Half-duplex radio-frequency network

Abstract

Disclosed is a communication method, comprising the following first steps, performed by a current node (300): - during a first phase: - the current node (300) being in a reception mode in which it is able to receive via a channel (c2), the channel being a half-duplex radio-frequency communication channel, then - reception, via the channel (c2), of a first discovery message (d1) containing an identifier (P1) of a parent node (100), then, storing of the identifier of the parent node, and: ▪ a first switching of the current node (300) to a transmission mode, then ▪ transmission, via the channel (c2), of a second discovery message (d2) containing an identifier (P2) of the current node (300), - then, during a second phase: - determining a time slot, then: - during the time slot, transmitting, via the channel (c2), a first memory-data message to the parent node (100).

Description

[0001] Description

[0002] Title: Communication method in a semi-duplex radio frequency network, associated electronic device and system.

[0003] technical field

[0004] The present invention relates to radio frequency ad-hoc computer communication networks.

[0005] Technical problem

[0006] There is a need for a low-cost, ad-hoc radio frequency computer communication network that is capable of reliably transmitting information collected by network nodes to a central network node.

[0007] Communication method

[0008] The invention aims to achieve this objective and relates, according to one of its aspects, to a communication method (in a semi-duplex radio frequency computer communication network), comprising the following initial steps, implemented by a standard node:

[0009] - During the first phase:

[0010] - The current node being in a receive mode (after, possibly, an initial transition of the current node into receive mode) (only) via a channel, the channel being a half-duplex radio frequency communication channel (thus the current node, in this mode, can receive data via the channel but cannot transmit data via the channel), reception (by the current node), via the channel, of a first discovery message including an identifier of a parent node that sent said discovery message, then, upon receipt of the first discovery message, storage (by the current node) of said parent node identifier (in a memory of the current node), and: ■ First transition of the current node into a transmit mode, where the current node is transmitting (only) via the channel (thus the current node, in this mode, cannot send data via the channel and cannot receive data via the channel), then

[0011] ■ Transmission, via the channel, of a second discovery message including an identifier of the current node,

[0012] - Then, during a second phase (following the first phase):

[0013] - Determination (by the current node) of a time slot, then:

[0014] - During the time slot, the current node being in the transmit mode (after, possibly, an implementation of a second passage of the current node in the transmit mode then), transmission (by the current node), via the channel, of a first data message in memory (of the current node) to the parent node.

[0015] By using a half-duplex radio frequency communication channel, the invention reduces the cost of network nodes and thus the overall network cost, while limiting or eliminating the risk of collisions during the transmission of the first data message. For example, the communication channel could be of the "Wi-Fi" or "LoRa" type.

[0016] For example, the first phase is implemented at the start of the current node, or during a repetition (among the repetitions below), after a previous second phase, possibly after the current node has been put into sleep mode.

[0017] According to one embodiment, if after the first discovery message has been received, during the first phase, another discovery message containing another parent node identifier is received by the current node through the channel while the current node is still in a receive mode, this discovery message is, for example, ignored.

[0018] Of course, the first phase can be implemented at other times or following other events.

[0019] For example, the second discovery message includes part of the first discovery message, for example, all or part of the time-division information (below) from the first discovery message and / or all or part of the assignment information (below) and / or all or part of the synchronization information (below).

[0020] The concept of a half-duplex channel is well known to those skilled in the art. However, it can be specified, for example, that it is a channel where communication is possible in two directions, transmission and reception, but only in one of these two directions at a time.

[0021] For example, the first discovery message and / or the second discovery message do not include a recipient identifier. The first discovery message and / or the second discovery message can therefore be communicated (in other words: sent, transmitted, or received) in a mode known as broadcast.

[0022] Conversely, the first and / or second data message below includes, for example, a recipient identifier, namely an identifier of the parent node. The first and / or second data message can thus be communicated (in other words: sent, transmitted, or received) in a point-to-point mode.

