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

Abstract

Method for activating transmitting antennas of relay nodes, relay node and associated destination device. 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: a selection of a set of undecoded source devices, and a subset of transmitting antennas to be activated by relay nodes ( ) of a set of relay nodes associated with the set , r; and, a transmission, to the selected relay nodes, of a retransmission instruction including the selected antenna subset. Figure for the abstract: Fig. 3.

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 relaying 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. Previous technique

[0005] Conventionally, the source devices of an OMAMRC-type communication system transmit messages to a single destination, if necessary via relay nodes. The relay nodes are, for example, of the "Half Duplex" type (i.e., a relay node cannot receive and transmit simultaneously) and receive messages from the source devices before decoding them. When retransmission of these messages is required by a destination device, the relay nodes access the communication channel linking these nodes to a destination device using an orthogonal multiple access scheme to transmit the messages to the destination device, thereby limiting interference.This orthogonality is usually obtained by time multiplexing in the form of disjoint time intervals (such as "Time Division Multiple Access", TDMA), but orthogonality resulting from frequency multiplexing in the form of sub-bands of . Disjoint frequencies (such as "Frequency Division Multiple Access", FDMA) is also conceivable.

[0006] The document "Efficient Cooperative HARQ for Multi-Source Multi-Relay Wireless Networks", Cerovié, S. & Al., In 2018 14th 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] Fig. 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 PI phase and a second P2 phase.

[0009] During the INIT initialization phase, the destination device determines a number of bits 9 carried by a modulation and a coding efficiency R for the first transmission from each source, according to a quality criterion of the communication channel.

[0010] To do this, the destination device determines a representative value of 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 sound reference signals as defined by the 3GPP LTE consortium). During a retransmission, a relay node is associated with a source device and may 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 R and a number of bits carried by a modulation for a number A of channel uses ("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 L of the message to be transmitted by a source device is defined as follows: L - NY x R x q. The message is encoded with a low-yield mother code Rq. (for example, 1 / 3), and this coded message of length Lc — L / Rq > L is subsequently stored in a circular buffer, an example of which is described with reference to [Fig. 2].

[0013] The data transmission cycle in an OMAMRC-type communication system further includes a first PI phase during which the M sources successively transmit their message during M time slots, respectively using the modulation and coding schemes determined during the INIT initialization phase. During this first PI phase, 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 M 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 PI phase, so as to allow the destination device to decode the messages from all the 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 PI phase.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 PI phase, then re-encode the received message and store it in its own circular buffer. This second phase P2 lasts a maximum of TMAX time intervals. During this phase, the number N2 of channel uses 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 TUSED < TMAX, the destination device broadcasts an acknowledgment. In this case, a new frame transmission cycle begins with the erasure of the memories of the relay nodes and the destination device, and with the transmission of new messages by the source devices.

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

[0017] As mentioned previously, during the INT initialization phase, a message encoded with a yield Rq 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 of a source device encoded by a low yield mother code / ?o (eg, 1 / 3) and allows selection of a particular redundancy of the message to be transmitted, depending on a starting reading position.

[0018] Indeed, these starting read positions POS0, POS1, POS2, and POS3 are associated with different redundancy versions: RVO, 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, RVO, can be decoded independently of the other versions.

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

[0020] During the second phase P2, the relay node determines the bits to be transmitted during a first retransmission TX2 by reading, from the circular buffer, the N2q bits encoded from position POS2, where N2 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 N2q bits encoded from position POS3, and the bits to be transmitted during a third retransmission TX4 by reading, from the circular buffer, the N2q bits encoded from position POS1. Thus, the sequence of transmissions for a source s> is, for example, as follows: TX1, TX2, TX3, TX4, TX1, TX2, TX3, TX4, ...

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

[0022] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those described above, by proposing a solution that allows the selection of transmitting antennas to be activated at relay nodes, so as to optimize a channel quality criterion. communication between these transmitting antennas and the destination device. This strategy proves particularly effective when each relay node b has its own power budget P. 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 M > 2 messages transmitted successively by M > 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 5* comprising one or more source devices undecoded, and a subset of transmitting antennas to be activated by relay nodes of a set B, relay nodes associated with set 5*, according to a quality criterion of a communication channel between the antennas of said subset and the destination device, at least one relay node of set B* comprising a plurality of transmitting antennas; and,

[0025] - a transmission to the relay nodes of assembly B, of an instruction of retransmission including the selected antenna subset, so that the relay nodes of set B simultaneously transmit a second redundant version resulting from the encoding of the information message associated with each undecoded source device of set 5* by activating only the antennas of subset a*-

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

[0027] By activating only the transmitting antennas of selected relay nodes that allow optimization of 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 allow optimization of this quality criterion.

[0028] In general, it is considered that the steps of a process should not be interpreted as being linked to a notion of temporal succession.

