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US-12627365-B2 - Method for processing radio-frequency signals received on R antennas, and corresponding reception method, decoding method, computer program and system

US12627365B2US 12627365 B2US12627365 B2US 12627365B2US-12627365-B2

Abstract

A method of processing radio-frequency signals received on R antennas, and corresponding reception method, decoding method, computer program and system. The method for processing radio-frequency signals received on R antennas, where R≥2, includes, implemented by a radio unit: obtaining a frequency representation of the radio-frequency signal received on an antenna, demapping the frequency representations, estimating the transmission channel of the radio-frequency signals and a noise-plus-interference covariance, projecting a vector of R associated complex samples onto a vector of L complex samples, referred to as projected samples, transmitting at least one item of control information and the vector of L projected samples to a base band processing unit, and the following, implemented by the base band processing unit: receiving the item of control information transmitted by the radio unit, receiving the vector of L projected samples transmitted by the radio unit, equalising the L projected samples, processing the equalised symbols.

Inventors

  • Raphaël Visoz
  • Atoosa Hatefi

Assignees

  • ORANGE

Dates

Publication Date
20260512
Application Date
20220603
Priority Date
20210604

Claims (12)

  1. 1 . A method of processing radio-frequency signals received on R antennas, where R≥2, implementing a radio unit communicating with a base band processing unit, wherein the method comprises, implemented by the radio unit: for each of the antennas, obtaining a frequency representation of the radio-frequency signal received on the antenna, formed by a set of complex samples; demapping the frequency representations, identifying useful resource elements, carrying data, and reference resource elements, carrying at least one reference signal, a useful resource element carrying v data symbols, where v≥1 is the number of spatial layers used for transmitting the data, performing an estimation of a transmission channel of the radio-frequency signals and a noise-plus-interference covariance from the at least one reference signal of a DeModulation Reference Signal (DMRS) type, for at least one useful resource element, projecting a vector of R complex samples associated with the at least one useful resource element, obtained respectively from each of the frequency representations, onto a vector of L complex samples, taking account of the estimation of the transmission channel and of the noise-plus-interference covariance, where R>L≥v, transmitting at least one item of control information, obtained from the estimation of the transmission channel, to the base band processing unit, transmitting the vector of L complex samples to the base band processing unit, and wherein the method comprises, implemented by the base band processing unit: receiving the at least one item of control information transmitted by the radio unit, receiving the vector of L complex samples transmitted by the radio unit, equalising the L complex samples, taking account of the at least one item of control information, processing equalised data symbols.
  2. 2 . The method according to claim 1 , wherein the at least one item of control information belongs to a group comprising: a channel matrix H representative of the transmission channel, a covariance matrix K I representative of the noise-plus-interference covariance, a projection matrix G, a whitening projection matrix G b = ( G ⁢ K I ⁢ G † ) - 1 2 ⁢ G , a product GH, and a product GK I G † .
  3. 3 . The method according to claim 1 , wherein the transmitting of at least one item of control information is implemented for a set of resource elements.
  4. 4 . The method according to claim 2 , wherein, for the at least one useful resource element, the vector of R complex samples as input to projecting is expressed as: y = H ⁢ x + n where y∈ R , H∈ R×v is the channel matrix representative of the transmission channel, x∈ v is a vector of data symbols, and n∈ R is a noise-plus-interference vector whose covariance matrix is K I = {nn † }∈ R×R , wherein the vector of L complex samples as output from the projection is expressed as: y 1 = Gy = GHx + G ⁢ n = G ⁢ H ⁢ x + n 1 where ⁢ y 1 ∈ ℂ L , G ∈ ℂ L × R , K 1 = E ⁢ { n 1 ⁢ n 1 † } = ( G ⁢ K I ⁢ G † ) and wherein the transmitting of at least one item of control information transmits: the channel matrix H, the projection matrix G, and the covariance matrix K I , or the projection matrix G, the product GH and the covariance matrix K I , or the product GH and K 1 =(GK I G † ).
  5. 5 . The method according to claim 1 , wherein, for the at least one useful resource element, the vector of R complex samples as input to the projection is expressed as: y = H ⁢ x + n where y∈ R , H∈ R×v is a channel matrix representative of the transmission channel, x∈ v is a vector of data symbols, and n∈ R is a noise-plus-interference vector whose covariance matrix is K I = {nn † }∈ R×R , wherein the vector of L complex samples as output from the projection is expressed as: y 1 = ( G ⁢ K I ⁢ G † ) - 1 2 ⁢ Gy = G b ⁢ y = G b ⁢ H ⁢ x + n 1 where ⁢ y 1 ∈ ℂ L , K 1 = 𝔼 ⁢ { n 1 ⁢ n 1 † } = I L , where G is a projection matrix, and wherein the transmitting of at least one item of control information transmits the product G b H.
