CN107293127B - Charging square congestion monitoring system based on multi-beam wide-area microwave detection - Google Patents

Abstract

The invention provides a toll plaza congestion monitoring system based on multi-beam wide-area microwave detection, comprising a plurality of microwave sensors, a communication module, a congestion analysis module and an early warning module; the microwave sensor, the communication module, the congestion analysis module and the early warning module are connected in sequence; The microwave sensor sends the road information of the toll plaza to the congestion analysis module in real time through the communication module. The congestion analysis module uses the real-time information received continuously, analyzes the real-time road conditions through delay calculation, and sends it to the early warning module in real time. In the present invention, 16 or 32 fixed-angle microwave sensors are used to analyze and calculate the congestion situation of the toll plaza by obtaining the presence or absence of vehicles in the ground area covered by the microwave sensors, and correspondingly make an early warning according to the situation to help the toll collection. The station decides to increase or decrease the charging personnel in time.

Description

A toll plaza congestion monitoring system based on multi-beam wide-area microwave detection

technical field

The invention relates to a congestion monitoring system for a toll plaza. Specifically, it relates to a toll plaza congestion monitoring system based on multi-beam wide-area microwave detection.

Background technique

The endpoint of the expressway is the toll station. In order to save manpower and material resources, the toll ramps of the toll station are often not all open, but some or all of the ramps are opened according to the size of the traffic. Therefore, judging whether to increase or decrease the open ramp according to the congestion situation is particularly important in terms of safety and economy.

SUMMARY OF THE INVENTION

In view of the problems existing in the background art, the present invention provides a toll plaza congestion monitoring system based on multi-beam wide-area microwave detection. The system analyzes and calculates the congestion of the toll plaza by obtaining the presence or absence of vehicles in the ground area covered by the microwave sensor, and makes a corresponding warning according to the situation, helping the toll station to decide on the increase or decrease of the toll collectors in time.

The present invention adopts the following technical scheme to realize:

A toll plaza congestion monitoring system based on multi-beam wide-area microwave detection, comprising a plurality of microwave sensors, a communication module, a congestion analysis module, and an early warning module; the microwave sensor, the communication module, the congestion analysis module, and the early warning module are connected in sequence; The communication module sends the road information of the toll plaza to the congestion analysis module in real time. The congestion analysis module uses the real-time information received continuously, analyzes the real-time road conditions through delay calculation, and sends it to the early warning module in real time.

The microwave sensor includes DDS+LO double sideband signal input, quadrature mixing unit, frequency doubling unit, power divider, power amplifier unit, high frequency radio frequency switch, transmitting antenna, receiving antenna, LNA, mixer, intermediate frequency filtering unit , differential IF amplifier, signal conditioning unit, A/D, FPGA, DSP; DDS+LO double-sideband signal input, quadrature mixing unit, frequency multiplying unit, power divider, power amplifier unit, high-frequency RF switch, and transmitting antenna in turn Connection, receiving antenna, LNA, mixer, intermediate frequency filter unit, differential intermediate frequency amplifier, signal conditioning unit, A/D, FPGA, DSP are connected in sequence; DSP is connected with the communication module.

The congestion analysis module realizes the measurement of the slant distance between the vehicle and the microwave sensor, the measurement of the vehicle position, and the discrimination of the vehicle lane occupancy time; the vehicle position is obtained by calculating the slant distance, and the lane occupancy time is discriminated according to the vehicle position information;

The judging method is as follows: according to the area projected by the microwave sensor to the ground, draw a box in a manner of simulating a ground-sensing coil, and define it as an analog coil;

After obtaining the accurate position information of the vehicle, by comparing it with the preset "virtual coil" position information, if a certain box is continuously occupied for more than 50s time threshold, and there is no continuous window time in the middle, it is inferred that the "virtual coil" There is a vehicle parked above the virtual coil.

The measurement process of the slope distance is as follows;

The signal obtained from the RF front-end is first subjected to clutter suppression, detection, and data acquisition of analog-to-digital conversion, and then peak monitoring is performed to obtain the final processing result—the slope distance Δl of the vehicle distance from the radar; Puler, the transmission signal is in the form of a frequency step chirp;

Using the signal form of stepping chirp, its oblique distance resolution reaches:

Among them, B _n is the working bandwidth of the radio frequency;

为车辆位置的准确提供了足够的精度。Calculated to the horizontal resolution, better than

Sufficient accuracy is provided for the accuracy of the vehicle position.

