SU-MIMO communication method distinguishing between data and reference symbols for power allocation and corresponding devices

Abstract

SU-MIMO Communication Method Distinguishing Between Data and Reference Symbols for Power Allocation and Corresponding Devices. The invention relates to a method (1, 2) for communication between a transmitter and a receiver of a SU-MIMO system, the system comprising transmit antennas, at least transmit antenna ports, and receive antennas, which includes: a transmission (11) to the receiver of control information comprising a power ratio () per time-frequency resource element between reference symbols and data transmitted to that user equipment for a given antenna port (). Figure for the abstract: Fig. 5

Description

Title of the invention: SU-MIMO communication method distinguishing between data and reference symbols for power allocation and corresponding devices Field of invention

[0001] The present invention relates to the field of telecommunications. Within this field, the invention relates more particularly to digital communications implemented by a communication system with a transmitter with M transmitting antennas and a receiver with N receiving antennas called MIMO (Multiple Input Multiple Output) which makes it possible to allocate a power level per spatial layer, i.e., per transmitting antenna port while maximizing a transmission rate.

[0002] For downlink communication, the transmitter may be a base station, for example of the eNodeB (evolved Node B) or gNodeB type for networks based on LTE, LTE Advanced and subsequent technologies (5G, etc.), or a Wi-Fi access point, etc. A receiver may be a terminal such as a smartphone, tablet, connected object, etc. For uplink communication, the transmitter may be a terminal and the receiver may be a base station.

[0003] The invention finds applications in any beamforming-based system, in particular in radio communication networks according to the 4G, 5G and following standards defined by the 3GPP, WiFi communication networks according to the various IEEE 802.11 standards, etc. Prior art

[0004] Figure 1 illustrates a MIMO communication system with a transmitter with M transmitting antennas ANT_E and a receiver with NR receiving antennas ANT_R with Nr < M. The system comprises at least one access point, called base station SB in cellular systems, and a terminal UE, that of the user.

[0005] In the LTE (3 / 4G) standard specified in 3GPP, the number of receiving antennas for a so-called "smart phone" terminal is at least two, while for the NR (5G of 3GPP) standard, the number of receiving antennas for this type of terminal is specified at at least four antennas for certain bands (3.5GHz n77 / 78). For base stations, the number of transmitting antennas has continued to increase to reach up to 64, or even 128 antennas in massive MIMO.

[0006] Note that an antenna port in the context of 3GPP mobile standards and in the context of the application is associated with a “logical” antenna which can group together one or more RF (Radio Frequency) chains, each RF chain including a conversion digital to analog and / or including analog to digital conversion. The mapping of a logical antenna to N > 1 RF chains is done via a complex vector of dimension N: the signal sent to a logical antenna is multiplied by this complex vector to generate the N inputs of the N RF chains.

[0007] Each antenna comprises one or more radiating elements.

[0008] If the number of transmit RF chains and receive RF chains is the same at the base station, this is not the case for mobiles which may have a number of transmit RF chains lower than the number of receive RF chains, typically two transmit RF chains for four receive RF chains. With regard to a base station, a transmit / receive RF chain is called "TXRU, Transceiver Units" in the 5G standard.

[0009] [Fig.2] which corresponds to [Fig.6].3-1 of the TS36.211 specification schematically illustrates part of the baseband processing of the data to be transmitted, in the downlink. According to this standard, it is expected that the data can be coded according to two streams with different rates. The coded data put in the form of Cw code words are scrambled with an SCR scrambler, then mapped onto a constellation with a C_MAP mapper. The outputs of the mapper are distributed into spatial layers by an L_MAP layer mapper. The different Lay spatial layers are then pre-coded by a PRE_COD pre-coder. The pre-coded data of the different spatial layers are mapped by resource element by a RE_MAP resource mapper. At the output of the resource mapper, the data of each spatial layer are injected into an OFDM multicarrier modulator to generate an OFDM symbol. These OFDM symbols feed the antenna ports.Each spatial layer to which an antenna port corresponds supplies a single user (or recipient) at a given time. A user (or recipient) can benefit from several spatial layers simultaneously. In the upstream channel, the processing specified by the normative document TS36.211 and corresponding to [Fig.5].3-1 of this document is very similar to that of [Fig.2]. .

[0010] Conventionally for telecommunication systems with a transmission channel CH between a transmission part EM and a reception part RX the transmission resources are represented according to one or more time-frequency grids of which a representation is given by [Fig.3] which corresponds to [Fig.6].2.2-1 of the TS36.211 specification of the LTE (4G) standard of the 3GPP.

[0011] If we place ourselves in the context of the 4G or 5G standard of the 3GPP, a radio time-frequency resource is a resource element (Resource Element, RE). A resource element, in this context, designates the smallest time-frequency granularity which is identified by the indices k and l (i.e. a subcarrier and a symbol time corresponding to the duration of a multi-carrier symbol, typically OFDM in the case of an OFDM multi-carrier transmission) on the time-frequency grid of [Fig.3]. On this grid, frequencies follow the vertical axis and time the horizontal axis.

[0012] For the 5G standard there is a time-frequency grid per antenna port and for each of the uplink and downlink directions. According to the terms of this standard, a frame is divided into subframes. The spacing between subcarriers of an OFDM symbol being configurable, each subframe includes a number of OFDM symbols which varies according to the spacing between subcarriers since the duration of a symbol is the inverse of the spacing between subcarriers. The OFDM symbols are grouped into slots, each slot corresponding to the granularity of a scheduling decision known by elementary time interval (TTI).

[0013] With reference to the radio communication networks specified within 3GPP, mechanisms are specified for a terminal to be connected to a base station. The Physical Downlink Shared Channel (PDSCH) or Physical Uplink Shared Channel is the main channel used for the transmission of data in unicast form and for the transmission of system information, later called the data channel.

[0014] The receiver determines the time-frequency resource elements that it must decode by exploiting control information defined semi-statically at the level of high layers (RRC) and control information transmitted dynamically. A dedicated physical control channel per terminal, called PDCCH (Physical Downlink Control Channel), is used for the dynamic transmission of control information for the downlink and for the uplink, and for the scheduling of the physical transmission channels PDSCH and PUSCH.

[0015] The PDCCH channel is organized according to several possible formats, called DCI (Downlink Control Information) formats. A DCI format comprises several fields, each field carrying specific information (e.g. transport blocks or PRB (Physical Resource Block) allocated (one or two transport blocks can be allocated), modulation and coding schemes or MCS (for "Modulation and Coding Scheme") allocated for each transport block, identification of the allocated antenna ports corresponding to the configuration by the RRC layer (semi-static) of the reference symbols, DMRS, number of spatial layers (rank), etc.). The information bits of a PDCCH channel (i.e. the bits of the DCI format) are then associated with a CRC ("Cyclic Redundancy Check") code to allow error detection. The particularity of this CRC code is that it is scrambled with the RNTI identifier of the terminal to which the PDCCH channel is dedicated.This allows the terminal to validate that the PDCCH channel it is decoding is indeed intended for it. Indeed, if another terminal (which has a different RNTI identifier) ​​tries to verify the validity of the PDCCH channel using this other RNTI identifier, the verification of the CRC code will . returns an error.

[0016] As is known, the capacity of cellular mobile telecommunications networks, and in particular that of the networks specified in 3GPP (LTE / 3G-4G, 5G, etc.) is limited by interference. This interference can be of different types. Among the most damaging in terms of cellular network capacity, we can distinguish in particular - SU-MIMO interference (for Single User - Multiple Input Multiple Output) linked to the use of multiple antennas in transmission and reception, and which corresponds to the interference generated between MIMO data streams allocated to the same destination device (receiver); - MU-MIMO (for Multiple User - Multiple Input Multiple Output) interference linked to the use of multiple antennas in transmission and reception which corresponds to the interference generated between MIMO data streams allocated to different destination devices (receivers); and - intercellular interference, generated between signals emitted by different cells and intended for different recipient devices (receivers).

[0017] Various methods for reducing the effect of such interference on network performance are known in the prior art.

[0018] Thus, SU-MIMO type interference can be treated in particular using beamforming.

[0019] Beamforming is a signal processing technique used in MIMO communication systems comprising arrays of antennas or sensors for the directional transmission or reception of signals. This method consists of applying complex coefficients to the data streams transmitted or received by the antennas so as to assign them particular spatial properties (for example a preferred direction).

