A wide-area positioning method and system based on LoRa Mesh

Abstract

This invention discloses a wide-area positioning method and system based on LoRa Mesh. This method requires a server and gateway to broadcast a search for located tags through a mesh network composed of anchor points. The tags then join the network and initiate time-of-flight ranging measurements with surrounding anchor points. After the ranging is complete, the tags transmit the data via the mesh network to the gateway and server. The server locates the tags based on the anchor point locations and the tag ranging results. The system includes a server, a gateway, LoRa located tags, and a large number of low-cost, low-power LoRa positioning anchor points. By deploying a large number of positioning anchor points, it covers positioning blind spots blocked by buildings and provides wide-area positioning services. This system offers the advantages of low equipment cost, low power consumption, ease of deployment, and wide coverage.

Description

Technical Field

[0001] The present invention belongs to the field of Internet of Things positioning, and in particular relates to a wide-area positioning method and system based on LoRa Mesh. Background Art

[0002] The rapid development of IoT technology has driven the emergence and maturity of mass applications such as smart manufacturing, smart cities, and smart agriculture. Spatial positioning, especially in outdoor scenarios, is a mainstream application and key feature of IoT and will become even more important in the next generation of IoT. However, mainstream IoT outdoor positioning technologies, such as global navigation satellite systems and cellular mobile networks, suffer from high power consumption and high costs, requiring frequent charging, and cannot meet the needs of low-power, wide-area IoT positioning. Therefore, obtaining accurate position estimates from radio signals transmitted by low-power, low-cost devices is essential. Existing positioning systems based on low-power, wide-area IoT technologies such as LoRa often suffer from three drawbacks: First, wireless signals are easily obstructed by buildings and trees, resulting in limited coverage; second, positioning performance is susceptible to non-Gaussian noise such as multipath, resulting in low position estimation accuracy; finally, existing positioning systems typically separate positioning and data transmission, resulting in low spectral efficiency and limited anchor point deployment. Currently, there is an urgent need for an outdoor wide-area positioning system that is low power, low-cost, and easy to deploy. Summary of the Invention

[0003] In response to the above needs, the present invention proposes a wide-area positioning method and system based on LoRa Mesh.

[0004] The purpose of the present invention is to achieve the following technical solution: a wide-area positioning method based on LoRa Mesh, the method comprising the following steps:

[0005] Step 1: The set of gateways and LoRa positioning anchor points B{B1,...,B i ,...,B m} Maintain network connection, where B m Indicates the mth LoRa positioning anchor point, where m represents the total number of LoRa positioning anchor points. After the user generates a positioning demand for a LoRa tag, the server continuously sends a LoRa tag search instruction to the LoRa positioning anchor point set B through the gateway. After receiving the positioning instruction, the LoRa positioning anchor point set B broadcasts and forwards the instruction.

[0006] Step 2: After the LoRa tag hears the command to find itself, it locates the LoRa positioning anchor point set B'{B j ,......,B k} selects the LoRa positioning anchor point with the greatest attraction to itself as the parent node and issues an application instruction to join the Mesh network. The LoRa positioning anchor point with the greatest attraction to the LoRa tag then establishes a connection with the LoRa tag and forwards the LoRa tag's network access application to the gateway through the Mesh network. After receiving the LoRa tag's network access application through the gateway, the server adds the LoRa tag to the Mesh network and stops sending instructions to search for LoRa tags.

[0007] Step 3: The LoRa tag acts as the host to initiate ranging to all anchor points in the LoRa positioning anchor point set B' in sequence. The LoRa positioning anchor point acts as a slave to cooperate in ranging. The distance is estimated by measuring the time of flight between a pair of transmitting and receiving radios. The estimated results are corrected by actual environment experimental data.

[0008] Repeat step 3 until the LoRa tag completes ranging with the surrounding LoRa positioning anchor point set B' that can perform ranging;

[0009] Step 4: The LoRa tag continuously sends ranging results to the gateway through the Mesh network and radio signal strength The LoRa positioning anchor set B participates in forwarding the data packet. After receiving the data packet from the LoRa tag, the gateway replies to the LoRa tag through the Mesh network. After receiving the reply, the LoRa tag exits the Mesh network and enters the standby state.

