A passive positioning system based on reconfigurable intelligent surface and a positioning accuracy optimization method

Abstract

The application discloses a passive positioning system based on a reconfigurable intelligent surface and a positioning precision optimization method. The system can use an additional RIS as a positioning reference point on the basis that there is a line-of-sight link between a target and a reconnaissance station, realize passive cross positioning of the detected target, and thus improve positioning precision. In a special scene (for example, a dense city scene or a mountain pass scene) in which the line-of-sight link between the reconnaissance station and the detected target is blocked, multiple RISs form multiple cascaded links, cross positioning of the detected target is realized, the positioning effect of the system on the target is ensured, and the applicability and stability of the system are enhanced. The precision optimization method maximizes SNR by optimizing the position and phase shift of the RIS in the system, so that the purpose of improving positioning precision is achieved.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication and passive positioning technology, specifically relating to a passive positioning system based on a reconfigurable smart surface and a method for optimizing positioning accuracy. Background Technology

[0002] Reconfigurable Intelligent Surfaces (RIS) are a novel wireless communication technology that requires no changes to the wireless device or network; instead, RIS are added to the transmission path to control and optimize signal propagation. RIS consists of multiple passive reflective elements, each composed of passive components such as capacitors and resistors. These passive reflective elements have the ability to individually reflect the original transmitted signal, offering advantages such as low power consumption and low cost. By controlling their amplitude or phase, these elements can perform various functions, such as signal amplification, attenuation, deflection, focusing, and scattering.

[0003] Passive positioning can be categorized based on its different working principles into direction-finding cross-location methods based on angle of arrival, time-difference-of-arrival (TDOA) positioning methods based on signal arrival at the observation station, and positioning methods based on the received signal strength. In applications of angle-of-arrival passive positioning, the noise measurement equation is highly nonlinear with respect to the unknown target position. Currently, various passive positioning schemes exist. However, despite the progress made in the field of passive positioning, significant challenges remain when dealing with complex environments (such as densely built-up areas, mountainous terrain, or scenarios with severe multipath effects).

[0004] 1) In traditional passive positioning systems, when there is a line-of-sight link between the target and the reconnaissance station, the system mainly relies on a single line-of-sight link for signal measurement and positioning. This single signal path lacks sufficient spatial information, making it impossible to form effective cross-location and limiting the improvement of positioning accuracy, especially in tasks with high requirements for high-precision positioning.

[0005] 2) In complex environments, the signal quality of traditional passive positioning systems is easily affected by factors such as path loss, multipath interference, and environmental noise. These factors result in a low signal-to-noise ratio (SNR) when the signal reaches the reconnaissance station, thus limiting the system's positioning accuracy. Due to the lack of dynamic channel optimization methods, the system struggles to maintain stable high-precision positioning performance in different scenarios.

[0006] 3) In dense urban environments or complex environments such as mountainous areas, the line-of-sight link between the target and the reconnaissance station is often easily obstructed, making it difficult for the signal to reach the reconnaissance station directly, thus preventing the system from acquiring effective measurement information. These obstruction and signal loss problems in special environments seriously affect the system's coverage capability and the reliability of target positioning. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention provides a passive positioning system based on a reconfigurable smart surface and a method for optimizing positioning accuracy.

[0008] The technical problem to be solved by this invention is achieved through the following technical solution:

[0009] This invention provides a passive positioning system based on a reconfigurable smart surface, comprising: a reconnaissance station, N RIS modules, and a detection target, wherein there are links between the detection target and each RIS module, between each RIS module and the reconnaissance station, and between the detection target and the reconnaissance station;

[0010] Each RIS is used to reflect the signal emitted by the detected target to the reconnaissance station; the reconnaissance station is used to receive the signal directly emitted by the detected target and the signals reflected by the N RIS, and to locate the detected target based on the signal directly emitted by the detected target and the signals reflected by the N RIS, or the reconnaissance station is used to receive the signals reflected by the N RIS and to locate the detected target based on the signals reflected by the N RIS.

