Precoding and reception processes, transmitting device and receiving device

Abstract

Precoding and reception methods, transmitter device and receiver device. The invention proposes a method for precoding, by a transmitter device (2), sequence(s) of symbol(s) spatially distributed on layers of Mlayer symbols using a plurality of complex precoding matrices of dimensions Px, where P denotes a number of antenna ports of the transmitter device, each precoding matrix being constructed from a combination of a complex matrix W of dimensions Px, a complex diagonal matrix D of dimensions x introducing a variety of cyclic delays and a complex rotation matrix U of dimensions x, said precoding method being characterized in that, for >1 and P>min(1,), the P columns of the complex matrix W are linear combinations of distinct vectors from a basis of P orthogonal vectors, p=0,..,P-1. Figure for the abstract: Fig. 1.

Description

Title of the invention: Precoding and reception methods, transmitter device and receiver device technical field

[0001] The invention belongs to the general field of telecommunications.

[0002] It relates more particularly to a precoding technique for a multiple input single output system (or MISO for "Multiple Input Single Output" in English) or a multiple input multiple output system (or MIMO for "Multiple Input Multiple Output" in English), operating in open loop (or "open-loop" in English).

[0003] The invention has a preferred, but not limiting, application in the context, for example, of 5G or 6G communication networks, as defined by the 3GPP standard, in which such systems are considered. However, the invention may also be applicable in other contexts. Previous technique

[0004] Many MIMO and MISO techniques, based on multiple transmitting antennas and one or more receiving antennas, are used today in industry, particularly in mobile communication networks such as those defined by the 3GPP standard. The term "antennas," or equivalently here "antenna ports," refers to both physical antennas or radiating elements and logical antennas. An antenna port is an abstract concept, defined, for example, in paragraph 4.4.1 of 3GPP document TS 38.211 entitled "Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 17)" v 17.7.0 (2024-03), according to which the channel on which a symbol from an antenna port is transmitted can be deduced from the channel on which another symbol from the same antenna port is transmitted.

[0005] Among these MIMO / MISO techniques, the 3GPP standard specifically envisions the implementation of precoding techniques enabling spatial multiplexing while benefiting from transmission diversity. Such techniques rely on the application of linear precoding to the data symbols during transmission (typically in the form of a matrix or a combination of matrices), allowing these data symbols to be distributed across different antenna ports in order to compensate for the effects of the propagation channel and optimize reception performance.

[0006] MIMO / MISO precoding techniques can be classified into two categories: - MIMO / MISO precoding techniques operating in a closed loop; and - MIMO / MISO precoding techniques operating in open loop (or "open loop" in English).

[0007] Closed-loop MIMO / MISO precoding techniques rely on the transmission from receiver to transmitter of an estimate of the radio propagation channel seen by the receiver. This allows the transmitter to determine the precoding to use when communicating with the receiver. Alternatively, the transmission relies on information representing the precoding to be used by the transmitter (for example, an index pointing to a particular precoding, also called a PMI for "Precoding Matrix Indicator") in a predefined dictionary (or "codebook") known to both the transmitter and the receiver. Such a dictionary is an indexed list of precoders that can be used by the transmitter when communicating with the receiver. According to this latter variant, the precoding is thus optimized by the receiver and then transmitted to the transmitter for given reception conditions (radio channel).

[0008] However, the transmission of information representative of the receiver-optimized precoding, even if reduced to an index pointing to a particular precoder in a dictionary, proves costly in terms of the amount of information to be sent back via the network, especially when the dictionary is large and many user devices are considered.

[0009] Open-loop MIMO / MISO precoding techniques do not require the transmission of such information between the receiver and the transmitter. Therefore, to determine the precoding to be applied during transmission, the transmitter must scan a set of precoders that provide acceptable performance at the receiver, regardless of the radio transmission conditions between the transmitter and the receiver.

[0010] By way of illustration, the 3GPP standard has adopted for 4G networks known as LTE (for "Long Term Evolution") an open-loop diversity technique called "Large Delay CDD" (for "Cyclic Delay Diversity") or large-delay cyclic diversity. This technique consists of introducing a delay between the signals emitted by the different spatial layers. It is described in particular in section 6.3.4.2.2 of the 3GPP document TS 36.211 entitled "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 17)", v 17.4.0 (September 2023). It is intended for downlink transmissions (base station to user equipment) and configurations with a number of transmit antenna ports equal to 2 or 4, limiting the maximum number of spatial layers that can be considered to 2, respectively to 4.

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[0027] More specifically, if x(i) denotes a vector of r complex symbols, v representing the number of spatial layers considered for spatial multiplexing, the vector X(f) precoded using a "large delay CDD" technique is defined as follows: X(Z) = W(i)D(i)Ux(i\ig{(), M^-l} Or : - ^^^ denotes the number of uses of the channel (or equivalently, the size of the sequence of symbols sent on each spatial layer); - D(i) is a complex diagonal matrix of dimensions vxv, which manages the cyclic delay diversity. The values ​​on the diagonal of the matrix D(i) represent phase shifts applied for each spatial layer / e {0, ..., v - 1} - More precisely: D(i) - diag(l, e^, ..., ) - U is a fixed rotation matrix of dimensions vx v (also called a DFT matrix for "Discrete Fourier Transform" in English), which is written as follows: 1 1 1 1 u= 1 ¢-4- - / 2.TH e— .1 ■ iQjrnh-l) ey • VV The matrix H(i) is a complex matrix (called a precoding matrix) of dimensions P x v, selected from the elements of a predefined dictionary (each element defining a precoder), configured at the base station and user equipment levels. The construction of the dictionary precoders is described in 3GPP TS 36.211 for specific configurations, namely for V=1 or 2 when P=2, and for F<4 when P=4. More precisely, for P=2 transmit antenna ports, the matrix W(i) remains constant regardless of the use of channel i and is taken as equal to: - for F=l: - for v=2: = ?] For P=4 transmit antenna ports, the dictionary precoders are cyclically allocated to the vectors x(i) corresponding to different uses i of the channel, with a different precoder being used every v vectors. The precoder WU) is selected as follows: W(i)=C k with £= (B 4) + the {1,2, 3,4}

[0028] where Cj, Cj, Cj, C4 are matrices given in Table 6.3.4.2.3-2 of document 3GPP TS 36.211 (corresponding to precoder indices 12, 13, 14 and 15 respectively), as a function of the number of spatial layers v and for r<4. The corresponding rows of Table 6.3.4.2.3-2 are reproduced below: [Tables 1] Index "B Number of layers v 1 2 3 4 12 "I2=[l O 'IO j. 2. vj J / j 13 "13=[i -ii -ir ' : 4 "■ wW 14 "14= [1 1 -1 -1] 15 "15= [1 1 1 if Pi' / 2

[0029] More specifically, the matrices W(i) are obtained from the elements of this table by applying a Householder construction. The columns of the matrix W(i) are derived from the 4 vectors mh- Bis reported in the table, to which the Householder transformation is applied according to:

[0030] Wn = I- 2u„u% / u^un

[0031] where I denotes the 4-dimensional identity matrix and hg {12,13,14,15}, s°it:

[0032] - jyW is the vector corresponding to column i of

[0033] jyM is the 4x2 matrix formed by columns i and j of

[0034] jyf'Al is the 4x3 dimension matrix formed by columns i, j, and k of and

[0035] is the 4x4 dimension matrix formed from columns i, j, k, and 1 of Wn.

