Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/345—Interference values
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
  • H04B7/0621—Feedback content
  • H04B7/063—Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
  • H04B7/0689—Hybrid systems, i.e. switching and simultaneous transmission using different transmission schemes, at least one of them being a diversity transmission scheme
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/021—Estimation of channel covariance
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0224—Channel estimation using sounding signals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/382—Monitoring; Testing of propagation channels for resource allocation, admission control or handover
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/024—Channel estimation channel estimation algorithms
  • H04L25/0242—Channel estimation channel estimation algorithms using matrix methods
  • H04L25/0248—Eigen-space methods

Definitions

• the invention relates to the field of wireless communications.
• the invention proposes a technique making it possible to optimize the formation of beams obtained from an array of antennas, so as to improve the transmission of information between a transmitter and a receiver, in the uplink channel as well as in the channel. descending.
• the invention finds applications in any system based on beamforming, in particular in radio communication networks according to the 4G or 5G standards defined by the 3GPP, WiFi communication networks according to the various IEEE 802.11 standards, etc.
• the transmitter can be a base station, for example of the eNodeB type (in English “evolved Node B”) for networks based on LTE or LTE Advanced technologies, or else an access point WiFi, etc.
• a receiver can be a terminal such as a smartphone, tablet, connected object, etc.
• the transmitter can be a terminal, and the receiver a base station.
• Beamforming, or precoding is a signal processing technique used in antenna or sensor arrays for directional transmission or reception of signals.
• the transmitters and/or receivers can focus the radiation of the transmitted wave in a particular direction, which makes it possible to obtain spatial selectivity.
• Beamforming is achieved by combining the elements of a phase and amplitude controlled antenna array so that: the signals combine constructively in particular directions, resulting in an increase in useful power received, the signals combine destructively in the other directions, resulting in a decrease in the power of the received interference.
• a complex coefficient called the precoding coefficient
• All of these coefficients form a precoding matrix.
• the precoding coefficients must be chosen correctly.
• the fundamental problem for the selection of this precoding is the acquisition of the knowledge of the channel in transmission or “transmit Channel State Information” (CSI) in English.
• CSI Channel State Information
• the first technique based on the use of a precoding dictionary, denoted CSI-D is based on the use of a limited return path between the receiver and the transmitter and on the precoding dictionary (hence the “D” of CSI-D, for dictionary).
• the transmitter emits a reference signal, also called pilot signal.
• a reference signal is typically denoted CSI-RS in the 4G and 5G standards, for “Channel State Information - Reference Signal”.
• the receiver estimates on the one hand the transmission channel between the transmitter and the receiver (/.e. in the direction transmitter to receiver), and on the other hand a covariance matrix of the interference, representative of the spatial structure of the interference between the receiving antennas.
• the receiver Based on the estimation of the transmission channel between the transmitter and the receiver and the spatial characteristics of the interference, the receiver chooses the precoding matrix to be used by the transmitter from the finite precoding dictionary.
• This precoding dictionary is generally defined by a standard, such as the 4G standard or the 5G standard.
• the receiver then sends this precoding choice back to the transmitter via the limited return channel, for example in the form of an indicator of the “Precoding Matrix Indicator” (PMI) type.
• the feedback of the precoding choice can optionally be accompanied by a channel quality indicator (or "Channel Quality Indicator", CQ.I) and/or an indicator of the number of spatial layers ("Rank Indicator", RI ).
• CSI-R is based on the reciprocity of the channel between transmitter and receiver (hence the R, for reciprocity).
• R for reciprocity
• the transmission channel between the receiver and the transmitter is the same as the transmission channel between the transmitter and the receiver (/.e. in the direction transmitter to receiver).
• the channel includes the effects of the radiofrequency chains which are not a priori reciprocal in transmission and reception, but which can be calibrated to become so.
• the CSI-R technique thus assumes the use of the same frequency resources and a time separation of the uplink and downlink channels, or “Time Division Duplex”, TDD).
• the receiver transmits a reference signal, for example of the SRS type (for “Sounding Reference Signal”) in the 4G and 5G standards.
