Satellite-based node position sensing method under Mesh network

Abstract

The invention discloses a node position sensing method under a Mesh network based on satellites, and belongs to the technical field of node position sensing, and the method comprises a node position sensing step under the condition that all nodes can receive satellite signals: obtaining an observation equation of the nodes in the Mesh network about a Beidou satellite pseudo-range, and carrying out linear processing and expansion at approximate points to obtain an observation equation of the nodes in the Mesh network; obtaining a pseudo-range error matrix expression; fitting the pseudo-range error matrix expression by using a least square method to obtain an offset at an approximate point, and further obtaining a position coordinate of a node; a node position sensing step under the condition that part of nodes in the controlled blocking domain receive satellite signals: determining a reference node based on the signal receiving condition of the nodes in the controlled blocking domain and the node positions; and obtaining a distance matrix equation from a reference node to an unknown node by using a bilateral bidirectional ranging technology, and performing fitting solution by using a least square method to obtain position coordinates of the unknown node. The method can be suitable for multi-node communication with all nodes being equal in status.

Description

Technical Field

[0001] The present invention relates to the technical field of node location perception in a global navigation satellite system and a Mesh network with a controlled barrier domain, and more particularly to a method for node location perception in a satellite-based Mesh network. Background Art

[0002] In recent years, with the rapid development of wireless communication technology, highly reliable and scalable distributed networks have rapidly become popular and widely used. Mesh networks are also a typical distributed network. In a mesh network, there is no central node, and all nodes have equal status. Due to the wide distribution of nodes, they have high transmission fault tolerance, easy resource sharing, and collaborative work. Currently, mesh networks can adapt to complex environments and are used in self-organizing network communications such as the Internet of Things and the Internet of Vehicles. They can adapt to frequent changes in node location and network topology, effectively improving communication efficiency.

[0003] However, in complex IoT environments, the actions of network nodes need to be scheduled in real time. Furthermore, in some cases, each node must clearly understand its own location and the locations of surrounding nodes to facilitate message transmission and forwarding. Therefore, sensing the location of nodes in mesh networks has become a challenge. BeiDou satellite positioning is a global navigation satellite system independently developed by my country. Under good satellite service conditions, it can locate people and objects on the ground with an accuracy of 5-10 meters, making it a promising solution for mesh network positioning. However, due to the low satellite coverage issues encountered in complex environments, where only some nodes within a controlled isolation domain can receive satellite signals, a node awareness solution within the mesh network that can integrate BeiDou satellites has become a necessity. Double-Side Two-Way Ranging (DS-TWR) is a solution that requires less clock synchronization and can reduce clock skew. It is applicable to round-trip time and can address the location awareness of nodes within a mesh network while maintaining a certain level of accuracy when a reference node is available.

[0004] Currently, there are still some gaps in the design of node location awareness solutions within mesh networks, both domestically and internationally. Taking into account the network characteristics of mesh networks, this invention is based on the good satellite service provided by Beidou satellites, i.e., all nodes within the mesh network can receive satellite signals, and the design of a location awareness solution within the controlled barrier domain of the mesh network under low satellite coverage. This solution guarantees location awareness accuracy to a certain extent, while also providing a foundation for information transmission and forwarding among nodes within the mesh network, thus possessing certain practical application value. Summary of the Invention

[0005] In view of this, the present invention provides a node location perception method in a satellite Mesh network, which is used to at least solve some of the technical problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for sensing node locations in a satellite-based Mesh network, comprising:

[0008] a) Node location awareness steps when all nodes can receive satellite signals:

[0009] Obtain the observation equation of the nodes in the Mesh network regarding the Beidou satellite pseudorange;

[0010] The observation equation is linearized and expanded at the approximate point using Taylor series to obtain the pseudorange error matrix expression of the node;

[0011] The pseudorange error matrix expression is fitted using the least square method to obtain the offset of the node at the approximate point;

[0012] The position coordinates of the node are obtained according to the approximate value and offset at the approximate point;

[0013] b) Node location awareness steps when some nodes in a controlled isolation domain receive satellite signals:

[0014] Based on the situation of receiving BeiDou satellite signals by nodes in the controlled blocking area and the location of the nodes, the reference node is determined when only some nodes in the controlled blocking area can receive satellite signals under low satellite coverage;

[0015] The distance matrix equation from the reference node to the unknown node is obtained using bilateral two-way ranging technology, and the distance matrix equation is fitted and solved using the least squares method to obtain the position coordinates of the unknown node.

[0016] Furthermore, the node location sensing step in which all nodes can receive satellite signals further includes:

[0017] Convert the node's position coordinates into coordinates in the geodetic coordinate system.

