Method for activating transmitting antennas of relay nodes, and associated relay node and destination device

Abstract

The invention relates to a method for activating transmitting antennas of relay nodes, implemented following the inability of a destination device to decode messages transmitted by M≥2 source devices: selecting a set S* t of undecoded source devices, and a subset (I) of transmitting antennas to be activated by relay nodes B* t of a set (b* t ) of relay nodes associated with the set S* t ; r; and transmitting, to the selected relay nodes, a retransmission instruction including the selected subset of antennas.

Description

Description Title of the invention: Method for activating transmitting antennas of relay nodes, relay node and associated destination device Technical Field

[0001] The present invention belongs to the general field of digital communications. It relates more particularly to the activation of transmitting antennas of relay nodes in a cooperative communication system.

[0002] As discussed in more detail below, an orthogonal multiple-access multiple-relay channel scheme, denoted OMAMRC ("Orthogonal Multiple-Access Multiple-Relay Channel" according to Anglo-Saxon terminology), is for example used for transmissions between relay nodes and a destination of a cooperative communication system.

[0003] The invention finds a particular, but not limiting, application in the transmission of data via mobile networks, for example from sensors capable of autonomously collecting and transmitting data to a base station. The network then comprises, for example, several sources corresponding to sensors, several relay nodes, and a destination device corresponding to a base station.

[0004] The invention also finds a particular application in the transmission of data between several nodes of an ad hoc wireless network. The network then comprises several nodes, some of which act as source devices, relay nodes, or destination devices. Prior art

[0005] Conventionally, the source devices in an OMAMRC communication system transmit messages to a single destination, if necessary via relay nodes. Relay nodes are typically half-duplex (meaning they cannot receive and transmit simultaneously) and receive messages from the source devices before decoding them. When a destination device requires retransmission of these messages, the relay nodes access the communication channel connecting them to the destination device using an orthogonal multiple access scheme to transmit the messages to the destination device, thus minimizing interference. This orthogonality is usually achieved through time-division multiplexing (TDM). in the form of disjoint time intervals (such as "Time Division Multiple Access", TDMA), but orthogonality resulting from frequency multiplexing in the form of disjoint frequency sub-bands (such as "Frequency Division Multiple Access", FDMA) is also conceivable.

[0006] The document "Efficient Cooperative HARQ for Multi-Source Multi-Relay Wireless Networks", Cerović, S. & Al., In 201814th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob) proposes a version of the OMAMRC protocol which considers an incremental redundancy retransmission of the HARQ type ("Hybrid Automatic Repeat reQuest").

[0007] Figure 1 is a representation of a frame transmission cycle in an OMAMRC type communication system.

[0008] The data transmission cycle in an OMAMRC type communication system comprises three phases, an initial INIT phase and, for each TF frame to be transmitted, a first phase P1 and a second phase P2.

[0009] During the INIT initialization phase, the destination device determines a number of bits ^^^^ carried by a modulation and a coding efficiency ^^^^ for the first transmission from each source, based on a communication channel quality criterion.

[0010] To do this, the destination device determines a value representing a quality, for example, the signal-to-noise ratio (SNR) of the direct links between this destination device and relay nodes using known techniques based on the use of reference signals (e.g., pilot symbols, SRS audio reference signals as defined by the 3GPP LTE consortium). During a retransmission, a relay node is associated with a source device and can correspond either to the source device to which it is associated, to another source device, or to an intermediate node located between the source device and the destination device.Similarly, source devices and intermediate nodes determine representative quality values ​​for source / source, intermediate node / intermediate node, and source / intermediate node links, which are then transmitted to the destination device.

[0011] Based on these representative quality values, the destination device determines, for each source device, a coding efficiency and a number of bits carried by a modulation for a number of uses of the channel ("Resource Element"). (according to the terminology of the 3GPP consortium or "channel use" according to terminology inherited from information theory). This data is then transmitted, by the destination device, to each of the source devices.

[0012] Thus, the size ^^^^ of the message to be transmitted by a source device is defined as follows: ^^^^ = ^^^^1 × ^^^^ × ^^^^. The message is encoded with a low-yield mother code ^^^^0 (for example, 1 / 3), and this coded message of length ^^^^^^^^ = ^^^^ / ^^^^0 > ^^^^ is subsequently stored in a circular buffer, an example of which is described with reference to Figure 2.

[0013] The data transmission cycle in an OMAMRC-type communication system further includes a first phase P1 during which the ^^^^ sources (^^^^1, … , ^^^^^^^^) successively transmit their message during ^^^^ time slots, using respectively the modulation and coding schemes determined during the initialization phase INIT. During this first phase P1, the number of times the channel is used is fixed and identical for each of the source devices.

[0014] In response to a determination that one or more messages transmitted by these source devices have not been decoded by the destination, the second phase P2 is implemented, during which the undecoded messages are cooperatively retransmitted by the relay nodes. A relay node associated with source devices then retransmits the undecoded messages from these source devices at the end of the first phase P1, so as to allow the destination device to decode the messages from all source devices without errors. More precisely, this relay node transmits to the destination device a redundant version of a message from a source device that it has correctly decoded and that had not been decoded by the destination device at the end of the first phase P1.Thus, when the relay node is separate from the source device to which it is associated, said relay node must have received the message transmitted by the source device during the first phase P1, then re-encode the received message and store it in its own circular buffer. This second phase P2 lasts a maximum of ^^^^^^^^^^^^^^^^ time intervals. During this phase, the number ^^^^2 uses of the channel is fixed and identical for each of the relay nodes.

[0015] Finally, if the messages from all source devices are decoded without errors by the destination device within a time interval ^^^^^^^^^^^^^^^^^^^^^ ≤ ^^^^^^^^^^^^^^^^^, the destination device broadcasts an acknowledgment. In this case, a new frame transmission cycle begins with the clearing of the memories of the relay nodes and the destination device, and with the transmission of new messages by the source devices.

[0016] Figure 2 represents a circular buffer allowing the selection of redundancy in the message to be transmitted.

[0017] As mentioned previously, during the INT initialization phase, a message encoded with a yield of 0 is stored in a circular buffer. As illustrated in Figure 2, this circular buffer has several read start positions: POS0, POS1, POS2, and POS3. Such a circular buffer contains the encoded bits of a message from a source device encoded with a low yield of 0 (e.g., 1 / 3) and allows for the selection of a specific redundancy of the message to be transmitted, depending on a read start position.

[0018] Indeed, these starting read positions POS0, POS1, POS2, and POS3 are associated with different redundancy versions: RV0, RV1, RV2, and RV3. In the chosen example, there are four possible redundancy versions. For each redundancy version, a node reads the number of coded bits to be sent. This number corresponds to the number of channel uses for a given modulation and message size, starting from the corresponding redundancy position, by moving through the circular buffer in the direction of the initial filling (in this example, clockwise). The selected coded bits are then interleaved and modulated. The first redundancy version, RV0, can be decoded independently of the other versions.

[0019] Thus, during the first phase P1, a source device transmits a TX1 message corresponding to the first redundancy RV0. To do this, this source device determines the bits to be transmitted by reading, in the circular buffer, the bits coded from position POS0.

[0020] During the second phase P2, the relay node determines the bits to be transmitted during the first retransmission TX2 by reading, from the circular buffer, the 2 bits encoded starting from position POS2, where 2 is the number of possible uses of the channel for retransmissions. If necessary, this source device then determines the bits to be transmitted during a second retransmission TX3 by reading, from the circular buffer, the 2 bits encoded starting from position POS3, and the bits to be transmitted during a third retransmission TX4 by reading, from the circular buffer, the 2 bits encoded starting from position POS1. Thus, the sequence of transmissions for a source For example, it is as follows: TX1, TX2, TX3, TX4, TX1, TX2, TX3, TX4, …

[0021] However, when a relay node selected to retransmit a message includes multiple transmitting antennas, all the transmitting antennas of that node are activated, regardless of the quality of the links between the transmitting antennas and the destination device. Thus, the transmit power of a relay node is distributed evenly among the source devices whose messages must be retransmitted by that relay node. Description of the invention

[0022] The present invention aims to overcome all or part of the drawbacks of the prior art, particularly those described above, by providing a solution that allows the selection of transmitting antennas to be activated at relay nodes, so as to optimize a quality criterion of the communication channel between these transmitting antennas and the destination device. This strategy proves particularly effective when each relay node b has its own power budget. This total power P is shared equally among the active antennas of node b; that is, if Q antennas of node b are active, the power that can be transmitted by each antenna is expressed as P / Q.

