Wireless positioning method based on cooperation of multiple intelligent reflecting surfaces

Abstract

The invention belongs to the technical field of wireless communication signal processing, and particularly relates to a wireless positioning method based on cooperation of multiple intelligent reflecting surfaces. The present invention comprises: a base station sending a positioning reference signal; and the to-be-positioned user receives the positioning reference signal, processes the positioning reference signal and feeds back the processed signal to the network side of the base station. And the network side of the base station receives a feedback signal, and the base station constructs a related parameter measurement matrix by using multi-RIS codebook information and combining a singular value decomposition (SVD) algorithm, and then solves path time delays of different base station-RIS-users. And the base station network side matches the estimated time delay parameter with each base station-RIS-user path by using a path energy sorting method based on a path time delay estimation result. And the network side of the base station solves the user position information by using the geometrical relationship through the time delay of each path and the position relationship of the RIS. According to the method, in the whole positioning process, multiple RISs work at the same time, and the resource utilization rate is remarkably increased.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication signal processing technology, specifically relating to a wireless positioning method based on multi-intelligent reflective surface collaboration. Background Technology

[0002] Reconfigurable Intelligent Surfaces (RIS) have attracted widespread attention from researchers in the field of wireless communication due to their potential to improve the performance of wireless communication systems. RIS deploys a large number of low-cost electromagnetic reflection units, and by controlling the electromagnetic characteristics of each unit (such as capacitive reactance, impedance, and inductive reactance), it can dynamically adjust the propagation path of electromagnetic waves, thereby enabling the reconstruction of wireless channels and optimizing signal propagation quality.

[0003] In wireless positioning systems, the introduction of RIS (Reference Reference Path) can significantly improve the propagation path of the positioning reference signal and enhance positioning accuracy by adjusting the reflection coefficient. By deploying multiple RIS nodes, wireless positioning systems can optimize the signal propagation path over a wider range, thereby providing more accurate and stable positioning services and effectively overcoming the limitations of traditional positioning technologies.

[0004] However, despite the significant advantages of RIS technology, collaborative RIS-assisted localization still faces some key challenges. Traditional RIS-assisted localization systems typically assume that the RIS can obtain the user's orientation information in advance and adjust the reflection coefficient to a specific direction to enhance the propagation of the positioning reference signal. However, for users without prior orientation information, this method lacks effective processing methods and struggles to achieve universal positioning functionality.

[0005] Furthermore, existing multi-RIS positioning systems typically employ time-division multiplexing control, allowing only one RIS to operate within each time slot. This leads to inefficient use of system resources and increased time slot overhead, thus limiting the system's positioning accuracy and efficiency. Simultaneously, the lack of an effective matching mechanism between RIS and user positioning information makes multi-RIS cooperative positioning difficult to achieve.

[0006] Therefore, how to intelligently configure multiple RIS reflection units to ensure their efficient collaboration in complex environments and optimize positioning performance has become a key issue in improving the performance of wireless positioning systems. Summary of the Invention

[0007] This invention proposes a wireless positioning method based on multi-intelligent reflective surfaces (RIS) collaboration to solve the problem of collaborative positioning of RIS in wireless positioning process and improve the low positioning accuracy of users in complex environments.

[0008] The technical solution of this invention is as follows:

[0009] A wireless positioning method based on multi-intelligent reflective surface cooperation, such as Figure 1 As shown, the established positioning model includes a... The system comprises a base station with one antenna, Q intelligent reflective surfaces (RIS), and a user equipment to be located. The locations of the base station and the RIS are known. The base station can control the updating of the RIS's relevant reflection coefficients and the reflection coefficient codebook. Each RIS has a RIS reflection coefficient codebook, and each codeword in the codebook represents a phase setting of the RIS. The wireless positioning method includes:

[0010] S1, base station sent a total of Q snapshots of the positioning reference signal are sent to the user equipment, and Q RIS reflect the positioning reference signal back to the user equipment. A RIS reflection coefficient codebook is defined, including... Each codeword corresponds to a codeword in the codebook. The RIS changes its reflection unit coefficients sequentially according to the reflection coefficient codebook to achieve scanning of the user to be located.