[0018] Furthermore, the position coordinates of the node are converted into coordinates in the geodetic coordinate system, specifically including:

[0019] Get the position coordinates (x, y, z) of the node, where x represents the axis pointing to the intersection of the prime meridian and the equator based on the Earth-centered Earth-fixed coordinate system, y represents the axis pointing to the intersection of 90 degrees east longitude and the equator based on the Earth-centered Earth-fixed coordinate system, and z represents the axis pointing to the North Pole based on the Earth-centered Earth-fixed coordinate system;

[0020] Based on the x-axis and y-axis in the Earth-centered Earth-fixed coordinate system, the longitude λ in the geodetic coordinate system is calculated:

[0021]

[0022] Initialize the altitude and latitude in the current geodetic coordinate system:

[0023] h0=0

[0024]

[0025] where e 2 represents the first eccentricity of the Earth reference ellipsoid;

[0026] For the jth iteration, j ≥ 1, j ∈ Z, where Z is an integer, calculate the curvature radius G of the current Earth's y-axis. j :

[0027]

[0028] Calculate the height h in the current geodetic coordinate system j :

[0029]

[0030] Update the latitude φ in the geodetic coordinate system j :

[0031]

[0032] Until the latitude in the updated geodetic coordinate system meets the iteration condition |φ j -φ j-1 |<ε, where ε satisfies ε<10 -5 constant;

[0033] The latitude in the geodetic coordinate system that meets the iteration conditions is the converted latitude, and the height in the converted geodetic coordinate system is obtained according to the converted latitude.

[0034] Furthermore, the observation equations of the nodes in the Mesh network regarding the Beidou satellite pseudorange are obtained, which specifically include the following observation equations:

[0035]

[0036] Among them, ρ l A visible satellite l(x s,l ,y s,l ,z s,l ) represents the pseudorange size to the node P(x, y, z) to be determined, c represents the satellite signal propagation speed of the visible satellite, δt eis the estimated clock error parameter, and L is the number of visible satellites (L≥4).

[0037] Furthermore, the observation equation is linearized and expanded at the approximate point using Taylor series to obtain the pseudorange error matrix expression from the satellite to the node, which specifically includes:

[0038] The observation equation is applied at the approximate point P a =(x0,y0,z0,δt e,0 ) is linearized to obtain the pseudorange error from the visible satellite l to the node:

[0039] Δρ l =-G α,l ·Δx-G β,l ·Δy-G γ,l ·Δz+Δb

[0040] Where Δρ l is the pseudorange error from visible satellite l to the node, G α,l With G β,l and G γ,l is the distance at the approximate point P a =(x0,y0,z0,δt e,0 ) with respect to x, y, and z, respectively. Δx, Δy, and Δz represent the node position relative to the approximate value P a The three-axis offset at Δb is the estimated clock error δt e and the initial estimated clock error δt e,0 The error term caused by the difference;

[0041] The observation equation from L visible satellites to the node is linearized and expanded using Taylor series to obtain the pseudorange error matrix expression from the satellite to the node:

[0042] Δρ=HΔP a

[0043] Where Δρ represents the pseudorange error matrix; H is the partial derivative coefficient matrix expanded at the approximate point; ΔP a is the offset of the node to be solved at the approximate point.

[0044] Furthermore, the pseudorange error matrix expression is fitted using the least squares method to obtain the offset of the node at the approximate point, which specifically includes the following expression:

[0045] ΔP a =(H T H) -1 H T Δρ.

[0046] Furthermore, the position coordinates of the node are obtained according to the approximate value and offset at the approximate point, specifically including the following expressions:

[0047] P=P+ΔP

[0048] Where P represents the position coordinate of the node in the Earth-centered Earth-fixed coordinate system, P a Represents the approximate value at the approximate point, ΔP a Indicates the offset at the approximate point.

[0049] If you want to get a more accurate position solution, use the P obtained this time as a new approximate point and repeat the above steps to calculate until the obtained ||ΔP a ||<κ, where the threshold κ is a very small constant.

[0050] Furthermore, based on the situation of the nodes in the controlled blocking area receiving the Beidou satellite signal and the location of the nodes, the reference nodes when only some nodes in the controlled blocking area can receive the satellite signal under low satellite coverage are determined, specifically including:

[0051] If the number of nodes in the controlled isolation domain that have calculated their own positions through satellite signals is less than 3, the Beidou receiver device on the controlled node is activated, and the node with the Beidou receiver device activated is used as the reference node;

[0052] If the number of nodes in the controlled blocking domain that obtain their own positions through satellite signal calculation is greater than or equal to 3, then n nodes located at the edge of the controlled blocking domain are directly selected as reference nodes, where n is greater than or equal to 3 and less than or equal to the number of nodes in the controlled blocking domain that can receive satellite signals.