[0036] The disadvantage of this construction is that it is only defined for a number of transmitting antenna ports equal to 4, and incidentally, a maximum number of spatial layers equal to 4. Description of the invention

[0037] The invention notably overcomes this drawback by proposing a method for precoding, by a transmitting device, v sequence(s) of symbol(s) spatially distributed on v layers of Mlayer symbols using a plurality of complex precoding matrices of dimensions PxF, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a combination of a complex matrix W of dimensions PxF, a complex diagonal matrix D of dimensions FxF introducing a variety of cyclic delays, and a complex rotation matrix U of dimensions FxF, said precoding process being characterized in that, for V>1 and P>min(l,v), the P columns of the complex matrix W are linear combinations of distinct vectors of a basis of P orthogonal vectors p=0,..,Pl.

[0038] Correspondingly, the invention also relates to a transmitter device comprising a precoding module, configured to precode v sequence(s) of symbols spatially distributed over v layers of Mlayer symbols using a plurality of complex precoding matrices of dimensions Pxv, where P denotes a number of antenna ports of the transmitter device, each precoding matrix being constructed from a combination of a complex matrix W of dimensions Pxv, a complex diagonal matrix D of dimensions vxv introducing a diversity of cyclic delays and a complex rotation matrix U of dimensions vxv, said transmitter device being characterized in that, for V>1 and P>min(l,,,), the P columns of the complex matrix W are linear combinations of distinct vectors from a basis of P orthogonal vectors p=0,..,Pl.

[0039] It should be noted that the invention can be applied in both downlink and uplink configurations. Thus, for example, in a downlink configuration, the transmitting device can be a base station of a communication network and the receiving device a user device. Conversely, in an uplink configuration, the transmitting device can be a user device of a communication network and the receiving device a base station of that network.

[0040] But the invention also applies to a transmitting device and a receiving device distributed over a plurality of distinct physical or logical entities. For example, each antenna port of the transmitting device can be located on a distinct physical entity (this is referred to as a distributed MIMO system).

[0041] The invention thus proposes a very simple construction technique for a precoding matrix intended for use in an open-loop MIMO communication system (i.e., without knowledge of the propagation channel during transmission), this technique being applicable to any number P of antenna ports and v of any spatial layers, provided that these numbers satisfy the following conditions: V>1 and P>min(l,v).

[0042] The precoding matrix thus constructed, with this configuration of antenna ports and spatial layers, makes it possible to benefit advantageously from both spatial multiplexing, which improves the spectral efficiency of the system, and from a diversity of cyclic delays (CDD) provided by the diagonal matrix D, which offers the possibility of having a more reliable transmission.

[0043] Furthermore, the construction of the matrix W from linear combinations of distinct orthogonal vectors forming a basis allows the space to be swept in Different directions are used to compensate for the lack of knowledge of the transmitting channel. Each spatial layer corresponds to a beam formed in a particular direction by the column of the precoding matrix applied to it. As a result, if a channel corresponding to a given spatial layer suffers from significant attenuation, channels corresponding to other spatial layers can offer better signal quality. This creates diversity in the transmission, further enhancing its reliability.

[0044] This effect can be amplified via beam prediction that varies according to channel usage (i.e., symbols). Typically, in a particular embodiment, a separate precoding matrix can be used for precoding all Q symbols, where Q is an integer such that 1 <Q< Mlayer. Par exemple, Q=1 correspond à une variation de la matrice de précodage appliquée à chaque utilisation du canal. Ce mode de réalisation permet de moyenner sur les différentes utilisations du canal la phase des coefficients du canal de propagation s’appliquant à chaque couche spatiale, et ainsi de bénéficier de davantage de diversité.

[0045] The proposed construction of the precoding matrix can also be completed so as to cover the configurations where P=v or F=l.

[0046] Thus, in a particular embodiment, for r>l and P=v, the matrix W is the identity matrix of dimensions vxv.

[0047] In another embodiment, for v=l, the West matrix obtained by cyclically selecting a vector wp, p=0,..,Pl from the basis.

[0048] In this way, the precoding method according to the invention can be applied to any configuration of transmitting antennas and spatial layers.

[0049] As mentioned previously, according to the invention, the columns of the matrix W are advantageously constructed from linear combinations of distinct orthogonal vectors forming a basis. In a particular embodiment, the P orthogonal vectors wp, p=0,..,Pl of the basis used to construct the matrix W can be defined by:

[0050] __L [ij^-fp-ÿp i T np, yP

[0051] Such vectors are commonly called "IDFT vectors" (for "Inverse Discrete Fourier Transform"). A basis formed from IDFT vectors is particularly advantageous in the case of an antenna array with a spacing of X / 2 between the antennas, where X denotes the wavelength considered for transmissions.

[0052] However, other orthogonal vector bases can be used in the context of the invention. For example, a Hadamard basis, known to those skilled in the art, can be used.

[0053] In a particular embodiment, V-1 columns of the matrix W result from a linear combination of 4c |_ £ J distinct basis vectors and one column of the matrix W results from a linear combination of ( |_£ J + p mo^ distinct basis vectors.

[0054] By "linear combination", we mean here any weighted sum of basis vectors provided that at least one weighting coefficient considered in the sum and applied to a basis vector is non-zero.

[0055] This embodiment allows the space to be divided uniformly into groups comprising an identical (when P is not a multiple of v) or similar (when P is not a multiple of v) number of vectors.

[0056] When all the weighting coefficients are non-null, we ensure that the entire space is covered by the precoding matrix, since each of the basis vectors is used to construct a precoding vector (i.e., a column of the matrix).

[0057] However, a suboptimal embodiment can also be considered in which only one weighting coefficient per group is non-zero, for example, the weighting coefficient applied to the vector located in the middle of the group under consideration. This amounts to favoring an average direction for each group and allows for constant magnitude precoding. Such precoding is particularly advantageous when the P antenna ports are associated with separate power amplifiers of power p / P, as it allows the full power p to be transmitted while respecting the power constraints per antenna port.