[0023] According to one embodiment, the second phase comprises the following steps:

[0024] - Outside the time slot, the current node being in a receive mode (after, possibly, an implementation of a second passage of the current node in the receive mode), reception (by the current node) of a second data message.

[0025] This embodiment corresponds to a current node whose identifier is a parent node identifier for a node (of the plurality of nodes below). When the identifier is not a parent node identifier for a node (of the plurality of nodes below), this step is not implemented.

[0026] In this embodiment, the second phase may include the following step, outside the time slot:

[0027] Upon receiving the second data message, the current node passes into transmission mode for the third time, then (re)transmits (by the current node), via the channel, the second data message to the parent node (in the memory of the current node), (then the current node passes into reception mode for the third time).

[0028] Alternatively, still in this embodiment, the second phase may include the following step, during the time slot: - The current node being in the transmit mode (after, possibly, an implementation of a second passage of the current node in the transmit mode), transmission (by the current node), via the channel, of the second data message (in memory of the current node) to the parent node (of course, for this, the second data message must have been stored in memory (of the current node) outside the time slot, upon receipt of the second data message).

[0029] According to one embodiment, the transmission, via the channel, of the second discovery message is preceded by a step of determining a delay and then by a waiting step during the delay.

[0030] A waiting step is of course well known to those skilled in the art. It can be implemented using data produced by a clock on the current node.

[0031] According to one embodiment, the delay determination step includes a number generation step by a pseudo-random number generator (the number is thus a pseudo-random number), the delay being equal to the number.

[0032] Pseudo-random number generators are well known to those skilled in the art, particularly in microprocessors.

[0033] Alternatively, for example, if an identifier of the current node is n, the delay in hundredths of a second can be n / 100.

[0034] According to one embodiment, the transmission is preceded by a channel listening stage, the transmission being conditioned on the fact that no emission is detected on the channel during the channel listening stage.

[0035] According to one embodiment, the channel listening step is repeated if a transmission is detected on the channel during the channel listening step.

[0036] Alternatively, the listening step is only implemented once.

[0037] The listening stage, for example, is of an estimated duration of the transmission.

[0038] According to one embodiment, the waiting stage precedes the listening stage.

[0039] The listening and / or waiting stage helps to avoid channel disruption in the event that two nodes transmit on said channel at the same time.

[0040] Alternatively, for example, only one or neither of the waiting and listening steps is implemented. In one embodiment, the first steps include a reception step by the current node (the current node being, of course, in this case, in reception mode) of synchronization data.

[0041] A clock on the current node can then be recalibrated from the synchronization data, the process including a determination from a clock time whether the time is within the time slot (on determination of the time network).

[0042] Alternatively, the current node includes a very precise clock that does not need to be resynchronized.

[0043] According to one embodiment, the current node includes a sensor and the first data message includes a physical quantity of an environment of the sensor, measured by the sensor, such as temperature or atmospheric pressure.

[0044] Other common types of nodes are of course conceivable, for example to collect maintenance data or location data.

[0045] On the other hand, the second data message may include a physical quantity of an environment from a sensor of a node of the plurality of nodes below, measured by that sensor, such as temperature or atmospheric pressure.

[0046] According to one embodiment, the process includes repetitions of the implementation of the first steps and / or the second steps and optionally a standby of the current node between repetitions, in order to save (electrical) energy consumed (by said current node) (optionally with a different channel).

[0047] The concept of putting a system to sleep is well known to those in the field. It consists of disabling certain parts of the current node, such as a module for communicating via the channel.

[0048] Alternatively, the first steps are not repeated.

[0049] According to one embodiment, the process further includes second steps, implemented by a root node (different from the current node), preceding the first steps and comprising a step of sending a discovery message (and / or a step of receiving the first data message and / or the second data message).

[0050] In one embodiment, the second steps include a step of transmitting the first data message and / or the second data message to a remote server via a mobile communication network and / or the internet. It is clear to those skilled in the art that the current node (and / or the root node) includes an antenna for communicating via the channel and / or that the current node (and / or the root node) is an electronic device.

