of
  • Figure 13 illustrates a quadrature part of a decoded sounding signal, when the sounding signal is phase-coded using B M1 3 code (M-code);
  • Figure 14(a) illustrates correlation function of the inner code of the
  • Figure 14(b) illustrates the correlation function of the inner code of B abC 3, which is an inverted version of the B 3 code
  • Figures 14(c) and 14(d) illustrate a correlation function of the outer code of the B abc 3 , when the side-lobe suppression filter not is applied and when the side-lobe suppression filter is applied, respectively;
  • Figure 14(e) illustrates the correlation function of the outer code of B abc 3 after a moving average filter is applied to the correlation function shown in Figure 14(d);
  • Figure 15 illustrates a quadrature part of a decoded sounding signal, when the sounding signal is phase-coded using B v 3 code (a V-code);
  • Figure 16(a) illustrates a correlation function of the inner code of the B V 3 code, when the side-lobe suppression filter is applied;
  • Figures 16(b) and 16(c) illustrate a correlation function of the outer code of the B v 3 code, when the side-lobe suppression filter not is applied and when the side-lobe suppression filter is applied, respectively;
  • Figure 16(d) illustrates the correlation function of the outer code of the B V 3 code after a moving average filter is applied to the correlation function shown in Figure 16(c).
  • the principles according to the present invention are especially applicable to a forward-looking sonar for receiving echoes of objects ahead of a surface vessel by use of transmitted and reflected sound waves (hereinafter referred to as acoustic sounding signal), and measuring and visually presenting the distance and direction of any such object, e.g. navigational hazards such as shallows and underwater obstacles ahead of a surface vessel, when the vessel is travelling at a high speed (e.g. up to 20 knots).
  • acoustic sounding signal transmitted and reflected sound waves
  • the invention is not restricted to forward looking sonars but may be applied to any type of sonars, such as side looking (scanning) sonars.
  • FIGs 1a, 1 b, and 1 c schematically illustrate a typical use of a forward looking (or forward scanning) sonar.
  • a sonar transducer unit e.g. sound signal transmitter and receiver 1 is located at the hull of the vessel 2 to cause an (acoustic) sounding signal, e.g. pulses, to propagate in the water ahead of the vessel and to receive reflections (echoes) of the sound pulses from underwater objects and the bottom 3.
  • the sonar transducer unit may have any desired overall beamwidth in the horizontal direction 4 and/or in the vertical direction 5.
  • the overall horizontal and/or vertical beamwidth 4, 5 can be set according to the requirements of each specific application of the sonar.
  • the overall beamwidth may be from 10 degrees to 60 degrees, for example.
  • the transducer unit 1 may typically contain an array of electro-acoustic transducers such that the overall beamwidth 4 and/or 5 may consist of a number of narrow sub- beams 4a and/or 4b, as illustrated In Figures 1 a and 1 b.
  • the number of sub- beams may any desired number, typically up to several dozen subbeams, sometimes even up to hundreds subbeams. If the transducer unit 1 contains a linear array of transducers horizontally, for example, there will be a number of narrow subbeams 4a in the horizontal direction (as shown in Figure 1 a) but not in the vertical direction (as illustrated in Figure 1 c). This setup is often used in a 2-dimensional (2D) forward looking sonar.
  • trans- ducer unit 1 contains a planar (2-dimensional) array of transducers, there will be narrow subbeams both in the horizontal direction (subbeams 4a illustrated in Figure 1 a and in the vertical direction (subbeams 4b illustrated in Figure 1 b).
  • This setup may be used to provide 3-dimensional (3D) forward looking sonar.
  • FIG. 2 is a block diagram of an exemplary sonar system in which embodiments according to the present invention may be applied.
  • the exem- plary sonar comprises the following main parts: a transducer unit 1 , an analogue input part 20, a digital signal processing part 22, a signal transmission part 24, and a data transmission part 23.
  • a transducer unit 1 an analogue input part 20
  • a digital signal processing part 22 a digital signal processing part 22
  • signal transmission part 24 a data transmission part 23.
  • the transducer unit 1 is a linear array
  • transmitting element t1 at one end of the transducer unit, or transmitting elements to and t-i at both ends of the transducer unit, or alternatively there may be any number of transmitting elements.
  • the linear array further comprises a plurality of, e.g. 31 , equally spaced receiving elements r 0 , r-i , ... , r 30 .