[0053] Furthermore, the distance matrix equation from the reference node to the unknown node is obtained using bilateral two-way ranging technology, and the least squares method is used for fitting and solving, specifically including:

[0054] Calculate the signal flight time from reference node i to an unknown node t

[0055]

[0056] in, It represents the time difference between the first signal sent by reference node i and the time when the unknown node t receives the return signal. It represents the time difference between the unknown node t sending the first signal and the second time receiving the signal sent by the reference node i, It represents the response time from when the unknown node t receives the first signal sent by the reference node i to when the signal is returned to the unknown node t. It represents the response time from the reference node i receiving the return signal to the second signal transmission to the unknown node t;

[0057] Based on signal flight time and signal transmission speed c prop , get the estimated distance from the reference node i to an unknown node t:

[0058] And there is a distance formula in the three-dimensional coordinate system:

[0059]

[0060] Among them, (x i ,y i ,z i ) represents the three-dimensional coordinates of the reference node i based on the Earth-centered Earth-fixed coordinate system, represents the three-dimensional estimated coordinates of the unknown node t based on the Earth-centered Earth-fixed coordinate system;

[0061] make:

[0062]

[0063] i=1,2,...,n and expand and simplify to get the distance matrix equation:

[0064]

[0065] in,

[0066]

[0067] The distance matrix equation is solved using the least squares method. Perform fitting and solving to obtain the position coordinates of unknown nodes

[0068] Furthermore, the above method also includes evaluating the positioning accuracy using a root mean square error, wherein the root mean square error specifically includes the following expression:

[0069]

[0070] Where η represents the root mean square error of the system position estimation, M represents the number of unknown nodes in the controlled blocking domain, (x t ,y t ,z t ) is the true value of the three-dimensional coordinate of the unknown node in the Earth-centered Earth-fixed coordinate system.

[0071] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for sensing node locations in a satellite-based Mesh network, which has the following beneficial effects:

[0072] The present invention addresses the problems of imperfect location awareness solutions and low positioning accuracy in mesh networks, and proposes a Beidou satellite-based location awareness system solution. It designs and mathematically describes node location awareness in networks with good satellite service (all nodes can receive satellite signals) and low satellite signal coverage (only some nodes in a controlled barrier domain can receive satellite signals). Furthermore, a reference node selection scheme is designed by introducing a controlled barrier domain in the case of low satellite coverage, and bilateral two-way ranging (BLR) applied to round-trip time is used to reduce the impact of clock synchronization and clock offset, thereby solving the location awareness problem of nodes in the controlled barrier domain of the mesh network and ensuring a certain degree of accuracy. At the same time, it can provide efficient and reliable location information for mutual communication and file transfer between nodes in the mesh network. The technology described in the present invention is applicable to multi-node communications where all nodes have equal status, including wireless sensor networks, the Internet of Things, and mobile ad hoc network communications, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0074] Figure 1 The figure is a flow chart of a node location awareness method in a satellite-based Mesh network proposed in an embodiment of the present invention.

[0075] Figure 2 The figure is a schematic diagram of the node location perception process in a Beidou satellite-based Mesh network when satellite service is good in an embodiment of the present invention.

[0076] Figure 3 2 is a system diagram of a location awareness solution under low satellite coverage conditions in an embodiment of the present invention.

[0077] Figure 4 The figure is a schematic diagram of the reference node selection process of the location awareness solution under low satellite coverage in an embodiment of the present invention.

[0078] Figure 5 The figure is a schematic diagram of the bilateral two-way ranging process of the position sensing solution under low satellite coverage in an embodiment of the present invention.

[0079] Figure 6 The figure is a schematic diagram of the location perception process of a movable unknown node in a controlled barrier domain in a Mesh network with a controlled barrier domain introduced under low satellite coverage in an embodiment of the present invention. DETAILED DESCRIPTION

[0080] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0081] An embodiment of the present invention discloses a method for sensing node locations in a satellite-based Mesh network, comprising:

[0082] Step 1. Build a flat network location awareness system architecture based on Beidou satellites. The system includes multiple nodes, each equipped with a Beidou positioning module. Each node establishes connections with each other based on autonomous collaborative communication and time division multiple access technology to implement a mesh network.

