Method for data transmission in an omamrc system and associated devices

Abstract

The invention relates to a data transmission method comprising the following steps, following the inability of the destination device to decode messages sent 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 "undecoded source device", each message sent by a source device comprising a first redundancy version resulting from encoding an information message associated with the source device: selecting a set S* t comprising a plurality of undecoded source devices and a set B* t of a plurality of relaying nodes associated with the set S* t , according to a quality criterion of a communication channel; transmitting a retransmission instruction to the selected relaying nodes (b* t ); and receiving the second redundancy versions resulting from encoding the information messages of the source devices.

Description

Description Title of the invention: Method for transmitting data in an OMAMRC system and associated devices Technical Field

[0001] The present invention belongs to the general field of digital communications. It relates more particularly to the transmission of data between source devices and a destination device having several receiving antennas, via a relay node.

[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 the destination device.

[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 (uplink communication). The network then comprises, for example, several source devices 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 of an OMAMRC communication system transmit messages to a single destination, if necessary via relay nodes. These 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 linking the source device to the destination using an orthogonal multiple access scheme. transmitting messages to the destination device helps to limit interference. This orthogonality is usually achieved by time-division multiplexing in the form of disjoint time intervals (such as "Time Division Multiple Access", TDMA), but orthogonality resulting from frequency-division multiplexing in the form of disjoint frequency sub-bands (such as "Frequency Division Multiple Access", FDMA) is also possible.

[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 passed on 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 channel uses ("Resource Element" according to the 3GPP consortium terminology 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 error. 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 error by the destination device within a time interval ^^^^^^^^^^^^^^^^^^^^^ ≤ ^^^^^^^^^^^^^^^^^, the destination device broadcasts an acknowledgment. In this case, a transmission cycle of a The new frame begins with the erasure of the memories of the relay nodes and the destination device, and with the transmission, by the source devices, of new messages.

[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, P2, and POS3. Such a circular buffer contains the coded 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 a first retransmission TX2 by reading, from the circular buffer, the 2 bits encoded 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 from position POS3, and the bits to be transmitted during a third retransmission TX4 by reading, from the circular buffer, the 2 bits encoded from position POS3. 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, existing methods do not focus on improving spectral efficiency, particularly when the relay nodes include a plurality of transmitting antennas and the destination device includes a plurality of receiving antennas. Description of the invention

[0022] The present invention aims to remedy all or part of the disadvantages of the prior art, in particular those set out above, by proposing a solution which makes it possible to exploit spatial multiplexing, i.e., the possibility of simultaneously transmitting several spatial layers on the same time or frequency radio resource.

[0023] To this end, and according to a first aspect, the invention relates to a data reception method comprising the following steps, implemented by a destination device comprising several receiving antennas, following the reception of ≥ 2 messages emitted successively by ≥ 2 source devices and the inability of the destination device to decode at least two messages received from at least two source devices, referred to as "undecoded source devices", each message emitted by a source device comprising a first redundancy version resulting from an encoding of an information message from the source device:

[0024] – a selection, from a set ^^^^ ^ ∗ ^ ^^ including several undecoded source devices and a set ℬ ^ ∗ ^ ^^ of several relay nodes associated with the whole ^^^^ ^ ∗ ^ ^^, based on a quality criterion of a communication channel between the relay nodes of the set ℬ ^ ∗ ^ ^^ and the destination device, a relay node of the whole ℬ ^ ∗ ^ ^^ corresponding to a source device or an intermediate device aware of the information messages from the undecoded source devices, at least one relay node of the set ℬ ^ ∗ ^ ^^ having several transmitting antennas;

[0025] – a transmission, to the selected relay nodes, of a retransmission instruction, so that the relay nodes simultaneously transmit second redundancy versions resulting from the encoding of the information messages from the undecoded source devices of the set ; And,

[0026] – a reception, by the destination device, of said second redundancy versions resulting from the encoding of information messages from the source devices of the set ^^^^ ^ ∗ ^ ^^ .

[0027] The second redundancies are typically used by the destination device to decode messages received from the source devices in the set

[0028] By enabling multiple relay nodes to simultaneously transmit redundant messages from source devices that have not been error-free decoded, and by allowing the destination device to receive this data via its multiple receiving antennas, the invention improves upon known methods. In particular, the simultaneous transmission of data between one or more relay nodes with multiple transmitting antennas and a destination device with multiple receiving antennas makes it possible to utilize multiple spatial layers, thereby improving spectral efficiency.

[0029] A relay node ^^^^ ^ ∗ ^ ^^ of the set ℬ ^ ∗ ^ ^^ has knowledge of a message to be retransmitted, either because it is his own message (and the relay 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.

[0030] In a specific implementation mode, 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 SDF (Selective Decode and Forward).

[0031] Generally speaking, the steps of a process should not be interpreted as being linked to a notion of temporal succession.

[0032] In particular modes of implementation, the transmission method may further include one or more of the following characteristics, taken individually or in all technically possible combinations.

[0033] In a particular implementation mode, the transmission process is iterated until a stopping criterion is reached (for example, a certain duration 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 it is noisy.

[0034] In a particular mode of implementation, the process further includes a transmission, by the ^^^^ source devices, of first redundancies (also referred to as "redundancy versions") of their information messages, during ^^^^ consecutive time intervals.

[0035] In a particular implementation mode, each source device transmits a first redundancy of its information message using a single antenna in omnidirectional transmission or after applying omnidirectional precoding to the antennas of that source device. This step is implemented within the framework of phase P1 previously described with reference to Figure 1. This feature is advantageous because it increases the number of relay nodes in the system capable of receiving and decoding these messages.

