Method and on-board system for selecting a communication channel between an aircraft and a remote station

Abstract

The invention relates to a method for selecting a communication channel, called the usage channel, comprising: - a step of determining, for each channel, one or more items of information representative of a quality of transmission of a message, the message being either a so-called "useful" message received by the embedded system, or a probe message, called a "ping" message, - a step of classifying the channels according to indices representative of the transmission qualities, from said information, - a step of selecting the usage channel as being the channel, having the best transmission quality from said indices, - a step (101) of determining a buffering time for each useful message received, and if this time is non-zero, - a step (102) of transmitting the useful message, called the eligible useful message, instead of a probe message. Abstract figure: Figure 4

Description

Title of the invention: Method and on-board system for selecting a communication channel between an aircraft and a remote station Technical field

[0001] The present invention relates to an on-board method and system for selecting a communication channel, from among a plurality of communication channels, between an on-board communication system of an aircraft and a communication station remote from the aircraft, for example arranged on the ground. Prior art

[0002] Aircraft most often use a data communication system to one or more ground stations, allowing operators to carry out radio surveillance of the aircraft, obtaining various operational and logistical information such as, for example, the location of the aircraft but also its condition, in detail, and information relating to possible breakdowns. It is thus possible to organize in advance maintenance actions, to be carried out after returning to the ground. A well-known system of this type is conventionally called ACARS, an acronym for the English term "Aircraft Communication Addressing and Reporting System". This system relies on means of communication initially based on HF and VHF transmission channels and more recently on SATCOM type satellite links, particularly in oceanic areas.

[0003] In many flight situations, several communications channels are available in parallel, and the quality of transmission on these channels may vary differently depending on the type of channel. In some uses, a list defining channel usage preferences is statically defined in an onboard database of the aircraft concerned. In addition, it is sometimes possible to select one channel rather than another channel with regard to operating cost.

[0004] However, such practices may lead to using a transmission channel that is not the most efficient at a given time. Furthermore, depending on the method of monitoring and managing transmission quality, successive switching of transmission channels may prove counterproductive and it is necessary to find a good balance between the advantage that a channel change can provide and the risks inherent in switching too frequently.

[0005] It is then possible to use the method of selecting a channel, called the usage channel, from among the plurality of communication channels between the aircraft and the remote station, known from document FR 22 02302, which associates a transmission quality index with each channel and makes it possible to choose the best communication channel in real time. This The method ensures increased reliability of data transmissions between the aircraft and the remote station by optimizing the selection of a transmission channel and the conditions for switching from one channel to another channel to minimize the risk of service interruption.

[0006] To do this, this state-of-the-art method provides for the analysis of the transmission of two types of messages. A first type of messages comprises so-called useful messages, which are messages comprising information to be sent by the aircraft to the remote station. A second type of messages comprises probe messages, sent regularly, and whose function is to be analyzed to enable the determination of a transmission quality index. These probe messages ensure proper operation of the selection method, even in the absence of transmission of useful messages.

[0007] However, this method requires the regular sending of probe messages in addition to useful messages. It would be desirable to limit the increase in information traffic resulting from this.

[0008] The aim of the invention is to at least partially remedy these drawbacks. Summary

[0009] To this end, a method is proposed for selecting a communication channel, called a usage channel, from among a plurality of communication channels between an onboard communication system of an aircraft and a communication station arranged at a distance from the aircraft, called a remote station, the method comprising: - a step of determining, for each of the communication channels, one or more items of information representative of a quality of transmission of a message between the on-board system and the remote station, the message being either a so-called “useful” message received by the on-board system, or a probe message, called a “ping” message, the ping messages being transmitted according to a given period, - a step of classifying said communication channels according to indices respectively representative of the transmission qualities determined for each of said channels, from said determined information; a single index being attributed for each of the channels, - a step of selecting the usage channel as being the channel, among the communication channels, presenting the best transmission quality from said indices, the method also comprising: - a step of determining a buffering time for each useful message received, called eligibility time, and, if the eligibility time is non-zero, - a step of transmitting the useful message, called eligible useful message, instead of a ping message via the usage channel.

[0010] Thus, thanks to the method according to the present invention, the traffic of the probe messages is reduced, which limits the mobilization of the communication system, and ensures good quality of the communication network while reducing the costs incurred by selecting a better channel.

[0011] It is noted that, by so-called "useful" message received by the on-board system, we mean a message transmitted to the on-board system by a source transmitter application itself on board the aircraft, that is to say a message entrusted by the source transmitter application to the on-board system for sending to said remote station, which should not be confused with a message received from the ground station.

[0012] According to another aspect, the method comprises a step of analyzing the buffering of the eligible useful message comprising a verification step depending on a state of the buffer memory and a parameter relating to the eligible useful message.

[0013] According to another aspect, the embedded system comprising at least one buffer memory, in which the step of analyzing the buffering of the eligible useful message comprises a step of determining an order for filling said at least one buffer memory.

[0014] According to another aspect, the embedded system comprises a respective buffer memory of each channel, wherein the buffering analysis step comprises a step of determining an order of filling of said buffer memories.

[0015] According to another aspect, the step of determining a filling order comprises a step of calculating a duration between the transmission of at least the next ping message on each channel and a reception time of the useful message eligible by the embedded system, and a classification in ascending order of the durations obtained, the order of filling the buffer memories following the classification obtained.

[0016] By reception time, we mean the maximum time for storing the eligible useful message.

[0017] According to another aspect, during the step of comparing a state of the buffer memory and a parameter of the eligible useful message, for the channel whose buffer memory is to be filled as a priority according to the order obtained at the end of the step of determining a filling order, if said buffer memory is empty, and if a maximum buffering time of the message is greater than the duration remaining until the next transmission of a ping message, then the eligible useful message is placed in the buffer memory, during the buffering analysis step.

[0018] According to another aspect, if the maximum buffering time of the message is less than or equal to the time remaining until the next transmission of a ping message, then the eligible payload is not buffered and is sent as a payload during a sending step.