[0023] To this end, and according to a first aspect, the invention relates to a method for activating transmitting antennas of relay nodes, the method comprising the following steps, implemented by a destination device, following the reception of ≥ 2 messages transmitted successively by ≥ 2 source devices and the inability of the destination device to decode at least one message received from at least one source device, referred to as the "undecoded source device", each message transmitted by a source device comprising a first redundancy version resulting from the encoding of an information message associated with the source device:

[0024] – a selection from a set ^^^^ ^ ∗ ^ ^^ including one or more undecoded source devices, and a subset � ^^ � ^ � ^ � ^ ∗^^^ of transmitting antennas to be activated by relay nodes of a set ℬ ^ ∗ ^ ^^ of relay nodes associated with the whole assembly ^^^^ ^ ∗ ^ ^^ , based on a quality criterion of a communication channel between the antennas of said subset ^^ � ^ � ^ � ^ ∗ ^^^ and the destination device, at least one relay node of the set ℬ^ ∗ ^ ^^ comprising a plurality of transmitting antennas; and,

[0025] – a transmission to the relay nodes of the entire ℬ ^ ∗ ^ ^^ , of a retransmission instruction including the subset ^ � ^ � ^ � ^ � ^ ∗ ^^^ of selected antennas, so that the relay nodes of the whole ℬ ^ ∗ ^ ^^simultaneously transmit a second redundant version resulting from the encoding of the information message associated with each undecoded source device in the set ^^^^^ ∗ ^^^ by activating only the antennas of the subset � ^^ � ^ � ^ � ^ ∗ ^ ^^.

[0026] A relay node ^^^^ ^ ∗ ^ ^^ of the set ℬ ^ ∗ ^ ^^ has knowledge of an informational message to be retransmitted, either because it is their own message (and the relaying node ^^^^ ^ ∗ ^ ^^ (This corresponds in this case to a source device), either because the relay node ^^^^ ^ ∗ ^ ^^has previously correctly decoded it. In the following description, a relay node is said to be associated with a set of source devices when that relay node has previously decoded the information messages from all the source devices in that set, and is therefore able to retransmit new redundancy versions of the messages from all the source devices in that set.

[0027] By activating only the transmitting antennas of selected relay nodes that optimize a quality criterion of the communication channel between these transmitting antennas and the destination device, the invention improves known methods since links that do not offer sufficient quality are not used, and transmitting power is supplied only to the transmitting antennas that optimize this quality criterion.

[0028] Generally speaking, the steps of a process should not be interpreted as being linked to a notion of temporal succession.

[0029] In particular modes of implementation, the activation process may further include one or more of the following characteristics, taken individually or in all technically possible combinations.

[0030] In specific implementation modes, an orthogonal multiple-access multiple-relay channel (OMAMRC) is applied to the transmission channel between the relay nodes and the destination. The system then implements an IR-HARQ (Incremental Redundancy Hybrid-ARQ) cooperation strategy based on selective decode and forward (SDF).

[0031] In certain implementation modes, the selection also includes the selection of the set ℬ ^ ∗ ^ ^^ of relay nodes.

[0032] In specific implementation modes, the selection of the set ℬ ^ ∗ ^ ^^ The number of relay nodes is determined from the selection of the subset antennas.

[0033] In specific implementation methods, the selection of of source devices, of the set ℬ^ ∗ ^^^ of relay nodes, and subsets ^ � ^ � ^ � ^ � ^ ∗ ^ ^^ of transmitting antennas is the result of an exhaustive search for each subset of undecoded source devices, each subset of relay nodes having decoded all source devices for that subset of undecoded source devices, and each possible subset of transmitting antennas.

[0034] In specific implementation methods, the selection of of source devices, of the set ℬ^ ∗ ^^^ of relay nodes, and subsets ^ � ^ � ^ � ^ � ^ ∗ ^ ^^ antenna transmission is carried out jointly, that is to say during the same iteration.

[0035] In specific implementation modes, the activation process further includes a selection of the relay nodes of the set ℬ ∗ ^ ^^^among a set of relay nodes, depending on the quality criterion of the communication channel between the antennas of the subset and the destination device.

[0036] Dans des modes particuliers de mise en œuvre, selected corresponds to the transmitting antennas to be activated from a node ^^^^ ∗ ^ ^^^ particular of the set ℬ ∗ ^ ^^^ .

[0037] Dans des modes particuliers de mise en œuvre, l'ensemble � ^^ � ^ � ^ � ^ ∗ ^^^ of selected antennas corresponds to the transmitting antennas to be activated from all nodes ^^^ of the set ℬ ^ ∗ ^ ^^ .

[0038] In specific implementation modes, this quality criterion is mutual information over the communication channel between the antennas of the subset. ^^ � ^ � ^ �∗^^^^ and the destination device.

[0039] This mutual information is representative of the quality of a multilayer channel. Of course, other quality criteria can be considered, such as a received bit error rate. Furthermore, during the selection process, one can aim to optimize such a quality criterion or, alternatively, ensure that this quality criterion reaches at least a given threshold value.

[0040] In specific implementation modes, the total number of transmitting antennas in the set � ^^ � ^ � ^ �∗ ^^^^ is greater than or equal to the number of undecoded source devices in the set ^^^^ ∗ ^ ^^^ .

[0041] To this end, the process includes a verification step, for the transmission of second redundancy versions, that the total number of transmitting antennas from the relay nodes of a set ℬ ^^^^ (test) is greater than or equal to a number of undecoded source devices (from a set ^^^^ ^^^^ test).

[0042] In specific implementation modes, the process further includes an evaluation of the quality criterion for different subsets of antennas of a together ℬ ^^^^ of relay nodes associated with undecoded source devices, the sub- e nsemble ^ � ^ � ^ � ^ �∗ ^^^^ of selected antennas optimizing the quality criterion.

[0043] Dans des modes particuliers de mise en œuvre, le sous-ensemble � ^^ � ^ � ^ � ^ ∗ ^^^ of selected antennas is a subset that maximizes this quality criterion. Alternatively, the sub- e nsemble ^ � ^ � ^ � ^� ^ ∗ The selected antenna array is a subset among several subsets. ^^ � ^ � ^ � ^^^^ of antennas which all provide a representative value of the quality criterion above a certain threshold.

[0044] In specific implementation modes, the transmission of second redundancy versions is of the "Maximum ratio transmission" type, MRT.

[0045] Multi-antenna Relay (MRT) is a wireless communication method used to improve the performance and reliability of data transmission within multi-antenna communication systems. To achieve this, the method utilizes multiple antennas at the transmitter (in our case, relay nodes associated with selected antennas) and the receiver (in our case, the destination device) to maximize the signal strength received by the receiver, while minimizing interference and noise.

[0046] In this particular case, the transmission of the second redundancy versions corresponds to a simultaneous transmission, by all the nodes of the set ℬ ^ ∗ ^ ^^(where applicable, after application of amplitude and phase coefficients previously transmitted through a precoding matrix ^^^^). These messages, which relate to the same redundancy, are then received in a "superimposed" manner through an "equivalent" channel corresponding to the superposition of all the sub-channels defined by the transmitting antennas and the destination device.

[0047] In particular implementation modes, the destination device includes a plurality of receiving antennas.

[0048] In other words, in this particular implementation mode, spatial multiplexing based on a "Multiple-Input Multiple-Output" (MIMO) channel is used. The communication channel between the transmitting antennas of the relay nodes and the receiving antennas then comprises a plurality of spatial layers.

[0049] In particular modes of implementation, the activation process further includes reception, by the plurality of receiving antennas of the destination device, of the second redundancies of the messages from the undecoded source devices.

[0050] In certain implementation methods, the activation process also includes determining the quality criteria for the communication channel, including:

[0051] – a calculation, for each undecoded source device in an eligible set, of a single-source quality criterion based on a precoding matrix and a transmission power to be allocated to each undecoded source device in the set; and,

[0052] – a calculation of the quality criterion of the communication channel, based on the single-source quality criteria calculated for each undecoded source device in the set ^^^^.

[0053] In certain implementation modes, the retransmission instruction also includes of selected undecoded source devices, and a precoding matrix to be applied by the relay nodes of the set ℬ ^ ∗ ^ ^^ .