  • Horizontal and/or vertical beamwidth (i.e. the subbeam) of an individual receiving or transmitting element may be set to any desired value, e.g. 30 degrees.
  • the spacing between receiving elements may be 2 ⁇ , where ⁇ is the wavelength of the sounding signal.
  • the transmitting and receiving elements may be embodied by electro-acoustic transducers, such as hydrophones, which transform electrical signals tse 0 , tsei into acoustic sound signals ts 0 , tsi to be transmitted, or transform received acoustic sound signals rso, rsi , ... , rs3o into respective electrical signals rseo, rsei , ... , rse 30 for further processing in the analogue input part 20.
  • electro-acoustic transducers such as hydrophones, which transform electrical signals tse 0 , tsei into acoustic sound signals ts 0 , tsi to be transmitted, or transform received acoustic sound signals rso, rsi , ... , rs3o into respective electrical signals rseo, rsei , ... , rse 30 for further processing in the
  • Signal transmission part comprises signal generator (SGEN) 24, which generates the sound signal selected by the user.
  • Transmission signal amplifier (A ts ) 25 amplifies the generated electrical sound signal tse 0 , tse 1 and sends it to the transmitting element to, ti located in the transducer.
  • the transmitted signal i.e. the sounding signal
  • the transmitted signal may 200 kHz sine wave signal, which is phase coded using binary codes. More detailed description of possible sounding signal shapes will be given below. It should be appreciated that the frequency of the sounding signal may vary from one application to another. Side-lobes of the radiation pattern of the transducer unit 1 may be suppressed by spatial windowing.
  • Window function can be, for exam- pie, Hamming, Blackman, Chebyshev windows of different side-lobe suppression values.
  • One or more of parameters of the sounding signal such as the frequency, type of the binary code, etc., may be definable through a control interface, e.g. over ethernet connection.
  • the analogue input part 20 may contain two pairs of a bandpass fil- ter and an amplifier, e.g. the bandpass filter F-i and the amplifier Ai , and the bandpass filter F 2 and the amplifier A 2 , for each input channel for analogue processing of the respective received electrical sound signal rseo, rsei , ... , rse 30 .
  • the filters Fi and F 2 may be, for example, 4 th order bandpass Butter- worth filters.
  • the bandpass filters Fi and F 2 may have a center frequency of 200 kHz and a band- width of 75 kHz at -3 dB level, for example.
  • the final stage in the analogue input part 20 is an analogue to digital converter (ADC) that converts (digitizes) the respective received analogue sound signal rse 0 , rse-i, ... , rse3o into a respective received digital sound signal rsdo, rsdi , ... , rsd 30 .
  • the digital sound signals rsd 0 , rsdi , ... , rsd 3 o are applied to the digital data processing part 22.
  • the sampling frequency of ADC may be 6.4 MHz and the resolution may be 16 bit.
  • the digital data processing may be performed by a field-programmable gate array (FPGA) 220 and a number of (e.g. four) digital signal processors (DSP) 221 , which are working parallel.
  • the pur- pose of FPGA 220 is to synthesize, i.e. form, new beamformed signals rb 0 , rbi , rb 30 corresponding to the different azimuth angles from the received digital sound signals rsd 0 , rsdi , ... , rsd 30 .
  • FPGA is used for that purpose due to its ability to perform parallel processing.
  • beamformed signals are formed but the invention is not restricted to any specific number of beams but the number may be selected according to each specific application.
  • the beamformed signals rb 0 , rb-i , rb 3 o may be applied to the DSPs over dedicated lines or shared buses.
  • DSPs 221 may perform several signal processing operations, such as matched filtering, range side-lobe suppression, calculating modulus, with previously synthesized signals rb 0 , rb-i , rb 30 in order to detect range information about possible objects inside sonar's field of view.
  • the processing method employed in the DSPs depends on the selected type of the sounding signal as will be explained below.
  • One or more of parameters of the sounding signal, such as the frequency, type of the binary code, etc., as well as one or more parameters of the processing method may be definable through a control interface, e.g. over ethernet connection.
  • the processed data from the DSPs is collected and provided to a computing device where the resulting online image may be visualized and displayed on a display unit.
  • the processed data is collected by a communication part 23, such as an ethernet chip, and sent (using TCP/IP and UDP protocols, for example) to a computing device 26, such as a PC, where the resulting online image is displayed.
  • the ethernet chip 23 may also receive information from PC 26 about the selected sounding signal that the user has defined from the user interface of the PC, and send the information to the DSPs 221 and the signal generator SGEN 24 over control connections 27 and 28 for configuration thereof.