[0019] According to another aspect, the embedded system comprising a buffer memory common to all the channels, during the step of comparison between a state of the buffer memory and a parameter of the eligible useful message, a number of messages contained in the buffer memory, called the number of messages, and a total number of ping messages to be sent are compared during a time equal to a maximum buffering time of the message, called the number of pings, and, if the number of pings is greater than the number of messages, then the eligible useful message is placed in the buffer memory, during the buffering analysis step.

[0020] According to another aspect, if the number of pings is less than or equal to the number of messages, then the eligible useful message is not buffered and is sent as a useful message during a sending step.

[0021] The invention also relates to an on-board communication system intended to equip an aircraft, configured to operate communications with a remote communication station through a communication channel called "best channel" among a plurality of communication channels, the on-board system comprising electronic and electromagnetic circuits configured to implement the following steps: - a step of determining, for each of the communication channels, one or more items of information representative of a quality of transmission of a message between the aircraft and the remote station, the message being either a so-called “useful” message received by the on-board system, or a probe message, called a “ping” message, the ping messages being transmitted according to a given period, - a step of classifying said communication channels according to indices respectively representative of the end-to-end transmission qualities determined for each of said channels, from said determined information; a single index being attributed for each of the channels, - a step of selecting the usage channel as being the channel, among the communication channels, presenting the best transmission quality from said indices, - a step of determining a buffering time for each useful message received, called eligibility time, and, if the eligibility time is non-zero, a step of transmitting the useful message, called eligible useful message, instead of a probe message.

[0022] More generally, the embedded system is configured to implement the selection method as described previously.

[0023] The invention also relates to an aircraft comprising an on-board communication system.

[0024] The invention also relates to a computer-readable medium comprising ins- instructions for carrying out the method as described above. Brief description of the drawings

[0025] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: Fig.l

[0026] [Fig.l] is a schematic representation of a communication system for transmitting data between an aircraft operating on the ground or in flight and a communication station remote therefrom. Fig. 2

[0027] [Fig.2] is a flowchart illustrating the overall progress of the process for evaluating the performance of each of the communication channels available between the aircraft and the remote station 3, of [Fig.l]. Fig. 3

[0028] [Fig.3] illustrates steps for selecting a communication channel referenced as being the best communication channel available between the aircraft 2 and the remote station 3, from among the channels C1, C2 and C3. Fig. 4

[0029] [Fig.4] illustrates a flowchart of the selection method according to the present invention. Fig. 5

[0030] [Fig.5] illustrates an example of the method of [Fig.4] according to a first embodiment. Fig. 6

[0031] [Fig.6] illustrates an example of the method of [Fig.4] according to a second embodiment. Fig. 7

[0032] [Fig.7] illustrates an example of internal architecture of an embedded system according to the present invention. Description of the embodiments

[0033] The examples and associated conditions detailed herein are primarily intended to assist the reader in understanding the principles of the present invention and not to limit its scope to these specific examples and conditions. It will be understood that those skilled in the art can devise various arrangements which, although not explicitly described or shown herein, nevertheless embody the principles of the present invention and are included within its spirit and scope.

[0034] Further, for ease of understanding, the following description may describe relatively simplified implementations of the present invention. As will be understood by those skilled in the art, other implementations of the present invention may be of greater complexity.

[0035] In some cases, examples of modifications of the present invention may also be presented. This is done merely as an aid to understanding, and, again, not to define the scope or establish the limits of the present invention. These modifications are not an exhaustive list, and those skilled in the art may make other modifications while remaining within the scope of the present invention.

[0036] Furthermore, all statements hereinafter relating to the principles, aspects, and implementations of the present invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof, whether presently known or developed in the future. Thus, for example, it will be understood by those skilled in the art that all block diagrams represent conceptual views of exemplary circuits incorporating the principles of the present invention. Likewise, it will be understood that all flowcharts, state transition diagrams, pseudocode, and the like, represent various processes that may be implemented on computer-readable media, and thus be executed by a computer or processor, whether such a computer or processor is shown in the figures or not.

[0037] The functions of the various elements shown in the figures, including any functional block, may be provided by the use of dedicated hardware as well as hardware capable of executing appropriate software. They may also be executed by a processor. Other hardware, conventional and / or customized, may also be used.

[0038] Software modules, or modules assumed to be software, may be represented herein as a combination of flowchart elements, or other elements indicating the execution of steps in a process, and / or as a textual description. Such modules may be executed by hardware that is expressly shown or not. In addition, it is to be understood that "module" may include, for example, but not limited to, computer program logic, computer program instructions, software, a software stack, firmware, hardware circuitry, or a combination thereof that provides the required capabilities.

[0039] As can be seen from the figures, the subject of the invention is a method 100 for determining a communication channel, called the usage channel, also called the best channel, from among a plurality of communication channels between a communication system 1 of an aircraft 2 and a communication station located at a distance from the aircraft, and referenced 3 in [Fig.l], and subsequently called remote station 3 or remote station 3. The present invention also relates to the communication system communication 1 for implementing the method 100.

[0040] In the following description, it is assumed, in a non-limiting manner, that the system 1 comprises three communication channels C1, C2 and C3.

[0041] The communication system 1 comprises an on-board communication system 4 equipping the aircraft 2 and a system 5, called ground-based, arranged at a distance from the on-board system 4, equipping the remote station 3. The system 1 also comprises a device 6 for transmitting the channels C1 to C3 for transmitting information between the aircraft 2 and the remote station 3.

[0042] Preferably, the on-board system 4 comprises a router 7. The system 4 also comprises an on-board application which is configured to ensure any downlink of the information traffic to the ground and possibly receive information from the on-board system 5.

[0043] Preferably, the ground system 5 comprises a router 9. The system 5 also comprises an application for receiving information traffic from the on-board system 4, and, possibly, for transmitting an uplink to the on-board system 4.

