Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
  • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
  • H04L1/0017—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy where the mode-switching is based on Quality of Service requirement
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
  • H04L1/0019—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy in which mode-switching is based on a statistical approach
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0053—Allocation of signaling, i.e. of overhead other than pilot signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
  • H04L1/0076—Distributed coding, e.g. network coding, involving channel coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1812—Hybrid protocols; Hybrid automatic repeat request [HARQ]
  • H04L1/1819—Hybrid protocols; Hybrid automatic repeat request [HARQ] with retransmission of additional or different redundancy
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L2001/0092—Error control systems characterised by the topology of the transmission link
  • H04L2001/0097—Relays
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
  • H04L5/0035—Resource allocation in a cooperative multipoint environment
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/003—Arrangements for allocating sub-channels of the transmission path
  • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver

Definitions

• 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.
• 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.
• 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 networks of sensors.
• 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).
• OMAMRC Orthogonal Multiple- Access Multiple-Relay Channel
• the M sources are configured to transmit messages over K time slots and B frequency sub-bands, with K > 1 and B > 1.
• 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 over T used time intervals and B frequency sub-bands.
• a frame consists of the data transmitted over the (K + T used ) time slots.
• 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.
• Various link adaptation techniques are known. For example, if the radio conditions vary rapidly, ie 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 (in English “Fast Link Adaptation” or FLA). The difference between these slow and fast link adaptation techniques lies in the knowledge of the various links in the system by the destination.
• 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).
• 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.
• 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 costly, since it requires an important exchange of control information between the sources, the relays and the destination.
• 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.).
• CDI information is assumed to be constant over several hundred frames.
• 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 for maximizing the average spectral efficiency (utility metric) within the considered system constrained to respect an individual quality of service (QoS) per source.
• QoS quality of service
• n t ⁇ is the number of sub-bands allocated to a user i for transmission over the time interval corresponding to the first transmission phase, or over a time interval t>0 corresponding to the cooperative transmission phase.
• K i the transmitted payload ⁇ F etime ⁇ frequency sources (also called “use of channel” 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 ⁇ to 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.
• the break indication is defined as a random variable that takes the value 1 if source i is not decoded correctly after the first phase of transmission and at each cooperative transmission l until If source i is decoded correctly before or on transmission t, the cut indication takes the value 0.
• the source i will not be decoded correctly during a frame (because the number transmission 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 time. If a fast link adaptation technique is implemented, the overall spectral efficiency can be expressed as: with: an individual break event for the source ⁇ at the end of the transmission phase cooperative 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):
• the fast link adaptation technique based on total knowledge of the global transmission channel (CSI) makes it possible to allocate throughputs to sources in a precise manner. Nevertheless, in a MAMRC system, the number of channels/links grows exponentially with the number of nodes (source or relay).
• 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 said M sources being configured to transmit, during a first transmission phase, messages over K time slots and B frequency sub-bands, with and , and a selection of said M sources and said L relays being configured to transmit, during a cooperative transmission phase, a signal representative of at least one of said messages over time slots and B frequency sub-bands, according to a scheduling chosen by said destination, the data transmitted over said time slots forming a data frame.
• said destination implements, for at least one data frame and the associated scheduling, an initial phase of link adaptation, prior to said first phase of transmission of said frame, comprising: the estimation transmission channels associated with the direct links between said sources and/or relays and said destination, called direct channels, - obtaining statistics of the transmission channels associated with the indirect links between said sources and/or relays and said destination, called channels 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.
• 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.
• 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.
• CDI distribution/statistic of the set of channels
• 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.
• 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.
• 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.
• 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 the techniques of fast link adaptation on the direct channels to optimize the bit rate allocation, and of slow link adaptation on the indirect channels to limit the exchange of control information.
• the proposed solution can therefore be considered as an intermediate link adaptation solution, based on partial knowledge of the global channel at the destination.
• 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 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
• 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 interval (time slot). Such a method is therefore well suited for demanding services in terms of latency.
• 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.
• a reference signal can be a sounding reference signal (SRS, as defined in the 3GPP LTE/NR standard).
• SRS sounding reference signal
• such reference signals can be transmitted by the sources and/or the relays, upon receipt of a request from the destination.
• such a request can be broadcast by the destination in an OMAMRC communication system prior to the transmission of a first data frame.
• the reference signal may be a demodulation reference signal (DMRS, as defined in the 3GPP LTE/NR standard).
• DMRS demodulation reference signal
• such reference signals can be transmitted together with the data frames during the first transmission phase or the cooperative transmission phase of a frame, and be used to update the direct channel estimate (ie when a first direct channel estimate is available at the destination).
• 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.
• 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.).
