Classifications

• • 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
  • H04J3/0652—Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP]

Definitions

• TITLE Delay compensation method in a data transmission network based on the TDMA protocol
• the present invention relates to data transmission networks, and relates more particularly to the temporal synchronization of the exchanges of such data according to the time division multiple access protocol.
• each sensor used in an aircraft is independently connected by a cable to a computer ensuring the processing of its data.
• the associated wiring to each of the sensors then becomes particularly imposing, which poses problems of mass and size. Therefore, adding new sensors is restrictive.
• AFDX Alteronics Full-Duplex Switched Ethernet in English
• a device M l configured as “master” and devices configured “slaves” El, E2, ..., EN.
• a master or slave device is defined as being a set of electronic components ensuring interfacing between the sensors and the computer and jointly ensuring communication between the sensors and the computer.
• “Slave” devices have the ability to interface with multiple sensors with different applications, and receive the data measured by them.
• the “master” device M l which is connected to an aeronautical computer, triggers the reception of data from each of the “slave” devices in order to transmit all of the data collected to the aeronautical computer.
• the “master” device manages communication on the sensor network.
• the master device M l transmits a setpoint TR3 in the form of a sequence of data to each “slave” node El, E2, ..., EN.
• each “slave” device El, E2, ..., EN has programmable electronic means configured to transmit data TR2 to the “master” device M l, to indicate to it that the task has been successfully completed. been carried out for example.
• a protocol used for this type of link is a so-called time multiplexing protocol, as by example TDMA - time division multiple access protocol (for “Temporal Division Multiple Access” in English).
• each TR3 sequence has a duration of around 1ms.
• the master device M l includes a master clock which clocks the transmission of data in each of the TR3 sequences.
• each slave device X I, X2, ..., XN includes a slave clock which clocks the reception of data in each of the TR3 sequences.
• Each data frame TR I includes a master signal M, comprising data relating to the master device M l such as sensor reading commands, or supervision and maintenance commands. Said frame TR I also includes an analog synchronization signal S.
• Each data frame TR2 comprises a plurality of time intervals X I, X2, ..., XN (time slots in English) intended for the transmission of data from each slave node E l, E2, ..., EN to the master device M l.
• N 20 slave devices.
• Each slave device El, E2, ..., EN then has the possibility of communicating the data TR2 with the master device M l during a time interval allocated to it and thus avoiding the risk of data interaction with the others slave devices.
• each slave device El, E2, ..., EN must be clocked on the same reference clock.
• Patent FR 3 108 817 describes the transmission of an analog synchronization signal S in each TRI data sequence.
• the synchronization signal S comprises an amplitude adjustment portion SI, which is in the form of a sinusoidal wave having a constant amplitude during a predetermined number of pulses and an optimized synchronization portion S2, which is in the form of the shape of a triangular-shaped amplitude modulation of the sine wave.
• the optimized synchronization portion S2 does not have a constant amplitude but a variable amplitude, thus the transition between the increasing phase and the decreasing phase is detectable quickly and precisely, which makes it possible to determine a very precise TOP reference instant. It is thus possible to synchronize the master and slave clocks and very precisely timestamp time intervals of each TR3 sequence.
• the reference instant TOP thus makes it possible to define the start of the period at which data XI, X2, ..., XN are sent respectively by each of the slave devices El, E2, ..., EN to the master device M l .
• each device whether master or slave, can lead, through their electronic components, to the addition of a propagation delay of the synchronization signal S or the data TR2.
• This delay also changes depending on the temperature at the level of the master device and the slave devices, which can become problematic in an environment with high thermal constraints.
• This delay can also change depending on the transmission time due in particular to a long distance between the master device and the slave devices.
• the challenge is therefore to overcome the problems mentioned above.
• the invention allows each of the master/slave nodes to synchronize independently.