[0044] The transmission device 6 comprises communication means initially based on HF and / or VHF and / or SATCOM type transmission channels, and / or any other communication means used in aeronautics, such as L-DACS for example, or as a “virtual” communication channel seen from a router, such as a local link, particularly of the Ethernet type, to a cabin system which provides a plurality of physical links in an agnostic manner.

[0045] Advantageously, and thanks to the communication system 1, the aircraft 2 can transmit a wide variety of data to the remote station 3, in particular for the purposes of precisely locating the aircraft but also of organizing management, operating, and maintenance actions, during the flight or after a return to the ground. In addition, the aircraft communication system makes it possible to provide relevant information useful for the operation of the aircraft, such as, for example, meteorological information or information relating to a flight plan of the aircraft or of a third-party aircraft.

[0046] The embedded system 4 is configured to execute the method 100.

[0047] As is known from document FR 22 02302, the “best channel” is selected from at least a first communication performance criterion and possibly other, second, communication criteria. The terms “performance criterion” here designate a criterion aimed at evaluating a transmission quality, or transmission link quality, from end to end (between the aircraft and a remote communication station).

[0048] Preferably, the first communication performance criterion is the latency of the channel considered and the second criteria, possibly considered, are criteria of quality of communications performance such as, for example, a signal-to-noise ratio or information representative of the use made of the channel (usage rate, duration of continuous use, error rate, etc.).

[0049] According to variants, the first performance criterion aimed at evaluating end-to-end transmission quality is a criterion other than latency, representative of the transmission quality via a communication channel, such as, by way of example, a signal-to-noise ratio or information representative of the use made of the channel (usage rate, duration of continuous use, error rate, etc.) possibly weighted by one or more second criteria.

[0050] The latency of a channel is defined here as the complete travel time of data transmitted from the aircraft 2 to the remote station 3 then retransmitted by the remote station 3 to the aircraft 2. The latency thus defined can be expressed as an addition of a so-called descending latency (from the aircraft 2 to the station 3) and a so-called ascending latency (from the station 3 to the aircraft 2), the local processing times of the remote station 3 preferably being neglected.

[0051] According to one embodiment, the latency of a channel is determined by means of an index representative of a determined latency value or of a set of successively determined latency values. The determined latency values ​​mainly constitute the information used to determine a single latency index for each of the channels. In other words, a latency index specific to a channel considered can be determined from a determined latency value or from a set of latency values ​​determined for this channel over a given time interval, such as, by way of examples, a minimum latency, a maximum latency or even an average or median latency. When latency indices are determined for each of the communication channels, the communication channels are classified by index.Thus, the lowest latency index corresponds to the latency index of the communication channel detected as offering the best communication performance among the available channels and the highest latency index corresponds to the latency index of the communication channel detected as offering the worst communication performance in the system illustrated in relation to the, or vice versa. According to one embodiment, information representative of the latency of a channel at a given time is determined from transmissions which have just been carried out by determining the travel time of an end-to-end data packet.

[0052] According to another embodiment, information representative of the latency of a channel at a given instant is determined by the use of a function called "ping", commonly used in communication networks, in particular computer networks, and based for example on TCP type communication protocols (acronym English: "Transmission Control Protocol" or ICMP (English acronym for "Internet control Message Protocol"). Overall, the ping function is a computer command intended to test the accessibility of a remote machine through a communication network and to measure, in the case where the remote machine is accessible, the time taken to receive a response, also called "round-trip time" (RTT) in English.

[0053] According to another embodiment, the latency of a communication channel is determined from “useful” communications carried out via this channel, and in the absence of sufficiently regular communications, the ping function is used in a manner complementary to the “useful” communications. In the case of a latency defined from “useful” communications carried out on a communication channel, the data packet(s) used to determine a latency include information similar to that used in the messages implementing a ping function.

[0054] The distribution between the transmission of useful messages and pings is detailed later in relation to the description of the method 100.

[0055] After having characterized the latencies of different communication channels available between the aircraft 2 and the remote station 3, and consequently, the performances of these different channels that are the channels C1, C2, C3, the on-board system 4 can check whether the channel offering the best communication performance is still the channel used initially (i.e. at the start of the activation of the method 100, which is assumed, for simplicity, to be the first channel C1), and, if necessary, change the channel of use. Thus, if the on-board system 4 detects that the channel determined as being the best channel is not the one on (via) which the first communications are operated, the system begins to operate second communications, via a second communication channel which is the best communication channel detected, in parallel with the first communications operated on the first channel.In this configuration, the transmissions between aircraft 2 and remote station 3 are redundant and the remote ground station manages the redundancy of the data it receives by eliminating duplicates.

[0056] The embedded system 4 scans the evolution of the ranking that it operates of the channels, in terms of performance, during a predetermined DP delay, so that, if at the end of the DP delay, the second channel is still the best channel, then the first communications operated via the first channel are interrupted. In this case, the second communication channel, then the only communication channel, “becomes” the first channel and the second communications “become” the first communications and the method for determining the best channel continues to be executed on this new basis. Failing this, the embedded communication system 4 continues to operate the first communications via the first communication channel. According to a variant, for the on-board communication system 4 to stop operating the first communications and to operate the channel switch between the first communication channel and the second communication channel (determined as the best communication channel), it is appropriate not only for the second channel to be the best channel at the end of the DP delay, but also for it to have remained so throughout the DP delay, which tends to show and makes it possible to verify that the second communication channel is sufficiently reliable at this instant, or at the very least that it offers performances in line with expectations at this instant. This also makes it possible to create a time filter avoiding operating a channel switch when the relative situation of the different channels is not at all stable in terms of performances (transient phenomena).

