Wireless telecommunications network

Abstract

The invention provides a network node for configuring a reconfigurable intelligent surface (RIS) in a wireless telecommunications network, the wireless telecommunications network comprising a transmitting node and a receiving node, the network node comprising a configuration module configured to: configure the RIS according to a beam training codebook to define a training beam pair; obtaining data indicative of a direction between the RIS and the receiving node, the direction between the RIS and the receiving node being derivable from a power of each beam in the training beam pair at the receiving node; the RIS is configured according to a data transmission codebook defining a data transmission beam in a direction between the RIS and the receiving node. The invention also provides a receiving node in a wireless telecommunications network, the wireless telecommunications network comprising a transmitting node and a reconfigurable intelligent surface (RIS), the receiving node comprising: a receiver configured to receive a training beam pair transmitted by the transmitting node and reflected by the RIS; a measurement module configured to determine a power of each training beam in the training beam pair at the receiving node; and a processor configured to determine a direction between the RIS and the receiving node based on a power of each beam in the training beam pair at the receiving node.

Description

Technical Field

[0001] The present invention relates to a wireless telecommunication network comprising a reconfigurable intelligent surface (RIS). Background Art

[0002] In wireless telecommunications, wireless signals transmitted between a transmitter and a receiver are often degraded due to interference from other wireless signals and / or other physical phenomena (e.g., fading and blocking). This is often addressed by improving transmission characteristics (e.g., higher power transmissions or repeaters) or transmission processing techniques (e.g., more robust modulation schemes). An emerging concept in wireless telecommunications is that of a reconfigurable propagation environment or "smart radio environment" that can improve transmission quality. This can be achieved using surfaces of electromagnetic materials, often referred to as reconfigurable smart surfaces (RIS), which can be manipulated to impose changes (such as changes in phase, amplitude, frequency, and polarization) on the incident wireless signal in order to improve the transmission quality between the transmitter and the receiver.

[0003] In a conventional system with only a transmitter and a receiver, the receiver can receive a wireless signal in a direct path between the transmitter and the receiver or via one or more reflected signals. In the first case, the receiver may not be able to successfully receive a direct or reflected signal from the transmitter (i.e., the receiver is in a "not-spot"). In the second case, a reflected signal between the transmitter and the receiver (e.g., reflected from a nearby building) degrades another received signal (e.g., a direct signal) by destructive interference. Both of these situations can be improved by introducing a RIS. In the first case, in which the receiver cannot receive a direct or reflected signal from the transmitter, the RIS can act on the reflected signal so that the reflected signal can be successfully received at the receiver. In addition, in the second case, the RIS can phase shift the incident wireless signal so that the incident wireless signal and the direct signal between the transmitter and the receiver produce constructive interference. Therefore, the RIS can be used to improve the transmission quality between the transmitter and the receiver.

[0004] Furthermore, since RIS is almost passive and easy to deploy, it can be a cost-effective solution to improve transmission quality compared to alternative solutions such as increasing the density of access points. Alternative names for RIS include smart reflective surfaces, large smart surfaces, large smart meta-surfaces, programmable meta-surfaces, reconfigurable meta-surfaces, smart reflective arrays, software-defined surfaces, and passive smart surfaces. The term "reconfigurable" is often used to indicate that the reflection angle can be configured independently of the angle of incidence.

[0005] Future wireless telecommunications networks may use relatively high frequencies (e.g., >6 GHz) in communications between transmitters and receivers. These high-frequency communications suffer from high path loss in free space and poor attenuation through materials. To address these problems, high-frequency communications are typically transmitted to users in narrow beams through a beamforming process. In RIS-assisted communications using beamforming technology, RIS generates multiple beams, each of which is transmitted in a different direction, and a "beam training" process is used to determine the best beam for a particular user. This typically involves transmitting multiple beams to the space where the user is located, and determining the beam that supports the best communication channel based on user measurements. An example of this method is described in detail in "Construction of a generalized DFT codebook using channel-adaptive parameters" (IEEE Commun. Lett., vol. 21, no. 1, pp. 196-199, Jan. 2017., J. Suh et al.).

[0006] "Fast beam training and alignment for IRS-assisted millimeter wave / terahertz systems" (IEEE Trans. Wireless Commun., pp. 1-1, Apr. 2021, P. Wang et al.) proposed a beam training framework based on multi-directional beams, which exploits the inherent sparse structure of the channel between the transmitter, RIS, and receiver. By randomly generating a sensing matrix and performing several rounds of full coverage scans, the optimal direction is located at the intersection of the generated multi-directional beams. Since multi-directional beams are generated simultaneously, the overhead of full coverage scanning is much lower than the exhaustive search method.

[0007] The RIS includes a plurality of reflective elements, each of which is independently controlled to apply a specific change (e.g., phase shift) to an incident wireless signal. It is generally desirable to increase the number of reflective elements of the RIS because this enables greater control of the beam and increased capacity. However, existing RIS beam training methods have a beam training time that is proportional to the number of reflective elements. It is generally desirable to shorten the beam training time because no user data is transmitted during beam training, and the process must be repeated when the communication channel between the RIS and the user has changed. Summary of the invention

[0008] According to a first aspect of the present invention, there is provided a network node for configuring a reconfigurable intelligent surface (RIS) in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a receiving node, the network node comprising a configuration module, the configuration module being configured to: configure the RIS according to a beam training codebook to define a training beam pair; obtain data indicating a direction between the RIS and the receiving node, the direction between the RIS and the receiving node being derivable from the power of each beam in the training beam pair at the receiving node; and configure the RIS according to a data transmission codebook, the data transmission codebook defining a data transmission beam in the direction between the RIS and the receiving node.

