Transmission and reception method and apparatus implementing multiple transmission and reception antennas, and corresponding computer program

Abstract

The present invention relates to a reception method implemented by a reception device having a plurality of reception antennas, including estimating (21) an interference covariance matrix representative of the spatial structure of the interference between the reception antennas. According to the invention, such a method further includes transmitting (23) at least one item of information regarding the quality of service associated with at least one acquisition technique that can be used by a transmission device having a plurality of transmission antennas for acquiring channel knowledge at the transmission side, the at least one item of information being obtained based on the interference covariance matrix.

Description

Field of the Invention

[0001] The field of the present invention is the field of wireless communication.

[0002] More specifically, the present invention proposes a technique that allows optimizing the formation of the beams obtained from an antenna array in order to improve the uplink or downlink information transmission between a transmitter and a receiver.

[0003] The present invention is applicable in any system based on beamforming, in particular in radio communication networks according to the 4G or 5G standards defined by 3GPP, in WiFi communication networks according to the IEEE 802.11 standard, etc.

[0004] For downlink communication, the transmitter can be a base station, for example, a base station of the eNodeB type (“evolved Node B”) for a network based on LTE or LTE-Advanced technology, or even a Wi-Fi access point, etc. The receiver itself can be a terminal such as a smartphone, a tablet, an Internet-of-Things object type, etc. For uplink communication, the transmitter can be a terminal and the receiver can be a base station. Background Art

[0005] Beamforming or precoding is a signal processing technique used in an antenna or sensor array for the directional transmission or reception of signals. In other words, thanks to the antenna array, the transmitter and / or the receiver can focus the radiation of the transmitted waves in a specific direction, which allows obtaining spatial selectivity.

[0006] Beamforming is performed by combining phase and amplitude to control the elements of the antenna array such that:

[0007] - the signals are combined constructively in a specific direction, resulting in an enhancement of the useful power received,

[0008] - the signals are combined destructively in other directions, resulting in a reduction of the interference power received.

[0009] Thus, for beamforming at the transmitter, complex coefficients called precoding coefficients are applied to each element of the transmitter's antenna array. All these coefficients form a precoding matrix.

[0010] Note that in order to direct the radiation pattern in the desired direction, the precoding coefficients must be correctly selected. However, the problem of precoding selection is to acquire the knowledge of the channel in transmission (i.e., the knowledge of the transmission channel at the transmitter between the transmitter and the receiver), or “Channel State Information at the Transmitter (CSIT)”, and / or the spatial structure of the interference perceived by the receiver.

[0011] Currently, for MIMO systems in the 4G, 5G, IEEE802.11x (IEEE802.11n, 802.11ac, 802.11ax) standards, two techniques for obtaining channel state information at the transmitter have been proposed. The techniques for obtaining channel state information and associated reference signals are described in more detail in the 3GPP TS36.213, TS36.211 for 4G and TS38.211, TS38.214 for 5G specifications. The first technique, denoted as CSI-D, is based on the use of the return path between the receiver and the transmitter. According to the first technique, the transmitter emits at least one reference signal, also known as a pilot signal. Such a reference signal is represented, for example, as a downlink CSI-RS ("Channel State Information - Reference Signal") in the 4G and 5G standards. When the (multiple) reference signals are received, the receiver can estimate the transmission channel between the transmitter and the receiver (i.e., in the direction from the transmitter to the receiver). In addition, the estimation of the spatial characteristics of the interference (or the covariance of the interference) can be done by a simple correlation of the received signals representing the interference on different receive antennas, that is, without relying on the transmitted reference signals. For example, the transmitter can configure resources (in time-frequency) prohibited for transmission (a technique called "zero-power CSI-RS" in the 3GPPZP-CSI-RS TS38.211 standard), which allows the receiver to more easily measure the interference on these resources and for each antenna. Other methods are possible based on obtaining a signal representing the interference on different receive antennas by subtracting useful data or reference signals from the signals received on each antenna (that is, from the perspective of the receiver responsible for measuring the interference, which does not form part of the interference).

[0012] Based on the estimation of the transmission channel between the transmitter and the receiver and the spatial characteristics of the interference, the receiver can determine the precoding matrix to be used by the transmitter and feedback this precoding selection to the transmitter in the return path, for example, in the form of an indicator of the "Precoding Matrix Indicator" (PMI) type. In particular, the precoding matrix can be selected from a finite dictionary of precoding matrices specified in the 4G or 5G standards.

