A signal source localization method based on a smart metasurface assisted by maximum parallelism

Abstract

This invention belongs to the field of radio positioning technology, specifically relating to a signal source positioning method based on a smart metasurface assisted by maximum parallelism. Utilizing the phase reconfigurability of the smart metasurface, a zero-mean phase coefficient is constructed. The user-access point direct channel matrix and the user-smart metasurface-access point cascaded channel tensor are separated, and parallelism operations are performed with the array response codebook matrix of the direct channel and the array response codebook tensor of the cascaded channel, respectively, to obtain the parallelism spatial spectrum of the user-access point and user-smart metasurface. The user's position is estimated by finding the angle corresponding to the peak of the spatial spectrum and using the least squares method. Compared to the traditional 2D-MUSIC method, which requires two-dimensional peak search, this invention employs two one-dimensional peak searches, significantly reducing computational and search complexity. Simultaneously, by setting time-varying smart metasurface phase coefficients, this invention maximizes the spatial degrees of freedom of the smart metasurface through spatiotemporal transformation.

Description

Technical Field

[0001] This invention belongs to the field of radio positioning technology, specifically relating to a signal source positioning method based on a smart metasurface assisted by maximum parallelism. Background Technology

[0002] Reconfigurable Intelligent Surface (RIS) is a novel material with reconfigurable electromagnetic properties. It consists of numerous units that can dynamically adjust their own electromagnetic parameters, enabling real-time adjustment of the amplitude, phase, and even polarization of incident electromagnetic waves. With its reconfigurable wireless propagation environment and its two-dimensional nature allowing for flexible installation on building surfaces, RIS holds great promise for improving data transmission rates, enhancing wireless signal quality, and increasing network capacity, making it a hot research topic in next-generation wireless communication systems.

[0003] Radio positioning is a method that utilizes the constant rectilinear propagation characteristic of electromagnetic waves. It involves using instruments to directly or indirectly measure changes in time, phase difference, amplitude, or frequency of a radio signal as it propagates between a known anchor point and the signal source. This data is used to determine positioning parameters such as distance, distance difference, and azimuth, and then a location line is used to pinpoint the signal source's location. Among these methods, azimuth-based positioning is a high-precision, low-overhead technique that requires only two anchor points to determine the signal source's location, and it has been widely used in 4G and 5G mobile communication systems.

[0004] Since the direction-finding accuracy of array antennas is positively correlated with the number of antennas, and RIS can provide additional degrees of freedom for wireless channels without changing the current wireless network infrastructure architecture, it is one of the alternative technologies for future mobile communication systems. Therefore, how to utilize the ultra-large-scale array characteristics of RIS to assist access points in performing high-precision positioning of users is a topic worthy of research in next-generation wireless communication. Summary of the Invention

[0005] To address the current research gap in fully utilizing the ultra-large-scale array characteristics of RIS to assist access points in high-precision positioning of signal sources, this invention proposes a positioning method based on RIS assisted by maximum parallelism.

[0006] To better illustrate the present invention, the terminology and system structure used in the technical solution of the present invention will be introduced first.

[0007] AP: Access Point.

[0008] LoS, Line-of-Sight, refers to the distance at which one's line of sight is reached.

[0009] MUSIC: Multiple Signal Classification.

[0010] NLoS, non-line-of-sight.

[0011] RIS: Reconfigurable Intelligent Surface.

[0012] UE: User.

[0013] 2D: Two-Dimensional.

[0014] Figure 1 The diagram shown is a schematic of the intelligent metasurface-assisted positioning system involved in this invention:

[0015] Assume that the number of antennas for the user UE and the access point AP are N respectively. U With N A The number of RIS units in the intelligent metasurface is N. R Without loss of generality, this invention considers a Ricean channel model in a two-dimensional scenario. That is, using a matrix... as well as These represent the uplink channels of UE-AP, UE-RIS, and RIS-AP, respectively, as follows:

[0016]

[0017]

[0018] as well as

[0019]

[0020] Where α l and κ l (l=0,1,2) represent the corresponding path loss and Rice factor, respectively; and For LoS components; and The NLoS component consists of elements that are independently and identically distributed in a complex Gaussian distribution. Let θ0, θ1, and θ2 represent the azimuth angles of UE-AP, UE-RIS, and RIS-AP, respectively. and Let represent the array tilt angles of UE, AP, and RIS, respectively. and It can be represented as:

[0021]

[0022]

[0023] as well as

[0024]

[0025] in Let be the array response vector. Assume that the RIS experiences no power loss on the reflected signal, and that at the nth (=1,2,…,N) k, the response vector is... T The phase shift within ) time slots is

[0026]

[0027] It satisfies the zero-mean property, that is

[0028]

[0029] Where N T This represents the total number of time slots. It also considers that the UE transmits the same positioning assistance signal in each time slot. Where N S ≥N U Let be the number of symbol vectors; therefore, the received signal matrix in the nth time slot can be expressed as:

[0030]

[0031] in It is Gaussian white noise, with each element independently and identically distributed in a complex Gaussian distribution. Where N0 is the noise power.

