FR3118551A1 - Method of receiving at least one data frame in an OMAMRC system, corresponding destination, computer program and system. - Google Patents

Abstract

Method of receiving at least one data frame in an OMAMRC system, corresponding destination, computer program and system. The invention relates to a method for receiving at least one data frame, in a communication system implementing M sources, possibly L relays and a destination, with and , according to which the destination implements, for at least one data frame and the associated scheduling, an initial phase of link adaptation, prior to the first phase of transmission of said frame, comprising: - the estimation (21) of the transmission channels associated with the direct links between said sources and /or relay and said destination, called direct channels, - obtaining (22) the statistics of the transmission channels associated with the indirect links between said sources and/or relays and said destination, called indirect channels, - determining (23), from said statistics of the indirect channels and estimates of the said direct channels, of M bit rates to be allocated to the M sources for the transmission of the said data frame. Figure for abstract: Figure 2

Description

Method of receiving at least one data frame in an OMAMRC system, corresponding destination, computer program and system.

1. Field of the invention

The present invention relates to the field of digital communications.

The invention relates more particularly to the transmission of data frames between at least two sources and a destination with relaying by at least one node which can be a relay or a source, and to the link adaptation phase implemented beforehand to the transmission of a frame.

It is understood that a relay has no message to transmit. A relay is a node dedicated to relaying messages from sources while a source has its own message to transmit and can also, in certain cases, relay messages from other sources. The source is said to be cooperative in this case.

There are many relaying techniques known by their Anglo-Saxon names: "amplify and forward", "decode and forward", "compress-and-forward", "non-orthogonal amplify and forward", "dynamic decode and forward". , etc.

The invention applies in particular, but not exclusively, to the transmission of data via mobile networks, for example for real-time applications, or via, for example, sensor networks.

Such a network can in particular be a multi-user network, consisting of several sources, several relays and a destination using an orthogonal multiple access scheme of the transmission channel between the sources, relays and the destination, denoted OMAMRC ( “Orthogonal Multiple- Access Multiple-Relay Channel” according to Anglo-Saxon terminology).

2. Prior Art

The prior art is described below in relation to an OMAMRC communication system implementing M sources, possibly L relays and a destination, with And .

In such a communication system, during a first transmission phase, the M sources are configured to transmit messages over K time slots and B frequency sub-bands, with And . During a second phase of cooperative transmission, a selection of relays among the M sources and the L relays is configured to transmit a signal representative of at least one of the messages on time slots and B frequency sub-bands.

A frame includes the data transmitted over the ( ) time intervals.

A link adaptation phase can be implemented prior to the transmission of at least one frame, to determine the resources to be allocated to the sources for the transmission of the frames.

Different link adaptation techniques are known.

For example, if the radio conditions vary rapidly, i.e. in the event of rapid variations in the global transmission channel between the sources and the destination (for example in a mobile situation), a slow link adaptation technique can be implemented ( in English “Slow Link Adaptation” or SLA). Conversely, if the radio conditions vary slowly, a fast link adaptation technique can be implemented (Fast Link Adaptation or FLA).

The difference between these slow and fast link adaptation techniques lies in the knowledge of the different links in the system by the destination.

Indeed, as such a communication system involves relays, the destination does not know all the links of the system and can directly observe only the direct links (source to destination or relay to destination). On the other hand, the indirect links between the sources (S-S), between the relays (R-R), between the sources and the relays (S-R) are not directly observable by the destination.

To obtain a total knowledge of all the links of the system at the level of the destination (in English "Channel State Information", CSI), the sources / relays can estimate the indirect channels and send this information back to the destination ("feedback"). The destination can estimate direct channels directly.

Such CSI knowledge by the destination is, however, particularly expensive, since it requires a large exchange of control information between the sources, the relays and the destination.

If the global transmission channel between the sources and the destination varies slowly, it is possible to raise all the estimates of the indirect channels to the destination (for example before the transmission of a new frame or a few frames, or as soon as a change in the estimation of an indirect channel is detected) and to implement an FLA type link adaptation technique to determine the bit rates to be allocated to the sources. A new allocation can thus be implemented frame by frame or for a group of a few frames, or as soon as a change of CSI is detected.

On the other hand, if the global transmission channel between the sources and the destination varies rapidly, the CSI knowledge at the destination becomes too expensive.

To limit the cost of feedback overhead, only Channel Distribution Information (CDI) of all links is assumed to be known by the destination. . For example, such channel distribution/statistics information is average quality (eg, average signal-to-noise ratio "average SNR", average signal-to-noise ratio plus interference "average SINR", etc.). Such CDI information is assumed to be constant over several hundred frames.

In this case, an SLA-type link adaptation technique is implemented to determine the bit rates to be allocated to the sources. A new allocation can thus be implemented for a group of a few hundred frames, or as soon as a change of CDI is detected.

Document WO 2019/162592 published on August 29, 2019 describes in particular an OMAMRC communication system implementing slow link adaptation. It proposes a technique to maximize the average spectral efficiency (utility metric) within the considered system under constraint to respect an individual quality of service (QoS) per source.

The overall spectral efficiency of an OMAMRC communication system implementing a bitrate allocation technique based on an FLA technique or on an SLA technique according to the prior art is presented below.

Either a random variable representative of the spectral efficiency per frame with respect to a rate allocation strategy P, denoted for a slow link adaptation technique and for a fast link adaptation technique, and H a matrix representative of the global transmission channel.

Two average spectral efficiencies are defined, one of which is a very good approximation of the other: the global spectral efficiencies per frame and overall spectral efficiency , which is the ratio of the average number of bits correctly received and the average number of channel utilization (radio resource under bands and time slot) required. It is assumed that the global transmission channel is invariant for the duration of a frame, ie that the direct and indirect links do not vary for the duration of a frame.

We define the vector representative of a number of sub-bands allocated for each node (source or relay), for a time interval t, as a vector with (M+L) dimensions . is the number of subbands allocated to a user for transmission over the time slot corresponding to the first transmission phase, or over a time interval t>0 corresponding to the cooperative transmission phase.

If a slow link adaptation technique is implemented, the overall spectral efficiency can be expressed as:

with the operator which corresponds to the mean/expectation on the distribution of the channel H

Or

with :

,

the transmitted payload time-frequency resources (also called “channel use” or “channel use” or “resource element” according to 3GPP terminology) by the source ,

the number of cooperative transmissions used during the cooperative transmission phase,

the maximum number of cooperative transmissions allowed during the cooperative transmission phase,

the expectation of an individual outage event indication for source at the end of the cooperative transmission phase.

