Three-dimensional positioning system and method based on bidirectional optical wireless communication

Abstract

The invention designs a three-dimensional positioning system and method based on bidirectional optical wireless communication. The system comprises a base station and a mobile terminal which are respectively provided with an LED light emitting module and a PD light receiving module, and can realize the sending and receiving of a positioning signal and a communication light signal at the same time. The base stations are arranged on a ceiling in a non-collinear mode, and coordinates are known; the mobile terminal freely moves in the space, and coordinates are unknown. And the mobile terminal receives the downlink positioning signal sent by the base station by using the optical receiving module, and feeds back the positioning data to the base station through the transmitting module. While decoding downlink data, the base station multiplexes uplink optical signals, captures downlink and uplink positioning signals, and transmits these data to the server via the Ethernet. And the server assumes that the terminal is located at different height layers, estimates the two-dimensional coordinates of the terminal at each layer by using linear least square, calculates the difference between the expected RSS and the actual RSS, and selects two layers with the minimum difference to carry out weighted average estimation on the height of the terminal so as to realize three-dimensional positioning.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical wireless communication positioning, and in particular, relates to a three-dimensional positioning system and method based on bidirectional optical wireless communication. Background Art

[0002] With the development of science and technology, people have an increasing demand for accurate positioning of mobile devices and personnel in indoor environments. Existing wireless positioning technologies, such as GPS and Beidou satellite wireless positioning, work well outdoors, but are less effective indoors or in places where satellite signals cannot cover. On the other hand, optical wireless positioning is based on the modulation of LED light sources to send optical signals. The receiving end analyzes the intensity and phase of the optical signal and combines the positioning algorithm to achieve accurate positioning. Compared with radio frequency positioning technologies such as WiFi, Bluetooth, and RFID, optical wireless positioning technology is cheaper and safer. Due to the widespread use of LED-based indoor lighting systems, optical wireless communication positioning systems can reuse existing lighting equipment or facilities to achieve data communication and lighting functions at the same time. Among them, LED has the characteristics of high energy efficiency, long life, low cost, and high security. In addition, optical wireless positioning is less affected by multipath interference in complex indoor environments and has higher positioning accuracy.

[0003] In the current optical wireless two-dimensional positioning system based on received signal strength (RSS), the downlink is usually used for positioning and indoor lighting. After receiving the RSS signal of the downlink, the receiving end uses a triangulation positioning algorithm to solve the coordinates, and then transmits the coordinates back to the back-end server through the uplink. Due to the limitations of the triangulation positioning algorithm, the receiving end must receive signals from no less than three anchor point LEDs before it can solve the two-dimensional coordinates. However, in actual scenarios, the deployment spacing of indoor installed LEDs is generally large, which will cause some points to be unable to receive enough anchor point LED signals, resulting in positioning blind spots. Therefore, the present invention notes that in the optical wireless two-dimensional positioning system based on RSS, the uplink signal can not only be used to return communication information, but also can be reused as a positioning signal. This method can reduce the system's requirements for the number of anchor points and reduce the system's positioning blind spots.

[0004] From the results of the existing optical wireless two-dimensional positioning system, the present invention also noticed that the error is large when the position of the measured object is close to the anchor point LED. Analyzing the reason, when the scene height is fixed, for targets close to the vertical angle, even a small error will produce a large offset on the plane. Therefore, the present invention expands the dimension based on the optical wireless two-dimensional positioning system, takes into account the height of the mobile terminal, and improves the practicality of the system so that it is no longer limited to positioning on a fixed plane.