[0011] The present invention also provides a positioning accuracy optimization method applied to the above-mentioned system, wherein each RIS has a physical location, and each RIS includes multiple arrayed reflective elements, each reflective element having a phase shift, and the method includes:

[0012] S1. Obtain the physical location range, phase shift range, preset location interval, and preset phase shift interval for each RIS; each range consists of a lower limit and an upper limit.

[0013] S2. For each RIS, each time a physical position is taken from the physical position range corresponding to the RIS according to the preset position interval, and a phase shift is taken from the phase shift range corresponding to the RIS according to the preset phase shift interval. Then, based on the physical positions and phase shifts of the N RIS taken this time, a SNR corresponding to the system is calculated. In this way, until the physical position ranges and phase shift ranges of the N RIS are traversed, multiple SNRs are obtained.

[0014] S3. Select the largest SNR from the plurality of SNRs, and use the physical position and phase shift of the N RIS corresponding to the largest SNR as the optimal configuration parameters;

[0015] S4. Deploy the N RIS in the system according to the optimal configuration parameters to locate the detected target, wherein the positioning error of the reconnaissance station for the detected target is negatively correlated with the SNR of the system.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention proposes a passive positioning system based on reconfigurable smart surfaces and a method for optimizing positioning accuracy. By introducing a Reflection Array (RIS) into the passive positioning system, a cascaded link (equivalent to adding a reconnaissance station) is added under line-of-sight conditions, enabling cross-location of the detected target and improving the system's positioning accuracy. Furthermore, this invention uses Spot Reflection Rate (SNR) as a metric for positioning accuracy and maximizes SNR by optimizing the phase shift and physical location settings of the RIS, further enhancing positioning accuracy. Finally, in complex special environments, this invention achieves cascaded reflection through the deployment of multiple RIS, enabling target location even when the line-of-sight link between the reconnaissance station and the detected target is blocked, thereby enhancing the system's applicability and stability.

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0019] Figure 1 This is a cross-positioning diagram of a passive positioning system based on a reconfigurable smart surface, provided in an embodiment of the present invention, applied in a general scenario.

[0020] Figure 2 This is a cross-positioning diagram of a passive positioning system based on a reconfigurable smart surface, provided in an embodiment of the present invention, applied in a special scenario.

[0021] Figure 3 This is a flowchart illustrating a positioning accuracy optimization method provided in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0023] First, addressing the limitation of positioning accuracy in complex environments by traditional passive positioning systems, this invention introduces a Reference Array (RIS) into the passive positioning system. Based on the line-of-sight link between the target and the reconnaissance station, cross-positioning is achieved using cascaded links provided by the RIS. In this case, the RIS acts as a new reconnaissance station, effectively increasing the number of positioning reference points and improving the system's positioning capability. Second, the increased number of reconnaissance stations improves positioning accuracy. Furthermore, this invention designs a positioning accuracy optimization method using SNR (Spot Reduction Ratio) to measure positioning accuracy. By optimizing the position and phase shift of the RIS, the SNR is maximized, thereby improving positioning accuracy. Finally, this invention proposes enhancing the system's applicability in special scenarios (such as dense urban environments or mountainous terrain). In these special scenarios, where the line-of-sight link between the reconnaissance station and the detected target may be blocked, this invention deploys multiple RIS to form multiple cascaded links, achieving cross-positioning, ensuring the system's target positioning effectiveness, and overcoming the problem of limited line-of-sight conditions in complex environments.

