CN103117007A - Vehicle positioning and anti-collision early warning system based on ZigBee and GPS - Google Patents

Abstract

The invention discloses a vehicle positioning and anti-collision early warning system based on ZigBee and GPS, which is characterized in that it includes an information collection and communication unit, a main controller unit, an information display and an audible and visual alarm unit: the information collection and communication unit passes GPS Module, electronic compass module and ZigBee communication module obtain the vehicle information of the vehicle and the wireless communication signal containing the vehicle information of the vehicle in front, and send the wireless communication signal containing the vehicle information of the vehicle to the rear vehicle; the main controller unit uses the vehicle information or Calculate the signal strength of the wireless communication signal and the distance between vehicles in front, and judge the danger level by using the vehicle speed, vehicle moving direction information and vehicle distance; the information display and sound and light alarm unit display and alarm the danger level. The invention is used to realize the acquisition of adjacent vehicle distance and vehicle speed information, and further realize early warning of the driver to control the vehicle speed so as to keep the vehicle running in a safe distance.

Description

Vehicle positioning and collision avoidance warning system based on ZigBee and GPS

technical field

The invention relates to the specific application of wireless sensor network technology in road vehicle driving, in particular to a ZigBee and GPS-based vehicle positioning and anti-collision early warning system.

Background technique

In the prior art, vehicle positioning basically adopts GPS (Global Positioning System) technology to obtain longitude and latitude position information of the vehicle itself. However, when using GPS positioning, at least four messages sent by GPS navigation satellites must be received at the same time to calculate the specific position of the vehicle. If the vehicle is in a complex terrain such as a mountainous area or a tunnel, the GPS cannot receive signals from four satellites at the same time, so positioning cannot be achieved; In addition, the current GPS technology can only realize the positioning of the vehicle itself, and cannot know the distance information between the vehicle and the adjacent vehicle in front. The method of visually judging the distance alone cannot meet the application requirements of vehicle collision avoidance.

The most common highway accidents are multi-vehicle rear-end collisions. This kind of accidents mostly occurs when the distance between vehicles is too small due to heavy traffic flow, high speed, bad weather, driver fatigue, etc., and the driver cannot deal with it in advance. The current vehicle-mounted anti-collision systems are mostly realized by means of camera shooting and analysis, which cannot be realized in conditions of poor visibility such as severe rain, snow, and fog.

Contents of the invention

The present invention is to solve above-mentioned deficiencies existing in the prior art, provides a kind of vehicle positioning and anti-collision warning system based on ZigBee and GPS, combines ZigBee and GPS, the distance between vehicles obtained through wireless communication signals, when possible In the event of danger, the driver will be warned in advance to control the speed of the vehicle to maintain a safe distance between vehicles.

The present invention solves technical problem and adopts following technical scheme:

A ZigBee and GPS-based vehicle positioning and collision avoidance early warning system of the present invention is characterized in that it includes an information collection and communication unit, a main controller unit, an information display and an audible and visual alarm unit;

The information collection and communication unit is composed of a GPS module, an electronic compass module and a ZigBee communication module, obtains the vehicle speed and the vehicle position information characterized by longitude and latitude with the GPS module; obtains the vehicle position information with the electronic compass module Vehicle moving direction information; obtain the wireless communication signal containing the vehicle information of the vehicle in front sent by the vehicle in front with the ZigBee communication module, and send it to the vehicle in the rear with the ZigBee communication module under the control of the main controller unit A wireless communication signal containing the vehicle information of the own vehicle; the vehicle information includes vehicle speed, vehicle position information and vehicle moving direction information;

The main controller unit uses the vehicle information to calculate the vehicle distance L1 between the vehicle and the vehicle in front, or calculates the distance between the vehicle and the vehicle in front by using the signal strength of the wireless communication signal sent by the vehicle in front received by the ZigBee communication module. The inter-vehicle distance L2 between the vehicles in front; use the vehicle speed, vehicle moving direction information and the calculated inter-vehicle distance L1 or inter-vehicle distance L2 to judge the danger level of the vehicle;

The information display and sound and light alarm unit is composed of a liquid crystal display module and a sound and light alarm module. Make an alarm.

The vehicle positioning and anti-collision warning system based on ZigBee and GPS of the present invention is also characterized in that: in the process of judging the danger level of the own vehicle, the vehicle distance L1 is preferentially used for the vehicle distance L1 and the vehicle distance L2.

