AU2018376171A1 - System for generating redundant synchronisation signals - Google Patents
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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
- 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
- G01S7/52004—Means for monitoring or calibrating
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- G—PHYSICS
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D9/00—Recording measured values
- G01D9/005—Solid-state data loggers
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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
- 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
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0008—Synchronisation information channels, e.g. clock distribution lines
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0602—Systems characterised by the synchronising information used
- H04J3/0605—Special codes used as synchronising signal
- H04J3/0608—Detectors therefor, e.g. correlators, state machines
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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Abstract
The invention concerns a method for generating a redundant synchronisation signal CMI_Backup (H) from a main synchronisation signal CMI that synchronises the operation of data acquisition modules positioned in a chain of acquisition modules and organised into groups, or HUBs, each HUB transferring the acquired data to a common data bus, said data circulating on the common data bus in the form of data frames (C), each comprising a frame start signal or Top_Frame_Line, the signal CMI being synchronous with the stream of frames (C) circulating on the data bus. A redundant synchronisation signal CMI_Backup is formed at each HUB by extracting the frame start signal (E) from each frame and by producing a internal synchronisation signal or Top_Frame_Backup (F), the period of which is slaved to the period of occurrence of the frame start signal (E).
Description
System for generating redundant synchronization signals
FIELD OF THE INVENTION
The invention relates to the field of digital towed linear acoustic antennas, of conventional electro-acoustic technology, and more particularly to electronic telemetry systems ensuring the digitization of the signals generated by the set of acoustic hydrophones constituting such an antenna and by Non-Acoustic Sensors (NAS) (sensors of temperature, immersion, heading, roll/pitch, etc.) required for the signal processing of Sonar pathways and for their utilization.
The invention relates directly to a method and a system for producing and distributing synchronization signals which are made redundant in an electronic telemetry system of a towed linear acoustic antenna.
Context of the invention - prior art
Globally in the field of anti-submarine warfare, listening capability at very low frequency remains a permanent challenge and a major issue, and technical solutions are constantly sought which touch in particular upon the hardware and/or the processing of sonar signals, in order to increase detection distances.
In the 1980s-90s, detection systems based on technologies of towed linear antennas with very low frequency listening (VLFL) capability radically advanced the capabilities of defense sonar systems by affording a listening capability making it possible to detect conventional threats in deep waters, sometimes beyond the first convergence zone.
However, a few years ago, new risks related to detection and counterdetection by sound waves at Ultra Low Frequency (« 100 Hz) started to appear, highlighting the need to adapt current listening means to this range of frequencies.
An effective response to this problem consists in producing towed linear antennas of very great length, several hundred meters for example, comprising an increased number of acoustic probes (hydrophones).
The creation and production of such antennas, antennas exhibiting at one and the same time a very great length and, for reasons of accommodatability of the antenna in the towing vessel, a small diameter, poses a significant problem of cabling on account of the volume occupied by the assembly of interconnections linking the various sensors to the central system which synchronizes the assembly, recovers and processes the signals originating from the sensors and feeds power to them, which system is generally situated at the level of the proximal end of the antenna.
Hence, the problem posed by the increase in the length of antennas and therefore in the number of sensors consists therefore, in practice, in seeking solutions making it possible to limit the density of the interconnection cabling inside the antenna, while neither sacrificing system robustness (tolerance to faults, operation in degraded mode with mechanisms which are the simplest possible ...), nor increasing the number and size of the electronic objects (small diameter constraint) involved in this interconnection or the antenna feed constraints (reduced number of feed lines, see a single line, constraints on isolation voltage limited to the usual values at the level of the hard-wired links, the antenna module junction connectors and at the level of the trailer rigging ...).
Presentation of the invention
The invention described in the text which follows is encompassed within an innovative global telemetry system, capable of supplying the power which feeds the various elements of the antenna, of distributing the various synchronization signals, and of collecting and conveying the data and adapting the signals at the antenna head, while proposing a complete solution to the technical problem mentioned above.
To this effect, said system comprises a device for collecting data, a device for distributing synchronization signals with redundancy and an antenna feed device, the simultaneous implementation of which makes it possible to solve the problem posed.
Hence, an aim of the present invention is to propose a redundant system for distributing synchronization signals in a towed linear acoustic antenna comprising a plurality of acoustic modules (hydrophones), said system comprising a single synchronization pathway, so as to decrease the number of pairs of wires required to route the synchronization signals to the various modules.
Another aim of the invention is to propose a synchronization distribution system making it possible to guarantee, despite the absence of redundant synchronization transmitted, by hard-wired pathway, by the general synchronization system, the synchronization of one or the other of the acoustic modules no longer receiving the antenna synchronization signals.
To this effect the subject of the invention is, according to a first aspect, a method for generating a redundant synchronization signal CMI-Backup (H) of a main synchronization signal CMI conveyed by a general synchronization bus intended to synchronize the operation of various data acquisition modules; these modules forming a group of data acquisition modules, or HUBs, and being placed in a chain of acquisition modules, each module transferring the data acquired on a data bus which is common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus. The method according to the invention is characterized in that a redundant synchronization signal CMI_Backup is formed at the level of each HUB by extracting, the frame start pip (E) of each frame passing on the data bus and by producing an internal synchronization pip or Pip_Frame_Backup (F) whose period is slaved to the period of appearance of the frame start pip (E).