[0013] The second technique, denoted as CSI-R, is based on channel reciprocity, which assumes that the transmission channel between the receiver and the transmitter (i.e., in the receiver-to-transmitter direction) is the same as the transmission channel between the transmitter and the receiver (i.e., in the transmitter-to-receiver direction). Here, the channel includes the effects of the radio frequency chains, which are not a priori reciprocal in transmission and reception but can be calibrated to be so. Thus, the second technique assumes the use of the same frequency resources, and the uplink and downlink channels are separated in time, or "time division duplex" (TDD). According to the second technique, the receiver transmits at least one reference signal, e.g., a reference signal of the SRS ("sounding reference signal") type used in the uplink direction in 4G and 5G standards. Once the (multiple) reference signals are received, the transmitter can estimate the transmission channel between the receiver and the transmitter and derive therefrom the transmission channel between the transmitter and the receiver through reciprocity. Based on the estimation of the transmission channel between the transmitter and the receiver, the transmitter can select the precoding matrix to be used. For example, the transmitter determines the precoding matrix according to the criterion of maximizing the signal-to-noise ratio (SNR).

[0014] One drawback of the first CSI-D technique is that, although it is based on the knowledge of the transmission channel and the knowledge of the interference in reception, it does not allow for a fine feedback of the precoding coefficients to be used by the transmitter. In fact, since the precoding matrix is selected from a finite alphabet of precoding matrices and is fed back in the form of an indicator, quantization is implemented, resulting in information loss.

[0015] One 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 in reception. In fact, this technique determines the precoding matrix to be used by ignoring the spatial structure of the interference, and the interference in reception is not reciprocal. Then, the precoding at the transmitter according to the CSI-R technique may correspond to the direction with the strongest interference.

[0016] It is difficult to consider the covariance of the interference being fed back from the receiver to the transmitter according to the second technique, as this would consume too much of the return path. Thus, the precoding matrix based on the second technique is obtained without considering the covariance of the interference, or equivalently, by treating it as unstructured.

[0017] Therefore, there is a need for a new technique that allows the transmitter to select one technique from several available techniques to obtain the channel state information at the transmitter, which will be used to improve the information transmission between the transmitter and the receiver. Summary of the Invention

[0018] The present invention proposes a solution that does not have all these drawbacks in the form of a receiving method, which is implemented by a receiving device implementing multiple receiving antennas and includes estimating an interference covariance matrix representing the spatial structure of the interference between the receiving antennas.

[0019] Here, the structure of the interference refers to the correlation of the interference on different receiving antennas of subcarriers (given frequencies) of an OFDM symbol, for example. When the interference covariance matrix deviates from the identity matrix (within a multiplicative factor), that is, when the correlation between the receiving antennas is strong, the interference will be characterized as "structured".

[0020] In other words, if the distance between the interference covariance matrix and a multiple of the identity matrix of the same size as the interference covariance matrix is greater than a determined threshold, the interference is structured.

[0021] According to the present invention, this method further includes sending at least one item of information about the quality of service to a transmitting device implementing multiple transmitting antennas, the quality of service being associated with at least one technique that can be used by the transmitting device to obtain channel state information at the transmitter, and the at least one item of information being obtained based on the interference covariance matrix.

[0022] Therefore, the proposed solution allows taking into account the spatial characteristics of the interference in order to select a technique that can be used by the transmitting device to obtain channel state information at the transmitter for beamforming at the transmitting device.

[0023] Note that this method according to the present invention does not necessarily require estimating the transmission channel between the transmitting device (also called the transmitter) and the receiving device (also called the receiver). Therefore, it does not necessarily rely on the transmission of reference signals from the transmitter to the receiver.

[0024] In fact, the receiver can directly estimate the interference covariance matrix based on any signal received by the receiver that the receiver does not know or only partially knows.

[0025] Once this any signal is received, the receiver can estimate the interference covariance matrix and use the knowledge of the interference to feedback at least one item of information about the quality of service to the transmitter, the quality of service being associated with at least one technique that can be used by the transmitter to obtain channel state information at the transmitter.

[0026] According to a first embodiment, the interference covariance matrix can be used to determine whether the interference is structured.

[0027] According to this first embodiment, it is assumed that the transmitting device implements a technique for obtaining channel state information at the transmitter based on reciprocity. This technique is based on the assumption that interference is not structured or poorly structured. If the receiving device determines that the interference in reception is structured, i.e., deviates from the diagonal matrix, it can thus return a warning indicator to the transmitter to inform the transmitting device that the assumption that the interference is not structured or poorly structured in reception is invalid.

[0028] For example, such an indicator is carried by a single bit, which is equal to 0 if the interference is structured or equal to 1 (or vice versa) if the interference is not structured. Thus, such an indicator consumes very little bandwidth on the return path.

[0029] Once the alert indicator is received, if the indicator indicates that the use of the technique for obtaining channel state information at the transmitter based on reciprocity is based on an invalid assumption of unstructured or poorly structured interference (i.e., ignoring structured interference), the transmitter can choose to implement a CSI-D type of technique for obtaining channel state information at the transmitter or any other technique.

