UWB radar is an augmentation of current ultra-wideband (UWB) ranging techniques. To understand the technical side and potential applications of UWB radar, let’s start at the beginning with the platform it builds on. UWB is a communication protocol that uses radio waves over a wide frequency bandwidth, using multiple channels anywhere within the 3.1 to 10.6 GHz spectrum. The most common frequency ranges for UWB are generally between 6 and 8 GHz.
While we’ve only recently seen its use in automotive and other industries, UWB has been around for a very long time, originally used back in the 1880s when the first radio-signal devices relied on spark-gap transmitters to generate radio waves.
Due to certain restrictions, UWB was mainly used for government and military applications in the intervening years. In 2002, however, the modulation technique was opened for public use at certain frequencies in the GHz range and has since proliferated into various applications across multiple industries.
The wide bandwidth delivers a host of benefits in the automotive world, not least that UWB is less susceptible to interference than narrowband technologies. What makes UWB truly transformative is its ability to measure distances precisely and accurately to perform real-time localization. When two devices directly connect and communicate using UWB, we can measure how long it takes for the radio wave pulses to travel between them, which is commonly referred to as Time-of-Flight (ToF).
Figure 1 For automotive applications, UWB radar provides greater precision for real-time localization with a single device. Source: NXP
This enables UWB to achieve hyper-accurate distance measurements in real-time. This accuracy, along with security features incorporated within the IEEE 802.15.4z standard, makes UWB particularly useful where security is paramount—such as keyless entry solutions.
Digging into the details
Where typical UWB applications require two sensors to communicate and operate, UWB radar only requires a single device. It uses an impulse radio technique similar to UWB’s ranging concept, where a sequence of short UWB pulses is sent, but in place of a second device actively returning the signal, a UWB radar sensor measures the time it takes for the initial series of pulses to be reflected by objects. The radar technology benefits from the underlying accuracy of UWB and provides extremely accurate readings, with the ability to detect movements measured in millimeters.
For a single UWB radar sensor to receive and interpret the reflected signal, it first must be picked up by the UWB antenna and then amplified by a low noise amplifier (LNA). To process the frequencies, the signal is fed into an I/Q-mixer powered by a local oscillator. The resulting baseband signal can be digitized using an analog to digital (ADC) converter, which in turn is fed into a symbol accumulator, and the results are correlated with known preamble sequence.
This generates a so-called channel impulse response (CIR), which represents the channel’s behavior as a function of time. This can be used to predict how the signal will distort as it travels. The sequence of CIR measurements over time are the raw data of a UWB radar device.
Additionally, the principles of the Doppler effect can be exploited, measuring the shift in a wave’s frequency as the object it’s reflecting off moves; it’s used to calculate velocity to generate a range-Doppler plot.
Figure 2 Doppler effect turns UWB technology into a highly effective radar tool. Source: NXP
This process makes it possible to use UWB as a highly effective radar device which can detect not only that an object is present, but how it’s moving in relation to the sensor itself, opening a new world of applications over other wireless standards.
How automotive industry is unlocking new applications
UWB radar has a huge potential with its specific attributes delivering plenty of benefits. It operates at comparatively low frequencies, typically between the 6 to 8 GHz range, and these lower wavelengths make it highly effective at passing through solid materials such as clothing, plastics, and even car seats.
What’s more, the combination of pinpoint accuracy, coupled with UWB radar’s ability to detect velocity, low latency, and clear signal is very powerful. This delivers a whole range of potential applications around presence and gesture detection, intrusion alert, and integration with wider systems for reactive automation.
The automotive sector is one industry that stands to gain a lot from UWB ranging and radar. OEMs have previously struggled with weaker security standards when it comes to applications such as keyless entry, with consumers facing vehicle thefts and rising insurance premiums as a result.
Today’s key fob technologies are often the subject of relay station attacks, where the car access signals are intercepted and replicated to emulate a valid access permission signal. With UWB sensors, their ability to protect the integrity of distance estimation prevents the imitation of signals.
UWB is already found in many smartphones, providing another possibility that OEMs can use to increase connectivity, turning phones into secure state-of-the-art key fobs. This enables a driver to open and even start a car while leaving their phone in their pocket or bag, and the same secure functionality can be applied to UWB-enabled key fobs.
UWB radar goes one step further with applications such as gesture control, helping drivers to open the trunk or bonnet of a car without using their hands. Of course, such features are already available using kick sensors at the front or rear of the vehicle, but this requires additional hardware, which means additional costs.
UWB anchor points can either be used in Ranging Mode for features such as smart access and keyless entry, or in Radar Mode for features like kick sensing, helping to increase functionality without adding costs or weight.
UWB radar’s greater fidelity and ability to detect signs of life is where the most pressing use case arguably lies, however. Instances of infants and children accidentally left in vehicles and suffering heatstroke and even death from heat exposure have led to the European New Car Assessment Program (Euro NCAP), introducing rating points for child presence detection systems, instructing that they become mandatory features from 2025 onward.
Figure 3 UWB radar facilitates child presence detection without additional hardware. Source: NXP
A UWB radar system can accurately scan the car’s interior using the same UWB anchor points as the vehicle’s digital key without needing additional sensors. This helps OEMs to implement child presence detection systems without having to invest in, or package, additional hardware. By detecting the chest movements of the child, a UWB radar system can alert the driver with its penetration capabilities, helping pulses to easily pass through obstructions such as blankets, clothing, and even car seats.