According to various provisions which may each be considered separately or in combination with others, the method according to the invention can comprise diverse provisions enumerated hereinafter.
According to a first provision, the Pip_Frame_Backup signal (F) produced forms the subject of a temporal resetting dependent on the position of the group of acquisition modules which is considered in the chain.
According to another provision, after temporal resetting, the Pip_Frame_Backup signal (F) is used to form the synchronization signal CMI_Backup.
According to another provision, the method according to the invention implements a detection operation for detecting the presence of the CMI signal on the general synchronization bus, the CMI-Backup signal being substituted for the CMI signal in case of failure of the latter.
According to another provision, the Pip_Frame_Line signal being a periodic signal of period Tech equal to the renewal period of the data frames, the Pip_Frame_Backup signal produced is a periodic signal, the value of whose period is defined on the basis of a local clock T125M, at a given instant and for a given number N of periods, by the following relation:
x mmm + (N — x) (mmm + 1)
TpipFrameBackup ~ ' ^12 5M = mmm, zzz T125M where mmm, zzz represents a positive decimal number, whose value is defined by taking into account, at the instant considered, the result of a given number of measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
According to another provision, the number N of periods considered being equal to 128, the number mmm, zzz is determined by taking into account, at the instant considered, the result of 128 measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
According to another provision, the numbermmm, zzz is determined on the basis of the mean of 128 consecutive measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
According to another provision, the number mmm,zzz is determined by filtering, by means of an FIR, the value of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced over a depth of 128 measurements.
The invention also pertains to a method for synchronizing a plurality of data acquisition modules forming a group of acquisition modules, the data acquisition modules being placed in a chain of acquisition modules, each module transferring the data acquired on a data bus which is common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus, the method comprising, for each acquisition module, a step of using a main synchronization signal CMI conveyed by a general synchronization bus to synchronize the data acquisition module with the other acquisition modules of the group of data acquisition modules and, when a failure of the main synchronization signal CMI is detected, using the redundant synchronization signal, in place of the main synchronization signal CMI, to synchronize the data acquisition module with the other acquisition modules of the group of data acquisition modules.
The invention also pertains to a synchronization device able to implement, within the HUB to which it belongs, the method according to the invention, characterized in that it comprises means for generating a redundant synchronization signal CMI_Backup comprising; for example mainly:
- a module for extracting the frame pip, or Pip_Frame_Line, of each frame passing on the data bus,
- a set of modules generating the internal synchronization pip or Pip_Frame_Backup on the basis of the Pip_Frame_Line signal extracted by the extraction module.
The Pip_Frame_Line can be obtained by detection and extraction of the data frame synchronization word.
The device comprises, for example, mainly:
- the module for extracting the frame pip, - a set of modules constituting the mechanism which generates a Pip_Frame_Backup signal on the basis of the Pip_Frame_Line signal extracted by the extraction module;
and optionally:
- a module which carries out the checking of the presence and of the integrity of the CM I synchronization signal provided by the synchronization bus as input to the HUB;
- a multiplexing module which delivers to the various acquisition units of the HUB, on command of the integrity checking module, either the CMI synchronization signal received on the synchronization bus, or the CMI_Backup synchronization signal synthesized locally by the device.
And/or optionally:
- a module which ensures the temporal resetting of the Pip_Frame_Backup signal generated by the set of modules and forms a rephased (i.e. temporally reset) signal Pip_Frame_Backup_dly;
- a module which generates a backup synchronization signal, or CMI_Backup, on the basis of the Pip_Frame_Backup signal generated and rephased.
According to a particular provision, the set of modules which generates the Pip_Frame_Backup signal, comprises mainly:
- a module which generates the Pip_Frame_Backup signal on the basis of an information item of mean period setpoint (mmm,zzz T125m)’
- a Phase-comparator module which measures the temporal offset ATinst between the Pip_Frame_Backup signal generated and the Pip_Frame_Line signal extracted by the extraction module;
- an accumulator module which produces the sum, over 128 consecutive periods, of the instantaneous offsets ATinst between the Pip_Frame_Backup signal and the Pip_Frame_Line signal which are measured by the Phase-Comparator module;
- a Filtering module which calculates a mean error per period, ATmean, this error being calculated by the following formula:
128
- 1 V
ATmean ^28 ' · k=l
- a setpoint generating module which delivers the information item of mean period setpoint (mmm,zzz T12sm) to the module which generates the Pip_Frame_Backup signal, the setpoint information item being formulated starting from the value of the mean error per period provided by the filtering module, said information item being reupdated every N=128 periods;
- a lock-on module which calculates a first mean frequency value by integrating the Pip_Frame_Line synchronization signal over 1024 frames and delivers a first initial setpoint (mmm0,zzz0') to the setpoint generating module.
The frame start pip (E) of each frame passing on the data bus can be extracted by means of an autonomous asynchronous clock.
The invention also pertains to a data acquisition module comprising an acquisition device according to the invention.
The invention also pertains to a system comprising a group of data acquisition modules placed in a chain of acquisition modules, the system comprising a general synchronization bus intended to convey a main synchronization signal intended to synchronize the operation of the acquisition modules, the system comprising a data bus, each module transferring the data acquired on the data bus, the data bus being common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus, in which each data acquisition module is a data acquisition module according to the invention.
