Precoding and reception methods, transmitter device and receiver device

Abstract

The invention proposes a method, using a transmitter device (2), for precoding v sequence(s) of symbol(s) 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 complex matrix W of dimensions Pxv, said precoding method being characterised in that, for v> 1 and P> min(1,v), the v columns of the complex matrix W are linear combinations of distinct vectors from a basis of P orthogonal vectors wp, p=0,..,P-1.

Description

Description Title of the invention: Precoding and reception methods, transmitter device and receiver device Technical Field

[0001] The invention falls within the general field of telecommunications.

[0002] It relates more specifically to a precoding technique for a multiple input single output system (or Ml SO for "Multiple Input Single Output" in English) or a multiple input multiple output system (or Ml MO 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 of, for example, 5G or 6G communication networks, as defined by the 3GPR standard, in which such systems are considered. However, the invention may also be applicable in other contexts. Previous technique

[0004] Many M1 MO and M1 90 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 3GPR 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 section 4.4.1 of the 3GPP TS 38.211 document entitled "Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 17)" v17.7.0 (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 transmit diversity. Such techniques rely on the application of linear precoding to 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 propagation channel effects and optimize receive performance.

[0006] MIMO / MISO precoding techniques can be classified into two categories: MIMO / MISO precoding techniques that operate in a closed loop (or "closed mouth" in English); and MIMO / MISO precoding techniques operate 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 transmitter receives information representing the precoding to be used (for example, an index pointing to a particular precoding, also called a PMI for "Precoding Matrix Indicator") from 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 approach, the precoding is optimized by the receiver and then transmitted to the transmitter for given reception conditions (radio channel).

[0008] However, transmitting 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 over 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 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 receiver.

[0010] For example, the 3GPP standard adopted an open-loop diversity technique for 4G LTE (Long Term Evolution) networks called Large Delay CDD (Cyclic Delay Diversity). This technique introduces a delay between the signals transmitted by the different spatial layers. It is described in particular in section 6.3.4.2.2 of the 3GPP TS 36.211 document entitled "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 17)," v17.4.0 (September 2023). It is intended for downlink transmissions (base station to user equipment) and configurations with two or four transmit antenna ports, limiting the maximum number of spatial layers to two and four, respectively.

[0011] More specifically, if x(i) denotes a vector of v complex symbols, v representing the number of spatial layers considered for spatial multiplexing, the vector x(i) precoded using a "large delay CDD" technique is defined as follows: x (i) = U7(i)D(i)t / x(i), ie {0, - 1} where: _ M iayer denotes the number of uses of the channel (or equivalently, the size of the symbol sequence 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 to each spatial layer on {0,...,v - 1}. More precisely: ( -J27TÎ -j'27T(vl)i \ l, evvj - U is a fixed rotation matrix of dimensions vxv (also called a DFT matrix for "Discrete Fourier Transform" in English), which is written as follows: rl 1 ••• 1 li -j2it -J2rm -j27r(vl) g _ 1 ev ••• ev ••• ev -J2n(y-1') -j2mi(yl) -J'2TT(V-1)(V-1) L1 e v... Q vev J

[0012] The PK(i) matrix 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 v < 4 when P = 4.

[0013] 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 v= 1: m 11 o = c 1 = i[j] - for v=2: 1 V

[0014] For P=4 transmit antenna ports, the dictionary precoders are cyclically allocated to the vectors CO L^Jrs x(i) corresponding to different uses i of the channel, a precoder S II Different, with all v vectors being used. The PK(i) precoder is selected as follows: (0 = c k with k = where C 1;C2, C3, 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 v<4. The corresponding rows of Table 6.3.4.2.3-2 are reproduced below: [Table 1] Number of layers v Hint 1 2 3 4 12 «12 T.9 r,, :: / ^2 rrf^ / 2 = [1 -1 - 1 1] T 13 A / 2 "14 14 ÎT~ = [ii -i - i] T 1 15 «15 = [1 1 1 1] T T'-V ' AF T'. / 2

[0015] In particular, the PK(i) matrices are obtained from the elements of this table by applying a Householder construction. The columns of the PK(i) matrix are derived from the 4 vectors u 12 ,u 13 ,u 14 ,u isreported in the table, to which the Householder transformation is applied according to:W n = I — 2u n u H uu n where I denotes the 4-dimensional identity matrix and ne {12,13,14,15}, i.e.: - wÿ is the vector corresponding to column i of W n . is the 4x2 matrix formed by columns i and j of W n . W„ Jk l is the 4x3 matrix formed by columns i, j, and k of W n , and n klJ is the 4x4 matrix formed by columns i, j, k, and I of W n .