The measurement process of the vehicle position is as follows;

Since the height of the radar erection is known, set it as h, after measuring the slant distance Δl between the vehicle and the radar, the horizontal slant distance between the vehicle and the radar can be calculated:

Since the beam pointing of the radar receiving antenna deviates from θ=30°, the horizontal distance of the target from the radar is:

Assuming that the horizontal distance between the antenna erection position and the road edge is ΔP, and the lane width is evenly distributed, the lane position of the measured vehicle is:

Among them, [ ] represents rounding, and W _lane is the width of a single lane.

The congestion analysis module realizes the measurement of vehicle speed; when any two known beams detect the same vehicle, the speed measurement can be completed:

Among them, d is the distance between the two antennas, and Δt is the time difference when the vehicle enters the two receiving beams respectively.

The congestion analysis module realizes the measurement of vehicle length;

After measuring the speed v of the vehicle and the slope distance Δl of the vehicle from the radar, the measurement of the vehicle length l can be completed;

That is, the vehicle length l is:

为两束微波信号之间的夹角。Among them, t ₁ and t ₃ are the time for the car to pass through two adjacent microwave signals, respectively,

is the angle between the two beams of microwave signals.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The invention has the advantages of accurate measurement, strong pertinence, and measurement under all-weather conditions. Compared with the ground sensor, which needs to cut the sensor installation groove on the road surface, the system can not damage the road, and there is no contact between the detection device and the vehicle, which is not easy to be damaged, and has high reliability.

In the present invention, 16 or 32 fixed-angle microwave sensors are used to analyze and calculate the congestion situation of the toll plaza by obtaining the presence or absence of vehicles in the ground area covered by the microwave sensors, and correspondingly make an early warning according to the situation to help the toll collection. The station decides to increase or decrease the charging personnel in time.

The invention can realize automatic dispatching of high-speed toll stations, save manpower and material resources, and help expressway managers and toll collectors to achieve greater results in terms of safety, economy, and driver satisfaction.

Description of drawings

Figure 1 is a block diagram of the structure of the toll plaza congestion monitoring system;

Figure 2 is a schematic diagram of the principle of multi-beam detection;

Figure 3 is a schematic diagram of the ground coverage area of the microwave sensor;

Fig. 4 is the hardware block diagram of microwave sensor;

Fig. 5 is the working flow chart of microwave sensor;

Figure 6 is a schematic diagram of the principle of speed measurement;

7 is a schematic diagram of time difference detection;

Fig. 8 is the signal processing realization algorithm diagram;

9 is a time-frequency relationship diagram of a transmitted signal;

Figure 10 is a schematic diagram of lane discrimination;

Figure 11 is a schematic diagram of the principle of vehicle length measurement.

Detailed ways

The toll plaza congestion monitoring system based on microwave detection is composed of microwave sensor, communication module, congestion analysis module and early warning module. The principle block diagram is shown in Figure 1. Among them, the congestion analysis module and the early warning module are integrated on the host computer, and the host computer uses an industrial computer; the communication module is respectively on the microwave sensor and the host computer. There are two ways of wired connection and wireless transmission. The wired connection is RS232 connection. way, the wireless transmission uses WIFI way.

The invention utilizes a plurality of fixed angle microwave sensors to poll and scan the target area at high speed, and utilizes the industrial computer to realize the congestion monitoring of the toll plaza under any weather conditions 24 hours a day.

The microwave sensor sends real-time road information of the toll plaza to the congestion analysis module through the communication module every 50ms. The congestion analysis module uses the continuously received real-time information, analyzes the real-time road conditions through delay calculation, and displays it on the screen of the industrial computer through the early warning module in real time. If congestion occurs, the congestion analysis module will send congestion information. On the LCD screen, it is highlighted. For toll station managers to decide to open a new toll channel.

In order to make the coverage area of the microwave sensor meet the technical requirements, the suspension height H, the depression angle α and the angle β between the emission angle and the road line need to meet the measurement requirements. The schematic diagram of the multi-beam detection principle is shown in Figure 2.