The system can furthermore comprise groups of sensors, each acquisition module being associated with one of the groups of sensors.
Description of the figures
The characteristics and advantages of the invention will be better appreciated by virtue of the description which follows, which description is supported by the appended figures which present:
figurel, a schematic illustration of the architecture of a global telemetry system able to integrate the synchronization system according to the invention;
figure 2, a timechart representing the general synchronization signal CMI;
figure 3, a schematic illustration demonstrating the layout of the various synchronization devices according to the invention in the global system of figure 1;
figure 4 a timechart illustrating the principle of the rephasing of the Pip_Frame_Backup signal at the level of each HUB;
figure 5, a flowchart describing the essential steps of the method implemented by a synchronization device according to the invention to generate the signal CMI_Backup;
figure 6, a block diagram describing the main functional modules of a synchronization device according to the invention;
figure 7, an illustration of the operating principle of the whole of the generating system according to the invention.
Detailed description
The synchronization system according to the invention is integrated into a global telemetry system 11 which is represented in a schematic manner in figure 1 and in which the various acoustic probes (hydrophones) constituting the antenna are managed by a set of acquisition modules 12 or HUBs. Each HUB manages a given group of acoustic probes and is labeled by its rank n which corresponds to the position occupied by the acoustic probes which are associated with it. The HUBs thus arranged form a chain, each HUB being labeled by its rank in the chain.
In such a system, each HUB 12 of rank n receives from the Hub of rank n-1, HUB n-1, which precedes it in the chain, the data BUS conveying the digital data frames corresponding to the signals received by the various probes associated with the HUBs which precede it, as well as a (main) general synchronization signal CMI delivered by a general synchronization BUS 13 of the antenna. Each HUB is furthermore fed by a general feed loop 14.
During nominal, that is to say fault-free, operation, each acquisition module, or HUB, is synchronized, by the (main) common synchronization signal CMI.
The CMI signal as illustrated by figure 2 is a composite signal, of periodicity Tech, which conveys a clock Hrap, termed fast clock, and an antenna synchronization pip 21 which serves to regulate in a perfectly synchronous manner the sampling of the set of antenna signals to be digitized.
The fast clock Hrap, synchronous with the sampling pip (synchronization pip), is also used by each module HUB 12 of the system to drive, inter alia, the Analogic/Digital converters (generation of a synchronous clock for the Sigma-Delta modulators and the FIR filters integrated into the analogic-digital converters (ADC)...).
In case of incorrect reception of the signal CMI, it is impossible for the HUB to synchronize itself.
The solution commonly used to alleviate a possible defection of the CMI signal consists in envisaging a backup synchronization signal which is transmitted by a dedicated line and onto which the hub switches. However, such a solution requires that an additional synchronization line be put in place in the antenna.
The synchronization system according to the invention proposes a different solution based, as illustrated by figure 3, on the implementation of a set of synchronization devices 31 linked in parallel to the synchronization Bus 13 which conveys the signal CMI. Each synchronization device 31 is dedicated to a particular HUB 12. Stated otherwise, each synchronization device 31 belongs to the HUB 12 to which it is dedicated.
The function of each synchronization device 31 is, as illustrated by the timechart of figure 4, to implement a method consisting in recreating locally, at the level of each HUB 12, a synchronization signal CMI Backup, by generating an internal synchronization signal or Pip_Frame_Backup on the basis of the frame synchronization pip contained in each incoming data frame Data in traveling on the data BUS and, when a failure of the CMI synchronization signal occurs, to substitute the CMI_Backup signal thus formed for the failed signal CMI, so as to ensure continuity of operation of the HUB. According to the invention, the method implemented consists mainly in detecting the occurrence of the frame synchronization pips on the data BUS, to form on the basis of these pips an isolated signal or Pip_frame_Line signal, and to generate an internal synchronization signal Pip_Frame_Backup whose period is slaved to the mean period of the Pip_frame_Line signal formed.
The backup synchronization thus obtained does not require any cabling other than the synchronization bus 13 and the data bus.
Advantageously, the internal synchronization signal Pip_Frame_Backup is generated with the aid of an autonomous asynchronous clock. This clock is internal to the HUB.
Advantageously, the frame start pip (E) of each frame passing on the data bus is extracted with the aid of an autonomous asynchronous clock. This clock is internal to the HUB.
Advantageously, this clock is a fast clock (relative to the period of appearance of the data frames on the BUS).
The principle of forming the Pip-Frame-Backup signal on the basis of the Pip_Frame_Line signal is described in greater detail hereinafter in the text within the framework of the description of means able to implement the method according to the invention.
According to the embodiment considered, a synchronization device 31 can be designed as a dedicated programmable component, configured to carry out the synchronization function described hereinafter in the document.
Alternatively, a synchronization device 31 can be integrated with the programmable component, of FPGA type, ensuring the global management function (nominal Synchro, collection of data, driving of the ADCs...) of the HUB 12 to which it is dedicated.
Figure 6 presents the general functional diagram of a synchronization device 31 according to the invention. This device forms part of a HUB which is linked to the data bus and to the general synchronization bus 13. This device comprises various functional modules which are described in greater detail hereinafter in the text. These modules are configured and arranged functionally with respect to one another in such a way as to implement the steps of the method, illustrated by figure 5, making it possible to generate the signal CMI_Backup.