[0010] Step 5: The server receives the data packet sent from the LoRa tag through the gateway, and the LoRa positioning anchor point B{B1,...,B i ,...,B m The position coordinates of} are stored in the server in advance; the server selects the measurement data between the three anchor points and the LoRa tag that minimize the posterior error; assuming that the coordinates of the three selected anchor points are (x a ,y a )、(x b ,y b )、(x c ,y c ), the ranging results between the LoRa tag and the three anchor points are Represents the estimated LoRa tag location coordinates;

[0011] The best solution is obtained through iterative method So that the ranging error function smallest;

[0012] Step 6: The server summarizes and calculates the position coordinates of each tag through steps 1 to 5 and displays the positioning results on the terminal and control web page.

[0013] Furthermore, when the LoRa tag does not detect an instruction to search for itself, it is in a standby state to save energy.

[0014] Furthermore, the distance between the master and the slave Estimated based on the flight time N between a pair of transmitting and receiving radios:

[0015]

[0016] Where c represents the speed of light, and BW is the bandwidth of the wireless signal;

[0017] During radio transmission and reception, the master records the radio signal strength from the slave Estimated distance Make corrections to get the final result Complete the distance measurement between two points:

[0018]

[0019] Among them, γ is an empirical parameter, α is the path loss coefficient, both of which are determined by analyzing actual environmental experimental data, and r0 is the radio signal strength at an interval of 1 meter.

[0020] Furthermore, the process of searching for LoRa tags in step 1 is as follows: the gateway first checks the routing table. If there is a valid routing path to the LoRa tag, it is directly sent to the next hop according to the route. If there is no valid routing path, a broadcast routing search is performed until a valid routing path to the LoRa tag is found; if the LoRa tag is not in the network, it will reply when it hears a broadcast packet searching for itself and join the network.

[0021] Furthermore, the process of selecting the parent node of the LoRa tag in step 2 is as follows: the LoRa tag listens to the surrounding anchor point B. i When forwarding the broadcast packet, record the LoRa positioning anchor point B i Number of hops to the gateway T i and LoRa positioning anchor B i The number of data packets currently to be transmitted M i , and measure the LoRa positioning anchor point B i Wireless signal strength Then calculate the LoRa positioning anchor point B i The attraction of LoRa tags i :

[0022]

[0023]

[0024] Among them, R min To ensure the minimum signal strength for network connection, LoRa tag A selects the LoRa positioning anchor point with the greatest attraction to itself as the parent node.

[0025] Furthermore, the a posteriori error in step 5 uses an a posteriori signal strength estimation error or an a posteriori position estimation error; the a posteriori signal strength estimation error BRE is expressed as:

[0026]

[0027] in, Indicates the wireless signal strength calculated based on the estimated location; r0 is the radio signal strength at an interval of 1 meter;

[0028] The posterior position estimation error BDE is expressed as:

[0029]

[0030] in To estimate the position and coordinates of each LoRa anchor point (x i ,y i ) between them.

[0031] Furthermore, the optimal The ranging error Minimum; the k+1th iteration expression is written as:

[0032]

[0033]

[0034] According to another aspect of this specification, there is provided a LoRa Mesh-based wide-area positioning system, which consists of a server, a gateway, a LoRa tag, and a LoRa positioning anchor point;

[0035] LoRa positioning anchor points and LoRa tags achieve data communication through wireless Mesh networking;

[0036] The LoRa positioning anchor point is used to broadcast the instructions for searching for LoRa tags sent by the forwarding server to the LoRa positioning anchor point B through the gateway after receiving the positioning instructions, establish a connection with the LoRa tag, and forward the LoRa tag's network access application to the gateway through the Mesh network, acting as a slave to cooperate in ranging;

[0037] The LoRa tag can estimate the distance between the LoRa tag and the LoRa positioning anchor point based on the flight time of the signal transmitted by the received LoRa positioning anchor point, and send the ranging result to the gateway through the LoRa Mesh network;

[0038] The gateway communicates with the server through the wired serial port and receives ranging results and radio signal strength through the LoRa Mesh network The data packets formed communicate with each LoRa positioning anchor point and server;

[0039] The server receives the ranging results between each anchor point and the tag through the gateway, and calculates the position coordinates of the located tag based on the ranging results and the position coordinates of the LoRa positioning anchor points involved in the ranging.