  6. 6 . The method according to claim 4 , wherein for L=v, the projection matrix is equal to G = H † ⁢ K I - 1 ∈ ℂ v × R .
  7. 7 . The method according to claim 5 , wherein for L≥v, the projection matrix is equal to G = V † ⁢ K I - 1 2 ∈ ℂ L × R , where V=[u 1 , u 2 . . . , u L ]∈ R×L is a matrix carrying L vectors of dimension R corresponding to L directions of arrival at reception.
  8. 8 . The method according to claim 1 , wherein the method further comprises transmitting, from the radio unit to the base band processing unit, a type of projection implemented.
  9. 9 . A method of receiving radio-frequency signals on R antennas, where R≥2, implementing a radio unit communicating with a base band processing unit, wherein the method comprises, implemented by the radio unit: for each of the antennas, obtaining a frequency representation of the radio-frequency signal received on the antenna, formed by a set of complex samples; demapping the frequency representations, identifying useful resource elements, carrying data, and reference resource elements, carrying at least one reference signal of a DeModulation Reference Signal (DMRS) type, a useful resource element carrying v data symbols, where v≥1 is the number of spatial layers used for transmitting the data, performing an estimation of a transmission channel of the radio-frequency signals and a noise-plus-interference covariance from the at least one reference signal, for at least one useful resource element, projecting a vector of R complex samples associated with the at least one useful resource element, obtained respectively from each of the frequency representations, onto a vector of L projected samples, taking account of the estimation of the transmission channel and of the noise-plus-interference covariance, where R>L≥V, transmitting at least one item of control information, obtained from the estimation of the transmission channel, to the base band processing unit, and transmitting the vector of L projected samples to the base band processing unit.
  10. 10 . A method of decoding radio-frequency signals received on R antennas, where R≥2, implementing a radio unit communicating with a base band processing unit, wherein the method comprises, implemented by the base band processing unit: receiving at least one item of control information transmitted by the radio unit, obtained from an estimation of a transmission channel of the radio-frequency signals implemented by the radio unit, from at least one reference signal of a DeModulation Reference Signal (DMRS) type, receiving a vector of L complex samples, transmitted by the radio unit, obtained by projecting a vector of R complex samples associated with a useful resource element carrying v data symbols, the R complex samples being obtained from a frequency representation of the radio-frequency signal received on each antenna, onto the vector of L complex samples, where R>L≥v, and v≥1 is the number of spatial layers used for transmitting the data, equalising the L complex samples, taking account of the at least one item of control information, and processing equalised data symbols.
  11. 11 . A processing circuit comprising a processor and a memory, the memory storing program code instructions of a computer program for implementing the method according to claim 1 when the computer program is executed by the processor.
  12. 12 . A system comprising at least one radio unit, configured to process radio-frequency signals received on R antennas, where R≥2, and at least one base band processing unit, wherein the radio unit comprises at least a first processor configured to: obtain a frequency representation of the radio-frequency signal received on each of the antennas, each frequency representation being formed by a set of complex samples; demap the frequency representations, identifying useful resource elements, carrying data, and reference resource elements, carrying at least one reference signal of a DeModulation Reference Signal (DMRS) type, at least one useful resource element carrying v data symbols, where v≥1 is the number of spatial layers used for transmitting the data, estimate a transmission channel of the radio-frequency signals and a noise-plus-interference covariance from the at least one reference signal, project a vector of R complex samples associated with the at least one useful resource element, obtained respectively from each of the frequency representations, onto a vector of L complex samples, taking account of the estimate of the transmission channel and of the noise-plus-interference covariance, where R>L≥v, transmit at least one item of control information, obtained from the estimate of the transmission channel, to the base band processing unit, transmit the vector of L complex samples to the base band processing unit, and wherein the base band processing unit comprises at least a second processor configured to: receive the at least one item of control information transmitted by the radio unit, receive the vector of L complex samples transmitted by the radio unit, equalise the L complex samples, taking account of the at least one item of control information, process equalised data symbols.