[0016] 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

[0017] 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 M layer symbols using a plurality of complex precoding matrices of dimensions Pxv, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a complex matrix W of dimensions Pxv, said precoding method being characterized in that, for v > 1 and P > min(1,v), the v columns of the complex matrix IV are linear combinations of distinct vectors from a basis of P orthogonal vectors w p , p= 0, P-1.

[0018] Correspondingly, the invention also relates to a transmitter device comprising a precoding module, configured to precode v sequence(s) of symbols spatially distributed on v layers of M layersymbols using a plurality of complex precoding matrices of dimensions Pxv, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a complex matrix W of dimensions Pxv, said transmitting device being characterized in that, for v > 1 and P > min(1,v), the v columns of the complex matrix IV are linear combinations of distinct vectors from a basis of P orthogonal vectors w p , p= 0, P-1.

[0019] It should be noted that the invention can be applied to both downlink and uplink communications. For example, in a downlink, the transmitting device can be a base station of a communication network and the receiving device a user device. Conversely, in an uplink, the transmitting device can be a user device of a communication network and the receiving device a base station of that network.

[0020] However, the invention also applies to a transmitting device and a receiving device distributed across 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 then referred to as a distributed M1 MO system).

[0021] The invention thus proposes a very simple construction technique for a precoding matrix intended for use in an Ml MO communication system operating in open loop (i.e. without knowledge of the propagation channel in transmission), this technique being able to be applied to any number P of antenna ports and v of spatial layers, provided that these numbers satisfy the following conditions: v> 1 and P>min(1,v).

[0022] For example, each precoding matrix can be constructed from a combination of the 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.

[0023] The precoding matrix thus constructed, with this configuration of antenna ports and spatial layers, allows us 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.

[0024] Furthermore, constructing the IV matrix from linear combinations of distinct orthogonal vectors forming a basis allows for scanning the space in different directions, thus compensating 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. Consequently, 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 at the transmission level, further enhancing its reliability.

[0025] This effect can be amplified by predicting beams that vary according to channel usage (i.e., symbols). Typically, in a particular embodiment, a separate precoding matrix can be used to precode every Q symbols, where Q is an integer such that 1 < Q < M layer For example, Q = 1 corresponds to a variation of the precoding matrix applied to each use of the channel. This embodiment allows the phase of the propagation channel coefficients applied to each spatial layer to be averaged over the different uses of the channel, thus providing greater diversity.

[0026] The proposed construction of the precoding matrix can also be completed so as to cover the configurations where P= v or v= 1.

[0027] Thus, in a particular embodiment, for v>1 and P=v, the matrix M' is the identity matrix of dimensions vxv.

[0028] In another embodiment, for v=1, the matrix ' is obtained by cyclically selecting a vector w p , p=0,.., P-1 of the basis.

[0029] In this way, the precoding process according to the invention can be applied to any configuration of transmitting antennas and spatial layers.

[0030] As mentioned previously, according to the invention, the columns of the matrix M' are advantageously constructed from linear combinations of distinct orthogonal vectors forming a basis. In a particular embodiment, the P orthogonal vectors w p , p=0,.., P-1 of the basis used to construct the matrix W can be defined by: 1 r;27rp;27r2p;27r(Pl)p ] T w p = — |1 e? e P... e P j, p = 0,..., P — 1

[0031] 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 an Å / 2 spacing between antennas, where X denotes the wavelength considered for transmissions.

[0032] 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.

[0033] In a particular embodiment, v-1 columns of the matrix W result from a linear combination of | | distinct basis vectors and one column of the matrix tV results from a linear combination of (| | + P mod v) distinct basis vectors.

[0034] By "linear combination" we mean here any weighted sum of basis vectors as long as at least one weighting coefficient considered in the sum and applied to a basis vector is non-zero.

[0035] This embodiment allows the space to be divided uniformly into groups comprising an identical number (when P is a multiple of v) or a similar number (when P is not a multiple of v) of vectors.

[0036] 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).

[0037] However, a suboptimal implementation 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.

[0038] Thus, in a particular embodiment, at least one said c linear combination of |£| distinct vectors or | | + P mod v) distinct vectors includes a single non-zero weighting coefficient applied to one of the | | distinct vectors or (| | + P mod v) distinct vectors.

[0039] Other configurations can be considered, such as, for example, at least two weighting coefficients not affected by linear combination, or different numbers of vectors w p considered for each column of the matrix J4 etc. The invention offers great flexibility in implementation.

[0040] In a particular embodiment, each column of the matrix W is a linear combination of distinct adjacent basis vectors.

[0041] This embodiment is particularly simple to implement since it is sufficient to apply a cyclic shift of the basis vectors taken into account to construct each column of the precoding matrix (i.e. each precoding vector).

