Active reconfigurable intelligent surface beam training method based on actual amplification model

Abstract

The application discloses a kind of active reconfigurable intelligent metasurface beam training methods based on actual amplification model, belong to wireless communication field.The method includes generating final transmit beamforming vector codebook based on initial transmit beamforming codebook and transmit power codebook, so that the signal power incident to active reconfigurable intelligent metasurface is in the power interval of trigger reflection amplifier linear amplification;Reflection beamforming codebook is generated based on the array orientation vector of the cascaded channel assisted by the active reconfigurable intelligent metasurface arranged in the form of uniform plane array;The signal-to-noise ratio of the received signal is compared to obtain the optimal transmit power and the optimal reflection beamforming vector, and the maximum total rate of the communication system is obtained.The method of the application ensures that the signal power incident to the active reconfigurable intelligent metasurface can make the amplifier work in the linear amplification interval, realize the effective amplification of signal, without complete feedback CSI.This way reduces feedback overhead while ensuring beamforming effect.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to an active reconfigurable intelligent metasurface beam training method based on a practical amplification model. Background Art

[0002] In recent years, with the rapid development of advanced technologies, reconfigurable smart metasurfaces (SMARTs) have attracted significant interest from researchers as a revolutionary technology that can help meet the diverse needs of 6G communication systems. A SMART metasurface is a planar surface composed of low-cost, passive reflective elements. Each reflective element can independently induce a controllable amplitude and / or phase change in the incident signal, thereby enabling an intelligent and programmable wireless environment. However, in the cascaded channel consisting of the base station-SMART metasurface and SMART metasurface-user links, a fatal "double fading" effect occurs, resulting in the path loss of the signal reflected from the SMART metasurface being several orders of magnitude greater than that of an unobstructed direct link. Therefore, in practical deployments, when the SMART metasurface is not close enough to the user or base station, the system can only achieve minimal performance gains.

[0003] To effectively solve this problem, an active reconfigurable smart metasurface architecture equipped with a reflection amplifier was proposed. Compared with traditional passive reconfigurable smart metasurfaces, active reconfigurable smart metasurfaces can not only adjust the phase shift of the incident signal, but also amplify the weak incident signal propagating through the base station-reconfigurable smart metasurface channel at the electromagnetic level, thereby overcoming the influence of the "double fading" effect. Without the need for expensive and high-power radio frequency (RF) chains, active reconfigurable smart metasurfaces can be implemented through hardware-efficient active components such as tunnel diodes (see reference: Amato F, W. Peterson C, P. Degnan B, et al. Tunneling RFID tags for long-range and low-power microwave applications [J]. IEEE Journal of Radio Frequency Identification, 2018, 2(2): 93-103.).

[0004] Due to their low bias requirements and negative differential resistance, tunnel diodes are being used to create high-gain reflection amplifiers. These are designed based on oscillator concepts and implemented on microstrip lines. When properly biased, they lock onto the frequency of the input signal. When the reflection amplifier's impedance matches that of the microstrip line, it converts the DC power provided by the bias source into injection-locked RF power. This RF power is then amplified when the incident signal is reflected. The occurrence of locking and the reflection amplifier's impedance are both related to the amplitude of the incident signal. Most research on active reconfigurable smart metasurface beamforming designs is based on an idealized reflection-amplified signal model, without considering the characteristics of the amplifier's hardware structure. For example, tunnel diode-based reflection amplifiers, due to the hardware characteristics and limitations of the reflection amplifier circuit, only trigger the amplifier's linear amplification mechanism when the incident signal power falls within a specific linear amplification range, effectively amplifying the incident signal without distortion. Outside this range, due to the characteristics of the amplifier circuit, the device can only perform nonlinear amplification with significant distortion, or simply reflect the signal without amplification. Existing active reconfigurable smart metasurface beamforming designs do not consider the actual response of the amplification circuit with incident signals of different intensity levels, which will lead to performance degradation when inaccurate amplification modeling is used in active reconfigurable smart metasurface optimization.

