Research on automobile blind spot monitoring system based on millimeter wave radar

This paper proposes a design scheme for a blind spot monitoring system for automobiles based on millimeter - wave radar . The basic principles and  test methods of the blind spot monitoring system are discussed in detail, and the system is installed on a real vehicle for verification testing. The test results of the real vehicle show that the designed blind spot monitoring system can monitor the target vehicle within 10 m of the left and right adjacent lanes in real time. When the target vehicle continues to approach the vehicle equipped with the blind spot monitoring system, the blind spot monitoring system will provide the driver with early warning information in time to avoid a car collision, which greatly improves the level of intelligent driving assistance of the car.

This paper proposes a test method for the performance of AEBS millimeter-wave radar and conducts test applications. This method requires simple test equipment and can reduce test costs. It can also test millimeter-wave radars of different manufacturers and models, which is of great significance to the research and development of new products.

01. Design principle of automobile blind spot monitoring system

Generally speaking, you cannot see all the information around the vehicle by looking at the exterior rearview mirror. During the driving process, if the driver cannot see the vehicle in the blind spot before changing lanes, a collision accident may occur when changing lanes. The blind spot monitoring system is designed to reduce such risks. The blind spot of the exterior rearview mirror of a car is shown in Figure 1.

The blind spot monitoring system is a high-tech driving assistance configuration for contemporary cars. Its main function is to monitor the vehicles in the blind spot of the rearview mirror in real time through intelligent sensors such as radar and camera. When the rear vehicle approaches the car, the driver is reminded. The schematic diagram of the car blind spot monitoring system is shown in Figure 2.

Compared with other sensors, millimeter-wave radar sensors are small in size, light in weight, and highly accurate, and are not affected by the shape or color of the target object. Their wavelength is between centimeter waves and light waves, and they have a strong ability to penetrate fog, smoke, and dust. They have a long transmission distance and are capable of operating all day and all weather. They make up for the use scenarios that other sensors such as infrared, laser, ultrasonic, and cameras do not have in vehicle-mounted applications, and have been widely used in automotive blind spot monitoring systems.

Millimeter-wave radar emits electromagnetic waves, which are reflected back when encountering obstacles. The reflected echoes are received by the radar, and after signal processing and calculation, physical information such as the distance and speed of the obstacle is obtained. According to the operating frequency of millimeter-wave radar, it can be divided into 24 GHz millimeter-wave radar and 77 GHz millimeter-wave radar.

Taking into account the advantages and disadvantages of various intelligent sensors, reliability, accuracy, development cost and development cycle, 77 GHz millimeter-wave radar is finally selected as the perception sensor of the blind spot monitoring system, and a design scheme of the automobile blind spot monitoring system based on millimeter-wave radar is proposed.

The blind spot monitoring system is mainly composed of two millimeter-wave radars, a controller, a warning light, and related wiring harnesses, as shown in Figure 3. Two 77 GHz millimeter-wave radars are installed on the rear side of the vehicle body to monitor surrounding objects during driving, calculate the distance and speed information of the objects through the echo signal of electromagnetic waves, and trigger the corresponding alarm function when there is a risk of collision, reminding the driver and effectively improving the safety of vehicle lane changes and turns.

The system is powered by the original vehicle, obtains vehicle-related information through CAN (Controller Area Network), and outputs alarm information, control signals and status information to the corresponding modules for alarm prompts. The principle of the vehicle blind spot monitoring system is shown in Figure 4.

The two radars in this blind spot monitoring system have a master-slave relationship. The master radar contains a controller, which serves as the control decision center, communicates with the vehicle through the CAN bus, and provides relevant signals to other modules of the vehicle. The slave radar only plays a sensing role and sends target information to the master radar through the private CAN bus. The process of the automobile blind spot monitoring system is shown in Figure 5.

02. Test method of automobile blind spot monitoring system

2.1 Vehicle blind spot monitoring range

According to ISO 17387-2008 Intelligent Transport Systems - Lane Change Decision Support Systems - Performance Requirements and Test Procedures, the vehicle blind spot monitoring range is shown in Figure 6. All dimensions in the figure are relative to the test vehicle.