A break event indication is a random variable taking a value equal to 1 if a source node or a set of source nodes is not decoded correctly by the destination (in particular after a maximum number of cooperative transmissions allowed Tmax), 0 otherwise. More, generally, we define the cutoff indication as a random variable that takes the value 1 if the source i is not decoded correctly after the first phase of transmission and at each cooperative transmission until t . If the source i is decoded correctly before or at the transmission t, the cut indication takes the value 0. Thus, means that the source i will not be decoded correctly during a frame (because the number of transmissions during the cooperative transmission phase cannot exceed Tmax).

is therefore the probability of an outage event of the type “source i is not decoded correctly” and represents all the links having led to an outage of source i.

represents the expected number of time slots needed for the cooperative transmission phase, and can be determined as follows: .

A channel utilization is the smallest granularity in time-frequency resource defined by the system that allows the transmission of a modulated symbol. The number of channel uses is related to the available frequency band and the transmission duration.

If a fast link adaptation technique is implemented, the overall spectral efficiency can be expressed as:

with :

an individual cut event for the source at the end of the cooperative transmission phase as described above,

a variable corresponding to the minimum number of cooperative transmissions used during the cooperative transmission phase making it possible to decode all the sources (ie no source is cut):

In summary, the fast link adaptation technique, based on a total knowledge of the global transmission channel (CSI) makes it possible to allocate bit rates to sources in a precise way.

Nevertheless, in a MAMRC system, the number of channels/links grows exponentially with the number of nodes (source or relay). Therefore, there is a high probability that at least one link varies over time, causing the exchange of a large amount of control information between the sources/relays and the destination.

Such a fast link adaptation technique is therefore difficult to use.

To avoid the exchange of such a volume of control information, a slow adaptation technique can be used.

However, such a slow link adaptation technique is less accurate than a fast link adaptation technique. Indeed, the knowledge of a channel distribution/statistic (CDI) can be quite far from the real knowledge of the channels (CSI) at a given moment, which can generate approximations during the allocation of bit rates to sources and reduce the performance of the communication system, for example in terms of spectral efficiency.

There is therefore a need for a new link adaptation technique which does not have all the drawbacks of the prior art.

3. Disclosure of Invention

The invention proposes a solution, in the form of a method for receiving at least one data frame, in a communication system implementing M sources, possibly L relays and a destination, with And ,

said M sources being configured to transmit, during a first transmission phase, messages over K time slots and B frequency sub-bands, with And Or And , and a selection of said M sources and of said L relays being configured to transmit, during a cooperative transmission phase, a signal representative of at least one of said messages on time slots and B frequency sub-bands, according to a scheduling chosen by said destination,

the data transmitted on the said ( ) time slots forming a data frame.

According to the invention, said destination implements, for at least one data frame and the associated scheduling, an initial link adaptation phase, prior to said first transmission phase of said frame, comprising:

- the estimation of the transmission channels associated with the direct links between the said sources and/or relays and the said destination, known as direct channels,

- obtaining the statistics of the transmission channels associated with the indirect links between the said sources and/or relays and the said destination, known as indirect channels, and

- the determination, from said statistics of the indirect channels and of said estimates of the direct channels, of M bit rates to be allocated to the M sources for the transmission of said data frame.

Compared to a slow link adaptation technique according to the prior art, the proposed solution makes it possible to improve the precision of the bit rate allocation for the transmission of a data frame, since it takes into account the estimation of direct channels (CSI of direct links). The bit rates to be allocated to the sources can thus be determined from knowledge of the CSI information of the direct links. The proposed solution is therefore more robust, even in the event of mobility of the sources and/or the relays.

It is recalled that the classic link slow adaptation technique uses the knowledge of a distribution/statistic of the set of channels (CDI), and is implemented only when the statistics of the channels are updated, for example example every hundred frames. The destination therefore does not use all the information at its disposal, and in particular does not use knowledge of the direct source-destination and relay-destination links.

Compared to a technique for rapid link adaptation according to the prior art, the proposed solution makes it possible to reduce the quantity of control information exchanged, since it takes account of knowledge of a distribution/statistic of the indirect channels only (CDI of indirect links). The throughputs to be allocated to the sources can thus be determined from average values on the indirect links. In particular, the sources and/or relays are therefore adapted to estimate the CDIs of the indirect channels and to send them back to the destination.

The proposed solution therefore makes it possible, according to at least one embodiment, to use the information directly available at the destination (estimate of the direct channels), while limiting the volume of control information exchanged.

In particular, the proposed solution can be implemented when a fast link adaptation technique cannot be implemented because the global channel varies too quickly, or when a slow link adaptation technique is inefficient.

The proposed solution thus takes advantage of fast link adaptation techniques on direct channels to optimize bit rate allocation, and slow link adaptation techniques on indirect channels to limit the exchange of control information. The proposed solution can therefore be considered as an intermediate link adaptation solution, based on a partial knowledge of the global channel at the destination.

In particular, the proposed solution can be implemented in a communication system of the OMAMRC type implementing an orthogonal multiple access scheme in time (in English “Time Division Multiplexing”, TDM), with in this case And , or in frequency (in English “Frequency Division Multiplexing”, FDM), with in this case And .

A time slot associated with a frequency sub-band can in particular be divided into F time/frequency resources, with .

In particular, the allocation of sub-bands between the sources makes it possible to reduce the time required to transmit data since the sources transmit simultaneously in a single and same first time slot (time slot). Such a method is therefore well suited for demanding services in terms of latency.

According to a particular embodiment, as for the fast link adaptation technique, the estimation of the direct channels can be implemented for each data frame, for a group of a few frames (less than 10 frames for example), or as soon as a variation of a direct channel is detected.

The direct channels can in particular be estimated from at least one reference signal received by said destination, and transmitted by said sources and/or said relays.

For example, a reference signal can be a sounding reference signal (SRS, as defined in the 3GPP LTE/NR standard). In particular, such reference signals can be transmitted by the sources and/or the relays, upon receipt of a request from the destination. In particular, such a request can be broadcast by the destination in an OMAMRC communication system prior to the transmission of a first data frame.

Alternatively, the reference signal may be a demodulation reference signal (DMRS, as defined in the 3GPP LTE/NR standard). In particular, such reference signals can be transmitted together with data frames during the first transmission phase or the cooperative transmission phase of a frame, and be used to update the estimate of the direct channels (i.e. when an initial direct channel estimate is available at the destination).

According to another particular embodiment, as for the slow link adaptation technique, the obtaining of the statistics of the indirect channels can be implemented for a set of frames, for example around a hundred frames. Indeed, such CDI information is assumed to be constant over several hundred frames.

As a variant, the statistics of the indirect channels can be updated as soon as a variation of an indirect channel is detected.

The statistics of the indirect channels correspond for example to an average quality (for example an average signal-to-noise ratio “average SNR”, an average signal-to-noise plus interference ratio “average SINR”, etc.). For example, the distribution statistic of each indirect link follows a Gaussian distribution and only depends on one parameter which is the SNR. Other distributions can be considered, such as a Dirac distribution. In this case, the distribution statistic of each indirect link follows a Dirac distribution around the square root of the SNRs associated with each of the indirect channels.

For example, the sources or relays on an indirect link receiving a reference signal can estimate the transmission channel associated with this indirect link, then determine a statistic associated with this indirect link and relay this information to the destination.