[0029] In particular embodiments, the activation method may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0030] In particular implementation modes, an orthogonal multiple-access scheme, denoted OMAMRC ("Orthogonal Multiple-Access Multiple-Relay Channel" according to Anglo-Saxon terminology), is applied to the transmission channel between the relay nodes and the destination. 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 Decoded and Forward" according to Anglo-Saxon terminology).

[0031] In particular embodiments, the selection further includes the selection of the set B, of relay nodes.

[0032] In particular embodiments, the selection of the set B^ of relay nodes is determined from the selection of the antenna subset.

[0033] In particular embodiments, the selection of the set of source devices, the set B^ of relay nodes, and the subsets A* of transmitting antennas is obtained from an exhaustive search for each subset of undecoded source devices, each subset of relay nodes having decoded all the source devices for this subset of undecoded source devices, and each possible subset of transmitting antennas.

[0034] In particular embodiments, the selection of the set of source devices, the set B* of relay nodes, and the subsets of transmitting antennas is carried out jointly, i.e. during the same iteration.

[0035] In particular embodiments, the activation method further comprises a selection of the relay nodes of set B* from a set N of relay nodes, depending on the quality criterion of the communication channel between the antennas of the subset and the destination device.

[0036] In particular implementation modes, the selected set of antennas corresponds to the transmitting antennas to be activated from a particular node fa* of the set b?.

[0037] In particular implementation modes, the selected set of antennas corresponds to the transmitting antennas to be activated from all nodes of set B,-

[0038] In particular embodiments, said quality criterion is a mutual information of the communication channel between the antennas of the subset A* 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 selection, one can seek to optimize such a quality criterion or, alternatively, ensure that this quality criterion reaches at least a given threshold value.

[0040] In particular embodiments, the total number of antennas in The emission from the whole is greater than or equal to the number of non-source devices decoded from set 5*.

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

[0042] In particular embodiments, the method further includes an evaluation of the quality criterion for different subsets Âzd'antennes of a set Bz of relay nodes associated with the undecoded source devices, the selected subset ^d'antennes optimizing the quality criterion.

[0043] In specific implementation modes, the antenna subset The selected antenna subset is a subset that maximizes this quality criterion. Alternatively, the selected antenna subset is a subset from among several antenna subsets Ât, all of which provide a representative value of the quality criterion above a certain threshold.

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

[0045] MRT is a wireless communication method applied to improve the performance and reliability of data transmission within systems multi-antenna communication. To do this, this method uses the plurality of antennas of the transmitter (in our case relay nodes associated with the selected antennas) and of the receiver (in our case the destination device) to maximize the power of the signal received by this 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 Bz (where applicable, after application of amplitude and phase coefficients previously transmitted through a precoding matrix V). These messages, which relate to the same redundancy, are then received in a "superimposed" manner through a so-called "equivalent" channel corresponding to the superposition of all the sub-channels defined by the transmitting antennas and the receiving device.

[0047] In particular embodiments, the destination device comprises a plurality of receiving antennas.

[0048] In other words, in this particular embodiment, 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 embodiments, the activation process further includes a 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 particular embodiments, the activation process further includes a determination of the quality criterion of the communication channel, including:

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

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

[0053] In particular embodiments, the retransmission instruction further includes the selected set of undecoded source devices, and a precoding matrix to be applied by the relay nodes of the B*- set.

[0054] In particular modes of implementation, the retransmission instruction further includes an indication, for each relay node of the set Bp, of the coefficients of the precoding matrix to be applied by said relay node, for each undecoded source device of the set £*.

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

[0056] In particular modes of implementation, the retransmission instruction further includes an indication of a distribution of a transmission power transmitted by each relaying node of the Bp set between the undecoded source devices of the Ej set.

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

[0058] In particular embodiments, the method further includes a transmission, by the M sources, of messages including a first redundancy (also referred to as "redundancy version"), during M consecutive time intervals.

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

[0060] In particular embodiments, the relay nodes of set B* correspond to relay nodes that have decoded all the 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 the source devices, and not just some of them, offers the advantage of eliminating interference at the receiver.

[0061] In particular implementation modes, an orthogonal multiple access scheme, denoted OMAMRC ("Orthogonal Multiple Access Multiple-Relay Channel" according to 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" according to Anglo-Saxon terminology) based on selective relaying called SDF ("Selective Decoded and Forward" according to 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 may use any programming language, and be in the form of source code, object code, or intermediate code 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 can 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 disk 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 downloaded onto an Internet-type network.

[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, coming from a destination device, of a instruction for retransmitting 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 a* of transmitting antennas selected by the destination device for said retransmission; and,

[0072] - a transmission module configured to activate only the antenna(s) emission of the subset belonging to it to transmit to said device destination of said second versions of redundancy.