[0011] S2. The user equipment to be located receives the positioning reference signal and processes the positioning reference signal. The processing method is to obtain the set of received signals when the RIS scans the entire codebook and feed the processed signal back to the base station.

[0012] S3. After receiving the feedback signal, the base station uses the information of multiple RIS reflection coefficient codebooks and combines the singular value decomposition (SVD) algorithm to construct a relevant parameter measurement matrix. The path delay between the base station and the user equipment and between each base station, RIS and the user equipment is solved by the measurement matrix.

[0013] S4. Based on the obtained path delay estimation results, the base station uses the path energy ranking method to match the estimated delay parameters with the paths of the base station-user equipment and each base station-RIS-user equipment.

[0014] S5. The base station uses geometric relationships to solve for user location information by considering the time delays of each path and the positional relationships of the RIS.

[0015] Furthermore, in S1, it is defined that within a snapshot, the positioning reference signal transmitted by the base station contains... Individual with OFDM symbols for subcarriers, of which The number of OFDM symbols. Let be the total number of subcarriers, then in the m-th snapshot... Within the OFDM symbol period, the base station transmits the signal in the 1st... The positioning reference signal on each subcarrier can be represented as:

[0016] ,

[0017] in, In the m-th snapshot, the first... The OFDM symbol in the first The positioning reference signal is transmitted on each subcarrier; and the positioning reference signal is required to satisfy the following within one snapshot: , For one The identity matrix;

[0018] The number of reflection units in a RIS is defined as follows: All RIS are uniform linear arrays, and the reflection coefficient codebook of the q-th RIS is... Each codebook contains Each code word, and Each codeword represents a phase setting of the RIS, expressed as:

[0019] ,

[0020] in, This represents the m-th codeword of the q-th RIS;

[0021] The design method of the RIS reflection coefficient codebook is as follows: First, construct a set of preset angle cosine values. And generate the direction vector matrix accordingly. Its elements satisfy:

[0022] ,

[0023] in, The imaginary unit satisfies ; The interval between the reflective units; The carrier wavelength; The value is ; The value is ;

[0024] Then, based on the least squares criterion, solve the equation shown below to focus the reflected signal energy in the target direction:

[0025] ,

[0026] in, This is the steering vector for the AoA link between the base station and the RIS; For one The identity matrix;

[0027] Finally, the elements in the codebook are normalized to generate a set of codewords that satisfy the constant modulus constraint, which serves as the RIS reflection coefficient codebook. The RIS can determine the location of the user equipment by scanning the reflection coefficient codebook and adjusting the direction of the reflected beam.

[0028] Furthermore, in S2, the user in the... During the first snapshot, i.e., during the RIS scan... When the first codeword is received, the first... The OFDM symbol in the first Signals on each subcarrier It is expressed as follows:

[0029] ,

[0030] ,

[0031] in, In the scan of the first When the first character is typed, the first... Channel response on each subcarrier With zero mean and variance Additive white Gaussian noise, ; , and These are the channel responses between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively:

[0032] ,

[0033] ,

[0034] ,

[0035] in, This refers to the bandwidth of the OFDM signal. For subcarrier indexing; These are the large-scale path gains between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the time delays between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the Rice factors for the RIS and user equipment links, and the base station and user equipment links, respectively. These are respectively the base station and RIS, the RIS and user equipment, and the base station and user equipment AoD; For the AoA of the base station and RIS link; and Indicates the guide vector; These represent small-scale fading in the links between the RIS and user equipment, and between the base station and user equipment, respectively.

[0036] User equipment in The set of all received signals on each subcarrier can be represented as:

[0037] ,

[0038] in, ;

[0039] right Perform the following processing:

[0040] ,

[0041] The user equipment can then obtain all the data when the RIS scans the entire RIS reflection coefficient codebook. The set of:

[0042] ,

[0043] User equipment will Feedback is sent back to the base station.