In particular, if a source or a relay of an indirect link detects a change in the indirect channel, it can send a notification to the destination indicating a modification of at least one statistic of one of said indirect channels. Such a notification is for example of the “Event driven CDI update” type.

Thus, the destination can implement an update of the statistics of the indirect channels upon receipt of such a notification.

According to a particular embodiment, said determination of M bit rates to be allocated to the M sources implements a maximization of a quality of service metric of said communication system, knowing the estimation of the direct channels.

Such a quality of service metric is for example of the spectral efficiency type, BLER (“Block Error Rate”), etc. Maximizing the quality of service makes it possible, for example, to optimize the bit rate or to reduce the transmission power of the sources for the same bit rate.

For example, said maximization is expressed in the form:

under constraint that:

with :

all sources,

a variable representing the flow to be allocated to source i, ,

the number of sub-bands allocated to source i during the first transmission phase,

estimation of direct channels,

is the break indication which takes the value 1 if the source i is not decoded correctly during a frame,

the number of cooperative transmissions used during the cooperative transmission phase,

the maximum number of cooperative transmissions allowed during the cooperative transmission phase,

an average of the number of cooperative transmissions used during the cooperative transmission phase, knowing the estimate of the direct channels,

an average of the number of messages transmitted by the source i not decoded by the destination at the end of the cooperative transmission phase, knowing the estimation of the direct channels,

the acceptable average error rate with respect to a QoS quality of service, knowing the estimate of the direct channels.

According to a particular embodiment, said determination of M bit rates to be allocated to the M sources implements an iterative algorithm based on the determination of a bit rate to be allocated to the source i, for each , assuming the flows to be allocated to the other known sources.

For example, said determination implements an iterative algorithm of “Best Response Dynamics” type.

Such an algorithm notably makes it possible to reduce the complexity of the multi-dimensional maximization function.

In particular, such an iterative algorithm can be initialized using a “Genie Aided” type algorithm.

According to a particular embodiment, the determination of the M rates to be allocated to the M sources is implemented jointly with the determination of an optimized scheduling for said frame.

We then seek to solve a joint problem of optimizing the allocation of flows and the allocation of resources.

According to a particular embodiment, the destination transmits to said sources at least one piece of information representative of said bit rates (for example a modulation and coding scheme (in English “Modulation and Coding Scheme” or MCS), an index of a modulation scheme and encoding, bitrate itself, etc.).

For example, such information is broadcast by the destination, or transmitted in a control channel specific to each source or common to the various sources. In particular, the increase in flow rates can be carried out via very limited flow control channels.

The invention also relates to a corresponding destination node.

Such a destination node is in particular suitable for implementing the reception method described previously. This is for example a base station or an eNodeB. Such a destination could of course include the different characteristics relating to the method according to the invention, which can be combined or taken separately. Thus, the characteristics and advantages of the destination are the same as those of the method described previously. Therefore, they are not further detailed.

The invention further relates to a system comprising sources , Most often is "possibly relay and a destination , , , for an implementation of a reception method according to the invention.

The invention also relates to one or more computer programs comprising instructions for the implementation of a reception method as described above when this or these programs are executed by at least one processor.

In a particular embodiment, the reception method results from a software application split into several specific software applications stored in the sources, in the destination and possibly in the relays. The execution of these specific software applications is suitable for the implementation of the reception method.

In particular, the subject of the invention is each of the specific software applications on one or more information carriers, said applications comprising program instructions adapted to the implementation of the reception method when these applications are executed by processors.

The invention further relates to configured memories comprising instruction codes corresponding respectively to each of the specific applications.

4. List of Figures

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a particular embodiment, given by way of a simple illustrative and non-limiting example, and the appended drawings, among which:

- there illustrates an example of an OMAMRC type communication system in which the invention can be implemented;

- there presents the main steps implemented by a destination according to one embodiment of the invention;

- there illustrates the information exchanged between the sources/relays and the destination according to one embodiment of the invention;

- there illustrates an example of bit rate allocation for the sources in an OMAMRC type communication system;

- there presents the simplified structure of a destination node according to a particular embodiment.

5. Description of a particular embodiment

5.1 General principle

The invention is placed in the context of a cooperative communication system, implementing M sources, possibly L relays and a destination, with And , for example of the OMAMRC type.

FIG. 1 illustrates an example of an OMAMRC type communication system in which the invention can be implemented, implementing M sources , relay and a destination . Each source communicates with the single destination with the help of the other sources (in English “user cooperation”) and of the cooperating relays. A source can therefore behave like a relay when it does not send its own message. The destination can send information back to the sources and the relays (“feedback”), for example in control channels between the destination and each source or relay (shown in dotted lines on the ).

The M sources are configured to transmit, during a first transmission phase, messages over K time slots and B frequency sub-bands, with And The K first time slots are therefore dedicated to a first transmission of the messages from the M sources.

A selection of the M sources and the L relays is configured to transmit, during a second phase of cooperative transmission, a signal representative of at least one of the messages from the sources on time slots and B frequency sub-bands. THE following time slots the first K time slots are therefore dedicated to transmissions including at least one cooperative transmission. A cooperative transmission is either a transmission by a relay or a transmission by a source capable of helping the destination to decode at least one other source. More precisely, a cooperative transmission is a transmission by a node which contains information relating to at least one message from another node. The transmission of a relay is, by nature, a cooperative transmission but also the transmission of a source (which is capable of cooperation) which includes in its transmission information relating to at least one message from another source. The cooperation of the relay nodes ensures an increase in the reliability of the transmissions.

In a particular embodiment, the source and relay nodes operate according to a “full-duplex” mode. Each full-duplex node is thus allocated at least one frequency sub-band and can thus transmit in its sub-band and simultaneously listen to the other nodes transmitting in the other sub-bands. In other words, in "full-duplex" mode, a relay node can listen to the transmission of the other nodes (source, relay) at each time slot, even when it transmits, and a source node can listen to the transmission of the others nodes (source, relay) at each timeslot even when it is transmitting.

In another embodiment, the source and relay nodes operate according to a “half-duplex” mode. According to this "half-duplex" mode, a relay node can listen to the transmission of other nodes (source, relay) at each time slot when it is not transmitting, and a source node can listen to the transmission of other nodes (source, relay ) at each timeslot when it is not transmitting.

For each time interval, there is time-frequency resources, with the number of sub-bands available and the number of time-frequency resources associated with a time slot per sub-band. The number of time-frequency resources is assumed to be identical for each transmission interval. In the case of a transmission with an OFDM modulation, a time slot can correspond to 7 OFDM symbols and a sub-band to 12 sub-carriers, thus F=12*7 corresponds to the number of elementary resources of a block of physical resources (in English “Physical Resource Block”, PBR) in LTE, and B is the number of PRB (sub-bands) available for the frequency band considered.

The data transmitted on the ( ) time slots form a data frame.