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

[0074] In a particular embodiment, the communication system uses an orthogonal multiple access multiple-relay channel (OMAMRC) scheme between the relay nodes and the destination device. Brief description of the drawings

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

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

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

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

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

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

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

[0083] [Fig.7] [Fig.7] represents, in the form of a flowchart, a particular mode of implementation of a method for activating transmitting antennas of relay nodes.

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

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

[0086] [Fig. 10] [Fig. 10] represents, schematically, an example of implementation of the communication process in an OMAMRC system. Description of the 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 si, s2, a destination device d, and two intermediate nodes ri, r2 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 the present embodiment, and for the sake of simplicity in the description, the communication system is considered to have a single destination d. It should be noted, however, that there is no limitation on the number of destinations d. The following developments can indeed be easily 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 L of intermediate nodes, which only need be such that L > 0. Thus, in a particular implementation, the communication system SYS does not include any intermediate nodes.

[0090] In the following description, the "set N of relay nodes" refers to the set of nodes b comprising the intermediate nodes rLet of the source devices sm, which function as relays responsible for retransmitting messages to the destination, messages of which they are aware, which may originate from themselves or from other nodes. Thus, each of these sources si, s2, s3 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 relay 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 comprises several transmitting antennas. Hereafter, the number of transmitting antennas of a node be N is denoted

[0092] For the sake of simplification, 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 of the system are co-phased before any transmission. A phase calibration procedure is, for example, carried out periodically, and can be initialized by the destination device d.

[0094] An orthogonal multiple access scheme, denoted "OMAMRC" - an acronym for "Orthogonal Multiple Access 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 Decoded and Forward" according to Anglo-Saxon terminology).

[0095] Thus, the M source nodes and the L intermediate nodes access the transmission channel according to an orthogonal multiple access scheme that allows them to listen, without interference, to the transmissions of the other source nodes and the other intermediate nodes. In the following description, it is assumed that this orthogonality is obtained 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 conceivable.

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

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

[0098] - a MOD_SEL module of a 5* assembly comprising one or more devices undecoded sources and a subset of transmitting antennas to be activated by relay nodes of a set B, relay nodes associated with set 5*, according to a quality criterion of a communication channel between the antennas of said subset yç* and the destination device (d); and,

[0099] - a M0D_TX transmission module, at the relay nodes of the assembly B*, of a retransmission instruction including the selected antenna subset, so that the relay nodes of set B* simultaneously transmit a second redundancy 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

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

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

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

[0103] - a plurality of transmitting antennas;

[0104] - a MOD_RX receiving module, originating 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 (RVO) of said information messages not having been decoded by the destination device (d), the retransmission instruction including a subset of transmit antennas selected by the destination device for said retransmission; and,

[0105] - a M0D_TX transmission module configured to activate only the transmitting antennas 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 modes of implementation.

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

[0108] As illustrated in Figure 5, the destination device d has the hardware architecture of a computer. Thus, the destination device d 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] The read-only memory 3 of the destination device d constitutes a storage medium according to the invention, readable by the processor 1, on which a computer program PROG according to the invention is stored, comprising instructions for executing steps of the activation process according to the invention. The PROG program defines functional modules of the destination device d, which rely on or control the hardware elements 1 to 5 of the destination device d mentioned above. These functional modules are illustrated in [Fig. 4A] by way of no limitation, and are described in more detail below with reference to different embodiments.

[0110] In the implementations described below, the communication means 5 enable the destination device d 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 d to transmit the retransmission instruction to the relay nodes. To this end, the communication means 5 include a wired or wireless communication interface capable of implementing any suitable communication protocol.

[0111] Fig. 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 method includes a first link initialization and adaptation step S300 during which the destination device determines a number of bits 9 carried by a modulation and a coding efficiency R for the first transmission of each source device .... sWen 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 this 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 R 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] During this same step S300, each source device sr • ■ • ' sm encodes a message of size L = NA x R xq to be transmitted to the destination device d with a low yield mother code Rq (for example of 1 / 3), and the coded message of length Lc — L / Rq > L is subsequently stored in a circular buffer, an example of which is described with reference to [Fig.2].

[0116] The communication method further includes a step S100 during which the M source devices AT • • • ' sm successively transmit their message during M consecutive time intervals, using respectively the modulation and coding schemes determined during step S300. During this first phase, the number of channel uses is fixed and identical for each of the source devices 5r •••' sm. The redundancy versions RV0}, ..., ^V0M transmitted by the source devices si' • • • ' sm during this step S100 correspond to the first RV0 redundancies of their messages.

[0117] These initial redundancies are, for example, transmitted 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 transmitting antennas, the precoding results, for example, from a superposition of discrete Fourier transform vectors of dimension n. This characteristic is advantageous since it increases the number of relay nodes in the system capable of receiving and decoding these messages.