[0024] First, this invention provides a passive positioning system based on a reconfigurable smart surface, comprising: a reconnaissance station, N RIS modules, and a detection target. Links exist between the detection target and each RIS module, between each RIS module and the reconnaissance station, and between the detection target and the reconnaissance station. Each RIS module reflects a signal emitted by the detection target back to the reconnaissance station. The reconnaissance station receives the signal directly emitted by the detection target and the signals reflected by the N RIS modules, and performs target positioning based on these signals; alternatively, the reconnaissance station receives the signals reflected by the N RIS modules and performs target positioning based on these signals. For example, when the reconnaissance station positions the detection target, it can employ an existing cross-positioning method; the specific principles of the cross-positioning method are not elaborated here.

[0025] In some embodiments, when N is a positive integer greater than or equal to 1, the reconnaissance station receives the signal directly transmitted by the target and the signals reflected by N RIS (Radio Router Reflectors), and locates the target based on these signals. In this case, the system can be applied to general scenarios where the link (i.e., the line-of-sight link) between the target and the reconnaissance station is not blocked, thereby improving positioning accuracy. Specifically, the signal transmitted by the target has two paths: one directly to the reconnaissance station, and the other via RIS reflection. The reconnaissance station achieves cross-location by receiving the direct signal from the target and the RIS reflection, thereby accurately determining the target's position.

[0026] In some embodiments, N is a positive integer greater than or equal to 2; the reconnaissance station receives signals reflected by N RIS and locates the target based on the signals reflected by the N RIS. In this case, the system can be applied to special scenarios where the link (i.e., line-of-sight link) between the target and the reconnaissance station is blocked (e.g., dense urban scenarios or mountainous passage scenarios). In such scenarios, due to obstructions from buildings or mountains, a line of sight cannot be maintained between the reconnaissance station and the target, making it difficult to achieve effective localization using traditional direct-transmission radiation source localization methods. Therefore, multiple RIS are introduced, which reflect the signals emitted by the target, enabling the signals to reach the reconnaissance station. Specifically, the signal emitted by the target is reflected by multiple RIS and ultimately received by the reconnaissance station. The reconnaissance station achieves cross-localization by receiving signals reflected from multiple RIS, thereby accurately determining the target's location.

[0027] In this invention, the positioning error of the reconnaissance station in detecting the target is negatively correlated with the system's SNR. Specifically, in this system, each RIS has a physical location, and each RIS includes multiple arrayed reflective elements, each with a phase shift. For example, the phase shifts of the reflective elements in each RIS are identical. The physical location of each RIS is the physical location coordinate of the central reflective element of that RIS, and these physical location coordinates refer to the position coordinates in a coordinate system shared by the RIS, the reconnaissance station, and the detected target. The system's SNR is related to the phase shift of the reflective elements in each RIS and the physical location of each RIS. By adjusting the physical location of the RIS and the phase shift of the reflective elements in the RIS, the SNR received by the reconnaissance station can be maximized, thereby further improving the positioning accuracy. Specifically, in the optimization calculation process, the specific optimization problem can be formulated as follows:

[0028]

[0029]

[0030] The RIS consists of M reflecting units, m ∈ {1, ..., M}, and the phase shift of each reflecting unit is controlled by b bits. Therefore, the phase shift of each reflecting unit can be tuned to 2^n. b One of the different perspectives. The total time slot T represents the number of time slots into which the entire communication process is divided, indicating that the system divides the entire communication period into multiple small time units for processing. For each time slot t, its value ranges from t∈{1,…,T}. The phase shift matrix of the i-th RIS in the t-th time slot is represented as... in It is the phase shift of the m-th reflecting element of the i-th RIS, i∈{1,…,I}, where I represents the total number of RIS in the system, for example, I=2. The set of discrete values ​​is: (That is, the phase shift of each reflecting element is selected from this set), where, λ(t) represents the signal-to-noise ratio of the system in time slot t. p1 and p2 represent the three-dimensional coordinate vectors of the physical locations of the first RIS and the second RIS, respectively. The set of discrete values ​​for the physical location coordinates of each RIS is as follows: S represents the number of intervals, and 0 represents the coverage radius of the detected target (i.e., the physical location coordinates of each RIS are taken from this set). In specific optimization, after calculating the SNR value in each time slot, the RIS controller dynamically adjusts the physical location of the RIS and configures the phase shift of each reflection unit to obtain a set of configuration parameters. Then, the SNR value of the system under the configuration parameters in the next time slot is calculated. After that, the physical location of the RIS is dynamically adjusted and the phase shift of each reflection unit is configured to obtain another set of configuration parameters. This process is repeated multiple times to obtain a set of configuration parameters that maximizes the system's SNR. This set of configuration parameters is the optimal location coordinates and optimal phase shift configuration of the RIS. At this point, the target location obtained by the reconnaissance station through cross-positioning is the most accurate, greatly improving the positioning accuracy and reliability.