The art of mastering UWB radar
UWB radar has proven its effectiveness in detecting the presence of objects of interest with an emphasis on signs of life. The focus of UWB in the automotive sector is currently on short-range applications typically measured within meters, which makes it ideal for use within the cabin or trunk of a vehicle.
There are some interesting challenges when it comes to interpreting data with UWB radar. With automotive applications, the software and algorithms need to detect the required information from the provided signals, such as differentiating between a child and an adult, or even an animal.
Using UWB radar as a child presence detection solution is also more energy-hungry than other UWB applications because the radio for radar is on for longer period. It’s still more energy efficient than other technologies, however, and it doesn’t necessarily pose a problem in the automotive sphere.
Research is currently being done to optimize the on-time of the USB chip, along with enabling different power modes on an IC level that allows the development of smarter and more effective core applications, particularly regarding how they use the energy budget. These updates can be carried out remotely over-the-air (OTA).
Interference is another area that needs to be considered when using UWB radar. If multiple applications in the vehicle are designed to use UWB, it’s important that they are coordinated to avoid interference. The goal is that all UWB applications can happily coexist without interference.
UWB radar outside automotive
Through child presence detection, UWB radar will save lives in the automotive sector, but its potential reaches far and wide, not least because of its ability to calculate velocity and accurately detect very small movements. Such abilities make UWB radar perfectly suited to the healthcare industry.
There is already literature available on how UWB radar can potentially be used in social and healthcare situations. It can recognize presence, movement, postures, and vital signs, including respiration rates and heartbeat detection.
These same attributes also make UWB radar an appealing proposition when it comes to search and rescue. The ability to detect the faintest of life signs through different materials can make a huge difference following earthquakes, where time is of upmost importance when it comes to locating victims buried under rubble.
UWB radar’s precise movement detection also enables highly effective gesture recognition capabilities, offering a whole host of potential applications outside of the automotive sector. When combined with computer vision and AI technologies, for example, UWB radar could provide improved accessibility and user experiences, along with more consumer-led applications in gaming devices.
One of the most readily accessible applications for UWB radar is the augmentation of smart home and Internet of Things (IoT) deployments. Once again, presence detection capabilities can provide a cost-effective alternative to vision or thermal cameras while affording the same levels of reliability.
Figure 4 UWB radar can be employed in smart home and IoT environments. Source: NXP
When combined with power management systems such as heating, lighting and displays, buildings can achieve far greater levels of power efficiency. UWB radar also has exciting potential when it comes to making smart homes even smarter. For example, with the ability to recognize where people are located within rooms, it can control spatial audio, delivering a more immersive audio experience as a result.
Such spatial awareness could also lead to additional applications within social care, offering the ability to monitor the movement of elderly people with cognitive impairments. This could potentially negate the need for wearables for monitoring purposes, which can easily be forgotten or lost.
Looking to the future
The sheer breadth of possibilities that UWB radar enables is what makes the technology such a compelling proposition. Being able to detect precise micro movements while penetrating solid materials opens the door to near endless applications.
UWB radar could provide more effective and accurate information for seatbelt reminder systems, for example, with the ability to detect where passengers are sitting. Combined with information about whether the seatbelt is plugged in or not, this can help to avoid setting off alarms by accident, such as when a bag is placed on a seat. The seat belt reminder is a natural extension to child presence detection, but where the position of the occupant also needs to be determined.
UWB radar could also be used for more accurate security and movement detection, not only outside the vehicle, but inside as well. It’s especially effective as an intrusion alert, detecting when somebody has smashed a window or entered the vehicle.
This extra accuracy can help to avoid falsely setting off alarms during bad weather, only alerting the owner to possible thefts when signs of life are detected alongside movement. It even opens the door to greater gesture recognition within the vehicle itself, enabling drivers or passengers to carry out additional functions without having to touch physical buttons.
The ability to integrate these features without requiring additional sensors, while using existing hardware, will make a huge difference for OEMs and eventually the end consumer. Through a combination of UWB ranging and UWB radar, there’s potential to embrace multiple uses for every sensor, from integrating smarter digital keys and child presence detection to kick sensing, seatbelt reminders, and intrusion alert. This will save costs, weight, and reduce packaging challenges.
Such integration can also impact the implementation of features. Manufacturers will be able to utilize OTA updates to deliver additional functionality, or increased efficiency, without any additional sensors or changes to hardware. In the spirit of software-defined vehicles (SDV), this also means that OEMs don’t need to decide during production which feature or technology needs to be implemented, with UWB radar helping to deliver maximum flexibility and reduced complexity.
We’re at the beginning of an exciting journey when it comes to UWB radar, with the first vehicles set to hit the road in 2025, and a whole lot more to come from the technology in the future. With the ability to dramatically cut down on sensors and hardware, it’s one of the most exciting and transformative wireless technologies we’ve seen yet, and as industry standards, integrations, and guides are put in place, adoption will rise and applications proliferate, helping UWB radar to meet its incredible potential.
Bernhard Großwindhager, Marc Manninger and Christoph Zorn are responsible for product marketing and business development at NXP Semiconductors.
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