The method for calculating and obtaining the vehicle distance between the vehicle and the vehicle in front by using the vehicle information is:

Let the longitude of the vehicle (B) be N2 and latitude E2; the longitude N1 and latitude of the vehicle in front (A) be E1, and the distance L1 between the vehicle (B) and the vehicle (A) in front can be obtained by calculating according to formula (1) :

$\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), a=E1-E2, b=N1-N2.

The method that the signal strength calculation of the wireless communication signal sent by the vehicle in front that utilizes ZigBee communication module to receive to obtain the vehicle distance between this car and the vehicle in front is:

Let the ZigBee communication signal strength received by the vehicle (B) in front of the vehicle (A) be RSSI, and calculate the distance L2 between the vehicle (B) and the vehicle in front (A) according to formula (2):

$\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 40.2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\\ {\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 58.5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 33</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Pt in formula (2) is the transmission power value of the ZigBee communication module in the vehicle that is set uniformly.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

1. The present invention aims at situations such as dangerous distances between adjacent vehicles, dense vehicle groups, and abnormal vehicle speeds on high-speed sections that may cause collisions or serial rear-end collisions. The ZigBee communication module is used to broadcast the positioning information of a single vehicle to nearby vehicles, which solves the problem of GPS Locate the problem that the vehicle distance information cannot be obtained, realize the acquisition of adjacent vehicle distance and vehicle speed information, and then realize the anti-collision warning;

2. The present invention uses GPS positioning data in combination with ZigBee positioning data. For the inability to receive GPS signals on complex road sections, ZigBee positioning is used as a supplementary method to realize vehicle positioning under any circumstances, and electronic compass modules are used to supplement ZigBee positioning information to realize the interpretation and early warning of vehicles in the same direction;

3. The present invention has strong expansion ability. By reserving interfaces in the main controller unit, various communication modules can be added, and remote data transmission modules such as GPRS and 3G can be easily connected to the system. Monitor the driving situation of the vehicle and obtain the reserved interface for driving data;

4. Aiming at the negligence of drivers and passengers on high-speed roads, or the decline in response ability caused by fatigue driving, the present invention uses an audible and visual alarm unit to combine voice reminders with LCD screen display, and at the same time, for different situations of vehicle distance and vehicle speed, Classification of dangerous situations, combined with different modes of sound and light alarms, to remind drivers to correctly handle dangerous situations and avoid accidents;

5. The present invention uses the vehicle-mounted power supply as the system power supply, and at the same time uses a lithium battery for backup power supply to ensure that the system always works stably.

6. The present invention combines the GPS module with the ZigBee module, and realizes the calculation and control by the ARM controller. The implementation method is simple, the reliability is high, and the cost is low.

Description of drawings

Fig. 1 is the explanatory schematic diagram that the present invention uses on highway;

Fig. 2 is the single device structure schematic diagram of vehicle positioning and anti-collision early warning system based on ZigBee and GPS of the present invention;

Fig. 3 is a schematic diagram of the vehicle distance between the vehicle and the vehicle in front obtained by calculating the vehicle information according to the present invention;

Fig. 4 is the vehicle location based on ZigBee and GPS of the present invention and the work flowchart of anti-collision early warning system;

Fig. 5 is a schematic diagram showing the vehicle-mounted LCD screen of the present invention;

Labels in the figure: 1 road; 2 vehicles.

Detailed ways

As shown in Figure 1, on highway 1, each vehicle 2 is equipped with a vehicle positioning and collision avoidance warning system based on ZigBee and GPS, paying attention to the distance and density of vehicles driving in the same direction in front of them, and keeping a safe distance from them , to avoid sending rear-end collisions and large-scale collision accidents.

As shown in Figure 2, the vehicle positioning and anti-collision warning system based on ZigBee and GPS in this embodiment includes: information collection and communication unit, main controller unit, information display and sound and light alarm unit:.

The information collection and communication unit is composed of a GPS module, an electronic compass module and a ZigBee communication module. The GPS module is used to obtain vehicle speed and vehicle position information represented by longitude and latitude; the electronic compass module is used to obtain vehicle moving direction information of the vehicle; The ZigBee communication module obtains the wireless communication signal containing the vehicle information of the vehicle in front sent by the vehicle in front, and sends the wireless communication signal containing the vehicle information of the vehicle to the rear vehicle with the ZigBee communication module under the control of the main controller unit; Vehicle information includes vehicle speed, vehicle location information and vehicle moving direction information;

When the driving environment of the vehicle is good and GPS positioning can be achieved, the system automatically selects GPS positioning; when encountering harsh environments such as tunnels and GPS cannot accurately locate, the system automatically selects ZigBee system positioning, and combines the electronic compass to determine the direction to ensure accurate data.