• the transmitter estimates the transmission channel between the receiver and the transmitter (/.e. in the receiver to transmitter direction) and deduces therefrom by reciprocity the transmission channel between the transmitter and the transmitter. receiver (/.e. in the direction from sender to receiver).
• the transmitter can select a precoding matrix to be used. For example, the transmitter determines a precoding matrix according to a criterion of maximizing the signal to noise ratio (SNR) or the predicted bit rate, neglecting the spatial structure of the interference (or covariance of the interference).
• SNR signal to noise ratio
• the receiver estimates an interference covariance matrix and returns a compressed version of this interference covariance matrix to the transmitter.
• This compressed version can for example take the form of the / largest eigenvalues of the covariance matrix (the latter being of dimension NR X NR, where NR is the number of reception antennas of the receiver).
• the covariance matrix of the interference being positive-definite, it is ortho-diagonalizable, and it is easy to deduce its eigenvalues and to order them.
• the CSI-R1 technique although it allows the transmitter to know the transmission channel without quantization, does not allow the transmitter to know the interference in reception. Indeed, such a technique determines the precoding matrix to be used by neglecting the spatial structure of the interference, the interference in reception not being reciprocal. It is then possible that the precoding on transmission according to the CSI-R technique corresponds to directions where the interference is the strongest.
• Raising the covariance of the interference from the receiver to the transmitter according to this CSI-R1 technique is difficult to envisage, because it would consume too much of the quantity of return channel.
• the precoding matrix based on the CSI-R1 is therefore obtained without taking into account the covariance of interference or, what comes to the same thing, by considering it unstructured.
• the CSI-D and CSI-R2 techniques (respectively via a predetermined dictionary and via a return of a compressed version of the covariance matrix of the interference) only allow the sender to determine a quantized version (therefore approximate ) of the precoding to use.
• this precoding is taken from a predetermined precoding dictionary
• this precoding is taken from an approximate version of the covariance matrix of the interference.
• the invention improves the situation.
• the invention proposes a solution that does not have all of these drawbacks, in the form of a communication method implemented in a transmission system comprising a transmitter and a receiver
• the communication method implemented at the level of the receiver, is of the type comprising the estimation of a covariance matrix of the interference, representative of the spatial structure of the interference in reception.
• This communication method is remarkable in that it also implements: the selection of a technique for acquiring knowledge of the transmission channel, from a group of techniques comprising a first technique based on a compressed version of said interference covariance matrix and at least one second technique, and the transmission to said transmitter of at least one piece of information allowing the transmitter to determine a precoding matrix taking into account the interference covariance matrix according to said technique acquisition of knowledge of the transmission channel selected by said receiver.
• this communication method makes it possible to simulate the implementation of different techniques for acquiring knowledge of the channel in transmission, and to select the technique considered to be optimal, for example that offering the best transmission rate for a transmission rate. error given.
• the expression "the information allowing the sender to determine a precoding matrix taking into account the covariance matrix of the interference in reception according to a transmission channel knowledge acquisition technique” is abbreviated as information relating to such a technique.
• the feedback to the transmitter of at least one piece of information relating to the technique for acquiring knowledge of the channel selected by the receiver allows the transmitter to determine a data transmission format from this information, in particular a precoding matrix (and possibly a modulation and coding scheme and/or a number of spatial layers to be used in transmission), then to transmit the data using this transmission format.
• a precoding matrix and possibly a modulation and coding scheme and/or a number of spatial layers to be used in transmission
• the first technique is of the CSI-R2 type.
• Said at least one second technique can be of the CSI-R1, CSI-D, etc. type.
• the selection of a technique for acquiring knowledge of the transmission channel comprises the prediction of a transmission parameter associated with each technique of the group of techniques and the selection of the technique whose said transmission parameter meets a first criterion.
• the transmission parameter is of the transmission bit rate type
• the first criterion is of the best bit rate type between the bit rates obtained by the simulation of the various techniques for acquiring knowledge of the channel.
• the selection of a technique on the basis of a transmission parameter makes it possible to improve the quality of the transmission at the within the transmission system.
• said prediction of the transmission parameter associated with a given technique of the group of techniques comprises: for each sub-band k of a plurality of channel frequency sub-bands between said transmitter and said receiver, the obtaining a set of precoding matrices, the selection, in each set of precoding matrices associated with a sub-band, of a precoding matrix so that the transmission parameter resulting from this selection respects a second criterion.