[0005] For passive reconfigurable smart metasurface-assisted systems, the design of the transmitter at the base station and the receiver at the user only requires the concatenated channel state information (CSI) of the transmitter-reconfigurable smart metasurface-receiver link. Due to the introduction of amplifiers, for active reconfigurable smart metasurface-assisted systems, the transceiver design needs to consider the amplified reconfigurable smart metasurface transmit power and thermal noise, which requires separate CSI for the base station-reconfigurable smart metasurface link and the reconfigurable smart metasurface-user link. However, due to the lack of an RF chain, active reconfigurable smart metasurfaces cannot estimate two separate channels. Therefore, existing work on active reconfigurable smart metasurfaces assumes perfect CSI for both the base station-reconfigurable smart metasurface and the reconfigurable smart metasurface-user link, which is difficult to achieve in practice. The introduction of a codebook allows the receiver to simply select the best codeword from a predefined codebook for feedback, without the need to provide complete CSI feedback. This approach reduces feedback overhead while ensuring beamforming effectiveness. Therefore, it is crucial to design a beam training method for active reconfigurable smart metasurfaces based on a realistic amplification model. Summary of the Invention

[0006] In order to solve the problems that most existing active reconfigurable intelligent metasurface assisted communication systems are based on ideal amplification models and ignore the hardware limitations of actual amplifiers, resulting in significant signal distortion and additional performance loss when the incident signal power exceeds the linear amplification range of the amplifier; and the acquisition of precise cascade link individual CSI for active reconfigurable intelligent metasurface reflection phase shift beamforming design is limited, the present invention provides an active reconfigurable intelligent metasurface beam training method based on an actual amplification model to achieve actual and effective linear amplification effect of the amplifier, ensure that the active reconfigurable intelligent metasurface can still achieve effective linear signal amplification under the condition of incomplete CSI feedback, improve beamforming performance, optimize the overall rate performance of the communication system while reducing dependence on feedback information.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A beam training method for an active reconfigurable intelligent metasurface based on a practical amplification model is applicable to a communication system including a multi-antenna base station, an active reconfigurable intelligent metasurface, and a single-antenna receiving end device, wherein the direct path between the base station and the receiving end is blocked; the base station is equipped with M transmitting antennas arranged in a uniform linear array; the active reconfigurable intelligent metasurface is equipped with N reflective units arranged in a uniform planar array, each reflective unit is connected to a tunnel diode-based reflective amplifier to perform phase shift adjustment and electromagnetic level power amplification on the incident signal; the spacing between the base station antennas and the spacing between the reflective units of the active reconfigurable intelligent metasurface are both set to half the signal wavelength; through codebook generation, power control based on the practical amplification model, and exhaustive search, main path beamforming between the base station and the active reconfigurable intelligent metasurface is achieved, and the signal is controlled within the linear amplification range of the tunnel diode-based reflective amplifier to achieve precise beam steering and signal amplification; the method specifically comprises the following steps:

[0009] Step 1: Design a beamforming codebook for a base station based on a uniform linear array arrangement. Combined with the channel characteristics from the base station to the active reconfigurable smart metasurface, an initial transmit beamforming vector codebook is generated. The final base station transmit beamforming vector codebook is then generated using the transmit power codebook.

[0010] Step 2: generating an active reconfigurable intelligent metasurface reflection beamforming codebook based on the array steering vector of the cascaded channel assisted by the active reconfigurable intelligent metasurface arranged in a uniform planar array;

[0011] Step 3: Perform codebook training. By calculating the incident signal power of the active reconfigurable intelligent metasurface under each transmit beamforming vector codeword one by one, the response of the tunnel diode-based reflection amplifier is determined. Then, the pre-calculated reflection beamforming vector codewords in the reflection beamforming codebook are searched one by one to determine the codeword that can maximize the signal-to-noise ratio of the received signal at the receiving end, that is, the optimal transmit beamforming vector codeword and the optimal reflection beamforming vector codeword, thereby obtaining the maximum total rate of the communication system.

[0012] Furthermore, in step 1, the initial transmit beamforming vector codebook is generated as follows:

[0013] The channel G between the base station and the active reconfigurable smart metasurface is decomposed by SVD, and the obtained right singular vectors are used as candidate directions for base station beamforming to optimize the signal gain in the main path direction of the channel; the formula is:

[0014] G=UΣV H (1)

[0015] in: represents the channel from the base station to the active reconfigurable smart metasurface; U is the left singular vector matrix, describing the receiving direction space of the channel; Σ is a diagonal matrix, whose diagonal elements are arranged in descending order according to the non-negative singular values; V is the right singular vector matrix, describing the transmitting direction space of the channel;

[0016] The initial transmit beamforming vector codebook generation method is expressed as:

[0017]

[0018] The right singular vector V(:,1) corresponding to the maximum singular value represents the optimal transmission direction at the transmitter; V * (:,1) represents the conjugate of V(:,1), which enables the transmitted signal to obtain optimal gain in the main path direction, thereby maximally concentrating the signal energy on the main path from the transmitter to the active reconfigurable smart metasurface, improving the transmission signal-to-noise ratio and system performance.