According to the requirements, the system needs two 16-channel microwave sensors, so that the covered area can reach the optimal area for judging the congestion phenomenon. The schematic diagram of the microwave sensor covering the ground is shown in Figure 3.

The monitoring controller used for the system adopts industrial industrial computer, the operating system is Windows XP, and the software used is C++.

The detection controller of the system is composed of a communication module, a congestion analysis module and an early warning display module.

The communication module is used for the information transfer between the microwave sensor and the monitoring controller, including the formulation of the communication protocol and the transmission of effective data. There are two types of communication methods, wired and wireless, according to the complexity of the site.

After receiving and extracting the information transmitted by the communication module, the congestion analysis module analyzes whether there is congestion on the road, and if so, sends the information to the early warning display module.

The early warning display module is used to remind the user of the complexity of the toll plaza. If there is congestion, the display will highlight the reminder.

Each constituent part of the present invention is described in detail below:

1. Design index of microwave sensor

1. Microwave working frequency

24-24.24GHz, BW=240MHz

2. Antenna characteristics

Single antenna with 16 groups of antennas for transmitting and one horizontal narrow beam for receiving

Receiving antenna horizontal beam width≤6°, side lobe level≤-40dB

The vertical beam width of the receiving antenna is greater than or equal to 72°, and the side lobe level is less than or equal to -40dB

3. Transmitting power

_Pout ≥10dBm

4. Receiver sensitivity

Assuming that the microwave sensor is erected at a height of 7m and the lateral distance from the first lane is 2m, the maximum working distance of the microwave sensor Rmax=70.2m and the minimum working distance Rmin=5.57m.

Assume that the scattering cross-sectional area of the microwave sensor of the target vehicle is 1m ² , the transmitter power is 10mW, and the antenna beam width is 5° (ie, the antenna gain is about 17.78dB). According to the microwave sensor equation:

Among them: P _t is the transmit power, G is the gain, σ is the effective area of the target ground, and R is the action distance of the microwave;

It can be seen that the range of the echo signal power received by the microwave sensor is [-99.4dBm,-55.4dBm], and the dynamic range is 44dB.

Taking the working bandwidth of the RF front-end LNA as 240MHz, the noise power at the input end of the LNA is:

N _i =kT ₀ B _n =1.38×10 ⁻²³ ×293×240×10 ⁶ =9.6×10 ⁻¹³ W=-90.2dBm(2)

Among them: k Boltzmann constant, T ₀ is the absolute temperature, B _n is the working bandwidth of the radio frequency;

Therefore, the noise figure of the LNA should satisfy the following formula:

N _LNA ≤-99.4-(-90.2)=-9.2dB(3)

The LNA chip currently selected has a noise figure of 2.5dB, which fully meets the system index requirements.

2. System plan

The microwave sensor adopts digital direct synthesis (DDS) technology to generate the intermediate frequency emission waveform of the microwave sensor. After the waveform is mixed and up-converted, it is up-converted to a radio frequency of 24 to 24.24 GHz and radiated through the transmitting antenna. After the radiated microwave sensor electromagnetic wave irradiates the target, it forms a reflected wave, which is received by the microwave sensor receiving antenna. After two-stage high-frequency amplification, after harmonic mixing, it is down-converted to an intermediate frequency. After intermediate frequency amplification and filtering, the intermediate frequency echo signal is obtained. The signal is converted into a digital intermediate frequency signal after AD conversion, and then through digital filtering, ground clutter suppression, pulse compression, high-resolution synthetic distance, threshold detection, and cell average constant false alarm (CFAR) processing, the presence of the target is detected. On the basis of detecting the existence of the target, the time-frequency analysis of the echo is further carried out, so as to complete the functions such as target speed measurement and distance measurement.

The emission waveform of the microwave sensor is proposed to use the frequency step chirp waveform, which is a compromise between the Chirp signal and the frequency step signal, and has the advantages of both signals. Instantaneous bandwidth of the system.

1. Speed measurement function

Basic principle: When any two known beams detect the same vehicle, the speed measurement can be completed

Among them, d is the distance between the two antennas, and Δt is the time difference when the vehicle enters the two receiving beams respectively. See Figure 6 for details.

Because d is very short (only 13.8cm), in order to ensure the accuracy of speed measurement, high repetition frequency pulses must be used, and PRF=1MHz is currently selected.