[0036] In a particular implementation mode, the retransmission instruction transmitted to the relay nodes includes the entire and a precoding matrix associated with the source devices

[0037] In a particular implementation mode, the retransmission instruction further includes an ordered list ^^^^ of the relay nodes of the set ℬ ^ ∗ ^ ^^ . The transmission of the list ^^^^ to the relay nodes allows each of the relay nodes to identify the precoding coefficients of the precoding matrix ^^^^ to be applied.

[0038] In a particular implementation mode, the retransmission instruction sent to the relay nodes also includes an indication of the distribution of transmission power by each relay node. ∗ of the set ℬ ^^^^ , between the undecoded source devices

[0039] According to one particular implementation, this indication takes the form of an ordered list of powers to be applied to each of the source devices. When the power allocated to the selected source devices sont different, this ordered list ^^^^ allows a relay node to determine the power it must allocate to each source device.

[0040] In a particular implementation mode, the retransmission instruction transmitted to the relay nodes further includes an ordered list of antennas to be activated or deactivated by each of the relay nodes of at least a subset of the set. Activating or not certain transmitting antennas allows for the optimization of a channel quality criterion, since only the strongest transmitting antenna / destination device links are considered.

[0041] In a particular implementation method, this quality criterion is a mutual information exchange over the communication channel between the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^∗ ^ ^^ and the destination device (d).

[0042] In the following description, this "mutual information" is also called "equivalent mutual information" when referring to the quality of a multi-layer channel. Of course, other quality criteria can be considered, such as a receive 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.

[0043] In a particular implementation method, the selection includes:

[0044] – a determination of eligible sets ^^^^ of undecoded source devices and sets ℬ of relay nodes associated with the eligible sets ^^^^, such that 2 ≤ |^^^^| ≤^^^^ ^^^^,ℬ with | ^ | the cardinality operator and ^^^^ ^^^^,ℬthe total number of transmitting antennas of the relay nodes of the set ℬ;

[0045] – une détermination, pour chacune des combinaisons d'ensembles éligibles ^^^^ et of sets ℬ of relay nodes, of the quality criterion of the communication channel between the relay nodes of set ℬ and the destination device (d);

[0046] and the sets of source devices (^^^^ ^ ∗ ^ ^^ ) and ℬ ^ ∗ ^ ^^ relay nodes selected optimizing said quality criterion.

[0047] Thus, in a particular mode of implementation, an exhaustive search of eligible set combinations ^^^^ and ℬ is carried out, and the one providing optimal quality is selected.

[0048] In a particular implementation, the selection process further includes, for each of the eligible subsets of source devices, a step to determine the relay nodes in set ℬ that have decoded all the source devices in the considered eligible set. 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 all the source devices, and not just some of them, offers the advantage of eliminating interference at the receiver.

[0049] In a particular implementation mode, a maximum number of source devices whose messages can be simultaneously retransmitted by the relay nodes is parameterized, and the determination of eligible sets of source devices is limited to subsets such that | ≤ ...

[0050] In a particular implementation mode, the determination of the quality criterion for the communication channel between the relay nodes of the set ℬ and the destination device includes:

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

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

[0053] In a particular embodiment, the method further includes a selection of antennas to be activated for each of the relay nodes of at least one subset of the set ℬ ^ ∗ ^ ^^ This step can be implemented if the total number of transmitting antennas from the relay nodes of the entire ℬ ^ ∗ ^ ^^ is greater than the number of source devices

[0054] In a particular implementation mode, antenna selection includes:

[0055] – une détermination de sous- antennas that can be activated by each of the relay nodes of at least one subset of the set ℬ ^ ∗ ^ ^^ ;

[0056] – pour chaque sous- of antennas determined, a calculation of the quality criterion of a communication channel between the antennas of said subset � ^^ � ^ � ^ � ^^^^, and the destination device;

[0057] – une sélection, parmi les sous-ensembles � ^^ � ^ � ^ � ^^^^, of the subset � ^ � ^^ � ^ �∗ ^^^^ of antennas to activate optimizing said quality criterion.

[0058] In a particular implementation mode, the quality criterion of the communication channel between the relay nodes of the set ℬ ^∗ ^ ^^ and the destination device is determined based on a combination of single-source quality criteria for sub-channels of said communication channel, each sub-channel being defined for a source device

[0059] According to a second aspect, the invention relates to a data transmission method comprising the following steps, implemented by a relay node comprising several transmitting antennas, following the reception of ≥ 2 messages transmitted successively by ≥ 2 source devices and an inability of the device to purpose of decoding at least two messages received from at least two source devices called "undecoded source devices", each message emitted by a source device including a first redundancy version resulting from an encoding of an information message associated with the source device:

[0060] – receiving an instruction to retransmit second redundancy versions resulting from the encoding of information messages from undecoded source devices of a set said relay node knowing said information messages from the undecoded source devices of the set ^^^^ ^ ∗ ^ ^^ ; And,

[0061] – simultaneous transmission of the second redundant versions of the information messages from the source devices of the set via the transmitting antennas of said relay node and towards the destination device, said second versions of redundancies being used by the destination device to decode messages received from the undecoded source devices of the set

[0062] According to a third aspect, the invention relates to a computer program comprising instructions for implementing a reception method according to the first or a transmission method according to the second aspect, 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 fourth 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 fifth aspect, the invention relates to a destination device (or "destination node" or "destination") comprising several receiving antennas and configured to implement a receiving method according to the invention.

[0069] According to a sixth aspect, the invention relates to a relay node comprising several transmitting antennas and configured to implement a transmission method according to the second aspect.

[0070] Selon un septième aspect, l’invention concerne un système comprenant ^^^^ ≥ 2 source devices, a destination device according to the fifth aspect and a plurality of relaying nodes of which at least one conforms to the sixth aspect.