[0020] Thus, the complex coefficient applied to each antenna or antenna port is called the pre-coding coefficient and all of these coefficients form the pre-coding matrix implemented by the pre-coder PRE_COD. This pre-coding can be used to separate in space streams intended for the same device in order to allow this receiving device to detect a stream with reduced interference from other streams.

[0021] Beamforming is thus achieved by combining the elements of a phase- and amplitude-controlled antenna array in such a way that:

[0022] • the signals interfere constructively in particular directions,

[0023] • the interference is destructive in other directions.

[0024] Beamforming can be used on the transmitter side but also on the receiver side to achieve spatial selectivity.

[0025] By applying appropriate pre-coding, the transmitter can transmit data on the same time-frequency radio resources allocated to several spatial layers allocated to a single receiver, so-called SU-MIMO mode.

[0026] The selection of the transmitter side of the appropriate pre-coding which maximizes spectral efficiency, evaluated for example by the sum of the rates of the MIMO flows, is subject to a transmission power constraint.

[0027] The majority of prior art precoding algorithms are based on optimizing the performance of a MIMO transmission under a single total transmission power constraint. For example, water-filling power allocation, which allocates power based on channel conditions, makes it possible to maximize SU-MIMO capacity under a single total transmission power constraint per resource element. each component of which has a power normalized to one, 1 the number of spatial layers transmitted to the receiver on given radio resources, 2 < v, v < N r) with 'c number of transmitting antennas and NR the number of receiving antennas, W the pre-coding matrix, W e CMxv and Q the diagonal matrix of powers transmitted per antenna port, Q=dia^QtQ? -.gjeC'”-

[0029] The pre-coding matrix W performs a virtualization of the M transmit antennas into r antenna ports. The antenna concept can itself be based on a virtualization of radiating elements. For example, two radiating elements can have the same signal as input and therefore share the same virtualized antenna port.

[0030] The pre-coding W is described by a matrix of size M xv, that is to say of M lines, number of transmission antennas, and v columns, number of antenna ports, which can be written: [wl,l ' - [ wm,i ] with fn=t . ..,M and 1= L ..., v

[0031] The total transmission power constraint for a given resource element can then be expressed in the following form:

[0032] trfwew* )sp,„ax(1)

[0033] where fr( ... ) is the trace, jyf is the transconjugate matrix, called "daguer", that is to say the transposed matrix of the conjugate matrix of the matrix W, P max is the maximum energy per resource element (EPRE).

[0034] In the TS38.214 standard published by the 3GPP (5G), under clause 4.1 “Power allocation for downlink”, respectively under clause 6.2.2 “UE DM-RS transmission procedure" for the uplink, the ratio fl between the energy per resource element (EPRE) of the DMRS references and the energy per resource element (EPRE) of the PDSCH channel, respectively of the PUSCH channel, of data is tabulated according to the configuration of the DMRS. The disadvantage of this approach is that a spatial layer with a very low power allocation will have a very noisy channel estimate because the associated DMRS will have a very low power. By misuse of language in the application, the power per resource element refers to the energy per element of resource.

[0035] The approach recalled above is not well suited to real MIMO systems since these are characterized by a limitation of transmission power per power amplifier, i.e., per antenna.

[0036] Precoding algorithms must therefore satisfy these power constraints per antenna while maximizing the performance of MIMO communications. The power constraint transmitted by an antenna m must therefore satisfy the following expression:

[0037] meh

[0038] Which can also be written in the form: 100391 LL.k / es

[0040] where P ant is the maximum power per antenna per resource element and ôj the power per resource element for layer l.

[0041] The pre-coded channel for the receiver corresponds to: HWQi with |c channel corresponding to the receiver.

[0042] At the receiver, the pre-coded channel, i.e., which includes the pre-coding Wf is estimated from the demodulation reference signals (Demodulation Reference Signal or DMRS for LTE or NR systems (5G of 3GPP)) orthogonal to each other (in frequency and / or in time and / or in code) which are transmitted on the same antenna ports as the data (data) intended for this receiver and which have therefore undergone the same pre-coding W. This estimation of the pre-coded channel is used in reception during the demodulation of the received signals and the decoding of the data. The reference symbols (DMRS) carried by a spatial layer to which an antenna port corresponds are orthogonal to the reference symbols (DMRS) carried by another spatial layer, i.e., another antenna port, and are not interfered with by useful symbols. A reference symbol (DMRS) is specific to a receiver.

[0043] The quality of the estimation of the pre-coded channel made in reception depends on the reception power of the reference signals (DMRS). However, these reference signals (DMRS), as for data, are transmitted with a single maximum total power constraint Pmax per resource element knowing that the different antenna ports share the same time-frequency resource elements.

[0044] The disadvantage of this approach is that when the data and demodulation reference symbols (DMRS) transmitted by an antenna port benefit from a very low allocated power then the channel estimation is very noisy. Main characteristics of the invention

[0045] The subject of the invention is a method of communication between a transmitter and a receiver of a SU-MIMO system, the system comprising M >2 transmitting antennas, at least v 4 2 transmitting antenna ports and N > 2 receiving antennas, 2 £ v < min(M, N), using transmission time-frequency radio resource elements allocated to the v antenna ports allocated to the receiver and dedicated to communication between the transmitter and the receiver. The method implemented by the transmitter is such that: - information for controlling the communication between the transmitter and the receiver, emitted by the transmitter, include a power ratio per radio resource element time frequency between reference symbols and data transmitted to this receiver for a given transmit antenna port.

[0046] The invention further relates to a communication method intended to be implemented by a receiver of a SU-MIMO system which further comprises a transmitter, the system comprising M > 2 transmitting antennas, v > 2 transmitting antenna ports and TV = TVfi > 2 receiving antennas, 2 < v < N), using elements of radio resources transmission time-frequency allocated to the v antenna ports assigned to the receiver and dedicated to communication between the transmitter and the receiver. The method is such that: - communication control information between the transmitter and the receiver, received by the receiver, include a power ratio per radio resource element time frequency between reference symbols and data transmitted to this receiver for a given antenna port.

[0047] The invention further relates to a communication method intended for a SU-MIMO system, the system comprising a transmitter with M > 2 transmission antennas, at least r transmission antenna ports and a receiver &N = NR>2 reception antennas, 2 < v < min^M, TV), such that the power allocation distinguishes between power allocated to data and power allocated to reference symbols intended for the receiver and takes into account a maximum power per transmission antenna.

[0048] The invention further relates to an access point comprising M antennas transmitting, at least v transmitting antenna ports, a transmitter. The transmitter is such that it is capable of transmitting: - data to user equipment having Nr receiving antennas, - reference symbols for estimating a channel between the access point and the user equipment, - control information indicating radio resource elements time frequency transmission allocated to the v antenna ports assigned to the user equipment, 2 < y < Net - via a control channel dedicated to the user equipment, a power ratio per radio time frequency resource element between the reference symbols and the data transmitted to this user equipment for a given antenna port.

[0049] The invention further relates to an access point comprising N >2 reception antennas, a receiver, such that the receiver is capable of receiving: - reference symbols transmitted by a terminal having at least v transmitting antenna ports, - control information including a power ratio per radio resource element time frequency, between the reference symbols and data transmitted to this access point for a given antenna port, transmitted by the terminal.

[0050] The invention further relates to a terminal comprising M transmitting antennas, at least v transmitting antenna ports and a transmitter, such that the transmitter is capable of transmitting: - data to an access point having NR receiving antennas using radio resource elements time frequency transmission allocated to the v antenna ports assigned to the access point, 2 < v < NR), - reference symbols for estimating a channel between the terminal and the access point, - a power ratio per radio resource element time frequency between the reference symbols and the data transmitted to this access point for a given antenna port.

[0051] The invention further relates to a terminal comprising NR >. 2 reception antennas, a receiver, such that the receiver is capable of receiving: - reference symbols transmitted by an access point having at least v transmitting antenna ports, - control information indicating radio resource elements time frequency transmission allocated to the v antenna ports, transmitted by the point access, 2 < v <min(M, NR), - control information including a power ratio per radio resource element time frequency, between the reference symbols and data transmitted to this terminal for a given antenna port, transmitted by the access point.

[0052] The invention further relates to a digital signal transmitted between a transmitter having M > 2 transmission antennas, at least v > 2 transmission antenna ports and a receiver having N > 2 reception antennas, 2 < v < min( M, N ) using transmission time-frequency radio resource elements allocated to the v antenna ports allocated to the receiver and dedicated to communication between the transmitter and the receiver, such that it comprises a power ratio per radio time-frequency resource element, between reference symbols and data transmitted to this receiver for a given transmission antenna port.