[0042] In a particular embodiment, the plurality of precoding matrices is obtained by cyclically traversing a dictionary of dimension Kv, when M layer> KvQ with Q as introduced previously and: K = |- j + P mod v

[0043] This embodiment allows adaptation to various symbol sequence lengths and precoding matrix dictionary (codebook) dimensions.

[0044] According to another aspect, the invention also relates to a method of receiving, by a receiving device, a signal carrying v sequence(s) of symbols spatially distributed over v layers of M layer symbols and pre-coded by a transmitting device using a pre-coding process according to the invention, the receiving process 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.

[0045] Correspondingly, the invention also relates to a receiving device, comprising: - a receiving module configured to receive a signal carrying v sequence(s) of symbols spatially distributed over v layers of M layer 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.

[0046] The receiving process and the receiving device benefit from the same advantages mentioned above as the precoding process and the transmitting device according to the invention.

[0047] 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.

[0048] 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.

[0049] In one particular embodiment, the precoding and reception processes are implemented by a computer.

[0050] 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 conforming to the invention and comprising instructions adapted to the implementation of a precoding process as described above.

[0051] 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 process as described above.

[0052] Each of these programs can use any programming language, and be in the form of source code, object code, or code somewhere between source code and object code, such as in a partially compiled form, or in any other desirable form.

[0053] The invention also relates to an information carrier or a recording medium readable by a computer, and comprising instructions for a computer program as mentioned above.

[0054] 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 drive, or a flash memory.

[0055] On the other hand, the information or recording medium can be a transmissible medium such as an electrical or optical signal, which can be carried via an electrical or optical cable, by radio link, by wireless optical link or by other means.

[0056] The program according to the invention can in particular be downloaded onto an Internet-type network.

[0057] 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.

[0058] The invention also relates to a communication system comprising: - a transmitting device according to the invention; and - a receiving device according to the invention.

[0059] 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.

[0060] According to another embodiment, the transmitting device and its P antenna ports can be distributed over a plurality of distinct physical entities.

[0061] It can also be envisaged, in other embodiments, that the precoding and reception processes, the transmitter and receiver devices and the system according to the invention have in combination all or part of the aforementioned characteristics. Brief description of the drawings

[0062] 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: [Fig. 1] Figure 1 represents a communication system according to the invention, in a particular embodiment; [Fig. 2] Figure 2 represents the hardware architecture of a transmitter device and a receiver device of the system of Figure 1, in a particular embodiment; [Fig. 3] Figure 3 illustrates the construction of a matrix used by the transmitter device of the system of Figure 1 for precoding according to the invention, in a particular embodiment; [Fig. 4] Figure 4 represents, in flowchart form, the main steps of a precoding process as implemented respectively by the transmitting device of the system in Figure 1; and [Fig. 5] Figure 5 represents, in flowchart form, the main steps of a reception process as implemented respectively by the receiving device of the system in Figure 1; and [Fig. 6] Figure 6 represents the different treatments carried out at the level of the physical layer by the emitting device of Figure 1, in a particular embodiment.

[0063] The Annex illustrates an advantage resulting from the construction proposed by the invention for the precoding matrix used by the emitting device of Figure 1. Description of the invention

[0064] 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" in English) network defined by the 3GPR 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.).

[0065] Communication system 1 includes: - a transmitting device 2 according to the invention; and - a receiving device 3 according to the invention.

[0066] In the embodiment described here, 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 are integers. There are no limitations on the nature of the user equipment 3; it can be a terminal such as a smartphone, tablet, laptop, etc., an IoT (Internet of Things) device, etc.

[0067] As mentioned previously, an antenna port is an abstract concept, defined in particular in section 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 may comprise one or more radiating elements), but which reflects what is visible from the perspective of a device communicating with the device in question.Typically, an antenna port can correspond to one or more RF (for "Radio Frequency") or TXRU (for "Transceiver Unit") chains, which themselves can correspond to one or more radiating elements.

[0068] As an example, in the embodiment described here, we assume 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.

[0069] 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 a single entity (for example, a single physical device), or distributed across several entities (for example, across several physical devices). In the latter case, this is referred to as distributed M1 MO.

[0070] 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.

[0071] According to the invention, an open-loop linear precoding technique, enabling 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.

[0072] To benefit from the combined advantages of spatial multiplexing and CDD diversity, the communication system 1 must be sized so 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= 1.

[0073] 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).

[0074] 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.

[0075] In the embodiment described here, the transmitter 2 and receiver 3 devices have the hardware architecture of a computer 4 as shown in Figure 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 means of communication.

[0076] 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.