  • the sounding signal is a 200 kHz sinusoidal signal, preferably a signal pulse, which is phase coded according to a predetermined code sequence, such as a binary code.
  • the phase-coding divides the transmitted sounding pulse into sub- pulses or segments of equal duration and each having a certain phase.
  • the code sequence selects the phase of each subpulse.
  • the most popular phase coded waveform called binary or biphase coding, has two phases.
  • the binary code is made up of 0s and 1 s or "+1 "s and "-1 "s, and the phase of the signal alternates between 0 degrees or 180 degrees ( ⁇ ) based on the code sequence.
  • the bits of the binary code are used to set the phase of the each corresponding segment in the transmitted waveform.
  • There are usually discontinuities in the coded signal at the phase reversal points because the transmitted frequency is not typically a multiple of the reciprocal of the sub- pulse width.
  • the transmitted signal is compressed into the width of subpulse by either matched filtering or correlation processing.
  • Optimal binary sequences are binary sequences whose correlation (e.g. autocorrelation) peak sidelobe is the minimum possible for a given code length.
  • a special class of binary codes is known as Barker codes.
  • the number in the name of Barker code denotes its length.
  • the longest known Barker codes, called Barker 13 codes are of length 13.
  • Barker 13 codes Take, for example, the application of Barker code of length 4, i.e., ⁇ 1 , 1 , -1 , 1 ⁇ , for phase coding of the transmitted signal.
  • the phases of the first, second and the fourth segments or subpulses of the transmitted signal are set to 0 degrees, and the phase of the third one is set to 180 degrees.
  • Barker codes The benefit of the Barker codes is that correlating or match filtering for these codes gives a main lobe peak of N and a minimum peak sidelobe of 1 , where N is the number of subpulses (length of the code, i.e. the number of the bits or code elements in the selected code).
  • N the number of subpulses (length of the code, i.e. the number of the bits or code elements in the selected code).
  • the correlation func- tions of all Barker codes suffer from the relatively high side-lobe level since the codes themselves are short.
  • the magnitude of correlation function side- lobes is reciprocal to the length of the corresponding code. For example, side- lobe level of correlation function of Barker 5 code is 1/5 (-13.98 dB), and for Barker 3 code the corresponding quantity is 1/3 (-9.54 dB).
  • Barker 13 code has the following coefficients:
  • a sounding signal according to Figure 3 is generated by the SGEN 24 and amplified by the amplifier 25, and the converted by the transducer ti into an acoustic sounding signal ts1 , and transmitted (step 101 in Figure 10).
  • echoes or reflections i.e. acoustic sounding signals rs 0 , rs-i , ...
  • rs 30 of the transmitted signal according to Figure 3 are received by the transducers r 0 , n , ... , r 30 , (step 02) and converted into electrical analogue signals rse 0 , rsei , ... , rse 30 which are further processed (step 103) and digitized into digital signals rsd 0 , rsd-i , ... , rsd 30 by the analogue input part 20 (step 104).
  • an analogue processing of the received signals is not an essential part of the present invention but may be implemented in various ways without departing from the spirit and scope of the invention.
  • the first phase of the digital signal processing is synthesis, i.e. mathematical beamform- ing, of new signals rb 0 , rb-i, rb 30 containing information from certain azimuth angles (step 105).
  • the synthesis is done by the FPGA 220 which simultaneously receives the digitized input signals rsd 0 , rsd-i, ... , rsd 30 from all 31 input channels and forms signals for different azi- muth angle inside the sonar's field of view, for example, by using delay-and- sum method.
  • the number of data samples per one signal period is originally 32 since the sampling frequency of the system is 6.4 MHz and the frequency of the sounding signal is 200 kHz.
  • Figure 4 illustrates one digitized signal/code element for the signal shown in Figure 3. As shown, the signal element comprises three periods of the sounding signal, and each period of the sounding signal is presented with 32 data samples.
  • the number of data samples per one signal pe- riod is reduced for the further processing (step 106).
  • the reduction may be performed by selecting every sample, wherein k is an integer greater than 1.
  • the number of data samples per one period is reduced to 4, i.e. every 8 th sample is used.
  • the selected data samples are denoted as ⁇ q-i ; ; q 2 ; 12 ⁇ .
  • the selected data samples are used for dividing signal into quadrature components, i.e. quadrature, Q and in-phase, /, parts (step 107).