• the transmission parameter is of the transmission bit rate type
• the second criterion is of the best bit rate type between the bit rates obtained by the different combinations of precoding matrices.
• This prediction using a set of precoding matrices, also called a dictionary advantageously makes it possible to determine an optimal precoding for the technique which will ultimately be selected.
• This precoding also guarantees compliance with the first criterion for the transmission parameter.
• the selection of the precoding matrices comprises at least one iteration of the following steps for a transmission of rank /: the determination of a signal to interference plus noise ratio for each frequency sub-band, from the precoding matrix associated with the transmission of rank i for the considered sub-band, the determination of an effective signal to interference plus noise ratio from the signal to interference plus noise ratios determined for each sub-band, the determination of a modulation and coding scheme based on said effective signal-to-interference plus noise ratio and a target error rate, and the estimation of the transmission parameter for the transmission of rank i, based on the modulation and coding scheme thus determined ,
• the receiver can thus select the combination of precoding matrices which maximizes the estimated transmission parameter, for example a bit rate, for the given technique.
• the selection of an acquisition technique makes it possible to optimize the throughput offered by this technique. This therefore improves the transmission between transmitter and receiver.
• the given technique is the first technique of the group of techniques
• obtaining the set of precoding matrices associated with the first technique for the subband k comprises: determining a matrix of channel after interference whitening, denoted H ok , such as 1
• the determination of the set of precoding matrices associated with the first technique for a frequency sub-band, or, in other words, of the dictionary of the CSI-R2 technique, explicitly provides a set of precoding matrices from which one can select a precoding matrix to be used within the framework of the CSI-R2 technique.
• the set of precoding matrices associated with the second technique is predefined by a given standard.
• the technique based on a preset precoding dictionary, CSI-D is employed as the second technique.
• said at least information relating to the transmission channel knowledge acquisition technique selected by said receiver belongs to the group comprising: said compressed version of said interference covariance matrix when the first technique (for example of the CSI-R2 type) is selected; at least one piece of information from among a channel quality indicator (CQ.I) - making it possible in particular to deduce a modulation and coding scheme to be used for transmission, a rank indicator (RI) - making it possible to determine the number of spatial layers to be use for transmission, or a precoding indicator (PMI) when the second technique (e.g. CSI-D type) is selected.
• CQ.I channel quality indicator
• RI rank indicator
• PMI precoding indicator
• the communication method of the invention comprises receiving an indicator representative of a compression technique to be implemented to determine said compressed version of the covariance matrix of the interference.
• This reception of an indicator makes it possible to choose the type of compression on which the first technique for acquiring knowledge of the channel in transmission is based.
• At least one of said steps of estimating the covariance matrix of the interference, of selecting a technique for acquiring or transmitting at least one piece of information allowing the transmitter to determine a precoding matrix taking into account the covariance matrix of the interference according to said selected acquisition technique is carried out periodically and/or following a variation of the channel between said transmitter and said receiver.
• the selection of the acquisition technique periodically or following a variation of the channel between the transmitter makes it possible to maintain a relevant choice of acquisition technique, even if the communication conditions between the transmitter and the receiver change.
• the communication method includes transmitting a reference signal to said transmitter.
• this reference signal (for example of the SRS type for “Sounding Reference Signal”) makes it possible to adapt the choice of precoding over time. It can in particular be implemented when the first technique is selected.
• the transmission of the reference signal (for example of the SRS type for “Sounding Reference Signal”) can be periodic.
• the transmission of the reference signal can be aperiodic, and triggered by the reception of a request originating from the transmitter.
• the invention also proposes the communication method implemented at the level of the transmitter.
• This method according to the invention is remarkable in that it comprises: the reception of at least one piece of information from the receiver and allowing the transmitter to determine a precoding matrix taking account of a covariance matrix of the interference, representative of the spatial structure of the interference in reception, according to a technique for acquiring knowledge of the channel in transmission selected by said receiver from a group of techniques comprising a first technique based on a compressed version of a matrix of interference covariance and at least one second technique.
