With the development of unmanned driving technology, the amount of radar used as the "eye of the car" has continued to grow rapidly. Future vehicles may use up to eight radar sensors to provide a 360-degree panoramic view of the car. The increasing complexity of radar technology also makes testing difficult. But with the NI Vehicle Radar Test System (VRTS), this is not an issue. Jump to the March/April 2018 issue of the Microwave Journal. Listen to NI technology expert Matt Spexarth to talk about the least time and the lowest test cost solution.
Compared with other sensing technologies, radar has several advantages. These advantages ensure that its role in active vehicle safety and automatic driving will be fully realized in the future. The radar can detect the speed of the detected object in real time through the radar Doppler shift characteristics of the detected object, and is suitable for bad weather conditions such as rain, fog, and snow. These advantages have prompted car manufacturers to increasingly use radar.
In the United States, the National Highway Traffic Safety Administration (NHTSA) of the United States has reached an agreement with 20 car manufacturers (these car manufacturers account for more than 99% of the U.S. market), and voluntarily allocates automatic emergency systems for all production vehicles prior to 2022. The AEB system, AEB, is a radar-based security feature. As the car evolved from advanced driver assistance systems (ADAS) to fully autonomous driving, sensors such as radar, lidar, and cameras became key input devices that ensure the vehicle's ability to accurately sense the surrounding environment, providing the vehicle with the information it needs to make decisions. .
The development and progress of automotive radar have brought many challenges to radar sensor testing and verification. In short, they can be summarized as two major challenges.
Challenge 1: Meeting the ever-increasing technical requirements of modern automotive radars
The core of the first challenge is to meet the increasing technical requirements for testing modern automotive radars while maintaining or reducing production test costs. Modern radar sensors typically require 1 GHz bandwidth from 76 GHz to 77 GHz, and few companies have the expertise to build test systems in this frequency range. Higher bandwidth sensors provide higher resolution, and radar manufacturers have developed sensors with bandwidths near 4 GHz and a center frequency of 79 GHz, which makes testing even more challenging.
What was the early radar test method?
Although the technology of radar sensors in the future will continue to improve, the time and cost of testing these sensors must be optimized to meet the price and quantity requirements, and then the widespread adoption of radar. Early radar sensor manufacturers used large non-echo RF chambers and corner reflectors to test and calibrate the module's functionality. These test rooms are usually 3 or 5 meters long and occupy a large area of ​​manufacturing space. In order to reduce the floor space, radar functional tests evolved to use analog delay lines to simulate long-range radar obstacles, and then radar parameters were measured by a second test station.
The newest and most convenient radar test system VRTS
Dedicated systems such as the NI Car Radar Test System (VRTS) have further developed radar function tests. VRTS is a hybrid simulator with a built-in vector signal transceiver (VST) that integrates an instrument-level vector signal analyzer with a vector signal generator through a high-performance, low-latency FPGA (see Figure 1).
The method integrates a radar module production test unit by combining a functional test (object simulation) and a parametric test into a single test device. This combination reduces the footprint of the manufacturing floor and eliminates the overhead of converting radar modules between test stations, which not only improves throughput, but also frees up space for other test equipment.
Figure 1. Block diagram of a NI vehicle radar test system.
Challenge 2: Validate the increasingly complex software in the sensor
In addition to the higher frequency and bandwidth requirements for automotive radar testing, the next challenge for testing future radar sensors is to verify the increasingly complex software in the sensor. Radar sensors with a bandwidth of 1 GHz or higher generate large amounts of raw data. In order to avoid overloading the vehicle's communication bus and ECU, the radar sensor is also equipped with a processor that can reduce the data to a summary snapshot.
Radar periodically sends parameterized object tables through the summary of all objects currently tracked by the sensor. Each object contains information on distance, velocity, radar cross section (RCS), object ID, and confidence (measures the credibility of the presence of a radar object). Radar's software detects these objects and tracks their real-time actions. Software algorithms look for inconsistencies, such as obstacles moving away from the sensor, but their Doppler characteristics indicate they are approaching.
Using a Compact Radar Test System Allows Software Developers to Quickly Verify Software Changes Immediately
In the lab, engineers must verify these algorithms and the software that implements them. In-vehicle field testing of these algorithms is important, but laboratory testing using a compact radar test system allows software developers to quickly verify software changes immediately.
In combination with mechatronic components for mobile radar analog antennas, systems such as VRTS can generate standardized radar environments to describe and verify radar sensor software, including simulations of extreme scenarios that are difficult or impossible to simulate during driving tests. Simulator-based laboratory testing is critical to ensuring the pace of innovation in automotive radar sensor designs.
System verification through radar simulation system
In the entire ADAS or autopilot system, engineers must also consider radar simulation for system verification tests. These systems increasingly rely on a combination of sensors, including cameras, lidars, and radars. Verifying the overall performance of ADAS functions such as automatic emergency braking increasingly uses sensor fusion techniques to improve the quality or confidence of obstacle detection through a combination of two or more sensors. For example, if an ADAS radar sensor "sees" an obstacle but the camera indicates that nothing is on the road, the ECU can treat the obstacle detected by the radar as a phantom or interference.
Figure 2. Validation software for ADAS and autopilot requires the simultaneous simulation of multiple automotive sensors so that the car "thinks" that it is driving in a real environment.
When testing of these functions goes up to the system level, engineers need a test platform to support a large number of simultaneous sensor simulations to simulate the entire surrounding environment sensed by the vehicle. Since systems such as VRTS are based on the modular automation test equipment standard PXI-Express, engineers can support additional sensors by adding additional PXI modules (such as NI FlexRIO) to simulate digital camera input synchronized with radar simulation.
Finally, advanced radar modulation technology will have an impact on the future of automotive radar testing. Frequency modulated continuous wave (FMCW) radar has been a typical representative of automotive radar. Radar designers are now looking to use MIMO antennas to enhance automotive radar capabilities to accurately detect obstacle heights and even provide camera-like raster images.
Radar sensor researchers have found that higher performance can be achieved with a modulation scheme similar to that used in cellular communications. These schemes can channelize the spectrum allocated to car radars, enabling MIMO radars to perform single radar reflections between parallel transmit and receive paths. This method is expected to improve radar resolution and field of view while enhancing radar resistance to other vehicle disturbances. Correspondingly, radar test systems must also be more and more complex.
Accurate simulation of obstacles at the resolution of these imaging radars may require the demodulation of a single radar channel, the application of range, Doppler, and RCS obstructions for each transmission channel, and the modulation of each channel according to the original scheme, and then the obstacle The signal is reflected back to the sensor - all back and forth at the speed of light. These requirements pose serious challenges to radar test suppliers and suppliers, and a high-bandwidth, low-latency system architecture with extremely high signal processing capability is urgently needed.
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