[0054] In specific implementation modes, the retransmission instruction further includes an indication, for each relay node of the set ℬ ^ ∗ ^ ^^ , the coefficients of the precoding matrix to be applied by said relay node, for each undecoded source device in the set ^^^^ ∗ ^ ^^^ .

[0055] The indication of the precoding coefficients to be applied takes, for example, the form of an ordered list ^^^^ of relay nodes of the set ℬ ^ ∗ ^ ^^which allows these relay nodes to identify the precoding coefficient of the precoding matrix ^^^^ to be applied.

[0056] In specific implementation modes, the retransmission instruction further includes an indication of the distribution of transmitted transmission power by each relay node of the set ℬ ∗ ^ ^^^ , between the undecoded source devices of the set ^^^^ ∗ ^ ^^^ .

[0057] In certain implementation modes, the transmission of the second redundancy versions is iterated until a stopping criterion is reached (for example, a certain duration or a certain number of iterations). Using a stopping criterion offers the advantage of limiting the use of the communication channel, particularly when it is noisy.

[0058] In particular modes of implementation, the process further includes the transmission, by the ^^^^ sources, of messages including a first redundancy (also referred to as "redundancy version"), for ^^^^ consecutive time intervals.

[0059] In specific implementation modes, each source device transmits a message including initial redundancy using a single antenna in omnidirectional transmission or after applying omnidirectional precoding to the antennas of said source. This feature is advantageous because it increases the number of relay nodes in the system capable of receiving and decoding these messages.

[0060] In specific implementation modes, the relay nodes of the set ℬ ^ ∗ ^ ^^correspond to relay nodes that have decoded all undecoded source devices. When the communication channel between the relay nodes and the destination device is known (e.g., when the links between the relay nodes and the destination device are direct links), considering relay nodes that have decoded the messages from all source devices, and not just some of them, offers the advantage of eliminating interference at the receiver.

[0061] In specific implementation modes, an orthogonal multiple access scheme, denoted OMAMRC ("Orthogonal Multiple Access Multiple-Relay Channel" in Anglo-Saxon terminology), is applied to the transmission channel between the relay nodes and the destination device. The system then implements a cooperation strategy called IR-HARQ ("Incremental Redundancy Hybrid-ARQ" in Anglo-Saxon terminology) based on selective relaying known as SDF ("Selective Decode and Forward" in Anglo-Saxon terminology).

[0062] According to a second aspect, the invention relates to a computer program comprising instructions for implementing a method of activating transmitting antennas according to the invention, when said program is executed by a processor.

[0063] This program can use any programming language, and be in the form of source code, object code, or code somewhere between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0064] According to a third aspect, the invention relates to a computer-readable recording medium on which the computer program according to the invention is recorded.

[0065] The information or recording medium can be any entity or device capable of storing the program. For example, the medium may include a storage means, such as a ROM, for example a CD-ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a hard drive.

[0066] On the other hand, the information or recording medium can be a transmissible medium such as an electrical or optical signal, which can be transmitted via an electrical or optical cable, by radio, or by other means. The program according to the invention can, in particular, be uploaded to a network such as the Internet.

[0067] Alternatively, the information or recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the process in question.

[0068] According to a fourth aspect, the invention relates to a destination device configured to implement an activation method according to the invention.

[0069] According to a fifth aspect, the invention relates to a relay node comprising:

[0070] – a plurality of transmitting antennas;

[0071] – a receiving module, from a destination device, for a retransmission instruction of second redundancy versions of information messages from so-called undecoded source devices, the undecoded source devices having previously transmitted first redundancy versions of said information messages not having been decoded by the destination device, the retransmission instruction including a subset � ^^ � ^ � ^ � ^ ∗ ^^^ of transmitting antennas selected by the destination device for said retransmission; and,

[0072] – a transmission module configured to activate only the transmitting antenna(s) of the subset ^ � ^ � ^ � ^ � ^ ∗^^^ belonging to him to transmit to said destination device said second versions of redundancy.

[0073] According to a sixth aspect, the invention relates to a communication system comprising ^^^^ ≥ 2 source devices, a destination device conforming to the fourth aspect, and several relaying nodes conforming to the fifth aspect.

[0074] In a particular implementation mode, the communication system uses an orthogonal multiple access multiple-relay channel (OMAMRC) scheme between the relay nodes and the destination device. A brief description of the diagrams follows.

[0075] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings, which illustrate an example of an embodiment without being limiting in any way. In the figures:

[0076] [Fig.1] Figure 1, previously described, is a representation of a frame transmission cycle in an OMAMRC type communication system;

[0077] [Fig.2] Figure 2, previously described, represents a circular buffer allowing the selection of a redundancy of a message to be transmitted;

[0078] [Fig.3] Figure 3 schematically represents a communication system according to a particular embodiment of the invention;

[0079] [Fig.4A] Figure 4A represents modules embedded in a destination device, according to an example of implementation of the invention;

[0080] [Fig.4B] Figure 4B represents modules embedded in a relay node, according to an example of implementation of the invention;

[0081] [Fig.5] Figure 5 schematically represents an example of the hardware architecture of a destination device;

[0082] [Fig.6] Figure 6 represents, in the form of a flowchart, a particular method of implementing a communication process in an OMAMRC system, according to a first example.

[0083] [Fig.7] Figure 7 represents, in the form of a flowchart, a particular method of implementing a process for activating transmitting antennas of relaying nodes.

[0084] [Fig.8] Figure 8 represents, in the form of a flowchart, a particular method of implementing a communication process in an OMAMRC system, according to a second example.

[0085] [Fig.9] Figure 9 represents, in the form of a flowchart, a particular method of implementing a process for calculating equivalent mutual information from a channel linking the transmitting antennas of the relaying nodes to the receiving antennas of the destination device;

[0086] [Fig. 10] Figure 10 schematically represents an example of the implementation of the communication process in an OMAMRC system. Description of implementation methods

[0087] Figure 3 schematically represents a communication system according to a particular embodiment of the invention.

[0088] As illustrated in Figure 3, the SYS communication system comprises three sources ^^^^1, ^^^^2, ^^^^3, a destination device d, and two intermediate nodes ^^^1^, ^^^^2 positioned between the source devices and the destination. An intermediate node differs from a source device in that it does not have its own message to transmit. It only retransmits (relays) messages from other nodes.

[0089] In this embodiment, and for the sake of simplicity, the communication system is considered to have a single destination d. However, it should be noted that there is no limitation on the number of destinations d. The following developments can easily be generalized by those skilled in the art to cases where more than one destination device is considered. It should be noted that the number of source devices is not a limiting factor of the invention. Finally, there is no limitation on the number of intermediate nodes, which need only be such that n ≥ 0. Thus, in a particular implementation, the communication system SYS does not include any intermediate nodes.

[0090] In the following description, the "set of relay nodes" refers to the set of nodes comprising the intermediate nodes 1, ..., and source devices 1, ..., functioning as relays responsible for retransmitting messages they are aware of to the destination, messages that may originate from themselves or from other nodes. Thus, each of these sources ^^^^1, ^^^^2, ^^^^3 can function, at different times, either exclusively as a source device or as a relay responsible for retransmitting messages from other nodes to the destination and / or its own message. It should be noted that the number of relaying nodes is not a limiting factor of the invention, provided that this number is greater than or equal to 2.

[0091] Furthermore, at least one of the relay nodes includes several transmitting antennas. Hereafter, the number of transmitting antennas of a node ^^^^ ∈ ^^^^ is denoted ^^^^^^^^,^^^^.

[0092] For the sake of simplicity, it is also assumed that the source devices and intermediate nodes are equipped with a single receiving antenna; that the source devices, intermediate nodes and destination device are perfectly synchronized; and that the source devices are statistically independent, i.e. there is no correlation between them.

[0093] Furthermore, the antennas of all nodes in the system are co-phased before any transmission. A phase calibration procedure is performed periodically, for example, and can be initialized by the destination device.

[0094] An orthogonal multiple access scheme, denoted "OMAMRC" – an acronym for "Orthogonal MultipleAccess Multiple-Relay Channel" – is applied to the transmission channel. The system then implements a cooperation strategy called IR-HARQ ("Incremental Redundancy Hybrid-ARQ" according to Anglo-Saxon terminology) based on selective relaying called SDF ("Selective Decode and Forward" according to Anglo-Saxon terminology).