[0057] According to one embodiment, the on-board system 4 of the aircraft 2 transmits to the remote station 3 the ranking of the channels by performance index, so that the remote station 3 is informed of the relative quality of the communication channels as evaluated by the aircraft 2. This information can be sent to the remote station 3 in the form of coded data and identified according to a predefined protocol. For example, a packet header carries a recognizable identifier and comprises a number of channels, followed by a list of channel identifiers, ranked in ascending or descending order of performance. Thus, the remote station 3 can select a communication channel to operate uplink communications, in the case where the latter are not operated via the same communication channel as that used to operate downlink communications.According to one embodiment of the invention, the remote station 3 operates any uplink communication on the last channel used for a downlink communication. According to a variant, the remote station 3 uses the information received from the aircraft, relating to the performance of the channels, to select the channel to be used for the uplink communications to follow.

[0058] Advantageously, different techniques for evaluating the latency of the channels can be implemented to evaluate the latter depending on the type of channel used. For example, the evaluation of the latency of a first channel can be carried out using a ping network command (or function) according to an ICMP protocol and the evaluation of the latency of a second communication channel can be carried out using a ping network command according to a TCP protocol. According to a similar reasoning, the latencies of the downstream links only are used to operate a ranking of the channels in terms of performance.

[0059] According to one example, the latency of a communication channel can be determined by subtracting the time taken to send a message from the embedded system 4 from the time of reception of this same message by the remote station 3, with regard to a downlink latency. According to another example, the latency of a channel can be determined by deducting the time of reception of an acknowledgment, sent by the remote station 3 in response to a message sent by the aircraft, from the time of transmission of this message by the on-board system 4 of the aircraft. Furthermore, an approximation can be made to determine a latency of an uplink or downlink as being half of the complete travel time (RTT).

[0060] In the case where a ping function is used to determine a latency, the ping network commands or functions include information useful for their proper execution, namely a ping command identifier, a transmitter identifier, a recipient identifier, a transmission time, a reception time by the recipient, a type of link, one or more message routing device identifiers (of command), a quality index determined by the aircraft for the channel used, etc. This list of examples is not exhaustive.

[0061] Advantageously, the evaluation of a channel carried out by the embedded system 4 may comprise other parameters, such as, for example, a link quality index (signal-to-noise ratio, for example), a transmission error rate via the link concerned, a "jitter", defined as the variation in time of the latency, a number of latency measurements carried out over a predetermined time interval, such as to indicate a reliability rate of the determined latency, an occupancy rate of a communication channel. For example, the latency indices determined for each of the channels may be weighted by a weighting coefficient defined, for each of the channels, by a transmission quality index and / or by an index representative of a use of the channel considered over a predefined time interval.

[0062] According to one embodiment, the embedded system 4 executes in parallel a first method for evaluating the performance of each of the channels and for classifying the channels according to an index, mainly determined, for each of the channels, from the latency of this channel, and a second method for selecting a better communication channel from the classification carried out in the background. The two methods are in reality two sub-methods of the overall method for selecting a communication channel according to the invention.

[0063] [Fig.2] is a flowchart illustrating the overall progress of the process (or more exactly sub-process) of evaluating the performance of each of the communication channels available between the aircraft 2 and the remote station 3, of defining a single index per channel determined from the latency of the channel, possibly weighted by another transmission performance index, then of ranking the communication channels, according to the determined indices, so as to define an established order, starting from the best communication channel to the worst communication channel nication or vice versa.

[0064] As can be seen from [Fig. 2], a step S0 is a step of initializing the systems of the aircraft 2, at the end of which the systems of the aircraft are supplied with electrical energy, initialized and normally operational. In particular, the on-board system 4 is configured to be able to operate the first communications on a first available and selected communication channel, in particular to the remote station 3.

[0065] During a step SI, ping commands are executed at regular intervals on all the communication channels available between the aircraft 2 and the remote station 3, so as to define one or more latency information for each of the channels.

[0066] The ping command execution frequency is, according to one example, such that a ping command is sent once every x seconds, x being for example between 1 second and 60 seconds, for example 2 seconds, 6 seconds, 8 seconds, 10 seconds, 30 seconds. This frequency of measuring the latency of a communication channel can however be increased or decreased depending on the results observed on each of the communication channels. Furthermore, this evaluation frequency per channel can differ from one channel to another channel, depending on the type of channel, in particular.

[0067] According to the method 100, as will be detailed later, “useful” communications can be sent instead of ping messages, or can even be sufficiently frequent to avoid using ping commands, and the current communications are used to define the latency of each of the available communication channels. The data packets exchanged on the channel then contain all the information useful for determining a latency, that is to say information equivalent to that present in a ping command for performing a latency calculation. An interval of latency values ​​and an average latency value can be defined for each of the communication channels C1, C2, C3 and a latency index can be determined from this latency information.A latency index may be determined, for example, such that the channel with the highest latency is assigned a latency index equal to 10 and the channel with the lowest latency is assigned a latency index equal to 0, or vice versa, depending on the index definition convention used. Typically, in the embedded communication system 4, the latency values ​​are expressed in seconds. The evaluation of the latency of each of the channels is thus carried out over a duration T1, usually several minutes.

[0068] During a step S2, the latency indices defined for each of the channels are recorded in a table and the channels are classified in this table in order of performance (latencies or weighted latencies). The channel classification table is for example recorded in a volatile or non-volatile memory of the embedded system 4. of communication of the aircraft 1. A step S3 consists of identifying the communication channel whose index is representative of the best communication performance, so that the improved method of selecting a communication channel, executed by the on-board system 4, can, by a simple reading in memory, know the channel presenting the best communication conditions towards the remote station 10.

[0069] After step S3, the method loops back to step S1, which amounts to saying that the evaluation of the latency of the channels is carried out continuously, in the background, by the onboard system 4 of the aircraft 2. In the case where second information, representative of the quality of the transmission of the channels, is used to weight the latency indices of the channels, these operations are executed during step S1 and the weighted indices are considered for the classification carried out in step S2. In this case, the information representative of the quality of the transmissions is defined by protocol and transmitted during exchanges of messages between the aircraft 2 and the remote station 3, but also, possibly from third-party communications, carried out towards reference equipment.