[0005] The current three-dimensional positioning technology mainly includes the following methods, namely, vision-based three-dimensional positioning, wireless signal-based three-dimensional positioning, and visible light communication-based three-dimensional positioning. Vision-based three-dimensional positioning obtains the image information of the target through the camera, and realizes three-dimensional positioning in combination with computer vision algorithms. It has the disadvantages of environmental dependence and high complexity; wireless signal-based three-dimensional positioning uses the propagation characteristics of wireless signals, such as signal strength, arrival time, etc., to achieve three-dimensional positioning, but there are problems such as obvious signal attenuation and multipath effects, and high equipment costs; visible light communication-based three-dimensional positioning uses visible light signals for positioning, which has the characteristics of high precision and low latency, but there are blind spot problems as mentioned above. Therefore, the development of a three-dimensional positioning system and method based on bidirectional optical wireless communication has important research value and practical application needs. Summary of the invention

[0006] Aiming at the problem of blind spots in the current optical wireless positioning system based on received signal strength and vertical positioning errors in the existing optical wireless two-dimensional positioning system, the present invention proposes an architecture of a three-dimensional positioning system based on bidirectional optical wireless communication and a corresponding implementation method.

[0007] The three-dimensional positioning system based on bidirectional optical wireless communication adopted by the present invention to solve the problem includes two parts, a fixed base station and a mobile terminal, both of which are integrated with optical transmitting and receiving modules. During positioning, multiple base stations are installed on the ceiling and arranged in a non-collinear manner, and their specific coordinate positions are known. The mobile terminal moves freely in three-dimensional space, and its coordinate position is unknown. For the base station, its LED power is large, the LED light-emitting center and the PD photosensitive center do not overlap, and the distance between the two is recorded as L1. For the mobile terminal, its LED power is small, the LED light-emitting center and the PD photosensitive center do not overlap, and the distance is recorded as L2. The transmitting module of each base station controls the LED to emit a modulated optical signal with a specific fixed frequency, and the frequencies of the modulated optical signals emitted by different base stations are different from each other. These modulated optical signals emitted by the base station constitute the downlink in the positioning system and are received by the receiving module on the mobile terminal. At the same time, the transmitting module of the mobile terminal emits a modulated optical signal with a fixed frequency, which is received by multiple base stations on the ceiling as the uplink in the positioning system. After a fixed sampling time, the mobile terminal collects the optical signal strength data received from multiple base stations, organizes and packages these data into a fixed-length data frame, and then controls its transmitting module to send the start bit signal of the communication data frame. After the base station receives the start bit signal, it prepares to receive the data frame. The mobile terminal transmits the previously received downlink optical signal strength data to the base station through the uplink, and the base station transmits this data to the server through the network. The server assumes that the terminal is located at different altitude layers, and estimates its initial two-dimensional coordinates at each layer using linear least squares, and then further reduces the error according to the best selection configuration table to obtain new two-dimensional coordinates, and then calculates the expected and actual RSS difference, selects the minimum difference two layers weighted average to estimate the terminal height, and solves the coordinates of the mobile terminal in three-dimensional space.

[0008] Furthermore, the base stations are arranged on the ceiling using non-collinear methods, including square, rectangular, and triangular methods;

[0009] Furthermore, the distance L1 between the LED light emitting center and the PD photosensitive center on the base station is preferably in the range of 10 cm to 40 cm;

[0010] Furthermore, the distance L2 between the LED light emitting center and the PD photosensitive center on the mobile terminal is preferably in the range of 5 cm to 10 cm;

[0011] Furthermore, to ensure the uplink data return speed, the frequency of the modulated optical signal during uplink and downlink communications is not less than 200kHz;

[0012] Furthermore, in order to avoid mutual interference between the reflected light of the downlink and uplink, and to retain the indoor lighting function, the downlink uses white light for lighting, and the uplink uses infrared light;

[0013] Furthermore, the transmitting module is a high-speed electronic switch that can control the LED to turn on and off at a speed not lower than 1 MHz;

[0014] Furthermore, the receiving module is an optical receiving circuit that can convert optical signals into electrical signals for output;

[0015] Furthermore, in the downlink, multiple base stations on the ceiling transmit signals at different fixed carrier frequencies that are relatively prime;

[0016] Furthermore, when the mobile terminal moves within the positioning space, its sensor direction is upward, and the mobile terminal moves in a three-dimensional space;

[0017] Furthermore, the optimal selection configuration table is given as a prerequisite in the initial positioning and is configured for each height layer.