[0009] According to a second aspect of the present invention, there is provided a method for configuring a reconfigurable intelligent surface (RIS) in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a receiving node, the method comprising the following steps: configuring the RIS according to a beam training codebook to define a training beam pair; obtaining data indicating a direction between the RIS and the receiving node, the direction between the RIS and the receiving node being derivable from the power of each beam in the training beam pair at the receiving node; and configuring the RIS according to a data transmission codebook, the data transmission codebook defining a data transmission beam in the direction between the RIS and the receiving node.

[0010] The obtained data may indicate the power of each of the training beams in the training beam pair at a receiving node, and the method may further comprise the step of determining the direction between the RIS and the receiving node based on the power of each of the beams in the training beam pair.

[0011] The beam training codebook may define a plurality of training beam pairs, and the obtained data may indicate the power of each beam in each of the plurality of training beam pairs, and the method may further include the following steps (or the configuration module may further be configured to): identifying a training beam pair having the maximum power among the plurality of training beam pairs at the receiving node, wherein determining the direction between the RIS and the receiving node may be based on the power of each beam in the identified training beam pair.

[0012] The plurality of training beam pairs may include a first set, each training beam pair in the first set satisfying Bμ / f c >β, where B is the bandwidth used in the communication between the transmitter and the receiver, μ is the direction of the training beam pair from the RIS to the receiver, and f c is the center frequency of the training beam pair, and β is the beam splitting threshold configured so that the training beam pair has negligible beam splitting.

[0013] The plurality of training beam pairs may include a second set, each training beam pair in the second polarization satisfying Bμ / f c ≤β, where B is the bandwidth used in the communication between the transmitter and the receiver, μ is the direction of the training beam pair from the RIS to the receiver, and f c is the center frequency of the training beam pair, and β is the beam splitting threshold configured so that the training beam pair has non-negligible beam splitting.

[0014] Each training beam pair in the second set of the plurality of training beam pairs may be defined as in is the direction of the training beam from which RIS starts, and δ is the width of the training beam pair and is defined as

[0015] Each training beam pair in the second set of the plurality of training beam pairs may be defined as Where κ is a range limiting parameter. κ can be in the range of 0.7 to 0.9.

[0016] According to a third aspect of the present invention, there is provided a receiving node in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a reconfigurable intelligent surface (RIS), the receiving node comprising: a receiver configured to receive a training beam pair transmitted by the transmitting node and reflected by the RIS; a measurement module configured to determine the power of each training beam in the training beam pair at the receiving node; and a processor configured to determine the direction between the RIS and the receiving node based on the power of each beam in the training beam pair at the receiving node.

[0017] According to a fourth aspect of the present invention, there is provided a method for operating a receiving node in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a reconfigurable intelligent surface (RIS), the method comprising the following steps: receiving a training beam pair transmitted by the transmitting node and reflected by the RIS; determining the power of each training beam in the training beam pair at the receiving node; and determining the direction between the RIS and the receiving node based on the power of each beam in the training beam pair at the receiving node.

[0018] Receiving a training beam pair may include receiving a plurality of training beam pairs, and determining the power of each training beam in the training beam pair may include determining the power of each training beam in each of the plurality of training beam pairs, and the method further includes the following steps (or the processor may also be configured to): identifying a training beam pair with the maximum power in the plurality of training beam pairs at the receiving node, wherein determining the direction between the RIS and the receiving node may be based on the power of each beam in the identified training beam pair.

[0019] The method may also include the following steps (or the configuration module or the processor may also be configured to): normalizing the power of each training beam in each of the multiple training beam pairs, wherein identifying the training beam pair with the maximum power in the multiple training beam pairs at the receiver is based on the normalized power.

[0020] The direction between the RIS and the UE may be determined as:

[0021]

[0022] Here, χ is defined as:

[0023]

[0024] Among them, g I (φ) 2 is the power of the first training beam in the training beam pair at the receiver, g II (φ) 2 is the power of the second training beam in the training beam pair at the receiver, and δ is the width of the training beam pair and is defined as

[0025] The method may further include the following steps (or the processor may further be configured to): sending a message including the determined direction between the RIS and the receiving node so that the RIS uses a data transmission codebook defining a data transmission beam in the determined direction between the RIS and the receiving node.

[0026] According to a fifth aspect of the present invention, there is provided a computer program comprising instructions, which, when executed by a computer, cause the computer to perform the steps of the second aspect or the fourth aspect of the present invention. The computer program may be provided on a computer readable carrier medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order that the present invention may be better understood, embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0028] Figure 1 is a schematic diagram of a wireless telecommunication system according to a first embodiment of the present invention, the wireless telecommunication system comprising a base station, a reconfigurable intelligent surface (RIS) and a user equipment (UE);

[0029] Figure 2 The communication configuration method as a part of the first embodiment of the present invention is shown by Figure 1 A flowchart of the steps implemented by the base station;

[0030] Figure 3 The communication configuration method as a part of the first embodiment of the present invention is shown by Figure 1 Flow chart of steps implemented by a UE;

[0031] Figure 4 is shown in more detail Figure 2 A flowchart of the steps of generating multiple parameters of the communication configuration method;

[0032] Figure 5 is shown in more detail Figure 2 A flowchart of the steps of estimating the direction between the RIS and the UE in the communication configuration method;

[0033] Figure 6 is a schematic diagram showing received power of a wide beam pair at a first wide beam and a second wide beam;

[0034] Figure 7 is a schematic diagram showing the design of a wide beam pair and the corresponding beam training range;

[0035] Figure 8 It shows that Figure 2 A communication configuration method and a simulated graph of achievable rate performance relative to a signal-to-noise ratio SNR of a plurality of conventional technologies in which the number of reflective elements is equal to 1024;

