EP4078839A1

EP4078839A1 - Transmission and reception methods and devices implementing a plurality of transmit and receive antennas, and corresponding computer program

Info

Publication number: EP4078839A1
Application number: EP20842287.3A
Authority: EP
Inventors: Raphaël Visoz; Thierry Clessienne
Original assignee: Orange SA
Current assignee: Orange SA
Priority date: 2019-12-20
Filing date: 2020-12-10
Publication date: 2022-10-26
Also published as: FR3105668A1; CN114830561A; US20230040332A1; WO2021123579A1

Abstract

The invention relates to a reception method implemented by a reception device implementing a plurality of receive antennas, comprising estimating (21) an interference covariance matrix representative of the spatial structure of the interference between the receive antennas. According to the invention, such a method also comprises transmitting (23) at least one item of information about the quality of service associated with at least one acquisition technique for acquiring the knowledge of the channel at transmission, able to be used by a transmission device implementing a plurality of transmit antennas, obtained from said interference covariance matrix.

Description

DESCRIPTION

TITLE: Transmitting and receiving methods and devices implementing a plurality of transmitting and receiving antennas, and corresponding computer program.

1. Field of the invention

The field of the invention is that of wireless communications.

More precisely, 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 upstream or 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 3GPP, WiFi communication networks according to the IEEE 802.11 standard, etc.

For downlink communication, 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 even an access point. Wi-Fi, etc. A receiver can be a terminal of the smartphone, tablet, connected object, etc. type. For uplink communication, the transmitter may be a terminal and the receiver a base station.

2. Prior art

Beamforming, or precoding, is a signal processing technique used in antenna or sensor arrays for the directional transmission or reception of signals. In other words, thanks to the antenna arrays, the transmitters and / or receivers can focus the radiation of the emitted 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 constructively combine 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 interference received.

Thus, for the formation of beams at the level of a transmitter, a complex coefficient, called the precoding coefficient, is applied to each element of the antenna array of the transmitter. All of these coefficients form the precoding matrix.

It is noted that for the radiation pattern to be oriented in the desired direction, the precoding coefficients must be correctly chosen. But a problem for the selection of pre-coding is the acquisition of knowledge of the channel in transmission (ie knowledge, at the level of the transmitter, of the transmission channel between the transmitter and the receiver), or "Channel State Information at Transmitter" (CSIT) in English, and / or the spatial structuring of the interference perceived by the receiver.

Currently, two techniques for acquiring knowledge of the transmission channel are proposed for MIMO systems in the 4G, 5G, IEEE802.11x (IEEE802.11n, 802.11ac, 802.11ax) standards. The techniques for acquiring the knowledge of the channel, and the associated reference signals, are described more precisely in the 3GPP specifications TS36.213, TS36.211 for 4G and TS38.211, TS38.214 for 5G. technique, denoted CSI-D, is based on the use of a return path between the receiver and the transmitter. According to this first technique, the transmitter emits at least one reference signal, also called the pilot signal. Such a reference signal is for example denoted CSI-RS in the downward direction in the 4G and 5G standards, for “Channel State Information - Reference Signal”. On receipt of the reference signal (s), the receiver can estimate the transmission channel between the transmitter and the receiver (i.e. in the direction transmitter to receiver). Furthermore, the estimation of the spatial characteristics of the interference (or covariance of the interference) can be done by simple correlation of the signals received representative of the interference on the different reception antennas, that is to say without be based on transmitted reference signals. The transmitter, for example, can configure resources (in time-frequency) prohibited for transmission (technique known as “Zero-Power CSI-RS” in the 3GPP ZP-CSI-RS TS38.211 standard) which allow the receiver to more easily measure, on these resources and for each antenna, the interference. Other approaches are possible based on the subtraction of the useful data or reference signals (i.e. not forming part of the interference from the point of view of the receiver in charge of measuring it) from the signals received on each antenna to obtain signals representative of the interference on the various reception antennas.

From the estimation of the transmission channel between the transmitter and the receiver and the spatial characteristics of the interference, the receiver can determine a pre-coding matrix to be used by the transmitter, and reassemble this choice of pre-coding to the transmitter in the return channel, for example in the form of a “Precoding Matrix Indicator” (PMI) type indicator. In particular, the precoding matrix can be selected from a finite dictionary of precoding matrices specified by the 4G or 5G standard.