[0018] The implementation method of the three-dimensional positioning system based on bidirectional optical wireless communication for solving its problems in the present invention includes the following steps:

[0019] A. Multiple base stations use the transmitting module to drive the LED to emit modulated optical signals with different carrier frequencies. These signals form the downlink, and each carrier frequency is relatively prime;

[0020] B. When the receiving module of the mobile terminal receives the downlink signal, it starts to collect the signal strength and stores it in the buffer area. At the same time, it controls the transmitting module to emit an uplink signal with a specific carrier frequency;

[0021] C. When the base station receives the uplink signal, it also starts to collect and save it in the buffer area;

[0022] D. After a fixed sampling time T, the terminal and the base station stop sampling;

[0023] E. The terminal encapsulates the data in the buffer area into an optical communication format frame and controls the transmitting module to send the start bit of the optical communication to notify the base station to prepare to receive the optical communication data;

[0024] F. After receiving the start bit of the optical communication, the base station controls the transmitting module of the downlink to emit a signal indicating readiness to receive, and prepares to receive data;

[0025] G. After receiving the signal indicating readiness to receive from the base station, the terminal transmits the optical communication frame data through the uplink;

[0026] H. The base station receives the optical communication frame data and decodes the data to obtain the signal strength data of the downlink signal received by the terminal;

[0027] I. The base station returns the signal strength data of the uplink in the buffer area and the received signal strength data of the downlink to the backend server;

[0028] K. After receiving the signal strength data of the uplink and downlink, the server forms multiple position solving equations according to the pre-prepared altitude layers;

[0029] L. The linear least squares algorithm is used to find the solution that minimizes the sum of square errors of each set of equations. The system then obtains the initial two-dimensional position coordinates of the terminals at each altitude layer.

[0030] M. Reselect the combination equations according to the optimal selection configuration table prepared in advance in each altitude layer and the initial two-dimensional position coordinates to obtain new two-dimensional position coordinates;

[0031] N. In each altitude layer, the expected signal reception strength is calculated by combining the three-dimensional coordinates, and the difference is made with the received signal strength, and the absolute value is taken and then averaged;

[0032] O. By comparing and selecting the two adjacent altitude layers with the smallest difference, the actual height of the terminal is estimated by weighted average according to the error, and the final position solution equation group is formed. The three-dimensional position coordinates of the terminal are solved by the linear least squares algorithm.

[0033] The beneficial effects of the present invention are as follows: (1) Through bidirectional optical positioning, the system reduces the requirement on the number of base station signals received by the terminal, thus solving the problem of large lamp spacing, low density and many positioning blind spots faced by traditional optical wireless positioning systems during actual deployment; (2) Through the method of height layer calculation, the expansion of positioning dimension is realized, the two-dimensional vertical error is reduced, and it is more practical; (3) The positioning algorithm adopts a simple triangulation positioning algorithm with low deployment cost and strong adaptability; (4) Under the same system complexity, the method proposed in the present invention can achieve higher positioning accuracy than the traditional downlink-based optical wireless positioning system, and can be used in indoor positioning scenarios with higher accuracy requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the three-dimensional positioning system based on bidirectional optical wireless communication described in the present invention, an embodiment will be listed below and the drawings of the embodiment will be given for illustration. Obviously, the embodiment and the drawings are only an exemplary description of the present invention and are not equivalent to the limitation of the present invention.