[0036] Fig. 9 It is shown Figure 2 A communication configuration method and a simulated graph of achievable rate performance relative to SNR for a plurality of conventional technologies in which the number of reflective elements is equal to 2048;

[0037] Fig.10 It is shown Figure 2 A communication configuration method and a simulated graph of achievable rate performance of multiple conventional technologies with respect to beam training overhead where the number of reflective elements is equal to 1024; and

[0038] Fig.11 It is shown Figure 2A graph of simulations of achievable rate performance relative to beam training overhead for a communication configuration method and a plurality of conventional techniques where the number of reflective elements is equal to 2048. DETAILED DESCRIPTION

[0039] Notation: Lowercase and uppercase bold letters represent vectors and matrices, respectively; (·) T 、(·) H denote transpose and conjugate transpose respectively; ‖·‖ k represents the k-norm of a matrix; |·| represents the absolute operator; v[i] represents the i-th element in vector v; m[:,i] represents the i-th column in matrix m; CN(μ,Σ) represents a Gaussian distribution with mean μ and covariance Σ; and represents a uniform distribution between a and b.

[0040] Now refer to Figure 1 A first embodiment of a wireless telecommunication system is described. In this embodiment, the wireless telecommunication system is a cellular telecommunication network 1 having a base station 10, a reconfigurable intelligent surface (RIS) 20, and a user equipment (UE) 30. The base station 10 uses a single antenna, the RIS 20 has a uniform linear array (ULA) configuration including N reflective elements, and the UE 30 uses a single antenna. The base station 10 uses orthogonal frequency division multiplexing (OFDM) with M subcarriers to serve the UE. The bandwidth of the system is denoted as B.

[0041] like Figure 1 As shown, the communication path between the base station 10 and the UE 30 includes a first channel h between the base station 10 and the RIS 20. br and a second channel h between RIS 20 and UE 30 ru . In this example, the direct channel between the base station 10 and the UE 30 is blocked and is not considered in the following analysis. Considering the ray-based channel model for broadband terahertz (THz) channels (such as "BDMA for millimeter-wave / terahertz massive MIMO transmission with per-beam synchronization" (IEEE J. Sel. Areas Commun., vol. 35, no. 7, pp. 1550–1563, Jul. 2017, L. You et al.)), the downlink channel for the m-th subcarrier between the base station 10 and the RIS 20 is is represented as:

[0042]

[0043] in:

[0044] · represents the path gain of the l1th path, l1=1,2,…,L1;

[0045] · represents the time delay of the l1th path, l1=1,2,…,L1;

[0046] ·f m represents the frequency of the mth subcarrier, which satisfies And f c is the center frequency of the system;

[0047] L1 represents the number of paths;

[0048] · j is an imaginary unit (which satisfies j 2 = -1); and

[0049] · represents an array response vector that satisfies the following conditions:

[0050]

[0051] in:

[0052] · represents the spatial angle of the l1th path, which satisfies

[0053] and is the physical angle of the l1th path;

[0054] d is the antenna spacing;

[0055] c is the speed of light; and

[0056] ·λ c is the wavelength of the center frequency (note that ).

[0057] Similar to the above h br,m Definition of the downlink channel for the mth subcarrier between RIS 20 and UE 30 It is expressed as:

[0058]

[0059] in:

[0060] · represents the path gain of the l2th path, l2=1,2,…,L2;

[0061] · represents the time delay of the l2th path, l2=1,2,…,L2:

[0062] L2 represents the number of paths;

[0063] · represents the spatial angle of the l2th path; and

[0064] ·a N represents the array response vector that also satisfies equation (2).

[0065] At RIS20, each reflective element rescatters the incident signal with a specific phase shift (as described in "Reconfigurable intelligent surfaces: Principles and opportunities" (IEEE Commun. Surv. Tutorials, vol. 23, no. 3, pp. 1546–1577, Jul. 2021, Y. Liu et al.). n represents the phase shift of the nth reflective element of RIS 20 and β n In the case of representing the amplitude reflection coefficient of the nth reflection element of RIS20, the reflection matrix θ of RIS20 is expressed as:

[0066]

[0067] where, for all n=1,2,…,N,θ n ∈[0,2π) and β n ∈[0,1]. Equation (4) indicates that the reflective element of RIS20 is frequency independent. For simplicity, it is assumed that the phase can be shifted continuously and for all n∈{1,2,…,N}, β n =1.

[0068] Based on the channel model and reflection matrix discussed above, the received signal y at the mth subcarrier at UE 30 is m It can be expressed as:

[0069]

[0070] in:

[0071] s represents a signal transmitted at the base station 10,

[0072] n is n~CN(0,σ 2 I K ) is an additive white Gaussian noise (AWGN) vector, where σ 2 Represents the noise power.

[0073] Now refer to Figures 2 to 5 To describe Figure 1 A method for configuring communications in a cellular telecommunication network 1. Figure 2 is a flow chart showing the steps implemented by the base station 10 as part of the overall communication configuration method of this first embodiment. The communication configuration method is based on wide beam versus arithmetic beam training.

[0074] In the first step S101, the base station 10 generates a plurality of parameters including a vector μ representing the center direction of each beam pair, a vector ζ representing a power normalization coefficient, and a wide beam pair arithmetic codebook W for the RIS 20. The process for generating each of these parameters is described in detail below.

[0075] In step S103, the base station 10 sends a first message to the RIS 20 to configure the RIS 20 according to the wide beam pair arithmetic codebook W, and sends a vector including a power normalization coefficient to the UE 30. The second message of the present invention (the second message may be sent via the pre-existing channel between the base station 10 and the UE 30, via the RIS 20, and the RIS 20 may have been configured in the previous implementation of the first embodiment).