[0070] [Fig. 3] illustrates steps for selecting a communication channel referenced as being the best available communication channel between the aircraft 2 and the remote station 3, from among the channels C1, C2 and C3. This is also, more precisely, a sub-method of the improved method for selecting a communication channel according to the invention, since according to the embodiment described, two sub-methods executed in parallel operate the steps of the complete method. A step S0' corresponds to a step for initializing the systems of the aircraft 2, at the end of which the systems are powered, initialized and normally operational. In particular, the on-board system 4 is configured to be able to operate the first communications on a first available and selected communication channel, in particular to the remote station 3.According to one embodiment, steps S0 and S0' are combined into a single step called "starting up" the aircraft. During a step S10, the onboard communication system 4 of the aircraft 2 sends first information (data) to the remote station 3, after having selected a first communication channel to the remote station 10 and then waits, during a step S20, for a duration DPI (typically from several seconds to several minutes), for a determination of the best channel to be carried out in the background, so as to be able to determine, at the end of a step S30, whether the first channel selected to operate the first communications is the best channel or not. In the case where it is determined, in step S30, that the channel currently used (i.e. the first channel) is the best channel, the method loops back to step S10 and therefore continues to operate the communications with the remote station via the first channel.Otherwise, that is, if the current channel is not the best channel, the process initiates, . during a step S40, additional communications, also called here second communications, via a second communication channel which is none other than the channel determined as being the best channel by reading the information included in the memory of the embedded system 4, and updated by the continuous execution of the method 100. A new wait, of a duration DP2 is then carried out during a step S50, with the aim of carrying out a “time filter”, that is to say with the aim of being able to verify whether the second channel continues to offer the best communication performance at the end of the delay DP2. To do this, a new reading of the best communication channel is carried out during a step S60, at the end of the delay DP2. According to one embodiment of the invention, the duration DP2 is for example between 1 minute and 4 minutes, for example 2 minutes.

[0071] In the case where the second channel is still the best channel at the end of the delay DP2, the first communications carried out on the first channel are stopped during a step S70 and the method loops back to step S10. In this case, the second channel is then considered as the first channel for the reiteration of the sub-method described and the second communications are then considered as the first communications. In the opposite case, that is to say if another channel is determined as being the best communication channel at the end of the delay DP2 during step S60, the second communications carried out on the second channel are stopped during a step S80 and the first communications continue to be carried out on the first channel, then the method loops back to step S10.Advantageously and according to one embodiment of the invention, it is verified during steps S50 and S60 that the second communication channel remains the best communication channel throughout the duration of the delay DP2. Failing this, additional information is defined (an indicator of variation of the best channel during the delay DP2) making it possible to force the result of the test carried out during step S60.

[0072] According to one embodiment of the invention, the selection method described can be deactivated by an operator in the aircraft or on the ground to then operate a communication channel selection from a second selection method, using for example statically defined communication channel preference criteria.

[0073] Reference is now made to [Fig.4].

[0074] As is apparent from this figure, the method 100 also comprises, during step S1: - a step (101 - TAMP) of determining a time, Tbx, for buffering each useful message Mx received, called eligibility time, and, if the eligibility time is non-zero, - a step (102 - ENV ping) of transmitting the useful message as a probe message, i.e. instead of a ping message.

[0075] The buffering time Tbx may be, for example, the maximum possible buffering time, taking into account a delay considered acceptable for the message and, possibly, the transmission delay of the communication network. More generally, the buffering time may be any time characteristic of an acceptable buffering time.

[0076] "Non-eligible messages" are the useful messages whose buffering time is zero. "Eligible messages" are the useful messages whose buffering time is non-zero. For these messages, the method 100 preferably comprises in step S1, a step (103 - RAM) of analyzing the buffering of the useful message, the transmission of the message taking place during step 102 at an appropriate time instead of a ping message, as will be described later.

[0077] Thus, by buffering useful messages as soon as possible for sending instead of ping messages, the method 100 ensures a reduction in the number of messages exchanged between the aircraft 2 and the remote station 3, which preserves the communication network 1, reduces the energy required for the operation of the system 1 and ensures a reduction in the associated cost.

[0078] It is recalled that, for each channel C1, C2, C3, pings are emitted by the system 4 at a fixed frequency. We call Tpi the period of transmission of PI pings on the channel C1, Tp2 the period of transmission of P2 pings on the channel C2 and Tp3 the period of transmission of P3 pings on the channel C3.

[0079] As is also apparent from [Fig.4], the system 4 comprising at least one buffer memory, the step 103 of analyzing the buffering of the eligible useful message comprises a step (104 - ORD TAMP) of determining an order for filling said at least one buffer memory, described later for each of the two detailed embodiments

[0080] As also emerges from [Fig.4], step 103 of analyzing the buffering of the eligible useful message comprises a verification step (105 - VER) depending on a state of the buffer memory and a parameter relating to the eligible useful message, described later for each of the two detailed embodiments.

[0081] We now detail the first embodiment.

[0082] According to a first embodiment, each channel C1, C2, C3 has a respective buffer memory, denoted B1, B2, B3. According to this non-limiting embodiment, the buffer memories B1 to B3 have space for one message only.

[0083] According to this embodiment, illustrated in Figures 4 and 5, step 103 comprises a prior step (104 - ORD TAMP) of determining an order of filling the memories B1, B2, B3. The memories B1, B2, B3 are filled according to a filling order which follows a rule called the next ping, which will be explained.

[0084] During step 104, the method 100 calculates for each channel, at a given time T0 of reception of a message, the duration remaining until the transmission of the following ping(s).

[0085] It is noted that, in the present description, "reception of useful message" or "useful message received" corresponds to a message initiated by the source application of the message on board, and received (or transmitted) by the (or to the) on-board communication system responsible for managing communication to the ground.