[0053] The invention further relates to a computer program on an information medium, said program comprising program instructions adapted to the implementation of a method according to the invention when said program is loaded and executed in a terminal or an access point.

[0054] The invention further relates to an information medium comprising program instructions adapted to the implementation of a method according to the invention, when said program is loaded and executed in a terminal or an access point.

[0055] In the case of a SU-MIMO system, there is an overlap between the streams intended for the receiver and which are transmitted by the radio time-frequency resource elements dedicated to this receiver, even if the assigned antenna ports are different between the streams. The receiver benefits from at least two antenna ports, v S 2, for communication. The v assigned antenna ports correspond to inputs of a precoder whose M outputs feed the M transmit antennas of the SU-MIMO system. And the pre-coding applied to the reference symbols received by the receiver is the same as that applied to the data intended for this same receiver.

[0056] According to the method, whether or not the data benefits from a power different from that of the reference symbols for the same antenna port, the receiver uses the power ratio received for an antenna port to correct the estimation of the pre-coded channel carried out from the reference symbols by weighting this estimation with the received ratio.

[0057] The receiver can thus estimate, under good conditions, the pre-coded transmission channel, i.e., which includes the pre-coding, by exploiting the received reference symbols, without it being necessary to transmit to it the pre-coder or information on the choice of this pre-coder. Indeed, the transmission of the power ratio per element of resource between reference symbols and data for the same antenna port allows for a channel estimation to be carried out on reception independent of the power allocated to the data transmission channel.

[0058] The pre-coding used in transmission can vary dynamically, that is to say at the rate of sending communication control information, the sending of the power report(s) follows the same dynamic, that is, it(they) occurs at each transmission time interval (TTI).

[0059] The SU-MIMO system comprises for example a base station and a terminal. The radio transmission resources allocated to the receiver and associated with the v transmission antenna ports, 2 < v < min(M, NR) are identified by information communicated by the base station of the MIMO system to the terminal in communication control information according to semi-static mechanisms (RRC, ...) or dynamic via a control channel. This communication control channel is for example the PDCCH channel according to the 5 G standard of the 3GPP,

[0060] In particular, the invention relates to the optimization of power allocated per antenna port with a power constraint per antenna knowing the IL pre-coding by maximizing the dual function of the Lagrangian with an iterative “gradient descend” type algorithm. This approach significantly simplifies the calculations to be carried out by iteration compared to the state of the art.

[0061] According to one embodiment of the invention, the control information indicates a configuration of the reference symbols associated with the antenna ports.

[0062] According to one embodiment of the invention, the control information comprises as many power reports as there are antenna ports allocated to the receiver.

[0063] According to one embodiment of the invention, the configuration is such that the antenna ports are grouped to form NCDM groups such that the reference symbols are spatially code multiplexed between the antenna ports of the same group and according to which the control information comprises a unique power ratio for each set of antenna ports belonging to the same group and allocated to the receiver.

[0064] According to one embodiment of the invention, the method further comprises a use of the same pre-coding matrix to pre-code the data and the reference symbols to be transmitted to the receiver and the composition of which depends on an estimation of the channels between the transmitter and the receiver, all of the channels forming a global channel called SU-MIMO.

[0065] According to one embodiment of the invention, the pre-coding matrix is ​​based on a matrix of so-called input eigenvectors resulting from a decomposition into singular values ​​of the SU-MIMO channel.

[0066] According to one embodiment of the invention, the decomposition into singular values of the matrix H of the channel between the base station and the receiver is such that H — c with U e 'a matrix containing the set of vectors so-called output eigenvectors, ye |a matrix containing the set of eigenvectors said input andE = diag^ a square matrix containing the positive real singular values ​​arranged on the diagonal coefficients such that A ] ù / 1-2 ' ' " —

[0067] According to one embodiment of the invention, the method further comprises a determination reduction of power allocated to data allocated to antenna ports and intended for the receiver to maximize a sum of the receiver's flow rates, under constraint of a maximum power per transmitting antenna, alternating between a maximization of a Lagrangian L with respect to the power matrix Q for a given value of and then, after updating the value of the vector by taking taking into account its gradient, a maximization of the Lagrangian L with respect to with „ 1 vector of Lagrangian multipliers corresponding to the M power constraints per antenna.

[0068] According to one embodiment of the invention, the determination of a power allocated to the data also takes into account an electromagnetic exposure constraint at at least one point in space defined by a distance from the transmitter. This mode makes it possible to comply with a dual constraint of electromagnetic exposure and power by antenna.

[0069] According to one embodiment of the invention, the control information is carried by a physical downlink control channel according to a mobile telecommunications standard.

[0070] According to one embodiment of the invention, the data is transmitted via a downstream data channel of a 5G access network.

[0071] According to one embodiment of the invention, the control information is multiplexed in the uplink data channel according to a mobile telecommunications standard. List of figures

[0072] Other characteristics and advantages of the invention will appear more clearly on reading the following description of embodiments, given as simple illustrative and non-limiting examples, and the appended drawings, among which:

[0073] [Fig-1] [Fig.l] is a diagram of a SU-MIMO telecommunication system,

[0074] [Fig.2] [Fig.2] is a very generic diagram of a baseband architecture of a transmitter described in relation to the prior art,

[0075] [Fig.3] [Fig.3] is a diagram of a time-frequency grid of the elements of resources described in relation to the prior art,

[0076] [Fig.4] [Fig.4] is a diagram illustrating different configurations of the time grids frequencies associated with the antenna ports,

[0077] [Fig.5] [Fig.5] is a flowchart of an embodiment of a method according to the invention,

[0078] [Fig.6] [Fig.6] is a diagram of an embodiment of an access point according to the invention,

[0079] [Fig.7] [Fig.7] is a diagram illustrating a terminal according to the invention. Description of particular embodiments

[0080] The invention is placed in the context of a MIMO communication system illustrated by [Fig.l] already described in relation to the prior art. The MIMO system considered comprises at least one access point SB, called base station in cellular systems, and a terminal UE, that of a user.

[0081] Such a transmission system SYS comprises a transmitter EM and a receiver RX in communication with the transmitter via a global channel CH between the transmitting antennas ANT_E and the receiving antennas ANT_R. Depending on whether the transmission considered is uplink or downlink, the transmitter is hosted respectively in the terminal or the base station and the receiver is hosted respectively in the base station or the terminal.

[0082] In the case of a downlink transmission the receiver is also called “user equipment, terminal or user”.

[0083] The transmitter EM comprises M transmitting antennas ANT_E (M > 1), which can interfere with each other. In the same way, the receiver RE comprises NR receiving antennas ANT_R (NR > 2), which can interfere with each other. The global channel CH can be described by a matrix H of dimension N x M with 2V = N there is only one receiver. The invention is placed in the context where only the receiver is scheduled for given radio time frequency resources at a given transmission interval (TTI), the system is called SU-MIMO.

[0084] By applying an appropriate pre-coding W, the transmitter can transmit data to the receiver on v antenna ports and on the same time-frequency radio resources by limiting the interference at reception between the v received streams associated respectively with the v antenna ports, 2 < v, v being the number of spatial layers allocated to the receiver, y < min(M, N) with M the number of transmitting antennas and N the number of receiving antennas. In other words, the transmission system SYS is called single-user MIMO (SU-MIMO).

[0085] The pre-coding matrix W performs a virtualization of the M transmitting antennas into v antenna ports.

[0086] The data vector intended for the receiver before pre-coding is of size v, that is to say that the data before pre-coding are distributed over v spatial layers, i.e., antenna ports. The pre-coding W is described by a matrix of size M xv, that is to say of M rows and v columns. The number of spatial layers that a receiver can receive cannot exceed min( / V, M).

[0087] The transmitter transmits reference symbols to the receiver using the same antenna ports as those used for the data intended for this receiver, i.e., these reference symbols are therefore pre-coded like the data by means of the same pre-coding.

[0088] The pre-coding W, described by a matrix of size M xv, i.e. M rows and v columns, can be written:

[0089] ^L1 - [ w mi ] ~ t and ï- 1, ..., v wM,v

[0090] The reference symbols transmitted to the receiver are distributed in the time-frequency planes (grids) associated respectively with the antenna ports according to a determined configuration. The reference of this configuration is transmitted to the receiver via a protocol associated with the RRC layer and in a semi-static manner, that is to say on a time scale much greater than the scheduling of a receiver (downlink) or transmitter (uplink) equipment which is done on the scale of an elementary time, called TTI. It is possible to distinguish different configurations of the DMRS reference symbols which define CDM (Code Division Mul-tiplexing) groups associated with a number of antenna ports.

