Ultra-Wideband In-Cabin Sensing
Radar-based occupant and presence detection
UWB Radar Sensing for In-Cabin Applications
Ultra-Wideband can be used not only for communication and ranging, but also for radar-based sensing. In this mode, a UWB node transmits short pulses and analyzes the reflected signals from objects and occupants inside the cabin. The wide signal bandwidth enables high temporal resolution, making it possible to detect small changes in distance, movement patterns, and micro-motions.
As illustrated below, these reflections can reveal movements such as the motion of the chest during breathing. In principle, UWB radar can also capture even smaller vital-sign-related movements, although heartbeat detection is typically only feasible under controlled laboratory conditions, as it is often masked by stronger movements such as respiration. In practical in-cabin applications, reliable interpretation of the reflected signal patterns requires signal processing and embedded algorithms that can distinguish between static objects, moving occupants, breathing-related motion, seat occupancy, child presence, and intrusion events.
This enables a range of safety, comfort, and security functions based on compact UWB sensor setups and software-defined signal interpretation.
One UWB Setup, Multiple In-Cabin Applications
The UWB sensor setup defines which sensing functions can be covered and how robustly reflected signals can be interpreted inside and around the vehicle. Depending on the number and placement of UWB nodes, the same basic technology can support different functions such as child presence detection, seat occupancy, breathing or vital sign detection, keyless entry, kick opening, and intrusion-related monitoring.
For in-cabin monitoring, UWB anchors can be placed in different positions depending on the target use case and system requirements. A Minimal Setup can greatly reduce hardware complexity while still enabling selected sensing functions in defined areas of the cabin or around the vehicle. An Advanced Setup with additional or differently positioned UWB nodes can increase spatial coverage, improve robustness, and support more demanding use cases by providing additional observation angles. All kind of setups will allow the consolidation of multiple dedicated sensors.
The system architecture can therefore be adapted flexibly to the required detection quality, integration constraints, and cost target. Some signal processing, feature extraction, or event detection algorithms can run directly on the UWB nodes, while selected features are sent to the ECU. The ECU can then merge the intermediate results from multiple nodes and perform sensor fusion, improving spatial detection, accuracy, and overall sensing performance.
Use Case: Vital Sign and Breathing Detection
Embedded AI has multiple approaches for in-cabin sensing to determine vital parameters from respiration monitoring scenarios and is a leader in research and development in this field.
Use Case: CPD – Child Presence Detection
The Problem: Heatstroke
Especially during summer time or on days with high solar radiation, temperatures can become life-threatening in a locked car, particularly for babies and animals. The critical temperature of 42°C inside the car is reached after only 30 minutes at an outside temperature of 26°C and after 10 minutes at an outside temperature of 35°C. According to current statistics (and estimates), about 800 children worldwide die each year from heatstroke because they are left in a closed car on a hot day (underreported for animals).
The issue is so relevant that the European society for vehicle safety, EURO-NCAP, introduced both interior monitoring and driver monitoring as criteria for assessing passenger safety in 2023. In the USA, these technologies are even more highly valued. A bill called the “Hot Car Act” was passed by Congress in 2021.
The Solution: UWB Radar
UWB technology can detect vital signs of humans and animals and locate them inside the vehicle. UWB Radar has a distinct advantage over optical methods and even conventional FMCW Radar. This is because UWB Radar signals, characterized by longer wavelengths, can effortlessly penetrate materials such as clothing and blankets. Consequently, UWB technology excels at sensing the movement of living beings. Due to the lower frequencies compared to FMCW Radar, UWB has lower requirements for HF components, thus keeping material costs low.
Vital parameters are detected in the UWB Radar signal through AI-based recognition algorithms that run resource-efficiently in real-time on the microcontroller of the UWB sensor electronics.
Child Presence Detection (CPD) is undoubtedly the main motivator for investing in the UWB system in cars. The following sections highlight additional functionalities that can be achieved with the established UWB technology.
Use Case: Occupant Sensing During Driving
Driver/Occupant Monitoring
The system can also ensure that vital parameters of occupants and animals are monitored during the drive. The driver is alerted if vital parameters of the occupants reach dangerous levels.
Emergency Services Alert
If dangerous values in vital parameters occur for the driver, emergency services can be alerted automatically.
Vital Sign Information in Case of an Accident
In the event of an accident, data can be automatically transmitted to emergency services to save valuable time in life-saving efforts (who was sitting where and until when they were breathing, abnormalities in vital parameters of individual persons, e.g., irregular heartbeat, shallow, fast, or absent breathing).
Passive Driver Vital Monitoring
For autonomous driving up to Level 3, a person with a driver’s license must control the car or intervene in an emergency. During long, monotonous drives, fatigue can quickly set in for the passive observer – a latent danger. For this level of autonomous driving, the UWB system provides support in monitoring the (passive) driver by detecting fatigue, sleeping, atypical situations (such as a heart attack), or respiratory arrest.
Use Case: Intrusion Detection
Additional cost savings for the vehicle’s system costs arise by using the UWB system when in-cabin monitoring is also conducted in a parked and locked vehicle. The UWB system, through movement detection, can reliably detect break-ins. The costs for conventional alarm system sensors can thus be eliminated.
Unlike in-cabin monitoring during the drive, the “alarm system” mode operates with a significantly lower frequency of measurement cycles to minimize standby power consumption.
Extended UWB Automotive Platform: X-UWB™
In automotive projects, UWB in-cabin sensing can be combined with localization and other UWB-based functions. Our X-UWB concept shows how these capabilities can be integrated into a broader vehicle platform.
Looking for support with UWB in-cabin sensing?
We develop and validate UWB-based sensing algorithms, demos or live applications for presence detection, breathing analysis, child presence detection, intrusion detection, and other embedded sensing applications. Please get in touch with us.
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