[0077] 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 transmitter device 2 that rely on and / or control all or part of the PROC, MEM, ROM, NVM, and COM elements of the computer 4 mentioned previously. These functional modules include, in particular, in the embodiment described here, as illustrated in Figure 1: - a 2A precoding module, configured to precode v>l sequence(s) of symbols spatially distributed over v layers of M layer symbols, M layerdenoting an integer greater than 1, using a plurality of complex precoding matrices (i.e., precoders) of dimensions Pxv, with P>min(l,v) denoting the number of antenna ports of the transmitting device 2 dedicated to its communication with the receiving device 3 (P<NT). In the illustrative example of base station 2 considered here, for the sake of simplification, P=NT is assumed. The precoding matrices used by the precoding module 2A are constructed according to the invention, and are stored here in an ordered and indexed manner in the CODEB codebook; and - a 2B sending module, configured to send via the NT transmitting antennas of the transmitting device, the precoded symbols from the 2A precoding module to the receiving device 3, i.e. to the user equipment 3 in the example considered here.

[0078] 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 Figure 4.

[0079] 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 CODEB codebook is stored in the NVM memory of the receiving device 3. As previously mentioned, it is also possible, in another embodiment, for the receiving device 3 to not store the CODEB codebook.

[0080] 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 previously. These functional modules include, in particular, in the embodiment described here, as illustrated in Figure 1: - a 3A receiver module, configured to receive the signal carrying v>1 sequence(s) of symbols spatially distributed over v layer(s) of M layer 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 from the transmitting device 2 and the receiving device 3; - an estimation module 3B, configured to estimate the propagation channel between the transmitting device 2 and the receiving device 3, i.e., between the base station 2 and the user equipment 3, using uncoded reference signals emitted by the transmitting device 2. In the example of a 4G network, such reference signals are typically CRS (Cell-specific Reference Signal) for a 4G LTE network, or CSI-RS (Channel State Information Reference Signal) for a 5G NR network; and - 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.

[0081] The functions of modules 3A to 3C are described in more detail later, with reference to Figure 5.

[0082] 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(Rv) codebooks, each CODEB(Rv) codebook being associated with a particular (Rv) pair. The transmitting device 2 and the receiving device 3 are thus configured to refer to the appropriate CODEB(Rv) codebook, depending on the chosen configuration and, in particular, the values ​​of P and v considered for a given communication between the transmitting device 2 and the receiving device 3.

[0083] 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(Rv) codebook, and therefore evolve over time, in other words, the variation pattern of the precoding matrix, applied by the transmitter device 2, within the CODEB(Rv) codebook, is predefined and also known to the transmitter device 2, and in the embodiment described here, to the receiver device 3.

[0084] For example, such a variation pattern involves using a distinct precoding matrix for every Q symbols (i.e., every Q channel uses), where Q is an integer such that i < Q < M layerThe precoding matrix applied to all Q symbols is obtained by sequentially traversing (Le. in index order) the CODEB(Rv) codebook. For example, we consider here that Q = 1, meaning the precoding matrix applied by the transmitting device 2 changes at each time / frequency resource element i (or RE for "Resource Element") or at each use of channel i, with i = 0,..., M layer -1.

[0085] In the embodiment described here, a CODEB(Rv) codebook of dimension Kv is considered by construction, with: K = |- j + P mod v SM layerKvQ (or 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(Rv) codebook. This cyclic traversal of the CODEB(Rv) codebook is part of the known variation pattern of the transmitter 2 and receiver 3 devices.

[0086] For a number P of transmit antenna ports and v spatial layers, with P > min(1,v) and v > l, each precoding matrix applied by the transmitting device 2 at each use of channel i (in the illustrative example considered here) is denoted V(i) for i = 0,..., M layer- 1, and is extracted from the CODEB(Rv) codebook, which contains Kv precoding matrices. In the embodiment described here, each precoding matrix V(i) is, according to the invention, constructed from a combination of a complex matrix M(i) of dimensions Pxv, a complex diagonal matrix Z?(i) of dimensions vxv introducing a variety of cyclic delays, and a complex rotation matrix U of dimensions vxv. In other words, the "global" complex precoding matrix of dimensions Pxv is given, for the i-th use of the channel, by: V̄(i) = W(i)D(i)U for i=0,..., M layer -1 (Eq. 1)

[0087] More specifically, the diagonal matrix D(i) governing the "large delay CDD" technique introduces a phase shift between the spatial layers l ∈ {0, v — 1} for v>1. It is defined by: ( ~j2m -j2Tt(yi)i \ 1, evvj with j²=-1. In the illustrative example considered here where Q= 1, this is equivalent to: £)(i) = D k , k = i mod v with: ( -j2nk -J2nk(yi) \ 1, evvj, k E {0,...,v — 1}

[0088] In other words, the diagonal matrix £>(i) varies periodically with a period v.

[0089] 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: rl 1 ••• 1 li -J2n -j2mi -j2ir(yl) g _ 1 ev ••• ev ••• ev -J2n(y-1') -j2mi(y-î) -J27r(vl)(vl) L1 e v... Q vev J

[0090] 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.