[0095] Thus, the M source nodes and the ^^^^ intermediate nodes access the transmission channel according to an orthogonal multiple access scheme that allows them to listen, without interference, to transmissions from other source nodes and other intermediate nodes. In the following description, it is assumed that this orthogonality is achieved by time division multiplexing in the form of disjoint time intervals (such as Time Division Multiple Access, TDMA). However, orthogonality resulting from frequency division multiplexing in the form of disjoint frequency sub-bands (such as Frequency Division Multiple Access, FDMA) is also possible.

[0096] Figure 4A represents modules embedded in a destination device, according to an example of implementation of the invention.

[0097] As illustrated in Figure 4A, the destination device d includes, in particular:

[0098] – a MOD_SEL module of a set ^^^^^ ∗ ^ ^^ including one or more undecoded source devices and a sub- ^^^ of transmitting antennas to be activated by relay nodes of a set ℬ ^ ∗ ^ ^^ of relay nodes associated with the whole assembly ^^^^ ^ ∗ ^ ^^ , based on a quality criterion of a communication channel between the antennas of said subset ^^ � ^ � ^ � ^ ∗ ^^^ and the destination device (d); and,

[0099] – a MOD_TX transmission module, at the relay nodes of of a retransmission instruction including the subset ^ � ^ � ^ � ^ � ^ ∗ ^^^ of selected antennas, so that the relay nodes of the whole ℬ ^ ∗ ^ ^^simultaneously transmit a second redundant version derived from the encoding of the information message associated with each undecoded source device in the set by activating only the antennas of the sub- e nsemble ^ � ^ � ^ � ^ � ^ ∗ ^ ^^.

[0100] Their functionalities are described in more detail below with reference to different implementation methods.

[0101] Figure 4B represents modules embedded in a relay node, according to an example of implementation of the invention.

[0102] As illustrated in Figure 4B, the relay node r includes, in particular:

[0103] – a plurality of transmitting antennas;

[0104] – a MOD_RX module for receiving, from a destination device, an instruction to retransmit second versions of message redundancy information from so-called undecoded source devices, the undecoded source devices having previously transmitted first redundancy versions (RV0) of said information messages not having been decoded by the destination device (d), the retransmission instruction including a sub- of transmission antennas selected by the destination device for said retransmission; and,

[0105] – a MOD_TX transmission module configured to activate only the transmitting antenna(s) of the subset belonging to it to transmit to said destination device said second versions of redundancy.

[0106] Their functionalities are described in more detail below with reference to different implementation methods.

[0107] Figure 5 schematically represents an example of the hardware architecture of a destination device ^^^^.

[0108] As illustrated in Figure 5, the destination device ^^^^ has the hardware architecture of a computer. Thus, the destination device ^^^^ includes, in particular, a processor 1, random access memory 2, read-only memory 3, and non-volatile memory 4. It also has communication means 5.

[0109] La mémoire morte 3 du dispositif de destination ^^^^ constitue un supporta recording device according to the invention, readable by processor 1, on which is stored a computer program PROG according to the invention, comprising instructions for executing steps of the activation process according to the invention. The PROG program defines functional modules of the target device, which rely on or control the hardware elements 1 to 5 of the target device mentioned above. These functional modules are illustrated in Figure 4A by way of no limitation and are described in more detail below with reference to different implementation methods.

[0110] In the implementation modes described below, the communication means 5 enable the destination device to obtain the messages transmitted by the source M during the first phase, as well as the messages retransmitted by the relay nodes during the second phase. The communication means 5 also enable the destination device to transmit the retransmission instruction to the relay nodes. To this end, the communication means 5 include an interface for communication, wired or wireless, capable of implementing any suitable communication protocol.

[0111] Figure 6 represents, in the form of a flowchart, a particular method of implementing a data communication process in an OMAMRC system, according to a first example.

[0112] As illustrated by Figure 6, the data communication process includes a first S300 link initialization and adaptation step during which the destination device ^^^^ determines a number of bits ^^^^ carried by a modulation and coding efficiency ^^^^ for the first transmission of each source device ^^^^1, … , ^^^^^^^^ as a function of a communication channel quality criterion.

[0113] To do this, the destination device determines a representative quality value, for example, the signal-to-noise ratio of the direct links between that destination device and the relay nodes (e.g., between the destination device and the source devices, but also between the destination device and the intermediate nodes), using known techniques based on the use of reference signals (e.g., pilot symbols, SRS sound reference signals as defined by the 3GPP LTE consortium). Similarly, the source devices and intermediate nodes determine representative link quality values ​​between two sources, two intermediate nodes, and / or between a source device and an intermediate node, which are then transmitted to the destination.

[0114] Based on these representative quality values, the destination device determines, for each source device, a coding efficiency and a number of bits carried by a modulation for a number of channel uses. This data is then transmitted, by the destination device, to each of the source devices.

[0115] Au cours de cette même étape S300, chaque dispositif source ^^^^1, … , encode un message of size ^^^^ = ^^^^1 × ^^^^ × ^^^^ to be transmitted to the destination device ^^^^ with a low-yield codemother ^^^^0 (for example, 1 / 3), and the coded message of length ^^^^ ^^^^ = ^^^^ / ^^^^0 > ^^^^ is subsequently stored in a circular buffer, an example of which is described with reference to Figure 2.

[0116] The communication process further includes a step S100 during which the source devices 1, ..., successively transmit their message for consecutive time intervals, using the modulation schemes and coding determined during step S300. During this first phase, the number of uses of the channel is fixed and identical for each of the source devices 1, … , Les redundancy versions ^^^^^^^^01, … ,^^^^^^^^0^^^^transmitted by source devices ^^^^1, … , ^^^^^^^^ during this S100 step correspond to the first redundancies ^^^^^^^^0 of their messages.

[0117] These initial redundancies are transmitted, for example, using a single omnidirectional transmitting antenna or after applying omnidirectional precoding to the transmitting antennas of the source devices. Thus, for a source device comprising ^^^^ ^^^^,^^^^ For transmitting antennas, precoding results, for example, from a superposition of discrete Fourier transform vectors of dimension ^^^^ ^^^^,^^^^ This feature is advantageous because it increases the number of relay nodes in the system capable of receiving and decoding these messages.

[0118] Au moins certains des ^^^^ messages ^^^^^^^^01, … ,^^^^^^^^0^^^^ sont reçus par le dispositif dedestination ^^^^ during an S310 step. During an S320 step, the destination device ^^^^ determines the set ^^^^^^^^,^^^^−1 of the source devices whose messages have been decoded without errors during the time interval ^^^^ − 1. The process further includes an S330 step during which the destination device transmits, to the relay nodes ^^^^ ∈^^^^, an ACK / NACK message to indicate whether it has successfully decoded all the source devices or not.

[0119] In the following description, a source device whose message could not be decoded by the destination device is called an "undecoded source device." If at least one message from a source device could not be decoded by the destination device (i.e., if a NACK message is received), each relay node transmits its respective decoding set ^^^^^^^^,^^^^−1 to the destination device d. This decoding set ^^^^^^^^,^^^^−1 corresponds, for a relay node ^^^^ ∈ ^^^^, to the source devices whose messages were decoded without errors by that relay node. Each of the decoding sets ^^^^^^^^,^^^^−1 is received by the destination device ^^^^ during an S340 step. Thus, at a given interval ^^^^ ∈{1, … ,^^^^^^^^^^^^^^^^^^^^}, the destination device ^^^^ knows the decoding set ^^^^^^^^,^^^^−1 of all relaying nodes ^^^^ ∈ ^^^^.

[0120] The communication process further includes an S350 step during which the destination device selects, based on a quality criterion, a communication channel between the antennas of said sub- and the destination device:

[0121] – a set ^^^^ ^ ∗ ^ ^^ including several source devices ^^^^ ^ ∗ ^ ^^ ,

[0122] – a set ℬ ^ ∗ ^ ^^ relay nodes ^^^^ ^ ∗ ^ ^^ associated with the set , among a set ℬ of relay nodes ^^^^ ^^^^ , And

[0123] – un sous-ensemble � ^^ � ^ � ^ � ^ ∗ ^^^ of transmitting antennas from at least one relay node (^^^^^ ∗ ^ ^^) de the set ℬ ^ ∗ ^ ^^ to activate.

[0124] This S350 step is implemented, for example, by the MOD_SEL module described with reference to Figure 4A. A specific implementation method for this S350 selection step is described with reference to Figure 7.