This method comprises the following main steps (the alphabetic labels between parentheses refer to the corresponding labels of figure 6):
- a step 51 during which the device 31 of the HUB of rank n, HUBn, receives (C) the data frame of the HUB which precedes it in the chain, the HUBn-ι, with a delay θη = to + (n - l)tl with respect to the pip 21 provided by the general synchronization signal CMI transmitted by the general synchronization system of the antenna.
- a step 52 during which the synchronization device 31 dedicated to the HUBn extracts the Pip_Frame_Line signal (E), by decoding the synchronization word of the incoming message. The temporal phasing of the Pip_Frame_Line with respect to the CMI synchro pip is different for each of the HUBs and depends on the position of the HUB considered in the chain formed by the set of HUBs.
This detection of the Pip_Frame_Line signal is marred by jitter which is all the more significant the higher the rank n of the HUB considered, owing notably to the aggregate of the traversal time for the previous HUBs,
However, it should be noted here that the mean value of the jitter is advantageously zero, since the frequency of emission of the initial frame emitted by the HUB1 is equal to the sampling frequency.
- A step 53 during which the synchronization device filters the Pip_Frame_Line signal (E) recovered, said signal exhibiting jitter, with the aid of a mechanism incorporating a digital phase-locked loop, to create and deliver a Pip_Frame_Backup signal (F), created on the basis of a 125-MHz local clock and slaved to the Pip_Frame_Line signal (E) cleaned of its jitter.
Thus, the Pip_Frame_Backup signal delivered is a signal created on the basis of a fast local clock T125M (at 125MHz for example), internal to the HUB, whose period is slaved to the mean value of the period of appearance of the Pip_Frame_Line signal.
The Pip_Frame_Backup signal (F) synthesis mechanism consists of a set of modules whose manner of operation is detailed further on.
Advantageously this provision also allows the system to transmit an antenna synchronization via an asynchronous HD data transmission link regulated by a local clock (internal to the HUB) to avoid accumulation of jitter.
It should be noted that the position of the Pip_Frame_Backup (F) thus formed relative to the CMI synchro pip is different for each of the HUBs.
- A step 54 during which the synchronization device delays the Pip_Frame_Backup signal (F) by a delay Tech - t0 - nt1 dependent on the position in the chain of the HUB of rank n considered, so as to create a Pip_Frame_Backup_dly (G).
This temporal resetting function is necessary to the extent that, as was stated previously, not all the HUBs receive the data frame at the same moment.
Indeed, the first HUB of the chain (HUBo) emits its frame at the instant to after the reception of a frame pip (sampling pip) extracted from the external synchro signal (CMI). Thereafter this data frame is delayed by a time ti at each HUB traversal. The HUB of rank n therefore receives the data frame at the time t0 + (n- 1)^ as illustrated by the timechart of figure 4.
Hence, the PipFrameBackup signal (F) not being in phase with the CMI Pip in the various Hubs of the system, it is necessary at the level of the HUB considered to delay the PipFrameBackup signal (F) by a time equal to Tech. - to_ nti in order to trigger, if necessary, the delivery of a CMI_Backup signal (H) in phase with the input CMI signal.
In this way, the position of the Pip_Frame_Backup_dly (G) relative to the CMI synchro pip is advantageously identical for each of the HUBs.
- A step 55 during which the synchronization device recreates, on the basis of the local clock H125m(125MHz clock) a CMI_Backup signal (H) resynchronized by the Pip_Frame_Backup_dly (G) aligned with the CMI signal (A) present at the input of the HUB.
For each of the HUBs, the CMI_Backup signal (H) is therefore advantageously in phase with the CMI signal (A) thereby affording a common temporal reference and enabling the synchronous sampling of the data on the set of HUBs even in the absence of the CMI signal on some of them.
In order to implement these various steps, the synchronization device 31 according to the invention comprises, as illustrated by figure 6, a set of functional modules implemented in the form of digital functions which cooperate to generate the signal CMI_Backup.
The module 61 carries out, in a conventional manner, the checking of the presence and of the integrity of the CMI synchronization signal (A) provided by the synchronization bus 13 as input to the HUB 12 considered, to which the device is dedicated.
In case of absence, of loss, of the synchronization signal, and more generally in case of failure of the synchronization signal it emits a switching command 611 destined for the multiplexing module 66, which then switches the CMI_Backup synchronization signal (H) produced by the generating module 65. In this manner, the HUB uses the backup synchronization signal CMI_backup instead of the main synchronization signal CMI for its synchronization with the other HUBs.
Stated otherwise, the HUB uses the backup synchronization signal CMI_backup instead of the main synchronization signal CMI to synchronize, with the other HUBs, the acquisition of the signals arising from the sensors managed by the HUB and/or the injection of data frames by the HUB onto the data bus.
The module 62 for extracting the frame pip, or Pip_Frame_Line (E), carries out the operations of the previously described step 52.
To this effect, the Pip_frame_Line signal (E) is obtained by detection and extraction of the data frame synchronization word, according to a conventional extraction principle on a self-synchronizing code.
The Pip_frame_Line signal (E) thus extracted has a mean period T PipFrameLineMean equal to the sampling period Tech(\.e. to the mean travel period of a data frame). This period is measured by averaging over a number N of consecutive frames, with the aid of a clock H12sm (of period T125M). Hereinafter in the text, N=128 consecutive frames are considered by way of nonlimiting example.