[0091] For P>min(1,v) and v>1, the matrix W(i) is obtained from K matrices C0, C1... CK-1 by applying the following relation: W(i) = C k , k = |i / v| mod K where Co, Ci, ..., CKI denote matrices of dimensions Pxv. 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, M layer = 16 and K=4, this amounts to selecting the following matrices W(i) for i= 0,..., M layer -1: C0, C0, C0, C1, C1, C1, C2, C2, C2, C3, C3, C3, C0, C0, C0, C1, for uses of the channel indexed by i= 0, 1, 2, 3,..., 15 respectively.

[0092] Each matrix Ck, k= 0,..., K-1 has the following structure: C k = [v0 (k) v1 (k) ... v v-1 (k) ] v0 (k) v1 (k) ... v v-1 (k) ] where column v ; (fc) is the precoding vector to be applied for the layer l = 0,...,v - 1. According to the invention, each matrix Co, Ci,..., CK-I (and therefore incidentally, each matrix W(i) obtained from these matrices) is remarkable in that its v columns are linear combinations of distinct vectors from a basis of P orthogonal vectors w p , p=0,.., P-1. By "linear combination", we mean here any weighted sum of basis vectors as long as at least one weighting coefficient considered in the sum and applied to a basis vector is non-zero.

[0093] In the embodiment described here, we consider more specifically the basis formed by the P orthogonal vectors w p , p=0,.., P-1, defined by: w p = 1 epe p... e P, p = 0,..., P - 1 (Eq. 2)

[0094] These vectors w p, p=0,.., P-1 each represent a so-called "IDFT" beam. They are also referred to hereafter as "IDFT vectors".

[0095] Specifically, in the embodiment described here, v-1 columns (typically the first v-1) of each matrix Ck, k=0,..., K-1 result from a linear combination of || adjacent (consecutive) distinct vectors from the orthogonal basis of I DFT vectors, and one column of the matrix Ck, k=0,..., K-1 (typically the last) results from a linear combination of + P mod v distinct adjacent (consecutive) basis vectors. 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 v, if necessary. Of course, another position can be assigned to this column in the matrix C as an alternative, or other basis vectors besides adjacent vectors can be combined together. It should be noted that if P is a multiple of v, the v columns of the matrix Ck are then linear combinations of distinct adjacent vectors of the basis of vectors I DFT).

[0096] Furthermore, in the embodiment described here, the (K) distinct matrices Ck are obtained relative to each other by shifting the 1 er vector I DFT considered for the first column of each matrix Ck, k= 0,..., K-1.

[0097] Thus, the matrix C0 has the following structure: v0 (0) β0 (0) pi v l (0) = VV “ 1 R(°) ZJ v-1 p=(vi)[Ej where p ; (0) The {0,...,v - 1} represent real weighting coefficients, at least one of which is non-zero. These weighting coefficients p ; (0) The {0, 1} are chosen, for example, in such a way as to normalize the VQ precoding vectors 0) , V^ 0) ,....v^. In the embodiment described here, all the weighting coefficients p ; (0) , the {0,...,v - 1} are not harmed.

[0098] Fbur construct the matrix C1= [v”' v, 0 ... v ^J, as mentioned previously, the vectors I DFT w p considered for each precoding vector v (are shifted cyclically. Thus, iv0 is no longer considered for constructing the first column v”’’ but for constructing the last column v^. That is: 1 1 / β l (1) Σ w p , l = 0,...,v — 2 β l (1) v l (1) = p 1 Wp, mod P ' ZV 1 p + i where β l (1) , l ∈ {0,..., v - 1} represent real weighting coefficients. These weighting coefficients The {0,...,v - 1} are chosen, for example, in such a way as to normalize the precoding vectors ....v^. In the embodiment described here, all the weighting coefficients β l (1) , l ∈ {0,..., v - 1} are non-zero.

[0099] The precoding vectors v ; (fc) of matrix C kare defined similarly, as follows: (l+1)⌊P / v⌋+k-1 w p , l = 0,..., v — 2 p=l⌊P / v⌋ + k P+k-1 w p mod P , l = v — 1 p=(vl)[£]+k where β l (k) , l ∈ {0,...,v - 1} represent real weighting coefficients. These weighting coefficients β l (k) , l ∈ {0,...,v - 1} are chosen, for example, in such a way as to normalize the precoding vectors v0 (k) , v1 (k) ,...,v v-1 (k) In the embodiment described here, all the weighting coefficients β l (k) , l ∈ {0,..., v - 1} are non-zero.

[0100] The construction just described leads to obtaining the K matrices Ck, k= 0,..., K-1.