[0058] Thus, in a particular embodiment, at least one said linear combination of £ j distinct vectors or ( [£ J +p mod distinct vectors comprises a unique non-zero weighting coefficient applied to one of the |_ £ J distinct vectors or ( £ J +p nwd v ) distinct vectors.

[0059] Other configurations can be envisaged, such as, for example, at least two weighting coefficients not harmed by linear combination, different numbers of vectors wp considered for each column of the matrix W, etc. The invention offers great implementation flexibility.

[0060] In a particular embodiment, each column of the matrix W is a linear combination of distinct adjacent basis vectors.

[0061] This embodiment is particularly simple to implement since it suffices to apply a cyclic shift of the basis vectors taken into account for construct each column of the precoding matrix (i.e., each precoding vector).

[0062] In a particular embodiment, the plurality of precoding matrices is obtained by cyclically traversing a dictionary of dimension Kv, when Mlayer > k*'Q with Q as introduced previously and:

[0063] [ £ J + py

[0064] This embodiment allows adaptation to various lengths of symbol sequences and dimensions of the precoding matrix dictionary (codebook).

[0065] According to another aspect, the invention also relates to a method of receiving, by a receiving device, a signal carrying a sequence (or sequences) of symbols spatially distributed over F layers of M layers of symbols and pre-coded by a transmitting device using a pre-coding method according to the invention, the receiving method comprising: - a step of estimating a propagation channel between the transmitting device and the receiving device using reference signals emitted by the transmitting device; and - a step of processing the received signal using the estimated channel and said set of known precoding matrices of the receiving device.

[0066] Correspondingly, the invention also relates to a receiving device, comprising: - a receiving module configured to receive a signal carrying a sequence(s) of symbols spatially distributed on a layer of symbols and pre-coded by a transmitting device according to the invention; - an estimation module, configured to estimate a propagation channel between the transmitting device and the receiving device using reference signals emitted by the transmitting device; and - a processing module, configured to process the received signal using the estimated channel and said set of precoding matrices known from the receiving device.

[0067] The receiving method and the receiving device benefit from the same advantages mentioned above as the precoding method and the transmitting device according to the invention.

[0068] In a particular embodiment, the set of precoding matrices used by the transmitting device is known to the receiving device, and the estimation step, respectively the estimation module, of the propagation channel uses non-precoded reference signals emitted by the transmitting device.

[0069] Alternatively, the receiving device can use pre-coded reference signals, in which case it does not need to know the set of pre-coding matrices used by the transmitting device.

[0070] In a particular embodiment, the precoding and reception processes are implemented by a computer.

[0071] The invention also relates to a computer program on a recording medium, this program being capable of being implemented in a computer or more generally in a transmitting device according to the invention and comprising instructions adapted to the implementation of a precoding process as described above.

[0072] The invention also relates to a computer program on a recording medium, this program being capable of being implemented in a computer or more generally in a receiving device according to the invention and comprising instructions adapted to the implementation of a receiving method as described above.

[0073] Each of these programs can use any programming language, and be in the form of source code, object code, or code intermediate between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0074] The invention also relates to an information medium or a recording medium readable by a computer, and comprising instructions for a computer program as mentioned above.

[0075] The information or recording medium can be any entity or device capable of storing programs. For example, the medium may include a storage means, such as a ROM, for example a CD-ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a hard disk drive, or a flash memory.

[0076] On the other hand, the information or recording medium can be a transmissible medium such as an electrical or optical signal, which can be transmitted via an electrical or optical cable, by radio link, by wireless optical link or by other means.

[0077] The program according to the invention can in particular be downloaded onto an Internet-type network.

[0078] Alternatively, the information or recording medium may be an integrated circuit in which a program is incorporated, the circuit being adapted to execute or to be used in the execution of the precoding and reception processes according to the invention.

[0079] The invention also relates to a communication system comprising: - a transmitting device according to the invention; and - a receiving device according to the invention.

[0080] For example, in a particular embodiment, the transmitting device is a base station of a communication network and said at least one receiving device is a user device.

[0081] According to another embodiment, the transmitting device and its P antenna ports can be distributed over a plurality of distinct physical entities.

[0082] In other embodiments, it may also be envisaged that the precoding and reception processes, the transmitting and receiving devices, and the system according to the invention may, in combination, exhibit all or part of the aforementioned characteristics. Brief description of the drawings

[0083] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings, which illustrate an example of an embodiment without being limiting in any way. In the figures:

[0084] [Fig-1] [Fig.1] represents a communication system according to the invention, in a particular embodiment;

[0085] [Fig.2] [Fig.2] represents the hardware architecture of a transmitting device and a receiving device of the system of [Fig.1], in a particular embodiment;

[0086] [Fig.3] [Fig.3] illustrates the construction of a matrix used by the device transmitter of the system of [Fig.1] for precoding according to the invention, in a particular embodiment;

[0087] [Fig.4] [Fig.4] represents, in flowchart form, the main steps of a precoding process as implemented respectively by the transmitting device of the system in [Fig. 1]; and

[0088] [Fig. 5] [Fig. 5] represents, in flowchart form, the main steps of a reception process as implemented respectively by the receiving device of the system in [Fig. 1]; and

[0089] [Fig.6] [Fig.6] represents the different treatments carried out at the level of the physical layer by the emitting device of the [Fig.1], in a particular embodiment.

[0090] The Annex illustrates an advantage resulting from the construction proposed by the invention for the precoding matrix used by the emitting device of [Fig. 1]. Description of the invention

[0091] Figure 1 represents, in its environment, a communication system 1 according to the invention, in a particular embodiment in which the communication system 1 is deployed in the context of a mobile NW communication network, such as, for example, a 4G LTE or 5G NR (for "New Radio") network defined by the 3GPP standard. The invention can, however, be applied to any type of network capable of implementing linear precoding techniques (e.g. 6G network, proprietary network, etc.).

[0092] Communication system 1 includes: - a transmitting device 2 according to the invention; and - a receiving device 3 according to the invention.

[0093] In the embodiment described herein, the transmitting device 2 is an NW network base station, comprising NT>1 transmit antenna ports, and the receiving device 3 is a user equipment (UE), comprising NR>1 receive antenna ports, where NR and NT denote integers. There are no limitations on the nature of the user equipment 3; it may be a terminal such as a smartphone, tablet, laptop, etc., an IoT (Internet of Things) connected device, etc.