[0083] Step 2. Design and mathematically represent a node location awareness solution based on the BeiDou satellite system for a network with good satellite service (all nodes can receive satellite signals);

[0084] Step 3. Based on the BeiDou satellite system, we designed a reference node selection scheme and a round-trip time-based ranging scheme to address the location awareness problem of unknown nodes that can move within a controlled obstruction domain under low satellite signal coverage conditions (only some nodes within the controlled obstruction domain can receive satellite signals).

[0085] Step 4. Finally, the least squares method is used to solve the position perception of the unknown node, and the root mean square error method is used to estimate the node position perception error in a controlled barrier domain.

[0086] Specific implementation method of step 1 of the present invention:

[0087] The system is deployed within a 5km x 5km area, with Q nodes distributed throughout. Each node possesses a certain level of computing power and is equipped with an antenna and a BeiDou satellite navigation receiver module, enabling transmission and reception, as well as access to the BeiDou satellite system for position determination. Given good satellite positioning service, each node can receive radio signals carrying time and position information from L BeiDou satellites, enabling it to obtain position information using pseudoranges. Furthermore, to account for low satellite signal coverage, each node is equipped with a round-trip time-based ranging device. Given the characteristics of distributed networks, inter-node collaboration leverages local information to estimate the position of each node within the network. Nodes within the system establish connections to each other using autonomous cooperative communication and time division multiple access (TDMA) technology, forming a mesh network. All nodes within the system use a common TDMA frame format, enabling coarse slot-level synchronization through low-overhead pilot signaling. By dividing a TDMA frame into D time slots (D ≥ 3), the source node sends a data packet to a relay node one hop away in the first time slot of the first TDMA frame. The relay node then relays the data packet to the next-hop relay node in the second time slot. The next-hop relay node then forwards the data packet, and the above process is repeated in the next TDMA frame to complete the data broadcast. Autonomous collaborative communication is based on phase jitter and Turbo-Like error correction. Autonomous collaboration requires cooperating nodes to relay in the same time slot. To ensure that each node relays the same data packet, the network protocol stack can only modify the protocol header in a manner that depends on the number of hops.

[0088] Controlled Barrage Region (CBR) can divide the network into multiple separate parts by utilizing multiple buffer nodes that have lost their relay function, thereby forming multiple small groups within the network. Introducing controlled barrier regions in mesh networks can divide network areas, thereby helping to improve location awareness accuracy and efficiency. In a mesh network, the Barrage Access Control (BAC) protocol is used to broadcast request-to-send (RTS) and clear-to-send (CTS) messages to specify buffer nodes to form a controlled barrier domain. The source node broadcasts an RTS message, and each relay node increments by one hop, obtaining information about the shortest cooperative path to the source node at the destination node. The destination node broadcasts a CTS message containing the shortest path length S, and each relay node also increments by one hop, allowing the source to obtain the distance to the destination node. Each relay node also knows the shortest cooperative path length and the length of the cooperative path it is on. By using nodes on a cooperative path of length S+D as buffer nodes, a controlled barrier domain containing a cooperative path with a maximum length of S+D-1 can be constructed.

[0089] Specific implementation method of step 2 of the present invention:

[0090] like Figure 2 , a schematic diagram of the node location awareness solution process with good satellite service is given, which includes the following steps:

[0091] (1) Pseudorange measurement

[0092] Pseudorange is the geometric distance between the navigation receiver and the visible satellite. In practical applications, the pseudorange is generally measured and calculated by multiplying the propagation time of the signal transmitted by the satellite by the propagation speed:

[0093] ρ=c*(T re -T se ) (1)

[0094] In the formula, ρ represents the pseudorange, T re T is the time when the navigation receiver receives the signal sent by the Beidou satellite. se is the starting time of the Beidou satellite signal transmission, and c is the propagation speed of the satellite signal.

[0095] Taking into account the influence of errors such as the clock accuracy of the Beidou satellite and the navigation receiver, atmospheric resistance, etc., the clock of the Beidou satellite and the clock of the navigation receiver may not be highly synchronized, resulting in a certain error in the measured pseudorange. The pseudorange observation formula used in the present invention is expressed as:

[0096]

[0097] in, The time when the navigation receiver receives the signal sent by the Beidou satellite to remove the atmospheric error and the Beidou system time synchronization error. The starting time of the BeiDou satellite signal transmission to remove the BeiDou system time synchronization error. is the distance from the satellite to the receiver, δt se is the difference between the launch time of the satellite signal and the BeiDou system standard time, δt re is the difference between the time when the satellite signal reaches the navigation receiver and the Beidou system standard time. I and T are the delay errors of the Beidou satellite signal passing through the ionosphere and troposphere of the atmosphere, respectively. s ,y s ,z s is the three-dimensional coordinate of the visible satellite in the Earth-centered Earth-fixed coordinate system, x, y, z are the coordinates of the node in the Earth-centered Earth-fixed coordinate system, δt e The estimated clock error parameters take into account the ionospheric and tropospheric delays, and the clock synchronization errors between the satellite atomic clock and the receiver with the BeiDou system standard time.