[0118] At least some of the M messages RV0, ..., RV0M are received by the destination device during a step S310. During a step S320, the destination device determines the set of source devices whose messages have been decoded without errors during the time interval C1.The process further includes an S330 step during which the destination device transmits an ACK / NACK message to the 6th relay nodes 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 S^i to the destination device d. This decoding set corresponds, for a relay node 6 e € N, to the source devices whose messages were decoded without errors by that relay node. Each of the decoding sets is received by the destination device d during an S340 step. Thus, at a given interval fl y I, the destination device d knows the decoding set S^_j of all the relay nodes 6 e € N.

[0120] The communication method further includes a step S350 in which the destination device d selects, according to a quality criterion, a communication channel between the antennas of said subassembly and the destination device:

[0121] - an assembly g* comprising several source devices s*,

[0122] - a set B, of relay nodes associated with the set S*, from among a set B of relay nodes bh and

[0123] - a subset of transmitting antennas of at least one relay node Q,*) from set B, to be activated.

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

[0125] A relay node corresponds to a network node that has correctly decoded messages that were not decoded by the destination device during a previous time interval U1, and is therefore capable of transmitting a new redundant version of these messages to the destination device during the retransmission time interval z. This previous time interval t-1 does not necessarily correspond to the time interval immediately preceding the time interval f. Let S^_], be the decoding set of a node b at the time interval t-1. This set contains all the identifiers of the source devices that node b was able to decode without errors before the retransmission interval *. Thus, a relay node b is a potential candidate for transmitting the second redundant versions if the intersection between its decoding set and the complement of the decoding set of the destination device S^.j, is different from the empty set, i.e., if . Vm, vJe

[0126] The communication method further includes an S360 step during which the destination device calculates a precoding matrix to be applied by each of the relay nodes selected G g*, with X the set of complex numbers, the total number of transmitting antennas of the relay nodes g*, and v the number of sources whose messages must be simultaneously retransmitted. In other words, v = , with the cardinality operator.

[0127] During this same S360 step, the destination device d transmits to the relay nodes eg* all the identifiers of the source devices whose messages are to be retransmitted and the precoding matrix V, as well as all the antennas to be activated by each relay node. This S360 step is implemented, for example, by the M0D_TX module described with reference to [Fig. 4A].

[0128] The set of antennas to be activated by each relay node takes, for example, the form of a bitmap vector of size denoted a, which indicates the subset of antennas to be activated. If the element of the vector corresponding to antenna n of node bt is equal to 1 (an+^ = b-) then the antenna is activated (n Ab^), otherwise if an+^ - 0, it is not activated („ e Aa.), with (;) = r' N

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

[0130] Illustrative example

[0131] Let C = {1, 2, 3, 5}, Bf* = {1, 4, 7}, Nyj = 1, √74 ≈ 2 and NTj ≈ 3, and suppose that A(= {2, 5}). The bitmap vector of dimension NT⁻⁶ is as follows:

[0132] a= [1,0, 1,1,0,1]T

[0133] Alternatively, a vector a containing the indices in A is transmitted during this S630 step. Thus, considering the previous example, the vector a is expressed as follows:

[0134] a=[2,5]r

[0135] On the relay node side, this vector can be interpreted because the nodes activated during retransmission f are known thanks to the vector ¢, and the number of antennas of each node is also known. Thus, node 2 deactivates its first antenna and node 3 deactivates its second antenna.

[0136] 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 y — {yy^ y J. This matrix has the dimension ( / V^^-lA^I ) X V' °ù A^ denotes the set of antennas to be deactivated in the network. Thus, if antenna n of the node is activated, i.e., n ∈ A / ,., this antenna applies the coefficient corresponding to the element ,, .. of the vector v*, i.e., vp\nj)l. P(n,i) = Lj=} aj Subsequently, each activated antenna simultaneously transmits the same redundancy of the selected sf sources.

[0137] Returning to the S360 step, according to a particular implementation, the destination device also transmits the vector , r, » iT with P=[bïy ..., ^B;|j G the cardinality operator and [ ]r the transpose of the matrix M. This vector b includes the selected relay nodes eg*, so that each relay node can determine the precoding coefficients to be applied from each vector V / e / = ] y of the precoding matrix V. The relay nodes listed by the vector b are, for example, ranked according to their index, according to 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 apply, then applies the first coefficient associated with it to its first antenna, the second to its second antenna, etc.