• 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 envisaged, such as a Dirac distribution.
• 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.
• 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.
• 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.
• a notification is for example of the “Event driven CDI update” type.
• the destination can implement an update of the statistics of the indirect channels upon receipt of such a notification.
• 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 estimate of the direct channels.
• 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.
• said maximization is expressed in the form: ⁇ under constraint that: with: S the set of sources, a variable representing the bit rate to be allocated to the source e number of sub-bands allocated to source i during the first transmission phase, 'estimate of the direct channels, is the cutoff 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 transmission phase cooperative, an average of the number of cooperative transmissions used during the phase of cooperative transmission, knowing the estimation of 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 estimate of the direct channels, the average error rate acceptable with respect to a quality of QoS service, knowing the estimation of the direct channels.
• 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.
• said determination implements an iterative algorithm of “Best Response Dynamics” type.
• Such an algorithm allows in particular to reduce the complexity of the multidimensional maximization function.
• such an iterative algorithm can be initialized using a “Genie Aided” type algorithm.
• the determination of the M bit rates to be allocated to the M sources is implemented jointly with the determination of an optimized scheduling for said frame. One then seeks to solve a joint problem of optimization of the allocation of the bit rates and the allocation of the resources.
• 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 coding, bitrate itself, etc.).
• information for example a modulation and coding scheme (in English “Modulation and Coding Scheme” or MCS), an index of a modulation scheme and coding, bitrate itself, etc.
• MCS Modulation and Coding Scheme
• bitrate bitrate itself
• Such information is broadcast by the destination, or transmitted in a control channel specific to each source or common to the various sources.
• the increase in bit rates can be carried out via very limited bit rate 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 above. It is for example a base station or an eNodeB.
• the invention further relates to a system comprising sources , optionally L 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.
• 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 capable of implementing the reception method.
• 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.
• FIG. 1 illustrates an example of an OMAMRC type communication system in which the invention can be implemented
• ⁇ [Fig 2] presents the main steps implemented by a destination according to one embodiment of the invention
• ⁇ [Fig 3] illustrates the information exchanged between the sources/relays and the destination according to one embodiment of the invention
• ⁇ [Fig 4] illustrates an example of bit rate allocation for sources in an OMAMRC type communication system
• ⁇ [Fig 5] presents the simplified structure of a destination node according to a particular embodiment. 5.
• 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 d.
• 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 to the relays (“feedback”), for example in control channels between the destination and each source or relay (shown in dotted lines in FIG. 1).
• the M sources are configured to transmit, during a first transmission phase, messages on K time slots and B frequency sub-bands, with and The first K 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 cooperative transmission phase, a signal representative of at least one of the messages from the sources over time slots and B frequency sub-bands.
• the T time intervals following the K first time slots are therefore dedicated to transmissions including at least 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.
• 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.
• a relay node in "full duplex" mode, 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.
• the source and relay nodes operate in a "half-duplex" mode. According to this "half-duplex" mode, a relay node can listen to the transmission of the other nodes (source, relay) at each time slot when it is not transmitting, and a source node can listen to the transmission of the other nodes (source, relay ) at each timeslot when it is not transmitting.
• time-frequency resources For each time interval, there are time-frequency resources, with ⁇ the number of sub-bands available and F 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.
• PBR Physical Resource Block
• B is the number of PRB (sub-bands) available for the frequency band considered.
• the data transmitted over the time slots forms a data frame.
• a frame is therefore a set of consecutive time slots used for the transmission of messages from the M sources according to a schedule defined by the destination. It can thus be considered that a frame is composed of a first transmission phase and of a cooperative transmission phase.
• the first phase of transmission includes time intervals, during which the M sources can send their message orthogonally using the orthogonal subbands in frequency and/or time slots, on one or more subbands allocated to each source. If ⁇ ⁇ 1, the time interval corresponds to the first phase of transmission.
• the cooperative transmission phase includes time slots.
• a scheduler allocates at least one sub-band or one band 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”).
• 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.
• the partitions can be different between all time intervals, including the first.
• the selection of the nodes and the allocation of the subbands 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 can exceed time intervals, where ⁇ is the maximum number of cooperative transmissions allowed during the cooperative transmission phase
• ⁇ is the maximum number of cooperative transmissions allowed during the cooperative transmission phase
• none, one or more subbands can be allocated to a node.
• the orthogonality of the communication system can be obtained by time division multiplexing (TDM, with relying on the use of several time slots each allocated to a different source, or by frequency multiplexing based on the use of several frequency bands each allocated to a different source.
• TDM time division multiplexing
• the transmission of a frame can be preceded by a link adaptation phase, during which bit rates are allocated to the various sources.
