CN104809908A - Method of ZigBee network based vehicle positioning in indoor parking area environment - Google Patents

Abstract

The invention discloses a ZigBee network-based vehicle positioning method in an indoor parking lot environment. The method establishes a ZigBee wireless sensor network in the indoor parking lot, and divides the network into time-divided areas to calculate the distance between the vehicle to be positioned and the location. Positioning the distance between terminal nodes improves the calculation accuracy of the distance, thereby improving the accuracy of vehicle positioning, and helps to realize the rapid and accurate guidance of vehicles in the indoor parking lot environment.

Description

Vehicle positioning method based on ZigBee network in indoor parking lot environment

technical field

The invention belongs to the technical field of vehicle positioning, in particular to a ZigBee network-based vehicle positioning method in an indoor parking lot environment.

Background technique

Intelligent transportation occupies a very important position in the urban road traffic system. Reasonable planning, control, monitoring and guidance for urban traffic is of great significance to improve the efficiency of urban traffic network and improve the living standards of urban residents. The vehicle positioning system is one of the important supporting technologies of intelligent transportation. The correct positioning of the vehicle as a mobile node can directly and effectively observe and control the operation status of urban traffic.

In order to automatically guide the vehicle to the pre-planned destination parking space in a large indoor parking lot environment, it is necessary to first solve the positioning problem of the vehicle in the indoor parking lot. Because in the indoor parking lot environment, the satellite signal received by the navigator is usually relatively weak, which reduces the efficiency and accuracy of positioning parking. Therefore, more and more indoor parking lots use wireless communication technology between multiple points to realize indoor parking. At present, commonly used wireless communication technologies include: Bluetooth, WIFI, RFID, ZigBee, ultra-wideband communication, GPRS, 3G, 4G, etc. Considering various factors such as cost, power consumption, operating distance, accuracy, and network capacity, it is generally appropriate to use Vehicle positioning scheme based on ZigBee wireless sensor network technology. The vehicle positioning technology based on ZigBee wireless sensor network is to connect the commercialized ZigBee module to the smart phone of the vehicle. During the moving process of the vehicle, the module communicates with the ZigBee positioning terminal nodes around the vehicle to realize the location of the vehicle. Positioning, and then transmit the location information to the navigation module on the smartphone software. The navigation module uses the current location information of the vehicle and the electronic map of the parking lot to finally realize the path guidance to the target parking space.

According to the positioning technology theory based on RSSI in ZigBee technology and the Shadowing model in the field of wireless signal transmission, the relationship between the strength of the received signal and the distance between the transmitting and receiving nodes is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; nlg</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}$

Among them, d is the distance between the sending end and the receiving end, the unit is m; d ₀ is the reference distance, the unit is m; _PL (d) is the received signal power of the receiving end, the unit is dBm; P _L (d ₀ ) is The received signal power at distance d ₀ , in dBm; X _d is a random variable that obeys Gaussian distribution, with a mean value of zero, in dBm; n is the path attenuation index, which indicates the speed attenuation of the RSSI value as the distance increases. When performing a large number of independent measurements, X _d ＝0(dBm) can be set, at this time: in, is the average power of the received signal, in dBm; a is the opposite number of the received signal power 1m away from the sending end, in dBm. For example: if the average power of the received signal at 1m away from the sending end is -30dBm, then the value of parameter a is 30, after modifying the above formula, we can get: It can be seen that, if the values of the parameters a and n are known, the average value obtained after multiple measurements is After that, the distance between the sending and receiving nodes can be calculated. If there are more than 3 distance measurements, the coordinates of the nodes to be located can be determined according to the triangle centroid positioning algorithm or the maximum likelihood estimation method. The accuracy of a and n is the key factor that determines the distance measurement and even the positioning accuracy. The values of these two parameters are not only related to the local environment when the wireless signal is transmitted, but also change with time, so they bring a lot to their measurement. big difficulty. The more traditional method is the empirical value method, that is, a large number of experimental measurements are carried out in the positioning field before positioning, and the values of a and n are determined by linear regression. The specific implementation process is: in the area to be positioned, first install a fixed transmitting device, then place the receiving device at a certain position, accurately measure the distance between the transmitting device and the receiving device, collect a set of RSSI values and calculate the average; , move the receiving device to another location according to the pre-planned moving route, and repeat the above process; this measurement process is repeated until the entire area is "covered" by the moving route of the receiving device. The corresponding coefficient calculation formula is:

$\begin{array}{cc}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; lgd</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; RSSI</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 10</span>}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; lgd</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}& \stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 10</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; lgd</span>}}\end{array}$

In the formula, M is the number of measured points, d _i is the precise distance between the transmitter and the i-th receiving point, is the average value after logarithm of M distance values, RSSI _i is the average value of RSSI values obtained in multiple measurements at the i receiving point, is the average value of M RSSI _i values. It can be seen from the above measurement process that the workload of the traditional method is very large, and it cannot reflect the changes of a and n with time and space.