[0091] [Fig.4] illustrates the concept of CDM group configuration for the 5G standard. Each time-frequency grid whose structure corresponds to that of [Fig.3] corresponds to a spatial layer or to an antenna port. Whatever the configuration of the groups, when a resource element RE of a grid carries a reference symbol then there can be no data transmission for this same resource element on any of the grids (the power for data is therefore zero for this resource element for each of the grids), there is therefore no spatial interference between reference symbols (DMRS) and data. But, for this same resource element RE there can be a reference symbol (DMRS) on one or more other grids.In this case, to avoid interference between reference symbols (DMRS) between several grids, the reference symbols (DMRS) carried by the same resource element are coded with spreading codes of a so-called spatial code which are different between the grids. The reference symbols (DMRS) of a grid can be distributed only in frequency, only in time or in time and frequency, the spreading code has a frequency dimension, or a . time dimension or a frequency dimension and a time dimension.

[0092] The upper part of [Fig.4] represents a first example of configuration of the reference symbols, DMRS. This configuration defines the CDM groups 0, 1 and 2 for six antenna ports, 1000-1005, when the reference symbols, DMRS, are simple (distributed over a single OFDM symbol time) and such that for a grid the reference symbols, DMRS, are grouped by two and occupy two RE resource elements along the frequency axis. Between two grids, i.e., two ports, of the same group the reference symbols, DMRS, occupy the same RE resource elements and are therefore coded differently with a spatial code so that the receiver can distinguish the different ports. Therefore, within the same group and between two ports, the reference symbols, DMRS, are orthogonal to each other due to the spatial code.Between the grids of two successive groups, for example between groups CDM 0 and CDM 1, the reference symbols, DMRS, are offset by two resource elements RE along the frequency axis. Therefore, between the grids of different groups, the reference symbols, DMRS, are orthogonal to each other in frequency.

[0093] The lower part of [Fig.4] represents a second example of configuration of the reference symbols, DMRS. This configuration defines the CDM groups 0, 1 and 2 for twelve antenna ports, 1000-1011, when the reference symbols, DMRS, are double (distributed over two OFDM symbol times) and such that for a grid the reference symbols, DMRS, are grouped by four and occupy two RE resource elements along the frequency axis and two RE resource elements along the time axis. Between two grids of the same group the reference symbols, DMRS, occupy the same RE resource elements and are therefore coded differently so that the receiver can distinguish the different antenna ports. Therefore, within the same group and between two ports, the reference symbols, DMRS, are orthogonal to each other due to the spatial code.Between the grids of two successive groups, for example between groups CDM 0 and CDM 1, the reference symbols, DMRS, are offset by two resource elements RE along the frequency axis. Therefore, between the grids of different groups, the reference symbols, DMRS, are orthogonal to each other in frequency.

[0094] As indicated above, the receiving equipment knows the configuration of the reference symbols, i.e. the maximum number of groups and the structure of these groups (reference symbol spread over one or more symbol times, over one or more frequencies, spatial code used, ports per group).

[0095] According to the invention, the power allocation distinguishes between data and reference symbols. Power allocation to reference symbols

[0096] ^q(DMRS) the DMRS reference symbols of power ^DMRS) for the antenna port l and therefore for the estimation of the corresponding pre-coded channel hl, with t'E |LE} the index of the resource elements carrying these symbols, with E the number of reference symbols per antenna port. Depending on the configuration of the reference symbols, DMRS, the power per resource element (EPRE) per antenna, noted Pmt, is shared or not between several DMRS reference symbols. Indeed, several cases are to be considered depending on the configuration of the DMRS reference symbols: 1. Cases where DMRS reference symbols between different ports antenna ports are only code multiplexed (in the case of the examples in [Fig.4], they belong to the same CDM group, for example CDM group 0, that is to say they are spatially multiplexed within the "CDM group", ie, the reference symbols occupy the same resource elements between the antenna ports and the reference symbols of the same port are coded with a spreading code specific to the port and different from that of another port, the reference symbols of a port are therefore orthogonal in frequency and / or time with the reference symbols of another port), it comes by taking up the relation (3): [°°971 * Pa„ Vme {1, .... M}. • a. And in the case where the power between the antenna ports is identical, q{DMRS)_q is constant, V / œ {E ..., v], it comes: [0°98] < Pimt

[0099] In this case, according to the method according to the invention, the power allocated per element of resource to DMRS reference symbols for each antenna port that operates at best the power available per Pant antenna is:

[0100] (DMRS) attf

[0101] In this case, the powers of the DMRS reference symbols belonging to the same “CDM group” are therefore the same between the antenna ports but the ratio which can be different between antenna ports. There are therefore as many ratios between the energy per resource element (EPRE) of the DMRS reference symbols and the energy per resource element (EPRE) of the data channel as there are spatial layers, G {1, ..., v}. • b. Or in the case where a signaling constraint imposes the transmission of a single ratio / 1 between the energy per resource element (EPRE) of the DMRS reference symbols and the energy per resource element (EPRE) of the data channel:

[0102] then ^2 _ Pmt Qj

[0103] In this case, according to the method according to the invention, the power allocated per resource element to the DMRS reference symbols for each antenna port / is:

[0104] - 2. Cases where the DMRS symbols between different antenna ports are not multiplexed on the same resource element, that is to say that the vector a GC' Which is transmitted for the estimation of the pre-coded channel has a single non-zero element f^DMRS) corresponding to the layer l, it comes by taking the y £7^ Cl] e relation (3):

[0105] vmeU v / e(l,

[0106] In this case, according to the method according to the invention, the power allocated per resource element to the DMRS reference symbols for each antenna port / which best exploits the power available per Pant antenna is:

[0107] {DMRS) _Ç V the 1st, .. max h;,. J m 1 " • * 3. General case of several “CDM groups”, for example, the first vi DMRS reference symbols belong to one “CDM group” and the remaining v2 to another “CDM group”, • a. and in the case of an equidistributed allocation, the allocated power per resource element to the DMRS reference symbols for each antenna port / which best exploits the power available per antenna Pant is, according to the method according to the invention:

[0108] P 1 2 .................p V / e 1, ...,4

[0109] and

[0110] Q, =--“ V / G 1, V1+V2 maxLferj+ J wmj j • b. or in the case where a signaling constraint imposes the transmission of a single report per “CDM group”, the power allocated per resource element to the DMRS reference symbols for each antenna port / which best exploits the power available per Pant antenna is, according to the method according to the invention: = Q) y / e(L [YES]

[0112]

[0113]

[0114] And With „ _ IP^ — |c report corresponding to the first “CDM group” and "_ IP^ the report corresponding to the second "CDM group".

[0115] From case 3), the allocated power can be determined when there are more than two “CDM groups” associated with a number yma' of ports. ^1=1

[0116] In the case of an equidistributed allocation, the power allocated per resource element to the DMRS reference symbols for each antenna port / is, according to the method according to the invention:

[0117] / DMRS) _ Panl 7

[0118] And

[0119] / DMRS) _ P^ 7 maxL,_

[0120] And for Vj e { v3, ..., vmax = v}: Vj + v2

[0121] / DMRS) 7 Pam maxE;^^+

[0122] In the case where a signaling constraint imposes the transmission of a single report P per “CDM group”, the power allocated per resource element to the DMRS reference symbols for each antenna port / is, according to the method according to the invention:

[0123] v / e{l, .... v]

[0124] and

[0125] = Qt V / e^+l, ..., v1+v2|

[0126] And for v, e { v3, ..., vmax = v}: &DMRS) _ XQ{ V / e [tq + v2 + ... + V / -1 + h ..., + v2 + • • • + vj

[0127] With "_ IP^ the report corresponding to the first "CDM group", PcDM_l “ y v'< । |2„ o _ / the report corresponding to the second “CDM group” and ?CDM_2 “ \ । .2,,

[0128] o _ I the report corresponding to the jth “CDM group”. "cDAfj “ U i

[0129] The pre-coded channel can be expressed in the form of a matrix:

[0130] And the / th column of the matrix is ​​noted: h®MRS-

[0131] The signal received -¼ by the receiver corresponding to the transmission of a DMRS reference symbol carried by a resource element e associated with the spatial layer / has the following expression:

[0132] With nl# the noise at reception associated with the spatial layer / and the resource element e

[0133] The estimation of the pre-coded channel can be obtained by multiplying by a*e and by "averaging / interpolating" on e knowing that the other resource elements ee {1, of this layer / which do not carry DMRS reference symbols carry data symbols which benefit from a Qr II power then comes that 101341

[0135] where ^DMRS) is the power of the DMRS reference symbols for antenna port / (carrying the spatial layer / ) while Qj is the power of the data symbols for antenna port l, per resource element. The DMRS reference symbols and the data symbols carried by the resource elements of antenna port / are intended for the same receiver.