[0030] For example, if it is reported that:

[0031]

[0032] is greater than a determined threshold, the interference is structured,

[0033] where:

[0034] N R is the number of receiving antennas,

[0035] R I is the interference covariance matrix of size N R ×N R 2

[0036] σ 2 is the average power of interference and noise received on the receiving antennas,

[0037] I is the identity matrix of size N R ×N R F

[0038] |||| F is the Frobenius norm.

[0039] According to the second embodiment, which is implemented when the transmission channel between the transmitter and the receiver can be estimated, the receiving method implements:

[0040] - receiving at least one reference signal from the transmitting device,

[0041] - Estimate the transmission channel at the receiver between the transmitting device and the receiving device based on the reference signal(s) (i.e., in the direction from the transmitter to the receiver, also referred to as obtaining channel knowledge at the receiver, or "channel state information at the receiver" (CSIR)).

[0042] - Obtain a precoding matrix associated with at least two techniques for obtaining channel state information at the transmitter, taking into account the estimated transmission channel at the receiver.

[0043] - Estimate at least one parameter from the precoding matrix, which parameter represents the quality of service associated with each of the techniques for obtaining channel state information at the transmitter.

[0044] In this case, the interference covariance matrix can be used together with the estimated transmission channel at the receiver to determine a precoding matrix associated with certain techniques for obtaining channel state information at the transmitter, such as CSI-D techniques.

[0045] Note that this second embodiment can be implemented independently or in combination with the first embodiment.

[0046] For example, after the transmitter according to the first embodiment receives an alert indicator, the transmitter can send at least one reference signal for estimating the transmission channel at the receiver, which can be used according to this second embodiment. Thus, the receiver can obtain a precoding matrix for use with the technique for obtaining channel state information at the transmitter based on reciprocity according to the first embodiment, and determine at least one precoding matrix associated with at least one different technique for obtaining channel state information at the transmitter.

[0047] According to this second embodiment, the information fed back to the transmitter is a quality indicator indicating at least one of the techniques for obtaining channel state information at the transmitter, the estimated parameter of which meets a determined criterion.

[0048] For example, the parameter belongs to a group including the following:

[0049] - Throughput,

[0050] - Error rate,

[0051] - Etc.,

[0052] And the determined criterion is a criterion such as maximum throughput, target error rate, etc.

[0053] Such an indicator also consumes very little bandwidth on the return path.

[0054] The selection of the acquisition technique to be used by the transmitter can be performed by the receiver. In this case, the receiver can feedback a single quality indicator, i.e., several techniques for acquiring the channel state information at the transmitter allow achieving, for example, a target error rate.

[0055] Alternatively, the transmitter can perform the selection of the acquisition technique to be used by the transmitter. In this case, the receiver can feedback all quality indicators, or only feedback those quality indicators corresponding to the techniques for acquiring the channel state information at the transmitter, the estimated parameters of which satisfy a determined criterion.

[0056] Specifically, the receiving method implements the selection from the abstractions of the physical layer of the technique for acquiring the channel state information at the transmitter that provides the highest quality of service level.

[0057] Regardless of the embodiment considered, the estimation of the interference covariance matrix and the transmission of at least one information item regarding the quality of service associated with at least one technique for acquiring the channel state information at the transmitter can be performed periodically and / or after a change in the transmission channel between the transmitting device and the receiving device.

[0058] Therefore, the technique for acquiring the channel state information at the transmitter implemented by the transmitter is adaptive and can be changed during transmission, for example, when the terminal moves.

[0059] According to a specific embodiment, the transmitter (e.g., a base station) requests the receiver (e.g., a terminal) to feedback an information item regarding the quality of service associated with at least one technique for acquiring the channel state information at the transmitter.

[0060] According to another embodiment, for example, after detecting a change in the transmission channel, the receiver actively feedbacks an information item regarding the quality of service associated with at least one technique for acquiring the channel state information at the transmitter.

[0061] In another embodiment, the present invention relates to a corresponding receiving device implementing multiple receive antennas.

[0062] For example, such a receiving device includes at least one processor configured to:

[0063] - Determine an interference covariance matrix representing the spatial structure of the interference between the receive antennas,

[0064] - Transmit at least one information item regarding the quality of service associated with at least one technique for acquiring the channel state information at the transmitter that can be used by a transmitting device implementing multiple transmit antennas, the at least one information item being obtained based on the interference covariance matrix.

[0065] For example, if in the downlink direction, i.e., from the base station to the terminal, such a receiving device is the terminal. If in the uplink direction, i.e., from the terminal to the base station, such a receiving device is the base station.

[0066] The present invention also relates to a corresponding transmission method, which is implemented by a transmission device implementing a plurality of transmission antennas.