[0101] In view of the above and the variation patterns of the matrices W(i) (which can take K distinct values ​​given by the K matrices Ck, k = 0,..., K-1) and D(i) (which can take v distinct values ​​given by the v matrices Dj, j = 0,..., v-1), with the rotation matrix U being fixed, it is necessary to store in the codebook CODEB(Pv), in an ordered manner, the Kv possible combinations of the matrices Ck, k = 0,..., K-1, Dj, j = 0,..., v-1, and U (fixed for the Kv combinations). In the embodiment described here, the order is as follows: CoDoU, CoDiU,... CODV U, CIDOUCIDIU..., CiDv-iU,..., CKIDOU, CKIDIU,.., CKIDV-IU

[0102] Figure 3 illustrates the construction of the CODEB(Pv) codebook for v=3, P=10 and K=4, under the assumption of a uniform linear array (or UL for "Uniform Linear Array" in English), with a spacing of X / 2 between the antenna elements (or antennas), X denotes the wavelength considered.

[0103] By definition, the P vectors w p , p=0,.., P-1, and incidentally by construction, the vectors v CJ , / e {0,..., v - 1} of precoding of the matrices C, k=0,..., K-1, allow to scan uniformly the whole of the space covered by the antenna network.

[0104] Note that alternative constructions of the precoding vectors v®, the {0,..., v - 1}, can be considered as alternatives, 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).

[0105] The construction just described applies to a number of transmit antenna ports P strictly greater than the number of spatial layers v. When P=v, 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.:1 W(i) = 1 / √v I v , i ∈ {0,..., M layer - 1} Vv — — 1

[0106] Thus, in this case, the global precoding matrix V(i) is given by: V(i) = D(i)U for 1=0,.., M layer -1. The v possible values ​​of P(i) (resulting from the v possible values ​​of £>(0) are stored in codebooks CODEB(v,v) for the different values ​​of v that can be considered by the communication system 1.

[0107] As mentioned previously, in the embodiment described here, the communication system 1 is also capable of applying an open-loop linear precoding technique when v = 1. 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(P1) of dimension R. In the embodiment described here, the codebook CODEB(R1) consists of the P vectors I DFT w p , p=0,.., P-1 introduced previously and given by relation (Eq. 2) (the matrices D(i) and U of equation (Eq. 1) reduce for v=1 to D(i) = 1 and U = 1). When M layer > R the precoding vector applied by the transmitter device 2 is selected cyclically from the CODEB(R1) dictionary of I DFT vectors of dimension R which amounts to scanning the different I DFT directions, as illustrated in figure 3.

[0108] The plurality of CODEB(Rv) codebooks thus constructed for different values ​​of Pet and v comprise 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 P(i). According to this variation pattern, regardless of 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 P(i) for the use of channel i, i=0,.., M layer -1, is obtained by sequentially traversing, and cyclically when M layer > KvQ (in other words, Kv in the example considered here where Q=1), the codebook CODEB(Rv). The precoding matrix applied is assumed here to be normalized and such that: V̄(i) H V̄(i) = 1 / v I v v V where V̄(i)H is the transposed conjugate matrix of V̄(i).

[0109] We will now describe how this CODEB codebook is advantageously used by devices 2 and 3 of communication system 1, according to the invention, to implement an open-loop linear precoding technique.

[0110] 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 considered here) and by the receiving device 3 (i.e. the user equipment 3, in the illustrative example considered here), in a particular reception mode.

[0111] With reference to Figure 4, we assume here as a preliminary matter that v>l sequences of M layerEach symbol was generated by the sending device and spatially distributed across v layers by the sending device 2 (step F00). It should be noted, however, that the following also applies for v = 1 by applying the appropriate CODEB(RI) codebooks.

[0112] No limitations are attached to the way in which 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 a physical layer processing as described for example for a 4G network in document TS 36.211 in paragraph 6.3, and shown schematically in figure 6. It should be noted that a similar processing is applied in the case of a 5G network, with a few adjustments, mentioned below.

[0113] More specifically, according to such processing, useful (binary) data intended for the receiving device 3 is first encoded according to one or two streams (for example, in 5G, a single stream can be used for up to v = 4 spatial layers), resulting in at most two streams of coded data or CW codewords, each stream being encoded with a specific channel coding efficiency. These at most two streams of coded data are scrambled with an SCR scrambler, and 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 outputs of the mapper are then distributed across v spatial layers by an L_MAP layer mapper with M layer symbols per layer, which are provided as input to the precoding module 2A of transmitter device 2.

[0114] The spatial layers with Mlayer symbols per layer are then precoded by the 2Ade precoding module of the transmitter device 2 using a PRECOD linear precoder (step F10 in figure 4).