[0051] The invention can thus be implemented by a current node, in particular by a computer program of the current node (executed by a microprocessor of the current node).

[0052] For example, when the first phase begins, all nodes of the following plurality of nodes are put into receive mode or are in receive mode.

[0053] Among the plurality of nodes, at least one node is within radio range, via the channel for said at least one node, of the root node, and in this case, the discovery message is the first discovery message for said at least one node. Each node among the other nodes (i.e., other than said at least one node) of the plurality of nodes is within radio range, via the channel for said each node, of a parent node among the plurality of nodes, and in this case, the first discovery message for said each node is the second discovery message for the parent node.

[0054] For example, prior to the time slot determination step, the current node has in memory information for dividing time into periods and assignment information indicating which period among the periods corresponds to the time slot. In this case, determining the time slot may involve reading the division and assignment information from memory and possibly performing calculations based on this information.

[0055] The segmentation information can include a duration for each time slot and a reference time, but other implementations are of course possible.

[0056] The splitting information may be contained in the discovery message, in the first discovery message, and in the second discovery message (or in another message).

[0057] Alternatively, the slicing information can be stored in the current node's memory prior to the initial steps.

[0058] The second phase can begin at the reference time or (immediately) after transmission, or at another time (for example at periodic times)

[0059] The duration of each time slot and / or the difference between the reference time and the discovery start time can be a function of a maximum feasible depth, for example, denoted pmax; of a tree spanning the plurality of nodes below (an edge between two nodes is present if the two nodes communicate via a half-duplex radio frequency communication channel); and / or of the estimated time for a message to travel from one node of the plurality of nodes to another, for example, denoted tmess. For example, the duration of each time slot and / or this difference is equal to pmax x tmes.

[0060] The assignment information may also be contained in the discovery message, in the first discovery message, and / or in the second discovery message (or in another message), for example in an ordered list of identifiers of the plurality of nodes (for example in the form of an array) (included in the discovery message, in the first discovery message, and / or in the second discovery message).

[0061] Alternatively, the assignment information can be in the current node's memory prior to the initial steps.

[0062] Such an ordered list assumes that the identifiers of the plurality of nodes are recorded in a memory of the root node prior to the first steps.

[0063] For example, the first discovery message includes an initial ordered list of identifiers for the plurality of nodes. The second discovery message includes a second ordered list of identifiers for the plurality of nodes identical to the first list, but with the additional identifier of the parent node associated with the identifier of the current node.

[0064] A person skilled in the art can of course devise many variations for the implementation of the determination of the time slot, whether from the information of the segmentation and the information of the allocation or from other information, without it being necessary to limit the invention to a particular method.

[0065] For example, the time slot (or the segmentation information or the allocation information) is defined directly in the memory of the current node when the current node is commissioned, before the initial steps are implemented. The time slot determination step then consists of reading the time slot from the memory of the current node.

[0066] For example, the synchronization data comes from the root node (or alternatively, from another device).

[0067] For example, the synchronization data can be included in the discovery message, the first discovery message, and the second discovery message (or in another message). The synchronization data can include a discovery start time (in Universal Time or according to another time slot, or in another type of time, for example, Unix time) generated by the root node at the time the root node sends (i.e., on-sends) the discovery message.

[0068] Alternatively, the synchronization data comes from another device.

[0069] The synchronization data may include a number of nodes encountered to estimate and / or account for the time required for the discovery start time to reach the current node from the root node, based on an average communication time, between any two nodes in the plurality of nodes, on said channel.

[0070] For example, a clock on the current node is set to a time equal to H300 where H300 = H100 + NI x M, where H100 is the start time of discovery, NI is the number of nodes encountered, and M is the estimated average time of communication between two nodes.

[0071] For example, the first discovery message includes a number of nodes encountered having a first value, and the second discovery message also includes a number of nodes encountered having the first value plus one.

[0072] Alternatively, the transmission time between two nodes is too short to require consideration of the time taken from the start time of discovery to reach the current node.