A frame is therefore a set of consecutive time intervals used for the transmission of messages from the M sources according to a schedule defined by the destination.

We can thus consider that a frame is composed of a first transmission phase and a cooperative transmission phase.

The first phase of transmission includes time slots, during which the M sources can send their message orthogonally by using the orthogonal frequency sub-bands and/or the time slots, on one or more sub-bands allocated to each source. Whether , the time interval corresponds to the first phase of transmission.

The cooperative transmission phase includes time intervals. For a given time interval, a scheduler allocates at least one sub-band or one band (if ), to a relay or source node, so that it transmits to the destination the redundancies according to the message(s) received that it has correctly decoded (in English “decoding set”). In other words, at each time interval , the destination can allocate at least one subband to a node (or no node). This resource allocation can be fixed for one or more consecutive frames or for all frames.

Thus, during this phase of cooperative transmission, only the nodes selected from among the sources and the relays transmit, and their transmission takes place on the sub-band or bands (or the band, if B = 1) which are respectively allocated to them according to a partition determined for each current interval. Thus, the partitions can be different between all time intervals, including the first.

The selection of the nodes and the allocation of the sub-bands are conventionally implemented by a scheduler, typically hosted by the destination. This phase is more generally called “resource allocation” or scheduling.

A transmission cycle therefore lasts time intervals. The duration of a frame cannot exceed ( + ) time intervals, where is the maximum number of cooperative transmissions allowed during the cooperative transmission phase ( ). At each time interval, none, one or more sub-bands can be allocated to a node.

According to the invention, the orthogonality of the communication system can be obtained by time division multiplexing (TDM, with ) based on the use of several time slots each allocated to a different source, or by frequency multiplexing (FDM, with ) based on the use of several frequency bands each allocated to a different source.

Subsequently, for the sake of simplification, it is assumed that the number of sub-bands B is greater than or equal to the number of sources or users M, ie, . We also place ourselves in the context of a first phase of transmission of a frame implementing an orthogonal multiple access scheme in FDM frequency, ie (FDM OMAMRC), according to which the nodes, springs and relays, operate in a full-duplex mode that allows them to listen to transmissions from other nodes without interference.

Of course, this is a simple illustrative and non-limiting example. The generalization to a first phase of transmission implementing time intervals and is deduced directly and without ambiguity, since it is similar to an allocation of resources on BK sub-bands for the first phase of transmission.

As already indicated, the transmission of a frame can be preceded by a link adaptation phase, during which bit rates are allocated to the different sources. For example, we consider a finite set of bit rates (or modulation and coding schemes), and we allocate to each source a bit rate among the finite set of bit rates.

The invention relates to the link adaptation phase. The general principle of the invention is based on the knowledge of the direct links by the destination, and the obtaining of a statistics of the indirect links by the destination, to optimize the link adaptation, i.e. the allocation of speeds to the different sources .

There illustrates the main steps implemented by the invention, in a communication system as described above.

For at least one data frame and the associated scheduling, which can be chosen by the destination, the destination d implements an initial link adaptation phase, prior to the first transmission phase of said frame.

The link adaptation phase includes a step 21 of estimating the transmission channels associated with the direct links between the sources and/or relays and the destination, called direct channels . For example, with reference to Figure 1, the direct channels that the destination can directly estimate are the channels , , , And .

The link adaptation phase also includes a step 22 for obtaining the statistics of the transmission channels associated with the indirect links between the sources and/or relays and the destination, called indirect channels (STAT on ). For example, with reference to Figure 1, the indirect channels are the channels , , , , , , , , . In particular, this step 22 for obtaining takes account of the estimation of the direct channels (since a statistic is determined only for the indirect channels).

From the estimation of the direct channels , and indirect channel statistics knowing , the destination can determine, during a determination step 23, M bit rates to be allocated to the M sources for the transmission of said data frame.

The destination can in particular transmit to the M sources, during a transmission step 24, at least one piece of information representative of said at least one bit rate.

The link adaptation phase is therefore based on the knowledge of the CSIs of the direct links and of the CDIs of the indirect links. To do this, the destination can directly determine the CSI of the direct links (for example for a frame or a group of a few frames) and obtain the CDI information of the indirect channels (received for example for a hundred frames). The destination does not need to obtain the CSIs of the indirect links, only the CDIs of the indirect links (i.e. the statistics, for example SNR, of the links which evolve very slowly over time).

As we use a partial knowledge of the CSIs (i.e. the CSIs associated with the direct channels), we can consider that the proposed solution is of the FLA fast link adaptation type. However, the quantity of information necessary for the destination is greatly reduced compared to the fast link adaptation techniques according to the prior art. Such a solution is for example called “fast link adaptation with partial knowledge of the CSIs”.

In particular, the link adaptation phase can be implemented frame by frame, or for a group of a few frames, before the first transmission phase of a frame. It can in particular be updated when a variation of a direct or indirect channel is detected.

5.2 Description of a particular embodiment

We present below, in relation to the , the information exchanged between the sender nodes (sources or relays, s/r) and the destination (d) according to one embodiment of the invention.

According to the example illustrated, if no transmission is in progress, the destination d can broadcast a message 31 requesting the broadcasting of a reference signal (“SRS request”). Upon receipt of this message, the sources and/or relays can each send a reference signal 32.

By exploiting the reference signals received (pilot symbols of the DMRS 3GPP LTE/NR type, reference signals of the SRS 3GPP LTE/NR type, etc.), the destination can directly estimate the transmission channels associated with the direct source to destination and relay links to destination (CSI), i.e. determine the gains of the direct links.

Concerning the indirect source-source, relay-relay, or source-relay links, only the sources or relays on these links can estimate the associated transmission channels, for example by exploiting the reference signals received, in a manner similar to that used for direct links. For example, a source or a relay can estimate metrics / statistics of these indirect links (CDI) in reception by considering a slow adaptation, and transmit these metrics / statistics to the destination at a rate lower than that of the adaptation phase of link (for example every hundred frames). As a variant, the destination can broadcast a message requiring the obtaining of such metrics (“CDI request”), and receive return messages (“CDI feedback”) from the sources / relays of the indirect links. In particular, the sources transmit to the destination the statistics of the source-source or source-relay links, and the relays transmit to the destination the statistics of the relay-relay links.

From the estimation of the direct channels and the statistics of the indirect channels, the destination can determine the rates to be allocated to the sources for the transmission of the first frame. For example, the destination broadcasts information representative of the bit rates to be allocated to the various sources for the transmission of a first frame in a bit rate allocation message 33.

Upon receipt of this bit rate allocation message 33, each source transmits its data 34 using the bit rate obtained from the bit rate allocation message 33. As detailed above, the data from the different sources form the first frame, corresponding to a first transmission phase and a cooperative transmission phase.

According to a particular embodiment, the data 34 transmitted by a source or a relay can carry pilot symbols (DMRS) which can be used for coherent demodulation of the signal received at the destination. Such symbols can in particular be used to update the estimation of the direct channels to the destination.