[0044] Furthermore, in S3, let ,right Perform SVD decomposition, that is:

[0045] ,

[0046] in, for The left singular vector matrix; for The right singular vector matrix; for The singular value matrix, It is a diagonal matrix whose main diagonal elements are arranged in descending order. eigenvalues;

[0047] make Combination Definition, for Perform the following processing to obtain the parameter measurement matrix. :

[0048] ,

[0049] exist and Dimensional General Reconstructed as:

[0050] ;

[0051] in, It is a coefficient matrix; The reconstructed noise signal;

[0052] Since the locations of the base station and RIS are known... It can be obtained directly from the location information, so we only need to find the solution. The following optimization problem can be solved. And define the estimated value obtained by solving the optimization problem as :

[0053] ,

[0054] in, , ; and The mathematical expression is ;

[0055] exist and Dimensional General Reconstructed as:

[0056] ,

[0057] in, For the measurement matrix of relevant parameters; It is a coefficient matrix; and The mathematical expression is ;

[0058] The Root Music algorithm is used to solve for the time delay parameters of each path: the correlation matrix is ​​calculated. Eigenvalue decomposition and sorting are performed to obtain the noise subspace. Find the roots of the following polynomial:

[0059] ,

[0060] in, The mathematical expression is ;

[0061] because Choose to satisfy And closest to the unit circle root This allows us to obtain the estimated time delay parameters for each path. .

[0062] Furthermore, in S4, after obtaining the estimated value... Afterwards, Substitution We can obtain:

[0063] ,

[0064] in, They represent in and The path energy from base station to user equipment and from each base station to RIS to user equipment in terms of dimensions;

[0065] For and By sorting the path energies along the dimensions, a sequence related to the path energies between base stations and user equipment, as well as between each base station, RIS, and user equipment, can be obtained. This is used to match the delay parameters corresponding to different paths;

[0066] Similarly, substitute the estimated time delay parameter values ​​into From this, we can obtain:

[0067] ,

[0068] in, ; Each represents in each Path energy in the dimension;

[0069] For each After sorting the path energy in the dimension and... The sorting results correspond one-to-one, enabling the matching of the estimated delay parameter value with different paths, ultimately obtaining the path delay after matching. .

[0070] Furthermore, in S5, the location of the base station is set as... The position of the q-th RIS is Then the following geometric relationship holds:

[0071] ,

[0072] in, denoted as the coordinates of the user equipment location; c represents the propagation speed of electromagnetic waves in free space.

[0073] make The following linear relationship can be obtained:

[0074] ,

[0075] The above equation can be solved using the least squares method to obtain... This means obtaining the user's location information.

[0076] The beneficial effects of this invention are that multiple RISs work simultaneously throughout the positioning process, significantly improving resource utilization. Furthermore, by employing a reasonable codebook design at the RIS level and dynamically adjusting the parameters of the reflection units during positioning, the overall system achieves optimal performance, greatly enhancing the system's positioning capabilities. Attached Figure Description

[0077] Figure 1 This is a schematic diagram of the system composition of the present invention.

[0078] Figure 2 This is a block diagram of the positioning reference signal frame structure of the present invention.

[0079] Figure 3 This is a schematic diagram comparing the ToA estimation performance of different estimation schemes in this invention.

[0080] Figure 4 This is a schematic diagram comparing the positioning performance of different estimation schemes of the present invention. Detailed Implementation

[0081] The present invention will now be described in detail with reference to the accompanying drawings.

[0082] Set the number of antennas for the base station to be The number of reflection units in RIS is And all are uniform linear arrays; define the first The reflection coefficient codebook of each RIS is Each codebook contains Each code word, and Each codeword represents a phase setting of the RIS, expressed as:

[0083] ,

[0084] The RIS codebook design scheme is characterized by including: firstly constructing a set of preset angle cosine values. And generate the direction vector matrix accordingly. Its elements satisfy:

[0085] ,

[0086] in, The interval between the reflective units; The carrier wavelength;

[0087] Then, based on the least squares criterion, solve the equation shown below to focus the reflected signal energy in the target direction:

[0088] ,

[0089] Finally, the elements in the codebook are subjected to modulus normalization to generate a set of codewords that satisfy the constant modulus constraint, which serves as the phase configuration codebook for the RIS.