[0076] In step S105, the base station 10 performs a beam training process during a plurality of time slots designated for beam training. Specifically, the base station 10 transmits training signals, wherein each training signal is transmitted in the i-th time slot of the plurality of time slots. As configured in step S103, the RIS 20 applies a phase shift to each training signal according to Θ=diag(W[:,i]).

[0077] Go to Figure 3 , Figure 3 1 shows the steps implemented by UE 30 as part of the overall communication configuration method of the first embodiment. In step S201, UE 30 measures the received power in each time slot p[i] until the multiple time slots designated for beam training are completed. In step S203, UE 30 processes the measured received power p[i] in each time slot p[i] to determine the direction between RIS 20 and UE 30. The direction determination step is also discussed in more detail below. In step S205, the UE 30 sends a message to the base station 10 including the determined direction between the RIS 20 and the UE 30. news.

[0078] Return to Figure 2 In step S107, the base station 10 receives a signal indicating the direction between the RIS 20 and the UE 30. In step S109, the base station 10 generates a data transmission codebook for the RIS 20. The data transmission codebook for the RIS 20 is generated so that the RIS 20 generates a direction between the RIS 20 and the UE 30. The beam on the data transmission line is received as received in step S107. The generation of the data transmission codebook according to step S109 will be described in more detail below.

[0079] In step S111, the base station 10 configures the RIS 20 according to the data transmission codebook. In step S113, the base station 10 sends data to the UE 30 via the RIS 20, wherein the RIS 20 applies a phase shift according to the data transmission codebook.

[0080] Steps S101 to S113 may be repeated at a later time to reconfigure the base station 10 and RIS 20 for communication with the UE 30 according to then-current conditions (eg, if the UE 30 is in a new location).

[0081] Now refer to Figure 4 The step S101 of generating multiple parameters is described. This process uses input parameters known to the base station 10 and can be configured and updated by the operator, including the number of reflective elements N in the RIS, the bandwidth B, the center frequency f c , a range parameter κ, and a partition parameter β. The range parameter κ has values ​​in the range from 0 to 1, and has a value of 0.8 in this embodiment. Suitable values ​​of the range parameter can be determined by simulation. When the range parameter is relatively high (e.g., >0.9), the beam training accuracy will decrease at the end of the estimation range, but the beam training overhead will be reduced accordingly. When the range parameter is relatively low (e.g., <0.7), the beam training accuracy will improve, but the beam training overhead will be higher. Simulations by the inventors show that range parameters in the range of 0.7 to 0.9 perform well.

[0082] The split parameter is an operator defined threshold such that a first plurality of parameters are generated for directions where beam splitting is negligible and a second plurality of parameters are generated for directions where beam splitting is not negligible. In this embodiment, the split parameter β is 1 / N.

[0083] In step S301, the base station 10 generates an initial vector for the center direction of the beam pair Initial vector for estimating range and the initial vector for the power normalization coefficients

[0084] In step S303, the base station 10 enters a first loop in which the vector μ of the center direction of the beam pair, the vector ρ of the estimated range and the vector of the power normalization coefficient are calculated. They are updated according to the following logic:

[0085] while Bμ[0] / f c >-βdo

[0086]

[0087] end while

[0088] In notation, the numbers in square brackets indicate the position in the vector (so that for In the first iteration of the first loop after the initialization of μ, μ[0] is ). In addition, each vector is updated to include the previous version of the vector (i.e., ).

[0089] When the beam splitting effect can be ignored, this first loop generates multiple parameters to define a traditional narrow beam for the direction between RIS 20 and UE 30. The difference in the center direction of each beam pair is 2 / N. The direction of the narrow beam is equivalent to the estimated range, so p is equal to μ and the power normalized is equal to the width of the narrow beam.

[0090] Once the base station 10 has completed the first loop, the base station 10 enters (in step S305) a second loop in which the vector μ of the center direction of the beam pair, the vector ρ of the estimated range and the vector of the power normalization coefficients are calculated. They are updated according to the following logic:

[0091] whileρ[0]>-1do

[0092]

[0093] end while

[0094] This second loop generates a plurality of parameters to define a wide beam for the direction between the RIS 20 and the UE 30, in which direction the beam splitting effect is not negligible. This second loop will be discussed in more detail below.

[0095] Based on previous estimated range The center direction of the next wide beam pair should satisfy:

[0096]

[0097] The array gain of each wide beam is different because the total transmit power is fixed, but the width of each wide beam varies. Therefore, a power normalization coefficient is generated for each wide beam, and the value of the power normalization coefficient is proportional to the beam width.

[0098] Once the base station 10 has completed the second cycle, it has generated a vector μ of the center direction of the beam pair, a vector ρ of the estimated range, and a vector of the power normalization coefficients In step S307, the base station 10 generates a wide beam pair arithmetic codebook W based on the following equation (12).

[0099] An example of steps S301 to S307 will now be described. In this example, the number N of reflective elements of RIS 20 is 100, the bandwidth B is 1e10, and the center frequency f c is 1e11, the range parameter κ is 0.8, and the partition parameter β is 0.01. In step S301, the base station 10 generates an initial vector for the center direction of the beam pair Initial vector for estimating range and the initial vector of power normalization coefficients In step S303, the base station 10 determines is greater than -0.01, so the base station 10 enters the first iteration of the first loop:

[0100]

[0101] After this first iteration, for the value μ[0] after the first iteration of the first loop, the base station 10 determines is greater than -0.01, so the base station 10 enters the second iteration of the first loop:

[0102]

[0103] This iterative process continues until the condition Bμ[0] / f is no longer satisfied c Once completed, the base station 10 has already provided the vector μ of the center direction of the beam pair, the vector ρ of the estimated range, and the vector of the power normalization coefficient The following values ​​were determined:

[0104]

[0105] In step S305, the base station 10 determines is greater than -1, so the base station 10 enters the first iteration of the second loop:

[0106]

[0107] After this first iteration of the second loop, for the value of ρ[0] after this first iteration of the second loop, the base station 10 determines whether ρ[0] is greater than -1. If so, the base station 10 enters the second iteration of the second loop. If not, the process ends, and the vector μ of the center direction of the beam pair, the vector ρ of the estimated range, and the vector of the power normalization coefficients are calculated. Then, the wide beam pair arithmetic codebook W is generated according to equation (12).