This shows that the prior art needs to be further improved and improved.

Contents of the invention

In order to avoid the disadvantages of the prior art, the present invention provides a ZigBee network-based vehicle positioning method in an indoor parking lot environment.

The technical scheme adopted in the present invention is:

A vehicle positioning method based on ZigBee network under indoor parking lot environment, the method comprises the following steps:

Step 1: Set up the ZigBee wireless sensor network system in the indoor parking lot. The ZigBee wireless sensor network system includes a ZigBee network, and a central node, several router nodes and more terminal nodes are set in the ZigBee network. The terminal node includes the positioning terminal node for locating the vehicle to be positioned; the driver and passenger of the vehicle to be positioned hold a smart phone, and the smart phone is equipped with a ZigBee module, and the vehicle to be positioned sends a positioning request through the smart phone;

Step 2: According to the distribution of parking spaces in the indoor parking lot, the above positioning terminal nodes are divided into several non-overlapping areas, and each area is numbered. Each area is triangular or quadrilateral. Positioning Terminal nodes are installed on the vertices of each triangle or quadrilateral, and in each area, each positioning terminal node communicates directly with two adjacent positioning terminal nodes;

Step 3: After accurately measuring the coordinates of each positioning terminal node in each of the above areas, calculate the distance between two adjacent vertices, and calculate the two undetermined values of the surrounding environment of a certain positioning terminal node in the area according to the following formula: Constants a _i , n _i :

$\left\{\begin{array}{c}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; dBm</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ {\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; dBm</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.$

Among them, d _i1 and d _i2 are the distances between the i-th positioning terminal node in the area and the surrounding first and second adjacent positioning terminal nodes, and is the average power of the signal sent by the i-th positioning terminal node in the area received by the surrounding first and second adjacent positioning terminal nodes;

Step 4: Based on the calculated distance values d _i1 and d _i2 , and the measured values and Calculate a _i and n _i , and take the average of a _i and n _i of all positioning terminal nodes in the area as the values of a and n in the area, and obtain:

$\left\{\begin{array}{c}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ \stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\end{array}\right.$

in, and is the average value of two undetermined constants in this area, and L is the number of positioning terminal nodes in this area;

When a vehicle is detected to enter or leave at the entrance or exit of the parking lot, the central node sends commands to each positioning terminal node through the router node, and each positioning terminal node communicates with the adjacent positioning terminal node. The values of a _i and _ni are updated, and the undetermined constants obtained by recalculation and After the vehicle to be positioned makes a positioning request, all positioning terminal nodes within the direct communication range with it will respond by sending the average value of a and n of the area where the positioning terminal node is located to the vehicle to be positioned. Terminal nodes are usually divided into multiple areas, so this type of positioning terminal node will send the average value of multiple a and n and the number of the corresponding area, and the smart phone of the vehicle to be positioned receives the feedback from the nearby positioning terminal node After the information is displayed, select the area with the highest number of occurrences to proceed to the next step;

Step 5: Calculate the distance d between the vehicle to be positioned entering a certain area and the positioning terminal node of the selected area by the following formula,

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{{\mathrm{<span\; class="notranslate">\; RSSI</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 10</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}}}$

Among them, a and n take the average value in step 4, is the average power of the received signal.

Step 6: After calculating the distance between more than 3 above-mentioned vehicles to be positioned and the positioning terminal node, calculate the coordinates of the vehicle to be positioned by the triangle centroid positioning algorithm or the maximum likelihood estimation method.

Each of the positioning terminal nodes is provided with a power amplification module.

The terminal node in described step 1 also comprises the monitoring terminal node that is used to monitor parking space state, between location terminal node and monitoring terminal node, there is no communication between adjacent two monitoring terminal nodes; Described router node The point is set at the center of the encirclement of several monitoring terminal nodes, and the router node is used to relay the communication.

In the step 2, the central node communicates with its adjacent router node, and the central node is installed at the entrance, exit, or center of the parking lot.

Owing to adopting above-mentioned technical scheme, the beneficial effect that the present invention obtains is:

The present invention provides a vehicle positioning algorithm for time-division and area-division in an indoor parking lot environment, which helps to guide vehicles to a pre-planned target parking space quickly and accurately, and has the advantages of fast positioning speed, high precision, and good real-time performance. Significant advantages.