• the subject of the invention is a method for compensating delay in a bidirectional data transmission network based on the TDMA protocol, between a master device and at least one slave device, said delay being due to electronic means of transmission of internal data to the master and slave devices, the method comprising the following iterative steps:
• Each node is thus capable of measuring its own electronics by “looping back”, without affecting other nodes on the electrical cable. Each node then uses this measurement to change the instant at which it will transmit on the electrical cable and center its listening window for the receiving signal.
• each device autonomously measures the delay generated by the propagation of signals within its circuit.
• electronic transmission namely transmission and reception of data.
• a master or slave device when a master or slave device is in a communicating group, it is not essential that it acquires the values of the delays generated by other devices.
• the slave device is synchronized to an analog synchronization signal transmitted by the master device.
• a reference instant defining the start of a period of sending data to each slave device is extracted from the data transmitted by the master device.
• the internal delay is measured by looping a loopback signal between the output and the input of each master and slave device and by measuring the propagation time of the looped signal between the output and the input of each master and slave device.
• the loopback signal is generated at regular time intervals.
• the invention also relates to a bidirectional data transmission system comprising a master device and at least one slave device, said system being capable of implementing bidirectional data communication between the master device and the slave device, the master device and the slave device comprising electronic means for transmitting data according to a time division multiple access protocol, the data transmission system comprising means for synchronizing the slave device on the master device, by synchronization on a synchronization signal emitted by the master device, means for measuring the internal delay introduced by the electronic data transmission means for each master and slave device and means for compensating the measured internal delay.
• the means for measuring the internal delay comprise means for looping a signal between the output and the input of each master and slave device and means for measuring the duration propagation of the signal looped between the output and the input of each master and slave device.
• the invention also relates to a turbomachine comprising at least one system as defined above.
• the invention also relates to an aircraft comprising a turbomachine as defined above.
• the invention also relates to an aircraft comprising at least one system capable of implementing bidirectional data communication as defined above.
• FIG. l schematically presents a master device communicating with a set of slave devices
• FIG.2 schematically represents a data frame transmitted by the master device to the slave device according to the invention
• FIG.3 illustrates a data communication system comprising a master device and a slave device according to the prior art
• FIG.4b illustrate means for measuring a delay by looping between the data transmission and acquisition means of the master device and the slave device, respectively, according to one embodiment of the invention
• FIG.5b illustrate the principle of delay compensation implemented by means of the method and device according to the invention, and illustrate the transmission of a data sequence respectively without delay compensation, and with delay compensation;
• FIG.6 presents a flowchart of a compensation process according to one mode of implementation of the invention.
• FIG 3 there is shown an electronic system 1 which comprises the master electronic device M l as well as the slave electronic device E l.
• slave devices E2, ..., EN are not illustrated in said figure. Reference will then be made to a single slave device El but this does not exclude the coupling of the device master M l with a plurality of slave devices having an electronic architecture similar to the slave device E l.
• the electronic system 1 comprises a transmission line 2 capable of propagating a signal analog electric.
• the transmission line 2 is then coupled to transmission means 4 and to acquisition means 5 of the master device 1 on the one hand, and to transmission means 6 and reception means 7 of the slave device E l, d ' somewhere else.
• the transmission means 4 comprise a chain of electronic components capable of transforming a digital signal into an analog signal and then transmitting it to the slave device E l via the transmission line 2.
• each TR3 data sequence comprises a TRI header frame and a TR2 data frame.
• the TRI frame comprises a master signal M, comprising data from the master device M l, transmitted by the master device M l for the slave devices E l, E2, ..., EN, an analog synchronization signal S, transmitted by the master device M l for slave devices E l, E2, ..., EN.
• the signal S makes it possible in particular to timestamp the time intervals of the frames of the TR3 data sequence very precisely.
• Each TR2 frame also includes time intervals X 1 -X20 intended for the transmission of data from each slave device to the master device M l.