If the destination has decoded all the sources (ie all the messages / data transmitted by the sources) before (Or corresponds to the maximum number of cooperative transmissions allowed during the cooperative transmission phase) then the destination can send an ACK 35 message, triggering the clearing of the source buffers.

The sources can then transmit a second frame.

The estimation of the direct channels can in particular be updated, for example following the reception of pilot symbols. Indirect channel stats, on the other hand, can remain unchanged.

The destination can then determine the rates to allocate to the sources for the transmission of the second frame from the updated direct channel estimate and the indirect channel statistics, and transmit this information in a rate allocation message 36 .

Upon receipt of this bit rate allocation message 36, each source transmits its data 37 using the bit rate obtained from the bit rate allocation message 36. As detailed above, the data from the different sources form the second frame, corresponding to a first transmission phase and a cooperative transmission phase.

If the destination has not decoded all the sources (ie all the messages / data transmitted by the sources) until ( included), then the source buffers are cleared (e.g. based on dedicated counters/timers) and the sources can transmit a third frame.

In particular, at least part of the messages from the sources transmitted in the second frame is lost, since the maximum number of cooperative transmissions authorized during the cooperative transmission phase is reached without all the sources being decoded.

Again, the estimation of the direct channels can be updated, for example following the reception of pilot symbols. Indirect channel stats, on the other hand, can remain unchanged.

The destination can then determine the rates to allocate to the sources for the transmission of the third frame from the updated direct channel estimate and the indirect channel statistics, and transmit this information in a rate allocation message 38 .

Upon receipt of this rate allocation message 38, each source transmits its data 39 using the rate obtained from the rate allocation message 38, and so on.

As noted above, forward channel estimates may be updated for every frame, or for a few frames. On the other hand, the statistics of the direct channels can be updated at a lower rate, for example of the order of a hundred frames.

If, however, a source or a relay detects a change in the statistics of an indirect channel, it can notify the destination of this change, either by transmitting a new statistics to the destination or by transmitting a notification, for example of the “Event driven” type. CDI update”. Upon receipt of such a notification, the destination may in particular broadcast a message requesting new statistics (“CDI request”), and receive return messages (“CDI feedback”) from sources / relays of indirect links .

An example of determining the bit rates to be allocated to the various sources is described below, making it possible to maximize a quality of service metric of the communication system, knowing the estimation of the direct channels.

According to this example, the proposed approach relies on a performance prediction based on information theory considerations, in particular the outage probabilities. This approach makes it possible to predict the result of the implementation of a parity check (CRC check) without going through the simulation of the entire chain of transmission (coding modulation) and reception (detection/demodulation, decoding ). In this, it defines an abstraction of the physical layer. Certain adjustments obtained by simulation (called calibration within the framework of the abstractions of the physical layer) for a given coding scheme can be carried out by introducing weighting parameters of the mutual information and/or of the SNRs of the links.

As described above, the proposed link adaptation takes into account the knowledge of the distribution (i.e. distribution statistics) of the channel on the direct links. In other words, for CSIs known for the direct links, the destination can determine the bit rates to be allocated to the sources by taking into account the statistics (CDI) of the indirect links.

For example, it is sought to maximize the real average bit rate, that is to say the overall bit rate over a set of frames.

To simplify the description, the following assumptions are made on the OMAMRC system:

• the sources, the relays are equipped with a single transmission antenna;
• the sources, the relays, and the destination are equipped with a single reception antenna;
• sources, relays, and destination are perfectly synchronized;
• the sources are statistically independent (there is no correlation between them);
• all the nodes transmit with the same power;
• use is made of a supposed CRC code included in the information bits from each source to determine if a message is correctly decoded or not, ;
• links between different nodes suffer from additive noise and fading. The fading gains are fixed during the transmission of a frame carried out for a maximum duration of time intervals (with K=1 according to the example described), but can change independently from one frame to another. is a system parameter;
• the instantaneous quality of the channel/direct link in reception (CSIR Channel State Information at Receiver) is available at the destination, at the sources and at the relays;
• the returns are error-free (no error on the control signals) .
• the information used to estimate the direct channels (reference signals for example) is transmitted in unicast control channels (from a source or a relay, to the destination) assumed to be error-free,
• the statistics of the indirect channels are also transmitted in unicast control channels (from a source or a relay, towards the destination) assumed to be error-free, the sources transmitting to the destination the statistics of the source-source links and possibly of the links source-relay, and the relays transmitting to the destination the statistics of the relay-relay links and possibly of the source-relay links,
• indirect channel statistics can be transmitted to the destination when a change is detected, or for example every hundred frames.

We then use the following notations:

• whether the node i selected is a source i denoted , ; Otherwise and the selected node is a relay denoted , ,
• is a B-dimensional vector of the selected nodes for the time interval t, during the first transmission phase or during the cooperative transmission phase, with all sources and all the relays. THE element vector means the sub-band and the selected active node (ie transmits) during this time interval t in this sub-band i , . The order in the vector corresponds to the order of the subbands,
• is the M+L dimension vector of the number of sub-bands allocated for each node which varies between 0 (the node is inactive) and B (the node occupies all the sub-bands), source or relay, for the time interval t, during the first transmission phase or during the cooperative transmission phase. THE element vector denotes the number of sub-bands allocated to node i at time interval t, . The sum of the elements composing the vector is equal to B the number of sub-bands,
• is the realization of the transmission channels associated with the direct links between the sources/relays and the destination and
• the realization of the transmission channels associated with the indirect links between the sources, between the relays, and between the sources and the relays.

An achievement is the value taken for a random draw from a statistic.

A channel estimate estimates a channel realization, which is also a CSI. The terms "estimate" or "implementation" are therefore considered equivalent below, and used interchangeably.

Using the total expectation theorem, ie, , we obtain an average flow rate on the global transmission channel such as:

According to the invention, a new throughput allocation strategy is proposed (fast link adaptation with partial knowledge of CSI), which does not depend on the realization but that changes for each achievement . Thus, the throughput allocated to each source, denoted , does not change with conditional expectation .

To maximize the average throughput , the destination can select for each frame (hence the name fast link adaptation), the bit rates to be allocated to the sources to maximize the internal variable:

knowing the realization . We can use as an approximation of which corresponds to the global spectral efficiency knowing ( is the overall spectral efficiency per frame knowing ) and so to obtain the flow rate per frame, the destination therefore seeks to determine the internal variable Or , using on the one hand the CDIs of the indirect links, and on the other hand the CSIs of the direct links.

The global spectral efficiency based on the knowledge of the CSI of the direct links can be written:

with the probability of having an individual outage event equal to 1 for source i, based on the probability distribution of the indirect links knowing the CSIs of the direct links.

In particular, according to the example illustrated in FIG. 4, it is considered that the direct links are the links , , And , and the indirect links are the links , , , , And .