  • the Q and / components may be formed as follows:
  • Equation (E.2a) and (E.2b) it is possible to use only two data points per period by applying equations (E.2a) and (E.2b) to the selected data samples: one for quadrature (Q) part and one for in-phase (/) part.
  • This procedure allows easily perform decoding, i.e. extracting the original code from the received sounding signal.
  • Decoding results for the / and Q parts of the decoded signal (in the case of the sounding signal according to Figure 3) are shown in Figures 5 and 6, respectively. Note that there are three sets or copies (1 , 2, 3) of original codes in both the / component and the Q component, since one code element contains three periods of sounding signal.
  • the 1 st column depicts a copy of the original code from the 1 st period of the 1 st signal element
  • the 2 nd column depicts a copy of the original code from the 2 nd period of the 1 st signal element
  • the 3 column depicts a copy of the original code from the 3 period of the 1 signal element
  • the 4 th column depicts a copy of the original code from the 1 st period of the 2 nd signal element, etc.
  • the second phase of digital signal processing is detection the range of possible objects based on the previously synthesized signals rbo, rbi, rb 30 from the FPGA 220.
  • the object detection may be performed by DSPs 221 which are working in parallel.
  • the object detection may be divided into the following sub-parts described below.
  • a matched filtering i.e. a correlation operation
  • a correlation operation is performed in order to obtain correlation function of the decoded signals shown in Figures 5 and 6 (step 108 in Figure 10).
  • the idea behind of this procedure is the following: If the synthesized signal rb 0 , rb-i , rb 30 contains a reflected impulse of the transmitted sound signal ts 0 , ts-i , then there will appear relatively clear code in the decoded sounding signal. This, in turn, means that there also will be a clear and dominating peak of large magnitude presented in the correlation function of the synthesized signal rb 0 , rb-i, rb 30 . That peak of the correlation function can be used for detecting exact distance of the objects.
  • Matched filtering is applied separately to both quadrature and in- phase part of the decoded signal.
  • the result of this procedure, applied to the decoded signal shown in Figures 5 and 6, is shown in Figures 7(a)-(c).
  • the resulting correlation functions for the signal periods 1 , 2 and 3 shown for the in-phase (/) part in Figure 5 are illustrated on the right-hand side in Figures 7(a), 7(b) and 7(c), respectively.
  • the resulting correlation functions for the signal periods 1 , 2 and 3 shown for the quadrature (Q) part in Figure 6 are illustrated on the left-hand side in Figures 7(a), 7(b) and 7(c), respectively.
  • all three correlation functions of the / component may be com- bined together as shown on the right-hand side in Figure 7(d) and a rectangular shaped overall correlation function for the / component is obtained.
  • all three correlation functions of the Q component may be combined together as shown on the left-hand side in Figure 7(d) and a rectangular shaped overall correlation function for the Q component is obtained (step 109 in Figure 10).
  • the moving average filter, h ma may be applied to the rectan- gular shaped correlation function (step 1 10 in Figure 10) in order to obtain triangular shaped correlation function.
  • Triangular shaped correlation function enables more accurate range detection.
  • the coefficients of the moving av- erage FIR filter may be defined as shown in the Equation (E.4)
  • Figure 7(e) illustrates the resulting triangular shaped correlation functions ⁇ cofest and Q CO rr obtained for the / component and the Q component, respectively, as a result of applying moving average filter to the rectangular shaped combined correlation functions of Figure 7(d).
  • a correlation function is computed separately for each individual copy of the code, i.e. the process is divided into number of steps, which is equal to the number of data points (signal periods) per code element. After correlation functions of all individual copies of the code are computed the results are combined (aligned) and the moving average filter is applied resulting in an overall correlation function.
  • side-lobe level of correlation function of Barker 13 code is 1/13, i.e. - 22.28 dB, which can be quite considerable compared to the magnitude of the main lobe. It should be noted that lower side lobe level results in better quality of the final picture on the sonar display.
  • step 1 1 1 1 in order to reduce side-lobe level of the correlation function, so-called side-lobe suppression filter may be applied (step 1 1 1 ).
  • side-lobe suppression filters for Barker codes.
  • An example of a simple side-lobe suppression filter for the correlation function of Barker 13 code is given by the following FIR filter coefficients h B i3 ' .
  • the filtering operation may be done using convolution operation of the filter h B13 and the correlation function to be filtered.