[0071] According to an eighth aspect, the invention relates to a communication method including the data reception and data transmission methods previously mentioned, for example, implemented by the system conforming to the sixth aspect. Brief description of the drawings

[0072] 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:

[0073] [Fig.1] Figure 1, previously described, is a representation of a frame transmission cycle in an OMAMRC type communication system;

[0074] [Fig.2] Figure 2, previously described, represents a circular buffer allowing the selection of a redundancy of a message to be transmitted;

[0075] [Fig.3] Figure 3 schematically represents a communication system according to a particular embodiment of the invention;

[0076] [Fig.4] Figure 4 represents modules embedded in a destination, according to an example of implementation of the invention;

[0077] [Fig.5] Figure 5 schematically represents an example of the hardware architecture of a destination device;

[0078] [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.

[0079] [Fig. 7] Figure 7 represents, in the form of a flowchart, a particular method of implementing a step in the selection of a set of source devices whose messages are to be simultaneously retransmitted to the destination device and of a set ℬ ^ ∗ ^ ^^ relay nodes adapted to this retransmission;

[0080] [Fig.8] Figure 8 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;

[0081] [Fig.9] Figure 9 represents, in the form of a flowchart, a particular method of implementing a selection of the antennas of a relay node to be activated (resp. to be deactivated);

[0082] [Fig. 10] Figure 10 represents, in the form of a flowchart, a particular method of implementing a communication process in an OMAMRC system, according to a second example; and,

[0083] [Fig. 11] Figure 11 schematically represents an example of the implementation of the communication process in an OMAMRC system. Description of implementation methods

[0084] In general, the invention proposes cooperation between different devices of a communication system to enable a destination device to correctly decode the information messages from the source devices of that system. To this end, the invention relies on selecting a set of several source devices to be "assisted" and a set of several relay nodes adapted to these source devices. However, the invention is described in a more general context, and more particularly is integrated in the following description into an algorithm that can, in certain cases, select a set ℬ ^ ∗ ^ ^^ including a single multi-antenna relay node, for example when this configuration offers optimal quality.

[0085] Figure 3 schematically represents a communication system according to a particular embodiment of the invention.

[0086] 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 and destination devices. 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.

[0087] 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, provided that this number is greater than or equal to 2. 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 SYS communication system does not include any intermediate nodes.

[0088] 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 from other nodes to the destination. 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.

[0089] Furthermore, at least one of the relay nodes includes several transmitting antennas. Hereafter, the number of transmitting antennas of a node ^^^^ ∈ ^^^^ is denoted ^^^^^^^^,^^^^.

[0090] 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.

[0091] 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.

[0092] In a particular implementation mode, an orthogonal multiple-access multiple-relay channel scheme, denoted "OMAMRC" – an acronym for "Orthogonal Multiple-Access Multiple-Relay Channel" – is applied. The system then implements a cooperation strategy called IR-HARQ ("Incremental Redundancy Hybrid-ARQ" in Anglo-Saxon terminology) based on a Selective Decode and Forward relaying, also known as SDF ("Selective Decode and Forward" according to Anglo-Saxon terminology).

[0093] 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.

[0094] Figure 4 represents modules embedded in a destination device, according to an example of implementation of the invention.

[0095] As illustrated in Figure 4, the destination device d includes, in particular:

[0096] – a MOD_SEL module of a set including several undecoded source devices and a set ℬ ^ ∗ ^ ^^ of several relay nodes associated with the whole ^^^^ ∗ ^ ^^^ , based on a quality criterion of a communication channel between the relay nodes of the set ℬ ^ ∗ ^ ^^ and a destination device, a relay node of the whole ℬ ^ ∗ ^ ^^ corresponding to a source device or an intermediate device aware of the information messages from the undecoded source devices, at least one relay node of the set ℬ ^ ∗ ^ ^^ having several transmitting antennas;

[0097] – a MOD_TX transmission module, to the selected relay nodes, of a retransmission instruction, so that the relay nodes simultaneously transmit second redundancy versions resulting from the encoding of information messages from the undecoded source devices of the set ;

[0098] – a MOD_RX module for receiving, by the destination device, said second redundancy versions resulting from the encoding of the information messages from the source devices (^^^^ ^ ∗ ^ ^^ ) of the whole thing ^^^^ ^ ∗ ^ ^^ said second redundancies being used by the destination device (d) to decode messages received from undecoded source devices.

[0099] Their functionalities are described in more detail below with reference to different implementation methods.

[0100] Figure 5 schematically represents an example of the hardware architecture of a destination device ^^^^.

[0101] 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.

[0102] 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 receiving process according to the invention. The PROG program defines functional modules of the destination device, which rely on or control the hardware elements 1 to 5 of the destination device mentioned above. These functional modules are illustrated in Figure 4 by way of no limitation and are described in more detail below with reference to different implementation methods.

[0103] In the implementation modes described below, the communication means 5 enable the destination device to obtain the messages transmitted by the source devices 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 a wired or wireless communication interface capable of implementing any suitable communication protocol.

[0104] 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.

[0105] This communication method includes a data reception method implemented by a destination device (d) and comprising steps S300 to S380, and a data transmission method implemented by a relaying node (b) and comprising steps S210 to S240.

[0106] As illustrated by Figure 6, the 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 decoding efficiency ^^^^ for the first transmission of each source ^^^^1, … , as a function of a communication channel quality criterion.

[0107] 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.

[0108] 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 channel usage data is then transmitted by the destination device to each of the source devices.

[0109] 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

[0110] The communication process further includes a step S100 during which the ^^^^ source devices ^^^^1, … , transmit their message successively during consecutive time intervals, using respectively the modulation and coding schemes determined during step S300. During this first phase, the number The channel usage 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.