[0035] Figure 1 A system structure diagram of an embodiment of a three-dimensional positioning system based on bidirectional optical wireless communication designed according to the present invention;

[0036] Figure 2 A non-collinear triangle arrangement of base stations in an embodiment of the present invention, wherein the arrangement direction is inward;

[0037] Figure 3The schematic diagram of the high-speed LED driving circuit of the transmitting module on the base station and the mobile terminal in the present invention;

[0038] Figure 4 This is a schematic diagram of an optical signal receiving circuit of a receiving module on a base station and a mobile terminal in the present invention;

[0039] Figure 5 A schematic diagram of a system data flow of an embodiment of a three-dimensional positioning system based on bidirectional optical wireless communication provided in an embodiment of the present invention;

[0040] Figure 6 One of the optimal selection configuration tables of an embodiment of a three-dimensional positioning system based on bidirectional optical wireless communication provided in an embodiment of the present invention;

[0041] Figure 7 A flow chart of a server data processing module of an embodiment of a three-dimensional positioning system based on bidirectional optical wireless communication provided in an embodiment of the present invention; DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below in conjunction with the above specific embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0043] First, here is the formula introduction:

[0044] Lambert model formula:

[0045]

[0046] Where G is the channel gain of light transmission, d is the distance from LED to PD, θ is the emission angle of LED, ψ is the incident angle of light to PD, S is the photosensitive area of ​​PD, m is the Lambertian order of LED, M is the Lambertian order of ... max is the maximum emission angle of the LED, ψ max is the maximum incident angle of PD.

[0047] The formula for calculating the received signal strength using fast Fourier transform is:

[0048] RSS=FFT(AP r )=FFT(AηGP t +ξ),

[0049] Where RSS is the signal receiving strength, A represents the amplifier gain, Pr is the signal optical power at the receiving end, η is the photoelectric conversion efficiency of the PD, Pt is the transmitting end power, and ξ is the noise.

[0050] The distance estimation formula based on the received signal strength is:

[0051]

[0052] In the formula, Estimated distance from LED to PD.

[0053] The distance formula between base station and terminal is:

[0054]

[0055] In the formula, (x u ,y u ,z u ) is the coordinate of the terminal, (x i ,y i ,z i ) is the coordinate of the LED in the ith base station, (u i ,v i ,w i ) is the coordinate of PD in the i-th base station, is the square of the downlink distance, is the square of the uplink distance.

[0056] Triangulation positioning algorithm distance equation formula:

[0057] Au r =b,

[0058] In the formula,

[0059]

[0060] The least squares solution formula is:

[0061]

[0062] In the formula, To solve the two-dimensional coordinates of the terminal at a certain altitude.

[0063] The system structure diagram corresponding to this embodiment is shown in the attached figure. Figure 1 As shown in the figure, it includes three base stations 10, 11, 12 installed on the ceiling and a mobile terminal 2 located in the space. The base stations 10, 11, 12 respectively include LED modules 100, 110, 120 as transmitters and PD modules 101, 111, 121 as receivers, and the mobile terminal 2 also includes an LED module 20 as a transmitter and a PD module 21 as a receiver. The arrangement of the base stations 10, 11, 12 is shown in the attached figure. Figure 2 As shown in , it is a non-collinear triangle arrangement, and its arrangement direction is inward.

[0064] The schematic diagram of the LED driving circuit on the base station and mobile terminal is shown in the attached figure. Figure 3As shown, take the LED module 20 on the mobile terminal as an example. The circuit receives the control signal through the control pin, thereby realizing the switch control of the LED, so that it emits a signal of a specific frequency. The positive pole of the LED lamp is connected to the positive pole of the power supply, and the negative pole of the lamp is connected to the load end of the driving circuit.

[0065] The schematic diagram of the PD signal receiving circuit on the base station and mobile terminal is shown in the attached figure. Figure 4 As shown, the PD module 21 on the mobile terminal is taken as an example. The optical signal induces a current on the photodiode, and the current is then amplified by an amplifier circuit composed of amplifiers and finally output from the signal output terminal.

[0066] The system data flow diagram corresponding to this embodiment is shown in the attached figure. Figure 5 As shown. The signal received by the PD module 21 on the mobile terminal from the LED modules 100, 110, 120 of the base station is used as a downlink positioning signal, and the signal received by the PD modules 101, 111, 121 on the base station from the LED module 20 of the mobile terminal is used as an uplink positioning signal, and the RSS data of the downlink and uplink are obtained respectively. Then the mobile terminal 2 transmits the RSS data of the downlink to the base stations 10, 11, 12 through optical wireless communication means, and the base stations 10, 11, 12 transmit the uplink data and the downlink data together to the server 3 through the network.