[0073] Computer program, current node, and communication system

[0074] The invention also relates, according to another of its aspects, to a computer program comprising instructions executable by a microprocessor or a microcontroller (or the computer program) for the implementation (of the steps) of the process according to the invention.

[0075] The invention also relates to a current node (in other words: a communication node) capable of (in other words: configured to) implement the steps of the process according to the invention (i.e., the first steps of the process, or the repetitions). The invention also relates to a communication system (in other words: a communication network) (radio frequency) comprising:

[0076] - A plurality of nodes, each node of the plurality of nodes having the characteristics of the current node according to the invention, and - A root node (not included in the plurality of nodes) capable of implementing the second steps.

[0077] For example, the time slots determined by the plurality of nodes are disjoint.

[0078] For example, for this purpose, the information of affection and the information of cutting determine, for example, periods without overlap, that is to say a partition (of the duration) of the second phase.

[0079] Alternatively, temporal overlaps are possible between time slots, for example, between a node close to the root and a node far from the root.

[0080] A distance between a node and the root can be determined by the number of nodes mentioned above or by other means (for example, location by radio means).

[0081] A certain risk of collision on the channel can also be accepted, and that, for example, some data may be lost. This might be acceptable, for instance, due to the aforementioned repetitions. With this in mind, the time slot can include the generation of a pseudo-random number, with the time slot itself being obtained from this pseudo-random number. This limits the risk of collision on the channel. When the probability of selecting a given period is low (for example, less than 0.1, 0.01, or 0.001), the probability of a collision on the channel can be considered very low.

[0082] The advantages and characteristics of the computer program, the current node and / or the communication system are identical to those of the process, mutatis mutandis, and vice versa, without it being necessary to repeat it here.

[0083] Brief description of the drawings

[0084] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawings, in which:

[0085] [Fig 1] Figure 1 is a schematic view of a system according to one embodiment of the invention;

[0086] [Fig 2] Figure 2 is a schematic view of a current node of the system in Figure 1;

[0087] [Fig 3] Figure 3 schematically illustrates a root node of the system in Figure 1;

[0088] [Fig 4] and [Fig 5] Figure 4 and Figure 5 represent discovery messages exchanged during the process shown in Figure 6. [Fig 6] Figure 6 represents a process according to an embodiment of the invention implemented by the system of Figure 1 and by the current node of Figure 2.

[0089] Detailed description

[0090] Figure 1 represents a computer system or network 1000 according to an embodiment of the invention. It is a computer network comprising a node 100, a node 200, a node 300 and a node 400.

[0091] For a clear and concise presentation, this computer network contains only 4 nodes. However, in practice, the network can be much larger, and include several dozen, hundreds, thousands, or more nodes, depending on the applications.

[0092] Figure 2, The node 300 includes an atmospheric temperature sensor 310 and a microprocessor 320 comprising a computer program 321 and a memory 322.

[0093] The node 300 further includes a (single) antenna 330 and a communication module 340 to enable the node 300, more specifically the microprocessor 320, to communicate via the c2 channel with the node 100 and the node 400.

[0094] The c2 channel is a half-duplex radio frequency communication channel. Thus, node 300 can either receive data via the c2 channel, in receive mode, or send data via the c2 channel, in transmit mode, but cannot simultaneously receive data via the c2 channel and send data via the c2 channel.

[0095] The node 300 may also include a power supply battery (not shown) to power the microprocessor 320, the sensor 310 and the communication module 340.

[0096] Memory 322 stores an identifier for node 300 equal to 1300.

[0097] Node 200 and node 400 have an identical architecture to that of node 300, and store an identifier equal to 1200 and 1400 respectively.

[0098] Node 100, shown in Figure 3, comprises a communication module 110 connected to a mobile telephone network, a microprocessor 120 containing a computer program 121, and a memory 122. Node 100 further comprises an antenna 130 and a communication module 140 identical to the antenna 330, and a communication module 340. The memory 122 contains the identifier of node 100, equal to 1100, and the ordered list L1 shown in Table 1. [Table 1]

[0099] Node 300 is within radio range of node 100 via channel c2. Node 400 is within radio range of node 300 via channel c2. Node 200 is within radio range of node 100 via channel cl, which is of course a half-duplex radio frequency channel.