H125M being asynchronous with respect to Hech, the relation between the two clocks defines a mean period which may be written:
^PipFrameLineMean Tech. nnn,yyy ’ T^25m [001]
Where nnn and yyy represent respectively the integer part and the decimal part of the ratio between Tech and T125M. The error in this measurement is thus less than ±t^T125m (or more generally ±-T125M).
As stated previously, it is however marred, by jitter, of zero mean value. The instantaneous value (i.e. for a given frame of rank k) of the period of the Pip_Frame_line signal (E) can therefore be expressed by the following relation:
TpipFrameLmeInst(JT) — Tec}l + 6k [002] where 0k represents the disparity between the period TPipFrameLineInst of the frame k and Tech.
Moreover, it exhibits with respect to the CM I signal (A) a delay whose duration depends on the position of the HUB considered in the chain. It is recalled here that the CMI signal (A) carries a fast clock and a sampling pip 21 as illustrated by figure 2.
The set of modules 63 constitutes the mechanism which carries out the operations of step 53 which is intended to generate a Pip_Frame_Backup signal (F) on the basis of the Pip_Frame_Line signal (E) extracted by the module 62. Its manner of operation is detailed further on in the description.
The module 64 carries out the operations of step 54 which is intended to ensure the temporal resetting of the Pip_Frame_Backup signal (F) generated and to form a rephased (i.e. temporally reset) signal Pip_Frame_Backup_dly (G);
The temporal resetting of the Pip_Frame_Backup signal (F) consists in applying to the latter a delay whose value is defined by the rank n of the HUB considered.
The module 65 carries out the operations of step 55, which is intended to generate a backup synchronization signal, or CMI_Backup (H)s, on the basis of the Pip_Frame_Backup signal (F) generated and rephased.
The module 65 generates on the basis of the internal clock H125M a CMI_Backup synchronization signal (H) exhibiting the same characteristics as the input CMI signal (A) and resynchronized by the Pip_Frame_Backup_dly signal (G) delivered by the delay-generating module 64.
The function of the multiplexing module 66 is, on command of the integrity checking module 61, to deliver to the various acquisition units of the HUB 12, either the CMI synchronization signal (A) received on the bus 13 or the CMI_Backup synchronization signal (H) synthesized locally at the level of the HUB considered. The main synchronization signal CMI is delivered to the acquisition units of the HUB when no failure of the synchronization signal is detected, and the CMI_Backup backup synchronization signal (H) is delivered to the acquisition units of the HUB in place of the synchronization signal when a failure of the synchronization signal is detected.
Advantageously, the main synchronization signal CMI is used, by the HUB, to regulate a sampling of the signals arising from sensors managed by the HUB and/or to regulate the injection of data frames by the HUB onto the data bus, when no failure of the main synchronization signal CMI is detected, and the CMI_Backup backup synchronization signal (H) is used in place of the synchronization signal to regulate a sampling of the signals arising from sensors managed by the HUB and/or to regulate the injection of data frames by the HUB onto the data bus, when a failure of the main synchronization signal CMI is detected.
As stated previously, the function of the set of modules 63 is to generate, on the basis of the Pip_Frame_Line signal (E), extracted from the data frame traveling on the data bus, a Pip_Frame_Backup signal (F) used to form the CMI_Backup synchronization signal (H).
In a particular embodiment taken as example, illustrated by figure 6, it consists of the modules 631 to 636 arranged so as to produce a phaselocked loop making it possible to synchronize in the most precise manner possible the Pip_Frame_backup signal (F) generated and the Pip_Frame_Line signal (E), stated otherwise to slave the first to the second.
This set of modules 63 is organized around a module 631 which ensures the generation properly speaking of the Pip_Frame_Backup signal (F).
The module 631 generates the Pip_Frame_Backup signal (F) on the basis of the information item of mean period setpoint (mmm,zzz T12sm)’ calculated by the block 635, where τητητη,ζζζ represents a given decimal number. The module 631 is a digital VCO whose output frequency is dependent on an input setpoint (mmm,zzz), refreshed every 128 frames.
Hence, to generate a Pip_Frame_Backup signal of mean period mmm,zzz T125m, the module 631 generates a sequence of N=128 Pip_Frame_Backup sequenced in the following manner:
-Creation of a sub-sequence of k Pip_Frame_backup of period mmm-T125M.
-Creation of a sub-sequence of (128 - k) Pip_Frame_backup of period (mmm+ 1) -T125M.
This scheme advantageously makes it possible to limit the jitter to +T125M during the generation of the sequence of 128 Pip_Frame_backup.
The mean period TpipFrameBackup of such a sequence of N=128
Pip_Frame_backup is defined by the following relation:
k mmm + (128 — fc) (mmm + 1) TpipFrameBackup Λ no ' ^12SM
128 , (128 mmm + ——— T125M IZo 1 = mmm,zzz T12SM [003] where mmm,zzz represents a given decimal factor.