[0040] Furthermore, the LoRa tag and LoRa positioning anchor have wireless ranging and wireless communication capabilities, and the hardware parts of both are composed of a LoRa radio frequency module, a control module and an antenna module;

[0041] The LoRa RF module is used for independent communication of multiple channels, and the control module is responsible for controlling the LoRa RF module and uploading data.

[0042] Furthermore, the gateway is: an interface module is added to the LoRa positioning anchor point to serve as a gateway, which is used to provide wired network access and data reporting functions.

[0043] The beneficial effects of the present invention are:

[0044] This paper proposes the system logic of integrating LoRa communication and positioning functions for the first time, builds a LoRa communication-positioning perception system and designs corresponding networking and positioning algorithms. Specific advantages include:

[0045] (1) The present invention fully exploits the wireless sensing capabilities of LoRa and integrates data transmission and time-of-flight ranging functions based on low-cost, low-power hardware with a single radio frequency channel. LoRa ranging positioning and data transmission do not interfere with each other, greatly expanding the application potential of low-power wide-area Internet of Things infrastructure;

[0046] (2) The LoRa Mesh networking and communication process designed by the present invention can optimize data packet congestion through routing algorithms and improve communication reliability; anchor points are interconnected through wireless Mesh networking, data is automatically backhauled, and anchor points are easy to deploy, thereby achieving wide-area coverage of the system's positioning capabilities;

[0047] (3) The present invention takes advantage of the collaborative positioning of multiple anchor points in the LoRa Mesh network, optimizes ranging data through a posteriori error, overcomes the interference of non-Gaussian noise, and improves the accuracy of tag positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the overall structure of the system of the present invention;

[0049] Figure 2 This is a schematic diagram of the hardware composition of the device in the present invention;

[0050] Figure 3 It is a schematic diagram of the workflow of positioning in the present invention;

[0051] Figure 4 This is a schematic diagram of the working process of networking communication in the present invention;

[0052] Figure 5 It is a cumulative distribution diagram of the positioning error probability when the system of the present invention is deployed in an actual scenario. DETAILED DESCRIPTION

[0053] The technical solutions and effects of the present invention are further described in detail below with reference to the accompanying drawings.

[0054] Outdoor wide-area positioning is a supporting technology for many IoT applications. However, traditional outdoor positioning methods, such as the Global Positioning System (GPS) and cellular networks, are costly and energy-intensive, failing to meet the low-cost, low-power requirements of some IoT applications. This paper proposes a low-cost, low-power, and wide-coverage outdoor wide-area positioning system and method.

[0055] like Figure 1 As shown, the present invention designs a wide-area positioning system based on LoRa Mesh. The system consists of a server, a gateway, LoRa tags to be located, and a large number of low-cost, low-power LoRa positioning anchor points. The anchor points and tags achieve data communication through a wireless mesh network. The tags calculate the flight time of the signals transmitted by the surrounding anchor points, thereby estimating the distance between the tag and the anchor point, and send the ranging results to the gateway via the LoRa Mesh network. The gateway communicates with the server via a wired serial port and with each anchor point via the wireless mesh network. The server receives the ranging results between each anchor point and the tag through the gateway and calculates the location coordinates of the located tag based on the ranging results and the position coordinates of the anchor points involved in the ranging.

[0056] The hardware structure of anchors and tags is as follows Figure 2As shown, the system consists of a LoRa radio module, a control module, an interface module, and an antenna module. The LoRa radio module uses the SX1276 / SX1278 / SX1280 chip, enabling 40 independent communication channels within a 2 km range. The control module is based on the low-power STM32L476RGT6 ARM Cortex-M4 microprocessor. The control module is responsible for controlling the LoRa radio module and uploading data. It connects to the LoRa radio module via SPI. The antenna module consists of a high-gain antenna and a low-noise amplifier. The low-noise amplifier has a built-in automatic transmit / receive switching circuit, providing 11dB of transmit gain and 10dB of receive gain. The gateway, based on the anchor point, adds an interface module. This interface module uses a serial-to-Ethernet port chip, providing wired network access and data reporting. Hardware costs are kept below 100 yuan, with maximum power consumption exceeding 120mW. The system can be used with solar panels or batteries for long-term operation. In typical operating mode, a tag with a 3000mA battery can operate for 11 years.