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is filed under 35 U.S.C. § 371 as the U.S. National Phase of Application No. PCT/FR2022/051058 entitled “METHOD FOR PROCESSING RADIO-FREQUENCY SIGNALS RECEIVED ON R ANTENNAS, AND CORRESPONDING RECEPTION METHOD, DECODING METHOD, COMPUTER PROGRAM AND SYSTEM” and filed Jun. 3, 2022, and which claims priority to FR 2105929 filed Jun. 4, 2021, each of which is incorporated by reference in its entirety. BACKGROUND Field The field of the development is that of telecommunications. More specifically, the development relates to uplink communications, that is from the mobile terminals (or UE for “User Equipment”) to a base station (or eNodeB, gNodeB, etc.). In particular, the development proposes a new distribution of the functionalities implemented by a radio unit and by a base band processing unit, for decoding radio-frequency signals received on a plurality of antennas of a base station. The proposed solution applies in particular, but not exclusively, in the context of 5G NR (“New Radio”) mobile networks. Description of the Related Art Typically, a radio-frequency signal received on an antenna undergoes analogue processing, analogue-to-digital conversion and then digital processing. Digital processing can be performed by a base band processing unit, also referred to as a Base Band Unit (BBU) or a Distributed Unit (DU). The active part of the analogue processing can be performed by a Radio Unit (RU), also referred to as a Remote Radio Head (RRH). For this purpose, it is recalled that within the analogue processing part, a distinction can be made between a passive part, comprising in particular the antenna radiating elements, and an active part, comprising in particular the filters, amplifiers, analogue/digital converters, etc. The evolution of base stations and of associated antenna structures has involved separating analogue and digital processing functionalities, bringing analogue processing as close as possible to the antenna, or even integrating it into the antenna panel. Thus, the first generations of antennas implemented only one antenna. The base station BTS (Base Transceiver Station) was connected to the passive elements of the antenna by means of a coaxial cable, via a limited number of antenna ports (maximum 4). The disadvantage of this architecture is the loss of radio-frequency signal power between the antenna ports and the base station. It also limits the acceptable distance between the BTS and the passive antennas. The centralised RAN (Radio Access Network) architecture, based on a geographical separation of the base band computing capacities (DU) for digital processing operations and the radio transmitters (RUs) for active analogue processing operations, was then developed. This type of architecture offers both functional benefits, thanks to better coordination between cells at centralised unit level, and cost benefits, through pooling the computing capacities of the various cells in common servers. For example, several RUs can communicate with one DU. The interface between the DU and the RU is referred to as a “FrontHaul”, and can be used to move the RU up to a maximum distance of 20 km to centralise DUs. As 3GPP specifications have introduced the concept of logical antenna port defined by a virtualisation (precoding/beam creation) of the logical antenna ports to the physical antenna ports, the physical antenna ports are now identified as Transceiver Units (TXRUs). In addition, TXRUs integrate the active analogue part by antenna port, thus defining an input port to the analogue domain. The evolution of base stations has consisted in bringing the TXRUs as close as possible to the antenna, or integrated into the antenna in a radio unit RU. The base band processing unit DU is thus connected to the RU via an optical fibre carrying a digital signal, thereby limiting the propagation losses associated with the use of a coaxial cable. In addition, the number of TXRUs has increased significantly over time, and can now reach the value of 64 for 5G (massive MIMO). As illustrated in FIG. 1, several splits of functionalities between the RU and the DU have been proposed, with different requirements in terms of complexity of the RUs, intelligence of the DUs, or required bandwidth for transport. The split of functionalities between the DU and the RU depends on the split option chosen. However, these splits do not provide a complete standardisation of interfaces that enable genuine interoperability between the various providers. The xRAN Fronthaul working group, and more recently the O-RAN standardisation alliance, have taken charge of the complete specification of a single open and interoperable interface between different RU and DU providers (“Open Fronthaul”). To this end, they have defined the 7.2x split, that is an adaptation of the 7.2 split specified in the 3GPP and that reduces the complexity of the RU by moving processing functions up to the DU level.