[0125] A relay node is a network node that has correctly decoded messages that were not decoded by the destination device during a previous time interval ^^^^ − 1, and is therefore able to transmit a new redundant version of these messages to the destination device during the retransmission time interval ^^^^. This previous time interval ^^^^ − 1 does not necessarily correspond to the time interval immediately preceding the time interval ^^^^. Let ^^^^^^^^,^^^^−1 be the decoding set of a node ^^^^ at the time interval ^^^^ − 1. This set contains all the identifiers of the source devices that the node ^^^^ was able to decode without errors before the retransmission interval ^^^^. Thus, a relay node ^^^^ is a potential candidate for transmitting second redundancy versions if the intersection between its decoding set and the complement of the decoding set of the destination device ^^^^^̅^^^,^^^^−1, is different from the empty set,

[0126] The communication process further includes an S360 step during which the destination device calculates a precoding matrix = [, …, apply by each of the selected relay nodes ^^^^* *^^^^ ∈ ℬ^^^^, with ℂ the set of complex numbers, ^^^^ ^^^^,ℬ^ ∗ ^ ^^ the total number of transmitting antennas of the relay nodes ^^^^* ∈ ℬ*, and ^ ∗^^^^ ^^^^ ^^^ the number of sources ^^^^^^^^ whose messages must be simultaneously retransmitted. In other words, ^^^^ = |^^^^*^^^^|, with |^| the cardinality operator.

[0127] During this same S360 step, the destination device ^^^^ transmits, to the relay nodes ^^^^* ∈ ℬ*^^^^, the entire identifiers of the source devices whose signals must be retransmitted and the precoding matrix ^^^^, as well as all the antennas to be activated by each relay node. This S360 step is implemented, for example, by the MOD_TX module described with reference to Figure 4A.

[0128] The set of antennas to be activated by each relay node takes, for example, the form of a bitmap vector of size ^^^^ ^^^^,ℬ^ ∗ ^ ^^ , denoted ^^^^, which indicates the subset of antennas to activate. If the element of the vector ^^^^ corresponds to the antenna ^^^^ of the node ^^^^ ^^^^ is equal to 1(^^^^^^^^+^^^^(^^^^) = 1), then the antenna is activated (^^^^ ∉ ^^^^^^^^^^^^), otherwise if ^^^^^^^^+^^^^(^^^^) = 0, it is not (^^^^ ∈

[0129] This vector ^^^^ is, for example, constructed from the set ^^^^ ^ ∗ ^ ^^in the following way: the vector ^^^^ is first initialized with "1", then the elements of the vector ^^^^ that correspond to the index ^^^^ ∈ ^^^^*^^^^ are instantiated as "0".

[0130] Illustrative example

[0131] Soit ^^^^∗ = {1,2,3,5}, ℬ∗ = {1,4,7}, ^^^^ = 1,^^ ∗ Let t = 2 and t = 7 and t = 3, and suppose that t = {2, 5}. The bitmap vector of dimension 6 is: t = [1, 0, 1, 1, 0, 1]

[0132] Alternatively, a vector ^^^^ containing the indices in ^^^^ ^ ∗ ^ ^^ is transmitted during this S630 step. Thus, considering the previous example, the vector ^^^^ is expressed as follows: ^^^^ = [2,5]^^^^

[0133] On the relay node side, this vector can be interpreted because the nodes activated for retransmission are known thanks to the vector, and the number of antennas on each node is also known. Thus, node 2 deactivates its first antenna and node 3 deactivates its second antenna.

[0134] It is also important to note that the set of antennas to be activated by each relay node must also be considered to determine the position of the precoding coefficients in the matrix ^^^^ = [^^^^^^^^, … , ^^^^^^^^, … , ^^^^^^^^]. This matrix has dimension (^^^^^^^^,ℬ^* ^^^ − |^^^^∗ ^^^^| ) × ^^^^, where ^^^^*^^^^ denotes the set of antennas to be deactivated in the network. Thus, if the antenna ^^^^ of the node ^^^^^^^^ is activated, i.e., ^^^^ ∉ ^^^^^^^^^^^^ , this antenna applies the coefficient corresponding to the element ^^^^′(^^^^, ^^^^) = of the vector ^^^^ ^^^^ either ^^^^ ^^^^ Each activated antenna simultaneously transmits the same redundancy of the ^^^^ sources selected.

[0135] Back at the S360 stage, according to a particular implementation, the destination device also transmits the vector. , avec | | the cardinality operator and [^^^^] ^^^^ the transpose of the matrix ^^^^. This vector ^^^^ includes the selected relay nodes ∈ ℬ*, so that c* ^^^^ each relay node ^^^^^^^^determine the precoding coefficients to apply to each vector 1, … , ^^^^ of the precoding matrix ^^^^. The relay nodes ^^^^*^^^^ listed by the vector ^^^^ are, for example, ranked according to their index, in ascending order. Knowing the other active nodes and their number of antennas, each relay node ^^^^ ^ ∗ ^ ^^ then determines the position of the precoding coefficients to be applied, then applies the first coefficient associated with it to its first antenna, the second to its second antenna, etc.

[0136] In a particular implementation mode, each of the selected source devices ^ ^^^∗^^^^ ∈ ^^^^∗^^^^ applies the same power ^^^^^^^^ = ^^^^0, ^^^^ = 1, … , ^^^^. Alternatively, the selected source devices ^^^^ ^ ∗ ^ ^^ ∈ ^^^^ ^ ∗ ^ ^^ apply potentially different powers, and the destination device also transmits, during this S360 step, a vector = [1, ...,] containing the power to be applied for each source device Selon une In this particular implementation, the powers ^^^1^ , … ,^^^^^^^^ are ranked in ascending order of the source device indices ^^^^ ^ ∗ ^ ^^ .

[0137] devices ∗ ifs sources ^^^^ ^^^^The precoding matrix ^^^^, the vector ^^^^ (optionally the vector ^^^^) are received by the nodes ^^^^* ∗^^^^ ∈ ℬ^^^^ during an S230 step. This S230 step is implemented, for example, by the MOD_RX module described with reference to Figure 4B. In response, each relay node ∗ ∈ ℬ^^^^ simultaneously transmits a redundancy, called a second redundancy, of messages from the ^^^^ selected sources, i.e., Step S240. This step S240, for example, is implemented by the MOD_TX module described with reference to Figure 4B. To facilitate understanding and for the sake of brevity, the index "^^^^ + ^^^^(^^^^), ^^^^" is described in more detail with reference to Figure 9. These second redundancies are received by the receiving antennas of the destination device ^^^^ during an S370 step.

[0138] Based on this retransmission, the destination device attempts to decode the source devices. during a stage

[0139] In a particular implementation mode, the communication process is iterated until a stopping criterion is reached. This stopping criterion corresponds, for example, to a duration or a number of iterations reached. Alternatively, the communication process is iterated until all messages are decoded without errors by the destination.

[0140] Figure 7 represents, in flowchart form, a specific implementation method for activating transmitting antennas at relay nodes. This method corresponds to a specific implementation of step S350, which selects, at a certain interval, a set of sources whose messages are simultaneously sent to the destination device d, from a set ℬ ^ ∗ ^ ^^of relay nodes and a subset of transmitting antennas to activate relay nodes of the set ℬ ^ ∗ ^ ^^ .

[0141] The equivalent mutual information of the channel can be optimized by selecting, within a relay node ∈ ℬ∗ ^^^^, that the antennas offering the highest quality connections. This selection is only possible, however, if > | ^^^^|. Furthermore, the maximum number of antennas that can be deactivated is equal to − | ^^^^|.

[0142] De manière plus formelle, of all antenna subsets that can be deactivated with cardinality ^^^^′ ∈ {0, … ,^^^^^^^^,ℬ − | ^^^^|} . ^^^^^^^^^^^^^^^^−^^^^^^^^^^^^^ denotes the set of all antenna subsets that can be deactivated in the network, and is expressed as follows:

[0144] À titre d'exemple illustratif, on considère ^^^^ = {1,2,3,5}, ℬ = {1,4,7}, ^^^^^^^^,1 = 1,^^^^^^^^,4 = 2 et^^^^^^^^,7 = 3. The set ^^^^ is indeed eligible for antenna selection since = ^^^^^^^^,1 +^^^^^^^^,4 + ^^^^^^^^,7 = 6 > | ^^^^| = 4.