[0019] Furthermore, in step 1, to further optimize the incident signal power, the base station transmit power is adjusted using a transmit power codebook containing a series of candidate power values. By traversing the transmit power codebook, the optimal transmit power value is selected to ensure that the signal power incident on the active reconfigurable smart metasurface meets the linear range of the amplifier, thereby avoiding signal distortion and performance degradation caused by abnormal amplifier amplification. Therefore, the codeword of the final base station transmit beamforming vector codebook is represented as:

[0020]

[0021] Among them, P BS Represents the base station's transmit power codebook, which is generated at equal intervals according to the step size within the set power range; P BS (i) represents the base station transmit power codebook P BS The i-th value of .

[0022] Furthermore, in step 2, by modeling the array steering characteristics of the cascaded channel between the base station and the active reconfigurable intelligent metasurface, a phase-shifted reflection codebook arranged in a uniform planar array is generated to ensure the phase adjustment and reflection direction optimization of the reflected signal; the active reconfigurable intelligent metasurface reflection beamforming codebook is expressed as:

[0023]

[0024] Wherein, a(α,β) represents the array response vector of the active reconfigurable smart metasurface related to the uniform planar array arrangement; α and β represent the spatial angles related to the active reconfigurable smart metasurface, n1 = [0, 1, …, N1-1] T , n2=[0,1,...,N2-1] T , the number of active reconfigurable smart metasurface reflection units N = N1 × N2, where N1 and N2 are the number of columns and rows of the active reconfigurable smart metasurface, respectively.

[0025] Furthermore, in step 3, an exhaustive search method is used to perform codebook training, and the specific process is as follows:

[0026] For the i-th transmit beamforming vector codeword w(i), the incident signal power of the n-th reflective unit on the active reconfigurable smart metasurface is expressed as:

[0027] p in,n =|G(n,:)w(i)| 2 (5)

[0028] Where G(n,:) represents the nth row of channel G, corresponding to the nth reflection unit of the active reconfigurable smart metasurface, n = 1,...,N;

[0029] In the present invention, the linear amplification mechanism of the tunnel diode reflection amplifier that triggers the active reconfigurable intelligent metasurface is p in,n The tunnel diode reflection amplifier linearly amplifies it at a constant multiple. in,n When the power is less than the linear amplification requirement, the active reconfigurable intelligent metasurface only adjusts the phase and reflects the signal because the impedance of the tunnel diode does not match the microstrip line and the incident signal power is too weak to trigger the locking phenomenon. in,nWhen it is greater than the linear amplification requirement, the codebook training procedure stops to avoid abnormal amplification by the amplifier, which may cause additional uncontrollable losses.

[0030] The signal received by the user is expressed as:

[0031]

[0032] in: represents the channel from the active reconfigurable smart metasurface to the user; represents the base station's transmitted signal, x=w(i)s, s represents the transmission signal, and satisfies denote the amplification factor matrix and reflection phase shift matrix of the active reconfigurable smart metasurface, represents the first codebook of the active reconfigurable smart metasurface reflective beamforming Code words, represents the thermal noise introduced by the active reconfigurable smart metasurface, n represents the additive Gaussian white noise at the user, with a mean of 0 and a variance of σ 2 ;

[0033] The user receiving signal-to-noise ratio is expressed as:

[0034]

[0035] The total rate of the communication system is expressed as:

[0036] sum_rate=log(1+SNR) (8)

[0037] By searching the transmit beamforming power codewords pre-calculated in the transmit beamforming codebook and the reflection beamforming vector codewords pre-calculated in the reflection beamforming codebook one by one, the transmit beamforming vector codeword w that maximizes the signal-to-noise ratio of the received signal at the receiving end shown in formula (7) is found. best Active reconfigurable smart metasurface reflective beamforming vector codeword

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. Codebook-based beamforming optimization to reduce feedback overhead and improve system feasibility: The present invention proposes a beamforming method under non-perfect CSI conditions, using a predefined codebook and a beam training scheme based on exhaustive search, so that the system can still achieve optimal beamforming effects through codebook optimization in the absence of independent CSI feedback. The receiving end only needs to select the best codeword in the predefined codebook for feedback, without the need to feedback the complete CSI, thus avoiding the complex CSI feedback process. Through codebook design and one-by-one selection, the present invention eliminates the need for the system to re-estimate the complete CSI when each channel changes, thereby effectively reducing the burden on the feedback link, significantly improving the system response speed and operating efficiency, and greatly improving the real-time and feasibility of the system.

