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摘要:
分析雾环境下利用LED交通灯进行车辆定位的性能，讨论了接收角度、道路宽度、雾环境下接收端信噪比等对车辆定位范围的影响。仿真结果表明：信号最佳接收角度为25°；车辆距离LED交通灯20 m之内时，道路宽度对信号的接收功率影响较大；在靠近交通灯处，车辆位于第二车道上的定位距离比车辆位于第一车道的定位距离少2.2 m；晚间接收端的信噪比优于白天，晚间的定位范围大于白天；与晴朗天气相比，雾天信噪比下降较大，将极大影响车辆的可定位范围，因此为保证安全驾驶，车辆在雾天行驶过程中需要更多的制动时间。
Abstract:In order to analyze the performance of vehicle positioning using LED traffic lights in foggy environment, the influences of receiving angle, road width, and signal-to-noise ratio (SNR) at the receiver in foggy environment on vehicle positioning range are discussed. The simulation results show that the optimal signal reception angle is 25°; when the vehicle is within 20 m of the LED traffic light, the road width has a greater impact on the received power of the signal; near the traffic light, the positioning distance of the vehicle on the second lane is 2.2 m shorter than that of the vehicle in the first lane; the SNR of the receiver at night is better than during the day, and the positioning range at night is greater than during the day; compared with sunny weather, the SNR in the fog days decrease significantly, which will greatly affect the positioning range of the vehicle, so to ensure safe driving, vehicles need more braking time when driving in foggy days.
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Key words:
- LED traffic light /
- visibility /
- signal to noise ratio /
- positioning range
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Overview: The intelligent urban transportation system is an important direction for the development of urban road traffic in the future. It mainly uses the communication between transportation infrastructure and vehicles to build a safe, convenient and green intelligent information platform. Intelligent urban transportation system based on visible light communication has LED traffic lights and vehicle lighting. It can not only realize communication between infrastructure and vehicles, and between vehicles, but also obtain traffic road condition information in real time and accurately obtain vehicle position information. It is of great significance to carry out intelligent highway construction, promoting road network management and vehicle coordination. However, the outdoor atmospheric channel has a great influence on the intelligent urban transportation system based on visible light communication. A large amount of small water droplets or dust particles contained in the air will scatter or absorb the LED beam, causing loss of optical power. Many scholars at home and abroad are studying the communication performance of visible light in atmospheric channels, which lays a foundation for vehicle positioning using LED traffic lights. However, the positioning performance between outdoor LED traffic lights and vehicles in typical weather still needs further study. In this paper, the influence of fog on the vehicle positioning performance using visible light is studied. The influence of the receiving angle on the positioning range is analyzed, and the vertical angle is 45°, 55°, 65°. When the receiver receives a change in angle, the optimal receiving angle for the visible light is determined. By comparing the receiving power of the vehicle in different lanes, it can be seen that the road width has a great influence on the positioning performance within 20 m of traffic lights. The signal-to-noise ratio of the receiver at night is better than during the day under the same visibility. The positioning range of the vehicle at night can be greater than during the daytime. By comparing different concentrations of fog and sunny weather, it can be seen that fog has a greater influence on vehicle positioning based on visible light. Therefore, in order to ensure safe driving in the intelligent urban transportation system, the influence of the weather environment on the positioning distance should be considered when performing visible light vehicle positioning.
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图 2 传输衰减与能见度的关系
Figure 2. Relationship between transmission attenuation and visibility
图 3 接收角度与光信号水平传输距离的关系
Figure 3. Relationship between receiving angle and horizontal transmission distance of optical signal
图 4 接收功率与光信号水平传输距离的关系
Figure 4. Relationship between received power and horizontal transmission distance of optical signal
图 5 白天不同能见度情况下信噪比和定位距离之间的关系。
Figure 5. Show the relationship between signal-to-noise ratio and positioning distance for different visibility during the day.
图 6 夜晚不同能见度情况下信噪比和定位距离之间的关系。
Figure 6. Show the relationship between signal-to-noise ratio and positioning distance for different visibility at night.
表 1 雾的等级与水平能见度的关系
Table 1. Relationship between fog level and horizontal visibility
等级 水平能见度/m 0(浓雾) < 50 1(大雾) 50~200 2(中雾) 200~500 3(轻雾) 500~1000 4(薄雾) 1000~2000 
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表 2 系统参数
Table 2. System parameters
参数 数值 LED波长/nm 525 LED功率半角/(°) 15 接收机最大视角/(°) 25 透镜折射率 1.7 光电感应面积/cm2 1 光电转换速率 0.35 平均发射功率/W 0.314 LED灯高度/m 5.5 发射角度/(°) 30 道路宽度/m 7 光电探测器高度/m 1 绿灯坐标 (0, 3, 5.5)
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