Description of drawings

Figure 1 is a schematic diagram of the overall structure of the present invention.

Fig. 2 is a schematic diagram of area division in the present invention.

Fig. 3 is a schematic diagram of the variation of the maximum positioning error with time without considering the variation of a and n with time and space.

Fig. 4 is a schematic diagram of the variation of the maximum positioning error with time when a and n are not considered to vary with time, but only a and n are considered to vary with space.

Fig. 5 is a schematic diagram of the variation of the maximum positioning error with time when a and n are considered to vary with time, and a and n are also considered to vary with space.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited to these embodiments.

As shown in Figure 1 and Figure 2, the vehicle location method based on ZigBee network under indoor parking lot environment, this method comprises the following steps:

Step 1: Set up the ZigBee wireless sensor network system in the indoor parking lot. The ZigBee wireless sensor network system includes a ZigBee network, and a central node, several router nodes and more terminal nodes are set in the ZigBee network. The central node communicates with the router node adjacent to it. The central node is installed at the entrance, exit, or central position of the parking lot. The terminal node includes a positioning system for locating the vehicle to be positioned. terminal node; in order to reduce the layout amount of the positioning terminal node, each of the positioning terminal nodes is provided with a power amplification module, thereby expanding the direct communication range of the positioning terminal node; the terminal node also includes a Monitoring the monitoring terminal node of the parking space state, there is no communication between the positioning terminal node and the monitoring terminal node, and between two adjacent monitoring terminal nodes; the router node is set in the center of the encirclement circle of several monitoring terminal nodes Location, the router node is used for relay communication; the driver and occupant of the vehicle to be positioned holds a smartphone, which is equipped with a ZigBee module, and the vehicle to be positioned sends a positioning request through the smartphone;

Step 2: According to the distribution of parking spaces in the indoor parking lot, divide the above-mentioned positioning terminal nodes into several non-overlapping areas such as A, B, C, D, etc., and each area is triangular or Quadrilateral, the positioning terminal node is installed on the vertices of each triangle or quadrilateral, and in each area, each positioning terminal node communicates directly with two adjacent positioning terminal nodes;

Step 3: After accurately measuring the coordinates of each positioning terminal node in each of the above areas, calculate the distance between two adjacent vertices, and calculate the two undetermined values of the surrounding environment of a certain positioning terminal node in the area according to the following formula: Constants a _i , n _i :

$\left\{\begin{array}{c}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; dBm</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ {\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; RSSI</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; dBm</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; lg</span>}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.$

Among them, d _i1 and d _i2 are the distances between the i-th positioning terminal node in the area and the surrounding first and second adjacent positioning terminal nodes, and is the average power of the signal sent by the i-th positioning terminal node in the area received by the surrounding first and second adjacent positioning terminal nodes;

Step 4: Based on the calculated distance values d _i1 and d _i2 , and the measured values and After calculating a _i and n _i , the positioning terminal nodes in each area calculate their own a _i and n _i , and transmit them to the central node through the router node, and the central node calculates the average value of a and n in each area It is transmitted to each positioning terminal node, and each positioning terminal node stores the average value of a and n of its own area (usually multiple) in its own data storage device, and draws:

$\left\{\begin{array}{c}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ \stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\end{array}\right.$

in, and is the average value of two undetermined constants in this area, and L is the number of positioning terminal nodes in this area;

After the vehicle to be positioned makes a positioning request, all positioning terminal nodes within the direct communication range with it will respond by sending the average value of a and n of the area where the positioning terminal node is located to the vehicle to be positioned. Terminal nodes are usually divided into multiple areas, so this type of positioning terminal node will send the average value of multiple a and n and the number of the corresponding area, and the smart phone of the vehicle to be positioned receives the feedback from the nearby positioning terminal node After the information is displayed, select the area with the highest number of occurrences to proceed to the next step;

Step 5: Calculate the distance d between the vehicle to be positioned entering a certain area and the positioning terminal node of the selected area by the following formula,

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{{\mathrm{<span\; class="notranslate">\; RSSI</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 10</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}}}$

Among them, a and n take the average value in step 4, is the average power of the received signal.