[0094] As mentioned previously, an antenna port is an abstract concept, defined in particular in paragraph 4.4.1 of the previously cited 3GPP TS 38.211 document, according to which the propagation channel on which a symbol of an antenna port is transmitted can be deduced from the propagation channel on which another symbol of the same antenna port is transmitted. An antenna port is therefore a logical entity that does not necessarily coincide with a specific physical antenna or with a specific radiating element of a physical antenna of the device in question (a physical antenna being able to comprise one or more radiating elements), but which reflects what is visible from the point of view of a device communicating with the device in question.Typically, an antenna port can correspond to one or more RF (Radio Frequency) or TXRU (Transceiver Unit) chains, which themselves can correspond to one or more radiating elements.

[0095] By way of example, in the embodiment described here, it is assumed that the NT transmit antenna ports of the transmitting device 2 correspond to NT physical antennas or NT radiating elements of the base station, and that the NR receive antenna ports of the receiving device correspond to NR physical antennas of the user equipment, each physical antenna comprising a single radiating element.

[0096] The invention can, however, be applied to other antenna configurations, for example to a transmitting device and / or a receiving device comprising a single physical antenna, this antenna comprising several radiating elements, or to other configurations. Furthermore, the transmitting device, and more particularly its transmitting antenna ports, and the receiving device, and more particularly its receiving antenna ports, can be housed within from a single entity (for example, a single piece of physical equipment), or be distributed across multiple entities (for example, across multiple pieces of physical equipment). In the latter case, it is referred to as distributed MIMO.

[0097] Furthermore, in the embodiment described here, the invention is applied in the downlink, to precode data sent by the base station 2 to the user equipment 3. However, the invention can also be applied in the uplink, to precode data sent by a user equipment to a base station.

[0098] In accordance with the invention, an open-loop linear precoding technique, allowing spatial multiplexing of the data sent by the base station 2 to the user equipment 3 on V>1 spatial layer(s), and introducing cyclic delay diversity (CDD), is implemented within the communication system 1.

[0099] To benefit from the combined advantages of spatial multiplexing and CDD diversity, the communication system 1 must be dimensioned such that: 1 < v <min(NT,NR) (NR doit donc dans ce cas être supérieur à 1). Toutefois, dans le mode de réalisation décrit ici, et comme détaillé davantage ultérieurement, le système de communication 1 est également en mesure d’appliquer une technique de précodage linéaire en boucle ouverte lorsque v=l.

[0100] Furthermore, the use of an open-loop precoding technique requires that the transmitting device 2 be configured, for example by the NW network operator, with a CODEB dictionary or codebook comprising a plurality of predefined precoders (i.e., predefined precoding matrices).

[0101] It is assumed here that the receiving device 3 is also configured with the CODEB codebook. However, it should be noted that such a configuration is optional, as discussed in more detail later.

[0102] In the embodiment described here, the transmitter 2 and receiver 3 devices have the hardware architecture of a computer 4 as shown in [Fig.2]. This computer 4 includes, in particular, a processor PROC, a random access memory MEM, a read-only memory ROM, a non-volatile memory NVM, and COM communication means.

[0103] The non-volatile NVM memory of the transmitting device 2 constitutes a storage medium according to the invention, readable by the PROC processor of the transmitting device 2, and on which a PROG2 program according to the invention is stored. Furthermore, it is assumed here that the codebook CODEB is stored in the NVM memory of the transmitting device 2.

[0104] This PROG2 program includes instructions defining the main steps of a precoding process according to the invention, and more specifically defines the Functional modules of the transmitting device 2 that rely on and / or control all or part of the PROC, MEM, ROM, NVM, and COM components of the computer 4 mentioned previously. These functional modules include, in particular, in the embodiment described here, as illustrated in [Fig. 1]:

[0105] - a 2A precoding module, configured to precode v> I sequence(s) of symbols spatially distributed over v layers of Mlayer symbols, where Mlayer is an integer greater than 1, using a plurality of complex precoding matrices (i.e., precoders) of dimensions PxF, with P>min(l,F) denoting the number of antenna ports of the transmitting device 2 dedicated to its communication with the receiving device 3 (P <NT). Dans l’exemple illustratif de la station de base 2 envisagé ici, par souci de simplification, on considère que P=NT. Les matrices de précodage utilisées par le module 2A de précodage sont construites conformément à l’invention, et stockées ici de façon ordonnée et indexée dans le codebook CODEB ; et

[0106] - a 2B transmitting module, configured to transmit via the NT transmitting antennas from the transmitting device, the precoded symbols from the precoding module 2A to the receiving device 3, i.e. to the user equipment 3 in the example considered here.

[0107] The functions of modules 2A and 2B and the way in which the precoding matrices are constructed in accordance with the invention are described in more detail later, with reference to [Fig.4].

[0108] Similarly, the non-volatile NVM memory of the receiving device 3 constitutes a storage medium according to the invention, readable by the PROC processor of the receiving device 3, and on which a PROG3 program according to the invention is stored. Furthermore, it is assumed here that the codebook CODEB is stored in the NVM memory of the receiving device 3. As previously stated, it is also possible, in another embodiment, for the receiving device 3 to not store the codebook CODEB.

[0109] This PROG3 program includes instructions defining the main steps of a reception process according to the invention, and more specifically defines the functional modules of the receiving device 3 that rely on and / or control all or part of the PROC, MEM, ROM, NVM, and COM elements of the computer 4 mentioned above. These functional modules include, in particular, in the embodiment described here, as illustrated in [Fig. 1]:

[0110] - a 3A receiving module, configured to receive the signal carrying F>1 sequence(s) of symbols spatially distributed on F layer(s) of Mlayer symbols and precoded by the transmitting device 2, i.e. by base station 2 in the example considered here, using a set of complex precoding matrices extracted from the CODEB codebook known to the transmitting device 2 and the receiving device 3;

[0111] - a 3B estimation module, configured to estimate the propagation channel between the transmitting device 2 and receiving device 3, i.e., between base station 2 and user equipment 3, using uncoded reference signals emitted by transmitting device 2. In the example of a 4G network, such reference signals are typically CRS (Cell Specified Reference Signal) for a 4G LTE network, or CSLRS (Channel State Information Reference Signal) for a 5G NR network; and

[0112] - a 3C processing module, configured to process the received signal using the estimated channel and the set of complex precoding matrices extracted from the CODEB codebook.

[0113] The functions of modules 3A to 3C are described in more detail later, with reference to [Fig.5].

[0114] As mentioned previously, the invention relies on an open-loop linear precoding technique using precoding matrices extracted from (or deterministically derived from) a known CODEB codebook of the transmitting device 2 and, in the embodiment described here, also of the receiving device 3. In the embodiment described here, the CODEB codebook is composed of a plurality of CODEB(P,V) codebooks, each CODEB(P,V) codebook being associated with a particular (P,V) pair. The transmitting device 2 and the receiving device 3 are thus configured to refer to the appropriate CODEB(P,V) codebook, depending on the chosen configuration and, in particular, the values ​​of P and v envisaged for a given communication between the transmitting device 2 and the receiving device 3.