[0040] 2. Beam training based on actual amplification model ensures efficient operation of the amplifier: The present invention proposes a beam training method based on actual amplification model. It introduces the actual amplification model of active reconfigurable smart metasurface for the first time in the beamforming design of the system, fully explores the hardware characteristics and working mechanism of the reflection amplifier based on tunnel diode, and comprehensively considers the triggering mechanism, nonlinear factors and impedance mismatch problems of the amplifier, so that the signal power incident on the active reconfigurable smart metasurface is always kept within the range of linear amplification of the triggering amplifier, thereby avoiding signal distortion and additional power consumption caused by abnormal operation of the amplifier. Through exhaustive search, the optimal transmit beamforming vector codeword is selected at the base station end to ensure that the signal can be linearly amplified by the amplifier without distortion and to achieve maximum cascade channel gain, thereby optimizing the beamforming effect and amplification efficiency of the system, reducing unnecessary power consumption, and effectively avoiding potential signal distortion and performance degradation caused by ideal modeling in traditional methods.

[0041] 3. The codebook design combines actual channel conditions to simplify system design requirements: By designing the reflection beamforming and transmission power codebook, the present invention effectively reduces the dependence on the CSI of the base station-reconfigurable intelligent metasurface and reconfigurable intelligent metasurface-receiver links. The system searches for candidate beam vectors and power values ​​one by one to obtain the optimal configuration, ensuring that reliable beamforming can still be achieved under complex channel conditions. In addition, the present invention uses SVD decomposition to generate the beamforming vector of the base station to the active reconfigurable intelligent metasurface channel, and extracts the right singular matrix vector corresponding to the maximum eigenvalue of the channel as the candidate direction of the base station beamforming, which effectively improves the channel gain utilization. This design ensures the efficient operation of the system, enables the optimal configuration of the channel gain to be achieved, and reduces the feedback complexity and system design requirements while ensuring performance.

[0042] 4. Due to the outstanding advantages of active reconfigurable intelligent metasurfaces, such as low profile, lightweight, and low cost, they can be easily installed on / removed from building walls or ceilings. Furthermore, the proposed active reconfigurable intelligent metasurface beam training method based on a realistic amplification model can significantly reduce the number of components in the reconfigurable intelligent metasurface, addressing the issues of insufficient beamforming gain and limited service range of passive reconfigurable intelligent surfaces in existing transmission systems. By fully utilizing an accurate, realistic amplification model, the communication performance of receiving users in the system can be further improved.

[0043] In summary, the present invention ensures that the amplifier of the active reconfigurable smart metasurface operates efficiently and stably during signal transmission while reducing feedback overhead and improving system stability through beamforming and power control strategies based on actual amplification models. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the active reconfigurable intelligent metasurface assisted communication system in the present invention;

[0045] Figure 2 Schematic diagram of the response characteristics of the reflection amplifier based on the tunnel diode in the present invention;

[0046] Figure 3 This is a simulation diagram comparing the total communication rate with different numbers of transmitting antennas in the present invention;

[0047] Figure 4 This is a simulation diagram of the number of active reconfigurable smart surface reflection units versus the total communication rate in the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments. The following description of the exemplary embodiments is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0049] The present invention provides an active reconfigurable intelligent metasurface beam training method based on an actual amplification model, which includes the exploration of the hardware characteristics of the active reconfigurable intelligent metasurface amplifier, the design of the transmitter beamforming codebook, the design of the active reconfigurable intelligent metasurface reflection beamforming codebook, and the codebook training.

[0050] The exploration of the hardware characteristics of the active reconfigurable intelligent metasurface amplifier includes the exploration of the amplification principle of the reflection amplifier based on the tunnel diode, the exploration of the amplification characteristics, and the exploration of the effective linear amplification range of the reflection amplifier;

[0051] The base station transmit beamforming codebook design includes an initial transmit beamforming codebook design and a transmit power codebook design, thereby obtaining a final transmit beamforming vector codebook and an effective transmit signal, so that the signal power incident on the active reconfigurable smart metasurface is within the power range that triggers linear amplification of the reflective amplifier;

[0052] The active reconfigurable intelligent metasurface reflection beamforming codebook is generated by array steering vectors of cascade channels of an active reconfigurable intelligent metasurface auxiliary system arranged in a uniform planar array form;