[0136] Estimating the pre-coded channel associated with antenna port l requires knowledge of p _ n^TT / DMRR) since £ _ , $,DMRS P SC HI “ V 1^1 p SCH / l[

[0137] Control information, acquired semi-statically or dynamically via a control channel, for example the PDCCH channel in 4G or 5G, dedicated to the user equipment, indicates radio time-frequency resource elements RE allocated to this user equipment whether for the uplink or the downlink.

[0138] According to the invention, a control channel for data transmission between the transmitter and the receiver indicates r power ratios, qj ^DMRS) or J q(DMRS), per radio resource element RE time frequency, between DMRS reference symbols and data transmitted to the receiver. v is the number of transmitter transmit antenna ports assigned to transmit data to the receiver.

[0139] According to the invention, the control information intended for the receiver thus comprises v quantified power ratios for the spatial layers l — 1, ..., v allocated for transmission to the receiver: 101401 or

[0141] Figure 5 very schematically illustrates a method 1 according to the invention implemented by a transmitter, a downlink access point, for example a base station in the case of a mobile access network, or an uplink terminal. The transmitter comprises M > 2 transmit antennas and at least v 2 antenna ports. The transmitter implements the communication method 1 to communicate at a given transmission interval (TTI) with a receiver. The receiver comprises NR > 2 receive antennas. The system which comprises the base station and the user equipment therefore comprises N = NR receive antennas. The base station transmits, to the user equipment, information indicating radio resource time frequency transmission elements allocated to v 1 2 transmit antenna ports. This transmission is done using a control channel dedicated to the user equipment.

[0142] According to the mobile telecommunication standards published by 3GPP, for example 4G, 5G, this control channel is the PDCCH channel. And the information is carried by the DCI (Data Control Information) and indicates the radio resource elements RE time frequency for each transmit antenna port. The format of the DCI indicates whether the radio resources are specified for an uplink or a downlink. For example, a 0-1 format of the DCI specifies that the radio resources are specified for the uplink and a 1-0 format of the DCI specifies that the radio resources are specified for the downlink.

[0143] According to method 1, control information, transmitted 11 from the transmitter to the receiver, indicates a PSCHj ratio of powers per resource element RE time frequency between DMRS reference symbols and data transmitted to the receiver for a given antenna port / . For a downlink transmission, the control information is transported by the control channel which is dedicated to the user equipment and which is typically the PDCCH channel. For an uplink transmission, the control information can be multiplexed in the data channel, for example the PUSCH channel (Physical Uplink Shared Channel) in 4G or 5G.

[0144] The receiver, a downlink terminal, or an uplink access point, for example a base station in the case of a mobile access network, implements a communication method 2 according to the invention illustrated very schematically by figure 5. The receiver receives 21 the control information, transmitted from the transmitter to the receiver, indicating a PSCHj ratio of powers per resource element RE time frequency between DMRS reference symbols and data transmitted to the receiver for a given antenna port l.

[0145] When it receives the DMRS reference symbols associated with an antenna port / intended for it, the receiver estimates the pre-coded *DMRS pn channel exploiting the "I power report(s), tax or / « ]2' Received in the control information \ fiscal) according to the invention, the receiver weights the pre-coded channel estimated from the reference symbols, and thus obtains the pre-coded channel which subsequently allows it to equalize received data associated with the same antenna port / .

[0146] In the case of DMRS reference symbols belonging to different configuration groups, “CDM groups”, according to the invention the method can transmit only one power report, fiSCH, per CDM group, for the receiver, in the case where the ratio between the power of the DMRS and that of the data carried by the same antenna port is the same for all the ports carrying the DMRS reference symbols belonging to a CDM group.

[0147] Considering for illustrative purposes only a configuration with N CDM groups, the channel estimation for the receiver from the DMRS reference symbols is based on a set A of CDM groups taken from the ^cdm CDM groups. The receiver being mapped during transmission to several antenna ports, the set A indicates the port numbers assigned during transmission to this receiver.

[0148] The method according to the invention determines the power ratios, fiscn. between the data and the reference symbols for the receiver and for each port allocated to this receiver, ce A. According to one embodiment, the PSCHc power ratios, ce A , are quantized, each on a number of bits n > 1 (for example four), and are part of the control information transmitted to the receiver, for example transmitted in the control channel (PDCCH / DCI) in the downlink or multiplexed in the PUSCH channel in the uplink. SU-MIMO Downstream Channel SVD

[0149] The signal emitted from the M antennas is: [0i50] WQix

[0151] With:

[0152] x=[.t] Xv ]TG Cvxl the data vector to be transmitted to the receiver or scheduled at a given transmission interval (TTI) of which each

[0153]

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161]

[0162] component at a power normalized to one, x the data vector intended for the receiver is mapped onto v spatial layers, VF e CMxv the pre-coding matrix associated with the receiver where v is the number of spatial layers transmitted, Q — diag^Q ■ ■ ■ QJE CW> 'a diagonal matrix of power transmitted per antenna port, this matrix is ​​associated with the spatial layers on which the reference symbols and data transmitted and intended for the receiver are mapped. The signal received y qnr by the receiver can be written: y = HWQ^x + n With : jj g çN&M the transmission channel from the transmitter to M transmitting antennas to the receiver to NR receiving antennas with NR < M, n E the noise vector such that R = E {nn'} = diag ( According to a first embodiment of the invention, the transmitter's knowledge of the SU-MIMO channel (of matrix H, i.e. the channel between the M transmitting antennas and the N receiving antennas, H e cNxM, N = NR is the number of receiving antennas) is assumed to be perfect, the pre-coding matrix used VF corresponds to the first v columns of the matrix V of the so-called input eigenvectors resulting from the SVD decomposition of the channel H and makes it possible to cancel the interference between the v spatial layers, i.e., the layers are orthogonal to each other. For the receiver, the channel matrix H can be decomposed into singular values ​​(SVD, Singular Value Decomposition) as follows: H — E with jy e the matrix containing the set of so-called output eigenvectors, ye çMxNR |a matrix containing the set of so-called input eigenvectors and £ _ j a matrix square containing the positive real singular values ​​(eigenvalues) arranged on the diagonal coefficients such that " - Ày • The received signal 3' can then to write:

[0163] ■ X! ' x2 ■ / ïj ■ / 12

[0164] y=UYV':W(p

[0165] Or again taking into account the composition of the matrix E:

[0166] According to this first embodiment of a method according to the invention, the technique Singular-Value Decomposition (SVD) is used and pre-coding used in SU-MIMO transmission for data and reference symbols intended for the receiver corresponds to the first v columns of V resulting from the SVD decomposition of the H channel. yy = [ ] e

[0167] The diagonal power matrix q _ ■■■ Q j ç= C'W describes the power allocated by spatial layer ZG {1, ..., v) where Q CW corresponds to the first v eigenvalues ​​of E.

[0168] The signal y' p^y qv with F = U can be written:

[0169]

[0170] where y _ pp is a spatially uncorrelated noise vector, i.e., J = diag^c^,

[0171] Subsequently, the eigenvalue is called the eigenvalue associated with the layer ZF {1, ..,, v} • Similarly, the variance aj is called the variance of the layer Ze {1, .v}.

[0172] SVD pre-coding makes it possible to cancel the interference between the different streams received by the receiver in order to obtain r parallel channels without interference. Thus, according to this first embodiment, with SVD pre-coding, the signal-to-noise plus interference ratio, SINR, (Signal-to-Interference-plus-Noise Ratio) of the spatial layer l is given by: [°1731 SINR, =

[0174] with the eigenvalue corresponding to the spatial layer / , the power allocated to the spatial layer l, aj the noise power of the spatial layer l.