• such a method can determine a data transmission format from this information (for example define a precoding matrix, a modulation and coding scheme, and/or a number of spatial layers to be used in transmission). The method can then transmit the data using the transmission format thus defined.
• a data transmission format for example define a precoding matrix, a modulation and coding scheme, and/or a number of spatial layers to be used in transmission.
• the method can implement a transmission technique capable of taking into account the information received by said transmitter.
• the method implements, when said information coming from the receiver is said compressed version of said covariance matrix of the interference: the reception of a reference signal coming from said receiver, the estimation of a channel between said receiver and said transmitter from said reference signal, the estimation of a channel between said transmitter and said receiver, from said estimation of the channel between said receiver and said transmitter, by reciprocity, the construction, for each sub-band of a plurality of frequency sub-bands, of a set of precoding matrices, from the estimation of the channel between said transmitter and said receiver and from said compressed version of the matrix covariance of the interference, and the selection, in each set of precoding matrices associated with a sub-band, of a precoding matrix, such that a transmission parameter resulting from this selection of matrices respects a criterion, also called second criterion in the description.
• the receiver selects a combination of precoding matrices, which when they are used by the transmitter, make it possible to maximize a transmission parameter, for example a transmission rate.
• this communication method when the CSI-R2 technique is selected, is able to determine the precoding to be applied by constructing the dictionary of the CSI-R2 technique. This makes it possible to implement the CSI-R2 technique in an efficient manner.
• the invention also proposes a receiver of a transmission system also comprising a transmitter, the receiver comprising means for estimating a covariance matrix of the interference, representative of the spatial structure of the interference in reception.
• the receiver further comprises: means for selecting a technique for acquiring knowledge of the transmission channel, from a group of techniques comprising a first technique based on a compressed version of the said interference covariance matrix and at the at least one second technique, and means for transmitting to said transmitter at least one piece of information allowing the transmitter to determine a precoding matrix taking into account the covariance matrix of the interference according to the technique for acquiring knowledge of the transmit channel selected by said receiver.
• the invention also proposes a transmitter of a transmission system comprising said transmitter and a receiver.
• the transmitter comprises: means for receiving at least one item of information from the receiver and enabling the transmitter to determine a precoding matrix taking into account a covariance matrix of the interference, representative of the spatial structure of interference in reception, according to a technique for acquiring knowledge of the transmission channel selected by said receiver from a group of techniques comprising at least a first technique based on a compressed version of said interference covariance matrix and at the least a second technique.
• the invention further proposes a computer program comprising instructions for the implementation of a method of the type described above, when this program is executed by a processor.
• FIG. 1 illustrates a transmission system comprising a receiver and a transmitter according to one embodiment of the invention
• FIG. 2 illustrates the communication method as implemented by a receiver according to one embodiment of the invention
• FIG. 3 illustrates an example of a selection step performed in the communication method of Figure 2
• FIG. 4 illustrates an example of a prediction step performed in the selection step of Figure 3
• FIG. 5 illustrates an example of an estimation step performed in the prediction step of Figure 4,
• FIG. 6 illustrates an example of a step for obtaining a set of precoding matrices performed in the prediction step of Figure 4,
• FIG. 7 illustrates the communication method as implemented by a transmitter according to one embodiment of the invention
• FIG. 9 schematically illustrates transmitter-receiver exchanges for the CSI-R2 technique in an aperiodic case
• FIG. 10 schematically illustrates transmitter-receiver exchanges for the CSI-R2 technique in a periodic case
• FIG. 11 illustrates the simplified structure of a receiver according to one embodiment of the invention.
• FIG. 12 illustrates the simplified structure of a transmitter according to one embodiment of the invention.
• a transmission system 1 comprises a transmitter 2 and a receiver 3, in communication via a channel 4.
• the transmitter 2 comprises N T transmission antennas 5 (N T >1).
• the receiver 3 comprises N R receiving antennas 6 (N R >1).
• the invention focuses on the feedback of information from the receiver 3 to the transmitter 2, whereby the transmitter can implement a transmission technique based on the feedback information. More specifically, the invention aims at a hybrid approach in which the receiver evaluates several techniques for acquiring knowledge of the channel in transmission, CSI ("channel state information”), at least one of which is based on a compression of the covariance matrix interference.