[0108] Return to Figure 2 After step S101 is completed, the base station 10 has generated the vector μ of the center direction of the beam pair, the vector ρ of the estimated range, and the vector of the power normalization coefficient and a wide beam pair arithmetic codebook W. In step S103, the base station 10 configures the RIS 20 according to the wide beam pair arithmetic codebook W, and converts the vector of power normalization coefficients Transmitted to UE 30.

[0109] In step S105, using the RIS 20 configured according to Θ=diag(W[:,i]), the base station 10 transmits training signals, wherein each training signal is transmitted in the i-th time slot of the plurality of time slots. In other words, in the first time slot (i=0), the RIS 20 is configured to apply a phase shift in the first time slot to produce a signal defined as and The beam pair (with width ), where μ[0] is the first element of the vector μ after the last iteration of step S305, and the phase shift is applied in the second time slot (i=1) to produce a vector defined as and The beam pair (with width ), where μ[1] is the second element of vector μ after the last iteration of step S305, etc.

[0110] Go to Figure 3 In step S201, the UE 30 measures the received power in each time slot p[i] until the plurality of time slots designated for beam training are completed. In step S203, the UE 30 processes the received power measurements to determine the direction between the RIS 20 and the UE 30. Now refer to Figure 5 This is described in more detail.

[0111] In step S401, UE 30 calculates the power normalization coefficient vector to normalize the measured received power in each time slot.

[0112]

[0113] Therefore, for the corresponding time slot, the measured received power is multiplied by the power normalization factor In other words, the measured received power in time slot 0 is multiplied by The measured received power in time slot 1 is multiplied by wait.

[0114] In step S403, the UE 30 identifies the beam pair j having the largest normalized received power value (more specifically, the beam pair having the largest average normalized received power for each beam of the beam pair):

[0115]

[0116] The identified beam pair j may be one of the beam pairs generated in the first loop of step S303 or one of the beam pairs generated in the second loop of step S305.

[0117] In step S405, UE 30 sets the direction between RIS 20 and UE 30 Determined as:

[0118]

[0119] Here, χ is defined as:

[0120]

[0121] Among them, g I (φ) 2 is the normalized received power of the first beam in the identified beam pair j, and g II (φ) 2 is the normalized received power of the second beam in the identified beam pair j.

[0122] Return to Figure 3 After completing step S203, UE 30 has determined the direction between RIS 20 and UE 30. The direction is transmitted by the UE 30 (step S205) and received at the base station 10 (in step S107).

[0123] Return to Figure 2 In step S109, the base station 10 generates a data transmission codebook for the RIS 20, so that once configured according to the data transmission codebook, the RIS 20 is in the direction between the RIS 20 and the UE 30. The beam is generated based on the following equations (9) to (13), where the term μ in equation (11) c quilt Replace, and the beam width in equations (9) and (10) is set to The method is discussed in more detail in the paper “3-D Beamforming for Flexible Coverage in Millimeter-Wave UAV Communications” (L. Zhu et al., IEEE Wireless Communications Letters, vol. 8, no. 3, pp. 837-840, June 2019).

[0124] In step S111, the base station 10 configures the RIS 20 according to the data transmission codebook (eg, by sending a configuration message to the RIS 20). In step S113, the base station 10 sends data to the UE 30 via the RIS 20, wherein the RIS 20 applies a phase shift according to the data transmission codebook.

[0125] The derivation of the equation for determining φ is given below.

[0126] The method follows the concept outlined in "3-D Beamforming for Flexible Coverage in Millimeter-Wave UAV Communications" (IEEE Wireless Commun. Lett., vol. 8, no. 3, pp. 837–840, Jun. 2019, L. Zhu et al.), in which RIS20 is divided into multiple subarrays, each of which applies a traditional beamforming method. By configuring the direction of each beam of the multiple subarrays, a wide beam with a predetermined width is generated as a combination of beams of the multiple subarrays. Specifically, RIS20 is divided into K subarrays that satisfy the following conditions:

[0127]

[0128] in:

[0129] ·N S is a count of reflective elements in each of the plurality of sub-arrays; and

[0130] · is the expected width of the wide beam.

[0131] Since K and N S are all integers, then KN S ≤N, which means Therefore, by using Substituting K, we obtain a sufficient condition for equation (9):

[0132]

[0133] NS It needs to be large enough to achieve sufficient array gain to compensate for the path loss. S can be determined as the largest integer that satisfies equation (9). Then, K can be determined as

[0134] Once K and N are determined S , the direction of the beam for each of the multiple subarrays is determined. The central direction of the wide beam generated by the combination of all beams in the multiple subarrays is μ c , and the width of the beam of a specific subarray of the plurality of subarrays is 2 / N S In the case of , the direction of the beam of a particular subarray is:

[0135]

[0136] Therefore, the reflection matrix of RIS20 can be written as:

[0137]

[0138] in:

[0139] i(k,n)=(k-1)N s +n represents the index of the RIS20 unit, and ∈ k is the phase compensation to maintain a consistent phase for each subcarrier, which satisfies ∈ k = kΔε, where Δε is defined as:

[0140]

[0141] ∈ k The derivation of is shown in Appendix A below.