[0032] The technical solution adopted in this invention is as follows:

[0033] S1. Within each time slot, the AP performs channel estimation by multiplying the received signal by the right inverse of the pilot matrix, i.e.

[0034]

[0035] S2, with The time mean is used as an estimate of D, i.e.

[0036]

[0037] S3, Calculation and Parallelism, where Defined as

[0038]

[0039] This yields the parallelism spatial spectrum of the UE-AP path. The angle corresponding to the maximum value of the spatial spectrum is used as an estimate of θ0, specifically:

[0040] S31, Calculation and Parallelism is defined as and The square of the magnitude of the vectorized cosine of the included angle, i.e.

[0041]

[0042] S32. The angle corresponding to the peak value of P0(θ) is used as an estimate of θ0:

[0043]

[0044] S4, to minus As an estimate of the UE-RIS-AP concatenated channel, namely:

[0045]

[0046] S5, will According to n = 1, 2, ..., N T Arranged in order into tensors Calculate its relationship with tensor Parallelism, where Defined as

[0047]

[0048] According to n = 1, 2, ..., N T The tensor is arranged in order to obtain the parallelism spatial spectrum of the UE-RIS-AP channel. The angle corresponding to the maximum value of the spatial spectrum is used as the estimate of θ1, specifically:

[0049] S51, Calculation and Parallelism is defined as and The square of the magnitude of the vectorized cosine of the included angle, i.e.

[0050]

[0051] S52. The angle corresponding to the peak value of P1(θ) is used as an estimate of θ1:

[0052]

[0053] S6. Based on the results of S32 and S52, calculate the UE coordinates using the least squares method, specifically as follows:

[0054]

[0055] Where (x) I ,y I I = U, A, R represents the coordinates of UE, AP, and RIS.

[0056] The beneficial effects of this invention are as follows:

[0057] This invention proposes a smart metasurface-assisted positioning method based on maximum parallelism. This method utilizes the phase reconfigurability of the smart metasurface to construct zero-mean phase coefficients, thereby separating the user-access point direct channel matrix and the user-smart metasurface-access point cascaded channel tensor. Parallelism operations are then performed with the array response codebook matrix of the direct channel and the array response codebook tensor of the cascaded channel, respectively, to obtain the parallelism spatial spectrum of the user-access point and user-smart metasurface. The user position is estimated by finding the angle corresponding to the peak of the spatial spectrum and using the least squares method. This invention employs two one-dimensional peak searches, significantly reducing computational and search complexity compared to the traditional 2D-MUSIC method which requires two-dimensional peak searches. Simultaneously, by setting time-varying smart metasurface phase coefficients, this invention maximizes the spatial degrees of freedom of the smart metasurface through spatiotemporal transformation, resulting in a constructed parallelism spatial spectrum with sharper peaks and higher estimation accuracy. Attached Figure Description

[0058] Figure 1 : A schematic diagram of the intelligent metasurface-assisted positioning system involved in this invention;

[0059] Figure 2 The UE-AP channel parallelism spatial spectrum of the proposed scheme in this invention;

[0060] Figure 3 The spatial spectrum of UE-RIS-AP channel parallelism proposed in this invention;

[0061] Figure 4 The transmit / receive angles of traditional 2D-MUSIC solutions represent the two-dimensional MUSIC spatial spectrum.

[0062] Figure 5 : One-dimensional projection of the MUSIC spatial spectrum of the traditional 2D-MUSIC scheme; where (a) is AOD and (b) is AOD;

[0063] Figure 6 The results of 100 positioning simulations of the proposed solution in this invention. Detailed Implementation

[0064] The technical solution of the present invention has been described in detail in the invention summary section. The practicality of the present invention will be explained below with reference to the accompanying drawings and simulation examples.

[0065] exist Figure 2-6 In the simulation examples, unless otherwise specified, N is used. A =16, N U =4 and N R =255 system configuration, AP, UE, and RIS are all uniform linear arrays with an element spacing of half a wavelength, the positioning auxiliary signal S is an unit array, and the number of time slots N T =N R +1, AP and RIS coordinates are (10m, 0m) and (10m, 20m), noise power is -90dBm, angular interval is 0.1 degrees, Rice factor κ0=κ1=20dB, κ2=40dB.

[0066] Figure 2 The spatial spectrum of UE-AP channel parallelism for the proposed scheme is given when the UE is located at (20m, 15m). As can be seen from the figure, the highest peak of the spatial spectrum occurs at 56.3 degrees, which coincides with the azimuth angle of the UE-AP.

[0067] Figure 3 The spatial spectrum of UE-RIS-AP channel parallelism for the proposed scheme is presented when the UE is located at (20m, 15m). As shown in the figure, the highest peak of the spatial spectrum occurs at 153.4 degrees, which coincides with the azimuth angle of the UE-RIS. (Comparison) Figure 2 and Figure 3 It can be seen that the parallelism spatial spectrum of the UE-RIS-AP channel is sharper. This is because the present invention maximizes the spatial degree of freedom of RIS by setting time-varying intelligent metasurface phase coefficients and utilizing the transformation of time and space.