[0100] The computer network is designed to evolve over time. New nodes or channels can be added or removed.

[0101] With reference to Figure 6, at step S00, during a first phase, node 100 communicates via communication channel c2 and via communication channel cl, the first discovery message dl represented in Figure 4, through antenna 130 and a communication module 140.

[0102] For example, the c1 channel and the c2 channel can be of the so-called "WiFi" or "LoRa" type. For example, when the S00 step begins, node 200, node 300, and node 400 enter receive mode or are already in receive mode.

[0103] The first discovery message dl includes a discovery start time H100 which is the time at which the first discovery message dl was sent, by node 100, measured by clock 123, equals 1722033984 seconds, in Unix time.

[0104] The first dl discovery message also includes:

[0105] - The ordered list L 1,

[0106] - The parent node identifier PI is equal to 1100,

[0107] - Each time slot (dtl) has a duration of 100 seconds.

[0108] - A number of encountered nodes NI equal to 1,

[0109] A reference time REF100 equals 1722033984 seconds + 100 seconds, or 1722034084 seconds in Unix time.

[0110] For example, the system is configured to work with a maximum tree depth, covering the plurality of nodes, equal to 10. The communication time between two nodes is estimated at 10 seconds, hence the number 100 seconds.

[0111] At step S10, with node 300 in receive mode, it receives the first discovery message dl via antenna 330 and communication module 340. At step S20, node 300 stores, in memory 322, the identifier PI of node 100, equal to 1100, which is the parent node of node 300 in the tree covering the computer network 1000, currently under construction. Node 300 also stores the duration of each time slot dtl, the reference time REF100, the discovery start time H100, the number of nodes encountered NI, and the ordered list Ll.

[0112] At this stage, a clock 323 on node 300, initially set to a time of 1722033995 seconds, is then set to a time denoted H400 equal to 1722033994 seconds (1722033984 + 1 x 10). The clock 323 is then resynchronized.

[0113] At step S30, node 300, more precisely microprocessor 320, switches to transmit mode.

[0114] At step S40, node 300, more precisely microprocessor 320, transmits the second discovery message d2 to node 400.

[0115] The second discovery message d2 includes:

[0116] - Discovery start time H100

[0117] - The ordered list L2 below, table 2

[0118] - The parent node identifier PI is equal to 1300,

[0119] - The dtl duration (equal to 100 seconds),

[0120] - A number of nodes encountered N2 equal to 2,

[0121] The reference time REF100 (equal to 1722034084 seconds)

[0122] [Table 2]

[0123] According to one variant, the storage, in memory 322, of the identifier PI of node 100, equal to 1100, can be implemented by storing in memory 322 the ordered list L2.

[0124] During steps S10 to S40, node 200 performs the same operations as node 300, except for the ordered list L2, which is as represented in Table 3 below. [Table 3]

[0125] At step S50, with node 400 in receive mode, node 400 receives the second discovery message d2.

[0126] At step S60, node 400 stores in memory the identifier P2 of node 300, equal to 1300, which is the parent node of node 400 in the tree covering the computer network 1000. Node 400 also stores the duration of each time slot dtl, the reference time REF100, the start time of discovery H100, and the number of nodes encountered N2, and the ordered list L2.

[0127] At this stage, the clock on node 400, initially set to 1722034003 seconds, is then set to a time denoted H400 equal to 1722034004 seconds (1722033984 + 2 x 10). The clock on node 400 is then resynchronized.

[0128] At step S70, node 400 switches to transmit mode.

[0129] At stage S80, node 400 emits a third discovery message d3 represented in figure 5.

[0130] At step S90, node 300, if it has switched back to receive mode, receives the third discovery message d3 but ignores it since it already has the identifier 1100 in memory as the parent node identifier.