• bit rates For example, a finite set of bit rates (or modulation and coding schemes) is considered, and a bit rate from among the finite set of bit rates is allocated to each source.
• 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, ie the allocation of speeds to the different sources.
• FIG. 2 illustrates the main steps implemented by the invention, in a communication system as described above.
• 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
• the direct channels that the destination can directly estimate are the channels
• 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.
• indirect channels are the channels
• this step 22 for obtaining takes account of the estimation of the direct channels (since a statistic is determined only for the indirect channels).
• the destination can determine, during a determination step 23, M throughputs 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 several 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 (ie the statistics, for example SNR, of the links which evolve very slowly over time).
• the proposed solution can be considered to be of the FLA fast link adaptation type.
• 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”.
• the link adaptation phase can be implemented frame by frame, or for a group of a few frames, before the first frame transmission phase. It can in particular be updated when a variation of a direct or indirect channel is detected.
• the information exchanged between the transmitting nodes (sources or relays, s/r) and the destination (d) according to an embodiment of the invention.
• the destination d can broadcast a message 31 requesting the broadcasting of a reference signal (“SRS request”).
• SRS request a reference signal
• the sources and/or relays can each transmit a reference signal 32.
• the destination can directly estimate the transmission channels associated with the direct source-to-destination and relay-to-destination (CSI) links, ie determine the gains of the direct links.
• CSI direct source-to-destination and relay-to-destination
• 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.
• 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).
• the destination may broadcast a message requesting to obtain such metrics (“CDI request”), and receive return messages (“CDI feedback”) from sources / relays of indirect links.
• CDI request a message requesting to obtain such metrics
• CDI feedback from sources / relays of indirect links.
• the sources transmit to the destination the statistics of the source-source or source-relay links
• 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 bit rates to be allocated to the sources for the transmission of the first frame.
• 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.
• each source 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.
• the data from the different sources form the first frame, corresponding to a first transmission phase and a cooperative transmission phase.
• 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 estimate of the direct channels to the destination.
• DMRS pilot symbols
• 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 On 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.
• the data from the different sources form the second frame, corresponding to a first phase of transmission and a phase of cooperative transmission. 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 of the sources being decoded.
• 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.
• forward channel estimates can be updated for every frame, or for a few frames.
• 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 .
• CDI request a message requesting new statistics
• CDI feedback return messages
• 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.
• the proposed approach is based 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 ).
• CRC check parity check
• the proposed link adaptation takes into account the knowledge of the distribution (ie distribution statistics) of the channel on 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, we seek to maximize the real average throughput, that is to say the overall throughput over a set of frames.
• 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; - the sources, the relays, and the 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 bits of information from each source i to determine if a message is correctly decoded or not - the links between the different nodes suffer from additive noise and fading.
• the fading gains are fixed during the transmission of a frame performed for a maximum duration of time slots (with according to the example described), but may change independently from frame to frame. 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).
• CTR Channel State Information at Receiver channel State Information at Receiver
• the information used to estimate the direct channels is transmitted in unicast control channels (from a source or a relay, towards 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, to the destination) assumed to be error-free
• the sources transmitting to the destination the statistics of the source-source links and possibly of the source-relay links
• the relay transmitting to the destination the statistics of the relay-relay links and possibly of the source-relay links
• the statistics of the indirect channels can be transmitted to the destination when a change is detected, or for example every hundred frames.
• the element vector designates the sub-band and the node selected active (ie transmitting) during this time interval t in this sub-band 'order in the vector corresponds to the order of the subbands
• - is the vector of dimension M+L of the number of subbands 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 , of the vector ⁇ ⁇ denotes the number of subbands allocated to node i at time slot .
• 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 relays, and between sources and 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.
• estimate or “implementation” are therefore considered equivalent below, and used interchangeably.
• a new throughput allocation strategy is proposed (fast link adaptation with partial knowledge of CSI), which does not depend on the realization but which changes for each realization
• the bit rate allocated to each source denoted does not change with conditional expectation
• 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
• the destination can use as an approximation of who corresponds to the global spectral efficiency knowing is the global spectral efficiency by knowing frame and so to get the bitrate per frame, the destination therefore seeks to determine the internal variable, using on the one hand the CDIs of the indirect links, and on the other hand, the CSIs have direct links.
• the global spectral efficiency based on the knowledge of the CSI of the direct links can be written: ⁇ individual cut-off element equal to 1 for source i, based on the probability distribution of the indirect links knowing the CSIs of the direct links.
• the direct links are the links and the indirect links are the links
• 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.
• the throughput allocation is given for a known realization of the direct channels, as illustrated in figure 4.