Step 6: After calculating the distance between more than 3 above-mentioned vehicles to be positioned and the positioning terminal node, calculate the coordinates of the vehicle to be positioned by the triangle centroid positioning algorithm or the maximum likelihood estimation method; in different time periods, follow According to factors such as the entry and exit of vehicles in the parking lot, the two undetermined constants in all areas will change with time. Obviously, if they are updated more frequently, the positioning accuracy of the vehicle can be guaranteed, but it will obviously increase the number of components in each area. The power consumption of the vertices. For this reason, only when a vehicle enters or leaves is detected at the entrance or exit of the parking lot, the central node sends commands to each positioning terminal node through the router node, and each positioning terminal node connects with the adjacent positioning terminal node. point communication, update the values of a _i and ni _i , according to the undetermined constants obtained by recalculation and The distance d between the vehicle to be positioned and the positioning terminal node can be calculated, and then the coordinates of the vehicle to be positioned can be calculated.

It should be noted that for the ZigBee module connected to the smartphone on the vehicle to be positioned, after the broadcast information of the positioning request is sent, the router node does not forward the information, and only the positioning terminal node within the direct communication range with the node to be positioned It will receive the information and make a response; when positioning the vehicle to be positioned, the positioning terminal node will send its precise coordinates and the average value of a and n in the area to the ZigBee module of the smartphone, and the location solution is installed in the smartphone Calculation software to calculate the real-time position of the vehicle to be positioned. After that, the smartphone guides the vehicle step by step to the target parking space based on the built-in internal map of the parking lot and the calculated vehicle position.

In order to verify that the designed algorithm can improve the positioning accuracy, some parameters are set on the basis of Figure 2, and a computer simulation program is written using Matlab language. The specific parameters used are shown in Table 1:

Table 1 Parameters used by Matlab simulation program

In addition to the parameters listed in Table 1, the signal-to-noise ratio is set to 30; in each area to calculate the distance between a positioning terminal node and the node to be located, the number of measurements is 100 times.

Figure 3 does not consider the change of a and n with time and space (that is, in the process of calculating the distance using the formula in step 5, a and n in each area are uniformly used in the third and fourth columns of Table 1 The average value of ), the maximum positioning error of 11 areas from A to K in Fig. 3 changes with time from 0 to 100 hours. It can be seen from the figure that the error value is very large, and the largest error has reached 35m.

Figure 4 only considers the changes of a and n with space, but does not consider their changes with time (that is, in the process of calculating the distance using the formula in step 5, the a and n of each area are respectively taken from Table 1 This area corresponds to the values in the third and fourth columns of the row), and the maximum positioning error of the 11 areas from A to K in Figure 3 changes with time from 0 to 100 hours. Compared with Figure 4, the error has been reduced, but the maximum error is still nearly 30m.

Figure 5 is a case where not only the variation of a and n with space, but also their variation with time are considered (that is, in the process of calculating the distance using the formula in step 5, the a and n of each area are respectively taken as the current moment a and n), the maximum positioning error of 11 areas from A to K in Fig. 3 changes with time from 0 to 100 hours. It can be seen from the figure that the error is significantly reduced, basically controlled within 2m, and a very ideal positioning effect has been achieved.

It can be seen that the positioning method in the present invention significantly improves the positioning accuracy of the vehicle in the indoor parking lot environment, and helps to guide the vehicle to the target parking space planned in advance quickly and accurately.

The parts not mentioned in the present invention can be realized by adopting or referring to the prior art.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (4)

1. A vehicle positioning method based on a ZigBee network in an indoor parking lot environment is characterized in that: the method comprises the following steps:

step 1: the method comprises the steps that a ZigBee wireless sensing network system is arranged in an indoor parking lot and comprises a ZigBee network, a central node, a plurality of router nodes and a larger number of terminal nodes are arranged in the ZigBee network, and the terminal nodes comprise positioning terminal nodes used for positioning vehicles to be positioned; a driver of a vehicle to be positioned holds a smart phone, the smart phone is provided with a ZigBee module, and the vehicle to be positioned sends a positioning request through the smart phone;

step 2: according to the distribution of parking spaces in an indoor parking lot, carrying out region division on the positioning terminal nodes to enable the positioning terminal nodes to be divided into a plurality of non-overlapping regions, numbering each region, wherein each region is triangular or quadrilateral, the positioning terminal nodes are installed on the top points of each triangle or quadrilateral, and in each region, each positioning terminal node is in direct communication with two positioning terminal nodes adjacent to the positioning terminal node;

and step 3: accurately measuring the coordinates of each positioning terminal node of each region, calculating the distance between two adjacent vertexes, and calculating two undetermined constants a of the surrounding environment of one positioning terminal node in the region according to the following formula_i、n_i：