[0115] To enable open-loop operation, the way in which the precoding matrices are obtained from the CODEB codebook, and more particularly from a given CODEB(P,V) codebook, and therefore evolve over time, in other words, the pattern of variation of the precoding matrix, applied by the transmitter device 2, within the CODEB(P,V) codebook, is predefined and also known to the transmitter device 2, and in the embodiment described here, to the receiver device 3.

[0116] For example, such a variation pattern consists of using a separate precoding matrix for every Q symbols (i.e., every Q channel uses), where Q is an integer such that l <Q<Mlayer, la matrice de précodage appliquée tous les Q symboles étant obtenue en parcourant de façon séquentielle (i.e. dans l’ordre des index) le codebook CODEB(P,V). A titre illustratif, on considère par exemple ici que Q=l, autrement dit la matrice de précodage appliquée par le dispositif émetteur 2 change à chaque élément of time / frequency resource i (or RE for "Resource Element" in English) or at each use of channel i, with i=0,..., Mlayer-1.

[0117] In the embodiment described here, a codebook of dimension Kv is considered by construction, CODEB(P,V) with:

[0118] K = L t J + P mod v

[0119] If Mlayer > KFQ (in other words, Kv in the illustrative example considered here where Q = 1), the precoding matrix to be applied to all Q symbols (that is, all symbols in the illustrative example considered here where Q = 1) can be obtained by sequentially and cyclically traversing the CODEB(P,V) codebook. This cyclic traversal of the CODEB(P,F) codebook is part of the known variation pattern of the transmitter 2 and receiver 3 devices.

[0120] For a number P of transmit antenna ports and v spatial layers, with P > min(l,v) and V > 1, each precoding matrix applied by the transmitting device 2 to each use of channel i (in the illustrative example considered here) is denoted ÿ(i) for i = 0, ..., Mlayer-1, and is extracted from the codebook CODEB(P,F), which contains Kv precoding matrices. Each precoding matrix V(i) is, according to the invention, constructed from a combination of a complex matrix W(i) of dimensions Pxv, a complex diagonal matrix D(i) of dimensions vxv introducing a variety of cyclic delays, and a complex rotation matrix U of dimensions vxF. In other words, the "global" complex precoding matrix of dimensions Pxv is given, for the i-th use of the channel, by:

[0121] V(i)= W(î)D(Orpouri=0,...,MlayeM(E^

[0122] More specifically, the diagonal matrix D(i) governing the "large delay CDD" technique introduces a phase shift between the spatial layers / e {(), ..., y - 1} for v > I. It is defined by:

[0123] D(i) = diag(l ..., )

[0124] with j2=-l. In the illustrative example considered here where Q=l, this is equivalent to:

[0125] k-imodv

[0126] with:

[0127] = L .... ), *e{0, ..., v-1}

[0128] In other words, the diagonal matrix D(i) varies periodically with a period v.

[0129] The rotation matrix U is a fixed DFT (Discrete Fourier Transform) matrix (i.e., one that does not depend on the use of channel i), which is written as follows:

[0130] ri 1 1 1 -j2:Ta - / 2.70-?)

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143] 1 eO— The diagonal matrix of "large delay CDD" D( i) and the rotation matrix U are thus, in the embodiment described here, predefined as a function of the number of spatial layers v. For P>min(l,v) and V>1, the matrix W( i) is obtained from K matrices Co, Ci, CK-i by applying the following relation: W) =Ch k = UimodK where Co, CiCK i denote matrices of dimensions PxF. The matrix W(i) is therefore constant over v uses of the channel (during which, the matrix D(i) varies). Thus, for example, for v=3, Mlayer=16 and K=4, this amounts to selecting the following matrices W(i) for i=0,...,Mlayer-1: Co ,Co ,CoÇiÇiÇiÇ2Ç2Ç2Ç3Ç3Ç3Ço ,Co ,CoÇi, for channel uses indexed by i=0, 1, 2, 3, ..., 15 respectively. Each matrix Ck, k=0,..., Kl has the following structure: where the column v^ is the precoding vector to apply for the layer l = 0, ..., v- 1 According to the invention, each matrix Co, CiCK-i (and therefore incidentally, each matrix W d) obtained from these matrices) is remarkable in that its v columns are linear combinations of distinct vectors from a basis of P orthogonal vectors wp, p=0,..,Pl. By "linear combination", we mean here any weighted sum of vectors of the basis provided that at least one weighting coefficient considered in the sum and applied to a vector of the basis is non-zero. In the embodiment described here, we consider more specifically the basis formed by the P orthogonal vectors wp, p=0,..,Pl, defined by: w__L [ i 1 J (Eq. 2) Wp — r— [ 1 € p & p ... cp J, p — U, ..., r - L These vectors wp, p=0,..,Pl each represent a so-called "IDFT" beam. They are also referred to hereafter as "IDFT vectors". More specifically, in the embodiment described here, F-1 columns (typically the first Pl) of each matrix Ck, k=0,..., Kl result from a linear combination of J distinct adjacent (consecutive) vectors from the orthogonal basis of IDFT vectors, and one column of the matrix Ck, k=0,..., K-1 (typically the last) results from a linear combination of ( |_ J + p mo(iv ) Adjacent (consecutive) vectors are distinct from the basis. Thus, the v vectors corresponding respectively to the v columns of each matrix Ck are orthogonal. This last column allows for handling the case where P is not a multiple of r, if applicable. Of course, another position can be assigned to this column in the matrix Ck, or other basis vectors besides adjacent vectors can be combined together. It should be noted that if P is a multiple of v, the P columns of the matrix Ck are then linear combinations of [ ∑ J distinct adjacent basis vectors of IDFT vectors).

[0144] Moreover, in the embodiment described here, the (K) distinct matrices Ck are obtained relative to each other by shifting the 1st IDFT vector considered for the first column of each matrix Ck, k=0,..., Kl.

[0145] Thus, the matrix Co has the following structure:

[0146] .ou-LyWJ-i V0 “ pp) ^=0 WP

[0147] i

[0148]

[0149] WP

[0150]

[0151] ^oj-jLyP-* JP1W

[0152] where p(0) ∈ {0, ..., v - 1} represent real weighting coefficients, at least one of these coefficients being non-zero. These weighting coefficients p(0) ∈ G {0, ..., v - 1} are chosen, for example, so as to normalize the precoding vectors y0). .... In the embodiment described here, all the weighting coefficients p(0) ∈ G {0, ..., v - 1} are non-zero.