[0111] These initial redundancies are transmitted, for example, using a single omnidirectional transmitting antenna or after applying omnidirectional precoding to the transmitting antennas. Thus, for a source device comprising ^^^^ ^^^^,^^^^ antennas in transmission, precoding results, for example, from a superposition of the 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.

[0112] Au moins certains des ^^^^ messages ^^^^^^^^01, … ,^^^^^^^^0^^^^ sont reçus par le dispositif de destination ^^^^ 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 error 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.

[0113] 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 error by that relay node. Each of the decoding sets 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 ^^^^ ∈ ^^^^.

[0114] 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 subset. ^ ∗ ^ ^^ and the destination device:

[0115] – a set ^^^^ ^ ∗ ^ ^^ among the undecoded source devices comprising multiple source devices

[0116] – a set ℬ ^ ∗ ^ ^^ relay nodes ^^^^ ^ ∗ ^ ^^ associates among a set ℬ of relay nodes ^^^^ ^^^^ .

[0117] This S350 step is implemented for example by the MOD_SEL module described with reference to figure 4. A particular way of implementing this S350 selection step is described with reference to figure 7.

[0118] 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, to the destination device, a new redundancy version of these messages during the retransmission time interval ^^^^. This earlier 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. The latter contains all the identifiers of the source devices that the node ^^^^ was able to decode without error 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 is different from the empty set, i.e., if ∩ ^^^^^̅^^^,^^^^−1 ≠ ∅.

[0119] The communication process further includes an S360 step during which the destination device calculates a precoding matrix = [, …, apply by each of the relay nodes ^^^^* ^^^^ with ℂ being the set of complex numbers, ^^^^ ^^^^,ℬ^ ∗ ^ ^^ the total number of transmitting antennas from the relay nodes ^^^^ ∗ ∗ ^^^^ ∈ ℬ^^^^, and^^^^ the number of source devices ^^^^ ^ ∗ ^ ^^ whose messages must be simultaneously retransmitted. In other words, ^^^^ = |^^^^*^^^^|, with |^| the cardinality operator.

[0120] During this same S360 step, the destination device ^^^^ transmits to the relay nodes ^^^^* ^^^^ ∈ ℬ∗ ^^^^, the set ^^^^*^^^^ of identifiers of the source devices whose messages are to be retransmitted and the precoding matrix ^^^^. This S360 step is implemented, for example, by the MOD_TX module described with reference to Figure 4.

[0121] According to a particular implementation, the destination device ^^^^ also transmits the e vecteur of cardinality and [ ] transpose of the matrix ^^^^. This vector ^^^^ includes the selected relay nodes ^^^^ ^ ∗ ^ ^^ ∈ ℬ ^ ∗ ^ ^^ so that each relay node ^^^^ ^ ∗ ^ ^^ can determine the precoding coefficients to apply to each vector ^^^^ = 1, … , ^^^^ of the precoding matrix ^^^^.relay nodes ^^^^ ^∗ ^ ^^ Listed by the vector ^^^^ are, for example, sorted 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.

[0122] In a particular implementation mode, each of the selected source devices ^^^^* applies the same power ^^^^^^^^ = ^^^^0, ^^^^ = 1, … , ^^^^. Alternatively, the selected 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. Depending on a particular implementation, the powers are sorted in ascending order of the source device indices.

[0123] source devices ∗ ^^^^ ^^^^ The precoding matrix ^^^^, the vector ^^^^ (possibly the vector ^^^^) are received by the nodes * ∈ ℬ^^^^ during an S230.response step, each relay node ∈ ℬ∗ ^^^^ simultaneously transmits the same redundancy of messages from the ^^^^ selected source devices, i.e., ∑^^^^l=1 ^^^^^^^^^+^^^^(^^^^),^^^^ ^^^^^^^^ ,^^^^ ∈{1, … ,^^^^^^^^,^^^^^^^^}, ^^^^ ∈ {1, … , |ℬ^ ∗ ^ ^^|} during an S240 step. To facilitate understanding and for the sake of brevity, the index "^^^^ + ^^^^(^^^^), ^^^^" is described in more detail with reference to Figure 8. These redundancies are received by the receiving antennas of the destination device ^^^^ during an S370 step.

[0124] Based on this retransmission, the destination device attempts to decode the messages from the source devices. during a stage

[0125] 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 error by the destination.

[0126] Figure 7 represents, in flowchart form, a selection process corresponding to a particular implementation method of step S350, which involves selecting, at a certain interval ^^^^, a set of source devices whose messages are simultaneously retransmitted to the destination device and of a set ℬ ^ ∗ ^ ^^ of relay nodes adapted to this retransmission. This selection process is implemented by the destination device d.

[0127] As illustrated in Figure 7, this selection process includes a first step S510 during which the destination device calculates the set 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.

[0128] 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 ^^^^.

[0129] Par la suite, les sous-ensembles of cardinality ^^^^ ∈ {1, … ,^^^^^^^^} are dénotés tel que

[0130] The selection process further includes an S520 determination step, for each subset of source devices ∈ of the set of relay nodes ℬ that have decoded the messages from all the source devices of ^^^^. Considering the relay nodes that have decoded all the source devices and not just some of these source devices offers 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 , with ^^^^^^^^,ℬ = ∑^^^^∈ℬ ^^^^^^^^,^^^^ the total number of transmitting antennas in the set ℬ of relay nodes considered.