The direct links represent the realizations of the channel which are fixed, on which a CSI is determined, and the indirect links the realizations of the channel on which a statistic is determined.

In the expression for the internal expectation variable , the throughput allocation is given for a known realization of the direct channels, as illustrated in figure 4. Thus, knowing the direct links and statistics on the indirect links, we obtain Or .

Then the average flow can be determined by taking into account the expectation on the achievements of the direct links.

The spectral efficiency based on knowledge of the CSIs of the direct links can therefore be expressed in the form of a multivariate equation, a function of the bit rates of each source and the allocation vectors for each time slot t for the cooperative transmission phase. The spectral efficiency therefore depends on the selection of the nodes and the allocation of the sub-bands.

The allocation of bit rates (ie the determination of the bit rates to be allocated to the M sources) therefore implements a maximization of a quality of service metric of the communication system, which can for example, by using be expressed in the form:

under constraint that , for everything belonging to ,

with :

And the joint probability of realization of the global channel for all the links of the system, conditioned on the knowledge CSI of the direct channels.

If we assume that the achievements And are independent, we get:

Or :

is the mutual fading information block of the node at the destination for the sub-bands allocated to the node at the time interval

with represents a set of interfering sources,

represents the logical "and",

represents Iverson's brackets ie which gives the value 1 if the event is satisfied and the value 0 if not,

The condition ensures that the node considered at the time interval includes at least one subset node as a whole decoding (ie the intersection between the set of sources correctly decoded by the node at the time interval and the whole is not empty), and the node considered at the time interval has not decoded any interfering node (ie the intersection between the set of sources correctly decoded by the node at the interval and the set of interfering sources is empty).

From an analytical point of view, an outage event occurs if the vector of the bit rates of these sources is not included in the capacity region MAC (in English "Multiple Access Channel", in French "canal d'acces multiple ”) corresponding.

Appendix 1 presents outage events in more detail.

To determine flow rates to be allocated to the different sources, it is therefore necessary to solve a problem of optimization with several variables, by seeking to maximize a quality of service metric of the communication system as presented above.

According to a particular embodiment, it is possible to simplify the above equation, to dispense with the calculation of the integral for the outage event taking into account the realization of the channel , using a Monte-Carlo simulation method.

Thus, the expression for the cut event taking into account the realization of the channel can be expressed in the following approximate form:

Or is a realization of the channel based on the probability distribution of indirect links.

This expression can be further simplified by the cutoff due to the inequality of the sum flow

Alternatively, it is possible to assume that the statistical distribution of each indirect link follows an independent Dirac distribution around the square root of the SNRs of each indirect link by assuming a noise variance equal to 1 (white noise Gaussian additive), instead of calculating the above equation. For example, channel distribution whose SNR is is approximated by .

Such a variant may slightly reduce the performance of the communication system, but offers a solution to simplify the complexity of the rate allocation algorithm.

We also note that we have assumed until now a selection of nodes and allocation of known sub-bands, i.e. a known scheduling of the destination.

However, as indicated above, the spectral efficiency depends in particular on the selection of the nodes and the allocation of the sub-bands.

Thus, according to a particular embodiment, the problems of allocating the bit rates to the sources and of selecting the nodes can be solved jointly.

In particular, we see that a vector , representing the nodes selected for the time interval t, depends on the bit rates allocated to the sources and on the vectors representing the nodes selected for at least one previous time interval.

We consider for example that the node selection strategy is based on a mutual fading information block type selection metric.

We wish to select the vector which gives the greatest mutual information, for the cooperative transmission phase.

The vector selected for the cooperative transmission phase can be written:

with the set of all possible allocations , which corresponds to the activation of nodes that can help the destination at the time interval (“round”).

It is also desired to select the vector which gives the greatest mutual information, for the first transmission phase. However, for the first transmission phase of a frame, we want to allocate sub-bands only to the sources, by allocating at least one sub-band per source.

The vector selected for the first transmission phase can then be written:

with a subset of comprising the vectors associated with the sources, at the time interval .

According to a first approach, an exhaustive search can be implemented for the joint resolution of the flow allocation and node selection problems.

Such an approach being particularly complex and costly, approximations are proposed below.

According to a second approach, a BRD (“Best-Response Dynamic”) type algorithm can be used. Such an algorithm is notably presented in appendix 2.

According to this approach, rather than jointly solving the bitrate allocation and vector selection problems, a solution is sought for each user/source in an iterative manner. In other words, a sub-optimal solution for the BRD algorithm is based on determining an optimal throughput for a user/source for a given time interval, considering that other users/sources are idle, i.e. do not send data.

This algorithm is repeated successively for each user/source, then for all the users/sources, until reaching a point of convergence, beyond which any change in a bit rate allocated to a user/source leads to a decrease in spectral efficiency.

Classically, the BDR algorithm comprises two phases: an initialization phase and an iterative correction phase.

During the initialization phase, initial flow values are allocated to the different sources. Different techniques can be implemented for the initialization phase: random initialization, fixed value initialization, Genie Aided initialization, etc.

In particular, the initialization according to the "Genie Aided" approach makes it possible to allocate a bit rate to a source without taking into account the bit rates allocated to the other sources. To do this, for the calculation of the initial bit rate allocated to a source, it is assumed that the messages transmitted by the other sources are known to all the other nodes (source or relay). As a result, the sources do not interfere with each other. Another assumption can be made on the allocation of resources, for example by considering a random approach. Appendix 3 presents in particular an example of initialization of the initial flow values for the different sources according to the “Genie Aided” approach.

As indicated above, other techniques can be implemented for the initialization phase. In particular, the source memory can be used, for example by using the bit rates allocated to the various sources for the transmission of a previous frame, to initialize the iterative algorithm for determining the bit rates for the transmission of a current frame. Indeed, it is likely that the global transmission channel varies little between the transmission of a previous frame and the transmission of a current frame, which means that the allocation of bit rates for the current frame should be quite close to l bitrate allocation for the previous frame.

Whatever the technique used for the initialization phase, the choice of a good starting point allows the BRD algorithm to converge more quickly.

During the correction phase, the data rates obtained in the previous iteration are updated, seeking to optimize the performance of the communication system (i.e. the spectral efficiency).

5.3 Simplified destination structure

We finally present, in relation to the , the simplified structure of a destination node according to at least one embodiment described above.

As illustrated in , such a destination comprises at least one memory 51 comprising a buffer memory, at least one processing unit 52, equipped for example with a programmable calculation machine or a dedicated calculation machine, for example a processor P, and controlled by the computer program 53, implementing steps of the reception method according to at least one embodiment of the invention.

On initialization, the code instructions of the computer program 53 are for example loaded into a RAM memory before being executed by the processor of the processing unit 52.

The processor of the processing unit 52 implements the steps of the reception method described above, according to the instructions of the computer program 53, to:

- estimate transmission channels associated with direct links between said sources and/or relays and said destination, called direct channels,

- obtain statistics of the transmission channels associated with the indirect links between said sources and/or relays and said destination, called indirect channels,

- determining, from said statistics of the indirect channels and estimates of the said direct channels, M bit rates to be allocated to the M sources for the transmission of the said data frame.