[0053] The codebook training method is an exhaustive search method, which obtains the optimal codeword, that is, the optimal transmit power and the optimal reflection beamforming vector, by comparing and judging the signal-to-noise ratio of the signal received at the receiver, and obtains the maximum total rate of the communication system;

[0054] The tunnel diode-based reflection amplifier is based on the concept of an oscillator and consists of an inductor, a capacitor and a tunnel diode. The tunnel diode under proper bias naturally produces a negative differential resistance. Due to such low bias requirements and negative differential resistance characteristics, it is used to manufacture a reflection amplifier with high gain. The amplification principle of the reflection amplifier is that the properly biased tunnel diode reflection amplifier acts as a locked oscillator. The oscillator locks the frequency of the input signal and can amplify and reflect the impacting external signal. The occurrence of locking depends on multiple factors, among which the amplitude of the external signal (that is, the power intensity of the incident signal) is an important factor. In addition, the impedance of the reflection amplifier is also related to the power intensity of the incident signal. For different incident signal powers, the impedance value of the reflection amplifier shows a changing trend. In summary, as Figure 2 As shown in FIG, for incident signal powers of different intensities, the reflection amplifier will exhibit the characteristics of linear amplification, nonlinear amplification, and reflection without amplification.

[0055] It is worth noting that experiments have shown that a DC power consumption of 45 μW can usually support a power gain of 40 dB. Therefore, the active reconfigurable intelligent metasurface based on the tunnel diode reflection amplifier adopted in the present invention has very low energy consumption, low hardware complexity and strong feasibility.

[0056] An active reconfigurable intelligent metasurface beam training method based on a practical amplification model. The base station is equipped with M transmitting antennas to perform beamforming on the transmitted signal.

[0057] The effective transmitted signal x is expressed as:

[0058] x=w(i)s (9)

[0059] Where: s represents the signal transmitted by the transmitter, satisfying Represents the transmitting end beamforming vector, which is the channel from the base station to the active reconfigurable smart metasurface Perform SVD decomposition to generate the initial transmit beamforming vector codeword, and then further generate the final transmit beamforming vector codebook through the transmit power codebook;

[0060] Initial transmit beamforming vector codebook w ini The generation method is:

[0061] G=UΣV H (10)

[0062]

[0063] Among them: the left singular vector matrix U generated by SVD decomposition describes the receiving direction space of the channel, the diagonal elements of the diagonal matrix Σ are arranged in descending order according to the non-negative singular values, and the right singular vector matrix V describes the transmitting direction space of the channel; V * (:,1) represents the conjugate of V(:,1); the right singular vector V(:,1) corresponding to the maximum singular value represents the optimal transmission direction at the transmitting end; V * (:,1) The transmitted signal can obtain the best gain in the main path direction, so that the signal energy is concentrated to the maximum extent on the main path from the base station to the active reconfigurable smart metasurface, thereby improving the transmission signal-to-noise ratio and system performance.

[0064] The codeword w(i) of the final transmit beamforming vector codebook is generated in detail as follows:

[0065]

[0066] Among them, P BS Represents the base station's transmit power codebook, which is generated at equal intervals according to the step size within the set power range; P BS (i) represents the base station transmit power codebook P BS The i-th value of .

[0067] The signal power incident on the nth reflector unit on the active reconfigurable smart metasurface is expressed as:

[0068] p in,n =|G(n,:)w(i)| 2 (13)

[0069] Where: G(n,:) represents the nth row of channel G, corresponding to the nth reflection unit of the active reconfigurable smart metasurface.

[0070] The active reconfigurable intelligent metasurface is equipped with N reflection units, each of which is connected to a reflection amplifier based on a tunnel diode to perform phase shift adjustment and electromagnetic-level power amplification on the incident signal; the N reflection units are arranged in a uniform planar array; in the active reconfigurable intelligent metasurface structure, the number of reflection units affects the beamforming gain: the more reflection units, the greater the beamforming gain; the fewer reflection units, the smaller the beamforming gain.