<math> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <msub> <mover> <mi>RSSI</mi> <mo>&OverBar;</mo> </mover> <mrow> <mi>i</mi> <mn>1</mn> </mrow> </msub> <mo>[</mo> <mi>dBm</mi> <mo>]</mo> <mo>=</mo> <mo>-</mo> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mi>i</mi> </msub> <mo>+</mo> <mn>10</mn> <msub> <mi>n</mi> <mi>i</mi> </msub> <mo>&CenterDot;</mo> <mi>lg</mi> <msub> <mi>d</mi> <mrow> <mi>i</mi> <mn>1</mn> </mrow> </msub> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <msub> <mover> <mi>RSSI</mi> <mo>&OverBar;</mo> </mover> <mrow> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>[</mo> <mi>dBm</mi> <mo>]</mo> <mo>=</mo> <mo>-</mo> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mi>i</mi> </msub> <mo>+</mo> <mn>10</mn> <msub> <mi>n</mi> <mi>i</mi> </msub> <mo>&CenterDot;</mo> <mi>lg</mi> <msub> <mi>d</mi> <mrow> <mi>i</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> </math>

Wherein d is_i1And d_i2For the distance between the ith positioning terminal node and the 1 st and 2 nd adjacent positioning terminal nodes in the area,andreceiving average power of signals sent by 1 st and 2 nd adjacent positioning terminal nodes for the ith positioning terminal node in the area;

and 4, step 4: according to the calculated distance value d_i1And d_i2And measured valueAndcalculate a_iAnd n_iAnd a of all the positioning terminal nodes in the area_iAnd n_iTaking the average as the value of a and n in the area to obtain:

<math> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mover> <mi>a</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mfrac> <mn>1</mn> <mi>L</mi> </mfrac> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>L</mi> </munderover> <msub> <mi>a</mi> <mi>i</mi> </msub> </mtd> </mtr> <mtr> <mtd> <mover> <mi>n</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mfrac> <mn>1</mn> <mi>L</mi> </mfrac> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>L</mi> </munderover> <msub> <mi>n</mi> <mi>i</mi> </msub> </mtd> </mtr> </mtable> </mfenced> </math>

wherein,andthe average value of two undetermined constants in the region is obtained, and L is the number of positioning terminal nodes in the region;

when detecting that a vehicle enters or leaves at the entrance or exit of the parking lot, the central node sends a command to each positioning terminal node through the router node, and each positioning terminal node communicates with the adjacent positioning terminal node, and the pair a_iAnd n_iIs updated and recalculated to obtain the undetermined constantAndafter a vehicle to be positioned provides a positioning request, all positioning terminal nodes in a direct communication range respond, and send the average values of a and n of the areas where the positioning terminal nodes are located to the vehicle to be positioned;

and 5: calculating the distance d between a vehicle to be positioned entering a certain area and a positioning terminal node of the selected area by the following formula,

<math> <mrow> <msub> <mi>d</mi> <mi>i</mi> </msub> <mo>=</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mfrac> <mrow> <mo>(</mo> <mover> <mi>a</mi> <mo>&OverBar;</mo> </mover> <mo>+</mo> <msub> <mover> <mi>RSSI</mi> <mo>&OverBar;</mo> </mover> <mi>i</mi> </msub> <mo>)</mo> </mrow> <mrow> <mn>10</mn> <mover> <mi>n</mi> <mo>&OverBar;</mo> </mover> </mrow> </mfrac> </mrow> </msup> </mrow> </math>

wherein a and n are the average values in step 4,is the received signal average power.

Step 6: after the distances between more than 3 vehicles to be positioned and the positioning terminal nodes are calculated, the coordinates of the vehicles to be positioned are calculated through a triangular centroid positioning algorithm or a maximum likelihood estimation method.

2. The vehicle positioning method based on the ZigBee network in the indoor parking lot environment according to claim 1, wherein: and each positioning terminal node is provided with a power amplification module.

3. The vehicle positioning method based on the ZigBee network in the indoor parking lot environment according to claim 1, wherein: the terminal nodes in the step 1 further comprise monitoring terminal nodes for monitoring the parking space state, and no communication exists between the positioning terminal nodes and the monitoring terminal nodes and between two adjacent monitoring terminal nodes; the router nodes are arranged in the center positions of the surrounding rings of the monitoring terminal nodes and used for relay communication.

4. The vehicle positioning method based on the ZigBee network in the indoor parking lot environment according to claim 1, wherein: in the step 1, the central node communicates with the adjacent router node, and the central node is installed at an entrance, an exit or a central position of the parking lot.