[0098] When using L visible satellites to perform pseudo-range single-point positioning on a node, the observation equation can generally be expressed as

[0099]

[0100] where l=1,2,...,L,ρ l Indicates a visible satellite l(x s,l ,y s,l ,z s,l ) to the pseudo-range of the node P(x,y,z) to be determined, and x s,l ,y s,l ,z s,l is the three-dimensional coordinate of the visible satellite l in the Earth-centered Earth-fixed coordinate system, δt e is the estimated clock error.

[0101] (2) Pseudorange single point positioning based on observation equation

[0102] For the observation equation The observation equation is placed at the approximate point P a =(x0,y0,z0,δt e,0 ) is linearized (the approximate point here refers to the initial estimate of the node receiver position), we have:

[0103] Δρ l =-G α,l ·Δx-G β,l ·Δy-G γ,l ·Δz+Δb (4)

[0104] Where Δρ l is the pseudorange error from visible satellite l to the node, G α,l With G β,l and G γ,l is the distance at the approximate point P a =(x0,y0,z0,δt e,0 ) with respect to x, y, and z, respectively. Δx, Δy, and Δz represent the node position relative to the approximate value P a The three-axis offset at Δb is the estimated clock error δt e and the initial estimated clock error δt e,0 The error terms caused by different

[0105] Δb=c*(δt e -δt e,0 ) (5)

[0106] Linearize and expand the observation equations from L visible satellites to the node, where l = 1, 2, ..., L, and we have:

[0107] Δρ=HΔP a (6)

[0108] Among them, H is the partial derivative coefficient matrix expanded at the approximate point, is the observation matrix, and is:

[0109] Pseudorange error matrix The offset to be solved is expressed as ΔP a =[Δx,Δy,Δz,Δb].

[0110] Then use the least squares method to get the offset ΔP a =(H T H) -1 H T Δρ, and finally the obtained offset ΔP a Superimposed on the initial approximation P a In the present invention, the offset ΔP a In matrix form, the correct position solution matrix P is obtained as:

[0111] P=P a +ΔP a (7)

[0112] If you want to get a more accurate position solution, use the P obtained this time as a new approximate point and repeat the above steps to calculate until the obtained ||ΔP a ||<κ, where the threshold κ is a very small constant.

[0113] (3) Coordinate transformation

[0114] Generally, positioning by the BeiDou satellite system is based on the Earth-Centered, Earth-Fixed (ECEF) coordinate system. Therefore, the location of the node obtained is generally based on the ECEF format. For the macroscopic entity of the Earth, people are usually more accustomed to describing the location of objects in terms of latitude, longitude, and altitude. This requires a related conversion of the coordinate system. In the present invention, the following method is used to convert the coordinates (x, y, z) under ECEF into the coordinates (φ, λ, h) under the geodetic coordinate system:

[0115] Take G as the radius of curvature of the earth's elliptical circle, and e as the first eccentricity of the earth's reference ellipsoid. When the major axis a and minor axis b of the earth's elliptical orbit are known, G and e can be obtained. 2 , e 2 The calculation formula is as follows:

[0116]

[0117] Based on the x-axis and y-axis in the Earth-centered Earth-fixed coordinate system, the longitude λ in the geodetic coordinate system is calculated:

[0118]

[0119] The overall conversion method is as follows, where the height h0=0 in the current geodetic coordinate system and the latitude in the geodetic coordinate system need to be initialized. Formulas (10)-(12) are used for iterative solution, where j is the number of iterations, j ≥ 1, j∈Z, and Z is an integer.

[0120]

[0121] Until the latitude in the updated geodetic coordinate system meets the iteration condition |φ j -φ j-1 |<ε,where ε<10 -5 and is a constant;

[0122] The final converted coordinates are shown below. These geographic coordinates combined with the map can intuitively reflect the location of nodes in the network.

[0123]

[0124] Specific implementation method of step 3 of the present invention:

[0125] Consider a 100m×100m controlled isolation domain with W nodes, such as Figure 3 , and each node has the ability to move and is equipped with a Beidou satellite system receiver and a ranging device based on round-trip time. First, the Beidou satellite system is used to locate the position of each node in the controlled barrier domain. However, since the satellite signal may be weak in some cases, only the position of some nodes in the CBR can be determined. The other nodes need to use the reference nodes selected in the CBR and the ranging technology of the present invention to complete the position perception.