A second technique, denoted CSI-R, is based on the reciprocity of the channel, which supposes that the transmission channel between the receiver and the transmitter (ie in the direction receiver towards transmitter) is the same as the transmission channel between the transmitter and the receiver (ie in the direction transmitter to receiver). Here, 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. This second technique therefore assumes the use of the same frequency resources and a time separation of the uplink and downlink channels, or “Time Division Duplex”, TDD). According to this second technique, the receiver transmits at least one reference signal, for example of the SRS type (for “Sounding Reference Signal”) for the upstream direction in the 4G and 5G standards. On receipt of the reference signal (s), the transmitter can estimate the transmission channel between the receiver and the transmitter, and deduce therefrom by reciprocity the transmission channel between the transmitter and the receiver. From the estimation of the transmission channel between the transmitter and the receiver, the transmitter can select a pre-coding matrix to use. For example, the transmitter determines a precoding matrix according to a signal-to-noise ratio (SNR) maximization criterion.

A drawback of the first CSI-D technique is that, although it is based on knowledge of the transmission channel and on knowledge of interference on reception, it does not allow the precoding coefficients to be used by the operator to be finely traced. 'transmitter. Indeed, as the precoding matrix is chosen from among a finite alphabet of precoding matrices, and reassembled in the form of an indicator, a quantization is implemented, leading to a loss of information.

A drawback of the second CSI-R technique is that, although it allows the transmitter to know the transmission channel without quantization, it does not allow the transmitter to know the interference on reception. Indeed, such a technique determines the pre-coding matrix to be used while 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 second technique is difficult to envisage, since it would consume too much in terms of the quantity of return channel. The precoding matrix based on the second technique is therefore obtained without taking into account the covariance of the interference or, which amounts to the same thing, by considering it unstructured.

There is therefore a need for a new technique allowing a transmitter to select a technique for acquiring knowledge of the channel on transmission to be used among several techniques available to improve the transmission of information between a transmitter. and a receiver.

3. Disclosure of the invention

The invention proposes a solution which does not have all of these drawbacks, in the form of a reception method, implemented by a reception device implementing a plurality of reception antennas, comprising the estimation of d a covariance matrix of the interference, representative of the spatial structure of the interference between the receiving antennas.

Here, the structure of the interference refers to the correlation of the interference on the different reception antennas for a subcarrier (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 (up to a multiplicative factor), that is to say, when the correlation between the receiving antennas is strong.

In other words, the interference is structured if the distance between the interference covariance matrix and a multiple of an identity matrix of the same size as the interference covariance matrix is greater than a determined threshold.

According to the invention, such a method also comprises the transmission, to a transmission device implementing a plurality of transmission antennas, of at least one item of information on the quality of service associated with at least one transmission technique. acquisition of knowledge of the channel on transmission suitable for use by said transmission device, obtained from said interference covariance matrix.

The proposed solution thus makes it possible to take account of the spatial characteristics of the interference in order to select the technique for acquiring knowledge of the channel on transmission to be used by the transmission device, for beam forming at the level of the device. 'program.

It should be noted that such a method according to the invention does not necessarily require the estimation of the transmission channel between the transmission device, also called transmitter, and the reception device, also called receiver. It is therefore not necessarily based on the transmission of reference signals from the transmitter to the receiver.

Indeed, the receiver can directly estimate the covariance matrix of the interference on the basis of any signal received by the receiver, not known or partially known by the receiver.

On receipt of this arbitrary signal, the receiver can estimate the covariance matrix of the interference, and use the knowledge of the interference to go back to the transmitter at least information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission suitable for use by the transmitter.

According to a first embodiment, the covariance matrix of the interference can be used to determine whether the interference is structured or not.

According to this first embodiment, it is assumed that the transmission device implements a technique for acquiring knowledge of the channel on transmission based on reciprocity. Such a technique is based on the assumption that the interference is not, or only slightly, structured. If the receiving device determines that the receiving interference is structured, ie moving away from a diagonal matrix, it can thus return to the transmitter an alert indicator, informing the transmitting device that the hypothesis according to which the interference is not or is poorly structured on reception is not valid.

For example, such an indicator is carried by a single bit, equal to 0 if the interference is structured or equal to 1 if the interference is not structured (or vice versa). Such an indicator therefore consumes very little bandwidth on the return channel.