• CSI channel state information
• the number of reception antennas of a so-called “smart phone” terminal is at least two, while for the NR standard, the number of reception antennas for this type of terminal is specified at at least four antennas for certain bands (3.5GHz n77/78).
• the number of transmit antennas has continued to grow to reach up to 64 massive MIMO antennas. Note that an antenna in this context is an RF chain including digital to analog conversion and vice versa.
• the number of radiating elements can be greater than the number of antennas. If the number of transmitting and receiving antennas (or “transceiver units") is the same at the level of the base station, this is not the case for mobiles which can have a number of antennas of transmission lower than the number of reception antennas, typically two transmission antennas for four reception antennas. However, the terminal can send reference signals from its four reception antennas, even in this typical configuration, thanks to the technique known as “antenna switching” (the RF chain is switched to another radiating element).
• the communication method carried out by the receiver 3, comprises a step EST1 of estimating a covariance matrix of the interference 12, a step SEL1 of selecting 20 a CSI acquisition technique 22 and a step Transmission TR 30 of at least one piece of information relating to said acquisition technique 22 to the transmitter 2.
• the covariance matrix of interference 12 estimated during step EST1 is representative of the spatial structure of the interference in reception.
• the structure of the interference refers to the correlation of the interference on the different reception antennas for a sub-carrier (given frequency) of an OFDM symbol for example.
• the interference will be qualified as "structured" when the covariance matrix of the interference moves away from an identity matrix (within a multiplicative factor), that is to say, when the correlation between the reception antennas is strong.
• the interference comes for example from the use of several transmission antennas at the level of the transmitter.
• the interference covariance matrix 12 is a scalar.
• the interference covariance matrix can be representative of the spatial structure of the interference between the receiving antennas.
• the step EST1 is based on a configuration of CSI interference measurements (or “CSI interference measurement” in English, also denoted CSI-IM).
• CSI-IMs indicate positions of resource elements (or RE, for “resource element”) where nothing is transmitted by the transmitter, which gives an interference measurement window without signal from the transmitter 2.
• the time-frequency positions (i.e. resource elements) where the covariance must be estimated correspond to zero-power CSI-RS, i.e. resource elements that are not used for transmission.
• the estimate EST1 can be made by correlation of signals received representative of the interference on the various reception antennas 6, in the absence of reference signals CSI-RS.
• the transmitter 2 for example, can configure resources (in time-frequency) prohibited from transmission (technique known as “Zero-Power CSI-RS” in the 3GPP ZP-CSI-RS TS38.211 standard) which allow the receiver 3 more easily measure, on these resources and for each reception antenna 6, the interference.
• Zero-Power CSI-RS in the 3GPP ZP-CSI-RS TS38.211 standard
• Step SEL1 for selecting a CSI acquisition technique to be implemented is based on the covariance matrix, conventionally denoted R b determined prior to step EST1.
• Information relating to the CSI acquisition technique thus selected can be used by said transmitter 2 to determine a data transmission format, when this information is fed back to the transmitter, as will be seen below.
• This CSI acquisition technique is selected from a group of techniques comprising a first technique based on a compressed version of said interference covariance matrix (in other words, CSI-R2) and at least a second technique.
• a second technique is the CSI-D technique.
• the CSI-D technique can be Type I or Type II, depending on the choice of the dictionary.
• a second technique may be the CSI-R1 technique.
• the information relating to CSI-R2 fed back to transmitter 2 is the compressed version of the interference covariance matrix, denoted R ⁇ .
• the compression of this matrix can be achieved in several ways.
• R t CCI NR , by choosing a such that ae R + minimizes the difference and belongs to a discrete subset of 2 q positive real elements.
• the compression of the interference covariance matrix is thus given by the transmission of q bits from the receiver to the transmitter assuming that the discrete subset to which a belongs is known to the transmitter and the receiver as well as the correspondence between the q bits received and the associated value of a.
• the receiver receives (before compression of the interference covariance matrix) an indicator representative of the compression technique to be implemented.
