Transmitting and receiving two-dimensional pilot signals

Abstract

A technique for transmitting a two-dimensional pilot signal is provided. The method is implemented by a network node. The method includes generating the two-dimensional pilot signal by spreading an azimuth domain pilot sequence with an elevation domain pilot sequence in the elevation domain and spreading the elevation domain pilot sequence with the azimuth domain pilot sequence in the azimuth domain. The method includes transmitting the two-dimensional pilot signal over the air.

Description

[Technical Field]

[0001] The embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for transmitting a two-dimensional pilot signal. The embodiments presented herein further relate to a method, a user equipment, a computer program, and a computer program product for receiving a two-dimensional pilot signal. [Background technology]

[0002] In general terms, pilot signals, comprising pilot sequences, may be used for many different purposes in wireless communication systems. For example, pilot signals may be used for channel parameter estimation and tracking of user equipment (UE) in a cell. Pilot signals may also serve as reference signals communicated between network nodes on the network side and UEs on the user side. Such reference signals may be utilized for, for example, initial access, synchronization, etc.

[0003] Pilot signals are transmitted over wireless channels in wireless communication systems. The pilot signals are therefore affected by the characteristics of the wireless channel itself, such as noise and fading, as well as by characteristics, e.g., reflections, caused by the physical environment through which the pilot signals are communicated. As known in the art, there may be different types of wireless channels and physical environments in which wireless communication systems are deployed, each with its own challenges. As a non-limiting and illustrative example, consider a channel estimation procedure in an IRS-assisted network, where IRS is an abbreviation for intelligent reflective surface. In essence, an IRS is composed of a two-dimensional array of reflective elements, each of which acts as a passive reconfigurable scatterer, i.e., a piece of manufactured material, that can be programmed to alter incident electromagnetic waves in a customizable manner. Such elements are typically low-cost passive surfaces that do not require a dedicated power source, and radio waves incident on them can be forwarded without the need to employ power amplifiers or radio frequency (RF) chains. The network node can then transmit the pilot signal to the UE via the IRS. The UE then estimates a downlink channel matrix based on the received pilot signal and feeds back the downlink channel matrix to a network node (possibly via an IRS) for precoding design. In millimeter wave (mmWave) and terahertz (THz) communications, the use of large antenna arrays (e.g., consisting of tens to hundreds of elements) and hundreds of reflective elements used in an IRS makes pilot signal design a difficult task. Ensuring orthogonal pilot sequences implies transmitting pilot signals consisting of long sequences, thereby sacrificing system spectral efficiency.

[0004] The pilot sequence design does not exploit the geometry of the transmit and receive antenna arrays. Furthermore, at the receiver, the channel matrix is ​​typically estimated by solving a single optimization problem using, for example, the least squares (LS) method or the minimum mean square error (MMSE) method.

[0005] Therefore, there is a need for improved pilot signal designs. Summary of the Invention

[0006] An objective of the embodiments herein is to design pilot signals such that the above problems can be avoided, or at least reduced or mitigated.

[0007] According to a first aspect, a method for transmitting a two-dimensional pilot signal is provided, the method being implemented by a network node, comprising: transmitting an elevation domain pilot sequence S in an elevation domain z; z In the azimuth domain pilot sequence S y and spreading the azimuth domain pilot sequence S y In the elevation domain, the pilot sequence S z and spreading the two-dimensional pilot signal S to generate a two-dimensional pilot signal S. The method includes transmitting the two-dimensional pilot signal over the air.

[0008] According to a second aspect, a network node for transmitting a two-dimensional pilot signal is presented, the network node comprising a processing circuit, the processing circuit configured to cause the network node to transmit an elevation domain pilot sequence S in an elevation domain z. z In the azimuth domain pilot sequence S y and spreading the azimuth domain pilot sequence S y In the elevation domain, the pilot sequence S zThe processing circuitry is configured to cause the network node to transmit the two-dimensional pilot signal S over the air.

[0009] According to a third aspect, a network node for transmitting a two-dimensional pilot signal is presented, the network node transmitting an elevation domain pilot sequence S in an elevation domain z. z In the azimuth domain pilot sequence S y and spreading the azimuth domain pilot sequence S y In the elevation domain, the pilot sequence S z and a generating module configured to generate a two-dimensional pilot signal S by spreading a signal S. The network node comprises a transmitting module configured to transmit the two-dimensional pilot signal over the air.

[0010] According to a fourth aspect, a computer program for transmitting a two-dimensional pilot signal is presented. The computer program includes computer code that, when run on a processing circuit of a network node, causes the network node to perform actions. One action is for the network node to transmit an elevation domain pilot sequence S in an elevation domain z. z In the azimuth domain pilot sequence S y and spreading the azimuth domain pilot sequence S y In the elevation domain, the pilot sequence S z and generating a two-dimensional pilot signal S by spreading the two-dimensional pilot signal S. An action includes the network node transmitting the two-dimensional pilot signal over the air.

[0011] According to a fifth aspect, a method for receiving a two-dimensional pilot signal is presented. The method is implemented by a UE. The method includes receiving a two-dimensional pilot signal X over-the-air from a network node. The method includes deriving a two-dimensional pilot signal X from the two-dimensional pilot signal X by despreading the two-dimensional pilot signal X and solving a rank one matrix approximation problem for the two-dimensional pilot signal X: This includes estimating TIFF2025540801000002.tif12170.

[0012] According to a sixth aspect, a UE for receiving a two-dimensional pilot signal is presented. The UE comprises a processing circuit configured to cause the UE to receive a two-dimensional pilot signal X over-the-air from a network node. The processing circuit causes the UE to derive from the two-dimensional pilot signal X by despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X: It is set to estimate TIFF2025540801000003.tif12170.

[0013] According to a seventh aspect, a UE for receiving a two-dimensional pilot signal is presented. The UE comprises a receiving module configured to receive a two-dimensional pilot signal X over-the-air from a network node. The UE derives from the two-dimensional pilot signal X by despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X: The system is equipped with an estimation module configured to estimate TIFF2025540801000004.tif12170.