[0057] like Figure 3 The figure describes a wide-area positioning method based on LoRa Mesh, including the following steps:

[0058] Step 1: The gateway and the anchor point maintain a long-term network connection, and the tag is usually in standby mode to save energy. After the server generates a positioning demand for the tag, it continuously sends instructions to search for the tag (node ​​C) to the anchor point (node ​​B) through the gateway (node ​​A), such as Figure 4 As shown. The LoRa Mesh protocol designed by the present invention is an on-demand routing protocol. When there is no work in the network, all nodes remain silent. When there is work, the network starts the update and maintenance process. When node A starts to send a message, node A will search the routing table to find a valid route to its destination node C. If the route exists, the message will be sent along this path. If the route does not exist, a broadcast search message will be sent to start searching for the route. Each node B that receives the broadcast packet but does not have a valid route to the destination will forward this broadcast. If it is received by the destination node C or any node B with a valid route to the destination, they will reply to node A according to the path of the broadcast message. After node A sends the search message, it will be added to the timeout retransmission waiting list. Once the reply to the search message is received, the pending message packet will be sent to the destination via the discovered route.

[0059] Step 2: After the tag in standby state hears the command to find itself, it collects information about surrounding anchor nodes: i The forwarded broadcast packet obtains the number of hops T from the anchor point to the gateway i and current load conditions, and measure wireless signal strength Then calculate the anchor point B iAttraction to oneself K i :

[0060]

[0061]

[0062] Among them, R min The minimum signal strength required to establish a network connection is M i Anchor point B i The number of data packets to be transmitted; the tag then selects the anchor point B0 with the greatest attraction to itself as its parent node and replies with an application to join the Mesh network. Anchor point B0 then establishes a stable connection with the tag and forwards the tag's network access application to the gateway through the Mesh network. After receiving the tag's network access application through the gateway, the server stops resending the tag search instruction, and the gateway enters the idle state;

[0063] Step 3: The tag node selects an anchor node to prepare for ranging and sends a request to the first anchor node. After receiving the request, the anchor node replies and resends after a timeout. The tag node stops resending after receiving the timeout resend. The tag acts as the host and uses the ranging Master mode to send a range measurement to the nearby anchor node B. i Initiate ranging, anchor point B i As a slave, use the ranging Slave mode with ranging. Both use the ranging engine built into the RF module to perform flight time measurement between a pair of transceiver radios. The distance between the master node and the slave node It can be calculated based on the timer result N:

[0064]

[0065] Where c represents the speed of light, and BW is the bandwidth of the wireless signal;

[0066] During radio transmission and reception, the master records the radio signal strength from the slave Estimated distance Make corrections to get the final result

[0067]

[0068] Where γ is an empirical parameter and α is the path loss coefficient. Both are determined by analyzing actual experimental data. In urban environments, the path loss coefficient α is generally 40 dBm, and the empirical parameter γ can be 0.7. r0 is the radio signal strength at a 1-meter interval.

[0069] Repeat step 3 until the tag and surrounding anchor points that can enter ranging mode have completed ranging, then exit ranging mode.

[0070] Step 4: Pack the ranging results, and the tag node continuously sends the ranging results to the gateway through the Mesh network and radio signal strength The anchor participates in forwarding the data packet. After receiving the data packet from the tag, the gateway replies to the tag through the Mesh network. After receiving the reply, the tag stops retransmitting and exits the Mesh network to enter the standby state.

[0071] Step 5: The server receives a data packet from the tag through the gateway. The location coordinates of the anchor points are stored in the server in advance. The server selects the measurement data between the three anchor points and tag A that minimize the a posteriori error. The a posteriori error used to select the anchor points can be the a posteriori signal strength estimation error or the a posteriori position estimation error. The a posteriori signal strength estimation error (BRE) can be expressed as:

[0072]

[0073] in, Indicates that the wireless signal strength is calculated based on the estimated location. is the distance between the estimated position and each anchor point; the posterior position estimation error (BDE) can be expressed as:

[0074]

[0075] Assume that the coordinates of the three anchor points are (x a ,y a )、(x b ,y b )、(x c ,y c ),, the distance measurement results between the three anchor points are Represents the estimated label position coordinates. The best The ranging error Minimum; the k+1th iteration expression is written as:

[0076]

[0077]

[0078] Step 6: The server aggregates and calculates the location coordinates of each tag and generates a Kafka data stream. The control and application web pages will use this data and visualize it on the map.