ANNEX 1

The individual cut event indication of the source s after the interval t (round t) of transmission depends on the vector of selection of the nodes, of the vector allocation of sub-bands and clearance decoded sources at the end of the previous interval, t-1. It is further conditional on knowing the achievements of the direct links channel (channel gains) as well as . denotes the set of vectors of selection (therefore selected nodes) and vectors allocation with their set of decoded sources partner determined for the intervals (rounds) preceding the interval t, and the game of sources decoded by the destination. It should be noted that is the selection vector of source nodes transmitting during the first phase of transmission, that is the allocation vector of sub-bands allocated for each source during the first phase of transmission and that is the set of sources decoded by the destination at the end of the first phase.

The common break event indication for the source subset after the time interval t (round t) is the event that at least one source of the subgame is not decoded correctly by the destination at the end of this interval t. Subsequently, the dependencies of To and to are omitted to simplify the notations. We notice the play of the sources not successfully decoded by the destination at the end of the time interval t (round ).

From an analytical point of view, the common cut event indication of a subset of sources intervenes ie is satisfied if the vector of the bit rates of these sources is not included in the corresponding MAC capacity region.

Thus, for a subset of sources given, for a vector candidate of selected nodes and the vector allocation of corresponding sub-bands, this event can be expressed in the form:

translates the non-respect of the MAC inequality associated with the sum bit rate of the sources contained in :

with

• the time interval index (round) of the second phase with the convention that corresponds to the end of the first phase (transmission phase), ,
• the index corresponding to the source node, ,
• the index corresponding to any node (source and relay), ,
• the number of sub-bands allocated to the node for the time interval (round) ,
• the number of sub-bands allocated to the source by the destination for the first phase,

with , represents the set of interfering sources, is one if on the one hand the intersection between the set of sources correctly decoded by the node at the interval and the whole is not empty and on the other hand the intersection between the set of sources correctly decoded by the node at the interval and the set of interfering sources is empty,

• represents the logical "and",
• represents Iverson's brackets ie which gives the value 1 if the event is satisfied and the value 0 if not,
• the mutual node fading information block at the destination for the sub-bands allocated to the node at the time interval :

Or is the mutual information between the node to which the sub-band is allocated to time interval (round) and the destination . The mutual information depends on the power transmitted on the sub-band of the channel ie between the knot and the destination with the total power of this node. If node i is not selected at the time interval then the mutual information block is zero.

• the source fading mutual information block at the destination , For And data, at the time interval corresponding to the transmission phase (first phase),
• is the flow used during the first phase with the number of bits of useful information transmitted over channel uses.

Subsequently, the outage event for a given source s is defined in the form:

which is by definition the intersection of all common outage events corresponding to a set of sources including source s. A source s is in cut if and only there is no set of sources understanding her which can be associated with error-free decoding, i.e., . He comes :

This cut event indication indicates whether a source is decoded without error ( ) or if it is cut off . This approach makes it possible to predict the result of the implementation of a parity check (CRC check) without going through the simulation of the entire chain of transmission (coding modulation) and reception (detection/demodulation, decoding ). In this, it defines an abstraction of the physical layer. Certain adjustments obtained by simulation (called calibration within the framework of the abstractions of the physical layer) for a given coding scheme can be carried out by introducing weighting parameters of the mutual information and/or of the SNRs of the links.

APPENDIX 2 - GA Algorithm

Algorithm 1 – Monte-Carlo simulations to fix the initial value of the source using a “Genie Aided” (GA) approach :

1. (Initialization of maximum average spectral efficiency)
2. 1st loop ^on from 1 to ( = number of available modulation and coding schemes )
3. , The source adopt flow ( )
4. (Initialization of the Monte-Carlo achievement counter)
5. (Initialization of the counter of the sum of retransmission cycles used during the second phase)
6. Random selection of based on the probability distribution of the direct links ( , )
7. 2 ^th loop on from 1 to Nb_MC (example Nb_MC=1000)
8. Random selection of based on the probability distribution of indirect links ( , gold ).
9. = ( represents the channel realization at a current Monte-Carlo iteration , based on and on the current at iteration )
10. Initialization of to the value Ø (list containing the mutual information of all the links)
11. Initialization of activated_vector_list(0) to the value Ø (list containing the vector chosen at each retransmission phase)
12. Calculation of ( ) for all nodes . ( is an element of )
13. whether SO
14. continue or return to point 7, (no update of variables And ).
15. end of if
16. 3 ^th loop on from 1 to

1. Node vector selection by the destination using a two-step defined random selection strategy (i) infer from a uniform discrete variable whether a subband is occupied (until at least one subband is occupied) (ii) deduce from a uniform discrete variable which node is selected if the subband is occupied
2. Add And to activated nodes list activated_nodes_list(t) .
3. Calculate ( ) for all nodes . ( is an element of )
4. 4 ^th loop on from 1 to

1. end of 4th loop
2. whether SO

1. Interruption of the 3rd ^loop , go to point 33 (without changing the value of )
2. end of if
3. whether SO

1. .
2. end of if
3. end of 3rd loop

1. end of 2 ^th loop
2. Determining the Average Source Outage Probability for flow :
3. Determination of the average number of cycles used during the second phase:

1. whether And

1. end of if
2. end of the 1 ^time loop

APPENDIX 3: BRD Algorithm

Algorithm 2 – Best response dynamics (BRD) algorithm

1. ( Counter of the number of iterations)
2. Initialization of all available bit rates:
3. Initializing throughputs using a starting point ( init )

1. (In order to allow the while loop to start )
2. As long as for everything

1. For To do ( For each source, choose the best knowing all the other flow values )

Such as (which satisfies the condition)

1. End of for
2. End of while

Algorithm 3 - Monte-Carlo simulations to determine the spectral efficiency and the used in the BRD algorithm (step 8) :

1. , individual_counter[M]= {0,…,0}

Initialization of : cumulative number of cycles of the second phase (retransmission phase) on the Nb_MC loop

Individual_counter[M] Beam Initialization: Each individual_counter[i] element contains the number of individual interrupt event indications for the user on the Nb_MC loop