[0138] In a particular embodiment, each of the selected source devices sj G applies the same power Pi = Pq > l - 1, ..., v. Alternatively, the selected source devices apply powers that can be different, and the destination device d also transmits, during this S360 step, a vector p_pj containing the power to be applied for each Source device: According to a particular implementation, the powers Pv are ranked in ascending order of source device indices

[0139] The set of source devices s?, the precoding matrix V, the vector b and possibly the vector P are received by the nodes eg* during a step S230. This S230 step is implemented, for example, by the M0D_RX module described with reference to Figure 4B. In response, each relay node eg* simultaneously transmits the same redundancy, called the second redundancy, of messages from the selected source v, ic, V1, „, „ Mi_fi m I lAH during a «E|l, IG[1, ...,|ty Step S240. This step S240 is implemented, for example, by the M0D_TX module described with reference to Figure 4B. To facilitate understanding and for the sake of brevity, the subscript / " 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.

[0140] Based on this retransmission, the destination device attempts to decode the source devices during an S380 step.

[0141] In a particular embodiment, the communication process is iterated until a stopping criterion is reached. This stopping criterion corresponds, for example, to a maximum duration TMAX or to a certain number of iterations. Alternatively, the communication process is iterated until all messages are decoded without errors by the destination.

[0142] Figure 7 represents, in the form of a flowchart, a particular method of implementation implementation of a method for activating transmitting antennas at relay nodes. This a process corresponding to a particular mode of implementation of the S350 selection step, at a certain interval \ of a set of sources whose messages are to be simultaneously retransmitted to the destination device d, of a set Bj of relay nodes and a subset of transmitting antennas to activate nodes relaying of the entire B^ assembly •

[0143] The equivalent mutual information of the channel can be optimized by selecting, within a relay node eg*, only the antennas offering links whose the quality is the highest. However, this selection is only possible if Njg > I € EL Furthermore, the maximum number of antennas that can be deactivated is equal to - i € EL

[0144] More formally, let {1, ....), be the set of all antenna subsets that can be deactivated by cardinality El}- Ï^Ant-Off designates the set of all antenna subsets that can be deactivated in the network, and is expressed as follows: [01451 n^ / / = UgSr LHyi ) i, ...,¾) ) # ( 13)

[0146] As an illustrative example, we consider E = {1,2, 3,5}, B = {1,4, 7}, N ta — t N ta — 2 and N TJ — 3. The set E is indeed eligible for antenna selection since = Nta + N ta + ^tj = 6 > I € EI = 4.

[0147] Furthermore, the maximum number of antennas that can be deactivated is equal to Ntb - I ∩ EI = 2. In other words, Q ∈ {0, 1, 2}. If Q = 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}.

[0148] Thus, the set of subsets of antennas that can be deactivated is expressed such that n^T-^, {1}, {2}, {3}, .... {6}, {1,2}, {1,3}, ..., {1,6}, {2,2}, ..., {5,6}}.

[0149] We note the set of antennas to be deactivated in the system. To determine A}\ an exhaustive search on H^^yy is carried out, based on the equivalent mutual channel information between the activated antennas (complement of AÎeIIMdans {1, ..., N tb} ) and the receiving antennas at the destination.

[0150] As illustrated in Figure 7, the method for activating transmitting antennas includes a first step S710 during which the destination device d calculates the set ) of parts of by limiting itself to subsets of cardinality less than or equal to the number of NR receiving antennas and different from the empty subset. This constraint on the cardinality of the subsets aims to address the assertion that it is undesirable to simultaneously retransmit more streams than there are receiving antennas, in order to limit interference.

[0151] It is important at this stage to recall that the power set of a set A, denoted Il ( A ), corresponds to the set of all possible subsets of A.

[0152] Subsequently, the subsets of fly* ( Sjyj ) of cardinality ge {] A7^} are denoted such as = ).

[0153] The antenna activation process further includes an S720 determination step, for each subset of Ee sources IlV q (Sd । ) QG [1 TV | the set B of relay nodes that have decoded the messages from all the source devices of S. Considering the relay nodes that have decoded the messages from all the source devices and not just some of these source devices has the advantage of eliminating interference at the receiver. During this same step, only the eligible subsets E of and of B are selected such that ! E ! < Ntr, with Nf# = IL^TV^ the total number of transmitting antennas in the considered set B of relay nodes.

[0154] Step S720 is iterated for different values ​​of corresponding qe at different receiving antenna values. According to a particular implementation, if no eligible subset is found for a given Q0 value, other Q > Qq values ​​are not tested. Indeed, if no eligible subset E is determined for this Qq value, no eligible subset E can be determined for a value e > e0.

[0155] The antenna activation method further includes a step S730 in which activatable antenna subsets are determined for each part of the set B of relay nodes.

[0156] During an S740 step, a representative value of a quality criterion is calculated for one part of the source set E, one part of the relay node set B, and one part of the transmitting antenna set A. This representative value of a communication channel quality criterion, which corresponds, for example, to the equivalent mutual information of that channel, is calculated, for example, according to the calculation method described with reference to [Fig. 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 [Fig. 8].