[0079] The wide-area positioning system and method proposed in this invention provides wide-area positioning services by deploying a large number of low-cost, low-power LoRa anchor points to cover positioning blind spots blocked by buildings. This system and method offers the advantages of easy deployment, wide coverage, low power consumption, and low cost.

[0080] The effects of the present invention will be further described below with reference to application examples.

[0081] Application example: In a square area with a side length of 500 meters in the Yuquan campus of Zhejiang University, 9 or 18 anchor points are deployed respectively to calculate the position of tags at different locations. The position estimated by this system is compared with the position obtained by GPS, and the probability cumulative distribution diagram of the positioning error is drawn, such as Figure 5 As shown in the figure, the x-axis represents positioning error and the y-axis represents cumulative probability. This shows that the proposed system can provide positioning services with an error of less than 5 meters for most users in the area when 18 base stations are deployed. Furthermore, the maximum power consumption of the tag is less than 120mW, meeting the requirement of one charge per year.

[0082] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A wide-area positioning method based on LoRa Mesh, characterized in that: The following steps are involved: Step 1: The set of gateways and LoRa positioning anchor points B{B1,...,B i ,...,B m } Maintain network connection, where B m Indicates the mth LoRa positioning anchor point, where m represents the total number of LoRa positioning anchor points. After the user generates a positioning demand for a LoRa tag, the server continuously sends a LoRa tag search instruction to the LoRa positioning anchor point set B through the gateway. After receiving the positioning instruction, the LoRa positioning anchor point set B broadcasts and forwards the instruction. Step 2: After the LoRa tag hears the command to find itself, it locates the LoRa positioning anchor point set B′{B j ,......,B k } selects the LoRa positioning anchor point with the greatest attraction to itself as the parent node and issues an application instruction to join the Mesh network. The LoRa positioning anchor point with the greatest attraction to the LoRa tag then establishes a connection with the LoRa tag and forwards the LoRa tag's network access application to the gateway through the Mesh network. After receiving the LoRa tag's network access application through the gateway, the server adds the LoRa tag to the Mesh network and stops sending instructions to search for LoRa tags. Step 3: The LoRa tag acts as the host to initiate ranging to all anchor points in the LoRa positioning anchor point set B′ in sequence. The LoRa positioning anchor point acts as a slave to cooperate in ranging. The distance is estimated by measuring the time of flight between a pair of transceiver radios. The estimated result is corrected by actual environment experimental data. Repeat step 3 until the LoRa tag completes ranging with the surrounding LoRa positioning anchor point set B′ that can perform ranging; Step 4: The LoRa tag continuously sends ranging results to the gateway through the Mesh network and radio signal strength The LoRa positioning anchor set B participates in forwarding the data packet. After receiving the data packet from the LoRa tag, the gateway replies to the LoRa tag through the Mesh network. After receiving the reply, the LoRa tag exits the Mesh network and enters the standby state. Step 5: The server receives the data packet sent from the LoRa tag through the gateway, and the LoRa positioning anchor point B{B1,...,B i ,...,B m The position coordinates of} are stored in the server in advance; the server selects the measurement data between the three anchor points and the LoRa tag that minimize the posterior error; assuming that the coordinates of the three selected anchor points are (x a ,y a )、(x n ,y b )、(x c ,y c ), the ranging results between the LoRa tag and the three anchor points are Represents the estimated LoRa tag location coordinates; The best solution is obtained through iterative method So that the ranging error function smallest; Step 6: The server summarizes and calculates the position coordinates of each tag through steps 1 to 5 and displays the positioning results on the terminal and control web page.

2. A wide-area positioning method based on LoRa Mesh according to claim 1, characterized in that, When the LoRa tag does not detect an instruction to find itself, it is in a standby state to save energy.