[0142] As described above, the wide beam pair arithmetic codebook W is generated based on equation (12). s 、v k ,∈ k The value of can be obtained by equations (9), (10) and (12). Specifically, μ in equation (10) is c Let μ[i]-μ[i]×B / f be the beam pair c and μ[i]+μ[i]×B / f c For two beams, the beam width is set to μ[i]×B / f c .

[0143] For a target UE at φ and a steering with width 2δ to μ c wide beams (all in the spatial domain), and the subcarrier frequencies range from f1 to fM , the beam direction at each subcarrier ranges from arrive where ξ m =f m / f c As a result, when m p When the following conditions are met, UE 30 can satisfactorily receive the mth p Subcarrier.

[0144]

[0145] On the contrary, when m n When the following conditions are met, UE 30 cannot satisfactorily receive the mth n Subcarriers:

[0146]

[0147] Therefore, when μ changes, the received power at the UE 30 changes. This property is exploited to improve accuracy and reduce the overhead of beam training in a wideband communication system, such as a wideband THz communication system.

[0148] Figure 6 (a) The first wide beam (wide beam I) and (b) The second wide beam (wide beam II) are shown. For wide beam I, The subcarriers indexed by The subcarriers indexed by cannot transmit signals satisfactorily. For wide beam II, The subcarriers indexed by The indexed subcarriers cannot transmit signals satisfactorily. This phenomenon results in a difference in the received power corresponding to the two wide beams at UE 30. By appropriately designing the direction and width of the beam pairs (as described below), the received power at UE 30 can be used to calculate the physical direction of UE 30.

[0149] Figure 7 A wide beam pair and its corresponding beam training range are shown. The center direction of the wide beam pair is represented as Since the estimation of the direction is based on the received power, the beam width of each beam pair should be the same so that their respective array gains are the same. As mentioned above, the beam direction at each subcarrier is changed from arrive Therefore, we set the width of the beam pair to In order to make full use of the channel information carried by each subcarrier, the difference in the center direction of the two wide beams of the wide beam pair should be equal to the beam width. and With this configuration, when UE 30 is within the range When the RIS 20 is within the range of UE 30, it can receive signals of two wide beams and can calculate the physical direction between RIS 20 and UE 30 using the received power.

[0150] For those in The received power of the first wide beam for the UE at this time can be expressed as:

[0151]

[0152] in, is related to φ and μ I The derivation of equation (16) is shown in Appendix B.

[0153] Similarly, for For the same UE at the same time, the received power of the second wide beam can be expressed as:

[0154]

[0155] in, is related to φ and μ I Irrelevant constant. Because δ≈K / N s , according to equation (9), the numerators of equations (16) and (17) are equal. Therefore, the difference between the received power of the first wide beam at UE 30 and the received power of the second wide beam at UE 30 is based on the denominator.

[0156] Based on the received power of the wide beam pair, the following arithmetic direction estimation method is proposed. In order to estimate the direction, an appropriate metric must be selected. The value of the received power itself is useless considering the random noise and the unknown distance between the RIS 20 and the UE 30. Only the relative difference (of the received power of the first wide beam and the received power of the second wide beam) eliminates the uncertainty in the system and carries the actual information of the channel. The ratio metric x is introduced, which is given earlier in this specification as equation (9) and is repeated here:

[0157]

[0158] By applying equations (16) and (17), χ can be expressed as:

[0159]

[0160] in, The direction φ between RIS 20 and UE 30 can then be estimated using equation (8) presented earlier in this specification and repeated here (as ):

[0161]

[0162] As described above, in step S305, a vector μ of the center direction of the beam pair is generated in a direction where the beam splitting effect cannot be ignored. c , the vector of estimated ranges ρ and the vector of power normalization coefficients Theoretically it is possible to define the estimated range of these wide beams within the range However, the gradient near the boundary of this range is approximately zero, which means that small errors in χ lead to In actual communication systems, there are various noises, making errors in χ inevitable. Therefore, the second loop of step S305 introduces a range parameter k<1 to limit The estimation range in the , thereby improving the estimation accuracy.

[0163] Compared to the prior art method of beam training that relies solely on the UE selecting the beam with the maximum received power, this new arithmetic direction estimation method enables the direction between the RIS 20 and the UE 30 to be calculated by exploiting the information carried in the frequency domain and taking advantage of the beam splitting effect that is generally considered a problem in wideband communication systems. This new arithmetic direction estimation method improves the accuracy of beam training because the beam splitting effect is taken into account during the derivation. In addition, the proposed method has a reduced overhead (relative to the traditional exhaustive search method) because the width of the wide beam pair is much wider than the traditional narrow beam, which means that fewer beams are needed to search a specific space.

[0164] Reference below Figures 8 to 11 The simulation results of the arithmetic direction estimation method are given. In the first simulation, the parameters of the RIS-assisted broadband THz communication system are set to N BS =1, N RIS =1024, N UE =1, f c =100 GHz, B=10 GHz, and the number of subcarriers is set to 128. The THz channel is considered to be quasi-optical, and the number of paths L is set to 1. The direction between RIS 20 and UE 30 is set to satisfy

[0165] Figure 8 The achievable rate performance of the beam training method of the first embodiment of the present invention is shown compared with the multi-directional beam training framework and the traditional exhaustive beam training framework discussed in the background section above. In this example, the training overhead (i.e., the number of transmitted beams) is set to 128. The parameter Q in the multi-directional beam training framework represents the number of beams transmitted in each time slot. From Figure 8It can be observed that the beam training method of the first embodiment of the present invention outperforms other methods and can achieve near-optimal achievable rate performance compared to the optimal case where BS 10 and RIS 20 fully know the direction of UE 30. In addition, conventional exhaustive search cannot work with such low beam training overhead.