[0067] According to the present invention, such a transmission method includes:

[0068] - receiving at least one item of information on the quality of service, which is associated with at least one technique for obtaining channel state information at the transmitter that can be used by a transmission device implementing a plurality of transmission antennas, and the at least one item of information is obtained based on an interference covariance matrix representing the spatial structure of interference between a plurality of receiving antennas of the receiving device,

[0069] - implementing the technique for obtaining channel state information at the transmitter identified from the at least one item of information.

[0070] In other words, the transmitter receives information on the quality of service, which is associated with at least one technique for obtaining channel state information at the transmitter, and can implement the technique for obtaining channel state information at the transmitter identified from the received information on the quality of service.

[0071] According to a first embodiment, the received information is an alert indicator indicating that the use of the technique for obtaining channel state information at the transmitter based on reciprocity implemented by the transmission device is based on an invalid interference assumption.

[0072] According to this first embodiment, the present invention thus allows notifying the transmitter of the situation of structured interference in reception, and the transmitter may implement or switch to an acquisition technique different from the CSI-R technique.

[0073] In particular, after receiving the alert indicator, the transmission device may implement the transmission of at least one reference signal for estimating the transmission channel at reception.

[0074] According to a second embodiment independent of or implemented after the first embodiment, the at least one received item of information is a quality indicator indicating that at least one technique for obtaining channel state information at the transmitter, which represents a parameter of the quality of service, satisfies a determined criterion, and the transmission device implements the technique for obtaining channel state information at the transmitter identified by the quality indicator, which is selected from the (plural) techniques for obtaining channel state information at the transmitter.

[0075] In another embodiment, the present invention relates to a corresponding transmission device implementing a plurality of transmission antennas.

[0076] For example, such a transmitting device includes at least one processor configured to:

[0077] - receive at least one item of information regarding quality of service, the quality of service being associated with at least one technique that can be used by the transmitting device for obtaining channel state information at the transmitter, the at least one item of information being obtained based on an interference covariance matrix representing a spatial structure of interference between a plurality of receiving antennas of a receiving device,

[0078] - implement the technique for obtaining channel state information at the transmitter identified from the at least one item of information.

[0079] In particular, the different steps of the receiving and / or transmitting method according to at least one embodiment of the present invention can be implemented in different ways, in particular in hardware form and / or software form.

[0080] For example, at least one step of the receiving and / or transmitting method can be implemented:

[0081] - on a reprogrammable computing machine (computer, processor (e.g., DSP (“Digital Signal Processor”)), microcontroller, etc.) executing a program including a sequence of instructions,

[0082] - on a dedicated computing machine (e.g., a set of logic gates such as an FPGA (“Field Programmable Gate Array”) or an ASIC (“Application Specific Integrated Circuit”)) or any other hardware module).

[0083] Accordingly, embodiments of the present invention also aim to protect one or more computer programs and at least one computer-readable storage medium, the one or more computer programs including instructions adapted to implement the receiving and / or transmitting method according to at least one embodiment of the present invention as described above when the program or programs are executed by a processor, the at least one computer-readable storage medium including the instructions of the at least one computer program as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Other features and advantages of the present invention will become more apparent upon reading the following description of specific embodiments, which are given by way of simple illustrative and non-limiting examples and with reference to the drawings, in which:

[0085] Figure 1 a MIMO system in which the present invention can be implemented is shown;

[0086] Figure 2 main steps implemented by a receiving method according to an embodiment of the present invention are shown;

[0087] Figure 3Shows the main steps implemented by the transmission method according to an embodiment of the present invention;

[0088] Figure 4 and Figure 5 respectively show the simplified structures of a receiver and a transmitter according to an embodiment of the present invention. Detailed implementation

[0089] 5.1 General principle

[0090] The general principle of the present invention is based on the feedback of information from the receiver to the transmitter in a MIMO system ("multiple input multiple output"), so that the transmitter can implement techniques for obtaining channel knowledge at the transmitter (or "channel state information at the transmitter") considering the actual transmission conditions including interference in reception.

[0091] Figure 1 Shows a MIMO system in which the present invention can be implemented. Such a system includes a transmitter 11 including a plurality of transmitting antennas 111,..., 11m, and a receiver 12 including a plurality of receiving antennas 121,..., 12n.

[0092] The transmitter 11 can particularly implement encoding and modulation operations, and the receiver 12 can implement decoding and demodulation operations.

[0093] The transmission channel between the transmitter 11 and the receiver 12 can be represented by a channel matrix H.

[0094] Relative to Figure 2 and Figure 3 , shows the main steps of the receiving method according to an embodiment of the present invention implemented by the receiver 12, and the main steps of the transmitting method according to an embodiment of the present invention implemented by the transmitter 11, allowing the transmitter 11 to implement techniques for obtaining channel state information at the transmitter adapted to the transmission channel.