[0090] During the positioning process, such as Figure 2 The frame structure shown is configured to allow the base station to transmit a total of [number] frames. The positioning reference signal for each snapshot, each snapshot corresponding to a codeword in the codebook, i.e., a phase setting of RIS:

[0091] ,

[0092] RIS determines the location of user equipment by scanning the reflection coefficient codebook and adjusting the direction of the reflected beam.

[0093] Within a snapshot, the positioning reference signal transmitted by the base station contains... A person with OFDM symbols of subcarriers; then in the m-th snapshot Within one OFDM symbol period, the positioning reference signal on the k-th subcarrier can be expressed as:

[0094] ,

[0095] in, Indicates the first The OFDM symbol in the first The positioning reference signal is transmitted on each subcarrier; and the positioning reference signal is required to satisfy the following within one snapshot: .

[0096] definition , and The channel responses between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment are respectively represented as follows:

[0097] ,

[0098] ,

[0099] ,

[0100] in, This refers to the bandwidth of the OFDM signal. For subcarrier indexing; These are the large-scale path gains between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the time delays between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the Rice factors for the RIS and user equipment links, and the base station and user equipment links, respectively. These are respectively the base station and RIS, the RIS and user equipment, and the base station and user equipment AoD; For the AoA of the base station and RIS link; and Indicates the guide vector; These represent small-scale fading in the links between the RIS and user equipment, and between the base station and user equipment, respectively.

[0101] User equipment in The set of all received signals on each subcarrier can be represented as:

[0102] ,

[0103] in, ;

[0104] right Perform the following processing:

[0105] ,

[0106] The user equipment can then obtain all the data when the RIS scans the entire RIS reflection coefficient codebook. The set of:

[0107] ,

[0108] User equipment will Feedback was sent back to the base station;

[0109] make ,right Perform SVD decomposition, that is:

[0110] ,

[0111] in, for The left singular vector matrix; for The right singular vector matrix; for The singular value matrix, It is a diagonal matrix whose main diagonal elements are arranged in descending order. eigenvalues;

[0112] make , combined Definition, for Perform the following processing to obtain the parameter measurement matrix. :

[0113] ,

[0114] exist and Dimensional General Reconstructed as:

[0115] ;

[0116] in, It is a coefficient matrix; The reconstructed noise signal;

[0117] Since the locations of the base station and RIS are known... It can be obtained directly from the location information, so we only need to find the solution. The following optimization problem can be solved. And define the estimated value obtained by solving the optimization problem as :

[0118] ,

[0119] in, , ; and The mathematical expression is ;

[0120] exist and Dimensional General Reconstructed as:

[0121] ,

[0122] in, For the measurement matrix of relevant parameters; It is a coefficient matrix; and The mathematical expression is ;

[0123] The Root Music algorithm is used to solve for the time delay parameters of each path: the correlation matrix is ​​calculated. Eigenvalue decomposition and sorting are performed to obtain the noise subspace. Find the roots of the following polynomial:

[0124] ,

[0125] in, The mathematical expression is ;

[0126] because Choose to satisfy And closest to the unit circle root This allows us to obtain the estimated time delay parameters for each path. ;

[0127] After obtaining the estimated time delay parameters for each path, it is difficult to distinguish the estimated channel parameters of multiple reflection paths from those of the direct path. Therefore, it is necessary to match the estimated values ​​with each path one by one.

[0128] In obtaining the estimated value Afterwards, Substitution We can obtain:

[0129] ,

[0130] in, They represent in and The path energy from base station to user equipment and from each base station to RIS to user equipment in terms of dimensions;

[0131] For and By sorting the path energies along the dimensions, a sequence related to the path energies between base stations and user equipment, as well as between each base station, RIS, and user equipment, can be obtained. This is used to match the delay parameters corresponding to different paths;

[0132] Similarly, substitute the estimated time delay parameter values ​​into From this, we can obtain:

[0133] ,

[0134] in, ; Each represents in each Path energy in the dimension;

[0135] For each After sorting the path energy in the dimension and... The sorting results correspond one-to-one, enabling the matching of the estimated delay parameter value with different paths, ultimately obtaining the path delay after matching. ;

[0136] Set the location of the base station as The position of the q-th RIS is Then the following geometric relationship holds.