The value of the error ΔΤpipFrameBackup in th® mean period created with respect to the period of the Pip_Frame_Line signal is given by the relation:
ATpipFrameBackup ~ TpipFrameBackup ~ fpipFrameLineMean [004]
ATpipFrameBackup (mmm H ‘ 7125M — 117171, yyy ' T-^25M [005]
According to the invention, the value of x is chosen so as to minimize the absolute value of the disparity ATp^FrameBacfcltp. In this way, for N=128 frames, the error in TpipFrameBackup is less than +^T125M
Hence, each of the terms of equation [004] being marred by an error of less than ± — T125M, the maximum error in &TPipFrameBackup is also bounded, in such a way that we have:
ATpipFrameBackup — i ' T12SM [006]
Hence, two cases can then arise:
-TpipFrameBackup > TECh· in this case it is possible to have mmm = nnn or mmm = nnn + 1
-TpipFrameBackup <TEch·. in this case it is possible to havemmm = nnn or mmm = nnn — 1
The mean period setpoint (mmm, zzz), is updated every N=128 periods.
The changing of the setpoint value (therefore of the period of the Pip_Frame_Backup signal) constitutes the main cause of the jitter produced on this same signal, jitter whose amplitude versus time is dependent on the significance of the correction.
It should be noted that, given the stability of the various quartz that can be used to synthesize the clock H125M (quartz of stability of the order of 50 ppm), the value of Tech remains stable enough over 2 consecutive slices of 128 Pip_Frame_Line such that advantageously therefore the main aim of the correction to be made is to compensate the error related to the fact that the mean period of the Pip_Frame_Backup signal (mmm,zzz T^sm) is not strictly equal to Tech.
The formulation of this setpoint (mmm, zzz) is carried out by the modules 632 to 636 of the set 63 which are described hereinafter.
The Phase-comparator module 632 measures the temporal offset, the phase disparity, between the Pip_Frame_Backup signal (F) generated by the block 631 and the Pip_Frame_Line signal (E) extracted by the module 62.
For Frame k, the error (i.e. the disparity) in instantaneous phase &Tinst between Pip_Frame_Line and Pip_Frame_Backup is determined by the following relation:
— TpipFrameLine(Jt) TpipFram.eBa.ckup [008]
ATinst(k) = (nnn,yyy T_125M ± Sk) — mmm zzz T125M [009]
The accumulator module 633 produces the sum, over 128 consecutive periods, of the instantaneous temporal offsets between the Pip_Frame_Backup signal (F) and the Pip_Frame_Line signal (E) which are measured by the Phase-Comparator module 632. The quantity expressed as output is an integer number of periods T12sm·
The expression for the aggregate of these offsets ZATinst over N=128 frames is:
EfcliATinst = Efcli[ (nnn,yyy T125M ± 5k) - mmm,zzz T125M] [010]
Efcl=iATinst = ΣΐΙ^Κηηη,γγγ T125M) - (mmm,zzz T125M)] [011]
128 fc = l
The mean jitter δ having, a priori, a zero mean value over N=128 consecutive frames, the approximated expression for the aggregate ZATinst over 128 frames is then:
Efcli &Tinst ~ Efcl8i[ (nnn,yyy T125M) - (mmm,zzz T125M)] [012]
i.e., by taking account of condition [006]:
Σ£=ι ΔΤίη5ί. < Σλ=ι~ T125M < 2 T125m [013] □4
The Filtering module 634 calculates a mean error per period, ATmean, which corresponds to the mean over N=128 consecutive frames, of the Pip_Frame_Backup signal's phase error measured for each frame. This error in the period ATmean is then estimated by the following formula:
Δ7·^,ο„ = Σ12=?ιΔΤ,ηΛ [014]
The value of the mean error per period ATmean is provided to the module 635 so that it corrects its setpoint. On the basis of the value of the mean error per period 637 provided by the filtering module 634, the module 635 calculates the new setpoint value (mmm,zzz)for the generation of the next N=128 Pips_Frame_Backup by the module 631.
It should be noted, that upon initialization of the system, the first setpoint (mmm0,zzz0) is provided by the lock-on module 636 which calculates a first mean frequency value by integrating the Pip_Frame_Line synchronization signal (E) over 1024 frames so as to have the most precise possible initial period value. This initial value is transmitted to the module 635.
Thus constituted, the set 63 takes the form of a slaved system whose manner of operation can be illustrated, from a sequential point of view, by the diagram of figure 7. The aim of the system being to Create, on the basis of a local clock at 125MHz (Ti25M) a PipFrameBackup signal, of mean period Tech slaved to the Pip_Frame_Line signal present at E and cleaned of the jitter which affects this signal.
The operating sequence of the set 63 thus comprises:
- A first phase, or phase 1, of lock-on of the loop during which the mean period of the Pip_Frame_Line signal over 1024 data frames is measured. The jitter having a zero value, a mean value equal to Tech is found.
On completion of this phase the module 636 delivers to the module 635 an initial period setpoint (mmm0,zzzQ T12$m) which corresponds to the mean value calculated. This setpoint is maintained during the N=128 data frames which follow.
- a second phase, or phase 2, of closed-loop operation during which the module 631 generates in an iterative manner, during 128 periods, a Pip_Frame_Backup signal of given period.
The value of the period of the Pip_Frame_Backup signal thus generated is fixed at each iteration n, by the period setpoint (mmm,yyyn_1 T125M) calculated on the basis of the Pip_Frame_Line signal extracted from the 128 data frames considered at the previous iteration n-1.