  • the filtering of the correlation function Q corr of the Q component may be done using the following convolution operation:
  • the filtering of the correlation function / co/r of the / component may be done using similar convolution operation wherein Q corr is replaced by I co Resulting filtered correlation functions Q M cor r and l fllt ⁇ rr are illustrated in Figure 8(e).
  • the filter h B13 allows reducing the level of side-lobes to 1/50, i.e. to -33.98 dB.
  • the side-lobe suppression filter h B i3 may be applied to any or each of the correlation functions of Figures 7(a)-7(c), or to the combined correlation function of Figure 7(d), the resulting filtered correlation functions being illustrated in Figures 8(a)-8(d).
  • step 1 1 1 may be situated after any or each of steps 108, 109, and 1 10.
  • the final result is a triangular shaped correlation function Q m ⁇ rr or l M corr as illustrated in Figure 8(e) wherein the level of the side lobes is substantially reduced in comparison with the corresponding correlation functions shown in Figure 7(e).
  • side-lobe suppression filter h B i3, described by equation (E.5), as well as the filter h B 3 (that will be described below), described by equation (E.12) are used here for illustrative purposes only. These filters as such may not be directly applied for the real situations since their side-lobe suppression is often not sufficient. Instead, optimized versions of the filters may be used.
  • the filters may be optimized in the sense that the filter of minimum length would give maximal side-lobe suppression. Optimization may be done by using approaches like gradient decent method, or using minimax constraint solving techniques.
  • modulus of quadrature Q and in-phase / parts of the correlation function may be calculated (step 1 12). If the side-lobe reduction filtering is not applied, modulus of quadrature Q and in-phase / parts of the correlation function may be calculated as The resulting correlation function is illustrated in Figure 9(a).
  • modulus of quadrature Q and in- phase / parts of the correlation function may be calculated as:
  • a separate correlation (e.g. autocorrelation) function AQI may be obtained for each of the to the plurality of (e.g. 31 ) different azimuth angles in the selected azimuthal angle range, such ⁇ -15°,...., +15° ⁇ .
  • a time delay associated with a location of the main peak of the correlation function AQI provides a time delay for the reflected sounding signal received from the respective azimuthal angle, the time delay corresponding to a range to the target or objected from which the signal reflected.
  • the time delay may be determined by measuring pulse traveling time in both directions, i.e.
  • the cor- relation data for different azimuth angles may be collected from the DSPs 221 to a further computing device, such as the PC 23 for further processing and display.
  • the collecting and the transfer of the data may be provided by any suitable means, such as the ethernet chip 23 or other communication means.
  • the PC 23 displays a desired sonar view, such as the detected objects, on a display (integrated or separate display unit). Alternatively, all further processing and calculations as well as the display may be provided by the data processing part 22.
  • the further processing and display after determining a combined correlation function which represent both the / part and the Q part, such as AQI, are not essential to the present invention but they may embodied in any suitable manner and their realization will be apparent to a person skilled in the art.
  • the invention is directed to a new data processing for obtaining more accurate correlation functions in real time and with reduced data processing capacity, for use in such further processing.
  • Barker 13 code was used for phase coding the sounding signal.
  • Barker codes or their modifications, or other binary codes may be employed as well.
  • the choice of the binary code affects on the performance and signal processing of embodiments of the present invention.
  • code specific digital signal processing procedures are described; all examples are based on Barker 3 code.
  • all examples are given for only one quadrature component; processing another component is analogous.
  • Barker-on-Barker codes are also called as “compound Barker codes” or “nested Barker codes”. Barker-on-Barker code means that one Barker code is used to modulate another Barker code, i.e. there is an inner code and outer code.
  • the three elements Barker code B 3 is used as an example below but the processing is applicable to any Barker code.
  • the B 3 code has the following form:
  • B 3 xB 3 code is so-called outer code and another is so-called inner code.
  • An example of B 3 xB 3 code is shown in Figure 1 1 (corresponding to signal from step 107 in the general processing illustrated in Figure 10. Preceding processing may be similar to steps 101-106 in Figure 10). Note that there are four shifted copies of B 3 xB 3 , because one B 3 xB 3 code element contains four points (signal periods).
  • the first step may be matched filtering for B 3 code resulting in correlation functions of the inner codes.
  • B 3 xB 3 there will be three sets of correlation functions after matched filtering operation, since the length of the outer code is three.
  • each set of correlation function contains four copies of the correlation function.
  • the result is depicted in Figure 12(a).