• the average flow rate ⁇ can be determined taking into account hope ⁇ on the achievements of the direct links.
• the spectral efficiency based on a 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 interval t for the cooperative transmission phase.
• the spectral efficiency therefore depends on the selection of nodes and the allocation of subbands.
• the allocation of bit rates ie the determination of the bit rates to be allocated to the M sources
• aimed at achieving the best spectral efficiency therefore implements a maximization of a quality of service metric of the communication system with or without constraint per source.
• ⁇ under the constraint that , for all i belonging to S, with : and ⁇ ⁇ ⁇
• ⁇ ⁇ ⁇ represents a set of interfering sources
• ⁇ represents the logical "and”
• ⁇ represents the Iverson brackets ie which gives the value 1 if the event ⁇ is satisfied and the value 0 if not
• the condition ensures that the considered node 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 set is not empty), and that node i considered at time interval l has not decoded any interfering node (ie the intersection between the set of sources correctly decoded by node i at l interval and the set of interfering sources is empty).
• 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 the flow rates to be allocated to the different sources we must therefore solve a multivariate optimization problem, 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 overcome the calculation of the integral for the outage event taking into account the realization of the channel ⁇ using a Monte Carlo simulation method.
• the expression for the cut event taking into account the realization of the channel can be expressed in the following approximate form: where is a realization of the channel ⁇ based on the probability distribution of the 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, the distribution of channel h ⁇ , ⁇ whose SNR is ⁇ ⁇ , ⁇ is approximated by Such a variant may slightly reduce the performance of the communication system, but offers a solution for simplifying the complexity of the rate allocation algorithm.
• the problems of allocating the bit rates to the sources and of selecting the nodes can be solved jointly.
• 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. It is considered for example that the node selection strategy is based on a selection metric of mutual fading information block type.
• 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 time interval ⁇ , ⁇ ⁇ 0 (“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 subbands only to the sources, by allocating at least one subband 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 ⁇ ⁇ 0.
• an exhaustive search can be implemented for the joint resolution of the problems d flow allocation and node selection.
• a BRD Best ⁇ Response Dynamic
• Such an algorithm is notably presented in appendix 2.
• a solution is sought for each user/source in an iterative manner.
• a suboptimal solution for the BRD algorithm is based on the determination of an optimal bit rate for a user/source for a given time interval, considering that the other users/sources are inactive, ie do not transmit data.
• the BDR algorithm comprises two phases: an initialization phase and an iterative correction phase.
• initial flow values are allocated to the various sources.
• Different techniques can be implemented for the initialization phase: random initialization, initialization from a fixed value, initialization of Genie Aided type, etc.
• 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.
• the memory of the sources 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.
• 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.
• 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 implementation of the steps of the reception method described above, according to the instructions of the computer program 53, to: ⁇ estimate transmission channels associated with the 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 transmission of said data frame.
• the individual mute event indication ⁇ of the source s after the transmission interval t (round t) depends on the node selection vector ⁇ ⁇ , the subband allocation vector and the set , of sources decoded at the end of the previous interval, t ⁇ 1. It is also conditional on knowledge of the achievements of the channel of direct links (of gains of the channel) as well as d designates the set of selection vectors (therefore nodes selected) and allocation vectors with their set of decoded sources associated determined for the intervals (rounds) preceding the interval and the game ⁇ of sources decoded by the destination.
• the source node selection vector transmitting during the first phase of transmission which is the sub ⁇ granting allocation vector bands allocated for each source during the first phase of transmission and what is the set of sources decoded by the destination at the end of the first phase.
• the common break event indication for the sub source set after time interval t (round t) is the event that at least one source of the subset is not decoded correctly by the destination at the end of this interval t. Subsequently, the dependencies of ⁇ ⁇ , ⁇ are omitted to simplify the notations.
• the set of sources not successfully decoded by the destination at the end of 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.
• this event can be expressed as: translates the non ⁇ respect of the MAC inequality associated with the sum 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 subbands allocated to node i for the time slot (round) ⁇ the number of subbands allocated to the source by the destination for the first phase, with ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ represents the set of interfering sources is worth one if on the one hand the intersection between the set of sources correctly decoded by node i 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
• the mutual information depends on the power transmitted on the sub-band of the channel ie between the node a ⁇ , ⁇ 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 outage event for a given source s is defined in the form: which is by definition the intersection of all common cut events corresponding to a set of sources ⁇ including source s.
• a source s is out of order if and only there is no set of sources ⁇ comprising it which can be associated with error-free decoding, come
• This cut event indication indicates if a source is decoded without error ( 0) or if it is in cutoff ⁇
• CRC check parity check
• This approach makes it possible to predict the result of setting 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).
• CRC check parity check

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