[0031] To characterize the impact of SNR on positioning accuracy, a Cramer-Rao Lower Bound (CRLB) for array angle estimation is introduced: Where λ is the carrier wavelength and L is the effective aperture of the reconnaissance station's antenna array. According to this formula, the azimuth estimation variance... The angle measurement is inversely proportional to the system's λ(t) (i.e., the overall SNR); the larger the SNR, the more accurate the angle measurement. Furthermore, by incorporating multi-slot observations into the Fisher information matrix and calculating the inverse of its trajectory, a lower bound for the two-dimensional position estimation can be obtained: Here, the constant c1 depends on the array geometry and scene layout, but is independent of SNR. This equation further illustrates that the higher the cumulative SNR, the higher the mean square error (MSE) of the target position. pos The smaller the theoretical lower limit, the better. As can be seen from the above two equations, the positioning error MSE... pos It is strictly inversely proportional to λ(t). Therefore, as long as the SNR is maximized by optimizing the physical location and phase shift matrix of the RIS in the system design, it is equivalent to minimizing the lower bound of the positioning error, thereby effectively improving the positioning accuracy of the system.

[0032] For example, when N is 1, the expression for the system's SNR in the t-th time slot is as follows:

[0033]

[0034] Where λ(t) represents the SNR of the system in the t-th time slot, the value of t ranges from t∈{1,…,T}, T represents the total number of time slots, P represents the transmission power of the detected target, and σ 2 H represents noise power. R,B H represents the channel gain between the reconnaissance station and the RIS, and H represents the conjugate transpose symbol. R,v (t) represents the channel gain between RIS and the detected target, h B,v (t) represents the channel gain between the detected target and the reconnaissance station, θ t This represents the angle between the detected target and the RIS relative to the direction between the detected target and the reconnaissance station. ρ is the median of the average path gain at a reference distance of 1 meter, and K... R,B It is the Rician factor, where α is the path loss exponent, and d R,B Indicates the distance between the reconnaissance station and RIS. For the Loss component, The array response for the channel gain between the reconnaissance station and the RIS, f c For the carrier frequency, τ R,B This represents the link delay from the reconnaissance station to the RIS, where j represents an imaginary unit. Assume the physical coordinates of the reconnaissance station are (x...). B ,y B ,z B The physical location coordinates of RIS are (x R ,y R ,z R The physical location coordinates of the detected target v are (x... v (t),y v (t),z v (t)), the distance between the reconnaissance station and RIS is determined by (x) B ,y B ,z B ) and (x R ,y R ,z R It can be determined.

[0035] Channel gain h between the detected target and the reconnaissance station B,v The expression for (t) is as follows:

[0036]

[0037] Where, τ B,v (t) represents the link delay between the reconnaissance station and the target v, f m (t) represents the Doppler frequency shift generated when the detected target v moves relative to the reconnaissance station. d B,v ((t) represents the distance between the reconnaissance station and the target v.