During this second phase:
- for each received frame, the instantaneous phase offset of the Pip_Frame_Backup signal with the Pip_Frame_Line signal extracted from the frame considered is measured.
- the instantaneous phase offsets measured for the 128 data frames are aggregated and the mean thereof is taken so as to eliminate the jitter which affects the Pip_Frame_Line signal extracted from each frame.
- a new period setpoint (mmm,yyyn T125M) for the following slice n+1 of N=128 frames is generated, as a function of the value of this aggregate, so as to compensate the disparity measured.
As stated previously, the choice of the number N of data frames taken into account simultaneously to formulate the Pip_Frame_backup signal can vary from one application of the invention to another. In the above development, it has been considered that N was equal to 128.
However, more generally, it should be considered that the choice of the number N of data frames results from a compromise. Indeed, N must be chosen in such a way that it is possible to exploit the character centered on 0 (zero mean value) of the value of the jitter which affects the Pip_Frame_line signal.
Therefore N must necessarily take a sufficient value to obtain this benefit.
Moreover, it should be noted that on account of the constitution of the locking loop intended to slave the period of the Pip_Frame_backup signal to the period Tech and of the necessary accumulation of a sufficient number of measurements of phase disparities between Pip_Frame_backup and Pip_Frame_line, to manage an appreciable error signal 637, the correction made at the level of the synthesis of the Pip_Frame_backup signal occurs only every N frames.
Therefore, in order to prevent the correction made from bringing about in certain cases too significant a jump of the period of the signal generated, N must be chosen in such a way that the renewal of the correction setpoint is as frequent as possible.
The synchronization device, such as it is described in the foregoing text, according to the invention can very obviously form the subject of diverse structure variants, the essential thing being that the general principle of the method implemented to carry out the synthesis of the signal of the Pip_Frame_Line signal remains unchanged and that this signal is always obtained by recovery of the Pip_Frame_Line signal on the data bus measurement of the period of this signal and slaving of the period of the Pip_Frame_Backup signal to that of the Pip_Frame_Line signal.
In this regard in particular, it is possible to envisage various structure variants of the module 63 charged with the synthesis of the Pip_Frame_Backup signal on the basis of the Pip_Frame_Line signal.
It is for example possible to replace the modules 633 (accumulator of phase disparities) and 634 (filtering) by a single module carrying out a nonrecursive filtering function (FIR) over a depth of N frames (128 frame for example) and delivering an error signal 637 the value of which is dependent on the value delivered by the FIR.
In such a configuration, however, an error signal is delivered at the tempo of the frame and not every N frames. Hence, the module 635 charged with the calculation of the setpoint (mmm, zzz) applied to the module 631 must be configured to recalculate the value of this setpoint for each data frame.
Likewise, phase 2 of operation of the module 63 as a whole must comprise for each frame received:
- a measurement, (module 632) for each frame received, the instantaneous phase offset (i.e. for the frame considered) of the Pip_Frame_Backup signal with the Pip_Frame_Line signal extracted from the frame considered.
- the calculation of a disparity term 637, by FIR filtering over a depth of N values of the instantaneous phase offset measured frame after frame;
- the formulation for the forthcoming frame of a new period setpoint (mmm,yyyn T125M), the value of the setpoint being able in this case to be calculated for each frame and not just for the forthcoming N-frame group.
Claims (16)
1. A method for generating a redundant synchronization signal CMIBackup (H) of a main synchronization signal CMI conveyed by a general synchronization bus intended to synchronize the operation of various data acquisition modules forming a group of data acquisition modules, or HUBs, and placed in a chain of acquisition modules, each module transferring the data acquired on a data bus which is common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus, characterized in that a redundant synchronization signal CMI_Backup is formed at the level of each HUB by extracting the frame start pip (E) of each frame passing on the data bus and by producing, an internal synchronization pip or Pip_Frame_Backup (F) whose period is slaved to the period of appearance of the frame start pip (E).
2. The method as claimed in claim 1, characterized in that the Pip_Frame_Backup signal (F) produced forms the subject of a temporal resetting dependent on the position of the group of acquisition modules which is considered in the chain.
3. The method as claimed in claim 2, characterized in that after temporal resetting, the Pip_Frame_Backup signal (F) is used to form the synchronization signal CMI_Backup.
4. The method as claimed in one of claims 1 to 3, characterized in that it implements a detection operation for detecting the presence of the CMI signal on the general synchronization bus, the CMI-Backup signal being substituted for the CMI signal in case of failure of the latter.
5. The method as claimed in any one of the preceding claims, characterized in that the Pip_Frame_Line signal being a periodic signal of period Tech equal to the renewal period of the data frames, the Pip_Frame_Backup signal produced is a periodic signal, the value of whose period is defined on the basis of a local clock T12SM, at a given instant and for a given number N of periods, by the following relation:
_ x-mmm+(N-xy(mmm+l)
1 PipFrameBackup ‘ 125M = mmm, zzz T12sm where mmm, zzz represents a positive decimal number, whose value is defined by taking into account, at the instant considered, the result of a given number of measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
6. The method as claimed in claim 5, characterized in that, the number N of periods considered being equal to 128, the number mmm, zzz is determined by taking into account, at the instant considered, the result of 128 measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
7. The method as claimed in claim 6, characterized in that the number mmm, zzz is determined on the basis of the mean of 128 consecutive measurements of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced.