[0175] Power allocation to data per antenna port

[0176] The power allocation Q; to the data is determined to maximize the sum rates per antenna port which define channels orthogonal to each other due to pre-coding, under power constraints per antenna P ant:

[0177] max£ log ( ] + SNR, ) Q l=L ^2 x ' z

[0178] under the constraints that: |wQWl < PV ni G [h ..., Ml-

[0179] These constraints are also written in the form:

[0180] £;=iQjw„J2 <PcmtV me {1, V 1g{1, v}

[0181] According to the first embodiment, SVD pre-coding, the signal-to-noise ratio can be expressed in the form _ À where is the eigenvalue corresponding to the spatial layer l, is the power allocated to the spatial layer / and is the noise power for layer l.

[0182] Whatever the pre-coding e qA / xv, for a receiver of the LMMSE type (with a matched whitening filter), the signal-to-noise ratio of the layer l G {1, ..., v} can be expressed in the form: 101831 f H, W, {cT^^Qfn'G-^m,

[0184] Indeed, the received signal ye qnr for the receiver can be written:

[0185] J = + .By defining^ ■■■ mv] GC^'' U comes: 1 * V y = n = 4- yh »

[0186] ^niiQjXi + Wi

[0187] with:

[0188] To solve the optimization problem under constraints, whatever the precoding, the invention uses a Lagrangian defined by: 101891 L(Q, M ) =£^(1 + 8^) - OR[ W Q W L. m -M 101901^.log^l + SINR,) - E" -P aM )

[0191] With h — [|. h 1 Ie vector of the corresponding Lagrangian multipliers " [Pf •••' PmJ to the M power constraints per antenna.

[0192] According to the first mode, SVD pre-coding, the Lagangrian can be written in the form: 101931 L(Q, H ) =£^(1 + ^) -

[0194] Vv i / 1, 2 A \ (Vv I2 n \ — Ju ,log 114—— I - ) .il I 2j, .Q - P aTlt ) “Z=I ®2\ ct? / m-^ anr7

[0195] Whatever the pre-coding, the dual Lagrange function § is defined by:

[0196] g(g) =maxL(Q, g)

[0197] Since the utility function (sum of the flow rates) is convex, minimizing the function S is equivalent to optimizing the utility function. Calculating the vector P that minimizes g makes it possible to optimize the utility function and therefore the flow rate.

[0198] The method according to the invention maximizes the Lagrangian L with respect to the power matrix Q for a given value of P, updates the value of the vector P taking into account its gradient and maximizes the Lagrangian L with respect to P. Thus, the method according to the invention alternates between a maximization of the Lagrangian L with respect to the power matrix Q for a given value of P and, after an update of the value of the vector P taking into account its gradient, a maximization of the Lagrangian L with respect to P.

[0199] Repetition of these alternating maximizations according to a particular algorithm allows the method to converge towards the power allocation matrix which meets the power constraints per antenna.

[0200] An implementation of this algorithm according to a first mode, when the pre-coding is of the SVD type, is given in a condensed form in Appendix A and described below.

[0201] In an initial step, the following variables or parameters are initialized. The vector P is initialized to a value p = p(Q) = the power matrix is ​​initialized to 0 wv, — o ' the iteration index is initialized to zero, / = 0, the tolerance factor e is initialized to a given value, for example e = 10 the learning rates fi corresponding to the Lagrangian multiplier are initialized to a given value, for example fi = 0.2.

[0202] The function corresponding to the maximization of the Lagrangian with respect to the power matrix Q for a given value of P is noted:

[0203] q* = argmax L (Q, p) Q

[0204] The power allocated to the spatial layer l G {1, ..., v} corresponds to a maximum of the function Q*, ie, when its derivative is zero: Æ(Qp) _ g, and therefore:

[0205] J \ ^(4) 4 / ln(2U£

[0206] The diagonal matrix Q* of the allocated powers is given by:

[0207] = ) (5)

[0208] As by definition the dual Lagrange function is: g(y ) = maxL(Q, p) Mr.

[0209] then: g( M) =L( ¢( / / ), / / )-

[0210] The method can calculate the initial values ​​of Q*: - Q*(p(°))

[0211] After the initialization step, the flow of the algorithm of Appendix A is as follows. - 1. Increment the index of the current iteration, i = i+ 1, - 2. Given the value obtained in the previous iteration, the value current gradient of g( g ) is given by o _ l( pj and the gradient with respect to the vector I1 is calculated as follows for all ni G {1, ..., M] ;

[0212] / z) _ nVDi.., p dp “ dp - r ant J 1^1 - 3. Based on the gradient, updating each multiplier The Grangien for all m G {1, ..., M} is given by:

[0213] ^-^) +fi AS rmrmfm >n

[0214] with fie [0,1] the learning rate for the Lagrangian multiplier - 4. Calculation of q_ q*^(0 ) according to the equation Q*( / / ) = diag( ¢( / / ), ..., ¢( / / ))

[0215] And repeat 1-4 until Eli [ w1] |2< e 1 imjn 1 J www

[0216] At the last iteration when the difference is less than the threshold e, the determined matrix = diag} includes the powers = for the data for each antenna port among the v antenna ports.

[0217] According to a second mode, when the pre-coding is arbitrary, for example a pre-coding of MMSE type, the calculation of Q* = argmax L ( Q, g ) ^based on the derivation Q given by equation (4) requires a numerical derivation of the Lagrangian. An implementation is given in condensed form in Appendix B. According to this mode, to obtain the derivative with respect to Q} of the Lagrangian, 4L(Qji), the method according to the invention follows a gradient descend / ascend approach which relies on a numerical derivative of Æ(Q,m) assuming that the Lagrangian function is locally convex (around dQ; G <0> ).

[0218] Power allocation constrained by electromagnetic field exposure limit

[0219] According to one embodiment of the invention, it takes into account an additional constraint linked to exposure to electromagnetic fields (EMFE Electro-magnetic field exposure). The EMFE constraints are considered on a set Ï2 of points in space, of any shape which does not necessarily correspond to a sphere: the power received Pr at each point r € £2 must not exceed an EMFEnutx value determined by a regulatory text (Pr EMFE^ V r 6 / 2). Each point r € £2 can be identified by a distance to the transmitter.

[0220] The received power Pr at a point r 6 £2 in space is given by:

[0221] p^^WQ^x^

[0222] with

[0223] x the transmitted data vector re C?' of which each component to a power normalized to 1,

[0224] v the number of spatial layers transmitted to the receiver,

[0225] Q e C'XI the diagonal power matrix which describes the power allocated per spatial layer the {1, ..., v},

[0226] W e CMxv the precoding matrix and

[0227] h' GC,xM the vector representing the channel between the transmitter and the point r.

[0228] These EMFE constraints are added to the antenna transmission power constraints and the performance maximization problem is now given by:

[0229] max£ / =1log? (1 + SNRZ)

[0230]

[0231]

[0232]

[0233]

[0234]

[0235]

[0236]

[0237] under constraints that: [WQWl <Panl, V mek And under the constraints that: |^WQWV|<EMFEmaxV re / 2 Qz> 0 V le{l, To solve the constrained optimization problem, the invention uses a Lagrangian defined by: L(Q, g) = ^10^(1+5^) - |ArWQW¥f| - EMFEnrax) ^M+| / 2[ the vector of multipliers The Grangian whose first M elements correspond to the M antenna power constraints and the | Q | last elements correspond to the |X21 EMFE constraints.

[0238] According to this embodiment and with SVD pre-coding the Lagrangian becomes:

[0239] L(Q|l) = ^iiog2p+^j _ I^wqwVi- EMFE^)

[0240] The algorithm described for the first embodiment can be adapted by considering all the constraints: transmission power per antenna and EMF constraints on the different points X2 of the space. Thus, at iteration i, the calculation of the gradients for m G {1, ..., M} corresponding to the transmission power constraints per antenna is that given by expression (6) and the calculation of the gradients for me [M +1, ..., M + |} corresponding to the EMFE constraints on the different points £2 of space is given by the following expression: A® = = = EMFEmax-|hrWQ*(n) WV mg[m+ 1, ..., M + jQj] 'm 'ml J

[0241] Thus, according to this embodiment of the invention, the powers Qz determined according to the method respect the power constraint per antenna and are such that the power received at any point r € £2 does not exceed the regulatory EMFE constraint.

[0242] Figure 6 is a diagram of an embodiment of an access point according to the invention in the context of a 4G or 5G type telecommunications system. The access point PA comprises M transmitting antennas ANT_E, at least v antenna ports, N receiving antennas RX, a transmitter EM1, a receiver RE1, a memory MEM1 comprising a buffer memory, a computer (microprocessor) pP1 whose instructions allow the implementation of a method 1 and / or a method 2 of communication according to the invention. At initialization, the code instructions of the program Pgl are for example loaded into the buffer memory MEM1 before being executed by the microprocessor pP1. The microprocessor pP1 controls the different components of the access point, the transmitter EM1 and the receiver RE1.