[0131] L'étape S520 est itérée pour différentes valeurs de ^^^^ ∈ {1, … ,^^^^^^^^} correspondant à different cardinalities of the source set. According to a particular implementation, if no subset is eligible for a value ^^^^0, the other values ​​^^^^ > ^^^^0 are not tested. Indeed, if no eligible subset ^^^^ is determined for this value ^^^^0, no eligible subset ^^^^ can be determined for a value ^^^^ > ^^^^0.

[0132] The selection process further includes an S530 step in which a representative value of a quality criterion of a communication channel is calculated, for one of the parts of the set ℬ of relay nodes, ℬ being the set of relay nodes knowing ^^^^.

[0133] This value represents a corresponding quality criterion, in this particular implementation method, to a mutual information known as "equivalent mutual information," which characterizes the quality of a communication channel through which several messages are transmitted simultaneously by a plurality of transmitting antennas and received by a plurality of receiving antennas. An example of calculating equivalent mutual information is described in more detail with reference to Figure 8.

[0134] According to one particular implementation, this S530 step is repeated for each part of the set ℬ, and each source set ^^^^..

[0135] Finally, an S540 step is implemented during which the destination device d selects the set ^^^^ of sources, the part the set ℬ of relay nodes, and transmitting antennas optimize the quality criterion (e.g., equivalent mutual information). This S540 step is implemented, for example, by the MOD_SEL module described with reference to Figure 4.

[0136] In a particular implementation mode, the selected combination corresponds to the one that maximizes 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 (respectively below) a certain threshold.

[0137] The set of sources selected at this stage is noted. ^ ∗ ^ ^^, and the set ℬ of relay nodes is denoted ℬ ^ ∗ ^ ^^ .

[0138] Illustrative example

[0139] Steps S510 to S530 of this selection process are illustrated below through an example. Let ^^^^^̅^^^,^^^^−1 be the set of source devices whose messages were not decoded without error by the destination device such that ^^^^^̅^^^,^^^^−1 = {1,4,5}, and ^^^^^^^^ = 3,^^^^^^^^,1 = 2, ^^^^^^^^,4 = 3, ^^^^^^^^,5 = 1. In this case, parts of ^^^^^̅^^^,^^^^−1 is written tel que

[0140] Si ^^^^ = {4,5} et ℬ = {5} alors ^^^^ n’est pas éligible car

[0141] Si ^^^^ = {4,5} et ℬ = {4} alors ^^^^ est éligible bien qu’il n’y ait qu’un seul nœud actif car

[0142] ^^^^ = {1,4,5} et ℬ = {1} alors ^^^^ n’est pas éligible car

[0143] ^^^^ = {1,4,5} et ℬ = {1,5} alors ^^^^ est éligible bien qu’il n’y ait que deux nœuds actifs pour retransmit three source devices because |^^^^| = = ^^^^^^^^,1 + ^^^^^^^^,5 = 3.

[0144] ^^^^ = {1,4,5} et ℬ = {4} alors ^^^^ est éligible bien qu’il n’y ait qu’un seul nœud actif car |^^^^| = ^^^^^^^^,ℬ = ^^^^^^^^,4 = 3.

[0145] Complexity of the selection process

[0146] Lorsque toutes les cardinalités ^^^^ ∈ {1, … ,^^^^^^^^} sont considérées, une rechercheexhaustive is carried out on The cardinality of this set is as follows: ( 1)

[0147] Thus, complexity increases with the number of streams transmitted to the destination. One way to control this increase is to set a maximum number of messages to be retransmitted simultaneously. In this case, the search is limited to subsets; the number of iterations in this case is given by the following equation:

[0148] Ainsi, pour�^^^^^̅^^^,^^^^−1� = 7,^^^^^^^^ = 8 et ^^^^^^^^^^^^^^^^ = 2, 28 itérations sont exécutées contre 127 iterations in the case where the number of flows is not limited.

[0149] Figure 8 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.

[0150] Method for calculating equivalent mutual information

[0151] As illustrated in Figure 8, the calculation process includes a first step S610, which calculates a precoding matrix aimed at maximizing a channel quality criterion in the event of simultaneous transmission of messages from source devices. by the destination device ^^^^. This quality criterion corresponds, in this example, to the equivalent mutual information mentioned previously.

[0152] 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 of relay nodes ℬ with ∑^^^^∈ℬ ^^^^^^^^,^^^^ . From the set of relay nodes ℬ , a vector ^^^^ = is constructed such that ^^^^1 < ⋯ < ^^^^|ℬ| and ^^^^^^^^ ∈ ℬ,∀ ^^^^ ∈ {1, … , |ℬ|}.

[0153] The channel equivalent to the transmission from the source devices listed in ^^^^ by the nodes in ℬ is represented by a matrix ^^^^ ∈ ℂ^^^^^^^^×^^^^^^^^^,ℬ . 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 ^^^^.

[0154] La matrice de précodage ^^^^ = [^^^^1, … , ^^^^^^^^] ∈ ℂ^^^^^^^^,ℬ×^^^^ est constituée des ν meilleurs orthogonal eigenvectors of (ν vectors whose eigenvalues ​​are the most important), with ^^^^ † the adjoint matrix of ^^^^. The ^^^^-th vector ^^^^ ^^^^ ∈ℂ^^^^^^^^,ℬ is applied as precoding for the source ^^^^^^^^, such that the node ^^^^^^^^ ∈ ℬ uses ^^^^^^^^,^^^^^^^^vector coefficients ^^^^^^^^ .

[0155] 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:

[0156] And the signal ^^^^ received by the destination device is then expressed as follows: ^^^^ = ^^^^ ^^^^ ^^^^ + ^^^^ (4)

[0157] avec ^^^^ le signal émis, ^^^^ un vecteur de bruit, ^^^^�^^^^^^^^†� = ^^^^2^^^^^^^^^^^^ avec ^^^^{^} l'espérance mathematics, ^^^^ the power of noise., and ^^^^ ^^^^^^^^ an identity matrix.