[0014] According to an eighth aspect, a computer program for receiving a two-dimensional pilot signal is presented. The computer program includes computer code that, when run on a processing circuit of a UE, causes the UE to perform actions. One action includes the UE receiving a two-dimensional pilot signal X over-the-air from a network node. One action includes the UE deriving from the two-dimensional pilot signal X by despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X: This includes estimating TIFF2025540801000005.tif12170.

[0015] According to a ninth aspect, there is provided a computer program product comprising a computer program according to at least one of the fourth and eighth aspects and a computer-readable storage medium on which the computer program is stored. The computer-readable storage medium may be a non-transitory computer-readable storage medium.

[0016] Advantageously, these aspects provide a pilot signal that allows the above-mentioned problems to be avoided, or at least reduced or mitigated.

[0017] Advantageously, these aspects allow the overall computational complexity at the receiver side to be reduced. This is achieved by separating the channel estimation problem into two parallel and smaller problems.

[0018] Advantageously, these aspects allow for flexible transmission design by allowing for separation of pilot and data transmissions along the azimuth and elevation domains.

[0019] Advantageously, these aspects allow the length of the pilot sequence to be relaxed, and therefore, compared to existing methods, the computational complexity can be significantly reduced, both at the transmitter and receiver side.

[0020] Advantageously, these aspects are applicable to different types of wireless communication systems, such as wireless communication systems having one or more IRSs or network-controlled repeaters (NCRs), or wireless communication systems based on massive multiple-input multiple-output (mMIMO) techniques, or line-of-sight (LOS) MIMO techniques.

[0021] Advantageously, these aspects allow pilot signals and data to be transmitted in different regions, thereby increasing spectral efficiency compared to state-of-the-art pilot and data transmission strategies.

[0022] Advantageously, these aspects allow channel variations in azimuth and elevation to be tracked independently.

[0023] Other objectives, features, and advantages of the enclosed embodiments will become apparent from the following detailed disclosure, from the attached dependent claims, and from the drawings.

[0024] In general, all terms used in the claims should be interpreted according to their customary meaning in the art unless expressly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." should be openly interpreted as referring to at least one instance of that element, apparatus, component, means, module, step, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless expressly stated.

[0025] The inventive concept will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram illustrating a communication system according to an embodiment. [Figure 2]1 is a schematic diagram illustrating a communication system according to an embodiment. [Figure 3] FIG. 2 is a block diagram of a network node according to an embodiment. [Figure 4] 1 is a flowchart of a method according to an embodiment. [Figure 5] 1 is a flowchart of a method according to an embodiment. [Figure 6] FIG. 2 is a schematic diagram of a network node and a UE in a coordinate system according to an embodiment. [Figure 7] FIG. 2 is a schematic diagram of a network node and a UE in a coordinate system according to an embodiment. [Figure 8] FIG. 10 is a diagram illustrating a simulation result according to an embodiment. [Figure 9] FIG. 10 is a diagram illustrating a simulation result according to an embodiment. [Figure 10] FIG. 2 is a signaling diagram of a method according to an embodiment. [Figure 11] 1 is a flowchart of a method according to one embodiment. [Figure 12] FIG. 2 is a schematic diagram illustrating functional units of a network node according to an embodiment. [Figure 13] FIG. 2 is a schematic diagram illustrating functional modules of a network node according to one embodiment. [Figure 14] 2 is a schematic diagram illustrating functional units of a UE according to one embodiment; [Figure 15] 2 is a schematic diagram illustrating functional modules of a UE according to one embodiment; [Figure 16] FIG. 1 illustrates an example of a computer program product comprising computer readable means according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] The inventive concepts will now be described more fully hereinafter with reference to the accompanying drawings, in which several embodiments of the inventive concepts are shown. However, the inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concepts to those skilled in the art. Like numbers refer to like elements throughout the description. Any steps or features illustrated by dashed lines should be considered optional.

[0028] Consider the wireless communication system 100a shown in Figure 1, in which a network node 200 is in communication with a UE 300 over a wireless channel. The network node 200 may be a radio access network node, a radio base station, a base transceiver station, a Node B (NB), an evolved Node B (eNB), a gNB, an access point, an access node, or a radio access-backhaul integrated transmission node. The UE 300 may be a portable wireless device, a mobile station, a mobile phone, a handset, a wireless local loop telephone, a smartphone, a laptop computer, a tablet computer, a wireless modem, a wireless sensor device, an Internet of Things device, or a network-equipped vehicle.

[0029] For purposes of illustration, the network node 200 is configured to measure M y antenna elements and M z and therefore the total number of antenna elements M=M y M z Similarly, the UE 300 is assumed to be equipped with a uniform rectangular array (URA) with Q y It has antenna elements, and Q in the elevation angle domain z Therefore, the total number of antenna elements Q = Q y Q zTherefore, the network node 200 and the UE 300 are assumed to be equipped with a URA having It may be assumed that the signals communicate over a wireless MIMO channel characterized by TIFF2025540801000006.tif6170.

[0030] Consider the wireless communication system 100b shown in Figure 2, in which a network node 200 is communicating with a UE 300 over a wireless channel via an IRS 400. The network node 200 and the UE 300 are assumed to be configured in the same manner as in Figure 1. The IRS 400 is configured to provide a N y reflecting elements and N in the elevation angle domain (i.e., along the vertical axis) z reflective elements, so the total number N = N y N z Assume that we have Let TIFF2025540801000007.tif5170 be the MIMO channel between network node 200 and IRS 400, Let TIFF2025540801000008.tif5170 be the MIMO channel matrix between IRS400 and UE300, Let TIFF2025540801000009.tif5170 be a diagonal matrix holding the phase shifts of the IRS reflective elements.

[0031] In a line-of-sight (LOS) scenario or a non-line-of-sight (NLOS) scenario with a dominant LOS component, i.e., a higher Rician K-factor, the MIMO propagation channel is characterized by the Kronecker product of the horizontal and vertical components, i.e., TIFF2025540801000010.tif6170, where TIFF2025540801000011.tif6170 shows the Kronecker product operator. This is particularly the case in mmWave and terahertz communications. This Kronecker approximation model is also valid in multipath wireless channels when the angular spread in one region is negligible compared to the angular spread in other regions.