[0145] Furthermore, the maximum number of antennas that can be deactivated is equal to ^^^^ ^^^^,ℬ − |^^^^| = 2. In other words, ^^^^′ ∈ {0,1,2}. If ^^^^′ = 0, then no antenna can be deactivated. If Q=1, the subsets of antennas that can be deactivated are: {{1}, {2}, {3}, … , {6}}. If Q=2, the subsets of antennas that can be deactivated are: {1,2}, {1,3}, … , {1,6}, {2,2}, … , {5,6}.

[0146] Thus, the set of antenna subsets that can be deactivated is expressed as follows:

[0147] ^^^^^^^^^^^^^^^^−^^^^^^^^^^^^ = {∅, {1}, {2}, {3}, … , {6}, {1,2}, {1,3}, … , {1,6}, {2,2}, … , {5,6}}.

[0148] Noted ^^^ ^ ∗ ^ ^^ all the antennas to be deactivated in the system. To determine an exhaustive search on ^^^^^^^^^^^^^^^^−^^^^^^^^^^^^ is carried out, based on the equivalent mutual channel information between the activated antennas (complement of ^^^^∗^^^^ ∈ ^^^^^^^^^^^^^^^^^−^^^^^^^^^^^^ in�1, … ,^^^^^^^^,ℬ�) and the ^^^^^^^^ antennas receiving at the destination.

[0149] As illustrated in Figure 7, the transmitting antenna activation process includes a first step S710 during which the destination device calculates the entire process. ^^^^^^^^� ^^^^^̅^^^,^^^^−1 Parts of ^^^^^̅^^^,^^^^−1 by limiting ourselves to subsets of cardinality less than or equal to the number of receiving antennas ^^^^ ^^^^ and different from the empty subset. This constraint on the cardinality of the subsets aims to address the assertion that it is not desirable to simultaneously retransmit more streams than there are receiving antennas, in order to limit interference.

[0150] It is important at this stage to recall that the set of all subsets of a set ^^^^, denoted ^^^^ ( ^^^^ ) , corresponds to the set of all possible subsets of ^^^^.

[0151] Par la suite, les sous-ensembles de ^^^^^^^^^^^^�^^^^^̅^^^,^^^^−1� de cardinalité ^^^^ ∈ {1, … ,^^^^^^^^} sont dénotés tel que

[0152] The antenna activation process further includes an S720 step of determining, for each source subset ^^^^ ∈ ^^^^^^^^^^^^,^^^^�^^^^^̅^^^,^^^^−1�, ^^^^ ∈ {1, … ,^^^^^^^^} , the set ℬ of relay nodes that have decoded the messages from all the source devices of ^^^^. Considering the relay nodes that have decoded the messages from all the source devices and not just some of them has the advantage of eliminating interference at the receiver. During this same step, only the eligible subsets ^^^^ of ^^^^^̅^^^,^^^^−1 and of ℬ are selected such that |^^^^| ≤ ^^^^^^^^,ℬ, = ∑^^^^∈ℬ ^^^^^^^^,^^^^ the total number of transmitting antennas in the set ℬ of relaying nodes considered.

[0153] L'étape S720 est itérée pour différentes valeurs de ^^^^ ∈ {1, … ,^^^^^^^^} correspondant à different values ​​of receiving antennas. According to a particular implementation, if no subset is eligible for a value ^^^^0, the other values ​​^^^^ > ^^^^0 are not pastested. Indeed, if no eligible subset ^^^^ is determined for this value ^^^^0, no eligible subset ^^^^ can be determined for a value ^^^^ > ^^^^0.

[0154] The antenna activation process further includes an S730 step during which sub-assemblies � ^ � ^^ � ^ �∗ ^^^^ of activatable antennas are determined for each part of the set ℬ of relay nodes.

[0155] During an S740 step, a representative value of a quality criterion is calculated for one part of the set of sources, one part of the set of relay nodes, and one part of the set � ^ � ^ � ^^ � ^^^^ of transmitting antennas. This value, representing a quality criterion of a communication channel and corresponding, for example, to the equivalent mutual information of that channel, is calculated according to the calculation method described with reference to Figure 9. It characterizes the quality of a communication channel allowing the simultaneous transmission of messages and the reception of these messages by a plurality of antennas. An example of calculating the equivalent mutual information is described in more detail with reference to Figure 8.

[0156] According to one particular implementation, this S740 step is repeated for each part of the set ^^^^ of sources, each part of the set ℬ of relay nodes, and each part of transmitting antennas.

[0157] The process further includes an S750 step in which the combination of part of the set ^^^^ of sources, part of the set ℬ of relay nodes, and part of A transmission method that optimizes the quality criterion (e.g., equivalent mutual information) is implemented. This S750 step is, for example, implemented by the MOD_SEL module described with reference to Figure 4A.

[0158] In a particular implementation mode, the selected combination corresponds to the one that maximizes this quality criterion (or minimizes it, depending on how the criterion is defined). Alternatively, the selected combination corresponds to one of the possible combinations of parts providing a representative value of the quality criterion that is above (or below) a certain threshold.

[0159] The portion of the set of sources selected at this stage is noted. ^ ∗ ^ ^^ , the part of the set ℬ of relay nodes is denoted ℬ^ ∗ ^^^ and part of the set � ^ � ^ � ^^ � ^^^^ of transmitting antennas is noted ^ � ^ � ^ � ^ � ^ ∗ ^ ^^.

[0160] According to a particular implementation, if all the transmitting antennas of a relay node ^^^^ ^ ∗ ^ ^^ of the set ℬ ^ ∗ ^ ^^ should disable all its antennas, then this relay node is removed from the set ℬ ^ ∗ ^ ^^ .

[0161] Finally, during an S760 step, a retransmission instruction including the sub- e nsemble � ^^ � ^ � ^ � ^ ∗ ^^^ The selected antenna signal is transmitted to the relay nodes ^^^^^ ∗ ^^^ of the whole thingℬ ^ ∗ ^ ^^ so that they transmit the second redundancy versions by only activating the antennas of the subset ^ � ^ � ^ � ^ � ^ ∗^^^. This S760 step is implemented for example by the MOD_TX module described with reference to figure 4A.

[0162] The number of antennas to be deactivated is denoted by ^^^^′. The cardinality of the set on which the exhaustive search for antennas is performed is expressed as follows:

[0163] In a particular implementation mode, antenna selection corresponds to the selection of a subset of the relay node antenna set ^^^^* ∗^^^^ ∈ ℬ^^^^ offering the best links with the destination device d. In this particular case, a reduced-complexity search is performed on ^^^^^^^^| ^^^^^^^^^^^^^−^^^^^^^^^^^^^ = ^^^^^^^^′ with ^^^^ ^^^^′The Q' antennas have the weakest links to the destination device, for example, in terms of signal-to-noise ratio. Thus, the cardinality of the set on which the antenna search is performed is expressed as follows: 0, … ,^^^^ ^^^^,ℬ − | ^^^^| = ^^^^ ^^^^,ℬ - | ^^^^| + 1 (15)

[0164] Figure 8 represents, in the form of a flowchart, a particular method of implementing a communication process in an OMAMRC system, according to a second example.

[0165] This particular method of implementing a communication process differs from that described with reference to Figure 6 in that the destination device transmits, to the relay nodes ^^^^, the set ^^^^^^^^,^^^^−1 of the source devices whose messages have been decoded without errors and / or the set ^^^^^̅^^^,^^^^−1 of the source devices whose messages could not be correctly decoded, rather than an ACK / NACK message.

[0166] Steps S300, S100, S310 and S320 are identical to those described with reference to Figure 6, and are not re-described, for the sake of brevity.

[0167] The process further includes a step S330-1 in which the destination device transmits to the relay nodes the set of source devices whose messages have been decoded without errors. Alternatively, the destination device transmits to the relay nodes the complement of the decoding set of the destination device. This set is received by the relay nodes ^^^^ during an S210-1 step. Then, during an S215-1 step, each relay node ^^^^ determines the intersection ^^^^′^^^^,^^^^−1 between their respective decoding sets ^^^^^^^^,^^^^−1 and the complement of the decoding set of the destination device ie, ^^^^′^^^^,^^^^−1 = ^^^^^^^^,^^^^−1 ∩ ^^^^^̅^^^,^^^^−1. This set^^^^′^^^^,^^^^−1 of source devices not decoded during the time interval ^^^^ − 1 by the destination, but which have been decoded by the relay node ^^^^, is transmitted by said relay node during an S220-1 step, and received by the destination device during an S340-1 step.