[0126] (1) Node mobility within the network

[0127] Since the present invention considers that nodes in the network may have a certain mobility, the nodes selected as reference nodes may also have mobility, but remain stationary when serving as reference nodes. w The node moves within the range of , and its moving speed is represented by v. Considering the randomness of the node's movement, let the angle between the node's moving speed and the coordinate system be θ, and γ be the angle between its projection on the XOY plane and the x-axis, then the node's x-axis moving speed is v x =v·sinφ·cosγ, the y-axis moving speed is v y =v·sinφsinγ, the z-axis moving speed is vz =v·cosφ then t w The position of the node after moving is x'=x+v x ·t w and y'=y+v y ·t w and z'=z+v z ·t w .

[0128] That is, after t w The position of the node after time movement is (x',y',z')=(x+v x ·t w ,y+v y ·t w ,z+v z ·t w ). And so on, the node passes through s very small t w The coordinates after movement are:

[0129]

[0130] (2) Reference node selection scheme

[0131] like Figure 4 , a schematic diagram of the reference node selection process in the present invention is given. In the traditional method of this ranging invention, a base station is required as a reference benchmark. Taking into account the mobility of nodes in the network and the special serviceability of the Mesh network, the present invention considers selecting nodes at the edge of the controlled blocking domain as reference nodes to determine the positions of other nodes in the controlled blocking domain, and in order to ensure the accuracy of positioning, the nodes selected as reference nodes need to remain stationary. For Mesh networks, the edge nodes and buffer nodes of the controlled blocking domain when forming a controlled blocking domain may have the opportunity to serve as reference nodes of other controlled blocking domains to participate in the collaborative positioning of nodes with unknown positions. The selection of reference nodes in the present invention is divided into the initialization of reference nodes and the update of reference nodes.

[0132] Initialization of reference nodes: In the present invention, first, the nodes in the controlled blocking domain must receive the signals transmitted by the Beidou satellite for positioning, that is, initialize to obtain the position. The nodes that can obtain the position remain stationary, and then start to select the reference node: When the number of nodes in the controlled blocking domain that can obtain their own position information by receiving the Beidou satellite signal is less than 3, it indicates that the satellite signal in the area is very weak or strongly interfered with. At this time, in order to locate the node position in the network, it can be considered that m nodes (m≥3) in the network are equipped with another set of high-gain antenna receiver devices to better receive Beidou satellite signals. These devices are controlled and detachable due to their high cost, and will only be enabled when the number of reference nodes is insufficient.

[0133] When the number of nodes in the controlled barrier domain that can obtain their own location information by receiving Beidou satellite signals is k (3≤k<W), W is the total number of nodes within the controlled barrier domain. Among these nodes that can obtain location information, n (3≤n≤k) nodes located at the edge of the controlled barrier domain are selected to perform location perception of unknown nodes.

[0134] That is, if there are only three nodes in the controlled barrier domain that can receive Beidou signals and thus determine their own positions, then these three points will directly serve as reference nodes to assist other nodes in positioning; if there are a large number of nodes in the controlled barrier domain that can obtain their own positions through satellites, then n nodes located at the edge of the controlled barrier domain will be selected from these nodes as reference nodes.

[0135] Reference Node Update: Nodes within the controlled isolation domain that are not selected as reference nodes can move. Due to their mobility, some nodes will move to the edge of the controlled isolation domain over time. When these nodes move closer to the edge of the controlled isolation domain or become buffer nodes due to network topology changes, they will replace the reference node with the shortest communication time within their communication range. In other words, the closest reference node becomes the new reference node, and the replaced reference node can begin its movement. Nodes selected as reference nodes remain stationary until they are replaced by a new reference node.

[0136] (3) Location awareness scheme within controlled barrier domain based on round-trip time

[0137] In a mesh network with a potentially large number of nodes, achieving relatively accurate positioning is sometimes not feasible with only coarse time slot synchronization of TDMA. The present invention adopts a method based on reception time, namely Double-Side Two-Way Ranging (DS-TWR). It is a solution that does not require high clock synchronization and can reduce clock offset, and it is applicable to round-trip time. Assuming that the clock offset of the reference node is α and the clock offset of the node to be located is β, the flight time T is prop In a "virtual" clock, the clock would be the average of α and β.

[0138] like Figure 5 ,The process of DS-TWR is as follows: a reference node i actively sends data to the unknown node t, and the reference node i records the timestamp of the sending time. The unknown node t records the timestamp after receiving the information. After (reply time 1) After that, the data response is returned to the reference node i. After receiving the data, the reference node i records the timestamp. The time difference between the two timestamps recorded by the reference node i is (Round trip time 1), and after (response time 2) After that, the data response is returned to the unknown node t. After receiving it, the unknown node t records the timestamp. The time difference between the two timestamps recorded by the unknown node t is (Round trip time 2).