[0158] By applying ( ^^^^^^^^ )† We retrieve the ^^^^ symbols emitted without interference: ^^^^ = 1, … , ^^^^ (5)

[0159] où ^^^^{|w |2} = σ2λ avec λ la ^^^^-ième plus grande valeur propr † l ^^^^ ^^^^ e de ^^^^ ^^^^.

[0160] The calculation process further includes an S620 step in which a power allocation of 1, ..., 1, to each spatial layer (or equivalently, each source in the set) is determined. It is important to note that this power allocation is done per spatial layer (or equivalently per source) and not per antenna, in order to comply with the orthogonality constraint of the precoding vectors. This S620 step is described in more detail below.

[0161] Then, during an S630 step, a "single-source" quality criterion is calculated for each spatial layer ^^^^ = 1, … , ^^^^ (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 mode, the single-source quality criterion associated with each spatial layer ^^^^ corresponds to a signal-to-noise ratio.

[0162] The signal-to-noise ratio ^^^^^^^^^^^^ ^^^^ of the l-th spatial layer is expressed as follows: ^^^^^^^^^^^^ = with λ ^^^^ the ^^^^-th largest eigenvalue of ^^^^ † ^^^^, ^^^^ the power of the noise and the power to be allocated to the ^^^^-th spatial layer.

[0163] Furthermore, equivalent mutual information I ^^^^is defined as the sum of the mutual information of the different spatial layers, and is expressed as follows:

[0164] In the case of Gaussian inputs, the equivalent mutual information I ^^^^ is given by:

[0165] 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's to say = ^^^^, then ^^^^ = [^^^^1, … , ^^^^^^^^] ∈ℂ^^^^^^^^,ℬ×^^^^ is made up of the ν best orthogonal eigenvectors of ∈

[0166] Power Calculation Step S620

[0167] The transmission power of a node is limited by a power budget ^^^^ which is shared by the antennas of that node. In a particular implementation, an amplifier is connected to each antenna, allowing each of these antennas to transmit a signal at the power ^^^^. In this case, the power ^^^^ ^^^^ to allocate to each spatial layer ^^^^ = 1, … , ^^^^ (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:

[0169] The power allocation problem can then be written as:

[0171] 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.

[0172] One possible suboptimal solution is as follows: (11)

[0174] Variants

[0175] Dans un mode particulier de mise en œuvre, la matrice ^^^^ = [^^^^1 …^^^^ν] où ^^^^l est la ^^^^-ième The column of ^^^^ is quantized, and for example chosen with respect to a predefined set of vectors ℬ such that v�^^^^ = arg mv∈iℬn‖^^^^ − ^^^^l‖ 2 où ‖ ^ ‖ is any standard.

[0176] 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)

[0177] avec ^ � ^^^ the noisy precoding matrix.

[0178] 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 ′ + ^^^^� with ^^^^ = ^^^^ ^�^^^ which allows 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) ^^^^ ^^^^ .

[0179] Figure 9 represents, in the form of a flowchart, a particular method of implementing a selection of antennas of a relay node to be activated (resp. deactivated).

[0180] In the implementations described so far, all antennas of a given relay node are activated, even if one of the links between a transmitting antenna of the relay node and a receiving antenna of the destination device is of poor quality. However, the equivalent mutual information of the channel could be optimized by selecting, within a relay node, only the antennas offering the highest quality links. This selection is only feasible, however, if the maximum number of antennas that can be deactivated is equal to... and this is in order to maintain the eligibility criteria for the whole

[0181] De manière plus formelle, soit ^^^^ ′ 1, … of all the sub-antennas 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:

[0183] 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.

[0184] 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}.

[0185] Thus, the set of antenna subsets that can be deactivated is expressed as follows:

[0186] ^^^^^^^^^^^^^^^^−^^^^^^^^^^^^ = {∅, {1}, {2}, {3}, … , {6}, {1,2}, {1,3}, … , {1,6}, {2,2}, … , {5,6}}.

[0187] 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.

[0188] As illustrated in Figure 9, the process of selecting the antennas of a relay node to be activated (resp. deactivated) includes a first step S710 during which subsets of activatable antennas are determined at the relay nodes.

[0189] The selection process further includes an S720 calculation step, for each sub- e nsemble � ^ � ^ � ^^ � ^^^^ of antennas determined in step S710, with a value representative of a quality criterion of a communication channel allowing simultaneous transmission of messages from source devices ^^^^ ∈ ^^^^, by the antennas of said sub- vers ledestination device. This value, representing a quality criterion of a communication channel, corresponds to the equivalent mutual information mentioned previously, and is, for example, calculated in accordance with the calculation method described with reference to Figure 8.

[0190] Enfin, une étape S730 de sélection d'un sous- antennas that optimize (e.g., maximize) the representative value of a quality criterion (e.g., equivalent mutual information) are implemented. Alternatively, the subset � ^ � ^^ � ^ �∗ ^^^^ of selected antennas corresponds to one of the subsets � ^ � ^^ � ^ �∗ ^^^^ having a representative value of a quality criterion greater than a threshold.

[0191] One note afterwards ^^^^′ is the number of antennas to deactivate. The cardinality of the set on which the exhaustive search for antennas is performed is expressed as follows:

[0192] In a particular implementation, antenna selection corresponds to selecting a subset of the set of antennas from the nodes of set ℬ that offer the best links to the destination device d. In this particular case, a reduced-complexity search is performed on The Q' antennas have the worst connections to the destination, 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)

[0193] Figure 10 represents, in the form of a flowchart, a particular method of implementing a data communication process in an OMAMRC system, according to a second example.