[0032] As disclosed above, there is a need for improved pilot signal designs.

[0033] More specifically, during a certain time frame, the wireless channel may exhibit more variation in some regions compared to other regions. Even if the two endpoints of the wireless channel, i.e., network node 200 and UE 300, are at fixed locations, one of the regions may still exhibit lower variation (angular spread) in most cases compared to the other. Moreover, when the number of antenna elements is large, such as in a massive multiple-input multiple-output (MIMO) setup or in an IRS-assisted network with a large number of IRS elements, the estimation of channel parameters relies on a single pilot sequence, the design of which may become difficult due to the large number of antenna elements in network node 200 and / or the large number of reflecting elements in IRS 400.

[0034] Furthermore, the IRS 400 is not capable of estimating the wireless channel, only the UE 300 or the network node 200. Pilot sequences specified in 3GPP TS38.211 "NR; Physical channels and modulation," version 17.3.0, such as pseudorandom (PR) sequences and Zadoff-Chu sequences, do not exploit the separable geometric structure of antenna arrays. State-of-the-art designs of pilot signals typically imply transmitting different (possibly orthogonal) training sequences at each transmit antenna. Furthermore, existing pilot signal design strategies do not exploit the non-uniform behavior of the wireless channel across the horizontal (azimuth) and vertical (elevation) domains. Not exploiting the wireless channel structure can lead to inefficient use of spectrum resources.

[0035] Therefore, at least some of the embodiments disclosed herein propose a pilot signal design strategy that effectively exploits the geometry of a uniform rectangular array (URA) to separate the channel parameter estimation and tracking problem into azimuth and elevation domain sub-problems. The elevation domain is related to elevation spatial frequencies, and the azimuth domain is related to azimuth spatial frequencies. Pilot sequences can be designed independently for the azimuth and elevation domains, respectively. As described in more detail below, the final transmitted pilot signal is spread in both the azimuth and elevation domains. By jointly factoring the pilot sequences, the receiver can split the channel estimation problem into two smaller (and independent) sub-problems: one for the azimuth (horizontal) domain and one for the elevation (vertical) domain.

[0036] Reference is now made to FIG. 3, which shows a block diagram of a network node 200 according to an embodiment. Two independent pilot sequences, which are columns of TIFF2025540801000012.tif8170, The combination obtained by passing TIFF2025540801000013.tif7170 through combiner 240 is mapped to antenna elements (one of which is identified at 252) in antenna array 250 of network node 200. In the example of Figure 3, the Kronecker product is used as an example of how pilot sequences may be mapped to antenna elements such that the pilot sequences are combined and spread in the azimuth and elevation domains.

[0037] This significantly reduces the complexity of a large estimation problem to that of two smaller sub-problems. Moreover, the proposed independent pilot signal design in the azimuth and elevation domains significantly reduces the constraint on the length of the pilot sequences. In some embodiments, such separation also helps in joint pilot signal and data transmission due to the nature of the variation of the wireless channel along the azimuth and elevation domains. A network node can transmit more pilot signals along a domain (azimuth or elevation) that shows more variation compared to other domains (elevation or azimuth) that may be used (only) for data transmission.

[0038] The embodiments disclosed herein relate in particular to techniques for transmitting two-dimensional pilot signals and receiving two-dimensional pilot signals. To obtain such techniques, a network node 200, a method implemented by the network node 200, and a computer program product including code, e.g., in the form of a computer program, are provided, which, when run on processing circuitry of the network node 200, causes the network node 200 to perform the method. To obtain such techniques, a UE 300, a method implemented by the UE 300, and a computer program product including code, e.g., in the form of a computer program, are further provided, which, when run on processing circuitry of the UE 300, causes the UE 300 to perform the method.

[0039] Reference is now made to FIG. 4, which illustrates a method for transmitting two-dimensional pilot signals implemented by a network node 200, according to one embodiment.

[0040] S104: The network node 200 receives an elevation domain pilot sequence S in the elevation domain z. z In the azimuth domain pilot sequence S y and spreading the azimuth domain pilot sequence S y In the elevation domain, the pilot sequence S z A two-dimensional pilot signal S is generated by spreading the signal S.

[0041] S106: The network node 200 transmits a two-dimensional pilot signal over the air.

[0042] As a result, a different combination of azimuth and elevation pilot sequences is transmitted at each antenna element in the network node 200 .

[0043] In general terms, it is assumed that a two-dimensional pilot signal S is transmitted towards the UE 300 .

[0044] With continued reference to FIG. 4, an embodiment relating to further details of transmitting two-dimensional pilot signals implemented by the network node 200 will now be disclosed.

[0045] In some embodiments, the azimuth domain pilot sequence S y is the elevation domain pilot sequence S z It is designed independently.

[0046] If the radio channel is to be estimated at the UE 300, the network node 200 needs to share the azimuth and elevation domain pilot sequences (as well as the lengths of the pilot signals) with the UE 300 via some control signaling. Thus, in some embodiments, the network node 200 is configured to perform the (optional) step S102.

[0047] S102: Before transmitting the two-dimensional pilot signal, the network node 200 transmits the azimuth domain pilot sequence S y and the elevation domain pilot sequence S z A control signal is sent to set the

[0048] If the radio channel is to be estimated at the network node 200, the network node 200 only needs to share the length of the pilot signal with the UE 300 via some control signaling.

[0049] It is then assumed that the radio channel should be estimated at the network node 200. As will be further disclosed below, the UE 300 calculates the BER from the two-dimensional pilot signal received by the UE 300. TIFF2025540801000014.tif7170. Thus, in some embodiments, the network node 200 is configured to perform the (optional) step S108.

[0050] S108: The network node 200 transmits the information over the air from the UE 300. Receive TIFF2025540801000015.tif7170.

[0051] The estimated matrix TIFF2025540801000016.tif6170 and the transmitted pilot sequence, i.e., S y , S zFrom the knowledge of, the network node then TIFF2025540801000017.tif6170. In particular, in some embodiments, the network node 200 is configured to perform the (optional) step S110.

[0052] S110: The network node 200 Estimate TIFF2025540801000018.tif12170.