Note: 1 is the test vehicle; 2 is the center of the 95th percentile eyellipse, which shall comply with the requirements of GB/T36606-2018 and take the N1 class vehicle as reference; 3 is the area enclosed by lines F, C, G, and B, which is the left blind spot monitoring range of the vehicle under straight-line conditions; 4 is the area enclosed by lines K, C, L, and B, which is the right blind spot monitoring range of the vehicle under straight-line conditions; Line A is parallel to the rear edge of the test vehicle and is located 30.0 m behind the rear edge of the test vehicle; Line B is parallel to the rear edge of the test vehicle and is located 3.0 m behind the rear edge of the test vehicle; Line C is parallel to the front edge of the test vehicle and is located at the center of the 95th percentile eyellipse; Line D is the bidirectional extension of the front edge of the test vehicle; Line E is parallel to the center line of the test vehicle and is located at the outermost edge of the left side of the test vehicle body (excluding the exterior rearview mirror); Line F is parallel to the center line of the test vehicle, and located to the left of the left outermost edge of the test vehicle body, 0.5 m away from the left outermost edge; Line G is parallel to the center line of the test vehicle, and located to the left of the left outermost edge of the test vehicle body, 3.0 m away from the left outermost edge; Line H is parallel to the center line of the test vehicle, and located to the left of the left outermost edge of the test vehicle body, 6.0 m away from the left outermost edge; Line J is parallel to the center line of the test vehicle, and located to the right of the right outermost edge of the test vehicle body (excluding the exterior rearview mirror); Line K is parallel to the center line of the test vehicle, and located to the right of the right outermost edge of the test vehicle body, 0.5 m away from the right outermost edge; Line L is parallel to the center line of the test vehicle, and located to the right of the right outermost edge of the test vehicle body, 3.0 m away from the right outermost edge; Line M is parallel to the center line of the test vehicle, and located to the right of the right outermost edge of the test vehicle body, 6.0 m away from the right outermost edge; Line N It is the bidirectional extension line of the rear edge of the test vehicle; line O is parallel to the rear edge of the test vehicle and is located 10.0 m behind the rear edge of the test vehicle.

2.2 Vehicle Blind Spot Monitoring Test Method The test vehicle travels in a straight line at a constant speed of (50±2) km/h, and the target vehicle travels at a constant speed higher than the test vehicle and overtakes the target vehicle, as shown in Figure 7.

Initially, the target vehicle travels behind the test vehicle at the speed specified in the scenario in Table 1. When the leading edge of the target vehicle exceeds line A shown in Figure 6, the test begins;

The test ends when the leading edge of the target vehicle exceeds line C by 3 m as shown in Figure 6. After the test is completed, the test should be repeated on the other side of the test vehicle.

Taking scenario 1 as an example, the test vehicle speed is 50 km/h, the target vehicle speed is 60 km/h, and the target vehicle slowly overtakes the test vehicle.

In Figure 8, 1 is the test vehicle and 2 is the target vehicle. The left and right warning lights are recorded by monitoring, and the distance between the target vehicle and the test vehicle when the warning is established and when the warning is released is recorded in the test results.

The adjacent lanes of the test vehicle are divided into three zones, as shown in Figure 9. When the target vehicle drives to any position in Zone III, if the warning light is on (i.e., a warning is established), it is considered qualified;

When the target vehicle drives into area Ⅱ, if the warning light is always on (i.e. stable warning), it is considered qualified; when the target vehicle drives to any position in area I, if the warning light is off (i.e. warning is lifted), it is considered qualified; area Ⅱ is the vehicle blind spot monitoring range.

03. Real vehicle test results verification

Install the blind spot monitoring system on the actual vehicle, as shown in Figure 10. Two millimeter-wave radars are installed on both sides of the rear of the car, and the system warning lights are installed on the left and right exterior rearview mirrors. Connect the above parts through wiring harnesses and conduct a real vehicle road test according to the above test method.

The road test results show that when a target vehicle appears within 10m of the adjacent lane behind the test vehicle, the blind spot monitoring system can provide real-time warning to the driver.