On receipt of this alert indicator, the transmitter can choose to implement a technique for acquiring knowledge of the channel on transmission of the CSI-D type or any other technique, if the indicator indicates that the The use of a technique for acquiring knowledge of the channel on transmission based on reciprocity is based on an invalid hypothesis of unstructured or poorly structured interference (ie neglects structured interference).

For example, the interference is structured if the report: is greater than a determined threshold, with:

N _R the number of receiving antennas,

R; the interference covariance matrix of size N _R x N _R , s ² the average power of the interference and the noise received on the receiving antennas,

/ the identity matrix of size N _R x N _R , and Il || _F is the Frobenius norm.

According to a second embodiment, implemented when it is possible to estimate the transmission channel between the transmitter and the receiver, the reception method implements: the reception of at least one reference signal, in originating from said transmission device, the estimate of the transmission channel on reception between the transmission device and the reception device (ie in the direction from transmitter to receiver, also called acquisition knowledge of the channel on reception, or “Channel State Information at Receiver” CSIR), from the reference signal (s), obtaining pre-coding matrices associated with at least two knowledge acquisition techniques of the channel on transmission, taking into account the estimate of the transmission channel on reception, the estimate of at least one parameter representative of the quality of service associated with each of said techniques for acquiring knowledge of the channel on transmission, from said precoding matrices,

In this case, the interference covariance matrix can be used with the estimate of the transmission channel on reception to determine the pre-coding matrices associated with certain techniques for acquiring knowledge of the channel on transmission. , like the CSI-D technique for example.

Note that this second embodiment can be implemented independently or in combination with the first embodiment.

For example, following the reception by the transmitter of an alert indicator according to the first embodiment, the transmitter can transmit at least one reference signal for estimating the transmission channel on reception, which can be used according to this second embodiment. The receiver can thus obtain the precoding matrix used with a technique of acquiring knowledge of the channel on transmission based on reciprocity according to the first embodiment, and determine at least one precoding matrix associated with at least one distinct technique for acquiring knowledge of the channel on transmission.

According to this second embodiment, the information sent back to the transmitter is a quality indicator, indicating at least one technique for acquiring knowledge of the channel on transmission, the estimated parameter of which meets a determined criterion.

For example, the parameter belongs to the group comprising: a bit rate, an error rate, etc., and the determined criterion is a criterion of maximum bit rate, target error rate, etc.

Such an indicator also consumes very little bandwidth on the return channel.

The selection of the acquisition technique to be used by the transmitter can be made by the receiver. In this case, the receiver can report only one quality indicator, even if several techniques for acquiring knowledge of the channel on transmission make it possible to achieve, for example, a target error rate.

Alternatively, the selection of the acquisition technique to be used by the transmitter can be made by the transmitter. In this case, the receiver can return all the quality indicators, or only those corresponding to a technique for acquiring knowledge of the channel on transmission, the estimated parameter of which meets a determined criterion.

In particular, the reception method implements the selection of the technique for acquiring knowledge of the channel on transmission offering the highest level of quality of service, from an abstraction of the physical layer.

Whatever the embodiment considered, the estimation of the interference covariance matrix and the transmission of at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel at the same time. 'transmission can be carried out periodically and / or following a variation of the transmission channel between the transmission device and the reception device.

The technique for acquiring knowledge of the channel on transmission implemented by the transmitter is therefore adaptive, and can be modified during transmission, for example when a terminal is moving.

According to a particular embodiment, it is the transmitter, for example a base station, which asks the receiver, for example a terminal, to report information on the quality of service associated with at least one data acquisition technique. knowledge of the channel on issue.

According to another embodiment, it is the receiver who takes the initiative to feed back information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission, for example following the transmission. detection of a change in the transmission channel.

In another embodiment, the invention relates to a corresponding reception device, implementing a plurality of reception antennas.

For example, such a reception device comprises at least one processor configured to: determine a covariance matrix of the interference, representative of the spatial structure of the interference between the reception antennas, transmit at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission suitable for use by a transmission device implementing a plurality of transmission antennas, obtained from said interference covariance matrix.

For example, if we go in the downward direction, i.e. from a base station to a terminal, such a receiving device is a terminal. If we go in the up direction, i.e. from a terminal to a base station, such a receiving device is a base station.

The invention also relates to a corresponding transmission method, implemented by a transmission device implementing a plurality of transmission antennas.