[0137] ,

[0138] in, denoted as the coordinates of the user equipment location; c represents the propagation speed of electromagnetic waves in free space.

[0139] make The following linear relationship can be obtained:

[0140] ,

[0141] The above equation can be solved using the least squares method to obtain... This means obtaining the user's location information.

[0142] Simulation example:

[0143] The simulation parameters are set as follows: The location of the base station is... its tangent direction The location of the user equipment is The position of RIS is , The tangential direction of the RIS reflector unit is: Number of base station antennas Number of RIS reflection units The number of codewords in its reflection coefficient codebook ;

[0144] Considering the path loss coefficient between the base station and the user equipment Path loss coefficient between reflection paths Rice factor of the links between base stations and user equipment, and between RIS and user equipment. ;

[0145] Define signal-to-noise ratio ;

[0146] from Figure 3 It can be seen that the delay estimation method utilizing all codebook information proposed in this invention outperforms the energy detection-based method. In particular, this method can still accurately estimate path delays even under low signal-to-noise ratio (SNR) conditions. The position estimation performance under different estimation schemes and SNRs is shown below. Figure 4 As shown in the figure, the positioning error is represented by the root mean square. It can be seen that the proposed method significantly improves the position estimation performance under low signal-to-noise ratio conditions.

Claims

1. A wireless positioning method based on multi-intelligent reflective surface cooperation, characterized in that, The established positioning model includes a... The system consists of a base station with one antenna, Q smart reflectors (RIS), and a user equipment to be located. The locations of the base station and the RIS are known. The base station can control the update of the RIS's reflection coefficients and the update of the reflection coefficient codebook. Each RIS has a RIS reflection coefficient codebook, and each codeword in the codebook represents a phase setting of the RIS. The wireless positioning method includes: S1, base station sent a total of Q snapshots of the positioning reference signal are sent to the user equipment, and Q RIS reflect the positioning reference signal back to the user equipment. A RIS reflection coefficient codebook is defined, including... Each codeword corresponds to a codeword in the codebook. The RIS changes its reflection unit coefficients sequentially according to the reflection coefficient codebook to achieve scanning of the user to be located. S2. The user equipment to be located receives the positioning reference signal and processes the positioning reference signal. The processing method is to obtain the set of received signals when the RIS scans the entire codebook and feed the processed signal back to the base station. S3. After receiving the feedback signal, the base station uses the information of multiple RIS reflection coefficient codebooks and combines the singular value decomposition (SVD) algorithm to construct a relevant parameter measurement matrix. The path delay between the base station and the user equipment and between each base station, RIS and the user equipment is solved by the measurement matrix. S4. Based on the obtained path delay estimation results, the base station uses the path energy ranking method to match the estimated delay parameters with the paths of the base station-user equipment and each base station-RIS-user equipment. S5. The base station uses geometric relationships to solve for user location information by considering the time delays of each path and the positional relationships of the RIS.

2. The wireless positioning method based on multi-intelligent reflective surface cooperation according to claim 1, characterized in that, In S1, the positioning reference signal sent by the base station within a snapshot is defined as follows: Individual with OFDM symbols for subcarriers, of which The number of OFDM symbols. Let be the total number of subcarriers, then in the m-th snapshot... Within one OFDM symbol period, the positioning reference signal on the k-th subcarrier is represented as: ， ， in, In the m-th snapshot, the first... The OFDM symbol in the first The positioning reference signal is transmitted on each subcarrier; and the positioning reference signal is required to satisfy the following within one snapshot: , For one The identity matrix; The number of reflection units in a RIS is defined as follows: All RIS are uniform linear arrays, and the reflection coefficient codebook of the q-th RIS is... Each codebook contains Each code word, and Each codeword represents a phase setting of the RIS, expressed as: ， in, This represents the m-th codeword of the q-th RIS; The design method of the RIS reflection coefficient codebook is as follows: First, construct a set of preset angle cosine values. And generate the direction vector matrix accordingly. Its elements satisfy: ， in, The imaginary unit satisfies ; The interval between the reflective units; The carrier wavelength; The value is ; The value is ; Then, based on the least squares criterion, solve the equation shown below to focus the reflected signal energy in the target direction: ， in, This is the steering vector for the AoA link between the base station and the RIS; For one The identity matrix; Finally, the elements in the codebook are normalized to generate a set of codewords that satisfy the constant modulus constraint, which serves as the RIS reflection coefficient codebook. The RIS determines the location of the user equipment by scanning the reflection coefficient codebook and adjusting the direction of the reflected beam.