[0157] According to a particular implementation, this S740 step is repeated for each part of the set E of sources, each part of the set B of relay nodes, and each part of the set Ât of transmitting antennas.

[0158] The method further includes a step S750 in which the combination of the part of set E of sources, the part of set B of relay nodes, and the part of set Ât of transmitting antennas that optimizes the quality criterion (e.g., equivalent mutual information) is implemented. This step S750 is for example implemented by the MOD_SEL module described with reference to [Fig.4A].

[0159] In a particular embodiment, the selected combination corresponds to the one that maximizes this quality criterion (or minimizes this quality criterion, depending on how this quality 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.

[0160] The portion of set E of sources selected at this stage is denoted £*, the portion of set B of relay nodes is denoted B, and the portion of set Ât The number of transmitting antennas is noted.

[0161] According to a particular implementation, if all transmitting antennas of a relay node in set B* were to disable all of its antennas, then that node The relay is removed from assembly B, •

[0162] Finally, during an S760 step, a retransmission instruction including the selected antenna subset a* is transmitted to the relay nodes of set B) so that they transmit the second redundancy versions by activating only the antennas of the subset. This S760 step is implemented for example by the M0D_TX module described with reference to [Fig.4A].

[0163] We hereafter denote by Q' the number of antennas to be deactivated. The cardinality of the set on which the exhaustive search for antennas is performed is expressed as follows:

[0164] 1 n w / 1 = #(14)

[0165] In a particular embodiment, the antenna selection corresponds to a selection of a subset of the set of antennas of the nodes of relayage e B* offering the best links with the destination device d. In this particular case, a reduced complexity search is performed on U Off - with 'CS Q antcnncs having the links having the quality the weaker with 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:

[0166] |{0, A^r3-I€ El} | = l€ El + l #(15)

[0167] 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.

[0168] This particular mode of implementation of a communication process differs from that described with reference to Figure 6 in that the destination device transmits, to the relaying nodes 6, all the source devices whose messages have been decoded without errors and / or all the source devices whose messages could not be correctly decoded, rather than an ACK / NACK message.

[0169] Steps S300, S100, S310 and S320 are identical to those described with reference to [Fig.6], and are not re-described, for reasons of conciseness.

[0170] The method further includes a step S330-1 in which the destination device transmits to the relay nodes ô 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 b in a step S210-1. Then, in a step S215-1, each relay node b determines the intersection between their respective decoding sets ct 'c complement of the decoding set of the destination device ie, S'^.] = Sb / _] n Sdt.}. This set S'^ of source devices not decoded during the time interval / -1 by the destination, but which have been decoded by the relay node 6, is transmitted by said relay node during a step S220-1, and received by the destination device during a step S340-1.

[0171] Finally, steps S350, S360, S230, S240, S370 and S380 are identical to those described with reference to [Fig.6], and are not re-described, for reasons of conciseness.

[0172] Figure 9 represents, in flowchart form, a particular method of implementation implementation of a method for calculating equivalent mutual information from a channel linking the transmitting antennas of the relay nodes to the receiving antennas of the destination.

[0173] Method for calculating equivalent mutual information

[0174] As illustrated in Figure 9, the calculation method includes a first step S910, of calculating a precoding matrix aimed at maximizing the equivalent mutual information of a channel in the event of simultaneous transmission of messages from the source devices s of the set $ by the destination device

[0175] More formally, a vector x E XVcomPrenant 'cs v source devices in E sorted in ascending index order is generated. The source devices are jointly decoded by the set B of relay nodes with > ŒI, where Nf-g = From the set B of relay nodes, a vector ÿ — [it ...,b, .... is constructed, such that bY < ... < b^. and ^■eB, € V îe{1, ..., IBl}-

[0176] The channel equivalent to the transmission from the source devices listed in x by the nodes in B is represented by a matrix pj e The channel between the antenna The index re {1, ..., NR} of the destination device and the transmitting antenna n G {1, ...,} of the relay node b{ e B, corresponds to the coefficient of the matrix, such that Jd_ y'--1 represents the total number of transmitting antennas P\ll ~ nodes with k the index representing the order of the nodes in the vector b.

[0177] The precoding matrix y_yv_je consists of the v best orthogonal eigenvectors of pp_jj_{\ge, \ge, \ge, \vec}_{\ ... eigenvalues ​​are the most important, ranked in order of eigenvalues decreasing), with pp the adjoint matrix of H. The Leth vector y^e is applied as precoding for the source device such as node bt GB uses Nrj, coefficients of the vector yi.