  • Figure 12(a) illustrates the combined correlation function of the four copies (corresponding to the result of step 109 in the general processing illus- trated in Figure 10, i.e. the combined correlation function shown in Figure 7(e) or 8(a)).
  • the separate matched filtering of each copy of the code corresponding to step 108 and the combining corresponding to step 109 in the general processing may be performed also in this cpde specific processing.
  • Figure 12(a) also reveals that the correlation function of B3 code suffers from high magnitude sidelobes.
  • the height of side lobes is 1/3 (-9.54 dB).
  • side-lobe suppressing filtering may be applied to reduce the side-lobes of the correlation function (corresponding to step 1 1 1 in Figure 10, when applied after step 109).
  • the height of side-lobes of correlation function can be reduced to 1/28 (-28.94 dB) by using FIR type filter of the following coefficients as a side-lobe suppression filter /7 ⁇ 3 :
  • the result of the inner code processing is an outer code (i.e. correlation functions shown in Figure 12(a) or 12(b)), which is also B 3 code in this case, needs to be further processed. Therefore, the next step may be to apply matched filtering to the outer code shown in Figure 12(a) (in embodiments wherein the side-lobe suppression filtering is not applied) or the outer code shown in Figure 12(b) (in embodiments wherein the side-lobe suppression filtering is applied).
  • Figures 12(c) and 12(d) illustrates the results of the matched filtering without and with the side-lobe suppression filtering, respectively. It should be noted that in each case there are four shifted copies of the correlation function.
  • a moving average filter may be applied to the processed correlation function of the outer code of ⁇ 3 ⁇ 3 (corresponding to step 1 10 in Figure 10).
  • the resulting correlation function is shown in Figure 12(e).
  • M-codes are novel modified "Barker-on-Barker codes" developed by the inventor for sonar applications.
  • M-codes are used to form outer Barker code by using pairwise multiplication of correlation functions of inner code elements.
  • B 3 code as an example but it is applicable to any Barker code.
  • An outer code for which the corresponding M-code will be designed is selected, the outer code having length N, i.e. it comprises N code elements.
  • Inverted version of the outer code is found, i.e. the value of each code element of the outer code is inverted (e.g. "- ⁇ "+1 " or "+ ⁇
  • the first pair may be selected freely, and the first integer (e.g. in each subsequent pair may be selected to be the same integer (e.g. as the second integer in the next preceding pair.
  • the obtained presentations of the code elements are combined into an M-code having length ⁇ /+1 .
  • the value of the first code element may obtain the value of the first integer in the first pair
  • the value of the second code element may obtain the common value of the second integer of the first pair and the first integer of the second pair
  • the value of the Nth code element obtain the common value of the integer of the (A/-1) th pair and the first integer of the N pair
  • the value of the last, ( ⁇ /-1 ) , code element may obtain the value of the second integer of the /V th pair.
  • the B 3 code ⁇ +1 ; +1 ; -1 ⁇ is selected as an outer code.
  • the resulting M-code for the B 3 code can have one of the following forms:
  • the M-codes can be obtained without the code inversion (step (b) in above given scheme) as well.
  • the drawback of this approach is that then the number of phase changes ⁇ or " +1 " ⁇ " -1 ”) is smaller compared to the case when inverted version of code is used. Larger number of phase changes is more favourable in order to better detect the code in noisy conditions.
  • M-codes for other Barker codes can be obtained using the same scheme.
  • a complete list of M-codes for all binary Barker codes, when code inversion is used, is given below.
  • the code used for phase coding in embodiments of the invention may be based on any one of these M-codes.
  • the received signal is phase coded according to the B M1 3 code, i.e. equation (E.13).
  • the shape of the code is shown in Figure 13 (corresponding to signal from step 107 in the general processing illustrated in Figure 10. Preceding processing of the received signal may be similar to steps 101-106 in Figure 10). Note that there are four shifted copies of the B M1 3 code since one code element contains four points.
  • the first step may be matched filtering for B 3 code resulting in correlation functions of the inner codes.
  • the result is depicted in Figure 14(a).
  • Figure 14(a) illustrates the combined correlation function of the four copies (corresponding to the result of step 109 in the general processing illustrated in Figure 10, i.e. the combined correlation function shown in Figure 7(e) or 8(a)).
  • the separate matched filtering of each copy of the code corresponding to step 108 and the combining corresponding to step 109 in the general processing may be performed also in this code specific processing.
  • Figure 14(a) illustrated the correlation function, when a side-lobe reduction filtering is applied, but the processing may be performed without the side-lobe reduction filtering as well.