[0053] Next, the radio channel should be estimated at the UE 300, and therefore it is assumed that the network node 200 has shared the azimuth and elevation domain pilot sequences (as well as the length of the pilot signals) with the UE 300 via some control signal. TIFF2025540801000019.tif6170 is fed back to the network node 200. That is, in some embodiments, the network node 200 is configured to perform the (optional) step S112.

[0054] S112: The network node 200 transmits the information over the air from the UE 300. Receive TIFF2025540801000020.tif7170.

[0055] Regardless of whether the radio channel is estimated in the UE 300 or in the network node 200, the network node 200 may use these estimated channel matrices to further estimate the channel parameters, i.e. in some embodiments the network node 200 is configured to perform the (optional) step S114.

[0056] S114: The network node 200 TIFF2025540801000021.tif7170 Estimate azimuth domain channel parameters, TIFF2025540801000022.tif5170Estimate elevation domain channel parameters.

[0057] In some aspects, the azimuth and elevation domain channel parameters are used to design a two-dimensional precoder, or beamformer, consisting of horizontal and vertical components. In particular, in some embodiments, the network node 200 is configured to perform (optional) step S116.

[0058] S116: The network node 200 determines a two-dimensional precoder according to the azimuth component determined from the estimated azimuth domain channel parameters and the elevation component determined from the estimated elevation domain channel parameters.

[0059] In this regard, there are at least two ways in which a two-dimensional precoder can be designed. According to the first example, singular value decomposition (SVD) TIFF2025540801000023.tif6170Design an optimal precoder. According to the second example, first, assume that the channel parameters are TIFF2025540801000024.tif6170Then, an optimal precoder is designed based on the channel parameters.

[0060] In some aspects, additional pilot sequences are allocated in the azimuth and elevation regions according to the channel estimates. The pilot sequences may be selected to be longer in regions that show more variation compared to other regions. Additional two-dimensional pilot signals may then be transmitted. Thus, in some embodiments, the network node 200 is configured to perform the (optional) step S118.

[0061] S118: The network node 200 receives a further azimuth domain pilot sequence Sy and an additional elevation domain pilot sequence S z Further, the azimuth domain pilot sequence S y has a length proportional to how much the estimated azimuth domain channel parameters have varied compared to the previously estimated azimuth domain channel parameters. z has a length proportional to how much the estimated elevation domain channel parameters have varied compared to the previously estimated elevation domain channel parameters.

[0062] This allows the radio channel to be tracked separately in the two regions.

[0063] The two-dimensional pilot signal S is expressed as an azimuth domain pilot sequence S y and the elevation domain pilot sequence S z In some examples, the two-dimensional pilot signal S may be generated from the azimuth domain pilot sequence S. y and the elevation domain pilot sequence S z In this regard, a two-dimensional pilot signal S may be transmitted from a two-dimensional antenna with antenna elements arranged in rows and columns, where: TIFF2025540801000025.tif7170 transmitted at antenna element (i,j), where: TIFF2025540801000026.tif7170 is the azimuth domain pilot sequence for all antenna elements in row i of a two-dimensional antenna, where TIFF2025540801000027.tif7170 is the elevation domain pilot sequence for all antenna elements in column j of a two-dimensional antenna, where TIFF2025540801000028.tif6170 Shows the Kronecker product operator.

[0064] In some aspects, the network node 200 determines allocations of new pilot signals and data to be transmitted along azimuth and elevation domains toward the UE 300. More particularly, the network node 200 may determine the ratio of pilot signals to data in each domain. As a non-limiting example, the network node 200 may allocate only pilots in some domains and only data in other domains to simultaneously optimize channel tracking and data transmission. That is, in some aspects, depending on wireless channel variations along azimuth and elevation, pilot sequences may be transmitted in only one dimension (e.g., in the azimuth domain) and data may be transmitted in another dimension (e.g., in the elevation domain).

[0065] To inform the UE 300 about the pilot and data allocation scheme, the network node 200 may send control signals towards the UE 300, which determine the operation mode at the UE 300. A first possible operation mode involves channel tracking in both the azimuth and elevation domains. A second possible operation mode involves data transmission in both the azimuth and elevation domains. A third possible operation mode involves mixed channel tracking and data detection in different domains. The use of such operation modes leads to separation of pilot signal transmission and data transmission into two independent domains for more flexible system design and optimized data throughput.

[0066] In some aspects, the IRS 400 may provide capability reports to the network node 200, informing the network node 200 about, for example, the number and / or indexing of reflective elements along azimuth and elevation regions in the IRS 400.

[0067] Reference is now made to FIG. 5, which illustrates a method for receiving two-dimensional pilot signals implemented by a UE 300, according to one embodiment.

[0068] S204: The UE 300 receives a two-dimensional pilot signal X over the air from the network node 200.

[0069] S206: The UE 300 despreads the two-dimensional pilot signal X and obtains from the two-dimensional pilot signal X by solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X: Estimated to be TIFF2025540801000029.tif12170.

[0070] At the UE 300, the channel estimation is split into two smaller sub-problems: one for the azimuth domain and one for the elevation domain.

[0071] With continued reference to FIG. 5, an embodiment relating to further details of receiving two-dimensional pilot signals, as implemented by the UE 300, will now be disclosed.

[0072] As disclosed above, if the radio channel is to be estimated at the UE 300, the network node 200 needs to share the azimuth and elevation domain pilot sequences (as well as the lengths of the pilot signals) with the UE 300 via some control signal. Thus, in some embodiments, the UE 300 is configured to perform the (optional) step S202.

[0073] S202: Before receiving the two-dimensional pilot signal, the UE 300 receives the transmitted azimuth domain pilot sequence S y and the transmitted elevation domain pilot sequence S z and receives control signals from the network node 200 to set up the

[0074] As further disclosed above, if the radio channel is to be estimated at the network node 200, the network node 200 only needs to share the length of the pilot signal with the UE 300 via some control signaling.

[0075] It is then assumed that the radio channel should be estimated at the network node 200. The UE 300 derives the eigenvalues ​​from the two-dimensional pilot signal as in S206. TIFF2025540801000030.tif7170 and then feeds these estimates back to the network node 200. Thus, in some embodiments, the UE 300 is configured to perform the (optional) step S208.