[0139]

[0140] Finally, the flight time between two nodes can be calculated for:

[0141]

[0142] For the n reference nodes that have been selected, the coordinates are expressed as (x i ,y i ,z i ), where i = 1, 2, ..., n. Each reference node obtains its own position by solving the signal transmitted by the BeiDou satellite and can send information such as position, timestamp and label to other nodes in the network. For a total of M nodes in the network that need to further determine their positions, their coordinates are expressed as (x t ,y t ,z t ), its estimated value is Where 1≤t≤M, in the present invention, both the reference node and the unknown node are equipped with communication equipment and can send and receive messages. In order to make full use of the computing power of each node and speed up the speed of obtaining the position of the unknown node, this process is calculated by the unknown node itself. After receiving the information of the reference node i, the unknown node t combines the signal transmission speed c prop , using the formula:

[0143]

[0144] To calculate the estimated distance between it and the reference node i

[0145]

[0146] Among them, the left side of the equal sign is the actual measured distance between the coordinates of the i-th reference node and the unknown node t, and the right side is the distance between the unknown node t and the i-th reference node. Substitute i = 1, 2, ..., n into the equation and subtract the first equation (i = 1) from the other equations to obtain the formula:

[0147] And simplifying the formula, we can get:

[0148]

[0149] in,

[0150]

[0151] The overall satellite signal low coverage situation, the location perception flow chart of unknown nodes that can move within the controlled blocking area is as follows: Figure 6 shown.

[0152] Specific implementation method of step 4 of the present invention:

[0153] According to the equation in step 3 of the invention The coordinates of nodes with unknown positions can be calculated using the least squares method:

[0154]

[0155] Next, the error is calculated using the root mean square error method. For this controlled blocking domain with M unknown nodes whose coordinates need to be estimated, the root mean square error η of the system position estimation is calculated as:

[0156]

[0157] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0158] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for sensing node location in a satellite-based Mesh network, characterized in that: include: a) Node location awareness steps when all nodes can receive satellite signals: Obtain the observation equation of the nodes in the Mesh network regarding the Beidou satellite pseudorange; The observation equation is linearized and expanded at the approximate point using Taylor series to obtain the pseudorange error matrix expression of the node; The pseudorange error matrix expression is fitted using the least square method to obtain the offset of the node at the approximate point; The position coordinates of the node are obtained according to the approximate value and offset at the approximate point; b) Node location awareness steps when some nodes in a controlled isolation domain receive satellite signals: Based on the situation of receiving BeiDou satellite signals by nodes in the controlled blocking area and the location of the nodes, the reference node is determined when only some nodes in the controlled blocking area can receive satellite signals under low satellite coverage; The distance matrix equation from the reference node to the unknown node is obtained using bilateral two-way ranging technology, and the distance matrix equation is fitted and solved using the least squares method to obtain the position coordinates of the unknown node.

2. A method for sensing node location in a satellite-based Mesh network according to claim 1, characterized in that: The node location awareness step under which all nodes can receive satellite signals also includes: Convert the node's position coordinates into coordinates in the geodetic coordinate system.

3. The method for sensing node location in a satellite-based Mesh network according to claim 2, wherein: Convert the node's position coordinates into the coordinates of the geodetic coordinate system, including: Get the position coordinates (x, y, z) of the node, where x represents the axis pointing to the intersection of the prime meridian and the equator based on the Earth-centered Earth-fixed coordinate system, y represents the axis pointing to the intersection of 90 degrees east longitude and the equator based on the Earth-centered Earth-fixed coordinate system, and z represents the axis pointing to the North Pole based on the Earth-centered Earth-fixed coordinate system; Based on the x-axis and y-axis in the Earth-centered Earth-fixed coordinate system, the longitude λ in the geodetic coordinate system is calculated: Initialize the altitude and latitude in the current geodetic coordinate system: h0＝0 where e 2 represents the first eccentricity of the Earth reference ellipsoid; For the jth iteration, j ≥ 1, j ∈ Z, where Z is an integer, calculate the curvature radius G of the current Earth's y-axis. j : Calculate the height h in the current geodetic coordinate system j : Update the latitude φ in the geodetic coordinate system j : Until the latitude in the updated geodetic coordinate system meets the iteration condition |φ j -φ j-1 |<ε, where ε satisfies ε<10 -5 constant; The latitude in the geodetic coordinate system that meets the iteration conditions is the converted latitude, and the height in the converted geodetic coordinate system is obtained according to the converted latitude.