[0194] 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 error and / or the set ^^^^^̅^^^,^^^^−1 of the source devices whose messages could not be correctly decoded, rather than an ACK / NACK message.

[0195] 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.

[0196] The process further includes a step S330-1 in which the destination device transmits to the relay nodes ^^^^ ∈ ^^^^ the set ^^^^^^^^,^^^^−1 of the source devices whose messages have been decoded without error. Alternatively, the destination device transmits to the relay nodes ^^^^ ∈ ^^^^ the complement of the decoding set of the destination device ^^^^^̅^^^,^^^^−1. 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 ^^^^^̅^^^,^^^^−1, i.e., ^^^^′^^^^,^^^^−1 = This set ^^^^′^^^^,^^^^−1 of source devices whose messages have not been 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.

[0197] 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.

[0198] At this stage, it is important to note that in the case where the process of selecting the antennas of a relay node to activate or deactivate is applied, the set of antennas to be activated by each relay node is also transmitted, by the destination device ^^^^ and to the relay nodes, during the S360 step (in addition to the precoding matrix ^^^^ and the vector ^^^^).

[0199] 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 is activated (^^^^ ∉ ^^^^^^^^^^^^), otherwise if ^^^^^^^^+^^^^(^^^^) = 0, it is not (^^^^ ∈

[0200] 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".

[0201] Illustrative example

[0202] Soit ^^^^∗ = {1,2,3,5}, ℬ∗ = {1 ∗ t ^^^^ ,4,7}, ^^^^^^^^,1 = 1,^^^^^^^^,4 = 2 and ^^^^^^^^,7 = 3 and suppose that ^^^^^^^^ ={2,5}. The bitmap vector ^^^^ of dimension ^^^^^^^^,ℬ^*^^^ = 6 is as follows:^^^^ = [1,0,1,1,0,1]^^^^

[0203] 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]^^^^

[0204] 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.

[0205] 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 ^^^^′(^^^^, ^^^^) = ∑^^^^+^^^^(^^^^) ^^^^=1 ^^^^^^^^ of the vector ^^^^ ^^^^ either ^^^^ ^^^^ ′(^^^^,^^^^),^^^^. Subsequently, each activated antenna simultaneously transmits the same redundancy of information messages from the ^^^^ selected source devices.

[0206] Figure 11 schematically represents an example of OMAMRC systems in which the method according to the invention is implemented. In this example, we consider a system comprising two source devices, ^^^^1 and ^^^^2, and a destination device ^^^^, with ^^^^^^^^,1 = 2, ^^^^^^^^,2 = 2 and ^^^^^^^^ = 4.

[0207] As illustrated in Figure 11, the decoding set ^^^^ 1,^^^^−1of the source device ^^^^1 at the interval ^^^^ − 1 is such that ^^^^1,^^^^−1 = {^^^^1, ^^^^2}, the decoding set ^^^^2,^^^^−1 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 = {∅}.

[0208] Aussi, trois configurations sont envisageables : ^^^^ = {^^^^1} et ℬ = {^^^^1, ^^^^2} ou ^^^^ = {^^^^2} et = {^^^^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 transmit the same redundancies of the source devices ^^^^1 and ^^^^2, and ^^^^ = [^^^^1, ^^^^2]^^^^.

[0209] Le vecteur propre ^^^^ =�^^^^ ^^^^ ^ ^^^^ 11.1 2.1 3.1 4.1 corresponding to the largest eigenvalue of † ^^^^ −^^^^^^^^ 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 is applied as precoding of the source device ^^^^2.

[0210] 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 ^^^^2. transmits the signal ^^^^ 3,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 3,2 * ^^^^^^^^^^^^^ ^^^^2 and the second antenna of the source device ^^^^2.transmits the signal ^^^^ 4,1 * ^^^^^^^^^^^^^ ^^^^1 + ^^^^ 4,2 * ^^^^^^^^^^^^^ ^^^^2 .

[0211] Therefore, the power transmitted by each relay node is expressed as follows:

[0212] et l’information mutuelle équivalente :

[0213] Par ailleurs, puisque ^^^^^^^^,ℬ = 4 > | ^^^^| = 2, le procédé de sélection des dispositifs sources 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}�

[0214] with indices 1 and 2 corresponding to the antennas of source ^^^^1 and indices 3 and 4 to the antennas of source ^^^^2.

[0215] 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 ^^^^2 that is deactivated.

[0216] A new channel ^^^^ ′ is defined between the active transmitting antennas of the relay nodes and the ^^^^ ^^^^ Antennas receiving the destination signal. The eigenvector ^^^^ ^ ′ ^ ^^= ′ ^^^^ ′ ^^^^ ′ ^^^^ 2 ,1 3,1 - corresponding to the highest eigenvalue ^^^^′ is like precoding the source ^^^^ ′ ′ ′ ′ ^^^^ 1, the eigenvector ^^^^^^^^ =�^^^^1,2 ^^^^2,2 ^^^^3,2� corresponding to the second largest eigenvalue ^^^^ ′ of is applied as source precoding ^^^^2, In other words, the first antenna of the source device ^^^^1 transmits the signal ′ ′

[0217] The power transmitted by each relay node is then expressed as follows:

[0218] and the equivalent mutual information ^^^^ in the case of Gaussian inputs is expressed as follows:

Claims

Claims

1. A method for receiving data comprising the following steps, implemented by a destination device (d) comprising several (^^^^ ^^^^ ) receiving antennas, following the reception of ^^^^ ≥ 2 messages successively transmitted by ^^^^ ≥ 2 source devices and the inability of the destination device to decode at least two messages received from at least two source devices, referred to as "undecoded source devices", each message transmitted by a source device (^^^^ ∈ ℳ) comprising a first redundancy version (RV0) resulting from the encoding of an information message from the source device (^^^^ ∈ ℳ): - a selection (S350), from a set including several source devices (^^^^ ^ ∗ ^ ^^ ) not decoded and from a set ℬ ^ ∗ ^ ^^ of several relay nodes (^^^^ ^ ∗ ^ ^^ ) associated with the whole set ^^^^ ∗ ^^^^ , based on a quality criterion of a communication channel between the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ and the destination device (d), a relay node of the set ℬ ∗ ^^^^ corresponding to a source device (^^^^ ∈ ^^^^) or to an intermediate device(r) knowing the information messages of the undecoded source devices, at least one relay node (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ having several (^^^^ ^^^^,^^^^ ) transmitting antennas; − a transmission (S360), to the relay nodes (^^^^ ^ ∗ ^ ^^ ) selected, of a retransmission instruction, so that the relay nodes ( ^^^^* ^^^^ ) simultaneously transmit second redundancy versions resulting from the encoding of information messages from undecoded source devices (^^^^^ ∗ ^ ^^ ) of ; and, − a reception (S370), by the destination device (d), of said second redundancy versions resulting from the encoding of the information messages of the source devices (^^^^ ^ ∗ ^ ^^ ) of the whole thing ^^^^ ^ ∗ ^ ^^

2. A receiving method according to claim 1, wherein said quality criterion is mutual information of the communication channel between the relaying nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ and the destination device (d).

3. A receiving method according to claim 1 or 2, wherein the selection (S350) comprises: - a determination (S530) of eligible sets ^^^^ of undecoded source devices (s ^^^^) and sets ℬ of relay nodes associated with the eligible sets ^^^^, such that 2 ≤ |^^^^| ≤ with | | the cardinality operator and ^^^^^^^^,ℬ the total number of transmitting antennas of the relay nodes of set ℬ; − a determination (S540), for each of the combinations of eligible sets ^^^^ and sets ℬ of relay nodes, of the quality criterion of the communication channel between the relay nodes of set ℬ and the destination device (d); and the sets ^^^^ ^ ∗ ^ ^^ source devices ∗ ∗ and ℬ ^^^^ of relay nodes (^^^^ ^^^^) selected optimizing said quality criterion.

4. Reception method according to claim 3, wherein the determination (S540) of the quality criterion of the communication channel between the relay nodes of the assembly ℬ and the destination device (d) includes: − a calculation (S630), for each source device(s) of the eligible assembly ^^^^, of a single-source quality criterion for each source device(s) of the eligible assembly ^^^^, as a function of a precoding matrix and a transmit power to be allocated to said source device(s); and, − a calculation (S640) of the quality criterion of the communication channel, as a function of the single-source quality criteria calculated for each source device(s) of the eligible assembly ^^^^.

5. A receiving method according to any one of claims 1 to 4, further comprising a selection of transmitting antennas to be activated by each of the relay nodes ∗ of at least one subset of the set ℬ ^^^^

6. A receiving method according to claim 5, wherein the antenna selection comprises: −a determination (S710) of sub- antennas that can be activated by each of the relay nodes (^^^^ ^ ∗ ^ ^^ ) of at least one subset of the set ℬ ^ ∗ ^ ^^ ; −for each sub- of antennas determined, a calculation (S720) of the quality criterion of a communication channel between the antennas of said sub- e nsemble � ^^ � ^ � ^ � ^^^^, and the destination device (d); - a selection (S730), from among the subsets � ^ � ^^ � ^ � ^^^^, of the subset � ^ � ^^ � ^ �∗ ^ ^^^of antennas to be activated optimizing said quality criterion.

7. A reception method according to any one of claims 1 to 6, wherein the quality criterion of the communication channel between the relay nodes (^^^^ ^ ∗ ^ ^^ ) of the set ℬ ^ ∗ ^ ^^ and the destination device (d) is determined based on a combination of single-source quality criteria of subchannels of said communication channel, each subchannel being defined for a source device (^^^^ ^ ∗ ^ ^^ ) of

8. A method for transmitting data comprising the following steps, implemented by a relay node (^^^^ ^ ∗ ^ ^^ ) including several (^^^^ ^^^^,^^^^) transmitting antennas, following the reception of ^^^^ ≥ 2 messages transmitted successively by ^^^^ ≥ 2 source devices and the inability of a destination device to decode at least two messages received from at least two source devices, referred to as "undecoded source devices", 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 reception (S230) of a retransmission instruction of second redundancy versions resulting from the encoding of information messages from undecoded source devices (^^^^ ^ ∗ ^ ^^ ) of a set ^^^^ ^ ∗ ^ ^^ said relay node knowing said information messages from the undecoded source devices - a simultaneous transmission (S370) of the second redundancy versions of the information messages from the source devices (^^^^ ^ ∗ ^ ^^ ) of the set by the transmitting antennas of said relay node and towards the destination device, said second versions of redundancies being used by the destination device (d) to decode messages received from undecoded source devices

9. Computer program comprising instructions for implementing a receiving method according to any one of claims 1 to 7 or a transmission method according to claim 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) comprising several (^^^^ ^^^^ ) receiving antennas and configured to implement a receiving method according to any one of claims 1 to 7.

12. Relay node (^^^^ ^ ∗ ^ ^^ ) including several (^^^^ ^^^^,^^^^ ) transmitting antennas and being configured to implement a transmission method according to claim 8.

13. System (SYS) comprising ^^^^ ≥ 2 source device(s), a destination device (d) according to claim 11 and a plurality of relaying nodes of which at least one conforms to claim 12.

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