1. Random selection of based on the probability distribution of the direct links ( , ).
2. 1st loop on j from 1 to Nb_MC ⁽ example Nb_MC=100)
3. Random selection of based on the probability distribution of indirect links ( , gold ).
4. = ( represents the channel realization at a current Monte-Carlo iteration , based on and on the current at iteration )
5. Initialization of to the value Ø (list containing the mutual information of all the links)
6. Initialization of activated_vector_list(0) to Ø (list containing the vector chosen at each retransmission phase)
7. 2 ^th loop on t from 1 to
8. Calculation of ( ) for all nodes . ( is an element of )
9. = check_outage( , activated_nodes_list );
10. whether SO
11. ;
12. ;
13. Interrupt or exit loop 2 to go to point 3;
14. Otherwise
15. get_decoding_set( );
16. get_decoding_set( );
17. get_decoding_set( );
18. Node vector selection by destination (using a selection strategy)
19. Add And to activated nodes list activated_nodes_list(t) .
20. whether SO
21. ;
22. Calculation of ( ) for all nodes .
23. get_decoding_set( ));
24. 3 ^th loop on s from 1 to M.
25. whether SO
26. individual_counter[s]= individual_counter[s]+1;
27. End if
28. End of 3rd loop
29. End if
30. End of otherwise
31. End of 2 ^th loop
32. End of 1 ^time loop
33. 4 ^th loop on s from 1 to M
34. individual_counter[s]/ Nb_MC
35. End of 4 ^th loop
36. ;

Calculation of the spectral efficiency in step 8 of the BRD algorithm using

check_outage evaluates a set's common outage event indication

check_outage( , );

1. Initialization: , card = | |;
2. 1st loop on j from 1 to (2 ^card -1) (checking the ^interrupt event indication corresponding to each subset of )
3. Initialization: Successively take a subset , to stare , And (initialization of current mutual information, as well as total throughput and interfering source nodes for a subset ).
4. 2 ^th loop over k from 1 to M
5. whether SO
6. ;
7. ;

1. End if
2. End of the 2 ^th loop
3. 3 ^th loop on from 1 to ( is the node vector selected at cycle )
4. 4 ^th loop on from 1 to ( is the selected node vector at cycle )
5. whether And SO
6. ;
7. end if
8. End of the 3 ^th loop
9. End of the 4 ^th loop
10. whether SO
11. ;
12. Interrupt or exit loop 1 to go to step 23;
13. end if
14. End of the 1 ^time loop
15. back out

get_decoding_set calculates source set correctly or largest set which does not give a common interrupt event indication

get_decoding_set( );

1. (Initialization of the decoding set to phi)
2. 1st loop on card from M to 1 (loop on all the cardinality ^of the subsets)
3. 2nd loop ^of to 1 (loop on all subsets of a given cardinality)
4. Successively choose the subsets of sources: , Or

= check_outage( , );

1. whether SO
2. Interrupt or exit loop 2 to go to step 9;
3. End if
4. End of the 2 ^th loop
5. whether SO
6. ;
7. Interrupt or exit loop 2 to go to step 13;
8. End of the 1 ^time loop
9. feedback

Claims (15)

Method for receiving at least one data frame, in a communication system implementing M sources, possibly L relays and a destination, with And ,
said M sources being configured to transmit, during a first transmission phase, messages over K time slots and B frequency sub-bands, with And , Or And , and a selection of said M sources and of said L relays being configured to transmit, during a cooperative transmission phase, a signal representative of at least one of said messages on time slots and B frequency sub-bands, according to a scheduling chosen by said destination,
the data transmitted on the said ( ) time slots forming a data frame,
characterized in that said destination implements, for at least one data frame and the associated scheduling, an initial link adaptation phase, prior to said first transmission phase of said frame, comprising:
- the estimation (21) of the transmission channels associated with the direct links between said sources and/or relays and said destination, called direct channels,
- obtaining (22) statistics of the transmission channels associated with the indirect links between said sources and/or relays and said destination, called indirect channels,
- the determination (23), from said statistics of the indirect channels and estimates of the said direct channels, of M bit rates to be allocated to the M sources for the transmission of the said data frame. Method according to claim 1, characterized in that said forward channel estimation is performed for each data frame. Method according to either of Claims 1 and 2, characterized in that the said direct channels are estimated from at least one reference signal received by the said destination, and transmitted by the said sources and/or the said relays. A method according to any one of claims 1 to 3, characterized in that said indirect channel statistics follow a Dirac distribution around the square root of a signal-to-noise ratio of the corresponding indirect channel. A method according to any one of claims 1 to 4, characterized in that said obtaining of indirect channel statistics is implemented for a set of data frames. Method according to any one of claims 1 to 5, that it comprises receiving a notification of modification of at least one statistic of one of said indirect channels, and an update of said stats. Method according to any one of Claims 1 to 6, characterized in that the said determination of M rates to be allocated to the M sources implements a maximization of a quality of service metric of said communication system, knowing the estimation of the channels direct. Method according to Claim 7, characterized in that the said maximization is expressed in the form:

under constraint that:

with :
all sources;
a variable representing the flow to be allocated to source i, ,
the number of sub-bands allocated to source i during the first transmission phase,
estimation of direct channels,
the number of cooperative transmissions used during the cooperative transmission phase,
the maximum number of cooperative transmissions allowed during the cooperative transmission phase,
an average of the number of cooperative transmissions used during the cooperative transmission phase, knowing the estimate of the direct channels,
an average of the number of messages transmitted by the source i not decoded by the destination at the end of the cooperative transmission phase, knowing the estimation of the direct channels,
the acceptable average error rate with respect to a QoS quality of service, knowing the estimate of the direct channels. Method according to any one of Claims 1 to 8, characterized in that the said determination of M bit rates to be allocated to the M sources implements an iterative algorithm based on the determination of a bit rate to be allocated to the source i, for each , assuming the flows to be allocated to the other known sources. Method according to Claim 9, characterized in that the said iterative algorithm is initialized using a “Genie Aided” type algorithm. Method according to any one of Claims 1 to 10, characterized in that the said determination of M rates to be allocated to the M sources is implemented jointly with the determination of an optimized scheduling for the said frame. Method according to any one of Claims 1 to 11, characterized in that it comprises the transmission to the said sources of at least one item of information representative of the said bit rates to be allocated to the M sources. Destination of at least one data frame, in a communication system implementing M sources, possibly L relays and said destination, with And ,
said M sources being configured to transmit, during a first transmission phase, messages over K time slots and B frequency sub-bands, with And Or And , and a selection of said M sources and of said L relays being configured to transmit, during a cooperative transmission phase, a signal representative of at least one of said messages on time slots and B frequency sub-bands, according to a scheduling chosen by said destination,
the data transmitted on the said ( ) time slots forming a data frame,
characterized in that said destination comprises at least one processor configured to implement, for at least one data frame and the associated scheduling, an initial link adaptation phase, prior to said first transmission phase of said frame, including:
- estimate transmission channels associated with direct links between said sources and/or relays and said destination, called direct channels,
- obtain statistics of the transmission channels associated with the indirect links between said sources and/or relays and said destination, called indirect channels,
- determining, from said statistics of the indirect channels and estimates of the said direct channels, M bit rates to be allocated to the M sources for the transmission of the said data frame. Computer program comprising instructions for implementing a method according to any one of Claims 1 to 12 when this program is executed by a processor. System including sources ( ), Most often is "possibly relay ( ) and a destination ( ), , , for an implementation of a reception method according to any one of claims 1 to 12.