[0168] Finally, steps S350, S360, S230, S240, S370 and S380 are identical to those described with reference to Figure 6, and are not re-described, for the sake of brevity.

[0169] Figure 9 represents, in the form of a flowchart, a particular method of implementing a process for calculating equivalent mutual information of a channel linking the transmitting antennas of the relaying nodes to the receiving antennas of the destination.

[0170] Method for calculating equivalent mutual information

[0171] As illustrated by Figure 9, the calculation process includes a first step S910, of calculating a precoding matrix aimed at maximizing the equivalent mutual information of a channel in case of simultaneous transmission of messages from the source devices ^^^^ of the set ^^^^ by the destination device ^^^^.

[0172] De manière plus formelle, un vecteur ^^^^ ∈ ℂν comprenant les ^^^^ = |^^^^| dispositifs sources in ^^^^ sorted in order of increasing indices is generated. The source devices are jointly decoded by the set ℬ of relay nodes with = ∑^^^^∈ℬ ^^^^^^^^,^^^^ . From the set ℬ of relay nodes, a vector ^^^^ = is constructed such that ^^^^1 < ⋯ < ^^^^|ℬ| and ^^^^^^^^ ∈ ℬ,∀ ^^^^ ∈ {1, … , |ℬ|}.

[0173] The channel equivalent to the transmission from the source devices listed in ^^^^ by the nodes in ℬ is represented by a matrix ^^^^ ∈ The channel between the antenna with index ^^^^ ∈{1, … ,^^^^^^^^} of the destination device ^^^^ and the transmitting antenna ^^^^ ∈�1, … ,^^^^^^^^,^^^^^^^^� of the relay node ^^^^^^^^ ∈ ℬ , corresponds to the coefficient ℎ^^^^,^^^^+^^^^(^^^^) of the matrix, such that ^^^^(^^^^) = ∑ ^^^^−1 ^^^^=1 ^^^^^^^^,^^^^^^^^ represents the total number of transmitting antennas of the nodes ^^^^^^^^=1..^^^^−1, with k the index representing the order of the nodes in the vector ^^^^.

[0174] La matrice de précodage ^^^^ = [^^^^ , … , ^^^ ] ^^^^^^^^,ℬ×^^^^ 1 ^^^^^ ∈ ℂ is made up of the ν best orthogonal eigenvectors (e.g., the ν vectors whose eigenvalues ​​are the most important, ranked in descending order of eigenvalues), with ^^^^† the adjoint matrix of ^^^^. The ^^^^-th vector ^^^^^^^^ ∈ is applied as precoding for the source device ^^^^^^^^, such that the node ^^^^^^^^ ∈ ℬ uses ^^^^^^^^,^^^^^^^^ coefficients of the vector ^^^^^^^^.

[0175] Le coefficient de précodage appliqué par l’antenne ^^^^ ∈ {1, … ,^^^^^^^^,^^^^^^^^} du ^^^^-ème élément ^^^^^^^^in ^^^^ then corresponds to the element ^^^^ + ^^^^(^^^^) of the vector ^^^^^^^^ , i.e., ^^^^^^^^+^^^^(^^^^),^^^^ with ^^^^(^^^^) = ∑ ^^^^−1 ^^^^=1 ^^^^^^^^,^^^^^^^^ . In this way, the antenna ^^^^ of the relay node ^^^^^^^^ ∈ ℬ transmits:

[0176] And the signal ^^^^ received by the destination device is then expressed as follows: ^^^^ = ^^^^ ^^^^ ^^^^ + ^^^^ (4)

[0177] avec ^^^^ le signal émis, ^^^^ un vecteur de bruit, ^^^^�^^^^^^^^†� = ^^^^2^^^^^^^^^^^^ avec ^^^^{^} l'espérance mathematics, ^^^^ the power of noise., and ^^^^ ^^^^^^^^ an identity matrix.

[0178] By applying (^^^^^^^^) † , we recover the ^^^^ symbols emitted without interference: ^^^^^^^^ = λ^^^^^^^^^^^^^ + ^^^^^^^^ , ^^^^ = 1, … , ^^^^ (5)

[0179] où ^^^^{|w |2} = σ2λ avec λ la l-ième plus grande valeur propr † l ^^^^ ^^^^ e de ^^^^ ^^^^.

[0180] The calculation process further includes an S920 step during which a power ^^^^ ^^^^ to allocate to each spatial layer ^^^^ (or equivalently to each source ^^^^ ^ ∗ ^ ^^ of is determined. It is important to note here that this power allocation is done per spatial layer (or equivalently per source) and not per antenna, so as to respect the orthogonality constraint of the precoding vectors. This S920 step is described in more detail below.

[0181] Then, in step 930, a "single-source" quality criterion is calculated for each spatial layer (or equivalently for each source in the set) based on the precoding matrix and the transmission power to be allocated to said spatial layer (or equivalently to said source). In a particular implementation, the "single-source" quality criterion associated with each spatial layer corresponds to a signal-to-noise ratio.

[0182] The signal-to-noise ratio ^^^^^^^^^^^^ ^^^^ of the lth spatial layer is expressed as follows: ^^^^^^^^^^^^^^^^ = with λ ^^^^ the l-th largest eigenvalue of ^^^^ † ^^^^, ^^^^ the power of the noise and ^^^^ ^^^^ the power to be allocated to the lth spatial layer.

[0183] Furthermore, equivalent mutual information I ^^^^ is defined as the sum of the mutual information of the different spatial layers, and is expressed as follows:

[0184] In the case of Gaussian inputs, the equivalent mutual information I ^^^^ is given by:

[0185] It is important to note that in the case where the covariance of the noise (including interference) is not a multiple of the identity ^^^^ ^^^^ † ^^^^ , that is to say ^^^^�^^^^^^^^� = ^^^^, then ^^^^ = [^^^^1, … , ^^^^^^^^] ∈ℂ^^^^^^^^,ℬ×^^^^ is made up of the ν best orthogonal eigenvectors ∈

[0186] Power Calculation Step S920

[0187] The transmission power of a node is limited by a power budget, which is shared by the antennas of that node. Depending on a particular implementation, a An amplifier is connected to each antenna, allowing each antenna to transmit a signal at the specified power. In this case, the power... ^^^^ to allocate to each spatial layer ^^^^ (or equivalently to each source ^^^^ of the set ^^^^) is determined by maximizing the equivalent mutual information I ^^^^ (one expression of which is, for example, provided by equation #(7)) subject to the following local constraints:

[0189] The power allocation problem can then be written as:

[0191] Any method of satisfying constraints known to a person skilled in the art for solving such a problem can be considered; the choice of a particular method corresponds only to a variant of the invention's implementation. According to a particular implementation, this problem is solved by applying Lagrange multipliers with |ℬ| constraints.

[0192] One possible suboptimal solution is as follows:

[0193] ^^^^ = 1, … , ^^^^ ( )

[0194] Variants

[0195] In a particular mode of implementation, the matrix V is quantified, and for example chosen with respect to a predefined set.

[0196] In a particular implementation mode, the matrix V is received noisy by the relay nodes during the S230 step. In this case, the signal ^^^^ received by the destination device becomes: ^^^^ = ^^^^ ^�^^^ ^^^^ + ^^^^ (12)

[0197] avec ^ � ^^^ the noisy precoding matrix.

[0198] This signal no longer guarantees zero interference at the receiver. In this case, the receiving device can use an equalizer that minimizes the Linear Minimum Mean Squared Error (LMMSE) of the type: with ^^^^′ = ^^^^ ^�^^^ which reduces interference between the ^^^^ spatial layers. The destination device ^^^^ then calculates the ^^^^ Signal-to-interference-plus-noise ratio (SINR) ^^^^ ^^^^ at the output of the equalizer. Then the mutual information is calculated by considering the matrix ^ � ^^^, and the ^^^^ signal-to-interference-plus-noise ratios (SINR) ^^^^ ^^^^ .

[0199] Figure 10 schematically represents an example of the implementation of the communication process in an OMAMRC system.