[0038] For example, when N is 2 and the link between the detected target and the reconnaissance station is not blocked, the expression for the system's SNR in the t-th time slot is as follows:

[0039]

[0040] in, This represents the channel gain between the reconnaissance station and the first RIS, where H represents the conjugate transpose symbol. This represents the channel gain between the first RIS and the detected target. This indicates the channel gain between the reconnaissance station and the second RIS. θ represents the channel gain between the second RIS and the detected target. (1)t θ represents the angle between the detected target and the first RIS relative to the direction between the detected target and the reconnaissance station. (2)t The angle between the detected target and the second RIS relative to the direction between the detected target and the reconnaissance station.

[0041] Channel gain between the reconnaissance station and the first RIS The expression is as follows:

[0042]

[0043] Where α is the path loss exponent. This indicates the distance between the reconnaissance station and the RIS above. For LOS components, For the channel gain array response between the reconnaissance station and the first RIS, This indicates the latency of the link from the reconnaissance station to the first RIS.

[0044] Channel gain between the first RIS and the detected target The expression is as follows:

[0045]

[0046] in, The array response representing the channel gain between the first RIS and the detected target v. This represents the latency of the link from the first RIS to the detected target v. This indicates the Doppler frequency shift generated when the detected target v moves relative to the first RIS. K represents the distance between the first RIS and the detected target v. R,v It is the Rician factor.

[0047] Channel gain between the reconnaissance station and the second RIS The expression is as follows:

[0048]

[0049] in, This indicates the distance between the reconnaissance station and the second RIS. For LOS components, This indicates the latency of the link from the reconnaissance station to the second RIS.

[0050] Channel gain between the second RIS and the detected target The expression is as follows:

[0051]

[0052] in, This represents the latency of the link from the second RIS to the detected target v. This indicates the Doppler frequency shift generated when the detected target v moves relative to the second RIS. This represents the distance between the second RIS and the detected target v.

[0053] For example, when N is 2 and the link between the target and the reconnaissance station is blocked, the expression for the system's SNR in the t-th time slot is as follows:

[0054]

[0055] For example, Figure 1 This is a schematic diagram of a cross-positioning system based on a reconfigurable smart surface, applied in general scenarios. For example... Figure 1 As shown, in this scenario, the reconnaissance station on the left maintains a line-of-sight connection with the detected target on the right (i.e., the link is not blocked), allowing signals to propagate directly from the detected target to the reconnaissance station. To further improve positioning accuracy, two Reflection Arrays (RIS) are introduced to reflect the signals. The signals emitted by the detected target are reflected by the first and second RIS and then transmitted to the reconnaissance station. By receiving these two reflected signals from the RIS and the direct signal, the reconnaissance station can accurately calculate the position of the detected target using a cross-positioning method. During this process, the positions of the RIS and the phase shift configuration of each reflecting unit can be flexibly adjusted as needed to maximize the SNR received by the reconnaissance station, thereby optimizing positioning accuracy. Here, the combined use of two RIS effectively increases the number of positioning reference points, further improving the system's positioning capability.

[0056] For example, Figure 2 This is a schematic diagram of a cross-positioning system based on a reconfigurable smart surface, applied in a special scenario. For example... Figure 2As shown, in this scenario, there are line-of-sight obstructions (such as dense buildings or mountains) between the reconnaissance station and the target, preventing direct signal transmission from the target to the reconnaissance station. In this situation, the RIS (Reflection Array) in the system plays a crucial role. In this specific scenario, even though the line-of-sight connection is blocked, the RIS can still reflect the signal emitted by the target, allowing the signal to be transmitted to the reconnaissance station via the RIS. Through the paths reflected by multiple RIS, the signal received by the reconnaissance station is recovered, thus achieving cross-target localization. This mechanism ensures that the reconnaissance station can accurately locate the target even under complex terrain conditions. During this process, the position of the RIS and the phase shift configuration of each reflecting unit can be optimized according to actual needs to maximize the SNR (Signal NR) of the signal received by the reconnaissance station. Here, the role of the RIS in this specific scenario is to overcome the line-of-sight obstruction problem, ensure signal transmission, and improve positioning accuracy, thereby achieving accurate target localization.