According to the invention, such a transmission method comprises: the reception of at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission capable of being used by the transmission device, obtained from an interference covariance matrix, representative of the spatial structure of the interference between a plurality of reception antennas of a reception device, the implementation of a technique of acquiring knowledge of the channel on emission identified from said at least one item of information.

In other words, the transmitter receives information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission and can implement a technique for acquiring knowledge of the channel. on the transmission identified from the quality of service information (s) received.

According to a first embodiment, the information received is an alert indicator, indicating that the use of a technique for acquiring knowledge of the channel on transmission based on reciprocity, implemented by the device transmission, is based on an invalid interference assumption.

According to this first embodiment, the invention thus makes it possible to inform the sender of a situation of structured interference on reception, and the sender can optionally implement, or switch to, an acquisition technique distinct from the CSI-R technique.

In particular, following receipt of said alert indicator, the transmission device can implement the transmission of at least one reference signal for estimating the transmission channel on reception.

According to a second embodiment, implemented independently or following the first embodiment, said at least one item of information received is a quality indicator, indicating at least one technique for acquiring knowledge of the channel on transmission. for which a parameter representative of the quality of service meets a determined criterion, and the device transmission implements a technique for acquiring knowledge of the channel on transmission chosen from the technique or techniques for acquiring knowledge of the channel on transmission identified by the quality indicator.

In another embodiment, the invention relates to a corresponding transmission device, implementing a plurality of transmission antennas.

For example, such a transmission device comprises at least one processor configured to: receive at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission capable of being used by the transmission device, obtained from an interference covariance matrix, representative of the spatial structure of the interference between a plurality of reception antennas of a reception device, implementing a technique of acquisition of knowledge of the channel on the emission identified from said at least one item of information.

In particular, the different steps of the reception and / or transmission methods according to at least one embodiment of the invention can be implemented in various ways, in particular in hardware form and / or in software form.

For example, at least one step of the reception and / or transmission methods can be implemented: on a reprogrammable computing machine (a computer, a processor for example DSP (in English "Digital Signal Processor"), a microcontroller , etc) executing a program comprising a sequence of instructions, on a dedicated computing machine (for example a set of logic gates such as an FPGA (in English "Field Programmable Gâte Array") or an ASIC (in English "Application-Specific Integrated Circuit ”), or any other hardware module).

Consequently, an embodiment of the invention also aims to protect one or more computer programs comprising instructions adapted to the implementation of the reception and / or transmission methods according to at least one embodiment of the invention. invention as described above, when this or these programs are executed by a processor, as well as at least one information medium readable by a computer comprising instructions of at least one computer program as mentioned above -above.

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

[Fig 1] Figure 1 illustrates a MIMO system in which the invention can be implemented;

[Fig 2] FIG. 2 shows the main steps implemented by a reception method according to one embodiment of the invention;

[Fig 3] FIG. 3 shows the main steps implemented by a transmission method according to one embodiment of the invention;

[Fig 4]

[Fig 5] Figures 4 and 5 respectively illustrate the simplified structure of a receiver and a transmitter according to an embodiment of the invention.

5. Description of embodiments of the invention

5.1 General principle

The general principle of the invention is based on the feedback of information from a receiver to a transmitter, in a MIMO (“Multiple Input, Multiple Output”) system so that the transmitter can implement a data acquisition technique. knowledge of the channel on transmission (or “Channel State Information at Transmitter”) taking account of the actual transmission conditions, and in particular of the interference on reception.

FIG. 1 illustrates a MIMO system in which the invention can be implemented. Such a system comprises a transmitter 11, comprising a plurality of transmitting antennas 111, ..., 11m, and a receiver 12, comprising a plurality of receiving antennas 121, ..., 12n.

The transmitter 11 can in particular implement coding and modulation operations, and the receiver 12 can implement decoding and demodulation operations.

The transmission channel between the transmitter 11 and the receiver 12 can be represented by an H channel matrix.

Referring to FIGS. 2 and 3, we present the main steps of the reception method according to an embodiment of the invention, implemented by the receiver 12, and the main steps of the transmission method according to an embodiment. embodiment of the invention, implemented by the transmitter 11, allowing the transmitter 11 to implement a technique for acquiring knowledge of the transmission channel adapted to the transmission channel.