[0166] In order to illustrate the advantage that the beam training cost of the beam training method of the first embodiment of the present invention does not increase with the increase in the number of reflective elements of RIS 20, Fig. 9 A further simulation is shown in FIG. 1 , where the number N of reflective elements of RIS 20 is RIS is set to 2048. It can be observed that the multi-directional beam training framework suffers further performance degradation due to the increase of reflective elements, but the achievable rate performance of the beam training method of the first embodiment of the present invention remains the same, because the overhead of the beam training method is only related to the inherent parameters of the broadband communication system (i.e., it is independent of the number of reflective elements). Therefore, the beam training method is highly adaptive to future communication systems with a relatively large number of reflective elements.

[0167] To illustrate the beam training overhead for each beam training frame, Fig.10 The simulation of the rate performance of different frameworks when the beam training overhead is increased is illustrated. In this simulation, the SNR is set to 5dB. The horizontal axis represents the beam training overhead. Fig.10 It can be observed that the beam training method of the first embodiment achieves near-optimal achievable rate performance with sufficient overhead and outperforms existing frameworks. In addition, when the training overhead is limited, the achievable rate performance is much better than existing frameworks. This is because the beam training method of the first embodiment reduces the training overhead to a great extent when the UE is far away from 0°, because the beam splitting effect is severe. By scanning the space from 90° / -90° to 0°, most directions can be accurately estimated with very low training overhead. From Fig.10 It can also be seen that when the number of reflective elements is very large, the traditional exhaustive search framework hardly works.

[0168] like Fig.11 As shown, the number of reflective elements N is set to 2048. RIS To simulate the achievable rate performance and the beam training overhead. Fig.10 and Fig.11 , it can be observed that the beam training overhead of the beam training method of the first embodiment is independent of the number of reflective elements, because the achievable rate performance of the beam training method remains the same as N RIS=1024. It can also be observed that the multi-directional framework and the exhaustive search framework suffer from severe performance degradation. Therefore, the beam training method of the first embodiment has great potential in future broadband communication systems.

[0169] In summary, these simulations show that the beam training method of the first embodiment achieves near-optimal achievable rate performance, has low training overhead, and can be adapted to future communication systems with a relatively large number of reflective elements.

[0170] In the above-mentioned first embodiment, the base station 10 and the UE 30 cooperate to calculate the codebook for the RIS 20, and the base station 10 configures the RIS 20 to use the codebook by sending a configuration message. However, those skilled in the art will appreciate that any other network node (or multiple network nodes) may calculate (individually or collaboratively) the codebook and transmit the calculated codebook to the RIS 20. In addition, if the RIS 20 has sufficient processing power, the RIS 20 may determine the codebook.

[0171] Furthermore, those skilled in the art will appreciate that the RIS need not be a ULA, and may take any other form.

[0172] A person skilled in the art will appreciate that any combination of features is possible within the scope of the claimed invention.

[0173] Appendix A - Derivation of Phase Compensation in Equation (12)

[0174] In The array gain of the kth subarray can be expressed as:

[0175]

[0176] where (a) is explained by Lemma 1.

[0177] Lemma 1.

[0178]

[0179] prove.

[0180]

[0181] Due to the symmetry of the function, considering When p = k + 1 / 2, f(p) reaches its maximum value of 1. However, since p is an integer, when p * = k and p * = k+1, the actual maximum value of f(p) is reached. If p is not one of the two maximum points above, then

[0182]

[0183] In N s In relatively large cases, we have Therefore these terms can be neglected. The lemma can be proved by inverting the two maxima of f(p).

[0184] According to equation (19), The total array gain when can be expressed as:

[0185]

[0186] in, is a constant that is independent of ∈. These two terms have the same structure. To avoid aliasing and ensure sufficient array gain, Set as It is the designed array gain of each subarray. Thus,

[0187]

[0188] For simplicity, only the equation for the first term is derived. The equation for the second term is similar to equation (24) due to the same structure. Therefore, the phase compensation must satisfy equation (13) stated above and equation (13) is repeated here as follows:

[0189]

[0190] For all k=1,2,…,K,Δ∈=∈ k+1 -∈ k ∈ can be set to ∈ k =kΔ∈ Therefore, the reflection matrix of RIS20 can be obtained by equations (11), (12) and (13).

[0191] Appendix B - Derivation of Equation (16)

[0192]

[0193] According to Lemma 1, this expression can be further approximated as

[0194]

[0195] in, Here, (a) and (b) are phase compensations, so the two terms can be combined. Therefore,

[0196]

Claims

1. A network node for configuring a reconfigurable intelligent surface (RIS) in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a receiving node, the network node comprising a configuration module, the configuration module being configured to: Configuring the RIS according to a beam training codebook to define a training beam pair; obtaining data indicating a direction between the RIS and the receiving node, the direction between the RIS and the receiving node being derivable from the power of each beam in the training beam pair at the receiving node; as well as The RIS is configured according to a data transmission codebook, which defines a data transmission beam in the direction between the RIS and the receiving node.

2. The network node according to claim 1, further comprising a transmitter, the transmitter being configured to send a first configuration message to the RIS to configure the RIS according to the beam training codebook, and further configured to send a second configuration message to the RIS to configure the RIS according to the data transmission codebook.

3. The network node of claim 2, the network node being comprised in the transmitting node of the wireless telecommunications network.