• the analog synchronization signal S comprises an amplitude adjustment portion SI which is in the form of a sinusoidal wave having a constant amplitude during a predetermined number of pulses and a synchronization portion optimized so as to determine an instant of reference TOP according to patent FR 3 108 817.
• the reference time TOP makes it possible to define the start of the period at which data XI, X2, ..., XN are sent respectively by each of the slave devices to the master device.
• This TOP reference instant is known with great precision.
• it makes it possible to precisely determine the time period between two TOP reference instants, which is of the order of 1 ms, in order to deduce the frequency of the master clock and possibly correct the frequency of the slave clock.
• the reception means 7 comprise a chain of electronic components intended to filter the analog signal TR3 received by the transmission means 4 and to transform it into a digital signal to be processed.
• the transmission means 6 of the slave device E l their function is to transmit an analog signal to the acquisition means 5 capable of filtering it and then transforming it into a digital signal.
• the analog signal is ideally transmitted by the transmission means 6 during the time interval allocated to the slave device El and includes the data TR2 which are transmitted to the master device.
• the electronic components of the transmission means 4 and acquisition means 5 of the master device M l as well as those of the transmission means 6 and reception means 7 of the slave device E l are likely to add a propagation delay of the signal S synchronization or TRI and TR2 data.
• This delay also changes as a function of the temperature at the level of the master device M l and the slave device E l and/or as a function of the transmission time in particular due to a long connection distance between the master device and the slave devices.
• the delay remains substantially equal to DI because the delay linked to the propagation of the signal through the transmission line 2 remains negligible.
• the delay generated is of the order of 200 nanoseconds at most.
• MMSE frequency compensation for “Minimum Mean Square Error”
• the reception of the analog signal TR2 and its transformation into a digital signal by the acquisition means 5 is likely to extend the delay by a duration D4 measured at a fourth observation point N4.
• Knowing said delays D l, D2, D3 and D4 makes it possible to synchronize the windows for transmitting the signal X I -...XN and listening for the signal X I -...XN during such a data exchange.
• Figure 4a illustrates the master device M1 which further comprises measuring means 8a coupled to the transmission means 4 and to the acquisition means 5.
• Such measuring means 8a are capable of generating an analog loopback signal intended to propagate exclusively between the transmission means 4 and data acquisition means 5 and undergoing a propagation delay due to the electronic transmission means of the master device.
• the master device M l comprises a first switch 9a capable of coupling and decoupling the transmission means 4 and the acquisition means 5.
• the master device M l further comprises a second switch 10a capable of coupling and decoupling the transmission means 4 and the transmission line 2.
• a third switch l i a is also arranged between the acquisition means 5 and the transmission line 2 so as to couple and decouple the reception means 5 and the transmission line 2.
• the measuring means 8a can close the first switch 9a and open the switches 10a and 1 al to circulate the loopback signal only between the transmission means 4 and data acquisition means 5.
• the propagation delay of the loopback signal therefore corresponds to a first delay value Tl substantially equal to the sum of the delays D I and D4.
• this also includes an electronic architecture similar to that of the master device M l and comprises, likewise, measuring means 8b coupled to the transmission means 6 and to the means of reception 7, as well as switches 9b, 10b, and 1 1b, so as to generate a loopback signal intended to propagate exclusively between the reception means 7 and the transmission means 6 and undergoing a propagation delay due to the electronic means transmission of the slave device.
• a second delay value T2 is thus measured and corresponds substantially to the sum of the delays D2 and D3.
• each device M l, E l autonomously measures the delay generated by the propagation of data within its transmission circuit and its data reception circuit.
• the delay values Tl and T2 are measured periodically in order to update them according to the evolution of the temperature at the level of the master device M l and the slave device El.
• periodic we mean the fact that the master and slave devices are available (that is to say that they are not monopolized by sending data at this precise moment). This measurement is carried out once per cycle, each cycle preferably having a duration of 1 ms.