4. The method for sensing node location in a satellite-based Mesh network according to claim 1, wherein: Obtain the observation equations of the nodes in the Mesh network regarding the BeiDou satellite pseudorange, including the following observation equations: Among them, ρ l Indicates a visible satellite l(x s,l ,y s,l ,z s,l ) to the node P(x, y, z) to be determined, c represents the satellite signal propagation speed of the visible satellite, δt e is the estimated clock error parameter, L is the number of visible satellites, L ≥ 4.

5. The method for sensing node location in a satellite-based Mesh network according to claim 4, wherein: The observation equation is linearized and expanded at the approximate point using Taylor series to obtain the pseudorange error matrix expression from the satellite to the node, which specifically includes: The observation equation is applied at the approximate point P a =(x0,y0,z0,δt e,0 ) is linearized to obtain the pseudorange error from the visible satellite l to the node: Dr. l =-G α,l ·Δx-G β,l ·Δy-G γ,l ·Δz+Δb Where Δρ l is the pseudorange error from visible satellite l to the node, G α,l With G β,l and G γ,l is the distance at the approximate point P a =(x0,y0,z0,δt e,0 ) with respect to x, y, and z, respectively. Δx, Δy, and Δz represent the node position relative to the approximate value P a The three-axis offset at Δb is the estimated clock error δt e and the initial estimated clock error δt e,0 The error term caused by the difference; The observation equation from L visible satellites to the node is linearized and expanded using Taylor series to obtain the pseudorange error matrix expression from the satellite to the node: Dr=HΔP a Where Δρ represents the pseudorange error matrix; H is the partial derivative coefficient matrix expanded at the approximate point; ΔP a is the offset of the node to be solved at the approximate point.

6. The method for sensing node location in a satellite-based Mesh network according to claim 5, wherein: The pseudorange error matrix expression is fitted using the least squares method to obtain the offset of the node at the approximate point, which specifically includes the following expression: ΔP a =(H T H) -1 H T Δρ。 7. The method for sensing node location in a satellite-based Mesh network according to claim 6, wherein: The position coordinates of the node are obtained based on the approximate value and offset at the approximate point, including the following expressions: P=P a +ΔP a Where P represents the position coordinate of the node in the Earth-centered Earth-fixed coordinate system, P a Represents the approximate value at the approximate point, ΔP a Indicates the offset at the approximate point.

8. The method for sensing node location in a satellite-based Mesh network according to claim 1, wherein: Based on the BeiDou satellite signal reception status of the nodes in the controlled blocking area and the locations of the nodes, the reference nodes are determined when only some nodes in the controlled blocking area can receive satellite signals under low satellite coverage, specifically including: If the number of nodes in the controlled isolation domain that have calculated their own positions through satellite signals is less than 3, the Beidou receiver device on the controlled node is activated, and the node with the Beidou receiver device activated is used as the reference node; If the number of nodes in the controlled blocking domain that obtain their own positions through satellite signal calculation is greater than or equal to 3, then n nodes located at the edge of the controlled blocking domain are directly selected as reference nodes, where n is greater than or equal to 3 and less than or equal to the number of nodes in the controlled blocking domain that can receive satellite signals.

9. The method for sensing node location in a satellite-based Mesh network according to claim 1, wherein: The distance matrix equation from the reference node to the unknown node is obtained using bilateral two-way ranging technology, and the least squares method is used to fit and solve it, specifically including: Calculate the signal flight time from a reference node i to an unknown node t Based on signal flight time and signal transmission speed c prop , get the estimated distance from the reference node i to an unknown node t: And there is a distance formula in the three-dimensional coordinate system: Among them, (x i ,y i ,z i ) represents the three-dimensional coordinates of the reference node i based on the Earth-centered Earth-fixed coordinate system, represents the three-dimensional estimated coordinates of the unknown node t based on the Earth-centered Earth-fixed coordinate system; make: i=1,2,...,n and expand and simplify to get the distance matrix equation: in, The distance matrix equation is solved using the least squares method. Perform fitting and solving to obtain the position coordinates of unknown nodes 10. The method for sensing node location in a satellite-based Mesh network according to claim 9, wherein: The method further includes evaluating the positioning accuracy using a root mean square error (RMSE), wherein the RMS error specifically includes the following expression: Where η represents the root mean square error of the system position estimation, M represents the number of unknown nodes in the controlled blocking domain, (x t ,y t ,z t ) is the true value of the three-dimensional coordinate of the unknown node in the Earth-centered Earth-fixed coordinate system.

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