Testing ADAS Functions in Parallel with EMS Measurement
In vehicle final inspection, safety-relevant functions of the driver-assistance system can be tested in parallel with infotainment-system EMS measurements. This allows manufacturers to make the most of available time in the EMC test chamber.
Many advanced driver assistance systems (ADAS) use radar sensors for functions such adaptive cruise control (ACC) or autonomous emergency braking (AEB). These sensors are safety-relevant components and therefore must work reliably even in extremely demanding RF environments. This is checked in full-vehicle tests using stringent electromagnetic susceptibility (EMS) tests in line with ISO 11451-2. But can ADAS functional tests be performed under adverse electromagnetic compatibility (EMC) conditions?
ADAS tests in an electromagnetic-disturbance environment
In the test process, the ADAS test system runs through various simulated realistic test scenarios that activate the ADAS functions in the vehicle under test (VUT) and should trigger the intended response. The main challenge is that this must work reliably even under electromagnetic conditions when EMS measurements are being made at the same time in the EMC test chamber, for example on the vehicle radio. Otherwise, the ADAS functions cannot be evaluated in this environment.
The ADAS test system consists of a radar echo generator, a dynamic target positioning system and the electromagnetic susceptibility (EMS) test system. The vehicle usually has a long-range radar sensor for automatic distance control and several near-range radar sensors for collision avoidance systems.
On one hand, the tests check whether the sensors have been properly integrated in the bumpers so that the antennas can illuminate the intended sectors. On the other hand, in conjunction with the dynamic target-positioning system, they also check the behavior of the ADAS system.
To test ADAS functionality, the radar echo generator simulates a vehicle driving ahead of the VUT, which the VUT must detect at predefined distances and at different speeds. The test engineer can set up to four individually configurable test distances on the echo generator. It also enables a controlled Doppler shift, as well as settable radar cross-sections.
The target positioning system additionally simulates a lane change from left to right or right to left. It allows ±55° angular motion from the central position in front of the VUT. With these two devices, the test engineer can generate scenarios to check whether the VUT correctly performs automatic speed adjustments and autonomous emergency braking when adaptive cruise control is activated.
The EMS test system also feeds electromagnetic disturbances into the VUT so that performance impairments can be detected. Movable absorber walls are used to screen the radar system under test from the signals of other targets without restricting the field of view of the radar sensor.
If the tested radar sensor and the radar echo generator are configured with the same unique Doppler shift, it is also possible to filter out undesired echoes from multipath propagation, such as radar echoes with different Doppler shifts from other test stands or from other tests being performed in parallel.
The EMS test system can automatically perform radiated and conducted EMS measurements in line with ISO 114511-2. It consists of a signal generator with multiple amplifiers and antennas for different frequency bands to generate the necessary field strengths for EMS measurements on the vehicle. Figure 3 shows an example test setup with a test system (shaded dark gray) for frequencies from 9 kHz to 3.2 GHz. The system's EMC test software enables automatic EMS measurements and can also monitor the electronic devices under test. The software additionally controls the radar echo generator and the positioning system for the automatic ADAS tests.
First, an engineer tests the radar sensors at the front of the vehicle and the ADAS functions –ACC and AEB – without additional disturbance signals, in order to eliminate unforeseen problems before the EMS test and to ensure that the system generally is working properly. Next, the EMS signals are fed into the test scenario. They should simulate typical EMS measurements on vehicle radios and achieve a maximum field strength up to 30 V/m.
For the functional tests, the VUT operates on the vehicle test stand with the respective ADAS function activated. The system records any anomalies or malfunctions that occur due to electromagnetic disturbances. The response of the VUT is determined by the wheel speed on the test stand, the brake lights and the results displayed by warning lights or on the screen of the driver's console; an EMC camera is placed in the vehicle to record the cabin warnings.
To test the ACC function, a vehicle 15 meters in front of the VUT is simulated and initially travels at the same speed as the VUT on the test stand. The simulated object should be shown on the driver's screen. The simulated vehicle then brakes slightly and accelerates again. The VUT must adjust its speed accordingly, but only up to the speed set in the ACC and no higher.
To test the emergency braking function, the VUT drives at constant speed until a simulated vehicle driving in front of it suddenly brakes. Two test scenarios are used for this: one with a simulated vehicle constantly driving in front of the VUT and another with a simulated vehicle that suddenly changes lanes and brakes in front of the VUT. For this, the front radar sensor and the echo generator on the positioning system must be precisely aligned with one another. If the sensor behind its cover is not externally visible, its exact position can be determined with the aid of a laser pointer.
In total, ten different test scenarios for ACC and four scenarios for AEB are performed on the vehicle test stand with induced disturbance signals, with the field strength rising to 30 V/m.
Optimizing test-chamber time
To use the time in the EMC test chamber as efficiently as possible, the ADAS functions can be tested in parallel with EMS measurements of the infotainment system. It is important that the radar sensor has an unrestricted field of view to the radar echo generator during the measurements and both are precisely aligned.
Standard-compliant EMS measurements on radar sensors in line with ISO 11451-2 take place in the frequency range from 10 kHz to 18 GHz and typically achieve field strengths up to 200 V/m. With a suitably designed EMS test system, these tests can also be performed by the test engineer on the test bench.
Sam Chew is Rohde and Schwarz's technical salesperson for EMC projects, and Jacky Li, is a senior systems engineer.