[0076] S208: The UE 300 communicates with the network node 200 over the air. Send TIFF2025540801000031.tif12170.

[0077] Next, the radio channel should be estimated at the UE 300, and it is therefore assumed that the network node 200 has shared the azimuth and elevation domain pilot sequences (as well as the lengths of the pilot signals) with the UE 300 via some control signaling. In this case, the UE 300 is configured to perform the (optional) step S210.

[0078] S210:UE300 is Estimate TIFF2025540801000032.tif16170.

[0079] The UE 300 then TIFF2025540801000033.tif6170 will be fed back to the network node 200. That is, in some embodiments, the UE 300 is configured to perform the (optional) step S212.

[0080] S212: The UE 300 communicates with the network node 200 over the air. Send TIFF2025540801000034.tif7170.

[0081] As disclosed above, the two-dimensional pilot signal S is represented by the azimuth domain pilot sequence S y and the elevation domain pilot sequence S z In some examples, the two-dimensional pilot signal S may be generated from the azimuth domain pilot sequence S. y and the elevation domain pilot sequence S z Thus, in some embodiments, TIFF2025540801000035.tif7170 is estimated from the two-dimensional pilot signal X by Kronecker factorization of the two-dimensional pilot signal X. In some examples, the Kronecker factorization is performed by solving the Kronecker factorization problem formulated as follows: TIFF2025540801000036.tif10170

[0082] In some aspects, the UE 300 then estimates corresponding azimuth and elevation domain channel matrices and feeds them back to the network node 200 for further channel parameter estimation.

[0083] (regardless of whether this estimation is performed by the network node 200 or the UE 300) There can be different ways to estimate TIFF2025540801000037.tif6170. In some examples, a matched filter (MF) approach is used, thus TIFF2025540801000038.tif7170 is estimated as follows: TIFF2025540801000039.tif11170

[0084] Further details relating to embodiments, aspects and examples applicable to the above methods will now be disclosed.

[0085] The network nodes 200 each have a respective component for estimating the corresponding component of the wireless channel. TIFF2025540801000040.tif8170Two independent pilot sequences, Assume that we generate TIFF2025540801000041.tif7170. For antenna element (i, j), TIFF2025540801000042.tif7170From each antenna element, as shown in Figure 3, S y and S z Assume that the resulting orthogonal pilot sequences are transmitted, mapped to the antenna elements according to the Kronecker product between corresponding columns of TIFF2025540801000043.tif7170The received matrix of the pilot signal X is X = GΩHS + V, (1) can be written as where: TIFF2025540801000044.tif6170 is the received matrix of the pilot signal, TIFF2025540801000045.tif6170 is the transmitted matrix of pilot symbols, TIFF2025540801000046.tif6170 is a matrix of additive white Gaussian noise. As in Figure 2, the factor GΩH denotes the wireless channel with G, Ω, and H defined above.

[0086] Equation (1) can be rewritten as follows by using the knowledge of the proposed pilot signal design and considering the channel factorization properties: TIFF2025540801000047.tif5170TIFF2025540801000048.tif6170, equation (2) can be expressed as Resulting in TIFF2025540801000049.tif8170. X y =G y Ω y H y S y and X z =Gz Ω z H z S z It is important to provide for the following: Resulting in TIFF2025540801000050.tif5170.

[0087] According to equation (4), the received pilot signal is given as the Kronecker product of the azimuth and elevation domain received pilot signals plus additive noise. Therefore, separated estimates of the vertical and horizontal pilot sequences can be obtained by solving the following least squares (LS) Kronecker factorization problem: TIFF2025540801000051.tif8170

[0088] The problem in equation (5) can be efficiently solved as a rank-1 matrix approximation problem by truncated singular value decomposition (SVD) using state-of-the-art computational algorithms.

[0089] TIFF2025540801000052.tif7170 and the transmitted pilot sequence, i.e., S y , S z From the knowledge of We can obtain a separated estimate of TIFF2025540801000053.tif7170. As one non-limiting example, assuming matched filtering (MF), the corresponding LS estimate is given by: TIFF2025540801000054.tif12170

[0090] Other estimation methods, such as MMSE, zero-forcing (ZF), compressive detection, and high-resolution techniques, can be applied to obtain TIFF2025540801000055.tif7170.

[0091] In some embodiments, TIFF2025540801000056.tif7170, i.e., describing the wireless channel along the azimuth and elevation domains, is fed back to the network node 200 for further channel parameter estimation. The network node 200 may then estimate azimuth and elevation channel parameters. These parameters may be used by the network node 200 to design a two-dimensional precoder, or beamformer, consisting of azimuth and elevation components.

[0092] In some aspects, the network node 200 will first detect or measure the variation of the channel parameters in both the azimuth and elevation domains relative to a previous estimate of the same amount, and then determine whether the azimuth parameter, the elevation parameter, or both the azimuth and elevation parameters are changing faster compared to a previous estimate of the same amount. The network node 200 may then determine which mode of operation should be used by the UE 300 based thereon and notify the UE 300 accordingly.

[0093] In some aspects, the UE 300 may use the estimated azimuth and elevation matrices, i.e., Split TIFF2025540801000057.tif7170, To feed back TIFF2025540801000058.tif7170 to the network node 200, despreading will be applied, for example by the factorization given in equation (5). In this case, the estimation procedure at the UE 300 may be considered as a blind estimation.

[0094] In some aspects, when the network node 200 can estimate or predict the movement trajectory of the UE 300, the network node 200 can pre-design the pilot sequence.

[0095] The use of separated pilot sequences not only reduces the complexity in the pilot signal design (based on two independent pilot sequences), but also ultimately relaxes the constraint on the length of the pilot sequences compared to the typical sequence design used in 3GPP. In particular, the design complexity is reduced to O(M y M z ) to O(M y +M z ), which reduces the computational complexity of the algorithm to O(QT) 3 to O((Q y T y )+(Q z T z )) 3 where T is the total length of the pilot block and T y , T z are the lengths of the azimuth domain pilot sequence and the elevation domain pilot sequence, respectively.