• the receiver 3 When the CSI-D technique is selected by the receiver 3, the receiver 3 sends back to the transmitter 2 (via a limited return channel) a precoding indicator (PMI) identifying a precoding in the precoding dictionary.
• the receiver can also upload a channel quality indicator (CQI) - allowing in particular to deduce a modulation and coding scheme to be used for transmission, and/or a rank indicator (RI) - allowing the number of layers to be determined space to use for transmission.
• CQI channel quality indicator
• RI rank indicator
• one of the steps of estimation EST1, selection SEL1 or transmission TR is carried out periodically and/or following a variation of the channel between said transmitter and said receiver.
• the proposed solution thus makes it possible, according to at least one embodiment, to take into account structure of the interference, depending on the choice of the channel state acquisition technique and the compression method of the interference covariance matrix.
• the step SEL1 for selecting 20 a CSI acquisition technique comprises a step PRE 24 for predicting a transmission TP parameter 26 associated with each technique (for example CSI-D and CSI- R2) from the technique group.
• the technique to be implemented is then selected in a step CRI, referenced 28, on the basis of a first criterion relating to the predicted transmission parameter TP.
• the transmission parameter predicted for a given acquisition technique is a bit rate that this technique makes it possible to achieve.
• the first criterion is the maximization of this throughput.
• the first criterion may be to reach a target bit rate, and, if the two techniques offer this target bit rate, then to select the most bandwidth-efficient technique.
• this transmission parameter is signal to noise ratio (SNR), signal to noise plus interference ratio (SINR), error rate, interference margin, payload rate ...
• SNR signal to noise ratio
• SINR signal to noise plus interference ratio
• the prediction 24 of the transmission parameter associated with a given technique comprises: an iteration loop 240, each iteration of which comprises a step DICT for obtaining 242 dictionaries 244 for each sub-band k of a plurality of frequency sub-bands of channel 4, and a step SEL2 of selecting 250, in each set of precoding matrices associated with a sub-band k, a precoding matrix w k L 252, so that the transmission parameter TP resulting from this selection meets a second criterion.
• Each iteration loop 240 includes a DICT step 242 for obtaining a set of precoding matrices 244, also called the dictionary of the given technique CSI and denoted W k SI , for said sub-band k.
• the iteration loop ends with a check of whether the iteration reaches the end of the plurality of sub-bands. If this is not the case, one returns to the start of the loop by incrementing the sub-band index.
• the dictionary can be obtained 242 either by constructing a dictionary linked to the given technique (for example for CSI-R2, as will be seen below), or by obtaining a predetermined dictionary, typically defined by a standard.
• step SEL2 the precoding matrices w k (one per sub-band) are selected such that the transmission parameter TP resulting from this selection meets a second criterion .
• the precoding matrices of the same rank are selected making it possible to maximize a transmission parameter of rate type, as described below.
• the transmission parameter to be predicted for the given technique is the bit rate satisfied by the given technique.
• the selection SEL2 comprises at least one iteration of the following steps for a transmission of rank i, i E ⁇ 0, ..., v ⁇ : a step DET1 for determining 262 a signal to interference plus noise ratio 264 (SINR ) for each frequency sub-band k, denoted SINR k or y k , from the precoding matrix associated with the transmission of rank i for the considered sub-band. a step DET2 of determining 270 an effective signal to interference plus noise ratio SINR e ff 272 for the given technique from the signal to interference plus noise ratios determined for each sub-band k E ⁇ 0, ...
• SINR signal to interference plus noise ratio
• step DET3 for determining 274 an MCS modulation and coding scheme, referenced 276, from said effective SINR 272 and a target error rate
• step DET4 for estimating 278 the transmission parameter for the transmission of rank i, for example a debit referenced 280, satisfied by the technique given from the modulation scheme and coding thus determined.
• the receiver When all the combinations of precoding matrices associated with the different rank values are tested, the receiver has a set of bit rate values Dt, and can select the combination of decoding matrices associated with the maximum bit rate Di.
• the SINR of a linear receiver of the LMMSE-IRC type, for a sub-band k and a transmission of order i can be expressed in the form below: where w k , H k , R I are respectively a precoding matrix for a transmission of rank i on subband k and on a resource element l, the channel matrix of subband k and the covariance matrix .