[0178] The precoding coefficient applied by the antenna at l of the '-th • ■ •, f V element b in b then corresponds to the element n + ^i) of the vector vf i.e., vn+^i)j with In this way, antenna n of the bt c B relay node transmits:

[0179] v M „ #M#

[0180] And the signal received by the destination device is then expressed as follows:

[0181] y — HV x + w #(4)#

[0182] with x the emitted signal, w a noise vector, E {WW'} = rr2ZyK with E {} the mathematical expectation, 0 the noise power, and Ink an identity matrix.

[0183] By applying (HV) ' , we recover the r symbols emitted without interference:

[0184] ij v # (5) l l-fl7 7 \ f

[0185] °ù E { | Wj |2} = Œ2X? with 'a Biéme largest eigenvalue of HTH.

[0186] The calculation method further includes a step S920 in which a power Pi to be allocated to each spatial layer 1 (or equivalently to each source Sf of the set 5*) is determined. It is important to note here that this power allocation is done per spatial layer λ (or equivalently per source s) and not per antenna, so as to comply with the orthogonality constraint of the precoding vectors. This step S920 is described in more detail below.

[0187] Then, in a step 930, a "single-source" quality criterion is calculated for each spatial layer 1 (or equivalently for each source s of the set S) as a function of the precoding matrix V and the transmission power to be allocated to said spatial layer 1 (or equivalently to said sources). In a particular embodiment, the "single-source" quality criterion associated with each spatial layer V corresponds to a signal-to-noise ratio.

[0188] The signal-to-noise ratio SNR of the 1st spatial layer is expressed as follows: SNR — ' with 'a the i-th largest eigenvalue of HH, 17 'a power of the noise and Pi the power to allocate to the 1st spatial layer.

[0189] Furthermore, the equivalent mutual information L is defined as the sum of the mutual information of the different spatial layers, and is expressed as follows: 101901 4)

[0191] In the case of Gaussian inputs, the equivalent mutual information L is given

[0192] by : Ev / \ / \ fcllog2(l+") #(7)

[0193] It is important to note that in the case where the covariance of the noise (including interference) is not a multiple of the identity Inr, i.e. E {MW'} = R, then y = jy, V, ] E is made up of the v best eigenvectors orthogonal to g

[0194] Power calculation step S 9 20

[0195] The transmission power of a node is limited by a power budget P which is shared by the antennas of this node. According to a particular implementation, an amplifier is connected to each antenna, so as to allow each of these antennas to transmit a signal at power P. In this case, the power Pi to be allocated to each spatial layer 1 (or equivalently to each source in the set S) is determined by maximizing the equivalent mutual information E (an expression for which is, as an example, given by equation #(7)) subject to the following local constraints:

[0196] 1 |2r> n *1 idi 44 4- / =11 Éz+XO-d — ï—L ..., IBI # (8)

[0197] The power allocation problem can then be written as: [0W81 + / =1, .... IBI#(10)

[0199] Any method of satisfying constraints known to a person skilled in the art for solving such a problem may be considered; the choice of a particular method corresponds only to one variant of the implementation of the invention. According to a mode In particular, regarding implementation, this problem is solved by applying Lagrange multipliers with IBI constraints.

[0200] A possible suboptimal solution is as follows:

[0201] pl=p0=—-----, z = i,.... v #(ii) 1

[0202] Variant s

[0203] In a particular embodiment, the matrix V is quantified, and for example chosen with respect to a predefined set.

[0204] In a particular embodiment, the matrix V is received noisy by the relay nodes during step S230. In this case, the signal received by the destination device becomes:

[0205] y^HVx + w # (12)

[0206] with y the noisy precoding matrix.

[0207] This signal no longer ensures zero interference at the receiver. In this case, the receiving device can use an equalizer minimizing the Linear Minimum Mean Squared Error (LMMSE) of the type JJ * aveC — HV allows to reduce interference between the v spatial layers. The destination device d then calculates the v signal-to-interference-plus-noise ratios (SINR) at the equalizer output. Then the mutual information is calculated by considering the matrix y, and the v signal-to-interference-plus-noise ratios (SINR).

[0208] Fig. 10 schematically represents an example of implementation of the communication process in an OMAMRC system.

[0209] As illustrated by Figure 10, the decoding set Sy.j of the source device si at interval t-1 is such that = the decoding set S? / -! of the source device s2 at interval t-1 is such that j = {$[, y} and the decoding set of the destination device d at interval t-1 is such that - {0}.

[0210] Also, three configurations are possible: E = {$']} and B = {«j, s2} or E = {s2} and B = [s2} or E = {sj, s2} and B = {sj, s2}. We assume that the configuration where E = [sj, s2} and B = [s, s2] provides the best equivalent mutual information. In this case, the two transmitting antennas of the source device s2 simultaneously send the same redundancies of the source devices si and s2, and x = [Sj. s2]T-

[0211] The eigenvector = y2 1 U] V4 j ] ^corresponding to the largest eigenvalue A of is applied as precoding of the source device ■E' and the eigenvector v? — 2 U> V3 ? y4 2] ^corresponding to the second largest eigenvalue 0 of H' / f is aPPdqué as precoding of the source device s2.