[0071] Defining the reflection phase shift vector of active reconfigurable smart metasurface and the reflected phase shift matrix where θ n Represents the phase shift of the nth reflection unit; defines the amplification factor vector and the magnification matrix

[0072] The active reconfigurable intelligent metasurface reflection beamforming codebook design is based on array steering vector generation of cascaded channels. By modeling the array steering characteristics of the active reconfigurable intelligent metasurface cascaded channels arranged in a uniform planar array, the codewords of the reflection beamforming codebook are generated to ensure the phase adjustment and reflection direction optimization of the reflected signal. Specifically, the active reconfigurable intelligent metasurface reflection beamforming codebook is designed as follows:

[0073]

[0074] Wherein, a(α,β) represents the array response vector of the active reconfigurable smart metasurface related to the uniform planar array arrangement; α and β represent the spatial angles related to the active reconfigurable smart metasurface: β = Δd sin(ν) / λ, where and ν represent the azimuth and elevation angles of the physical space respectively, λ represents the wavelength of the electromagnetic wave of the transmitted signal, and Δd represents the array spacing. In the present invention, Δd = λ / 2; n1 = [0, 1, ..., N1-1] T , n2=[0,1,...,N2-1] T , N1 and N2 represent the number of columns and rows of the active reconfigurable smart metasurface, respectively; the number of active reconfigurable smart metasurface reflection units N = N1 × N2.

[0075] In the present invention, for the incident signal that triggers the linear amplification mechanism of the tunnel diode reflection amplifier of the active reconfigurable intelligent metasurface, the tunnel diode reflection amplifier linearly amplifies it at a constant multiple. in,nWhen the power of the incident signal is less than the linear amplification requirement, the active reconfigurable intelligent metasurface only adjusts the phase and reflects the signal because the impedance of the tunnel diode does not match the microstrip line and the incident signal power is too weak to trigger the locking phenomenon. in,n When it is greater than the linear amplification requirement, the codebook training procedure stops to avoid abnormal amplification by the amplifier, which may cause additional uncontrollable losses.

[0076] The codebook training method uses an exhaustive search, searching through the transmit beamforming vector codebook and the reflection beamforming codebook one by one to determine the codeword that maximizes the signal-to-noise ratio of the received signal at the receiving end, thereby achieving the maximum overall rate of the communication system. By using the transmit beamforming vector codebook and reflection beamforming codebook of the base station and the active reconfigurable intelligent metasurface, the system simply uses the pre-calculated transmit beamforming power codebook and reflection beamforming vector codebook in the codebook to test and select the appropriate transmit power value and reflection beamforming vector to maximize the user's received signal quality.

[0077] Example 1

[0078] The following takes the design of a single-user multi-input single-output wireless communication system assisted by an active reconfigurable intelligent metasurface as an example to further illustrate the technical solution of the present invention. Figure 1 As shown in the figure, the base station, acting as the transmitter, is equipped with M = 4 antennas and communicates with a single-antenna receiving user via an active reconfigurable smart metasurface with N = N1 × N2 = 8 × 8 reflective elements. Each reflective element is connected to a tunnel diode-based reflective amplifier that performs phase shift adjustment and electromagnetic power amplification on the incident signal. Specifically, in the Cartesian coordinate system, the base station is located at (5m, 0m, -30m), the active reconfigurable smart metasurface is located at (0m, 250m, 15m), and the receiving user is located at (-5m, 250m, 0m).

[0079] The present invention assumes that the direct channel between the transmitter and the receiver is blocked by an obstacle. By deploying an active reconfigurable intelligent metasurface, a virtual line-of-sight (LoS) path is established, and cascaded reflection channels from the transmitter to the active reconfigurable intelligent metasurface and from the active reconfigurable intelligent metasurface to the receiver are constructed. Deterministic LoS paths exist in both reflection channels.

[0080] The present invention adopts a commonly used geometric channel model, and the channel G from the base station to the active reconfigurable intelligent metasurface and the channel h from the active reconfigurable intelligent metasurface to the user are RU Respectively expressed as:

[0081]

[0082] in, represents the large-scale fading of the correlated channel, which is expressed as:

[0083] PL=PL0+10μlog d (17)

[0084] Wherein, PL0 is the reference path loss, which is usually set to 30dB; μ is the path loss index, and the path loss index of channel G is set to 2.8 in the present invention, and the path loss index of channel h is set to 2.8. RU The path loss index is set to 2; d is the distance between the two communication devices;

[0085] a(α, β) and b(α, β) represent the array steering vectors associated with the active reconfigurable smart metasurface arranged in a uniform planar array and the base station antennas arranged in a uniform linear array, respectively, which are specifically expressed as:

[0086]

[0087] b(α)=[1,e -j2πα ,...,e -j2π(M-1)α ] T (19)