As illustrated in FIG. 2, during a step 21, the receiver 12 determines a covariance matrix of the interference, representative of the spatial structure of the interference between the receiving antennas 121, ..., 12n of the receiver 12.

The matrix of the covariance of the interference can in particular be determined conventionally, as for the CSI-D technique for example.

Optionally, the receiver 12 also estimates the transmission channel between the transmitter 11 and the receiver 12, during a step 22, in particular if it receives reference signals from the transmitter 11.

From the interference covariance matrix, and possibly from the estimate of the transmission channel on reception, the receiver 12 determines, during a step 23, at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission, capable of being used by the transmitter 11, and transmits the information or information obtained to the transmitter 11, in a return channel.

As illustrated in FIG. 3, during a step 31, the transmitter 11 therefore receives at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission, obtained at from the interference covariance matrix. The transmitter 11 can receive several pieces of information on the quality of service associated with different techniques for acquiring knowledge of the channel on transmission, possibly obtained from the estimation of the transmission channel on reception.

During a step 32, the transmitter can implement a technique for acquiring knowledge of the channel on transmission, identified from the information (s) on the quality of service associated with at least one technique. acquisition of knowledge of the channel on transmission.

5.2 Description of a first embodiment

A first embodiment is described below for determining at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission.

It is considered according to this first embodiment that the receiver 12 cannot estimate the transmission channel (in the direction from transmitter 11 to receiver 12). For example, if receiver 12 does not receive a reference signal from transmitter 11, it cannot estimate the transmission channel.

According to this first embodiment, the receiver 12 can estimate the covariance of the interference (step 21 of FIG. 2), even if it cannot estimate the transmission channel.

By way of example, if it is assumed that the receiver 12 has N _R reception antennas and that the frequency band considered comprises K carrier frequencies (according to an OFDMA type modulation technique for example), then the receiver 12 can estimate the matrix of covariance of the interference R _j EC ^WRXWR such that:

K with: y _k e € ^NR an observation of the interference for a frequency k, measured by the receiver 12, and () ^† the conjugated transpose operator.

According to this example, the interference is structured (ie defined privileged directions where the interference is stronger than in the other directions) if the covariance matrix R _j is far from the matrix s ² I (ie is far from a diagonal structure), with: s ² = - - _f e = å i yîyk ^has the average power of the interference and noise received on

KNR receiving antennas and / the identity matrix of dimensions N _R x N _R.

In other words, if we define a matrix K; such that K; = R; - s ² I, the interference is considered to be structured if the following ratio is greater than a determined threshold T: where II || _F is the Frobenius norm and tr () is the trace operator.

For example, such a threshold is of the order of 30%.

If the receiver 12 determines that the interference is structured (or, equivalently, that the covariance matrix of the interference is structured), it can send back to the transmitter 11 an alert indicator (step 23 of FIG. 2), informing the transmitter that the interference in reception is structured and that the use of a technique of acquiring the knowledge of the channel on the transmission based on reciprocity neglects a structured interference in reception, ie is based on on an invalid hypothesis of unstructured or poorly structured interference in reception. Indeed, a structured interference in reception can prove to be problematic for the CSI-R acquisition technique, which neglects the spatial structure of the interference.

In this case, it may be preferable for the transmitter 11 to use a CSI-D type acquisition technique, or any other technique for acquiring knowledge of the channel on transmission capable of taking into account the covariance of the channel. interference in the selection of the precoding matrix.

For example, the information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission is an alert indicator “Indic” equal to 1 if the interference is structured, or equal to to 0 or an empty field if the interference is not structured.

On receipt of this alert indicator (step 31 of FIG. 3), the transmitter 11 knows whether the assumption made on reception interference was valid or not. If it was valid (alert indicator empty or equal to 0 according to the example above), it can continue to use a technique of acquiring the knowledge of the channel based on reciprocity. If the hypothesis is not valid (alert indicator equal to 1 according to the example above), he can decide to switch to another technique for acquiring knowledge of the channel on transmission, or to transmit reference signals so that the receiver can compare several techniques for acquiring knowledge of the channel on transmission and provide the transmitter with a quality indicator as described below.

5.3 Description of a second embodiment

A second embodiment is described below for determining at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission.

It is considered according to this second embodiment that the receiver 12 can estimate the transmission channel (in the direction from transmitter 11 to receiver 12).