The GPS module must have a supporting external antenna. Considering the vehicle use, this embodiment uses an antenna with an extended feeder. The ZigBee module and vehicles within a certain range traveling in the same direction use RSSI (received signal strength) based positioning technology to form an ad hoc network. The ZigBee module also completes the communication task of sending the data calculated by the main control unit to the rear vehicles. The data output by the electronic compass module includes data from two vehicles traveling in different directions. Since most of the dangers come from vehicles in the same direction ahead, the vehicle information of the vehicle in front of the vehicle is mainly considered.

The main controller unit uses the vehicle information to calculate the distance L1 between the vehicle and the vehicle in front, or calculates the distance between the vehicle and the vehicle in front by using the signal strength of the wireless communication signal sent by the vehicle in front received by the ZigBee communication module. The vehicle distance L2; use the vehicle speed, vehicle moving direction information and the calculated vehicle distance L1 or vehicle distance L2 to judge the danger level of the vehicle;

In a specific implementation, in the process of judging the risk level of the own vehicle, for the vehicle distance L1 and the vehicle distance L2, the vehicle distance L1 is given priority.

As shown in Figure 3, the method of using vehicle information to calculate the distance between the vehicle and the vehicle in front is:

Let the longitude of the vehicle (B) be N2 and latitude E2; the longitude N1 and latitude of the vehicle in front (A) be E1, and the distance L1 between the vehicle (B) and the vehicle (A) in front can be obtained by calculating according to formula (1) :

$\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), a=E1-E2, b=N1-N2.

The method to calculate the vehicle distance between the vehicle and the vehicle in front by using the signal strength of the wireless communication signal sent by the vehicle in front received by the ZigBee communication module is:

Let the ZigBee communication signal strength received by the vehicle (B) in front of the vehicle (A) be RSSI, and calculate the distance L2 between the vehicle (B) and the vehicle in front (A) according to formula (2):

$\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 40.2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\\ {\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 58.5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 33</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Pt in formula (2) is the transmission power value of the ZigBee communication module in the vehicle that is set uniformly.

The main controller unit is composed of an ARM core board module and an interface board module. It receives GPS and ZigBee positioning data from the information collection and communication unit, refers to the temperature and humidity information of the environment, and adopts a certain algorithm to calculate the absolute position of the vehicle. information or the relative position information of other vehicles within a certain range in front; at the same time combined with the data of other vehicles received by the ZigBee module, based on the position data, driving speed, direction and other information of the surrounding vehicles, it is comprehensively judged whether the vehicle has The risk of collision; at the same time, combined with the common sense of the distance between vehicles on the high-speed road section, the possibility of danger is graded. The main controller unit sends the collected, processed and analyzed positioning data and risk level information to different units such as information display and sound and light alarm through the interface board module; at the same time, the useful information is wirelessly transmitted to the surrounding vehicles through the ZigBee communication module .

As shown in Figure 4, the working process of the vehicle positioning and anti-collision warning system based on ZigBee and GPS in this embodiment is as follows:

a. After the system is powered on, the ARM controller first initializes the system process, and at the same time the ZigBee chip completes the wireless communication initialization network, and then feeds back to the ARM controller after the network is successful.

b. After receiving the successful signal of networking, the ARM controller issues a data collection command.

c. After receiving the GPS data and temperature and humidity sensor data, the ARM controller selects the appropriate subsystem and algorithm to calculate the initial position and driving data of the vehicle.

d. The system sends a location data request to other vehicles nearby through the ZigBee module, uses the ZigBee communication signal to obtain the data, and then sends it to the ARM processing center for data processing.

e. After the data processing is finished, the ARM will send the data processing results, display them on the display screen, and issue appropriate alarms at the same time.

The information display and sound and light alarm unit is composed of a liquid crystal display module and a sound and light alarm module. The liquid crystal display module receives the vehicle distance and the danger level of the vehicle from the main controller unit for display, and the sound and light alarm module gives an alarm.