[0088] Where: n1=[0,1,…,N1-1] T , n2=[0,1,…,N2-1] T ; α and β represent the spatial angles related to the active reconfigurable smart metasurface: β = Δd sin(ν) / λ, where and ν represent the azimuth and elevation angles in physical space, respectively; λ represents the wavelength of the transmitted signal electromagnetic wave; and Δd represents the array spacing. In this embodiment, Δd = λ / 2;

[0089] The base station's transmit beamforming vector codebook w is designed based on SVD decomposition. Specifically:

[0090] 1) Perform SVD decomposition on the channel matrix G from the base station to the active reconfigurable smart metasurface to obtain the right singular vector corresponding to the largest singular value of G. This allows the optimal transmission direction of the transmitting antenna at the transmitting end to achieve optimal gain in the main path direction, thereby maximizing the concentration of signal energy on the main path from the base station to the active reconfigurable smart metasurface, thereby improving the signal-to-noise ratio and system performance. The formula is expressed as:

[0091] G=UΣV H (20)

[0092]

[0093] Where: V * (:,1) represents the conjugate of V(:,1).

[0094] 2) To maximize the channel gain, when selecting the transmit beamforming vector, the adjustment of the incident signal power must be considered to meet the amplifier linear range requirements of the active reconfigurable intelligent metasurface. To this end, the transmit power codebook P is defined. BS , testing each possible transmit power value one by one. By calculating the power incident on each reflective unit n of the active reconfigurable smart metasurface, the optimal power codeword is selected while ensuring the linear amplification operating conditions of the amplifier, thereby achieving optimal system energy efficiency.

[0095] The signal power incident on the nth reflection unit is expressed as:

[0096] p in,n =|G(n,:)w(i)| 2 (twenty two)

[0097] Where: G(n,:) represents the nth row of channel G, corresponding to the nth reflection unit of the active reconfigurable smart metasurface.

[0098] The method for generating the codeword w(i) of the final transmit beamforming vector codebook is described in detail as follows:

[0099]

[0100] Ensure ||w(i)|| 2 =P BS (i). Where P BS (i) represents the base station transmit power codebook P BS The i-th value of P BS In the set power range, the power is generated at equal intervals according to the step size. BS Generate in the interval [0dBm, 30dBm] with a step size of 1.

[0101] The reflection beamforming codebook of the active reconfigurable smart metasurface is generated based on the array steering vector of the cascaded reflection channel to ensure that the signal is amplified in the optimal direction. The specific steps include:

[0102] 1) Generate a reflection beamforming codebook based on the array steering vector of the cascaded channel to ensure that the reflection direction of the active reconfigurable smart metasurface can be aligned with the user receiving end to achieve the optimal reflection gain; the reflection beamforming codebook is expressed as:

[0103]

[0104] 2) If the incident signal power meets the amplifier linear range condition, the active reconfigurable intelligent metasurface amplifies the signal. This embodiment assumes a 100-fold constant amplification.

[0105] Beam training and optimal codeword selection are performed by exhaustively searching the base station transmit beamforming vector codebook w and the active reconfigurable smart metasurface reflective beamforming codebook. Calculate each pair of candidate transmit beamforming vector w(i) and reflected beamforming vector The received signal-to-noise ratio under , is expressed as:

[0106]

[0107] in: Represents the effective transmission signal of the base station, x=w(i)s, and satisfies represent the amplification factor matrix and reflection phase shift matrix of the active reconfigurable smart metasurface respectively; represents the first codebook of the active reconfigurable smart metasurface reflective beamforming Code words, represents the thermal noise introduced by the active reconfigurable smart metasurface, n represents the additive Gaussian white noise at the user, with a mean of 0 and a variance of σ 2 .

[0108] By selecting the beamforming configuration that maximizes the received signal-to-noise ratio, the base station transmits the beamforming vector codeword w. best Active reconfigurable smart metasurface reflective beamforming vector codeword

[0109] The beam training process also includes power control and a jump-out mechanism, specifically including the following two aspects:

[0110] 1) The incident signal power is too small: If the incident signal power p in,n If the gain is less than the preset amplifier linear amplification start threshold, the active reconfigurable intelligent metasurface only reflects the signal without performing gain amplification;

[0111] 2) The incident signal power is too large: If the incident signal power p in,n If the upper limit of the linear operating range of the amplifier is exceeded, the exhaustive search loop is exited and the current optimal configuration is selected as the final beamforming solution to prevent the amplifier from entering the nonlinear operating region.