[0115] This precoding is achieved by applying a precoding matrix V̄(i) = W(i)D(i)U extracted from the CODEB(P,v) codebook, for each use of channel i, i= 0,..., M layer -1, as described previously, by sequentially and cyclically traversing the CODEB(P,v) codebook stored in the NVM memory of the transmitting device 2.

[0116] This precoding step amounts to applying to each symbol indexed by i of each IE layer {0,...,v - 1], for each antenna port indexed by p, p=0,..., R the coefficient Vp of the precoding vector v® = [v® / Vp... v®. corresponding to the Z-th column of the precoding matrix P(i).

[0117] Note that by construction, we have: V̄(i) = W(i)D(i)U 1 1 j2rtn j2it(yl) e~ v ■■■ e~ v j2nn(y—l) e~ v ■■■ e~ v with k = ⌊i / v⌋ mod K and K = ⌊P / v⌋ + P mod v.

[0118] The coefficient Applied for the p-th transmitting antenna port, layer l and for the use of the channel indexed by i, it is therefore written as follows: vl Y (k) V P, I = / . V ^, P e v a=0

[0119] Thanks to this pre-coding, the M layer The coded 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 coefficient in phase and amplitude (from the precoding matrix P(i)).

[0120] The precoded vector of dimension P, denoted x(i) = [x o (0 ^(i)... P (i)] r , intended to be transmitted by the P antenna ports of the transmitting device 2, on each use of channel i, is then given by the following equation: x (i) = = IV(i)D(i)t / x(i), ie {0,..., M la y er - 1} with: v-1 x̃ p (i) = Σ v̄ p,l (i) x l (i), p ∈ {0,..., P-1} 1=0 where x ; (i), i= 0,..., M layer -1 denotes the i-th coded symbol of the sequence of coded symbols associated with layer l.

[0121] As is well known, for each antenna port considered, the pre-coded complex constellation symbols are then mapped to Resource Elements (REs) by a Resource Mapper RE_MAP (see Figure 6). An RE 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 document TS36.211 v17.4.0, section 5.2.2, and for a 5G network in 3GPP document TS38.211 v17.7.0, 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). p , Ron a time-frequency resource grid, where p denotes a subcarrier spacing configuration, k is an index in the frequency domain, and I refers to a symbol position in the time domain relative to a reference point.

[0122] 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.

[0123] 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 GEN-OFDM multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) modulator 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).

[0124] It is noted that, as is known, 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 3GPR standard, the base station 2 more specifically transmits CRS reference signals (for a 4G network) or CSI-RS (for a 5G network), known to the user equipment 3, from its P antenna ports dedicated to its communications with the receiving device 3. As illustrated in Figure 6, these reference signals are not precoded, unlike other reference signals, such as DMRS signals (for "DeModulation Reference Signals"), also sent by the base station 2.

[0125] With reference to Figure 5, the signal carrying the v sequences of precoded OFDM symbols 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 receive antennas (NR> 1 for v>1) (step G10).

[0126] The receiving device 3, via its estimation module 3B, estimates the propagation channel matrix H as seen by the signal carrying the v 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 (CSI-RS) 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 were transmitted to it, for example, by base station 2 in transmission configuration information and control information in a manner known per se), it deduces the codebook CODEB(Rv) corresponding to these parameters. This codebook, in the embodiment described here, is stored in its non-volatile memory NVM. It also deduces the variation pattern of the precoding matrix P(i) within this codebook, and the equivalent channels HW(i)D(i)U corresponding to the Mlayer uses of the channel to transmit the pre-coded OFDM symbol sequences (G30 step).

[0127] It can thus process the received signal y using this estimation of the equivalent channels HW(i)D(i)U to extract the useful data sent by the transmitting device 2 (step G40). Such processing is known in itself, given the processing applied during transmission, and is not described in detail here.

[0128] In another embodiment, the estimation module 3B of the receiving device 3 can use 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 possible precoding matrices V(i) = W(i)D(i)U, i.e., Kv. To enable such estimation, a technique called "PRB bundling" (PRB for "Physical Resource Block") can be used in the DMRS signal example. This technique consists of 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 made using such a technique is less accurate than channel estimation based on unprecoded reference signals because it generally relies on a smaller number of reference signals.

[0129] Thanks to the invention, and in particular the generation of a matrix W using an orthogonal basis of P orthogonal vectors covering as much space as possible, with each column of the matrix W obtained from linear combinations of distinct vectors from said basis, a highly efficient open-loop linear precoding technique is obtained, offering the advantages of spatial multiplexing and emission diversity. As mentioned previously, the invention allows, in a very advantageous way, the scanning of 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.11. 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 depending on the channel's use, diversity is created at the transmission level, resulting in more reliable transmission.