According to this second embodiment, the receiver 12 can therefore estimate on the one hand the covariance of the interference (step 21 of FIG. 2), on the other hand the transmission channel between the transmitter and the receiver (step 22 in figure 2).

The R interference covariance matrix _; can be estimated as described in relation to the first embodiment.

The transmission channel H = {H, H ₂ , ..., H _K } by frequency, for a band in the direction transmitter 11 towards receiver 12, can be estimated from the reception by the receiver 12 of at least a reference signal from transmitter 11.

According to this second embodiment, the receiver 12 can determine which would be the precoding matrix to be used at the level of the transmitter 11 for various techniques for acquiring knowledge of the channel on transmission.

For example, the receiver 12 determines a precoding matrix associated with the CSI-R acquisition technique by taking into account the estimate of the transmission channel on reception and assuming that the covariance matrix of the interference is equal to s ² I. The receiver also determines a precoding matrix associated with the CSI-D acquisition technique by taking into account the estimate of the transmission channel on reception and the covariance matrix of the interference R as well as the finite dictionary W of precoding matrices defined by the 4G or 5G standard. Optionally, the receiver can determine one or more pre-coding matrices associated with one or more other techniques for acquiring knowledge of the channel to. the show. Such precoding matrices are for example chosen so as to maximize the signal-to-interference-plus-noise ratio.

These various precoding matrices can be used by the receiver 12 to predict the quality of service associated with the use of the various techniques for acquiring knowledge of the channel on transmission.

The receiver 12 can thus estimate at least one parameter representative of the quality of service associated with each of the techniques for acquiring knowledge of the channel on transmission, from the pre-determined pre-coding matrices, for example of bit rate type. , error rate, etc.

By way of example, for a given frequency k, the signal to interference plus noise ratio at reception (SINR) can be expressed as a function of the pre-coding vector chosen w _k , of the transmission channel H _k and of the matrix covariance of the interference R _; . We denote by SINR (w _fe , H _k , R _; ) such a signal-to-noise ratio, for a given frequency k, with k = 1, .., K, as described below.

The receiver 12 can implement a physical layer abstraction technique (in English “PHY abstraction”), to evaluate the different techniques for acquiring knowledge of the channel on transmission and to predict which transmission format allows, for example, to maximize the bit rate for the frequency band considered, or to reach a target error rate for the frequency band considered. Such a physical layer abstraction technique is presented in particular in the documents “Link performance models for System level simulations of broadband radio access Systems” (K. Brueninghaus et al., IEEE 16th Int. Symposium on Personal, Indoor and Mobile Radio Communications, 2005 (PIMRC 2005), vol. 4, 2005, pp. 2306-2311) and “Realistic Performance of LTE: In a Macro-Cell Environment” (JB Landre et al., Proc. IEEE VTCS-2012, Japan, Yokohama, May 2012).

For example, this physical layer abstraction matches the SINRs (w _fe , H _k , R _j ), for a frequency k, k = l, .., K, to “effective” SINRs, according to a mapping technique known as MIESM (“mutual information effective signal-to noise-ratio mapping”), then makes each “effective” SINR correspond to a bit rate using Gaussian quality tables associated with the family of coding and modulation schemes specified in the standard.

The receiver 12 can associate a rate D ₂ = f (H, s ² /) with the acquisition technique CSI-R and a rate D ₁ = f (H, R; \ W) with the acquisition technique CSI- D. Likewise, the receiver can associate other rates with other techniques for acquiring knowledge of the channel on transmission. The receiver 12 can thus select a technique for acquiring knowledge of the channel on transmission, the estimated parameter of which (for example flow rate, error rate, etc.) meets a determined criterion, and return to the transmitter 11 an indicator quality, indicating the acquisition technique (s) selected. For example, the receiver 12 feeds back to the transmitter 11 a quality indicator identifying the acquisition technique offering the best quality of service (in terms of throughput, error rate, or the like).

Thus, the information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission according to this second embodiment is a quality indicator, bearing for example an identifier of the transmission technique. acquisition of knowledge of the transmission channel to be implemented. For example, such an identifier is equal to 1 if the technique for acquiring knowledge of the channel on transmission offering the best quality of service is of the CSI-R type, equal to 2 if the technique for acquiring knowledge of the transmission channel. transmission channel offering the best quality of service is of CSI-D type, equal to 3 if the technique for acquiring knowledge of the transmission channel offering the best quality of service is of another type, etc. .