[0095] As Figure 2 shown, during step 21, the receiver 12 determines an interference covariance matrix representing the spatial structure of interference between the receiving antennas 121,..., 12n of the receiver 12.

[0096] In particular, for example, for CSI-D technology, the interference covariance matrix can be determined conventionally.

[0097] Possibly, during step 22, the receiver 12 also estimates the transmission channel between the transmitter 11 and the receiver 12, especially if it receives a reference signal from the transmitter 11.

[0098] Based on the interference covariance matrix and the estimation of the transmission channel at the possible receiving end, during step 23, the receiver 12 determines at least one information item regarding the quality of service associated with at least one technique that can be used by the transmitter 11 to obtain the channel state information at the transmitter, and sends the obtained information to the transmitter 11 in the return path.

[0099] As Figure 3 shown, during step 31, the transmitter 11 thus receives at least one information item regarding the quality of service associated with at least one technique for obtaining the channel state information at the transmitter, and this at least one information item is obtained based on the interference covariance matrix. The transmitter 11 can receive several information items regarding the quality of service associated with different techniques for obtaining the channel state information at the transmitter, and these information items may be obtained from the estimation of the transmission channel at the receiving end.

[0100] During step 32, the transmitter can implement the technique for obtaining the channel state information at the transmitter identified from the information regarding the quality of service associated with at least one technique for obtaining the channel state information at the transmitter.

[0101] 5.2 Description of the First Embodiment

[0102] The first embodiment is described below for determining at least one information item regarding the quality of service associated with at least one technique for obtaining the channel state information at the transmitter.

[0103] According to this first embodiment, it is considered that the receiver 12 cannot estimate the transmission channel (in the direction from the transmitter 11 to the receiver 12). For example, if the receiver 12 does not receive a reference signal from the transmitter 11, it cannot estimate the transmission channel.

[0104] According to this first embodiment, even if the receiver 12 cannot estimate the transmission channel, it can estimate the interference covariance ( Figure 2 step 21).

[0105] For example, if it is assumed that the receiver 12 has N R receiving antennas, and the considered frequency band includes K carrier frequencies (e.g., according to the OFDMA type modulation technique), then the receiver 12 can estimate the interference covariance matrix such that:

[0106]

[0107] where:

[0108] is the interference observation value at frequency k measured by the receiver 12, and

[0109] is the conjugate transpose operator.

[0110] According to this example, if the covariance matrix R I deviates from the matrix σ 2 I (i.e., deviates from the diagonal structure), then the interference is structured (i.e., defined in a preferred direction where the interference is stronger than in other directions), where:

[0111] - is the average power of the interference and noise received on the receiving antenna, and

[0112] -I is the identity matrix of dimension N R × N R of.

[0113] In other words, if the matrix K I is defined such that K I = R I - σ 2 I, then if the following ratio is greater than a determined threshold T, the interference is considered structured:

[0114]

[0115] where |||| F is the Frobenius norm, and tr() is the trace operator.

[0116] For example, such a threshold is in the range of 30%.

[0117] If the receiver 12 determines that the interference is structured (or equivalently, the interference covariance matrix is structured), it can feedback a warning indicator to the transmitter 11 ( Figure 2 step 23 of), notifying the transmitter that the interference in reception is structured, and using the technique of obtaining the channel state information at the transmitter based on reciprocity ignores the structured interference in reception, i.e., based on the invalid assumption of unstructured or poorly structured interference in reception. In fact, for CSI-R acquisition techniques that ignore the interference spatial structure, the structured interference in reception may be problematic.

[0118] In this case, it may be preferable for the transmitter 11 to use a CSI-D type acquisition technique, or any other technique for obtaining the channel state information at the transmitter, which can consider the interference covariance in the selection of the precoding matrix.

[0119] For example, information on the quality of service associated with at least one technique for obtaining channel state information at the transmitter is the alert indicator "indic", which is equal to 1 if the interference is structured, or equal to 0 or an empty field if the interference is not structured.

[0120] Once this alert indicator is received ( Figure 3 step 31), the transmitter 11 knows whether the hypothesis made about the interference during reception is valid. If it is valid (in the example above, the alert indicator is empty or equal to 0), it can continue to use the technique for obtaining channel state information at the transmitter based on reciprocity. If the hypothesis is invalid (in the example above, the alert indicator is equal to 1), it can decide to switch to another technique for obtaining channel state information at the transmitter, or transmit a reference signal so that the receiver can compare several techniques for obtaining channel state information at the transmitter and feed back a quality indicator to the transmitter, as described below.

[0121] 5.3 Description of the second embodiment

[0122] The 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 obtaining channel state information at the transmitter.