[0243] The transmitter EM1 comprises a transmission chain which generally comprises at least a channel coding (error corrector) COD of input data DATA, a MIMO coding and a multi-carrier modulation OFDM to generate data packets TB mapped onto the time-frequency resource grids of the antenna ports assigned to the user equipment (terminal) at a given transmission interval (TTI).

[0244] The transmitter EM1 makes it possible to transmit these TB data packets to the user equipment via a PDSCH data channel.

[0245] The transmitter EM1 also makes it possible to transmit: - DMRS reference symbols, - control information indicating v > 2 antenna ports allocated to the user equipment and identifying RE resource elements time frequency transmission allocated to the antenna ports, according to mechanisms semi-static (RRC) and / or dynamic via a PDCCH control channel dedicated to the user equipment, - a fiSCH power ratio {per time-frequency RE resource element, between DMRS reference symbols and data transmitted to this user equipment for a given antenna port l, this ratio being transported by the PDCCH control channel dedicated to the user equipment.

[0246] The receiver RE1 makes it possible to receive the DMRS reference symbols transmitted by the terminal to estimate the uplink channel from the terminal for the purpose of demodulating the data received by the receiver RE1. The receiver RE1 also makes it possible to receive: - a power ratio PSChi Per resource element RE time frequency, between DMRS reference symbols received and data transmitted to this access point, for a given antenna port l, this ratio being multiplexed in an uplink data channel, PUSCH.

[0247] By executing instructions, the microprocessor pP1 controls the transmitter EM1 so that it transmits control information indicating resource elements RE time frequency transmission allocated to at least two antenna ports assigned to the user equipment, via semi-static (RRC) and / or dynamic mechanisms (via a PDCCH control channel dedicated to the user equipment), and so that the PDCCH control channel dedicated to the user equipment indicates a power ratio fiSCH; per resource element RE time frequency between DMRS reference symbols and TB data transmitted to this user equipment by the access point, for a given antenna port / .By executing instructions specific to reception by the base station, the microprocessor pPl controls the receiver RE1 to receive DMRS reference symbols from the terminal and at least one power report PSChj P31 resource element RE time frequency, between reference symbols received and data from the terminal and intended for the access point, for a given antenna port / , this report being multiplexed in an uplink data channel, PUSCH. .

[0248] By executing the instructions, the microprocessor pPl determines a first estimate of the pre-coded SU-MIMO channel by exploiting the received DMRS reference symbols, for an antenna port / assigned to this access point, and weights this first estimate with the power ratio 0SCHj to obtain an estimate of the pre-coded channel of the data TB intended for this access point and received by the receiver RE1.

[0249] The simplified structure of an embodiment of a terminal according to the invention capable of implementing a communication method 1, 2 according to the invention is illustrated by [Fig.7].

[0250] The terminal UE comprises M transmitting antennas ANT_E, NR > 2 receiving antennas RX, a receiver RE2, a transmitter EM2, a memory MEM2 comprising a buffer memory, a computer (microprocessor) pP2 whose operation is controlled by the execution of a program Pg2 whose instructions allow the implementation of a method 1 and / or a method 2 of communication according to the invention. At initialization, the code instructions of the program Pg2 are for example loaded into the buffer memory MEM2 before being executed by the microprocessor p,P2. The microprocessor pP2 controls the different components of the terminal, the receiver RE2 and the transmitter EM2.

[0251] The receiver RE2 comprises an OFDM / MIMO / COD 1 reception chain which performs the inverse operations of the transmission chain of the access point to receive one or more TB data packets transmitted by this access point via a PDSCH data transmission channel.

[0252] The RE2 receiver also allows you to receive: - DMRS reference symbols emitted by the access point, - control information indicating v > 2 antenna ports allocated to this UE terminal and identifying RE resource elements, time, transmission frequency allocated to the antenna ports used for transmission by the access point, transmitted by the access point according to semi-static (RRC) and / or dynamic mechanisms via a PDCCH control channel dedicated to the UE terminal, - a power ratio fiSCH{per resource element RE time frequency, between DMRS reference symbols and data transmitted to this terminal for a given antenna port Z, this (or these) report(s) being carried by the PDCCH control channel dedicated to the terminal UE, and transmitted by the access point.

[0253] The EM2 transmitter allows: - to issue DMRS reference symbols.

[0254] The transmitter EM2 comprises a transmission chain which generally comprises at least a channel coding (error corrector) COD of input data DATA, a MIMO coding and a multi-carrier modulation OFDM to generate data packets TB mapped on the time-frequency resource grids of the antenna ports assigned to the receiver (base station) at a given transmission interval (TTI).

[0255] The EM2 transmitter allows these TB data packets to be transmitted to the base station via an uplink data channel, PUSCH.

[0256] The EM2 transmitter also allows the transmission of: - a PSCH power ratio) per RE time-frequency resource element, between DMRS reference symbols and data transmitted to the base station, for a given antenna port / , this report being multiplexed into the PUSCH data channel.

[0257] Thus, by executing the instructions, the microprocessor pP2 controls the receiver RE2 so that it receives DMRS reference symbols, control information indicating transmission time frequency RE resource elements allocated to at least two antenna ports allocated to this UE terminal as well as a power ratio ^schi P31 RE time frequency resource element between DMRS reference symbols and data transmitted, for a given antenna port / , to this UE terminal.

[0258] By executing the instructions, the microprocessor pP2 determines a first estimate of the pre-coded SU-MIMO channel by exploiting the received DMRS reference symbols, for an antenna port l assigned to this terminal, and weights this first estimate with the power ratio PSCIli to obtain an estimate of the pre-coded channel of the data TB intended for this terminal and received by the receiver RE2.

[0259] By executing transmission-specific instructions, the microprocessor pP2 controls the transmitter EM2 so that it transmits DMRS reference symbols via the PUSCH channel and a power ratio PSCHj per time-frequency resource element RE between DMRS reference symbols and data TB transmitted, for a given antenna port l, to the access point by the terminal, this ratio being multiplexed in the uplink data channel, PUSCH.

[0260] The power control of the reference symbols for the precoded channel estimation at the receiver makes it possible to have a channel estimation quality independent of the power allocated to the data per spatial layer. This power control strategy requires transmitting from the transmitter to the receiver v power ratios, v < N) being the number of spatial layers selected for the transmissions to the equipment.

[0261] Accordingly, the invention also applies to one or more computer programs, in particular a computer program on or in an information medium, adapted to implement the invention. This program may use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code such as in a partially compiled form, or in any other form desirable for implementing a method according to the invention.

[0262] The information carrier may be any entity or device capable of storing the program. For example, the carrier may comprise 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 USB key or a hard disk.

[0263] Furthermore, the information carrier may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention may in particular be downloaded from a network such as the Internet. Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

[0264] According to techniques known to those skilled in the art, the transmitter, in order to calculate the precoder and the power ratios between the DMRS and the data, must know the transmitter-to-receiver channel in advance. This knowledge can be based on the principle of reciprocity in TDD. The transmitter estimates the receiver-to-transmitter channel using reference signals transmitted by the receiver. The reciprocity of the channel makes it possible to deduce the transmitter-to-receiver channel from the estimated receiver-to-transmitter channel. In the downlink direction, the reference signals transmitted by the receiver (UE terminal) for the acquisition of the channel on transmission by reciprocity are the SRS while in the uplink direction the reference signals used are the CSLRS (transmitted by the access point).

[0265] Another approach can be based on the upload, from the receiver, of the “quantized” channel (codebook based MIMO) transmitter to receiver. For example, in the downlink direction, the receiver (UE terminal) can estimate this channel using the CSLRS transmitted by the transmitter (access point PA).

