Radar module – classic sensor technology
This is an active transmission and reception method in the microwave GHz range. This technology makes it possible to detect and localize one or more objects by means of electromagnetic waves.
The radar antenna emits signals in the form of radar waves. These waves cannot be perceived by humans and move at the speed of light. If one of these waves hits an object, the signal changes and is reflected back, like an echo. An antenna in the sensor receives the reflected signal which contains information about the object. For example, based on the signal’s transit time, it is possible to calculate the distance of the object to the vehicle. In a second step, information is now emitted to the vehicle electronics in order to trigger a reaction such as “reduce speed”.
A major advantage of this technology is that it is less sensitive to darkness, moisture, dirt and temperature.
However, there are also disadvantages such as radar-to-radar interference. This is when different radar sensors all operating in the same allocated frequency band mutually interfere with each other. This interference or these faults occur if the visual fields of the sensors overlap. However, work is currently being carried out on different approaches in order to fix this problem.
Radar sensors – differences and areas of use
In general, three different radar ranges can be distinguished in the vehicle:
- LRR Long Range Radar > 160 m
- MRR Mid-Range Radar 160 m
- SRR Short-Range Radar 50 m
The sensors use frequency ranges between 24, 77 and 79 GHz.
Front View (24/77 GHz)
Sensors for the LRR and SRR/MRR ranges are installed at the front of the vehicle. They are used as driver assistance systems, like a second pair of eyes, to support the driver. Data about the traffic ahead is collected in cycles.
Distance and speed are the main criteria that need to be measured here.
In this way, the vehicle’s assistance system can perceive the minimum distance to the car in front and, if necessary, apply the brakes to trigger an emergency stop and prevent an accident.
Rear View (24/77 GHz)
Sensors at the rear monitor, the area behind the vehicle.
As the driver focuses most of his attention on the area in front of the vehicle and can only assess the situation behind the car by briefly glancing in the rearview mirror, radar sensors are an extremely effective aid.
When overtaking or changing lane, an optical or acoustic signal can warn the driver if another car is rapidly approaching from behind.
The “blind zone warning” also falls into this category.
Surround View – 360° (77/79 GHz)
A combination of different radar sensors installed around the car provide a 360-degree, all-round view. This is possible both at close range to provide the driver with better visibility, as well as for medium to long distances for autonomous driving. A combination of 8 radar systems make a 360-degree all-round view possible.
Radar sensors – 1D to 4D
1D – Radar (CW)
CW – Continuous Wave Driving
With this sensing method, the radar beam is emitted and received continuously and simultaneously.
Only objects moving at different speeds can be distinguished.
Objects moving at the same speed cannot be distinguished.
Localization is not possible.
2D – Radar (FSK)
FSK – Frequency Shift Keying
In this case, the transmitting frequency switches rapidly between two frequencies.
This is a special form of FMCW technology (see 3D and 4D radar).
Only objects moving at different speeds and at different distances can be distinguished.
It is not possible to distinguish between objects moving at the same speed and located at the same distance.
Localization is possible on a one-dimensional level.
3D – radar (FMCW-MIMO)
FMCW-MIMO – Frequency Modulated Continuous Wave–Multiple Input Multiple Output
With this technology, the frequency is periodically modulated and transmitted with several emitter and receiver antennas. Every signal sent can be received by any antenna. The special arrangement of several antennas ensures spatial resolution and reduces susceptibility. It is now possible to distinguish between objects moving at different speeds and located at different distances and different angles. Objects moving at the same speed, and located at the same distance and angle can also be distinguished. Localization is possible on a two-dimensional level.
4D – radar (FMCW-MIMO)
Additional antennas installed in the elevation also make it possible to separate objects in the elevation angle.
This enables localization of objects in a 3D environment.
Radar – measurable information and analysis
The following information can be recorded and analyzed with radar sensor technology:
- Speed of objects
- Distance of objects
- Direction of movement
It is possible to create movement histories with intelligent algorithms.
Objects can also be classified, i.e. a differentiation can be made, for example, between people and vehicles.
All this information provides important building blocks for driver assistance systems and, together with cameras, Satnav and LiDAR systems, forms one of the four key pillars of autonomous driving (AD).
Radar – areas of use
Radar has found its way into many areas of the vehicle. However, in all cases, the stated objective is to achieve “zero accidents”.
Here are a few examples:
|ACC:||Adaptive Cruise Control|
|AEB:||Automatic Emergency Braking|
|FCW:||Forward Collision Warning|
|CTA:||Cross Traffic Alert|
|ALC:||Adaptive Light Control (cornering light, automatic switching on of headlights and dimming)|
Vehicle – Exit Assist (When opening the car door, gives a warning that a vehicle is approaching from behind)
|BSD:||Blind – Spot Detection|
|LCA:||Lane – Change Assist at the rear|
|RCTA:||Rear Cross Traffic Alert|
|AVP:||Automated Valet Parking|