[0123] According to this second embodiment, it is considered that the receiver 12 can estimate the transmission channel (in the direction from the transmitter 11 to the receiver 12).

[0124] According to this second embodiment, thus, on the one hand, the receiver 12 can estimate the interference covariance ( Figure 2 step 21), and on the other hand, the receiver 12 can estimate the transmission channel between the transmitter and the receiver ( Figure 2 step 22).

[0125] The interference covariance matrix R I can be estimated as described for the first embodiment.

[0126] For a frequency band in the direction from the transmitter 11 to the receiver 12, the transmission channel H = {H 1 , H 2 ,..., H K} for each frequency can be estimated based on the reception by the receiver 12 of at least one reference signal from the transmitter 11.

[0127] According to this second embodiment, the receiver 12 can determine which precoding matrix will be used at the transmitter 11 for different techniques for obtaining channel state information at the transmitter.

[0128] For example, the receiver 12 determines the precoding matrix associated with the CSI-R acquisition technique by considering the estimate of the transmission channel at the reception and by assuming that the interference covariance matrix is equal to σ 2 I. The receiver also determines the precoding matrix associated with the CSI-D acquisition technique by considering the estimate of the transmission channel at the reception and the interference covariance matrix R J , as well as the finite dictionary W of precoding matrices defined by the 4G or 5G standard. Possibly, the receiver can determine one or more precoding matrices associated with one or several other techniques for obtaining the channel state information at the transmitter. For example, such a precoding matrix is selected so as to maximize the signal-to-interference-plus-noise ratio.

[0129] The receiver 12 can use these different precoding matrices to predict the quality of service associated with the use of different techniques for obtaining the channel state information at the transmitter.

[0130] Thus, the receiver 12 can estimate at least one parameter representing the quality of service associated with each of the techniques for obtaining the channel state information at the transmitter from the previously determined precoding matrices, for example, throughput type, error rate type, etc.

[0131] For example, for a given frequency k, the signal-to-interference-and-noise ratio (SINR) in reception can be expressed according to the selected precoding vector w k , the transmission channel H k and the interference covariance matrix R I . For a given frequency k, such a signal-to-noise ratio is expressed as SINR(w k , H k , R I ), where k = 1,.., K, as described below.

[0132] The receiver 12 can implement a physical layer abstraction technique (“PHY abstraction”) to evaluate different techniques for obtaining channel state information at the transmitter and predict which transmission format allows, for example, maximizing the throughput of the considered frequency band or achieving the target error rate of the considered frequency band. Such a physical layer abstraction technique is specifically presented in the literature “Link performance models for system level simulations of broadband radio access systems” (K. Brueninghaus et al., IEEE 16th International 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” (J. B. Landre et al., Proc. IEEE VTCS 2012, Yokohama, Japan, May 2012).

[0133] For example, according to a mapping technique called MIESM (“Mutual Information Effective Signal-to-Noise Ratio Mapping”) technique, this abstraction of the physical layer will match the SINR (w k , H k , R I ) for frequency k (k = 1,.., K) to an “effective” SINR, and then use a Gaussian quality table associated with the family of coding and modulation schemes specified in the standard to match each “effective” SINR to throughput.

[0134] The receiver 12 can associate the throughput D 2 = f(H, σ 2 I) with the CSI-R acquisition technique and associate the throughput D 1 = f(H, R I |W) with the CSI-D acquisition technique. In the same way, the receiver can associate other throughputs with other techniques for obtaining channel state information at the transmitter.

[0135] Therefore, the receiver 12 can select a technique for obtaining channel state information at the transmitter whose estimated parameters (e.g., throughput, error rate, etc.) satisfy a determined criterion and feedback a quality indicator to the transmitter 11 indicating the selected (multiple) acquisition techniques. For example, the receiver 12 feeds back a quality indicator to the transmitter 11 identifying the acquisition technique that provides the best quality of service (in terms of throughput, error rate, etc.).

[0136] Thus, the information on the quality of service associated with at least one technique for obtaining channel state information at the transmitter according to this second embodiment is a quality indicator, e.g., an identifier carrying the technique for obtaining channel state information at the transmitter to be implemented. For example, if the technique for obtaining channel state information at the transmitter that provides the best quality of service is of the CSI-R type, this identifier is equal to 1; if the technique for obtaining channel state information at the transmitter that provides the best quality of service is of the CSI-D type, this identifier is equal to 2; if the technique for obtaining channel state information at the transmitter that provides the best quality of service is of another type, this identifier is equal to 3, and so on.

[0137] Alternatively, the receiver 12 can feedback one or more estimated parameters to the transmitter 11, and the transmitter can select, based on this or these estimated parameters, the technique for obtaining channel state information at the transmitter that it wishes to implement.