[0086] In other words, we determine the time difference between each of the times Tpi, Tp2, Tp3 and T0, and where appropriate the time difference between multiples of the periods Tpi (Tpi', Tpi”) at Tp3 and T0, and we classify each difference D in ascending order.

[0087] We deduce the order of filling of the buffer memories B1, B2, B3: the memory filled in priority, or priority memory, is that for which the channel presents the smallest time difference, Tmin, the second priority memory is that, among the memories other than the priority memory, for which the channel presents a smallest time difference (after Tmin), and so on until all the memories have been evaluated.

[0088] Each time an eligible useful message Mx is received by the embedded system 4, the method 100 comprises a step of verifying (105 - VER) the filling state of the priority buffer memory Bi.

[0089] If it is not empty, the filling status of the state of the second priority buffer memory is checked.

[0090] If it is empty, the method 100 comprises a step of comparing the time, D, which remains until the next transmission of a ping message on the channel Ci of the buffer memory Bi and the maximum buffering time of the message, Tbx. If the time Tbx is greater than the time D, then the message Mx is put in the buffer memory Bi, during step 103. Otherwise, the message Mx can no longer be delayed and it is sent as a useful message, during a sending step (106 -ENV ut).

[0091] Then, the method 100 comprises a step (107 - INIT) of re-initializing the sequence of ping messages.

[0092] Reference is made more particularly to [Fig.5] which illustrates an example of the embodiment, of course non-limiting, of the first embodiment of the method 100.

[0093] As can be seen from this figure, three communication channels are considered, C1, C2 and C3. Each of the channels has a “ping” period, respectively 2s (for C1), 4s (for C2) and 8s (for C3).

[0094] Consider three successive messages, denoted Ma, Mb and Mc. Each of the messages Ma, Mb and Mc have a maximum buffering time, denoted respectively as Tba, Tbb and Tbc, such as Tba=8s, Tbb=10s and Tbc=ls.

[0095] The message Ma is received by the on-board system 4 at T0. The message Mb is received by the system 4 at T0+0.5s. The message Mc is received by the on-board system 4 at T0+3.5s.

[0096] In [Fig.5], we have noted Tpi the transmission time of the first PI “ping” on the channel Cl immediately after T0, Tpi' the transmission time of the “ping” P'1 following the “ping” PI on the Cl channel, Tp2 the transmission time of the first “ping” P2 on the C2 channel immediately after T0, and Tp3 the transmission time of the first “ping” P3 on the C3 channel immediately after T0.

[0097] In [Fig.6], we have chosen T0=Tpl-ls =Tp2-2s = Tp3-3.5s.

[0098] In the example of [Fig.6], four “pings” are considered.

[0099] During step 104, the priority order for filling the buffer memories is defined according to the next "ping" to occur. As already indicated, during step 101, each of the following differences is calculated: Dl=Tpl-T0=ls; D2=Tp2-T0=2s; D3=Tp3-T0=3.5s; Dl'=Tpl'-T0=3s.

[0100] In this case, D1 <D2<D1’<D3. Ainsi, les « pings » seront successivement PI, P2, PI’ et P3. On en déduit l’ordre suivant de remplissage des mémoires : Bl, puis B2 et B3.

[0101] During step 105, it is determined whether the message Ma can be buffered, and if so, on which channel.

[0102] In this case, according to the order established for filling the memories, it is a question of knowing whether the message Ma can be buffered in the memory BL Two conditions must be fulfilled, namely: - Empty Bl, which is the case, and - maximum buffering time greater than PL ping time

[0103] By comparing DI and Tba, we can clearly see that Dl=ls <Tba=8s. Ainsi, le message Ma est effectivement mis en mémoire tampon dans la mémoire BL

[0104] Message Mb is received by system 4 at time T0+0.5s.

[0105] Since the memory Bl is full, the message Mb can be buffered in memory B2 if B2 is empty and its maximum time Tbb is greater than the ping time P2, which is the case, since DD2=Tp2-(T0+0.5)=1.5s <Tbb=10s.

[0106] The message Mb is thus buffered in memory B2.

[0107] At time TO+ls, the message Ma is sent instead of the “ping” PI on the channel Cl to remote station 3.

[0108] At time T0+2s, the message Mb is sent instead of the “ping” P2 on the channel C2 to the remote station 3.

[0109] At time T0+3s, it is again the turn of the first channel Cl to emit a "ping". The memory Bl being empty, no message can be sent as “ping” and a probe “ping” is then sent on channel Cl.

[0110] At time T0+3.5s, the message Mc is received by system 4.

[0111] At time T0+3.5s, the filling order is B1 - B2 - B3, according to a calculation identical to that already described.

[0112] For the message Mc to be buffered in the memory Bl, two criteria must be met: - B1 is empty, - the maximum buffering time (Tbc) is greater than the time difference Dl” between the time of the next ping PI” on the channel Cl and the current time (in this case T0+3.5s), Dl”=1.5s. However, this time Dl” is greater than the maximum buffering time Tbc of the message Mc.

[0113] The message Mc cannot be put in the buffer memory, and is sent directly on the usage channel. The channel quality index is then evaluated using this sending, in accordance with the teachings of patent FR 22 02302. If the usage channel is the second channel C2, then the message Mc is sent by the second channel C2 to the remote station 3.

[0114] Then, the chronology of the “ping” periods of the channel C2 is reset to the sending time of the message Mc, in step 107. Upon receipt of the next useful message, the method 100 can again establish the order of filling of the memories B1, B2, B3 according to step 104.

[0115] According to a second embodiment, the buffer memory B is common to the three channels C1, C2, C3. It is noted that, according to this embodiment, the method 100 maintains the chronological order of the pings at all times. It is also noted that, according to this embodiment, the buffer memory has a variable size.