[0131] The third discovery message d3 includes:

[0132] - The ordered list L3 below, table 4

[0133] - The identifier of the parent node P3 is equal to 1400,

[0134] - The dtl duration (equal to 100 seconds),

[0135] - A number of nodes encountered N3 equal to 3,

[0136] - Reference time REF100 (equal to 1722034084 seconds)

[0137] [Table 4] According to one variant, the memorization, in the memory of node 400, of the identifier P2 of node 300, equal to 1300, can be implemented by memorizing in memory 322 the ordered list L3.

[0138] For example, the first discovery message dl, the second discovery message d2 and the third discovery message d3 do not include a recipient identifier, the first discovery message dl and / or the second discovery message d2 can thus be communicated (in other words: sent, issued, or received) in a mode called broadcast.

[0139] According to one embodiment, the process of Figure 6 may include, prior to step S40 and after step S30, the following steps:

[0140] - Step S32, during which a delay is generated by a pseudo-random number generator of the 320 microprocessor, for example between 1 and 5 seconds,

[0141] - Stage S33, during which the 320 microprocessor waits for the specified time,

[0142] - Step S34, during which the microprocessor 320 listens to channel c2 (step S34 can be repeated if an emission is detected on channel c2 during the channel c2 listening step), the implementation of step S40 being conditional on no emission being detected on channel c2 during step S34.

[0143] The process may also include such steps (not shown), before step S00, and / or between steps S70 and S80

[0144] These steps help to avoid channel interference in the event that two nodes transmit on said channel at the same time, for example if node 400 was also within range of node 200, in addition to being within range of node 300.

[0145] Steps S00 to S90 constitute the first phase of the process shown in Figure 6.

[0146] At step S 100, when the clock 123 of node 300, the clock of node 400 and the clock of node 200 simultaneously show a time equal to the reference time REF100 equal to 1722034084 seconds, the process enters the second phase.

[0147] During this S 100 stage:

[0148] - Node 200 determines, from the list L1 stored in its memory, that its time slot is the first (since the identifier 1200 of node 200 is the first in the list L1). Node 200 then determines, from the reference time REF 100 and the duration of each time slot dtl equal to 100 seconds, a time slot for node 200 between the time equal to 1722034084 seconds and the time equal to 1722034184 seconds.

[0149] - Node 300 determines, from list L1 stored in its memory, that its time slot is the second (since the identifier 1300 of node 300 is the second in list L1). Node 300 then determines, from the reference time REF100 and the duration of each time slot dtl equal to 100 seconds, a time slot for node 300 between the time equal to 1722034184 seconds and the time equal to 1722034284 seconds.

[0150] - Node 400 determines, from list L2 stored in its memory, that its time slot is the third (since the identifier 1400 of node 400 is the third in list L2). Node 400 then determines, from the reference time REF100 and the duration of each time slot dtl equal to 100 seconds, a time slot for node 400 between the time equal to 1722034284 seconds and the time equal to 1722034384 seconds.

[0151] At step SI 10, extending over the duration of the time slot of node 200, node 300 and node 400 switch to receive mode, with node 200 in transmit mode.

[0152] Alternatively, node 300 and node 400 (as well as node 200) can of course be switched to receive mode before step SI 10, after step S40 for node 300, and after step S80 for node 400.

[0153] During the SI 10 step also, node 200 sends, via the channel cl, a data message, to node 100 (i.e. microprocessor 120), the parent node of node 200 in the memory of node 200, which receives it.

[0154] At step S 120, extending over the duration of the time slot of node 300, node 200 switches to receive mode, and node 300 switches to transmit mode.

[0155] During the S120 step also, node 300 sends, via the c2 channel, a data message, to node 100 (i.e. microprocessor 120) the parent node of node 300 in the memory of node 300, which receives it.

[0156] At step S130, which spans the time slot of node 400, node 300 switches to receive mode, and node 400 switches to transmit mode. Also during step S130, node 400 transmits, via channel c2, a data message to node 300 (i.e., microprocessor 320), the parent node of node 400, which is stored in node 400's memory and receives it.