[0138] Once the (multiple) quality indicator(s) Figure 3 in step 31) is / are received, the transmitter 11 can implement the technique for obtaining channel state information at the transmitter identified or selected from the (multiple) quality indicator(s).

[0139] Examples of determining the precoding matrix at the receiver for two CSI-R and CSI-D techniques for obtaining channel state information at the transmitter are presented below.

[0140] For simplicity, consider a single spatial layer and a given frequency.

[0141] It is considered that the transmitter can multiply the coded signal represented as x by a precoding vector of dimension N T where N T is the number of transmit antennas and transmit it via the transmission channel (in the transmitter-to-receiver direction). Since the precoding matrix has a single column in the context of considering a single spatial layer, it is referred to as a precoding vector.

[0142] The signal (represented as y) received by the receiver with dimension N R (where N R is the number of receive antennas) can be written as:

[0143] y = Hwx + I

[0144] where:

[0145] - is the matrix representing the MIMO channel for the frequency,

[0146] - ​is a vector representing interference and noise.

[0147] W is a finite dictionary of precoding matrices.

[0148] The precoding vector associated with CSI-D technology (constrained to belong to the dictionary W) can be represented in the following form:

[0149]

[0150] For the considered frequency k, the associated SINR(w k , H k , R I ) is where,

[0151] The precoding vector associated with CSI-R technology can be represented in the following form:

[0152]

[0153] For the considered frequency k, the associated SINR(w k , H k , R I ) is where,

[0154] Note that when the covariance matrix R I deviates from a multiple of the identity matrix, the precoding vectors and and the associated SINR may be different.

[0155] Thus, regardless of the considered embodiment, it may be desirable to perform the following steps periodically and / or after a change in the transmission channel: estimate the interference covariance matrix, transmit information about the quality of service associated with at least one technique for obtaining channel state information at the transmitter, and possibly channel estimation, in order to adapt the acquisition technique to the actual transmission channel, especially in the case of terminal displacement.

[0156] The use of two techniques for obtaining channel state information at the transmitter described in the 4G or 5G standard has been described above by way of example. Of course, the present invention according to these different embodiments is not limited to the use of these two techniques, but can be applied to any technique for obtaining channel state information at the transmitter.

[0157] 5.4 Devices

[0158] Finally, regarding Figure 4 and Figure 5 , a simplified structure of a receiving device and a transmitting device according to an embodiment of the present invention is introduced.

[0159] As Figure 4 shown, a receiver according to an embodiment of the present invention includes a memory 41 and a processing unit 42, which is equipped with, for example, a programmable computing machine or a dedicated computing machine (e.g., a processor P) and is driven by a computer program 43 to implement the steps of a receiving method according to at least one embodiment of the present invention.

[0160] At initialization, the code instructions of the computer program 43 are loaded into the RAM memory, for example, before being executed by the processor of the processing unit 42.

[0161] The processor of the processing unit 42 implements the steps of the aforementioned receiving method according to the instructions of the computer program 43 to:

[0162] - Estimate an interference covariance matrix representing the spatial structure of interference between the receiving antennas of the receiving device,

[0163] - Transmit at least one item of information about the quality of service, which is associated with at least one technique that can be used by a transmitter implementing multiple transmit antennas to obtain channel state information at the transmitter, and the at least one item of information is obtained based on the interference covariance matrix.

[0164] As Figure 5 shown, a transmitter according to an embodiment of the present invention includes a memory 51 and a processing unit 52, which is equipped with, for example, a programmable computing machine or a dedicated computing machine (e.g., a processor P) and is driven by a computer program 53 to implement the steps of a transmitting method according to at least one embodiment of the present invention.

[0165] At initialization, the code instructions of the computer program 53 are loaded into the RAM memory, for example, before being executed by the processor of the processing unit 52.

[0166] The processor of the processing unit 52 implements the steps of the aforementioned transmitting method according to the instructions of the computer program 53 to:

[0167] - Receive at least one item of information about the quality of service, which is associated with at least one technique that can be used by the transmitting device to obtain channel state information at the transmitter, and the at least one item of information is obtained based on an interference covariance matrix representing the spatial structure of interference between multiple receiving antennas of the receiving device,

[0168] - Implement the technique for obtaining channel state information at the transmitter identified from the at least one item of information.

Claims

1. A receiving method implemented by a receiving device implementing multiple receiving antennas, including estimating (21) an interference covariance matrix representing the spatial structure of interference between the receiving antennas, characterized in that, the method further includes transmitting (23) at least one item of information regarding the quality of service, the quality of service being associated with at least one technique that can be used by a transmitting device implementing multiple transmitting antennas to obtain channel state information at the transmitter, and the at least one item of information being obtained based on the interference covariance matrix; and characterized in that the at least one item of information is an alert indicator in the case where the interference is structured, indicating that the use of the technique for obtaining channel state information at the transmitter based on reciprocity by the transmitting device is based on an invalid interference assumption, and / or the at least one item of information is a quality indicator indicating at least one technique for obtaining channel state information at the transmitter, and a parameter representing the quality of service of the quality indicator satisfies a determined criterion.