• e t is the i-th vector of dimension v of the canonical basis, i.e. a vector with a coordinate 1 at position i, and 0 elsewhere
• the effective SINR is determined from the SINRs of each sub-band, via MIESM compression (“mutual information effective signal-to-noise-ratio mapping”).
• MCS modulation and coding scheme
• a target BLER error rate is fixed at 10% (or more generally less than 20%), which makes it possible to deduce the modulation and coding scheme to be used, knowing the effective SINR. This then makes it possible to obtain a flow rate for the selected technique.
• the transmission parameter may be the effective SINR, or the BLER error rate.
• the prediction step stops at the step delivering the effective SINR (DET2).
• the prediction step stops at the step delivering the modulation and coding scheme (DET3).
• the receiver 3 determines a CQI from the MCS, and transmits the determined CQI to the transmitter 2.
• the technique whose transmission parameter (not necessarily the bit rate) is sought to be predicted is the first technique, or, in other words, CSI-R2.
• obtaining the CSI-R2 dictionary for a sub-band of frequency k comprises a step DET5 of determination 282 of a channel matrix after whitewashing the interference (referenced 284 and denoted H ok ), a step SVD for determining 286 an input matrix (referenced 288 and denoted V ) and a step BLD for constructing 290 the dictionary 292 of CSI-R2.
• the transmitter 2 can know the channel matrix H k (by reciprocity) but not the interference covariance matrix R ⁇ . This prevents the transmitter from working with the complete and "exact" model based on H k and Rj.
• the issuer can therefore only work on a simplified model, in which the matrix R ⁇ is replaced by its compressed equivalent R ⁇ . It is then necessary to construct a precoding dictionary that both the sender and the receiver can obtain from the information available to them, namely R ⁇ and H k . This is the role of the steps described below.
• the channel matrix after interference whitening satisfies the equation H k R ⁇ H k .
• the matrix H ok is determined according to the following equation: where R ⁇ is the compressed version of the covariance matrix of the interference and H k the matrix representative of the channel on the given frequency sub-band k.
• the model of the signal received on a resource element l of the frequency sub-band k can be expressed in the following form: l N WHERE N R number of reception antennas 6 and x lk the precoded data vector.
• the matrix V k is called the input matrix (and V k its assistant matrix), the matrix U k is called the output matrix, and the matrix S , diagonal, contains in its diagonal coefficients the singular values of the matrix H ok , or said otherwise the roots of the eigenvalues of the matrix H ok H ⁇ k .
• the content of the precoding dictionary may differ.
• the precoding dictionary W k for a sub-band of frequency k is predefined by a given standard.
• Obtaining the CSI-D dictionary (W k ) for example implements the reading of a table defined in the standard considered.
• a communication method comprises a step 40 of reception 40 by the transmitter, coming from a receiver, of information 42 relating to an acquisition technique selected by the receiver 3.
• such information 42 can be used to define a transmission format to be used by the transmitter (for example a precoding matrix, a modulation and coding scheme and/or a number of spatial layers).
• a transmission format to be used by the transmitter for example a precoding matrix, a modulation and coding scheme and/or a number of spatial layers.
• the communication method also comprises the transmission 44 of data using the transmission format defined from said information 42 received.
• the information from the receiver is the compressed version of the interference covariance matrix R i (when the receiver 3 selects the CSI-R2 method).
• the communication method comprises: the reception of a reference signal coming from the receiver, the estimation of the channel matrix between the receiver and the transmitter from this reference signal, the estimation of a channel between said transmitter and said receiver, from said estimation of the channel between said receiver and said transmitter, by reciprocity of the channel, the construction, for each sub-band of a plurality of sub-bands, of a set of precoding matrices from the estimation of the channel between said transmitter and said receiver and of said compressed version of the covariance matrix of the interference, the selection, in each set of precoding matrices associated with a sub-band, of a precoding matrix such as a transmission parameter resulting from this selection meets the second criterion.
• the reference signal may be a signal of the SRS (Sounding Reference Signal) type.
• the step of receiving this reference signal can be carried out regularly or on request, as will be seen below.