The highest speed target speed that this device needs to measure is 200km/h=55.56m/s. When using PRF=1MHz, the number of pulses that the vehicle can receive when it passes through the two beams is:

n=10 ⁶ ×d/v _max =2484(5)

Among them: d is the projection distance between the two beams on the ground, and v _max is the highest speed target speed. Since a huge number of echo pulses can be received, the speed measurement accuracy can be guaranteed.

2. Ranging function

The measurement accuracy of the distance Δl between the vehicle and the microwave sensor directly determines the accuracy of the subsequent vehicle position determination. At present, the high-speed lane width of my country's expressways is 3.75 meters. If ordinary pulse signals are used, to achieve lane discrimination, the pulse width must satisfy the following formula:

Then, the pulse width τ≤0.0125us. If the pulse repetition period is selected as 1us, it can be known that the duty cycle is only 1.25%. With such a small duty cycle, the average transmission time interval of the microwave sensor will be very small, which will directly affect the working distance of the microwave sensor.

Therefore, in order to solve the above problems, this design adopts the signal form of stepping chirp, as shown in Figure 7. Its oblique distance resolution can reach:

Where: B _n is the working bandwidth of the radio frequency;

为车道的准确提供了足够的精度。具体信号处理流程见图8所示。Calculated to the resolution in the horizontal direction, it will be better than

Sufficient accuracy is provided for the accuracy of the lane. The specific signal processing flow is shown in Figure 8.

Figure 8 shows that the signal obtained from the RF front end is first subjected to clutter suppression, detection, and data acquisition of analog-to-digital conversion, and then peak monitoring is performed to obtain the final processing result Δl.

The principle used for ranging is pulse Doppler, and the transmitted signal is in the form of a frequency-stepped chirp. Taking a group of pulses (such as a group of 5 pulses) as an example, the time-frequency distribution of the transmitted signal is shown in 9.

3. Location discrimination

Since the height of the microwave sensor is known (set as h), after measuring the slant distance Δl between the vehicle and the microwave sensor, the horizontal slant distance between the vehicle and the microwave sensor can be calculated:

Since the beam pointing of the receiving antenna of the microwave sensor deviates from θ=30°, the horizontal distance between the target and the microwave sensor is:

Assuming that the horizontal distance between the antenna erection position and the road edge is ΔP, and the lane width is evenly distributed, the lane position of the measured vehicle is:

Where [ ] represents rounding, and W _lane is the width of a single lane.

For non-uniformly distributed lanes, that is, expressways with different W _lanes , it needs to be set according to the actual situation. That is, after the microwave sensor device is powered on and initialized, the parameters of the lane position are set by operating the software on the upper computer terminal screen (warning display module). Or train and learn according to a certain number of cars to realize automatic identification of lanes. This part of the content is realized by neural network. First, manually determine the occupancy status of the lane. If the lane is occupied or not, input the on-site situation to the congestion analysis module. The module will automatically learn according to the manual data and store the learning results in the back-end database for judging future congestion. . This method can exclude the places where the car cannot pass without judging it as the scope of a certain lane. Figure 10.

4. Vehicle length measurement

After the speed v of the vehicle and the slope distance Δl of the vehicle from the microwave sensor are measured, the measurement function of the vehicle length l can be completed by using the method shown in FIG. 11 .

That is, the vehicle length l is:

为两束微波信号之间的夹角。Among them, t ₁ and t ₃ are the time for the car to pass through two adjacent microwave signals, respectively,

is the angle between the two beams of microwave signals.

3. Congestion judgment (congestion analysis module)

After obtaining the accurate position information of the vehicle, it can be compared with the preset "virtual coil" position information. The virtual coil is a box drawn by simulating the ground-sensing coil according to the area of the 16-channel microwave sensor projected to the ground. , if a certain box is continuously occupied for more than 50s time threshold, and there is no continuous window time in the middle, it is inferred that there is a vehicle staying above the "virtual coil".

Drawing multiple virtual coils of the same area on the same lane can cover the measurement effective area of different lengths and realize the alarm function of different queue lengths.

This system does not need to damage the road surface, and realizes the clean and tidy road surface, and does not damage the sensor due to physical contact.