[0130] Note that in the embodiment described here, the basis of orthogonal vectors considered for constructing matrix IV is a basis of I DFT vectors as defined by equation (Eq. 2). Alternatively, other bases of P orthogonal vectors can be considered for constructing the precoding vectors and, incidentally, matrix IV, such as, for example, a Hadamard basis.

[0131] Furthermore, in the embodiment described here, a CODEB dictionary composed of a plurality of CODEB(Rv) codebooks for different values ​​of (Rv) is considered. Each of these codebooks contains global precoding matrices V. Alternatively, separate codebooks could be stored for each of the matrices W, D, and U and different values ​​of (Rv). Appendix

[0132] To illustrate how the invention works, we consider here a given receiving antenna of the receiver device 3 and v beams corresponding to v channels: h(i) = h(i)W(i) = [H®. H® 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. PK(i) is the precoding matrix of dimensions Pxv chosen from the codebook CODEB(Pv) configured at the transmitting device 2 for the use of channel i.

[0133] The signal received using the "large delay CDD" technique for channel i is given by: [H® h^D& Ux where x = [x0...x v-1 ]. Gold: .271 [D(ï)U] a l = e~ ] ~ a< - l+l \ a = 0,...,v — l, 1 = 0, It therefore follows that: vl / Vl \ [Ho. hy-JDWJx = H® II a=0 \l=O / 1=0 a=0

[0134] The "large delay CDD" therefore runs the precoding phase. e -j™... gj 271 ^"^] between the channel coefficients [H®,..., / ï®^, which gives the following equivalent channel for each layer l and use of channel i: H® a=0

[0135] This allows averaging the phase of the different channel coefficients in the absence of channel information (CSI) on the transmitting device side 2.

Claims

Demands

1. A method for precoding (F20), by a transmitting device, v sequence(s) of symbol(s) spatially distributed on v layers of M layer symbols using a plurality of complex precoding matrices of dimensions Pxv, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a complex matrix JV of dimensions Pxv, said precoding method being characterized in that, for v > 1 and P > min(1,v), the v columns of the complex matrix k are linear combinations of distinct vectors from a basis of orthogonal P vectors w p , p=0,.., P-1.

2. A precoding method according to claim 1 wherein the P orthogonal vectors w p , p= 0, P-1 of said basis are defined by: 1 r;27rp j2n2p j2n(, P -l'jpiJ w p = — |1 e? e P... e P j, p = 0,..., P — 1

3. A precoding method according to claim 1 or 2 wherein v-1 columns of the matrix JV result from a linear combination of | | distinct basis vectors and one column of the matrix JV results from a linear combination of + P mod v distinct basis vectors.

4. A precoding method according to claim 3, wherein at least one said linear combination of | | distinct vectors or (| | + P mod v distinct vectors) comprises a single non-zero weighting coefficient applied to one of the distinct vectors or (| | + P mod v distinct vectors.

5. Precoding method according to any one of claims 1 to 4 wherein each column of the matrix tV 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 < M layer .

7. A precoding method according to claim 6, wherein said plurality of precoding matrices is obtained by cyclically traversing a dictionary of dimension Kv, when M layer > KvQ with: K = |- j + P mod v

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

9. A precoding method according to any one of claims 1 to 8, wherein for v=l, the matrix tVest is obtained by cyclically selecting a vector w p , p=0,.., P-1 of the basis.

10. A precoding method according to any one of claims 1 to 9 wherein each precoding matrix is ​​constructed from a combination of the complex IV matrix of dimensions Pxv, a complex diagonal D matrix of dimensions vv introducing a diversity of cyclic delays and a complex rotational U matrix of dimensions mv.

11. A method for receiving, by a receiving device (3), a signal carrying v sequence(s) of symbols spatially distributed over v layers of M layer symbols and precoded by a transmitting device using a precoding method according to any one of claims 1 to 10, 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 known precoding matrices of the receiving device.

12. A receiving method according to claim 11 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.

13. Transmitter device (2) comprising a precoding module (2A), configured to precode v sequence(s) of symbols spatially distributed over v layers of M layersymbols using a plurality of complex precoding matrices of dimensions Pxv, where P denotes a number of antenna ports of the transmitting device, each precoding matrix being constructed from a complex matrix W of dimensions Pxv, said transmitting device being characterized in that, for v > 1 and R > min(1,v), the v columns of the complex matrix JV are linear combinations of distinct vectors from a basis of P orthogonal vectors w p , p=0,.., P- 1.

14. Receiving device (3), comprising: a receiving module (3A), configured to receive a signal carrying v sequence(s) of symbols spatially distributed over v layers of M layer symbols and pre-coded by a transmitting device according to claim 13; an estimation module (3B), 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 (3C), configured to process the received signal using the estimated channel and said set of known precoding matrices of the receiving device.

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

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

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

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