2. The method according to claim 1, characterized in that, the method includes a step of determining whether the interference is structured, by checking whether the distance between the interference covariance matrix and a multiple of the identity matrix of the same size is greater than a determined threshold.

3. The method according to any one of claims 1 and 2, characterized in that, the alert indicator is a binary indicator.

4. The method according to any one of claims 1 to 3, characterized in that, implementing: - receiving at least one reference signal from the transmitting device, - estimating (22) the transmission channel at the receiving side between the transmitting device and the receiving device based on the at least one reference signal, - obtaining a precoding matrix associated with at least two techniques for obtaining channel state information at the transmitter, taking into account the estimation of the transmission channel at the receiving side, - estimating from the precoding matrix at least one parameter representing the quality of service associated with each of the techniques for obtaining channel state information at the transmitter, and characterized in that the at least one item of information is a quality indicator indicating at least one technique for obtaining channel state information at the transmitter whose estimated parameter satisfies a determined criterion.

5. The method according to claim 4, characterized in that, the parameter belongs to a group including the following items: - throughput, - error rate.

6. The method according to any one of claims 4 and 5, characterized in that, implementing selecting, from the abstractions of the physical layer, the technique for obtaining channel state information at the transmitter that provides the highest quality of service level.

7. The method according to any one of claims 1 to 6, characterized in that, the estimation of the interference covariance matrix and the transmission of at least one item of information regarding the quality of service associated with at least one technique for obtaining channel state information at the transmitter are implemented periodically and / or after a change in the transmission channel between the transmitting device and the receiving device.

8. A transmitting method implemented by a transmitting device implementing multiple transmitting antennas, characterized in that, including: - Receive (31) at least one information item regarding the quality of service, where the quality of service is associated with at least one technique that can be used by the transmitting device to obtain channel state information at the transmitter, and the at least one information item is obtained based on an interference covariance matrix representing the spatial structure of interference between multiple receive antennas of the receiving device. The at least one information item is an alert indicator indicating that the use of the technique for the transmitting device to obtain channel state information at the transmitter based on reciprocity is based on an invalid interference assumption, and / or is a quality indicator indicating at least one technique for obtaining channel state information at the transmitter, and a parameter representing the quality of service of the quality indicator meets a determined criterion. - Implement (32) the technique for obtaining channel state information at the transmitter identified from the at least one information item. When the at least one received information item is the quality indicator, the implemented technique is identified by the quality indicator and selected from one or more techniques for obtaining channel state information at the transmitter.

9. The method according to claim 8, wherein, after receiving the alert indicator, the transmitting device implements the transmission of at least one reference signal for estimating the transmission channel at the receiver.

10. A receiving device implementing multiple receive antennas, including components for estimating an interference covariance matrix representing the spatial structure of interference between the receive antennas, wherein, the receiving device further includes components for transmitting at least one information item regarding the quality of service, where the quality of service is associated with at least one technique that can be used by a transmitting device implementing multiple transmit antennas to obtain channel state information at the transmitter. The at least one information item is obtained based on the interference covariance matrix. And when the interference is structured, the at least one information item is an alert indicator indicating that the use of the technique for the transmitting device to obtain channel state information at the transmitter based on reciprocity is based on an invalid interference assumption, and / or the at least one information item is a quality indicator indicating at least one technique for obtaining channel state information at the transmitter, and a parameter representing the quality of service of the quality indicator meets a determined criterion.

11. A transmitting device implementing multiple transmit antennas, wherein, the transmitting device includes: - A component for receiving at least one information item regarding quality of service, the quality of service being associated with at least one technique that can be used by the transmitting device to obtain channel state information at the transmitter, the at least one information item being obtained based on an interference covariance matrix representing a spatial structure of interference between a plurality of receive antennas of the receiving device, the at least one information item being an alert indicator indicating that the use of the technique for obtaining channel state information at the transmitter based on reciprocity by the transmitting device is based on an invalid interference assumption, and / or a quality indicator indicating at least one technique for obtaining channel state information at the transmitter, a parameter of the quality indicator representing the quality of service satisfying a determined criterion. - A component for implementing the technique for obtaining channel state information at the transmitter identified from the at least one information item, wherein when the at least one received information item is the quality indicator, the implemented technique is identified by the quality indicator and selected from one or more techniques for obtaining channel state information at the transmitter.

12. A computer program comprising instructions for implementing the method according to any one of claims 1 to 9 when the program is executed by a processor.

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