As a variant, the receiver 12 can feed back to the transmitter 11 one or more estimated parameters, and the transmitter can choose the technique for acquiring knowledge of the channel on transmission that he wishes to implement on the basis of this or these estimated parameters.

On receipt of the quality indicator (s) (step 31 of FIG. 3), the transmitter 11 can implement a technique for acquiring knowledge of the channel on the transmission identified or selected on the basis of the quality indicator (s). .

An example of the determination of the precoding matrices at the receiver level, for the two techniques for acquiring knowledge of the channel on transmission CSI-R and CSI-D, is presented below.

For simplicity, we consider a single spatial layer and a given frequency.

It is considered that the transmitter can multiply an encoded signal, noted x, by a pre-coding vector w E € ^NT of dimension N _T , with N _T the number of transmitting antennas, and transmit it through the transmission channel, direction transmitter to receiver. Since we are in the context of a single spatial layer, the precoding matrix has a single column, and is therefore called the precoding vector.

The signal received by the receiver, noted y, of dimension N _R , with N _R the number of reception antennas, can be written: y = Hwx + I with H e C ^NTXNR a representative matrix of the MIMO channel, for a frequency,

I e C ^NR a vector representative of interference and noise.

Let W be the finite dictionary of precoding matrices.

The precoding vector associated with the CSI-D technique, constrained to belong to the dictionary W, can be expressed in the following form: wopt = argmax _weW SINR (w) = argmax _weW tr {w ^† H ^† R ¹ Hw }

The associated SINR (w _fe , H _k , R _; ), for the frequency k considered, is w ^† H ^† R ¹ Hw with w =

The precoding vector associated with the CSI-R technique can be expressed in the following form: wopt ⁼ argmax _w SNR (w) = argmax _w tr {w ^† H ^† Hw}

The associated SINR (w _fe , H _k , R _; ), for the frequency k considered, is w ^† H ^† R ¹ Hw with w = w ^.

Note that the precoding vectors and w „ _pt , as well as the associated SINRs, can differ when the covariance matrix R _j moves away from a multiple of the identity matrix.

Thus, whatever the embodiment considered, it may be desirable to perform periodically and / or following a variation of the transmission channel, the steps of estimating the covariance matrix of the interference, of transmitting information. on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission, and possibly channel estimation, so as to adapt the acquisition technique to the actual transmission channel, in particular in the event of movement of the terminal.

The use of the two techniques for acquiring knowledge of the channel on transmission described in the 4G or 5G standard has been described above by way of illustration. Of course, the invention according to these different embodiments is not limited to the use of these two techniques, and can be applied to any technique for acquiring knowledge of the channel on transmission.

5.4 Devices

Finally, in relation to FIGS. 4 and 5, the simplified structures of a reception device and of a transmission device according to one embodiment of the invention are presented.

As illustrated in FIG. 4, a receiver according to one embodiment of the invention comprises a memory 41, a processing unit 42, equipped for example with a programmable computing machine or with a dedicated computing machine, for example a processor P, and controlled by the computer program 43, implementing steps of the reception method according to at least one embodiment of the invention.

On initialization, the code instructions of the computer program 43 are for example loaded into a RAM memory before being executed by the processor of the processing unit. 42.

The processor of the processing unit 42 implements steps of the reception method described above, according to the instructions of the computer program 43, to: estimate a covariance matrix of the interference, representative of the spatial structure of l 'interference between the reception antennas of the reception device, transmit at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission suitable for use by a transmission device implementing a plurality of transmit antennas, obtained from said interference covariance matrix.

As illustrated in FIG. 5, a transmitter according to one embodiment of the invention comprises a memory 51, a processing unit 52, equipped for example with a programmable computing machine or with a dedicated computing machine, for example a processor P, and controlled by the computer program 53, implementing steps of the transmission method according to at least one embodiment of the invention.

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

The processor of the processing unit 52 implements steps of the transmission method described above, according to the instructions of the computer program 53, in order to: receive at least one item of information on the quality of service associated with at least one technique acquisition of knowledge of the channel on transmission suitable for use by said transmission device, obtained from an interference covariance matrix, representative of the spatial structure of the interference between a plurality of d 'reception antennas of a reception device, implementing a technique for acquiring knowledge of the channel on the transmission identified from said at least one item of information.