8. The method as claimed in claim 6, characterized in that the number mmm,zzz is determined by filtering, by means of an FIR, the value of the temporal offset between the Pip_Frame_Line signal (E) extracted and the Pip_Frame_Backup signal (F) produced over a depth of 128 measurements.
9. A method for synchronizing a plurality of data acquisition modules forming a group of acquisition modules, the data acquisition modules being placed in a chain of acquisition modules, each module transferring the data acquired on a data bus which is common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus, the method comprising, for each acquisition module, a step of using a main synchronization signal CMI conveyed by a general synchronization bus to synchronize the data acquisition module with the other acquisition modules of the group of data acquisition modules and, when a failure of the main synchronization signal CMI is detected, using the redundant synchronization signal, in place of the main synchronization signal CMI, to synchronize the data acquisition module with the other acquisition modules of the group of data acquisition modules.
10. A synchronization device (31) able to implement, within the HUB (12) to which it belongs, the method as claimed in any one of claims 1 to 8, characterized in that it comprises means for generating a redundant synchronization signal CMI_Backup comprising:
- a module (62) for extracting the frame pip, or Pip_Frame_Line (E), of each frame passing on the data bus,
- a set of modules (63) generating the internal synchronization pip or Pip_Frame_Backup (F) on the basis of the Pip_Frame_Line signal (E) extracted by the extraction module.
11. The synchronization device (31) as claimed in the preceding claim, characterized in that it comprises:
- a module (64) which ensures the temporal resetting of the Pip_Frame_Backup signal (F) generated by the set of modules (63) and forms a rephased (i.e. temporally reset) signal Pip_Frame_Backup_dly (G);
- a module (65) which generates a backup synchronization signal, or CMI_Backup (H)s, on the basis of the Pip_Frame_Backup signal (F) generated and rephased.
12. The synchronization device (31) as claimed in any one of claims 10 to 11, characterized in that it comprises:
- a checking module (61) which carries out the checking of the presence and of the integrity of the CMI synchronization signal (A) provided by the synchronization bus (13) as input to the HUB (12);
- a multiplexing module (66) which delivers to the various acquisition units of the HUB (12), on command of the integrity checking module (61), either the CMI synchronization signal (A) received on the synchronization bus (13), or the CMI_Backup synchronization signal (H) synthesized locally by the device.
13. The synchronization device (31) as claimed in any one of claims 10 to 12, characterized in that the set of modules (63), which generates the Pip_Frame_Backup signal (F), comprises mainly:
- a module (631) which generates the Pip_Frame_Backup signal (F) on the basis of an information item of mean period setpoint (mmm,zzz 7125m)1
- a Phase-comparator module (632) which measures the temporal offset ATinst between the Pip_Frame_Backup signal (F) generated and the Pip_Frame_Line signal (E) extracted by the extraction module (62);
- an accumulator module (633) which produces the sum, over 128 consecutive periods, of the instantaneous offsets ATinst between the Pip_Frame_Backup signal (F) and the Pip_Frame_Line signal (E) which are measured by the Phase-Comparator module (632);
- a Filtering module (634) which calculates a mean error per period, ATmean, this error being calculated by the following formula:
128 - 1 V ATmean — ^2g / i ATinst k=l
- a setpoint generating module (635) which delivers the information item of mean period setpoint (mmm,zzz T12SM) to the module (631) which generates the Pip_Frame_Backup signal (F), the setpoint information item being formulated to start from the value of the mean error per period (637) provided by the filtering module (634), said information item being reupdated every N=128 periods;
- a lock-on module (636) which calculates a first mean frequency value by integrating the Pip_Frame_Line synchronization signal (E) over 1024 frames and delivers to the setpoint generating module (635) a first initial setpoint (mmm0,zzz0).
14. A data acquisition module comprising an acquisition device as claimed in any one of claims 10 to 13.
15. A system comprising a group of data acquisition modules placed in a chain of acquisition modules, the system comprising a general synchronization bus intended to convey a main synchronization signal intended to synchronize the operation of the acquisition modules, the system comprising a data bus, each module transferring the data acquired on the data bus, the data bus being common to all the acquisition modules of the chain, said data traveling on the common data bus in the form of data frames (C), each frame comprising a frame start pip or Pip_Frame_Line, said main synchronization signal CMI being synchronous with the flow of the frames (C) traveling on the data bus, characterized in that each data acquisition module is a data acquisition module as claimed in claim 14.
16. The system as claimed in the preceding claim, comprising groups of sensors, each acquisition module being associated with one of the groups of sensors.
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| FR1701250A FR3074303B1 (en) | 2017-11-28 | 2017-11-28 | SYSTEM FOR GENERATING AND DISTRIBUTING REDUNDANCED SYNCHRONIZATION SIGNALS IN A TOWED LINEAR ACOUSTIC ANTENNA |
| FR1701250 | 2017-11-28 | ||
| PCT/EP2018/082729 WO2019105945A1 (en) | 2017-11-28 | 2018-11-27 | System for generating redundant synchronisation signals |
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| US6697300B1 (en) * | 2002-09-13 | 2004-02-24 | General Dynamics Advanced Information Systems, Inc. | Method and apparatus for determining the positioning of volumetric sensor array lines |
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