[0057] Secondly, this invention also provides a positioning accuracy optimization method applied to the aforementioned system, in which each RIS has a physical location, and each RIS includes multiple arrayed reflective elements, each reflective element having a phase shift. This method is used to optimize the positioning accuracy of the system by optimizing the physical location and phase shift of each RIS. Figure 3 As shown, the method includes:

[0058] S1. Obtain the physical location range, phase shift range, preset location interval, and preset phase shift interval for each RIS; each range consists of a lower limit and an upper limit.

[0059] Here, the physical location range corresponding to each RIS refers to the range of values ​​for the physical location of that RIS, and the preset location interval corresponding to each RIS refers to the interval between values ​​taken from the physical location range corresponding to that RIS. The phase shift range corresponding to each RIS refers to the range of values ​​for the phase shift of the reflection unit of that RIS, and the preset phase shift interval corresponding to each RIS refers to the interval between values ​​taken from the phase shift range corresponding to that RIS. It should be noted that the physical location range, phase shift range, preset location interval, and preset phase shift interval corresponding to each RIS can be set according to actual needs, and the smaller the preset location interval and preset phase shift interval, the more possible physical locations and phase shifts the RIS can have.

[0060] S2. For each RIS, each time a physical position is taken from the physical position range corresponding to the RIS according to the preset position interval, and a phase shift is taken from the phase shift range corresponding to the RIS according to the preset phase shift interval. Then, based on the physical positions and phase shifts of the N RISs taken this time, a SNR corresponding to the system is calculated. In this way, multiple SNRs are obtained when the physical position ranges and phase shift ranges of the N RISs are traversed.

[0061] In some embodiments, for each RIS, when a value is first taken from the physical location range corresponding to that RIS, and when a value is first taken from the phase shift range corresponding to that RIS, the lower limit of the physical location range can be used as the physical location taken this time, and the lower limit of the phase shift range can be used as the phase shift taken this time. In other embodiments, for each RIS, when a value is first taken from the physical location range corresponding to that RIS, and when a value is first taken from the phase shift range corresponding to that RIS, the sum of the lower limit of the physical location range and a preset position interval can also be used as the physical location taken this time, and the sum of the lower limit of the phase shift range and a preset phase shift interval can be used as the phase shift taken this time.

[0062] S3. Select the largest SNR from multiple SNRs, and use the physical locations and phase shifts of the N RIS corresponding to the largest SNR as the optimal configuration parameters.

[0063] S4. Deploy N RIS in the system according to the optimal configuration parameters to locate the detected target. The positioning error of the reconnaissance station to the detected target is negatively correlated with the SNR of the system.

[0064] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0065] In this specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. While different embodiments may describe certain measures, this does not mean that these measures cannot be combined to produce a good effect.

[0066] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A passive positioning system based on a reconfigurable smart surface, characterized in that, include: The system includes a reconnaissance station, N reconfigurable intelligent surfaces (RIS), and a detection target, wherein there are links between the detection target and each RIS, between each RIS module and the reconnaissance station, and between the detection target and the reconnaissance station. Each RIS is used to reflect the signal emitted by the detected target to the reconnaissance station. When the link between the detected target and the reconnaissance station is not blocked, the reconnaissance station is used to receive the signal directly emitted by the detected target and the signals reflected by the N RIS, and to locate the detected target based on the signal directly emitted by the detected target and the signals reflected by the N RIS. When the link between the detected target and the reconnaissance station is blocked, the reconnaissance station is used to receive the signals reflected by the N RIS and to locate the detected target based on the signals reflected by the N RIS. The positioning error of the reconnaissance station for the detected target is negatively correlated with the SNR of the system; Each RIS has a physical location, and each RIS includes multiple arrayed reflective elements, each reflective element having a phase shift; the SNR of the system is related to the phase shift and the physical location of the RIS; When the link between the detected target and the reconnaissance station is blocked, N is a positive integer greater than or equal to 2. The reconnaissance station is used to receive the signals reflected by the N RIS and to locate the detected target based on the signals reflected by the N RIS. When N is 2, in the Nth... Within each time slot, the SNR of the system is expressed as follows: ； in, Indicates that the system in the first SNR of each time slot, The range of values ​​is , Indicates the total number of time slots. Indicates the transmission power of the detected target. Indicates noise power. This indicates the channel gain between the reconnaissance station and the first RIS. Indicates the conjugate transpose symbol. This represents the channel gain between the first RIS and the detected target. This indicates the channel gain between the reconnaissance station and the second RIS. This represents the channel gain between the second RIS and the detected target. This represents the angle between the detected target and the first RIS relative to the direction between the detected target and the reconnaissance station. The angle between the detected target and the second RIS relative to the direction between the detected target and the reconnaissance station.