4. The network node of claim 1, wherein the network node is included in the RIS.

5. A network node according to any one of the preceding claims, wherein: The obtained data indicates power of each of the training beams in the training beam pair at the receiving node, and the configuration module is further configured to determine the direction between the RIS and the receiving node based on the power of each of the beams in the training beam pair.

6. A receiving node in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a reconfigurable intelligent surface (RIS), the receiving node comprising: a receiver configured to receive a training beam pair transmitted by the transmitting node and reflected by the RIS; a measurement module configured to determine the power of each training beam in the training beam pair at the receiving node; as well as A processor is configured to determine a direction between the RIS and the receiving node based on the power of each beam in the training beam pair at the receiving node.

7. The receiving node according to claim 6, further comprising: A transmitter is configured to send a message including the determined direction between the RIS and the receiving node so that the RIS uses a data transmission codebook, wherein the data transmission codebook defines a data transmission beam in the determined direction between the RIS and the receiving node.

8. A method for configuring a reconfigurable smart surface (RIS) in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a receiving node, the method comprising the following steps: Configuring the RIS according to a beam training codebook to define a training beam pair; obtaining data indicating a direction between the RIS and the receiving node, the direction between the RIS and the receiving node being derivable from the power of each beam in the training beam pair at the receiving node; as well as The RIS is configured according to a data transmission codebook, which defines a data transmission beam in the direction between the RIS and the receiving node.

9. The method according to claim 8, wherein: The obtained data indicates the power of each of the training beams in the training beam pair at the receiving node, and the method further comprises the step of determining the direction between the RIS and the receiving node based on the power of each of the beams in the training beam pair.

10. The method according to claim 9, wherein: The beam training codebook defines a plurality of training beam pairs, and the obtained data indicates the power of each beam in each of the plurality of training beam pairs, and the method further comprises the following steps: identifying a training beam pair having a maximum power among the plurality of training beam pairs at the receiving node, The step of determining the direction between the RIS and the receiving node is based on the power of each beam in the identified training beam pair.

11. The method according to claim 10, wherein: The plurality of training beam pairs include a first set, in which each training beam pair satisfies Bm / f c >b Where B is the bandwidth used in the communication between the transmitter and the receiver, μ is the direction of the training beam pair from the RIS to the receiver, and f c is the center frequency of the training beam pair, and β is a beam splitting threshold configured to cause the training beam pair to have negligible beam splitting.

12. The method according to claim 10 or claim 11, wherein: The plurality of training beam pairs include a second set, in which each training beam pair satisfies Bμ / f c ≤β Where B is the bandwidth used in the communication between the transmitter and the receiver, μ is the direction of the training beam pair from the RIS to the receiver, and f c is the center frequency of the training beam pair, and β is a beam splitting threshold configured so that the training beam pair has non-negligible beam splitting.

13. The method according to claim 12, wherein: Each training beam pair in the second set of the plurality of training beam pairs is defined as in, is the direction of the training beam starting from the RIS, and δ is the width of the training beam pair and is defined as 14. The method according to claim 12, wherein: Each training beam pair in the second set of the plurality of training beam pairs is defined as where κ is the range limiting parameter.

15. The method according to claim 14, wherein: κ is in the range of 0.7 to 0.

9.

16. The method according to any one of claims 10 and 12 to 15, further comprising the steps of: normalizing the power of each training beam in each training beam pair in the plurality of training beam pairs, The step of identifying a training beam pair having a maximum power among the plurality of training beam pairs at the receiver is based on a normalized power.

17. The method according to any one of claims 9 to 16, wherein: The step of determining the direction between the RIS and the UE is determined as follows: where χ is defined as: Among them, g I (φ) 2 is the power of the first training beam of the training beam pair at the receiver, g II (φ) 2 is the power of the second training beam in the training beam pair at the receiver, and δ is the width of the training beam pair and is defined as 18. A method of operating a receiving node in a wireless telecommunication network, the wireless telecommunication network comprising a transmitting node and a reconfigurable smart surface (RIS), the method comprising the steps of: receiving a training beam pair transmitted by the transmitting node and reflected by the RIS; determining the power of each training beam in the training beam pair at the receiving node; as well as A direction between the RIS and the receiving node is determined based on the power of each beam in the training beam pair at the receiving node.

19. The method according to claim 18, wherein: The step of receiving a training beam pair comprises receiving a plurality of training beam pairs, and the step of determining the power of each training beam in the training beam pair comprises determining the power of each training beam in each training beam pair in the plurality of training beam pairs, and the method further comprises the steps of: identifying a training beam pair having a maximum power among the plurality of training beam pairs at the receiving node, The step of determining the direction between the RIS and the receiving node is based on the power of each beam in the identified training beam pair.

20. The method according to claim 19, further comprising the steps of: normalizing the power of each training beam in each training beam pair in the plurality of training beam pairs, The step of identifying a training beam pair having a maximum power among the plurality of training beam pairs at the receiving node is based on normalized power.

21. The method according to any one of claims 18 to 20, wherein: The step of determining the direction between the RIS and the UE is determined as follows: Here, χ is defined as: Among them, g I (φ) 2 is the power of the first training beam of the training beam pair at the receiver, g II (φ) 2 is the power of the second training beam in the training beam pair at the receiver, and δ is the width of the training beam pair and is defined as 22. The method according to any one of claims 18 to 21, further comprising the steps of: A message including the determined direction between the RIS and the receiving node is sent so that the RIS uses a data transmission codebook, the data transmission codebook defining a data transmission beam in the determined direction between the RIS and the receiving node.

23. A computer program comprising instructions which, when executed by a computer, cause the computer to perform the steps of any one of claims 8 to 22.

24. A computer readable carrier medium comprising a computer program according to claim 23.

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