[0096] T=16 and T y =4, T z = 4, M = 16, M y =4, M z =4 and Q=16, Q y =4, Q z = 4. Therefore, using the proposed scheme, the design complexity of the proposed pilot sequence is reduced from O(16) to O(8). Furthermore, the receiver computation complexity is reduced to O(256). 3 From O(32) 3 which is 512 times smaller than typical state-of-the-art approaches that do not separate pilot signal transmission or data reception processing into azimuth and elevation domains.

[0097] 6 and 7, a first example will now be disclosed. In FIGS. 6 and 7, the network node 200 and the UE 300 are shown in respective coordinate systems 600 and 700, where the UE 300 is moving from a source point to a destination point in the coordinate systems 600 and 700. As shown in FIG. 6, the UE 300 starts moving from the source point at time τ and reaches the destination point at time τ. During this movement, only the azimuth angle of departure φ is changed, and the elevation angle of departure θ is constant. Similarly, as shown in FIG. 7, the UE 300 starts moving from the source point along the elevation angle region at time τ and reaches the destination point at time τ. During this movement, the elevation angle of departure θ is changed, and the azimuth angle of departure φ is constant. To benefit from these scenarios, as well as other scenarios, the network node 200 will transmit pilot sequences more frequently along the varying regions and transmit data more frequently along the less varying regions, respectively, to track variations in the channel.

[0098] 8 and 9, a second example will now be disclosed. This second example shows channel variations along the azimuth and elevation domains. A Quadriga channel model (QuaDRiGa) is used to verify that a wireless channel can be factorized in two domains, namely, the azimuth domain and the elevation domain. It is assumed that the UE 300 is moving from a point in the yz domain. The angular variations along the elevation and azimuth domains are calculated and plotted as histograms and cumulative distribution functions (CDFs), as shown in FIGS. 8 and 9. It is clear from these figures that during the movement of the UE 300 from one point to another, variations in the azimuth domain occur more frequently compared to the elevation domain. This is because TIFF2025540801000059.tif6170, which further concludes that these scenarios can be exploited for joint pilot and data transmission, resulting in an increase in overall system throughput.

[0099] 10 and 11, one particular embodiment for transmitting and receiving two-dimensional pilot signals, based on at least some of the embodiments disclosed above, will now be disclosed in detail.

[0100] S300: The IRS 400 reports its capabilities to the network node 200.

[0101] S301: The network node 200 generates two independent pilot sequences, one in the azimuth domain and one in the elevation domain. The network node 200 maps the Kronecker product of these pilot sequences across the transmit antennas and transmits a two-dimensional (2D) pilot signal towards the UE 300.

[0102] S302: UE 300 receives a 2D pilot signal, possibly after reflection at IRS 400. UE 300 estimates azimuth and elevation domain pilot sequences by dividing the received 2D pilot signal and solving a rank-1 matrix approximation problem. UE 300 estimates corresponding azimuth and elevation components of the wireless channel, and therefore the channel matrix, from knowledge of the azimuth and elevation domain pilot sequences and the known pilot sequences.

[0103] S303: The UE 300 feeds back the estimated channel matrix to the network node 200.

[0104] S304: The network node 200 estimates respective channel parameters. The network node 200 designs an azimuth domain precoder and an elevation domain precoder based on the estimated channel parameters and possibly also based on the received capabilities of the IRS 400.

[0105] S305: The network node 200 provides information to the UE 300 about which operation mode to use.

[0106] Figure 12 illustrates, in terms of several functional units, components of a network node 200 according to one embodiment. The processing circuitry 210 is provided using any combination of one or more suitable central processing units (CPUs), multiprocessors, microcontrollers, digital signal processors (DSPs), etc., capable of executing software instructions stored, for example, in a computer program product 1610a (as in Figure 16) in the form of a storage medium 230. The processing circuitry 210 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0107] In particular, processing circuitry 210 is configured to cause network node 200 to perform a set of operations or steps, as disclosed above. For example, storage medium 230 may store a set of operations, and processing circuitry 210 may be configured to retrieve the set of operations from storage medium 230 to cause network node 200 to perform the set of operations. The set of operations may be provided as a set of executable instructions, thereby causing processing circuitry 210 to be configured to perform the methods disclosed herein.

[0108] The storage medium 230 may also comprise persistent storage, which may be, for example, any one or combination of magnetic memory, optical memory, solid state memory, and even remotely mounted memory.

[0109] The network node 200 may further comprise a communications (comm.) interface 220 for communicating with other entities, functions, nodes, and devices, such as the UE 300. Thus, the communications interface 220 may comprise one or more transmitters and receivers comprising analog and digital components.

[0110] Processing circuitry 210 controls the overall operation of network node 200, for example, by sending data and control signals to communication interface 220 and storage medium 230, by receiving data and reports from communication interface 220, and by retrieving data and instructions from storage medium 230. Other components of network node 200, and related functionality, are omitted so as not to obscure the concepts presented herein.

[0111]

[0013] Figure 13 illustrates, in terms of several functional modules, components of a network node 200 according to one embodiment. The network node 200 of Figure 13 comprises several functional modules: a generating module 210b configured to perform step S104, and a transmitting module 210c configured to perform step S106. The network node 200 of Figure 13 may further comprise several optional transmitting modules, such as any of a transmitting module 210a configured to perform step S102, a receiving module 210d configured to perform step S108, an estimating module 210e configured to perform step S110, a receiving module 210f configured to perform step S112, an estimating module 210g configured to perform step S114, a determining module 210h configured to perform step S116, and a determining module 210i configured to perform step S118.

[0112] In general terms, each functional module 210a:210i may be implemented in hardware or in software. Preferably, one or more or all of functional modules 210a:210i may be implemented by processing circuitry 210, possibly in cooperation with communications interface 220 and / or storage medium 230. Processing circuitry 210 may therefore be configured to fetch instructions provided by functional modules 210a:210i from storage medium 230 and execute these instructions, thereby performing any steps of network node 200 as disclosed herein.