[0116] According to this embodiment, illustrated in Figures 4 and 6, the method 100 comprises a step (105 - VER) of comparison between a state of the buffer memory B and a parameter relating to the eligible useful message. The state of the buffer memory B corresponds to the number of useful messages contained in the buffer memory B, Nm. The parameter relating to the eligible useful message is the number of pings to be transmitted on the three channels C1, C2, C3 during the maximum buffering time Tb, Np.

[0117] If the number of pings Np is greater than the number of messages Nm, then the eligible useful message is put into the buffer memory, during the buffering analysis step 103.

[0118] If the number of pings Np is less than or equal to the number of messages Nm, then the eligible useful message is not put in the buffer memory and it is sent as a useful message during a sending step (106 - ENV ut).

[0119] As visible in [Fig.4], the method 100 also comprises a step 104 of ordering for sending the messages contained in the buffer memory B. The The messages contained are classified according to a parameter which is a time difference between the maximum buffering time of the memory and the time at which the process 100 is located (which is a time of reception of a message by the embedded system 4). The time differences are classified in ascending order. It is this order which determines the order of passage of the messages, from the highest priority message (corresponding to the smallest time difference) to the lowest priority message (corresponding to the largest time difference).

[0120] An example illustrating this second embodiment is now described with reference to [Fig.6]. In this example, the periods of the pings on the channels C1, C2 and C3 are respectively: Tpl=2s, Tp2=4s, Tp3=8s.

[0121] As already indicated, the method 100 maintains the chronological order of the pings at all times. In the example, the sequence is as follows: Tpi, Tp2, Tpi, Tp3, Tpi, Tp2,..., as visible in [Fig.6] and summarized in the table below: Next Ping Time Tpi 3s Tp2 4s Tpi 5s Tp3 6s Tpi 7s Tp2 8s Tpi 9s Tpi They Tp2 12s Tpi 13s Tp3 14s

[0122] Consider three messages, a first message Ma received by the embedded system 4 at T0, with a maximum buffering time Tba=8s, a second message, Mb, received at T0+2s with a maximum buffering time Tbb=10s, and a third message Mc, with a maximum buffering time Tbc=5s, is received by the embedded system 4 at T0+3.5s.

[0123] At time T0, the message Ma is received by the on-board system 4.

[0124] The message Ma is put in the buffer memory if the number of useful messages in the buffer memory is less than the number of pings to be carried out in the time interval Tba. In this case, the buffer memory is empty so the message Ma is put into the buffer, with its initial Tba time, equal to 8s.

[0125] At time T0+2s, the message Mb is received by the embedded system 4.

[0126] The message Mb is put in the buffer memory if the number of useful messages in the buffer memory is less than the number of pings to be carried out in the time interval Tbb. In this case, the buffer memory includes a message (Ma) and the number of pings to be carried out in 10s is 7. Therefore, the message Mb is put in the buffer memory.

[0127] The buffering time at T0+2s for message Ma is Tba(T0+2s)=8-2=6 s, which is less than the maximum time Tbb of 10 s. Then, message Mb is placed at the second position in the buffer behind message Ma.

[0128] At T0+3s, the message Ma is sent on the channel Cl instead of a ping PL. Let us specify that Tbb(T0+3s)=9s. 1 second has passed since the buffering of the message Mb.

[0129] At T0+3.5s, the message Mc is received by the on-board system 4.

[0130] In the next 5s, there are 2 pings to be sent, while the buffer includes a single message (Mb). So, the message Mc is put into the buffer.

[0131] The buffering time at T0+3.5s for message Mb is Tbb(T0+3.5s)=10-3.5+2=10-1.5s=8.5s, which is greater than the maximum time Tbc of 5 s. Then, message Mb is placed in the second position in the buffer while message Mc is placed in the first position.

[0132] The next ping arrives at T0+4s. The first message in the buffer is sent as a ping. This is message Mc, which is therefore delayed by 0.5s before being sent for Tp2. Message Mb, which was originally supposed to be sent at T0+4s (i.e. a 2-second delay), spends 3 seconds in the buffer. It will therefore be delayed by 3 seconds.

[0133] Note that, when an ineligible useful message is sent on the usage channel, or best channel, the chronology of the channel “ping” periods is reset (step 107) to the time the message was sent.

[0134] For example, when the priority channel is C3 and an ineligible message arrives at T0, the sent ineligible message serves as a probe without being put in the buffer. Being ineligible, it is sent directly. Its sending still serves as a measurement.

[0135] At this point (T0 in the example), the ping timeline is reviewed. Link C3 benefits from a measurement at T0. Its ping period being Tp3 = 8sec, its next ping will take place at T0 + 8sec then T0 + 16 sec then T0 + 24sec ... The pings of the other channels remain unchanged. And so the list of next pings changes slightly since the Tp3 slide down the list). We note that then the system checks that there is no too many messages in the buffer. If there are too many, the first messages in the buffer are sent immediately.

[0136] It is noted that, whatever the embodiment, the number of ping messages necessary for the proper functioning of the communication system 1 is reduced, which frees up bandwidth, and reduces the energy to be supplied as well as the associated cost.

[0137] [Fig.7] schematically illustrates an example of internal architecture of the on-board system 4 of the aircraft 2. As is apparent from this figure, the on-board system 4 then comprises, connected by a communication bus 1000: a processor or CPU (“Central Processing Unit” in English) 1001; a RAM (“Random Access Memory” in English) 1002; a ROM (“Read Only Memory” in English) 1003; a storage unit such as a hard disk (or a storage media reader, such as an SD (“Secure Digital” in English) card reader) 1004; communication interfaces 1005, 1006 and 1007 configured to operate communications on, respectively, the communication channels C1, C2, C3. The on-board communication system 4 further comprises interfaces of the input / output port type, in particular of a nature to receive and transmit signals from and to third-party devices of the aircraft.

[0138] The processor 1001 is capable of executing instructions loaded into the RAM 1002 from the ROM 1003, from an external memory (not shown), from a storage medium (such as an SD card), or attached to a communication network. When the embedded system 4 is powered on, the processor 1001 is capable of reading instructions from the RAM 1002 and executing them. These instructions form a computer program causing the processor 1001 to implement the method 100.