[0153] To construct the matrix Cj = [ . V^( ] ' as mentioned previously, The IDFT vectors wp considered for each precoding vector v^ are cyclically shifted. Thus, is no longer considered for constructing the first column but for constructing the last column y(i). That is: y0) - 1 yAllrJ j_a O v^p v -1

[0155] where p0) / E (0. ..., v-1} represent real weighting coefficients. These weighting coefficients pU) le {0, ..., v-1} are chosen for example so as to normalize the precoding vectors y(i) , , y0) ■ In the embodiment described here, all the weighting coefficients pO) l E {0, ..., v -1} are non-nuis.

[0156] The precoding vectors yU) of the matrix Ck are defined similarly, as follows:

[0157] - | yP+Ll mod P, * “

[0158] where <A) / E {0. ..., y -1} représentent des coefficients de pondération réels. Ces Weighting coefficients p(k) / E {0, ..., y - 1} are chosen, for example, to normalize the precoding vectors y(D yGd , y(k). In the embodiment described here, all weighting coefficients p(k) on {0, ..., v- 1} are non-nuisance.

[0159] The construction just described leads to obtaining the K matrices Ck, k=0,

[0160] In view of the foregoing and the variation patterns of the matrices W(i) (which can take K distinct values ​​given by the K matrices Ck, k=0,..., Kl) and D(i) (which can take v distinct values ​​given by the v matrices Dj, j=0,..., Fl), with the rotation matrix U being fixed, it is necessary to store in the codebook CODEB(P, r), in an ordered manner, the Kv possible combinations of the matrices Ck, k=0,..., Kl, Dj, j=0,..., V-1 and U (fixed for the Kv combinations). In the embodiment described here, the order used is as follows:

[0161] CDLCDU ...CD? ..CD* lU^.^C^DoU.C^D^,...,^ jDv 1U

[0162] Figure 3 illustrates the construction of the codebook CODEB(P,r) for r=3, P=10 and K=4, under the assumption of a uniform linear array (or ULA for "Uniform Linear Array" in English), with a spacing of X / 2 between the antenna elements (or antennas), X denotes the wavelength considered.

[0163]

[0164]

[0165]

[0166]

[0167]

[0168] By definition, the P vectors wp, p=0,..,Pl, and incidentally by construction, the precoding vectors { q, , v _ ]} of the matrices Ck, k=0,... ,K-1, allow to sweep uniformly across the entire area covered by the antenna array. Note that alternative constructions of the precoding vectors yW / e{Q, v_1} can be considered, provided that the precoding vectors are obtained from linear combinations of distinct IDFT vectors to ensure the orthogonality of the precoding vectors with each other. For example, one can combine vectors that are not adjacent (which amounts to applying a permutation to the previous formulas), or combine a different number of vectors for the different precoding vectors, or consider only a reduced number of non-zero weighting coefficients per group of IDFT vectors (for example, a single non-zero weighting coefficient applied to the IDFT vector in the middle of the group considered, or two non-zero coefficients applied to vectors duly distributed within the group). The construction just described applies to a number of transmit antenna ports P strictly greater than the number of spatial layers F. When P=F, in the embodiment described here, a fixed matrix W(i) is used for all channel uses, taken to be equal to the normalized identity matrix of dimensions vxv, i.e.: W(i) = ie {(), ..., Mlayer -1} Thus, in this case, the overall precoding matrix V(i) is given by: uyCT-L The possible values ​​of V(i) (resulting V(i) = D(i)Upouri=0,...,M The possible values ​​of D(i) are stored in codebooks CODEB(F,F) for the different values ​​of F that can be considered by the system. communication 1. As mentioned previously, in the embodiment described here, the communication system 1 is also able to apply an open-loop linear precoding technique when F=L. In the case of a single spatial layer, the transmitting device 2 applies a matrix W(i) reducing to a precoding vector of dimension P selected from a codebook CODEB(P,1) of dimension P. In the embodiment described here, the codebook CODEB(P,1) consists of the P IDFT vectors wp, p=0,.. .,P-1 introduced previously and given by relation (Eq. 2) (the matrices D(i) and U of equation (Eq. 1) reduce for F=1 to D(i) = 1 and U = 1). When Mlayer>P, the precoding vector applied by the emitting device 2 is cyclically selected from the CODEB(P,1) dictionary of P-dimensional IDFT vectors, which amounts to scanning the different IDFT directions, as illustrated in [Fig.3].

[0169] The plurality of CODEB(P,V) codebooks thus constructed for different values ​​of P and v make up the CODEB codebook which, as mentioned previously, is stored by the transmitting device 2 and the receiving device 3 in their respective non-volatile NVM memories, with the variation pattern of the precoding matrices V(i). According to this variation pattern, whatever the values ​​of P and v used for a given communication between the transmitting device 2 and the receiving device 3, the "global" precoding matrix V(z) for the use of channel i, i=0,..., Mlayer -1, is obtained by sequentially and cyclically traversing the CODEB(P,V) codebook when Mlayer>K VQ (in other words, Kr in the example considered here where Q=1). The applied precoding matrix is ​​assumed here to be normalized and such that:

[0170] V(z)HV(i)

[0171] where ÿ( / )H is the transposed conjugate matrix of V (i ) •

[0172] We will now describe how this CODEB codebook is advantageously used by devices 2 and 3 of the communication system 1, according to the invention, to implement an open-loop linear precoding technique.

[0173] Figures 4 and 5 represent the main steps of the precoding and reception processes according to the invention, as implemented respectively by the transmitting device 2 (i.e. the base station 2 in the illustrative example envisaged here) and by the receiving device 3 (i.e. the user equipment 3, in the illustrative example envisaged here), in a particular reception mode.

[0174] With reference to Figure 4, it is assumed here as a preliminary step that V>1 sequences of MLayer symbols each were generated by the emitting device and spatially distributed over v layers by the emitting device 2 (step F00). It should be noted, however, that what follows also applies for V=1 by applying the appropriate CODEB(P,1) codebooks.

[0175] There are no limitations on how these symbol sequences were obtained by the transmitting device 2. In the case of a 4G or 5G network, these symbol sequences may, in particular, have been generated by applying physical layer processing as described, for example, for a 4G network in TS 36.211, paragraph 6.3, and schematically illustrated in [Fig. 6]. It should be noted that similar processing is applied in the case of a 5G network, with a few adjustments, mentioned below.

[0176] More particularly, in accordance with such processing, useful (binary) data intended for the receiving device 3 are first encoded according to one or two streams (for example, in 5G, there can be a single stream for up to v = 4 spatial layers), resulting in at most two streams of encoded data or CW codewords, each stream being encoded with a specific channel coding efficiency. These at most two streams encoded data is scrambled with an SCR scrambler (or "scrambling" in English), then the scrambled coded data is mapped onto the constellation of a modulation (for example, QPSK modulation, 16QAM, 64QAM, 256QAM) or 1024QAM) with a C_MAP mapper resulting in a sequence of M symbols. The mapper outputs are then distributed across v spatial layers by an L_MAP layer mapper, with Mlayer symbols per layer, which are provided as input to the precoding module 2A of transmitter device 2.