[0157] At step S140, node 300, after switching to transmit mode, retransmits the message received from node 400, to node 100, the parent node of node 300 in the memory of node 300.

[0158] For example, node 300 can then switch back to receive mode.

[0159] During stages SI 10 to S 140, the data message includes temperatures measured by sensors at nodes 200, 300, and 400.

[0160] At the S150 stage, these data messages are sent, by node 100, via communication module 110 with a mobile telephone network, and via the mobile telephone network.

[0161] It should be noted, of course, that data messages may include an identifier of the receiving node (i.e., an identifier of the parent node). This is, in fact, point-to-point communication. Steps S00 to S150 may be repeated (possibly without synchronization), possibly with the current nodes being put into standby mode between repetitions, in order to conserve energy.

Claims

Demands 1. Communication method, comprising the following initial steps, implemented by a current node (300): During the first phase: - The current node (300) being in a receive mode via a channel (c2), the channel (c2) being a half-duplex radio frequency communication channel, reception (S10), via the channel (c2), of a first discovery message (dl) including an identifier (PI) of a parent node (100) transmitter of said discovery message (dl), then, storage (S20) of said identifier of the parent node (100), and: • First pass (S30) of the current node (300) into a transmit mode, where the current node (300) is transmitting via channel (c2), then • Transmission (S40), via channel (c2), of a second discovery message (d2) including an identifier (P2) of the current node (300), Then, during a second phase: - Determination (S 100) of a time slot, then: - During the time slot, the current node (300) being in transmission mode, transmission (S 120), via channel (c2), of a first data message to the parent node (100).

2. A communication method according to the preceding claim, wherein the second phase comprises the following steps: Outside the time slot, the current node (300) being in a receive mode, reception (S130) of a second data message.

3. Communication method according to any one of the preceding claims, wherein the transmission (S40), via the channel (c2), of the second discovery message (d2) is preceded by a delay determination step (S32) and then by a waiting step (S33) during the delay.

4. Communication method according to the preceding claim wherein the step of determining a delay includes a step of generating (32) a number by a pseudo-random number generator, the delay being equal to the number.

5. Communication method according to any one of the preceding claims wherein the transmission is preceded by a listening step (34) of the channel (c2), the transmission (S40) being conditioned on no emission being detected, on the channel (c2), during the listening step of the channel (c2).

6. Communication method according to the preceding claim wherein the listening step (S34) of channel (c2) is repeated if an emission is detected on channel (c2) during the listening step (S34) of channel (c2).

7. Communication method according to any one of claims 5 or 6, taking into account claim 3 or 4 wherein the waiting step (S33) precedes the listening step (S34).

8. Communication method according to any one of the preceding claims wherein the first steps include a step of receiving by the current node (300) a synchronization data (H100, NI).

9. A communication method according to any one of the preceding claims in which the current node (300) comprises a sensor (310) and the first data message comprises a physical quantity of an environment of the sensor (310), measured by the sensor (310).

10. A communication method according to any one of the preceding claims comprising repetitions of an implementation of the first steps.

11. A communication method according to any one of the preceding claims comprising, furthermore, second steps, implemented by a root node (100), preceding the first steps and comprising a step of transmitting a discovery message.

12. Communication method according to the preceding claim wherein the second steps include a transmission step (150) of the first data message to a remote server via a mobile communication network or via an internet network.

13. Computer program (321) comprising instructions executable by a microprocessor or microcontroller for carrying out the process according to one any of claims 1 to 10, when executed by the microprocessor or microcontroller.

14. Current node (300) capable of implementing the steps of the process according to any one of claims 1 to 10.

15. Communication system comprising: - A plurality of nodes, each node (200, 300, 400) of the plurality of nodes having the characteristics of the current node (300) according to claim 14, and - A root node (100) capable of implementing the second steps according to claim 11 or 12.

16. Communication system according to the preceding claim, wherein the time slots determined by the plurality of nodes are disjoint.

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