[0212] In other words, the first antenna of the source device transmits the signal Vj j * RVXS}+ V] 2^RVXs^, the second antenna of the source device si transmits the signal V2.i * RVXS]+ 'a first antenna of the source device s2 transmits the signal V3; * / ?V XA + V3 j2*RVX.^, and the second antenna of the source device s2 transmits the signal

[0213] Also, the power transmitted by each relay node is expressed as follows:

[0214] p =----------------------Ç........................______ 0 max^ / +^ , (ji<3 / ^3. / +^4 / ^4. / )}

[0215] and the equivalent mutual information in the case of Gaussian inputs: • / X / A2P0 \ I = log2( 1 + — ) + log2( 1+) ■

[0216] Furthermore, since = 4 > ! € L i = 2, the joint selection process of Source devices and antennas to be activated by each relay node can be applied. The antenna subsets that can be deactivated are as follows:

[0217] {0, {1], {2}, {3}, [4], {1,2}, {1,3}, {1,4}, {2,3}, {2,4}, {3,4}}

[0218] with indices 1 and 2 corresponding to the antennas of the source device and indices 3 and 4 to the antennas of the source device s2.

[0219] We also assume that the subset of antennas to be deactivated is such that A =}3f- and that it is the first antenna (index 3) of the source device s2 that is deactivated.

[0220] A new channel H is defined between the active transmitting antennas of the relay nodes and the receiving antennas of the destination. The eigenvector y' = [vj j y2 ] y^ J2* corresponding to the largest eigenvalue of H is applied as precoding to the source device. If the eigenvector y{ = [ yj 2 y}, 2 2 ] corresponding to the second largest eigenvalue of H' is applied as precoding to the source device s2, then the first antenna of the source device transmits the signal yj * RVW + yj ^RVXg, the second antenna of the source device transmits the signal v2 * RVXSl + v'^RVXSv, and the second antenna of the source device s2 transmits the signal v' * RVXSl + v^*RVXSr

[0221] The power transmitted by each relay node is then expressed as follows:

[0222] p ---__P---.-------

[0223] and the equivalent mutual information I in the case of Gaussian inputs is expressed as follows: 102241 / =10^(1+^)+10^1 + ^)-

Claims

Demands

1. Method for activating transmitting antennas of relay nodes, the method comprising the following steps, implemented by a destination device (d), following the reception of M > 2 messages transmitted successively by M > 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 (se M) comprising a first redundancy version (RVO) resulting from the encoding of an information message associated with the source device ($ em): • a selection (S50) of a set S* comprising one or more undecoded source devices (s*), and a subset a* of transmitting antennas to be activated by relay nodes (^*) of a set B* of relay nodes associated with the set according to a quality criterion of a communication channel between the antennas of said subset a* and the destination device (d), at least one relay node Qj*) of set B, comprising a plurality of transmitting antennas; and, • a transmission (S60, S360), to the relay nodes Q,*) of the set Bp of a retransmission instruction including the selected antenna subset, so that the relay nodes (^*) of the set simultaneously transmit a second redundancy version resulting from the encoding of the information message associated with each undecoded source device of the set 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 the subset y^* of antennas and the destination device (d).

3. An activation method according to claim 1 or 2, wherein the total number of transmitting antennas in the assembly is greater than or equal to the number of undecoded source devices (s*) in the assembly Sf-

4. Activation method according to any one of claims 1 to 3, further comprising an evaluation (S40) of the quality criterion for different antenna subsets of a set Bf of relay nodes associated with the undecoded source devices, the selected antenna subset A* 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 S; 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 selected set of undecoded source devices, and a precoding matrix (V) to be applied by the relay nodes (jp) of the set r*'1<

8. Br Activation method according to claim 7, wherein the retransmission instruction further includes an indication of a distribution of a transmit power transmitted by each relay node of the assembly B*, between the undecoded source devices (s,) of the assembly £*.

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

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

11. Destination device (d) configured to implement an activation method according to any one of claims 1 to Q

12. O. Relay node Q,*) comprising • a plurality (NT) of transmitting antennas; • a receiving module (M0D_RX), from a destination device, of 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 (RVO) of said information messages not having been decoded by the destination device (d), the retransmission instruction including a subset A* of transmitting antennas selected by the destination device for said retransmission; and, • a transmitting module (M0D_TX) configured to activate only the transmitting antenna(s) of the subset a* belonging to it to transmit to said destination device said second redundancy versions.

13. Communication system (SYS) comprising M > 2 source device(s), one destination device (d) according to claim 11 and several relaying nodes Q?*) according to claim 12.

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

Images