[0177] The spatial v layers with Mlayer symbols per layer are then precoded by the precoding module 2A of the transmitter device 2 by means of a linear precoder PRECOD (step F10 in [Fig.4]).

[0178] This precoding is achieved by applying a precoding matrix ÿ ( î ) = W(i)D(i)U extracted from the CODEB(P,V) codebook, for each use of channel i, i=0,..., Mlayer-1, as described previously, by sequentially and cyclically traversing the CODEB(P,F) codebook stored in the NVM memory of the transmitting device 2.

[0179] This precoding step amounts to applying to each symbol indexed by i of each ZG layer {O, ..., v - 1}, for each antenna port indexed by p, p=0,...,P, the coefficient ÿ® of the precoding vector _ |" ?( / ) j7 corresponding to the same column of the precoding matrix V(i).

[0180] Note that by construction, we have:

[0181] [1 1 V(i) = W(i)D(i)U= [v^v®... v®] diag(l .... e-^ ) 1 .1

[0182] with £ - [ 1 j}no([ ^et £ J + p nio^ v.

[0183] The coefficient applied for the p-th transmitting antenna port, layer 7 and p / for the use of the channel indexed by i is therefore written as follows:

[0184] _ y ”'1 a) pi a,p K v

[0185] Thanks to this precoding, the coded Mlayer symbols of the v spatial layers are mapped to the resources of each antenna port. The precoder allows each symbol of a spatial layer to be transmitted from each antenna port of the transmitting device 2 (i.e., in the example considered here, of base station 2) with a phase and amplitude coefficient (from the precoding matrix).

[0186] The precoded vector of dimension P, denoted ~ z. x [~ M ~ ~ M]r, intended for X( 1 ) — [X^lj x^i)... to be transmitted by the P antenna ports of the transmitting device 2, at each use of channel i, is then given by the following equation:

[0187] V(i)x(i) - W(i)D(i)Ux(ÎL iz{Q, Mlayer-1}

[0188] with:

[0189] XP (1) = * / (4 P GI0' • • • ' P -

[0190] where x / i)' i=0, • • • ' Mlayer-1 denotes the i-th coded symbol of the sequence of coded symbols associated with the layer.

[0191] In a manner known per se, for each antenna port considered, the pre-coded complex constellation symbols are then mapped to RE (Resource Element) elements by an RE_MAP resource mapper (see [Fig. 6]). An RE resource element represents the smallest granularity of time-frequency radio resource used for transmissions on the network. For example, the concept of a resource element is described in detail for a 4G network in 3GPP TS36.211 vl7.4.0, section 5.2.2, and for a 5G network in 3GPP TS 38.211 vl7.7.0, section 4.4.3.A resource element is defined in this document as a physical resource identified for each antenna port p by indices (k,l)pp on a time-frequency resource grid, where p denotes a subcarrier spacing configuration, k is an index in the frequency domain, and 1 refers to a symbol position in the time domain relative to a reference point.

[0192] For an OFDMA (Orthogonal Frequency Division Multiplexing Access) type system such as that considered in 4G or 5G networks, such a resource element corresponds to a subcarrier and a symbol time corresponding to the duration of a multicarrier symbol.

[0193] At the output of the RE_MAP resource mapper, the resource elements associated with the different antenna ports are injected, in the embodiment described here, into a multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) modulator GEN-OFDM to generate an OFDM symbol. These OFDM symbols feed the antenna ports of the transmitting device 2 (i.e., here, base station 2) and are then transmitted to the receiving device 3 (user equipment 3 in the example considered here) (step F20).

[0194] It is noted that, in a manner known per se, the transmitting device 2 also transmits, via its P antenna ports, to the receiving device 3, SIG-REF reference signals known to the latter in order to allow it to estimate the propagation channel between the transmitting device 2 and the receiving device 3. In the example Considered here of an NW network conforming to the 3GPP standard, base station 2 emits in particular CRS reference signals (for a 4G network) or CSL RS (for a 5G network), known to the user equipment 3, from its antenna ports dedicated to its communications with the receiving device 3. As illustrated in [Fig.6], these reference signals are not precoded, unlike other reference signals, such as DMRS signals (for "DeModulation Reference Signals"), also sent by base station 2.

[0195] With reference to Figure 5, the signal carrying the precoded OFDM symbol sequences and the reference signals emitted by the transmitter device 2 are received by the receiver device 3 (i.e. by the user equipment 3 in the example considered here), via its receiver module 3A, on its NR receiving antennas (NR>1 for V>1) (step G10).

[0196] The receiving device 3, via its estimation module 3B, estimates the matrix H of the propagation channel seen by the signal carrying the F sequences of precoded OFDM symbols sent by the transmitting device 2 (step G20). For this purpose, it uses, for example, the non-precoded reference signals (CSLRS) sent by the transmitting device 2, in a manner known per se.From this estimation, knowing the number of antenna ports P used by the transmitting device 2 and the number v of spatial layers (which have been transmitted to it, for example, by base station 2 in transmission configuration information and in control information in a way known per se), it deduces the codebook CODEB(P,V) corresponding to these parameters and which it has, in the embodiment described here, in its non-volatile memory NVM, and the variation pattern of the precoding matrix within this codebook, the equivalent channels HWU corresponding to the Mlayer uses of the channel to transmit the F sequences of precoded OFDM symbols (step G30).

[0197] It can thus process the received signal y using this estimation of the equivalent channels HW(z)D(i)17 to extract the useful data sent by the transmitting device 2 (step G40). Such processing is known in itself, given the processing applied in transmission, and is not described in detail here.

[0198] In another embodiment, the estimation module 3B of the receiving device 3 can use the precoded reference signals sent by the transmitting device 2 (DMRS signals in the illustrative example considered here). In this case, the receiving device 3 does not need to know the CODEB codebook, nor the variation pattern within this codebook applied to obtain the precoding matrices, but it must independently estimate as many channels as there are precoding matrices, i.e., Kv. To enable such estimation, a technique called "PRB" can be used in the example of DMRS signals. "Bundling" (PRB stands for "Physical Resource Block") involves defining a group of resource elements that consecutively use the same precoding, such that the receiving device 3 knows in advance that the precoding is constant across this group of resource elements. However, it should be noted that channel estimation using this technique is less accurate than channel estimation based on unprecoded reference signals because it generally relies on a smaller number of reference signals.