According to the calculated vehicle distance and vehicle speed, the main controller conducts risk assessment based on various auxiliary information, such as temperature and humidity, regional vehicles, driving speed, weather conditions, road conditions, etc., and issues early warnings. In this embodiment, according to various information such as the safe driving distance of the expressway, road surface conditions, and weather conditions, the vehicle driving range is divided into four different areas: a safe area, a relatively safe area, a relatively dangerous area and a dangerous area, as shown in the figure As shown in 5, based on the vehicle, combined with the vehicle distance information, the number of vehicles within a certain range in front of the vehicle and the position of each vehicle are displayed. Each vehicle is displayed on the screen as a prominent point; at the same time, when the vehicle is in danger Informational alerts are provided when the situation arises. The sound and light alarm module is to provide sound and light alarms of different warning levels when the vehicle is in different danger levels, and inform the vehicle drivers and passengers of the danger information ahead.

In this embodiment, the information display and sound and light alarm unit adopts a liquid crystal screen, a warning light, a horn or a buzzer. Pre-store different levels of warning voices and emergency handling prompts in the main controller to prevent drivers from panicking. At the same time, to prevent the driver from falling asleep while driving in fatigue, it cooperates with a warning reminder with a certain light and sound intensity.

The power supply unit is composed of a lithium battery module, a power conversion and an interface module; the power conversion and interface module takes power from the vehicle power supply to solve the power supply for the module when the vehicle travels for a long distance, and can provide a charging interface for the lithium battery module at the same time. In case of instability or failure, a backup lithium battery is provided to ensure the safe and stable operation of the system.

Claims (4)

1. A vehicle location and anti-collision warning system based on ZigBee and GPS, is characterized in that: comprise information collection and communication unit, main controller unit, information display and acousto-optic alarm unit; The information collection and communication unit is composed of a GPS module, an electronic compass module and a ZigBee communication module, obtains the vehicle speed and the vehicle position information characterized by longitude and latitude with the GPS module; obtains the vehicle position information with the electronic compass module Vehicle moving direction information; obtain the wireless communication signal containing the vehicle information of the vehicle in front sent by the vehicle in front with the ZigBee communication module, and send it to the vehicle in the rear with the ZigBee communication module under the control of the main controller unit A wireless communication signal containing the vehicle information of the own vehicle; the vehicle information includes vehicle speed, vehicle position information and vehicle moving direction information; The main controller unit uses the vehicle information to calculate the vehicle distance L1 between the vehicle and the vehicle in front, or calculates the distance between the vehicle and the vehicle in front by using the signal strength of the wireless communication signal sent by the vehicle in front received by the ZigBee communication module. The inter-vehicle distance L2 between the vehicles in front; use the vehicle speed, vehicle moving direction information and the calculated inter-vehicle distance L1 or inter-vehicle distance L2 to judge the danger level of the vehicle; The information display and sound and light alarm unit is composed of a liquid crystal display module and a sound and light alarm module. Make an alarm. 2. The vehicle positioning and anti-collision warning system based on ZigBee and GPS according to claim 1 is characterized in that: in the process of judging the danger level of the vehicle, for the vehicle distance L1 and the vehicle distance L2, the vehicle is preferentially used distance L1. 3. the vehicle location and anti-collision warning system based on ZigBee and GPS according to claim 1, is characterized in that: the method that described utilization vehicle information calculates and obtains the vehicle spacing between this car and the front vehicle is: Let the longitude of the vehicle (B) be N2 and latitude E2; the longitude N1 and latitude of the vehicle in front (A) be E1, and the distance L1 between the vehicle (B) and the vehicle (A) in front can be obtained by calculating according to formula (1) : $\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\sqrt{{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ In formula (1), a=E1-E2, b=N1-N2. 4. the vehicle positioning and anti-collision warning system based on ZigBee and GPS according to claim 1, is characterized in that: the signal strength calculation of the wireless communication signal sent by the vehicle in front that utilizes ZigBee communication module to receive obtains this car The method of vehicle distance to the vehicle ahead is: Let the ZigBee communication signal strength received by the vehicle (B) in front of the vehicle (A) be RSSI, and calculate the distance L2 between the vehicle (B) and the vehicle in front (A) according to formula (2): $\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 40.2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\\ {\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 58.5</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; RSSI</span>}}{\mathrm{<span\; class="notranslate">\; 33</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span>& \mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; m</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Pt in formula (2) is the transmission power value of the ZigBee communication module in the vehicle that is set uniformly.

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