• guard interval we mean an interval in which the master or slave devices are free, that is to say they are neither transmitting nor receiving.
• FIGS. 5a and 5b represent the electronic system 1 in which the delays T l and T2 were measured before the transmission of a data sequence TR3, respectively before compensation and after compensation.
• observation points N 1 and N6 are observation points of the master device M l
• observation points N2 and N5 are observation points of the transmission line 2
• the points of observation observation N3 and N4 are observation points of the slave device.
• the channel delay De represents the propagation time between the master device and the slave device, which is smaller than the delay due to the electronics compensated by means of the delay compensation method according to the invention, and which will be compensated by the channel compensation.
• the delay due to the transmission chain (Tx) of the master device and the reception chain (Rx) of the slave device is: D l + D2.
• the delay due to the transmission chain (Tx) of the slave device and the reception chain (Rx) of the device is: D3+D4.
• N5 D 1 +D2+D3
• N6 (D 1+D4) + (D2+D3).
• the delay applies to both the TOP synchronization pulse and the data so that the time window is aligned with the allocated slot, without time offset.
• the synchronization problem arises in particular in the return direction, i.e. when transmitting signals from the nodes to the master device.
• the delay from the slave device E l is compensated by a movement of the temporal listening window of the slave device El.
• the acquisition means 5 of the master device M l they are able to start receiving the data TR2 as a function of the first delay value T l.
• the acquisition means 5 are configured to delay the activation of the temporal listening window of the device master M l of a duration substantially equal to the first measured delay value Tl.
• the receiver of the slave node sends its signal in anticipation.
• the balance of delays is thus D I +D2 - (D2 + D3) or D I - D3.
• the delay from the transmitter to the N5 device is compensated by anticipation.
• the balance of delays is D 1 -D3+D3, or D l. Note that this delay is compensated by another method (MMSE for example).
• FIG. 6 illustrates a flowchart of a delay compensation method implemented during bidirectional data communication between the master device M l and the slave device El implemented by the electronic system 1 according to the invention. Note that the steps of the process are implemented iteratively and are constantly looped.
• the method begins with a step 100, during which the transmission means 4 transmit a data sequence TR3 to the slave device E l.
• the data sequence TR3 includes data frames TR I and TR2.
• the reference TOP is extracted from the synchronization signal S, more particularly from the optimized synchronization portion S2, transmitted by the master device.
• the internal delay introduced by the electronics of each master and slave device is measured using the internal feedback system described previously.
• the transmission means 7 of the slave advance the data transmission TR2 by a duration equal to the second delay value T2.
• the slave devices When transmitting from slave devices to the master device, the slave devices must compensate for their time delay. Each slave device will transmit earlier in its slot Xn and advances its transmission window by T2.
• step 300 the acquisition means 5 receive the data TR2 and delay their temporal listening window by a duration equal to the first known delay value Tl, as described previously with reference to Figure 5a, 5b.
• the system uses the measured delay to compensate for delays in two steps:
• step 300 the delays are compensated using the measurements obtained in step 200.
• the TDMA protocol can be combined with the method of coding digital signals by orthogonal frequency division in the form of multiple OFDM subcarriers (for “Orthogonal Frequency Division Multiplex” according to the Anglo-Saxon term).
• Phase-Shift Keying it is possible to perform single-carrier modulation by PSK phase change (“Phase-Shift Keying”).

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Time-Division Multiplex Systems (AREA)
• Synchronisation In Digital Transmission Systems (AREA)

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• 2022
  • 2022-12-09 FR FR2213130A patent/FR3143241B1/fr active Active
• 2023
  • 2023-12-01 WO PCT/FR2023/051897 patent/WO2024121492A1/fr not_active Ceased
  • 2023-12-01 CN CN202380084708.7A patent/CN120345202A/zh active Pending
  • 2023-12-01 EP EP23841279.5A patent/EP4631194A1/de active Pending

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