  • the processing of the received outer (inverted) code may be analo- gous to the case of conventional Barker-on-Barker codes described above. That is, correlation function of the outer code may be computed and thereafter side-lobe suppression filter, as described by equation (E.12), may be applied. The results of those steps are illustrated in Figures 14(c) and 14(d), respec- tively.
  • the moving average filter may be applied to the processed correlation function of the outer code with the result shown in Figure 14(e).
  • the other quadrature component (/ or Q) is processed in an analogous way such that a correlation function of the type shown in Figure 14(d) is ob- tained also for the other component.
  • the modulus of quadrature components may be computed by using equation (E.8) or (E.7) (corresponding to step 1 12 in Figure 10).
  • V-codes are another modified outer code version by the inventor for sonar applications, resembling to the Barker-on-Barker codes.
  • inner code elements are modulated differently, when the outer code element has the value "-1 ", and processing of the inner code elements is done differently, as well.
  • B 3 code as an example below but the processing is applicable to any Barker code.
  • the main advantage of the V-codes over the conventional Barker-on-Barker codes, while being of comparable length, is that the V-codes are less sensible to the Doppler effect. This property allows using the algorithm at higher vessel speeds without modifications.
  • An outer code for which the V-code will be designed is selected, the outer code having length N, i.e. it comprises N code elements.
  • each code element of the outer code is formed a corresponding inner code.
  • Each inner code is formed of two equal halves.
  • the consecutive code elements of the inner code may be arranged into consecutive groups of L codes, such that first LI2 code elements in each group are designated to the first half of the inner code, and the last L/2 code elements in each group are designated to the second half of the inner code. If the value of the respective outer code element is "+ ⁇ , then the inner code is left unchanged, i.e. all code elements of the inner code are equal to the code elements of the outer code. If the value of the respective outer code element is then values of the first half of the code elements of the respective inner code are equal to the code elements of the outer code, whereas the values of the second half of code elements of the respective inner code are reversed, i.e.
  • the process may be done vice versa. That is, if the value of the outer code element is then the inner code is left unchanged, and if the value of the outer code element is then the values of the second half of inner code elements are reversed, i.e. "+ ⁇ "- ⁇ and "- ⁇ "+ ⁇ .
  • the corresponding V-codes are arranged into table row-by- row manner.
  • the first column (boldface) denotes the outer code B 5 .
  • Different elements of the outer code are denoted 'a' and '£>', depending on the polarity of the corresponding element.
  • columns 1 and 2 refer to the first and second halves of the inner code.
  • V-code using B 3 can be denoted as: i.e., 'a' corresponds to the and 'b' corresponds to
  • the code element 'a' consists of an unchanged B 3 code but the code element 'b' consists of a modified B 3 code, where the first half and the last half of the inner code elements have opposite phases. This condition also implies that there must be an even number of points in one code element.
  • the outer code elements 'a' and 'b' are described as follows:
  • FIG. 15 An example of a signal, which is phase coded according to B v 3 code, i.e. equation (E. 3), when an inner code element has four points, is shown in Figure 15 (corresponding to the signal from step 107 in the general processing illustrated in Figure 10. Preceding processing may be similar to steps 101-106 in Figure 10). Note that there are four shifted copies of the B v 3 code since one code element contains four points.
  • the processing of the inner code may start by splitting the content of each inner code into two equal halves. For example, if there are four data points per inner code element, then there are also four copies of shifted code, as illustrated in Figure 15.
  • the splitting means that the first half includes 1 st and 2 nd code from the whole set, while the second half includes 3 rd and 4 th code.
  • the correlation functions may be computed for both halves, and then the calculated correlation functions may be multiplied result- ing in one correlation function per outer code element.
  • the next step is computing a correlation function of the outer code of B V 3.
  • the result is shown in Figure 16(b).
  • a side-lobe reduction filter e.g. equation (E.12), may be applied to reduce the side-lobe level of the correlation function of the outer code of B v 3 .
  • the result is shown in Figure 16(c).
  • the moving average filter may be applied to the processed correlation function of the outer code so as to obtain the triangular correlation function shown in Figure 16(d).
  • the other quadrature component (/ or Q) is processed in an analogous way such that a correlation function of the type shown in Figure 16(d) is obtained also for the other component.
  • the modulus of quadrature components is computed by using equation (E.8) or (E.7) (corresponding to step 1 12 in Figure 10).