• the information from the receiver is at least one item of information from among a channel quality indicator (CQ.I), a rank indicator (RI), a precoding indicator (PMI) - for example if Receiver 3 selects the CSI-D method.
• the communication method comprises: the transmission of a reference signal, for example of the CSI-RS type, allowing the receiver in particular to estimate the channel in the transmitter-to-receiver direction, the identification of a precoding matrix to be used by the transmitter, from the information coming from the receiver (CQ.I, RI and/or PMI).
• one of the steps of estimation EST1, selection SEL1 or transmission TR implemented by the receiver is carried out periodically and/or aperiodically, for example following a variation of the channel between said transmitter and said receiver.
• the receiver 3 can in particular regularly transmit a reference signal to the transmitter 2, for example of the SRS (Sounding Reference Signal) type.
• SRS Sounding Reference Signal
• the receiver 3 can transmit a reference signal upon receipt of a request from the transmitter 2, for example of the “SRS trigger command” type.
• a reference signal upon receipt of a request from the transmitter 2, for example of the “SRS trigger command” type.
• FIGS. 8 to 10 schematically represent an order of exchanges between the receiver and the transmitter.
• the exchanges between transmitter 2 and receiver 3 may include, in order:
• S10 (E to R) send (optional) an instruction on the covariance compression method to be used for the receiver.
• the compression method can in particular be configured by the RRC layer in a semi-static way,
• the receiver can then implement the communication method described previously, and in particular the selection of a technique for acquiring knowledge of the channel in transmission.
• the technique selected by the receiver 3 is of the CSI-D type.
• the information then including the PMI, and possibly CQ.I and RI),
• the technique selected by the receiver 3 is of the CSI-R2 type. It is also assumed that the receiver transmits a reference signal SRS aperiodically, for example in response to a request from the transmitter.
• the technique selected by the receiver 3 is also of the CSI-R2 type. It is also assumed that the receiver transmits an SRS reference signal periodically.
• the transmitter may use the most recent SRS reference signal to estimate the channel.
• FIGS. 11 and 12 the simplified structures of a receiver and of a transmitter according to one embodiment of the invention are presented.
• a receiver 3 comprises a memory 300, a processing unit 310, equipped for example with a programmable calculation machine or a dedicated calculation machine, for example a processor P, and controlled by the computer program 320, implementing steps of the communication method according to at least one embodiment of the invention.
• the code instructions of the computer program 320 are for example loaded into a RAM memory before being executed by the processor of the processing unit 310.
• the processor of the processing unit 310 implements the steps of the communication method described previously, according to the instructions of the computer program 320, to: estimate a covariance matrix of the interference, representative of the spatial structure of the interference in reception, selecting a technique for acquiring knowledge of the channel in transmission, from a group of techniques comprising a first technique based on a compressed version of said interference covariance matrix and at least one second technique, and transmitting to said transmitter information relating to said technique for acquiring knowledge of the transmission channel selected by said receiver.
• a transmitter according to one embodiment of the invention comprises a memory 200, a processing unit 210, equipped for example with a programmable calculation machine or a dedicated calculation machine, for example a processor P, and controlled by the computer program 220, implementing steps of the communication method according to at least one embodiment of the invention.
• the code instructions of the computer program 220 are for example loaded into a RAM memory before being executed by the processor of the processing unit 210.
• the processor of the processing unit 210 implements implementation of the steps of the communication method described previously, according to the instructions of the computer program 220, for: receiving at least one piece of information from the receiver and relating to a technique for acquiring knowledge of the transmission channel selected by said receiver from a group of techniques comprising a first technique based on a compressed version of an interference covariance matrix, representative of the spatial structure of the interference in reception, and at least one second technique.

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• 2021
  • 2021-12-23 FR FR2114459A patent/FR3131498A1/fr not_active Withdrawn
• 2022
  • 2022-12-20 CN CN202280091230.6A patent/CN118661392A/zh active Pending
  • 2022-12-20 WO PCT/EP2022/086867 patent/WO2023118056A1/fr not_active Ceased
  • 2022-12-20 EP EP22836264.6A patent/EP4454166A1/de active Pending
  • 2022-12-20 US US18/723,371 patent/US20250096860A1/en active Pending

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