[0113] Network node 200 may be provided as a standalone device or as part of at least one additional device. For example, network node 200 may be provided in a node of a (radio) access network or in a node of a core network. Alternatively, the functionality of network node 200 may be distributed among at least two devices or nodes. These at least two nodes or devices may either be part of the same network portion (such as a (radio) access network or a core network) or may be spread between at least two such network portions. In general terms, instructions that need to be performed in real time may be performed in a device or node operatively closer to the cell than instructions that do not need to be performed in real time. Thus, a first portion of the instructions performed by network node 200 may be executed in a first device, and a second portion of the instructions performed by network node 200 may be executed in a second device, and embodiments disclosed herein are not limited to any particular number of devices on which instructions performed by network node 200 may be executed. Thus, methods according to embodiments disclosed herein are suitable for being performed by network node 200 residing in a cloud-computing environment. Thus, although a single processing circuit 210 is shown in Figure 12, processing circuit 210 may be distributed among multiple devices or nodes. The same applies to functional modules 210a:210i in Figure 13 and computer program 1620a in Figure 16.

[0114] 14 illustrates, in terms of several functional units, components of the UE 300 according to one embodiment. The processing circuitry 310 is provided using any combination of one or more suitable central processing units (CPUs), multiprocessors, microcontrollers, digital signal processors (DSPs), etc., capable of executing software instructions stored, for example, in a computer program product 1610b (as in FIG. 16) in the form of a storage medium 330. The processing circuitry 310 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0115] In particular, the processing circuitry 310 is configured to cause the UE 300 to perform a set of operations or steps, as disclosed above. For example, the storage medium 330 may store the set of operations, and the processing circuitry 310 may be configured to retrieve the set of operations from the storage medium 330 to cause the UE 300 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 310 is configured to perform the methods disclosed herein.

[0116] The storage medium 330 may also comprise persistent storage, which may be, for example, any one or combination of magnetic memory, optical memory, solid state memory, and even remotely mounted memory.

[0117] The UE 300 may further comprise a communication interface 320 for communication with other entities, functions, nodes, and devices, such as the network node 200. Thus, the communication interface 320 may comprise one or more transmitters and receivers comprising analog and digital components.

[0118] The processing circuitry 310 controls the overall operation of the UE 300, for example, by sending data and control signals to the communication interface 320 and the storage medium 330, by receiving data and reports from the communication interface 320, and by retrieving data and instructions from the storage medium 330. Other components of the UE 300 and related functions are omitted so as not to obscure the concepts presented herein.

[0119] Figure 15 illustrates, in terms of several functional modules, components of a UE 300 according to one embodiment. The UE 300 of Figure 15 includes several functional modules: a receiving module 310b configured to perform step S204, and an estimation module 310c configured to perform step S206. The UE 300 of Figure 15 may further include several optional functional modules, such as any of a receiving module 310a configured to perform step S202, a transmitting module 310d configured to perform step S208, an estimation module 310e configured to perform step S210, and a transmitting module 310f configured to perform step S212.

[0120] In general terms, each functional module 310a:310f may be implemented in hardware or in software. Preferably, one or more or all of the functional modules 310a:310f may be implemented by the processing circuitry 310, possibly in cooperation with the communication interface 320 and / or the storage medium 330. The processing circuitry 310 may therefore be configured to fetch instructions provided by the functional modules 310a:310f from the storage medium 330 and execute these instructions, thereby performing any steps of the UE 300 as disclosed herein.

[0121] 16 shows an example of a computer program product 1610a, 1610b comprising a computer-readable means 1630. A computer program 1620a may be stored on the computer-readable means 1630, and the computer program 1620a may cause the processing circuit 210 and entities and devices operatively coupled to the processing circuit 210, such as the communication interface 220 and the storage medium 230, to perform methods according to embodiments described herein. Thus, the computer program 1620a and / or the computer program product 1610a may provide means for performing any steps of the network node 200 disclosed herein. A computer program 1620b may be stored on the computer-readable means 1630, and the computer program 1620b may cause the processing circuit 310 and entities and devices operatively coupled to the processing circuit 310, such as the communication interface 320 and the storage medium 330, to perform methods according to embodiments described herein. Thus, the computer program 1620b and / or the computer program product 1610b may provide means for performing any of the steps of the UE 300 disclosed herein.

[0122] In the example of Figure 16, the computer program products 1610a, 1610b are shown as optical discs, such as CDs (compact discs) or DVDs (digital versatile discs), or Blu-ray discs. The computer program products 1610a, 1610b may also be embodied as memory, such as random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM), more particularly as a non-volatile storage medium of the device in an external memory, such as a USB (universal serial bus) memory or a flash memory, such as a compact flash memory. Thus, although the computer programs 1620a, 1620b are shown here schematically as tracks on the illustrated optical discs, the computer programs 1620a, 1620b may be stored in any manner suitable for the computer program products 1610a, 1610b.

[0123] The inventive concept has been described above primarily with reference to a few embodiments. However, as will be readily appreciated by those skilled in the art, other embodiments besides those disclosed above are equally possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A method for transmitting a two-dimensional pilot signal, said method being implemented by a network node (200), said method comprising the steps of: In the elevation angle region z, the elevation angle region pilot sequence S ｚ and the azimuth domain pilot sequence S ｙ and spreading the azimuth domain pilot sequence S in the azimuth domain y. ｙ and the elevation domain pilot sequence S ｚ (S104) generating the two-dimensional pilot signal S by spreading the Transmitting the two-dimensional pilot signal over the air (S106); A method comprising:

2. The azimuth domain pilot sequence S ｙ is the elevation domain pilot sequence S ｚ The method of claim 1 , wherein the design is independent of

3. The two-dimensional pilot signal S is transmitted towards a user equipment (UE) (300), and the method comprises: Prior to transmitting the two-dimensional pilot signal, the UE (300) receives the azimuth domain pilot sequence S ｙ and the elevation domain pilot sequence S ｚ Transmitting a control signal to set the 3. The method of claim 1 or 2, further comprising:

4. The two-dimensional pilot signal S is transmitted towards a user equipment (UE) (300), and the method comprises: Over the air from the UE (300), and receiving (S108). The method of any one of claims 1 to 3, further comprising:

5. The method comprises: The estimated Estimating (S110) The method of claim 4 further comprising:

6. The two-dimensional pilot signal S is transmitted towards a user equipment (UE) (300), and the method comprises: Over the air from the UE (300), and receiving (S112). The method of any one of claims 1 to 3, further comprising:

7. The method comprises: The aforementioned Estimate the azimuth domain channel parameters from Estimating elevation domain channel parameters from (S114) The method of claim 5 or 6, further comprising:

8. The method comprises: determining a two-dimensional precoder using an azimuth component determined from the estimated azimuth domain channel parameters and an elevation component determined from the estimated elevation domain channel parameters (S116); The method of claim 7 further comprising:

9. The method comprises: Further azimuth domain pilot sequences S ｙ and a further elevation domain pilot sequence S ｚ and determining (S118) the further azimuth domain pilot sequence S ｙ has a length proportional to how much the estimated azimuth domain channel parameters have varied compared to the previously estimated azimuth domain channel parameters, and the further elevation domain pilot sequence S ｚ is a further azimuth domain pilot sequence S having a length proportional to how much the estimated elevation domain channel parameters have varied compared to the previously estimated elevation domain channel parameters. ｙ and a further elevation domain pilot sequence S ｚ and determining (S118).

9. The method of claim 7 or 8, further comprising:

10. The two-dimensional pilot signal S is the azimuth domain pilot sequence S ｙ and the elevation domain pilot sequence S ｚ 10. The method of claim 1, wherein the vector is generated by taking the Kronecker product between

11. the two-dimensional pilot signal S is transmitted from a two-dimensional antenna having antenna elements arranged in rows and columns, is transmitted at antenna element (i,j), where: the azimuth domain pilot sequences for all antenna elements in row i of the two-dimensional antenna, where: the elevation domain pilot sequences for all antenna elements in column j of the two-dimensional antenna, where The method of claim 10 , representing the Kronecker product operator.

12. 1. A method for receiving a two-dimensional pilot signal, the method being performed by a user equipment (UE) (300), the method comprising: receiving (S204) the two-dimensional pilot signal X over the air from a network node (200); 2. Despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X, and estimating (S206). A method comprising:

13. The method comprises: Prior to receiving the two-dimensional pilot signal, the UE (300) receives the transmitted azimuth domain pilot sequence S ｙ and the transmitted elevation domain pilot sequence S ｚ receiving a control signal from the network node (200) to set up The method of claim 12 further comprising:

14. The method comprises: The network node (200) receives and estimates the received signal over the air. and the received and estimated and transmitting (S208).

14. The method of claim 12 or 13, further comprising:

15. The method comprises: The received and estimated and the received and estimated Estimating (S210) 14. The method of claim 12 or 13, further comprising:

16. The method comprises: The network node (200) over-the-air and the aforementioned presumed and transmitting (S212).

16. The method of claim 15, further comprising:

17. The aforementioned It is estimated as 17. The method of claim 15 or 16.

18. The aforementioned 18. The method of claim 12, wherein x and y are estimated from the two-dimensional pilot signal X by Kronecker factorization of the two-dimensional pilot signal X.

19. The Kronecker factorization is performed by solving the Kronecker factorization problem formulated as follows: where: denotes the Kronecker product operator, 20. The method of claim 18.

20. A network node (200) for transmitting a two-dimensional pilot signal, said network node (200) comprising a processing circuit (210), said processing circuit providing said network node (200) with: In the elevation angle region z, the elevation angle region pilot sequence S ｚ and the azimuth domain pilot sequence S ｙ and spreading the azimuth domain pilot sequence S in the azimuth domain y. ｙ and the elevation domain pilot sequence S ｚ generating the two-dimensional pilot signal S by spreading the transmitting said two-dimensional pilot signal over the air; A network node (200) configured to:

21. A network node (200) for transmitting a two-dimensional pilot signal, said network node (200) comprising: In the elevation angle region z, the elevation angle region pilot sequence S ｚ and the azimuth domain pilot sequence S ｙ and spreading the azimuth domain pilot sequence S in the azimuth domain y. ｙ and the elevation domain pilot sequence S ｚ a generating module (210b) configured to generate said two-dimensional pilot signal S by spreading a transmitting module (210c) configured to transmit said two-dimensional pilot signal over the air; A network node (200) comprising:

22. A network node (200) according to claim x or x, further configured to perform the method according to any one of claims 2 to 11.

23. A user equipment (UE) (300) for receiving a two-dimensional pilot signal, said UE (300) comprising a processing circuit (310), said processing circuit providing said UE (300) with: receiving said two-dimensional pilot signal X over the air from a network node (200); 2. Despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X, and to estimate A user equipment (UE) (300) configured to:

24. A user equipment (UE) (300) for receiving a two-dimensional pilot signal, said UE (300) comprising: a receiving module (310b) configured to receive said two-dimensional pilot signal X over the air from a network node (200); 2. Despreading the two-dimensional pilot signal X, and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X, an estimation module (310c) configured to estimate A user equipment (UE) (300) comprising:

25. 25. The UE (300) of claim 23 or 24, further configured to perform the method of any one of claims 13 to 19.

26. A computer program (1620a) for transmitting a two-dimensional pilot signal, said computer program being run on a processing circuit (210) of a network node (200) to cause said network node (200) to: In the elevation angle region z, the elevation angle region pilot sequence S ｚ and the azimuth domain pilot sequence S ｙ and spreading the azimuth domain pilot sequence S in the azimuth domain y. ｙ and the elevation domain pilot sequence S ｚ (S104) generating the two-dimensional pilot signal S by spreading the Transmitting the two-dimensional pilot signal over the air (S106); A computer program (1620a) comprising computer code for causing the

27. A computer program (1620b) for receiving a two-dimensional pilot signal, the computer program being run on a processing circuit (310) of a user equipment (UE) (300) to cause the UE (300) to: receiving (S204) the two-dimensional pilot signal X over the air from a network node (200); 2. Despreading the two-dimensional pilot signal X and solving a rank-1 matrix approximation problem for the two-dimensional pilot signal X, and estimating (S206). a computer program (1620b) including computer code for causing the

28. A computer program product (1610a, 1610b) comprising a computer program (1620a, 1620b) according to at least one of claims 26 and 27 and a computer readable storage medium (1630) on which said computer program is stored.

Images