[0266] Annex A

[0267] SU-MIMO power allocation algorithm - 1. Initialization of learning rates fie [0,1] V m — 1, ..., M for the M constraints, for example fi — 0.2, V m — 1, .... M, - 2. Initialization of the tolerance threshold e, for example g = 10'3, - 3. Initialization of the Lagrangian multipliers A to an initial value ^(°), by example ^(0) = - 4. Initialization of the matrix ^*00 — q , - 5. Initialization of the iteration index, i = 0, 6-Calculation ^(0)^(o)) _ qA0), -

[0268] with ^*(0)i 7. As long as ( y M . r iyzi*IOTy / / l [^-1'LL j 8. i = i+\ 9. Calculation of the derivative (gradient) a (0 for all m = 1, ..,, M: / A m

[0269]

[0270]

[0271]

[0272]

[0273]

[0274]

[0275]

[0276] di) _ dg(ii) _ ' V) “ of the • m of the * m 10. Based on the gradient, calculate the updates of the values ​​of the Lagrangian multipliers for all m = 1, ..., M: fi a with fi the learning rate for the Lagrangian multiplier ll.CalculQ^^ma^g^^ , e««)) with O { 1 - _________i______— - ' 1 ln( x' 12. End of while, 13. Supply of Q*. Appendix B SU-MIMO power allocation algorithm for any W precoding 1. Initialization of learning rates [0,1] V / = L ..., v, fi G [0,1] V m = 1, ..., M, for the M constraints, e.g. fi = 0.2, \ ....M, 2. Initialization of the tolerance threshold e, for example e = 1 (F3, 3. Initialization of Lagrangian multipliers to an initial value / °), for example / ») = llxA / , 4. Initialization of the matrix — A , 5. Initialization of qP) — 6. Initialization of the iteration index, i = 0, 7. As long as f ),_ / / ] r„ 112] do: > 8} mjn J » j 9. Calculation of the numerical derivative of the Lagangrian L at the value Qj for all l = 1, ..., v: / 0 _ f Z / L \ J -n 10. Calculation of the derivative a 0) for all m = 1, ..., M: ZA m \ du / ~ *ant Pvm,Zi 11. Based on the gradient, calculation of updates, • values ​​of the Lagrangian multipliers:

[0277] ^i) — ^ii) + p V m = L ..., • and power: 102781 ¢^=6^+0^ / =1 - 12. End of while, - 13. Supply of Q.

Claims

Claims

1. Method (1) for communication between a transmitter (EM) and a receiver (RX) of a SU-MIMO system, the system comprising M > 2 transmit antennas, at least v > 2 transmit antenna ports and N > 2 receive antennas, 2 < v < N), using transmission time-frequency radio resource elements (RE) allocated to the v antenna ports allocated to the receiver and dedicated to communication between the transmitter and the receiver, the method implemented by the transmitter is characterized in that: - control information for the communication between the transmitter and the receiver, transmitted by the transmitter, comprises a power ratio (Psçhj) per radio time-frequency resource element (RE) between reference symbols (DMRS) and data transmitted to this receiver for a given transmit antenna port (0-

2. The communication method (1) of claim 1, wherein the control information indicates a configuration of the reference symbols associated with the antenna ports.

3. A communication method (1) according to claim 1, wherein the control information comprises as many power reports as antenna ports allocated to the receiver.

4. A communication method (1) according to claim 2, wherein the configuration is such that the antenna ports are grouped to form Ncdm groups such that the reference symbols are spatially code multiplexed between the antenna ports of the same group and wherein the control information comprises a unique power ratio for each set of antenna ports belonging to the same group and allocated to the receiver.

5. Communication method (1) according to one of claims 1 to 4, further comprising a use of the same pre-coding matrix (VF) to pre-code the data and the reference symbols to be transmitted to the receiver and the composition of which depends on an estimation of the channels between the transmitter and the receiver, all of the channels forming a global channel called SU-MIMO.

6. A communication method (1) according to claim 5, such that the precoding matrix (VF) is based on a matrix of so-called input eigenvectors resulting from a singular value decomposition (SVD) of the SU-MIMO channel.

7. Communication method (1) according to the preceding claim, such that the singular value decomposition of the matrix H of the channel between the base station and the receiver is such that jj _ jj^y^ with y the matrix containing the set of so-called output eigenvectors, ye |a matrix containing the set of so-called input eigenvectors and E = , ) G a square matrix containing the positive real singular values ​​arranged on the diagonal coefficients such that .

8. Communication method (1) according to one of claims 1 to 7, further comprising a determination of an allocated power (Qp) to the data allocated to antenna ports and intended for the receiver to maximize a sum of the receiver rates, under the constraint of a maximum power per transmit antenna, by alternating between a maximization of a Lagrangian L with respect to the power matrix Q for a given value of and then, after an update of the value of the vector P taking into account its gradient, a maximization of the Lagrangian L with respect to 1*, with •.—[>. ni " vector of the Lagrangian multipliers corresponding to the M power constraints per antenna.

9. Communication method (1) according to claim 8, such that the determination of a power allocated (Q;.) to the data further takes into account an electromagnetic exposure constraint (EMF) at at least one point in space defined by a distance from the transmitter.

10. Communication method (2) intended to be implemented by a receiver (RX) of a SU-MIMO system which further comprises a transmitter (EM), the system comprising M > 2 transmit antennas, v > 2 transmit antenna ports and N = NR 2 receive antennas, 2 < v < min(M, N), using transmission time-frequency radio resource elements (RE) allocated to the v antenna ports allocated to the receiver and dedicated to the communication between the transmitter and the receiver, the method is characterized in that: - information for controlling the communication between the transmitter and the receiver, received by the receiver, com- take a power ratio per radio resource element (RE) time frequency between reference symbols (DMRS) and data transmitted to this receiver for a given antenna port ( / ).

11. Communication method (1) for a SU-MIMO system, the system comprising a transmitter (EM) with M £ 2 transmit antennas, at least v transmit antenna ports and a receiver (RX) with N = NR > 2 receive antennas, 2 < v < N), characterized in that the power allocation distinguishes between power allocated to data and power allocated to reference symbols intended for the receiver and takes into account a maximum power per transmit antenna.

12. Access point (PA) comprising M transmitting antennas (ANT_E), at least v transmitting antenna ports, a transmitter (EM1), such that the transmitter (EM1) is able to transmit: - data (TB) to a user equipment (UE) having NR receiving antennas, - reference symbols (DMRS) for an estimation of a channel between the access point and the user equipment (UE), - control information indicating transmission time frequency radio resource elements (RE) allocated to the v antenna ports allocated to the user equipment, 2 < v < min(M, NR), characterized in that the transmitter is further able to transmit, via a control channel (PDCCH) dedicated to the user equipment, a power ratio (PschÙ Pæ" radio time frequency resource element (RE) between the reference symbols (DMRS) and the data transmitted to this user equipment for a given antenna port ( / ).

13. Terminal (UE) comprising M transmitting antennas (ANT_E), at least v transmitting antenna ports, a transmitter (EM2), such that the transmitter (EM2) is capable of transmitting: - data (TB) to an access point (PA) having NR receiving antennas using radio time frequency transmission resource elements (RE) allocated to the v antenna ports allocated to the access point, 2 < v < min(M, NR), reference symbols (DMRS) for an estimation of a channel between the terminal and the access point (AP), a power ratio (fiscHj) Pæ" radio time frequency resource element (RE) between the reference symbols (DMRS) and the data transmitted to this access point (AP) for a given antenna port ( / ).

14.

15. Access point (AP) comprising N >2 receiving antennas (RX), a receiver (RE1), such that the receiver (RE1) is capable of receiving: reference symbols (DMRS) transmitted by a terminal (UE) having at least v transmit antenna ports, characterized in that the receiver (RE1) is further capable of receiving: - control information including a radio time resource element (RE) power report Pæ frequency, between the reference symbols (DMRS) and data transmitted to this access point for a given antenna port (1), emitted by the terminal. Telecommunications terminal (UE) including NR > 2 antennas of reception (RX), a receiver (RE2), such that the receiver (RE2) is capable of receiving: reference symbols (DMRS) transmitted by an access point (AP) having at least v transmitting antenna ports, control information indicating radio time frequency transmission resource elements (RE) allocated to the v antenna ports, transmitted by the access point, 2 < v < min(M, NR), characterized in that the receiver (RE2) is further capable of receiving: control information including a power ratio (^schi^ Pæ" radio time frequency resource element (RE), between the reference symbols (DMRS) and data transmitted to this terminal for a given antenna port (1), emitted by the access point.

16. Digital signal transmitted between a transmitter (EM) having M > 2 transmitting antennas, at least v > 2 transmitting antenna ports and a receiver (RX) having N £ 2 receiving antennas, 2 < v < min(M, N ) using transmission time-frequency radio resource elements (RE) allocated to the v antenna ports assigned to the receiver and dedicated to communication between the transmitter and the receiver characterized in that it comprises a power ratio Pæ" element of resource (RE) radio time frequency, between reference symbols (DMRS) and data transmitted to this receiver for a given transmit antenna port ( / ).

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