3. The wireless positioning method based on multi-intelligent reflective surface cooperation according to claim 2, characterized in that, In S2, the user is in the... During the first snapshot, i.e., during the RIS scan... When the first codeword is received, the first... The OFDM symbol in the first Signals on each subcarrier It is expressed as follows: ， ， in, In the scan of the first When the first character is typed, the first... Channel response on each subcarrier With zero mean and variance Additive white Gaussian noise, ; , and These are the channel responses between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively: ， ， ， in, This refers to the bandwidth of the OFDM signal. For subcarrier indexing; These are the large-scale path gains between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the time delays between the base station and the RIS, between the RIS and the user equipment, and between the base station and the user equipment, respectively. These are the Rice factors for the RIS and user equipment links, and the base station and user equipment links, respectively. These are respectively the base station and RIS, the RIS and user equipment, and the base station and user equipment AoD; For the AoA of the base station and RIS link; and Indicates the guide vector; These represent small-scale fading in the links between the RIS and user equipment, and between the base station and user equipment, respectively. User equipment in The set of all received signals on each subcarrier is represented as: ， in, ; right Perform the following processing: ， The user equipment then obtains all the data from when the RIS scanned the entire RIS reflection coefficient codebook. The set of: ， User equipment will Feedback is sent back to the base station.

4. The wireless positioning method based on multi-intelligent reflective surface cooperation according to claim 3, characterized in that, In S3, let ,right Perform SVD decomposition, that is: ， in, for The left singular vector matrix; for The right singular vector matrix; for The singular value matrix, It is a diagonal matrix whose main diagonal elements are arranged in descending order. eigenvalues; make , combined Definition, for Perform the following processing to obtain the parameter measurement matrix. : ， exist and Dimensional General Reconstructed as: ； in, It is a coefficient matrix; The reconstructed noise signal; Since the locations of the base station and RIS are known... It can be obtained directly from the location information, so we only need to find the solution. Solve the following optimization problem And define the estimated value obtained by solving the optimization problem as : ， in, , ; and The mathematical expression is ; exist and Dimensional General Reconstructed as: ， in, For the measurement matrix of relevant parameters; It is a coefficient matrix; and The mathematical expression is ; The Root Music algorithm is used to solve for the time delay parameters of each path: the correlation matrix is ​​calculated. Eigenvalue decomposition and sorting are performed to obtain the noise subspace. Find the roots of the following polynomial: ， in, The mathematical expression is ; because Choose to satisfy And closest to the unit circle root The estimated time delay parameters for each path are obtained. .

5. A wireless positioning method based on multi-intelligent reflective surface cooperation according to claim 4, characterized in that, In S4, after obtaining the estimated value Afterwards, Substitution ,have to: ， in, They represent in and The path energy from base station to user equipment and from each base station to RIS to user equipment in terms of dimensions; For and The path energy is sorted along the dimensions to obtain a sequence related to the path energy between base stations and user equipment, as well as between each base station, RIS, and user equipment. This is used to match the delay parameters corresponding to different paths; Similarly, substitute the estimated time delay parameter values ​​into In the middle, we get: ， in, ; Each represents in each Path energy in the dimension; For each After sorting the path energy in the dimension and... The sorting results correspond one-to-one, that is, the estimated delay parameter value is matched with different paths, and finally the path delay after matching is obtained. .

6. The wireless positioning method based on multi-intelligent reflective surface cooperation according to claim 5, characterized in that, In S5, the location of the base station is set as The position of the q-th RIS is Then the following geometric relationship holds: ， in, denoted as the coordinates of the user equipment location; c represents the propagation speed of electromagnetic waves in free space. make The following linear relationship is obtained: ， Solving the above equation using the least squares method yields the following results. This means obtaining the user's location information.

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