[0199] Thanks to the invention, and in particular the generation of a matrix W using an orthogonal basis of P orthogonal vectors covering the maximum space, each column of the matrix W being obtained from linear combinations of distinct vectors of said basis, a very efficient open-loop linear precoding technique is obtained, offering the advantages of spatial multiplexing and emission diversity. As mentioned previously, the invention makes it very advantageous to scan the space thanks to the proposed construction for the matrix W and, more generally, of the global precoding matrix V applied to the sequences of symbols sent on the spatial layers. Thus, each spatial layer corresponds to a given IDFT beam, and the entire space is covered by the v spatial layers.It follows that if a channel corresponding to a given spatial layer suffers from significant attenuation, channels corresponding to other spatial layers can offer better signal quality (see demonstration in the Appendix). Since these beams also vary according to channel usage, transmission diversity is created, resulting in more reliable transmission.

[0200] It should be noted that in the embodiment described here, the basis of orthogonal vectors considered for constructing the matrix W is a basis of IDFT vectors as defined by equation (Eq. 2). Alternatively, other bases of P orthogonal vectors can be considered for constructing the precoding vectors and incidentally the matrix W, such as, for example, a Hadamard basis.

[0201] Furthermore, in the embodiment described here, a CODEB dictionary composed of a plurality of CODEB(P,V) codebooks for different values ​​of (P,r) has been considered. Each of these codebooks contains global precoding matrices V. Alternatively, separate codebooks can be stored for each of the matrices WD and U and different values ​​of (P,v). Appendix

[0202] To illustrate how the invention works, we consider here a given receiving antenna of the receiver device 3 etv beams corresponding to v channels:

[0203] =h(i)W(i) = [C ••■'d

[0204] where h(i) is a complex vector of dimension P representing the channel between a fixed receiving antenna and the P transmitting antenna ports used by the transmitting device 2 to communicate with the receiving device 3. W(i) is the precoding matrix of dimensions Pxv chosen from the codebook CODEB(P,F) configured at the transmitting device 2 for the use of channel i.

[0205] The signal received using the "large delay CDD" technique for channel i is given by:

[0200] [A®, ]D(i)t7x

[0207] where x = [x0...xv4]. Or:

[0208] [D(i)U]aa = 0, ..., vl, Z = 0,

[0209] It therefore follows that: [021°] =

[0211] The "large delay CDD" therefore runs the precoding phase [1 e-] between the channel coefficients J which gives the Next equivalent channel for each layer1 and use of channel i:

[0212]

[0213] This allows the phase of the different channel coefficients to be averaged in the absence of channel information (CSI) on the transmitting device 2 side.

Claims

Demands

1. A precoding method (F20), by a transmitting device, of v sequence(s) of symbol(s) spatially distributed over F layers of Mlayer symbols using a plurality of complex precoding matrices of dimensions Pxr, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a combination of a complex matrix W of dimensions Pxv, a complex diagonal matrix D of dimensions Fxr introducing a diversity of cyclic delays and a complex rotation matrix U of dimensions rxv, said precoding method being characterized in that, for F>1 and P>min(l,r), the P columns of the complex matrix W are linear combinations of distinct vectors from a basis of P orthogonal vectors p=0,..,Pl.

2. A precoding method according to claim 1 wherein the orthogonal vectors P=0,..,Pl of said basis are defined by: 1 [ 1 j^p fbrlp j^P^P 1F ni wp = ^llep ep ... epj , p = 0,

3. A precoding method according to claim 1 or 2 wherein v-1 columns of matrix W result from a linear combination of |_ £ J distinct basis vectors and one column of matrix W results from a linear combination of ( |_£ J + pv) distinct basis vectors.

4. A precoding method according to claim 3 wherein at least one said linear combination of [_ £ J distinct vectors or ( L £ J 4- p mod v ) distinct vectors comprises a unique non-zero weighting coefficient applied to one of the |_ £ J distinct vectors or ( [£ J + pm()d distinct vectors.

5. A precoding method according to any one of claims 1 to 4 wherein each column of the matrix W is a linear combination of distinct adjacent basis vectors.

6. A precoding method according to any one of claims 1 to 5, wherein a separate precoding matrix is ​​used for precoding all Q symbols, where Q is an integer such that 1 <Q< Mlayer.

7. A precoding method according to claim 6, wherein said plurality of precoding matrices is obtained by cyclically traversing a dictionary of dimension Kv, where Mlayer > KVQ with: K - LvJ + P mod v

8. A precoding method according to any one of claims 1 to 7 wherein for F> 1 and P=v, the matrix W is the Identity matrix of dimensions Fxv.

9. A precoding method according to any one of claims 1 to 8 wherein for F=l, the matrix W is obtained by cyclically selecting a vector wp, p=0,..,Pl from the basis.

10. A method for receiving, by a receiving device (3), a signal carrying v sequence(s) of symbols spatially distributed over v layers of Mlayer symbols and precoded by a transmitting device using a precoding method according to any one of claims 1 to 9, said receiving method comprising: - a step (G20, G30) of estimating a propagation channel between the transmitting device and the receiving device using reference signals emitted by the transmitting device; and - a step (G40) of processing the received signal using the estimated channel and said set of precoding matrices known to the receiving device.

11. A receiving method according to claim 10 wherein said set of precoding matrices is known to the receiving device and the propagation channel estimation step uses non-precoded reference signals emitted by the transmitting device.

12. A transmitting device (2) comprising a precoding module (2A) configured to precode v sequence(s) of symbols spatially distributed over v layers of Mlayer symbols using a plurality of complex precoding matrices of dimensions PxF, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a combination of a complex matrix W of dimensions Pxv, a complex diagonal matrix D of dimensions vxr introducing a variety of cyclic delays, and a complex rotational matrix U of dimensions vxv, said transmitting device being characterized in that, for V>1 and P>min(l,v), the P columns of the complex matrix W are linear combinations of distinct vectors of a basis of P orthogonal vectors wp, p=0,..,Pl.

13. Receiver device (3), comprising: - a receiver module (3A), configured to receive a signal carrying a sequence(s) of symbols spatially distributed over F layers of M layers of symbols and pre-coded by a transmitter device according to claim 12; - an estimation module (3B), configured to estimate a propagation channel between the transmitter device and the receiver device using reference signals emitted by the transmitter device; and - a processing module (3C), configured to process the received signal using the estimated channel and said set of pre-coding matrices known to the receiver device.

14. Communication system (1) comprising: - a transmitting device (2) according to claim 12; and - a receiving device (3) according to claim 13.

15. Communication system (1) according to claim 14 wherein said transmitting device (2) is a base station of a communication network and said at least one receiving device (3) is a user equipment.

16. Communication system (1) according to claim 15 wherein the transmitting device and its P antenna ports are distributed over a plurality of distinct physical entities.

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