Claims

1. A reception method implemented by a reception device implementing a plurality of reception antennas, comprising the estimation (21) of a covariance matrix of the interference, representative of the spatial structure of the. interference between the receiving antennas, characterized in that said method also comprises the transmission (23) of at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission, suitable for use by a transmission device implementing a plurality of transmission antennas, obtained from said interference covariance matrix.

2. Method according to claim 1, characterized in that if the interference is structured, said information is an alert indicator, indicating that the use of a technique for acquiring knowledge of the channel on transmission based on on reciprocity, implemented by said transmission device, is based on an assumption of invalid interference.

3. Method according to claim 2, characterized in that it comprises a step of determining whether said interference is structured, verifying whether the distance between said covariance matrix of the interference and a multiple of an identity matrix of the same size is. greater than a determined threshold.

4. Method according to any one of claims 2 and 3, characterized in that said alert indicator is a binary indicator.

5. Method according to any one of claims 1 to 4, characterized in that it implements, the reception of at least one reference signal, coming from said transmission device, the estimation (22) of the transmission channel on reception between said transmitting device and said receiving device, from said at least one reference signal, obtaining pre-coding matrices associated with at least two techniques for acquiring knowledge of the channel on transmission, taking into account the estimate of the transmission channel on reception, the estimate of at least one parameter representative of the quality of service associated with each of said techniques for acquiring knowledge of the channel at transmission, from said precoding matrices, and in that said at least one item of information is a quality indicator, indicating at least one technique of acquiring knowledge of the channel on transmission, the estimated parameter of which meets a determined criterion.

6. Method according to claim 5, characterized in that said parameter belongs to the group comprising: a bit rate, an error rate.

7. Method according to any one of claims 5 and 6, characterized in that it implements the selection of the technique for acquiring knowledge of the channel on transmission offering the highest level of quality of service. , from an abstraction of the physical layer.

8. Method according to any one of claims 1 to 7, characterized in that said estimate of the covariance matrix of the interference and said transmission of at least one item of information on the quality of service associated with at least one technique. acquisition of knowledge of the channel on transmission are carried out periodically and / or following a variation of the transmission channel between said transmission device and said reception device.

9. A transmission method implemented by a transmission device implementing a plurality of transmission antennas, characterized in that it comprises: the reception (31) of at least one item of information on the quality of the transmission. service associated with at least one technique for acquiring knowledge of the channel on transmission suitable for use by said transmission device, obtained from an interference covariance matrix, representative of the spatial structure of interference between a plurality of reception antennas of a reception device, the implementation (32) of a technique for acquiring knowledge of the channel on transmission identified from said at least one item of information .

10. The method of claim 9, characterized in that said information received is an alert indicator, indicating that the use of a technique of acquiring knowledge of the channel on transmission based on reciprocity, setting. implemented by said transmission device, is based on an invalid interference hypothesis.

11. The method of claim 10, characterized in that, following receipt of said alert indicator, said transmission device implements the transmission of at least one reference signal for estimating the transmission channel to the reception.

12. Method according to any one of claims 9 to 11, characterized in that said at least one item of information received is a quality indicator, indicating at least one technique for acquiring knowledge of the channel on transmission, including a parameter. representative of the quality service complies with a determined criterion, and in that said transmission device implements a technique for acquiring knowledge of the channel on transmission chosen from the technique or techniques for acquiring knowledge of the channel on transmission. program identified by the quality indicator.

13. Reception device implementing a plurality of reception antennas, comprising means for estimating a covariance matrix of the interference, representative of the spatial structure of the interference between the reception antennas, characterized in that it also comprises means for transmitting at least one item of information on the quality of service associated with at least one technique for acquiring knowledge of the channel on transmission capable of being used by a transmission device putting using a plurality of transmit antennas, obtained from said interference covariance matrix.

14. Transmission device implementing a plurality of transmission antennas, characterized in that it comprises: means for receiving at least one item of information on the quality of service associated with at least one acquisition technique. knowledge of the channel on transmission capable of being used by said transmission device, obtained from a covariance matrix of the interference, representative of the spatial structure of the interference between a plurality of antennas of reception from a reception device, means for implementing a technique for acquiring knowledge of the channel on transmission identified from said at least one item of information.

15. A computer program comprising instructions for implementing a method according to any one of claims 1 to 12 when this program is executed by a processor.