[0200] As illustrated in Figure 10, the decoding set ^^^^ 1,^^^^−1 of the source device ^^^^1 at the interval ^^^^ − 1 is such that ^^^^1,^^^^−1 = {^^^^1, ^^^^2}, the decoding set of the source device ^^^^2 at the interval ^^^^ − 1 is such that ^^^^2,^^^^−1 = {^^^^1, ^^^^2} and the decoding set ^^^^^^^^,^^^^−1 of the destination device ^^^^ at the interval ^^^^ − 1 is such that ^^^^^^^^,^^^^−1 = {∅}.

[0201] Aussi, trois configurations sont envisageables : ^^^^ = {^^^^1} et ℬ = {^^^^1, ^^^^2} ou ^^^^ = {^^^^2} et ℬ = {^^^^1, ^^^^2} or ^^^^ = {^^^^1, ^^^^2} and ℬ = {^^^^1, ^^^^2}. We assume that the configuration in which ^^^^ = {^^^^1, ^^^^2} and ℬ = {^^^^1, ^^^^2} provides the best equivalent mutual information. In this case, the two transmitting antennas of the source device ^^^^2 simultaneously send the same redundancies of the source devices ^^^^1 and ^^^^2, and ^^^^ = [^^^^1, ^^^^2]^^^^.

[0202] Le vecteur propre ^^^^ ^^^^ 1 = ^^^^4,1�corresponding to the largest eigenvalue ^^^^1 is applied as precoding of the source device ^^^^1, and the eigenvector ^^^^ ^^^^ 2=�^^^^1,2 ^^^^2,2 ^^^^3,2 ^^^^4,2�corresponding to the second largest eigenvalue ^^^^2 of ^^^^ † ^^^^ −^^^^ ^^^^ is applied as precoding of the source device ^^^^2.

[0203] In other words, the first antenna of the source device ^^^^1 transmits the signal ^^^^ 1,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 1,2 * ^^^^^^^^^^^^^ ^^^^2 The second antenna of the source device ^^^^1 transmits the signal ^^^^ 2,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 2,2 * ^^^^^^^^^^^^^ ^^^^2 The first antenna of the source device transmits the signal. 3,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 3,2 * ^^^^^^^^^^^^^ ^^^^2 and the second antenna of the source device transmits the signal 4,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 4,2 * ^^^^^^^^^^^^^^^^^2 .

[0204] Therefore, the power transmitted by each relay node is expressed as follows:

[0205] et l’information mutuelle équivalente dans le cas d’entrées gaussiennes : ^^^^ =

[0206] Par ailleurs, puisque = 4 > | ^^^^| = 2 , the joint selection process for source devices and antennas to be activated by each relay node can be applied. The antenna subsets that can be deactivated are as follows: ^^^^^^^^^^^^^^^^−^^^^^^^^^^^^ =�∅, {1}, {2}, {3}, {4}, {1,2}, {1,3}, {1,4}, {2,3}, {2,4}, {3,4}�

[0207] with indices 1 and 2 corresponding to the antennas of the source device ^^^^1 and indices 3 and 4 to the antennas of the source device ^^^^2.

[0208] We also assume that the subset of antennas to be deactivated is such that ^^^^ = {3}, and that it is the first antenna (index 3) of the source device ^^^^2 that is deactivated.

[0209] A new channel ^^^^ ′is defined between the active transmitting antennas of the relay nodes and the ^^^^ ^^^^ Antennas receiving the destination signal. The eigenvector ^^^^ ^ ′ ^ ^^ = ^ ^1 ′ ,1^^^^2 ′ ^^^ �^^^ ,1 ^^^^3 ′ ,1° corresponding to the largest eigenvalue est applied as precoding of the source device ^^^^ ′ ′ ′ ′^^^^ 1, the eigenvector ^^^^^^^^ =�^^^^1,2 ^^^^2,2 ^^^^3,2� corresponds to the second largest eigenvalue ^^^^ ′ 2 of ^^^^′ is applied as precoding of the source device ^^^^2, In other words, the first antenna of the device

[0210] The power transmitted by each relay node is then expressed as follows:

[0211] and the equivalent mutual information ^^^^ in the case of Gaussian inputs is expressed as follows:

Claims

1. Claims

1. A method for activating transmitting antennas of relay nodes, the method comprising the following steps, implemented by a destination device (d), following the reception of ≥ 2 messages transmitted successively by ≥ 2 source devices and the inability of the destination device to decode at least one message received from at least one source device, referred to as the "undecoded source device", each message transmitted by a source device (∈ ℳ) comprising a first redundancy version (RV0) resulting from the encoding of an information message associated with the source device (∈ ℳ): - a selection (S50) of a set ^ ∗ ^ ^^ including one or more undecoded source devices (^^^^^ ∗ ^^^), and a subset � ^^ � ^ � ^ � ^ ∗^^^ of transmitting antennas to be activated by relay nodes of a set ℬ ^ ∗ ^ ^^ of relay nodes associated with the whole assembly ^^^^ ^ ∗ ^ ^^ , based on a quality criterion of a communication channel between the antennas of said subset � ^^ � ^ � ^ � ^ ∗ ^^^ and the destination device (d), at least one relay node (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ comprising a plurality of transmitting antennas; and, − a transmission (S60, S360), to the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ , of a retransmission instruction including the subset � ^^ � ^ � ^ � ^ ∗^^^ of selected antennas, so that the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ simultaneously transmit a second redundant version resulting from the encoding of the information message associated with each undecoded source device by activating only the antennas of the subset

2. A receiving method according to claim 1, wherein said quality criterion is mutual information of the communication channel between the antennas of u sous- ^^^ of antennas and the destination device (d).

3. Activation method according to claim 1 or 2, wherein the total number of transmitting antennas of the assembly ^ � ^ � ^ � ^ � ^ ∗ ^^^ is greater than or equal to the number of undecoded source devices (^^^^ ^ ∗ ^^^ ) of the set

4. Activation method according to any one of claims 1 to 3, further comprising an evaluation (S40) of the quality criterion for different sub-assemblies ^ � ^ � ^ � ^ � ^^^^ antennas of a set ℬ ^^^^ of relay nodes associated with undecoded source devices, the subset ^ � ^ � ^ � ^ � ^ ∗^^^ of selected antennas optimizing the quality criterion.

5. Activation method according to any one of claims 1 to 4, the destination device (d) comprising a plurality of receiving antennas.

6. Activation method according to any one of claims 1 to 4, further comprising a determination of the quality criterion of the communication channel including: − a calculation (S930), for each undecoded source device of an eligible set ^^^^, of a single-source quality criterion as a function of a precoding matrix and a transmit power to be allocated to each undecoded source device of the set ^^^^; and, − a calculation (S940), of the quality criterion of the communication channel, as a function of the single-source quality criteria calculated for each undecoded source device of the set ^^^^.

7. An activation method according to any one of claims 1 to 6, wherein the retransmission instruction further comprises the set of selected undecoded source devices, and a precoding matrix (^^^^) to be applied by the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^

8. An activation method according to claim 7, wherein the retransmission instruction further includes an indication of the distribution of transmitted transmission power by each relay node. ∗ of the set ℬ ^^^^ , between the undecoded source devices ∗ of the whole thing ^^^^ ^^^^

9. A computer program comprising instructions for implementing an activation method according to any one of claims 1 to 8, when said program is executed by a processor.

10. A computer-readable recording medium on which a computer program according to claim 9 is recorded.

11. A destination device (d) configured to implement an activation method according to any one of claims 1 to 8.

12. A relay node (^^^^ ^ ∗ ^ ^^ ) including − a plurality (^^^^^^^^,^^^^^ ∗ ^ ^^) transmitting antennas; − a receiving module (MOD_RX), from a destination device, of a retransmission instruction for second redundancy versions of information messages from so-called undecoded source devices, the undecoded source devices having previously transmitted first redundancy versions (RV0) of said information messages not having been decoded by the destination device (d), the retransmission instruction including a sub- e nsemble � ^^ � ^ � ^ � ^ ∗ ^^^ of transmitting antennas selected by the destination device for said retransmission; and, − a transmission module (MOD_TX) configured to activate only the transmitting antenna(s) of the subset belonging to it to transmit said second versions of redundancy to said destination device.

13. Communication system (SYS) comprising ≥ 2 source devices, a destination device (d) according to claim 11 and several relay nodes ^ ∗ ^ ^^ ) according to claim 12.

14. Communication system (SYS) according to claim 13 using an orthogonal multiple access scheme of type OMAMRC, Orthogonal MultipleAccess Multiple-Relay Channel, between the relaying nodes and the destination device (d).

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