[0112] Figure 3 A simulation diagram comparing the total communication rate with different numbers of transmitting antennas; Figure 4This is a simulation plot comparing the number of active reconfigurable smart metasurface elements versus the overall communication rate. It can be seen that the proposed active reconfigurable smart metasurface beam training method based on a realistic amplification model can achieve a higher overall communication rate and a more significant performance gain. In particular, as the number of active reconfigurable smart metasurface reflective units increases, the proposed method can achieve more sustained performance improvements.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. Active reconfigurable intelligent metasurface beam training method based on actual amplification model, characterized by: include: Step 1: Design a beamforming codebook for a base station based on a uniform linear array arrangement. Combine the channel characteristics from the base station to the active reconfigurable smart metasurface to generate an initial transmit beamforming vector codebook. Combine this with the transmit power codebook to generate the final base station transmit beamforming vector codebook. The initial transmit beamforming vector codebook is generated as follows: Channel between base station and active reconfigurable smart metasurface Perform SVD decomposition and obtain the right singular vector as the candidate direction for base station beamforming to optimize the signal gain in the main channel path direction; the formula is: （1） in: represents the channel from the base station to the active reconfigurable smart metasurface; is the left singular vector matrix, describing the receiving direction space of the channel; is a diagonal matrix whose diagonal elements are arranged in descending order of non-negative singular values; is the right singular vector matrix, describing the transmission direction space of the channel; The initial transmit beamforming vector codebook generation method is expressed as: （2） right singular vector corresponding to the largest singular value Indicates the best transmission direction at the transmitting end; express conjugation of; The codeword of the final base station transmit beamforming vector codebook is expressed as: （3） in, Indicates the base station's transmit power codebook, which is generated at equal intervals according to the step size within the set power range; Indicates the base station transmit power codebook No. i values; Step 2: generating an active reconfigurable intelligent metasurface reflection beamforming codebook based on the array steering vector of the cascaded channel assisted by the active reconfigurable intelligent metasurface arranged in a uniform planar array; Step 3: Perform codebook training to determine the response of the tunnel diode-based reflective amplifier by calculating the incident signal power of the active reconfigurable intelligent metasurface under each transmit beamforming vector codeword one by one. Specifically, for the first i transmit beamforming vector codewords The active reconfigurable intelligent metasurface n The incident signal power of a reflector unit is expressed as: （5） in, Indicates channel No. n row, corresponding to the first row of the active reconfigurable smart metasurface n Reflection unit, ; The linear amplification mechanism of tunnel diode reflective amplifier triggered by active reconfigurable smart metasurface , the tunnel diode reflection amplifier linearly amplifies it at a constant multiple; when When the linear amplification requirement is less than the linear amplification requirement, the active reconfigurable intelligent metasurface only adjusts the phase and reflects the signal; when When it is greater than the linear amplification requirement, the codebook training procedure stops; The pre-calculated reflection beamforming vector codewords in the reflection beamforming codebook are then searched one by one to determine the codeword that can maximize the signal-to-noise ratio of the received signal at the receiving end, namely the optimal transmit beamforming vector codeword and the optimal reflection beamforming vector codeword, thereby achieving the maximum total rate of the communication system.

2. The active reconfigurable intelligent metasurface beam training method based on the actual amplification model according to claim 1 is characterized in that: In step 2, the active reconfigurable intelligent metasurface reflection beamforming codebook is expressed as: （4） in, represents the array response vector of the active reconfigurable smart metasurface related to the uniform planar array arrangement; , 、 represents the spatial angle associated with the active reconfigurable smart metasurface, , , the number of active reconfigurable intelligent metasurface reflective units , N 1, N 2 are the number of columns and rows of the active reconfigurable smart metasurface, respectively.

3. The active reconfigurable intelligent metasurface beam training method based on the actual amplification model according to claim 2 is characterized in that: In step 3, the received signal-to-noise ratio is expressed as: （6） in, represents the channel from the active reconfigurable smart metasurface to the user; Represents the base station's transmission signal, , s Indicates the transmission signal and satisfies ; denote the amplification factor matrix and reflection phase shift matrix of the active reconfigurable smart metasurface, , represents the first codebook of the active reconfigurable smart metasurface reflective beamforming Code words, ; represents the thermal noise introduced by the active reconfigurable smart metasurface, ; represents the variance of additive white Gaussian noise at the user.

4. The active reconfigurable intelligent metasurface beam training method based on the actual amplification model according to claim 3 is characterized in that: In step 3, the total rate of the communication system is expressed as: （7）。

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