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

Selon l'invention, dans un récepteur de sonar, des signaux de son numérisés reçus (rsd0-rsd30) sont traités sous la forme de signaux formés en faisceau (rb0-rb30) correspondant à différents angles d'azimut. Ensuite, des composantes en quadrature et en phase sont décodées, contenant chacune N copies du code prédéterminé en résultat de la définition de chaque élément de code d'un code prédéterminé par les N périodes du signal sonore. Ensuite, une fonction de corrélation est calculée séparément pour chaque copie individuelle du code, ou, autrement dit, le processus est divisé en un certain nombre d'étapes, lequel est égal au nombre de points de données (périodes de signal) par élément de code. Après que des fonctions de corrélation de toutes les copies individuelles du code ont été calculées, les résultats sont combinés (alignés) et le filtre de moyenne mobile est appliqué, produisant en résultat une fonction de corrélation globale. Ce type d'approche de traitement, au lieu de calculer une fonction de corrélation directement, permet d'obtenir un calcul plus efficace, ou, autrement dit, moins d'opérations arithmétiques doivent être effectuées pour obtenir le résultat final. En résultat, une moindre capacité de calcul est nécessaire pour un traitement en temps réel.
PCT/IB2010/055168 2009-11-16 2010-11-15 Procédé et appareil pour traiter des signaux de sonar WO2011058527A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2557434A1 (fr) * 2011-08-09 2013-02-13 Valeo Schalter und Sensoren GmbH Procédé pour empêcher l'exploitation minière à l'origine d'un signal reçu par un capteur à ultrasons d'un véhicule automobile, dispositif d'assistance au conducteur de véhicules automobiles
WO2013107565A1 (fr) * 2012-01-19 2013-07-25 Robert Bosch Gmbh Procédé et dispositif de détection d'environnement pour déterminer la position et/ou le mouvement d'au moins un objet situé dans l'environnement d'un véhicule au moyen de signaux acoustiques réfléchis sur l'objet
CN112083402A (zh) * 2020-09-15 2020-12-15 哈尔滨工程大学 一种水池条件下的水下目标走航探测实验方法

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JPS54136294A (en) * 1978-04-14 1979-10-23 Nippon Telegr & Teleph Corp <Ntt> Ievel measurement unit of correlation signal
WO2007050289A1 (fr) * 2005-10-21 2007-05-03 Raytheon Company Systeme et procede de sonar a faible probabilite d'influence sur les mammiferes marins
US20070097785A1 (en) * 2004-11-03 2007-05-03 Larry Kremer Suppressed feature waveform for modulated sonar transmission
US20080111734A1 (en) * 2006-11-14 2008-05-15 Fam Adly T Multiplicative mismatched filters for optimum range sidelobe suppression in Barker code reception
US20090135672A1 (en) * 2007-11-27 2009-05-28 Denso Corporation Direction detecting device and direction detecting system

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Publication number Priority date Publication date Assignee Title
JPS54136294A (en) * 1978-04-14 1979-10-23 Nippon Telegr & Teleph Corp <Ntt> Ievel measurement unit of correlation signal
US20070097785A1 (en) * 2004-11-03 2007-05-03 Larry Kremer Suppressed feature waveform for modulated sonar transmission
WO2007050289A1 (fr) * 2005-10-21 2007-05-03 Raytheon Company Systeme et procede de sonar a faible probabilite d'influence sur les mammiferes marins
US20080111734A1 (en) * 2006-11-14 2008-05-15 Fam Adly T Multiplicative mismatched filters for optimum range sidelobe suppression in Barker code reception
US20090135672A1 (en) * 2007-11-27 2009-05-28 Denso Corporation Direction detecting device and direction detecting system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2557434A1 (fr) * 2011-08-09 2013-02-13 Valeo Schalter und Sensoren GmbH Procédé pour empêcher l'exploitation minière à l'origine d'un signal reçu par un capteur à ultrasons d'un véhicule automobile, dispositif d'assistance au conducteur de véhicules automobiles
WO2013107565A1 (fr) * 2012-01-19 2013-07-25 Robert Bosch Gmbh Procédé et dispositif de détection d'environnement pour déterminer la position et/ou le mouvement d'au moins un objet situé dans l'environnement d'un véhicule au moyen de signaux acoustiques réfléchis sur l'objet
CN112083402A (zh) * 2020-09-15 2020-12-15 哈尔滨工程大学 一种水池条件下的水下目标走航探测实验方法

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