[0067] One of the optimal selection configuration tables corresponding to this embodiment is shown in the attached Figure 6 As shown. The optimal selection configuration table shows the best RSS selection data set for each area in the altitude layer, which can effectively reduce the error. Since the RSS obtained by the terminal is generally an Nx2 matrix, where N is the number of base stations within the terminal's field of view, and position estimation requires 3 or more RSS data, there are a total of By traversing these data sets and performing repeated position estimation, the configuration with the minimum average error of each measurement point can be compared and obtained, which represents the optimal selected configuration data set for the area. In this embodiment, given 3 base stations, there are 6 RSS data sources, that is, there are 42 different data sets. Therefore, before the formal measurement, the area is divided at each preset altitude layer for bidirectional positioning, and the data accuracy calculated using different data sets is compared, and the one with the smallest average error is selected and filled in the configuration table. Figure 6 In each divided area, ui represents the RSS data of the i-th uplink, d i The RSS data representing the selection of the i-th downlink together constitute the optimal selection configuration data set for the area. The optimal selection configuration data sets of all areas in the altitude layer constitute the optimal selection configuration table. Ultimately, each altitude layer can obtain an optimal selection configuration table for use by server 3.

[0068] The server data processing flow chart corresponding to this embodiment is shown in the attached figure. Figure 7 As shown. After obtaining the RSS data from the uplink and downlink, the server 3 first performs 301 distance measurement, and converts the signal strength data into corresponding distance data according to the preset altitude layers. Then 302 uses the data to establish a position equation group, and solves the equation by the linear least squares method. 303 First, the initial two-dimensional coordinates obtained at each altitude layer are compared with its optimal selection configuration table, and the RSS data source is reselected to form an equation group to obtain a new two-dimensional coordinate of the mobile terminal. 304 The RSS data of each altitude layer is compared with the expected calculation, and the two adjacent candidate altitude layers with the minimum difference are selected. 305 According to the RSS data difference of the candidate altitude layers, the actual height of the terminal is estimated using the weighted average method to form the final position solution equation group. Finally, 306 outputs the three-dimensional positioning position of the mobile terminal through the linear least squares algorithm.

[0069] Please note that the above content only shows the preferred embodiments of the present invention and the technical principles used. However, for those skilled in the art, they are capable of making other different forms of changes or modifications based on the above description, and making various significant changes, adjustments or replacements to the embodiments. Therefore, although we have explained the present invention in detail through embodiments, the present invention is not limited to these examples, and the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention. As long as it does not deviate from the core idea of ​​the present invention, it can also include more equivalent embodiments. Ultimately, the scope of the present invention will be determined by the attached claims.

Claims

1. A three-dimensional positioning system and method based on bidirectional optical wireless communication, characterized in that: It consists of two parts: a base station and a mobile terminal. Each part is equipped with an LED light transmitting module and a PD light receiving module. The LED light emitting center and the PD photosensitive center do not overlap. During positioning, multiple base stations are arranged on the ceiling in a non-collinear form, and the mobile terminals are randomly distributed in three-dimensional space. After the mobile terminal obtains the downlink positioning data, it sends the positioning data to the base station through the uplink optical communication system; after the base station collects the downlink and uplink positioning data, it transmits the data to the backend server through Ethernet; the backend server first assumes that the terminal is at different altitudes, fuses the signal data to form a position equation group, and solves the equation group using the least squares algorithm to obtain the two-dimensional coordinates of the mobile terminal at the altitude, and then calculates the difference between the expected signal reception strength and the actually measured signal reception strength at each altitude, and finally estimates the actual height of the terminal by comparing and selecting the two adjacent layers with the smallest difference for weighted average, thereby obtaining the three-dimensional coordinates of the terminal; The LED light transmitting module is composed of an LED, a MOS tube and a MOS driving circuit, and can quickly control the switch of the LED to send modulated optical communication or positioning signals; The PD optical receiving module is composed of a PD photodiode and a signal amplifying circuit, and can convert the weak current signal generated by the PD into a voltage signal for receiving modulated optical communication or positioning signals; The positioning signal adopts frequency division in the downlink, and the carrier frequencies of each base station are different and mutually prime. After the receiving end receives the signal, it uses Fourier transform to distinguish different signals; The optical communication signal, the information is firstly Manchester encoded, converted into code elements with 0 / 1 accounting for half, and then converted into an optical signal through switch modulation.

2. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: Not only is the downlink optical signal in the full-duplex optical wireless communication system used for positioning, but the uplink optical signal used for communication is also multiplexed as a positioning signal.

3. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The base stations are arranged in a non-collinear form, including but not limited to a square, a rectangle, and a triangle.

4. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The center positions of the LED and PD on the base station and mobile terminal do not coincide.

5. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claims 1 and 4, characterized in that: When base stations are arranged, their orientations vary, and the arrangement is represented by orientation angles. Typical arrangements include inward orientation, outward orientation, and rotated orientation.

6. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The base station is connected to the backend server via Ethernet, specifically, via WiFi and a network port.

7. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The backend server has a certain amount of computing power and can complete the deployment of relevant algorithms and data recording.

8. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The value of the altitude layer is determined by the scene altitude, and its accuracy can be optimized iteratively.

9. A three-dimensional positioning system and method based on bidirectional optical wireless communication according to claim 1, characterized in that: The RSS configuration scheme is adopted to improve its positioning accuracy, and each altitude layer is equipped with an optimal selection configuration table.

10. A three-dimensional positioning system and method based on bidirectional optical wireless communication, characterized in that: The following steps are involved: A. Multiple base stations use transmission modules to drive LEDs to emit modulated optical signals of different frequencies. These signals constitute the downlink, and the carrier frequencies are mutually prime; B. When the mobile terminal receiving module receives the downlink signal, it starts to collect the signal strength and store it in the buffer area, and at the same time controls the transmitting module to send an uplink signal with a fixed frequency; C. When the base station receives the uplink signal, it also starts collecting and saving it to the buffer area; D. After a fixed sampling time T, the terminal and the base station stop sampling; E. The terminal encapsulates the data in the buffer area into an optical communication format frame, and controls the transmitting module to send the optical communication start bit to notify the base station to prepare to receive the optical communication data; F. After receiving the start bit of optical communication, the base station controls the downlink transmission module to transmit a ready-to-receive signal to prepare for data reception; G. After the terminal receives the signal from the base station that it is ready to receive, it transmits the optical communication frame data through the uplink; H. The base station receives the optical communication frame data and decodes the data to obtain the downlink signal strength data received by the terminal; I. The base station transmits the uplink signal strength data in the buffer area and the received downlink signal strength data back to the backend server; K. After receiving the signal strength data of the uplink and downlink, the server forms multiple position solving equations according to the pre-prepared altitude layers; L. The linear least squares algorithm is used to find the solution that minimizes the sum of square errors of each set of equations. The system then obtains the initial two-dimensional position coordinates of the terminals at each altitude layer. M. Reselect the combination equations according to the optimal selection configuration table prepared in advance in each altitude layer and the initial two-dimensional position coordinates to obtain new two-dimensional position coordinates; N. In each altitude layer, the expected signal reception strength is calculated by combining the three-dimensional coordinates, and the difference is made with the received signal strength, and the absolute value is taken and then averaged; O. By comparing and selecting the two adjacent altitude layers with the smallest difference, the actual height of the terminal is estimated by weighted average according to the error, and the final position solution equation group is formed. The three-dimensional position coordinates of the terminal are solved by the linear least squares algorithm.

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