Imaging radar: one sensor to rule them all

There is still some confusion in the industry about the different roles of the three main sensors (camera, radar and LIDAR) in the car and how they each meet the sensing needs of advanced driver assistance systems (ADAS) and autonomous driving.

Level 4 and 5 autonomous vehicles may require all three sensors: camera, LIDAR and radar to provide high reliability and a fully autonomous driving experience. However, for more economical Level 2 and 3 vehicles that require partial autonomy and are already in mass production, imaging radar using TI mmWave sensors can achieve high performance and cost-effectiveness, and enable widespread adoption of ADAS features.”

So, what is imaging radar?

Imaging radar is a subset of radar, so named for its ability to provide clear images at high angular resolution. Imaging radar is enabled by a sensor configuration where multiple low-power TI mmWave sensors are cascaded together and synchronized to operate as a unit. It has multiple receive and transmit channels that significantly improve angular resolution and radar range performance. When mmWave sensors are cascaded together, beamforming can be created using integrated phase shifters to achieve an extended range of 400 meters. The following figure shows the cascaded mmWave sensors and their antennas on an evaluation module.

An imaging radar evaluation module with four cascaded TI mmWave sensors

Millimeter-wave technology for imaging radar

Typical radar sensors have until recently been considered the primary sensor in a vehicle, primarily due to their limited angular resolution performance.

Angular resolution refers to the ability to distinguish objects at the same range and relative speed. A common use case where imaging radar sensors are advantageous is the ability to identify static objects at high resolution. Typical mmWave sensors have high speed and high range resolution performance, making it easy to identify and distinguish moving objects, but their ability to identify static objects is very limited.

For example, in order for a sensor to “see” a stopped vehicle in the middle of a lane and distinguish it from a light pole or fence, the sensor needs to have a certain angular resolution in both elevation and azimuth.

The picture below shows a car trapped in a tunnel with smoke coming out of it. The vehicle is about 100 meters away and the tunnel is 3 meters high.

Front radars for oncoming vehicles need high enough angular resolution to distinguish between tunnels and stopped vehicles. Millimeter wave sensors can penetrate any visibility conditions, such as smoke.

How mmWave sensors achieve high elevation resolution using multiple-input multiple-output (MIMO) radar

To identify a vehicle in a tunnel, the sensor needs to distinguish it from the tunnel ceiling and walls. Achieving scene classification requires utilizing these elevation and azimuth resolutions:

ɸ (elevation angle) = inverse tangent (2 m/100 m) = 1.14 degrees

ɸ (elevation angle) = arc tangent (3.5 m/100 m) = 2 degrees

Among them, 2 m is the value of tunnel height minus vehicle height, 100 m is the distance between the approaching vehicle with imaging radar and the vehicle parked in the tunnel, and 3.5 m is the distance between the vehicle parked in the tunnel and the tunnel wall.

Relying on other optical sensors can be challenging in certain weather and visibility conditions. Smoke, fog, bad weather, and light-dark contrast are challenging visibility conditions that inhibit optical passive and active sensors, such as cameras and LIDAR, causing them to be unable to identify targets. However, TI mmWave sensors maintain strong performance in adverse weather and visibility conditions.

Currently, imaging radar sensors are the only sensors that can maintain robust performance in all weather and visibility conditions, achieving angular resolution of 1 degree in both azimuth and elevation (or even lower when using super-resolution algorithms).

TI mmWave sensors’ imaging radar offers high flexibility

Imaging radars using TI mmWave sensors are highly flexible and can sense and classify objects in the near field with very high resolution, while being able to track targets in the far field up to 400 meters away. This cost-effective, high-resolution imaging radar system enables Level 2 and Level 3 ADAS applications as well as high-end Level 4 and Level 5 autonomous driving vehicles and can be used as the main sensor in the vehicle.

Please click here to browse the TI Embedded Simulator column and view more automotive millimeter wave sensor information>>>

(Author: Kevin Chen1 from E2E Community)