[0139] The RAM comprises at least one buffer memory: a respective memory for each channel C1, C2, C3, according to the first embodiment, and a memory common to the three channels C1, C2 and C3 according to the second embodiment.

[0140] All or part of the method implemented by the onboard system 4, or its described variants, may be implemented in software form by executing a set of instructions by a programmable machine, for example a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a machine or a dedicated component, for example an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). In general, the onboard system 4 comprises electronic circuitry configured to implement the methods and sub-methods described in relation to itself, making it possible to operate communications between the aircraft 2 and the remote station 3. Obviously, the onboard communication system 4 further comprises all the elements usually present in a system comprising a control unit and its peripherals, such as, in particular, a power supply circuit, a power supply supervision circuit, one or more clock circuits, a reset circuit, input-output ports, interrupt inputs, bus drivers, digital to analog and analog to digital converters, ideally fast, this list being non-exhaustive.

[0141] Although the implementations described above have been described and shown with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, subdivided, or reordered without departing from the teachings of the present disclosure. At least some of the steps may be performed in parallel or in series. Therefore, the order and grouping of the steps does not constitute a limitation of the present invention.

[0142] Modifications and improvements to the above-described implementations of the present invention may occur to those skilled in the art. The above description is illustrative by way of examples rather than limiting. The scope of the present invention is therefore limited only by the scope of the claims below.

Claims

Claims

1. Method for selecting a communication channel, called a usage channel, from among a plurality of communication channels (Cl, C2, C3) between an onboard communication system (4) of an aircraft (2) and a communication station (3) arranged at a distance from the aircraft (2), called a remote station (3), the method (100) comprising: - a step (S1) of determining, for each of the communication channels (Cl, C2, C3), one or more pieces of information representative of a quality of transmission of a message between the onboard system (4) and the remote station (3), the message being either a so-called "useful" message received by the onboard system (4), this useful message being a message transmitted to the onboard system (4) by a source transmitter application on board the aircraft, or a probe message, called a "ping" message, the ping messages being transmitted according to a given period, - a step (S2) of classifying said communication channels (Cl, C2,C3) according to indices respectively representative of the transmission qualities determined for each of said channels, from said determined information; a single index being assigned for each of the channels, - a step (S3) of selecting the usage channel as being the channel, among the communication channels (Cl, C2, C3), having the best transmission quality from said indices, the method also comprising: - a step (101) of determining a buffering time for each useful message received, called eligibility time, and, if the eligibility time is non-zero, - a step (102) of transmitting the useful message, called eligible useful message, instead of a ping message via the usage channel.,

2. Selection method according to claim 1, comprising a step (103) of analyzing the buffering of the eligible useful message comprising a step (105, 106) of verification depending on a state of the buffer memory and a parameter relating to the eligible useful message.

3. Selection method according to the preceding claim, the on-board system (4) comprising at least one buffer memory, in which the step (103) of analyzing the buffering of the eligible useful message comprises a step (104) of determining a replacement order- folding said at least one buffer memory.

4. Selection method according to the preceding claim, the embedded system (4) comprising a buffer memory dedicated to each channel (C1, C2, C3), in which, during the verification step (105, 106), for the channel whose buffer memory is to be filled as a priority according to the order obtained at the end of the step (104) of determining a filling order, if said buffer memory is empty, and if a maximum message buffering time (Tbx) is greater than the duration (D) which remains until the next transmission of a ping message, then the eligible useful message is placed in the buffer memory, during the buffering analysis step (103).

5. Selection method according to the preceding claim in which, if the maximum message buffering time (Tbx) is less than or equal to the duration (D) remaining until the next transmission of a ping message, then the eligible useful message is not put in the buffer memory and it is sent as a useful message during a sending step (106).

6. Selection method according to claim 2 or 3, the embedded system (4) comprising a buffer memory (B) common to all the channels (Cl, C2, C3), in which, during the step of comparison between a state of the buffer memory and a parameter of the eligible useful message, a number of messages contained in the buffer memory (B), called number of messages (Nm) and a total number of ping messages to be sent during a time equal to a maximum message buffering time (Tbx), called number of pings (Np), are compared, and, if the number of pings (Np) is greater than the number of messages (Nm), then the eligible useful message is placed in the buffer memory, during the buffering analysis step (103).

7. Selection method according to the preceding claim in which, if the number of pings (Np) is less than or equal to the number of messages (Nm), then the eligible useful message is not put in the buffer memory and it is sent as a useful message during a sending step (106).

8. On-board communication system (4) intended to equip an aircraft (2), configured to operate communications with a remote communication station (3) through a communication channel (Cl, C2, C3) called “best channel” among a plurality of communication channels (Cl, C2, C3), the on-board system being configured to put implement the following steps: - a step (S1) of determining, for each of the communication channels (Cl, C2, C3), one or more pieces of information representative of a quality of transmission of a message between the aircraft (2) and the remote station (3), the message being either a so-called "useful" message received by the onboard system (4), this useful message being a message transmitted to the onboard system (4) by a source transmitter application on board the aircraft, or a probe message, called a "ping" message, the ping messages being transmitted according to a given period, - a step (S2) of classifying said communication channels (Cl, C2, C3) according to indices respectively representative of the end-to-end transmission qualities determined for each of said channels, from said determined pieces of information; a single index being assigned for each of the channels, - a step (S3) of selecting the usage channel as being the channel, among the communication channels (Cl, C2, C3), having the best transmission quality from said indices, - a step (101) of determining a buffering time for each useful message received, called eligibility time, and, if the eligibility time is non-zero, and - a step (102) of transmitting the useful message, called eligible useful message, instead of a probe message.

9. Aircraft (2) comprising an on-board communication system (4) according to the preceding claim.

10. A computer-readable medium comprising instructions for carrying out the method according to one of claims 1 to 7.

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