The microwave sensor of this system can be adjusted by the installation height and inclination angle according to the actual situation of different sites, so as to reduce the possibility of being blocked and missed detection.

Claims (5)

1. a toll plaza congestion monitoring system based on multi-beam wide-area microwave detection, is characterized in that: comprise a plurality of microwave sensors, communication modules, congestion analysis modules, early warning modules; microwave sensors, communication modules, congestion analysis modules, early warning modules Connect in sequence; the microwave sensor sends real-time road information of the toll plaza to the congestion analysis module through the communication module, and the congestion analysis module uses the real-time information received continuously, analyzes the real-time road conditions through delay calculation, and sends it to the early warning module in real time; The microwave sensor includes DDS+LO double sideband signal input, quadrature mixing unit, frequency doubling unit, power divider, power amplifier unit, high frequency radio frequency switch, transmitting antenna, receiving antenna, LNA, mixer, intermediate frequency filtering unit , Differential IF amplifier, signal conditioning unit, A/D, FPGA, DSP; DDS+LO double sideband signal input, quadrature mixing unit, frequency multiplying unit, power divider, power amplifier unit, high frequency RF switch, transmitting antenna connected in sequence, receiving antenna, LNA, mixer, IF filter unit, differential IF Amplifier, signal conditioning unit, A/D, FPGA, DSP are connected in sequence; The DSP is connected with the communication module; The congestion analysis module realizes the measurement of the slant distance between the vehicle and the microwave sensor, the measurement of the vehicle position, and the discrimination of the vehicle lane occupancy time; the vehicle position is obtained by calculating the slant distance, and the lane occupancy time is discriminated according to the vehicle position information; The judging method is as follows: according to the area projected by the microwave sensor to the ground, draw a box in a manner of simulating a ground-sensing coil, and define it as an analog coil; After obtaining the accurate position information of the vehicle, by comparing it with the preset "virtual coil" position information, if a certain box is continuously occupied for more than 50s time threshold, and there is no continuous window time in the middle, it is inferred that the "virtual coil" There is a vehicle parked above the virtual coil. 2. a kind of toll plaza congestion monitoring system based on multi-beam wide-area microwave detection according to claim 1, is characterized in that: the measurement process of described slant distance is as follows; The signal obtained from the RF front-end is first subjected to clutter suppression, detection, and data acquisition of analog-to-digital conversion, and then peak monitoring is performed to obtain the final processing result—the slope distance Δl of the vehicle distance from the radar; Pler, the transmission signal form is frequency step chirp; using the step chirp signal form, the oblique distance resolution reaches:

Among them, B _n is the working bandwidth of the radio frequency; Calculated to the horizontal resolution, better than

Sufficient accuracy is provided for the accuracy of the vehicle position. 3. a kind of toll plaza congestion monitoring system based on multi-beam wide-area microwave detection according to claim 1, is characterized in that: the measurement process of described vehicle position is as follows; Since the height of the radar erection is known, set it as h, after measuring the slant distance Δl between the vehicle and the radar, the horizontal slant distance between the vehicle and the radar can be calculated:

Since the beam pointing of the radar receiving antenna deviates from θ=30°, the horizontal distance of the target from the radar is:

Assuming that the horizontal distance between the antenna erection position and the road edge is ΔP, and the lane width is evenly distributed, the lane position of the measured vehicle is:

Among them, [ ] represents rounding, and W _lane is the width of a single lane. 4. a kind of toll plaza congestion monitoring system based on multi-beam wide-area microwave detection according to claim 2, is characterized in that: described congestion analysis module realizes the measurement of vehicle speed; any two known beams detect the same When you are in the car, you can complete the speed measurement:

Among them, d is the distance between the two antennas, and Δt is the time difference when the vehicle enters the two receiving beams respectively. 5. A toll plaza congestion monitoring system based on multi-beam wide-area microwave detection according to claim 3, characterized in that: the congestion analysis module realizes the measurement of vehicle length; After measuring the speed v of the vehicle and the slope distance Δl of the vehicle from the radar, the measurement of the vehicle length l can be completed;

That is, the vehicle length l is:

Among them, t ₁ and t ₃ are the time for the car to pass through two adjacent microwave signals, respectively,

is the angle between the two beams of microwave signals.

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