3. A wide-area positioning method based on LoRa Mesh according to claim 1, characterized in that, The distance between the master and slave Estimated based on the flight time N between a pair of transmitting and receiving radios: Where c represents the speed of light, and BW is the bandwidth of the wireless signal; During radio transmission and reception, the master records the radio signal strength from the slave Estimated distance Make corrections to get the final result Complete the distance measurement between two points: Among them, γ is an empirical parameter, α is the path loss coefficient, both of which are determined by analyzing actual environmental experimental data, and r0 is the radio signal strength at an interval of 1 meter.

4. A wide-area positioning method based on LoRa Mesh according to claim 1, characterized in that, The process of searching for LoRa tags in step 1 is as follows: the gateway first checks the routing table. If there is a valid routing path to the LoRa tag, it directly sends it to the next hop according to the route. If there is no valid routing path, a broadcast routing search is performed until a valid routing path to the LoRa tag is found. If the LoRa tag is not in the network, it will reply when it hears a broadcast packet searching for itself and join the network.

5. A wide-area positioning method based on LoRa Mesh according to claim 4, characterized in that, The process of selecting the parent node of the LoRa tag in step 2 is as follows: The LoRa tag listens to the surrounding anchor point B. i When forwarding the broadcast packet, record the LoRa positioning anchor point B i Number of hops to the gateway T i and LoRa positioning anchor B i The number of data packets currently to be transmitted M i , and measure the LoRa positioning anchor point B i Wireless signal strength Then calculate the LoRa positioning anchor point B i The attraction of LoRa tags i : Among them, R min To ensure the minimum signal strength for network connection, LoRa tag A selects the LoRa positioning anchor point with the greatest attraction to itself as the parent node.

6. A wide-area positioning method based on LoRa Mesh according to claim 5, characterized in that: The a posteriori error in step 5 uses a posteriori signal strength estimation error or a posteriori position estimation error; The a posteriori signal strength estimation error BRE is expressed as: in, Indicates the wireless signal strength calculated based on the estimated location; r0 is the radio signal strength at an interval of 1 meter; The posterior position estimation error BDE is expressed as: in To estimate the position and coordinates of each LoRa anchor point (x i ,y i ) between them.

7. A wide-area positioning method based on LoRa Mesh according to claim 1, characterized in that: The best solution is obtained through iterative method The ranging error Minimum; the k+1th iteration expression is written as:

8. A LoRa Mesh-based wide-area positioning system implementing the method according to any one of claims 1 to 7, characterized in that: The system consists of a server, gateway, LoRa tags and LoRa positioning anchors; LoRa positioning anchor points and LoRa tags achieve data communication through wireless Mesh networking; The LoRa positioning anchor point is used to broadcast the instructions for searching for LoRa tags sent by the forwarding server to the LoRa positioning anchor point B through the gateway after receiving the positioning instructions, establish a connection with the LoRa tag, and forward the LoRa tag's network access application to the gateway through the Mesh network, acting as a slave to cooperate in ranging; The LoRa tag can estimate the distance between the LoRa tag and the LoRa positioning anchor point based on the flight time of the signal transmitted by the received LoRa positioning anchor point, and send the ranging result to the gateway through the LoRa Mesh network; The gateway communicates with the server through the wired serial port and receives ranging results and radio signal strength through the LoRa Mesh network The data packets formed communicate with each LoRa positioning anchor point and server; The server receives the ranging results between each anchor point and the tag through the gateway, and calculates the position coordinates of the located tag based on the ranging results and the position coordinates of the LoRa positioning anchor points involved in the ranging.

9. A LoRa Mesh-based wide-area positioning system according to claim 8, characterized in that: The LoRa tag and LoRa positioning anchor have wireless ranging and wireless communication capabilities. The hardware parts of both are composed of LoRa radio frequency modules, control modules and antenna modules; The LoRa RF module is used for independent communication of multiple channels, and the control module is responsible for controlling the LoRa RF module and uploading data.

10. A LoRa Mesh-based wide-area positioning system according to claim 9, characterized in that: The gateway is: an interface module is added to the LoRa positioning anchor point to act as a gateway, which is used to provide wired network access and data reporting functions.

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