2. The system according to claim 1, characterized in that, When the link between the detected target and the reconnaissance station is not blocked, N is a positive integer greater than or equal to 1; the reconnaissance station is used to receive the signal directly transmitted by the detected target and the signals reflected by the N RIS, and to locate the detected target based on the signal directly transmitted by the detected target and the signals reflected by the N RIS.

3. The system according to claim 2, characterized in that, When the link between the detected target and the reconnaissance station is not blocked and N is 1, in the first... Within each time slot, the SNR of the system is expressed as follows: ； in, Indicates that the system in the first SNR of each time slot, The range of values ​​is , Indicates the total number of time slots. This indicates the transmission power of the detected target. Indicates noise power. This indicates the channel gain between the reconnaissance station and the RIS. Indicates the conjugate transpose symbol. This represents the channel gain between the RIS and the detected target. This represents the channel gain between the detected target and the reconnaissance station. This represents the angle between the detected target and the RIS relative to the direction between the detected target and the reconnaissance station.

4. The system according to claim 2, characterized in that, When the link between the detected target and the reconnaissance station is not blocked and N is 2, in the... Within each time slot, the SNR of the system is expressed as follows: ； in, Indicates that the system in the first SNR of each time slot, The range of values ​​is , Indicates the total number of time slots. Indicates the transmission power of the detected target. Indicates noise power. This represents the channel gain between the detected target and the reconnaissance station. This indicates the channel gain between the reconnaissance station and the first RIS. Indicates the conjugate transpose symbol. This represents the channel gain between the first RIS and the detected target. This indicates the channel gain between the reconnaissance station and the second RIS. This represents the channel gain between the second RIS and the detected target. This represents the angle between the detected target and the first RIS relative to the direction between the detected target and the reconnaissance station. The angle between the detected target and the second RIS relative to the direction between the detected target and the reconnaissance station.

5. The system according to claim 1, characterized in that, The phase shift of the reflection unit is the same in each RIS.

6. A method for optimizing positioning accuracy, characterized in that, Applied to the system according to any one of claims 1 to 5, in the system, each RIS has a physical location, and each RIS includes a plurality of arrayed reflective elements, each reflective element having a phase shift, the method comprising: S1. Obtain the physical location range, phase shift range, preset location interval, and preset phase shift interval for each RIS; each range consists of a lower limit and an upper limit. S2. For each RIS, each time a physical position is taken from the physical position range corresponding to the RIS according to the preset position interval, and a phase shift is taken from the phase shift range corresponding to the RIS according to the preset phase shift interval. Then, based on the physical positions and phase shifts of the N RIS taken this time, a SNR corresponding to the system is calculated. In this way, until the physical position ranges and phase shift ranges of the N RIS are traversed, multiple SNRs are obtained. S3. Select the largest SNR from the plurality of SNRs, and use the physical position and phase shift of the N RIS corresponding to the largest SNR as the optimal configuration parameters; S4. Deploy the N RIS in the system according to the optimal configuration parameters to locate the detected target, wherein the positioning error of the reconnaissance station for the detected target is negatively correlated with the SNR of the system.

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