[0068] Figure 4 A 2D spatial spectrum heatmap of the traditional 2D-MUSIC scheme is presented when the UE is located at (20m, 15m). As shown in the figure, the highest peak of the spatial spectrum is located at (153.4°, 90°). Since the RIS-AP azimuth angle of 90° is known, 153.4° corresponds to the UE-RIS azimuth angle. The second highest peak is located at (56.3°, 56.3°), which has the same departure and arrival angles, corresponding to the UE-AP azimuth angle.

[0069] Figure 5 The one-dimensional spatial spectrum projection of the traditional 2D-MUSIC scheme is given when the UE is located at (20m, 15m). Combined with... Figure 2 , Figure 3 and Figure 5It is evident that the peak-to-average power ratio (PAPR) of the spatial spectrum proposed in this invention at the target direction is comparable to the maximum PAPR of the traditional 2D-MUSIC scheme at the target direction. However, the traditional 2D-MUSIC scheme requires calculating a two-dimensional spatial spectrum grid, performing a two-dimensional peak search, and determining the characteristics of the transmit / receive angle pair in order to determine the azimuth angles of the UE-AP and UE-RIS. The scheme proposed in this invention only requires calculating two one-dimensional spatial spectrum grids and performing two one-dimensional peak searches to determine the target azimuth angle, significantly reducing the computational load.

[0070] Figure 6 The simulation results of 100 simulations of the proposed scheme are presented, where "x" represents the true coordinates and "o" represents the estimated coordinates. As can be seen from the figures, the proposed scheme has high estimation accuracy, with the deviation between the estimated and true values ​​mostly on the order of centimeters. Only when the UE is close to the line connecting the midpoints of the AP and RIS does it exhibit a larger error (on the order of decimeters). This is a common limitation of azimuth-based positioning schemes: any point on the line connecting the midpoints of the AP and RIS has the same azimuth angle. Introducing more RIS can solve this problem.

[0071] As can be seen, the positioning scheme proposed in this invention has both high estimation accuracy and low complexity. It does not require judging the transmit and receive angle pair features, and only needs to search the peaks of two one-dimensional spatial spectra to determine the azimuth angles of UE-AP and UE-RIS, thus having high practicality.

Claims

1. A maximum parallelism based intelligent metasurface assisted signal source positioning method, the positioning system comprising a user of a root antenna, an access point of the root antenna, a number of units of intelligent metasurfaces, the uplink channels of user to access point, user to intelligent metasurface, intelligent metasurface to access point are , and respectively. ， ， ， in and These are the corresponding path loss and Rice factor, respectively. ; , and For LoS components; , and The NLoS components are independent and identically distributed in a complex Gaussian distribution. ;definition , and These represent the azimuth angles from the user to the access point, from the user to the smart metasurface, and from the smart metasurface to the access point, respectively. , and These represent the array tilt angles of the user, access point, and smart metasurface, respectively. , and Represented as: ， ， ， in, For array response vectors, The smart metasurface is designed to have no power loss for reflected signals, and in the first... The phase shift within each time slot is: ， , The total number of time slots satisfies the zero-mean property: ， Configure the user to send the same positioning assist signal in each time slot. ,in The number of symbol vectors, the first The received signal matrix within each time slot is represented as follows: ， in It is Gaussian white noise. , ; The positioning method is characterized by comprising the following steps: S1. Within each time slot, the access point performs channel estimation by right-multiplying the received signal by the right inverse of the pilot matrix, i.e. ； S2, with Time average as The estimate, i.e. ； S3, Calculation and parallelism, where Defined as ， This yields the parallelism spatial spectrum of the direct path from the user to the access point, with the angle corresponding to the maximum value of the spatial spectrum used as... The estimate is as follows: S31, Calculation and Parallelism is defined as and The square of the magnitude of the vectorized cosine of the included angle, i.e. ； S32, with The peak value corresponds to the angle as Estimate: ； S4, to minus This serves as an estimate of the cascaded channel from the user to the smart metasurface to the access point, namely: ； S5, will according to Arranged in order into tensors Calculate its relationship with the tensor parallelism, where Defined as ， according to The tensor is arranged in order to obtain the parallelism spatial spectrum of the channel from the user to the smart metasurface to the access point. The angle corresponding to the maximum value of the spatial spectrum is taken as the angle of the channel. The estimate is as follows: S51, Calculation and Parallelism is defined as and The square of the magnitude of the vectorized cosine of the included angle, i.e. ； S52, with The peak value corresponds to the angle as Estimate: ； S6. Based on the results of S32 and S52, calculate the UE coordinates using the least squares method, specifically as follows: ， in Represents the coordinates of the user, access point, and smart metasurface.

Images