A Comparison of 60 GHz FMCW Radar vs UWB for In-Cabin Monitoring

With increasing safety and security standards in the automotive industry, car manufacturers are compelled to incorporate additional features into their vehicles to maintain competitiveness. For instance, the Euro NCAP safety rating will require a vehicle to have a child presence detection (CPD) system that adheres to the CPD Test and Assessment Protocol by 2025 to get four points for this safety feature.

In the race to provide reliable, affordable, and multi-purpose solutions, sensor companies come to the market advocating the adoption of diverse technologies. In recent developments, we have seen radar-based solutions utilizing different frequency ranges and sensing approaches, namely 60 GHz FMCW and UWB sensors.

While both UWB (ultra-wideband) and FMCW (frequency-modulated continuous wave) solutions use radar technology, each has contrasting advantages, weak points, and possible applications. We will provide an overview of both sensor types along with their possible use for safety and comfort features inside the vehicle and in its proximity.

60 GHz FMCW Radar Basics

Continuous wave radars emit a constant electromagnetic wave signal to detect objects nearby. A simple CW radar cannot determine target range, which is why there are frequency-modulated CW radars that measure the difference in phase or frequency between the transmitted and received signal to derive object distance.

An FMCW radar that works on a 60 GHz frequency can sense very small movements, which makes it able to detect the heart rate or breathing rate of any person or pet in a vehicle, and be used for various in-cabin monitoring features like child presence detection.

UWB Basics

In contrast to the 60 GHz radar that transmits a signal in a very narrow range around the chosen frequency, ultra-wideband radar transmits across a wide bandwidth. This approach allows for very low-energy short-range communication, which gives UWB a big advantage over other types of radars.

Due to this ability, UWB technology has been adopted by phone manufacturers. In September 2019, Apple™ launched the iPhone™ 11 as the first smartphone with integrated UWB support. Today, several smartphone manufacturers provide UWB support for their phones, watches, and other IoT devices. When it comes to automotive applications, car manufacturers that use key fob technology have already adopted UWB, making it a convenient choice for other automotive applications.

Automotive Applications

Regarding automotive applications such as child presence detection, passenger localization and classification, seat occupancy detection, and others, each of the two radar technologies has its pros and cons. Here are the common use cases and technology limitations to consider:

Child Presence Detection (CPD)

Life presence detection, or the so-called CPD-Lite feature, or LPD, is easily obtainable by both 60 GHz FMCW and UWB radars. But for more complex features like child presence detection (with classification), UWB shows some shortcomings – like difficulty in detecting children in the foot well area and a high false positives rate compared to a 60 GHz radar. Due to this, UWB fails to perform well in all NCAP scenarios required to successfully obtain four safety points.

Multi-feature sensing

Cutting-edge vehicle monitoring systems aim to provide as many comfort and safety functions as possible with a single sensor. One of the main advantages of a 60 GHz FMCW radar sensor is that a single module can be used for child presence detection, seat occupancy detection (SOD), passenger localization and classification, intrusion & proximity alert, and others. When it comes to seat occupancy, 60 GHz radar can monitor foldable and removable seats. This type of radar can also provide cabin gesture recognition features, allowing for gesture control of vehicle commands.

UWB systems require several sensors to be able to cover the whole cabin, with respect to e.g. passenger localization. The limitations in bandwidth or the number of antenna channels require UWB sensors to work with complementary technology such as seat occupancy sensors (weight sensors or camera) to provide additional features like seat occupancy detection. Due to this, UWB is not the technology of choice to be used for complex in-cabin features, except LPD. UWB sensors currently available on the market are not suitable for cabin gesture recognition.

Solution complexity

One of the strongest arguments for using 60 GHz radar is its ability to cover the whole cabin of a five-seat vehicle and its close surroundings with only one sensor unit. A single UWB sensor cannot monitor more than one seat row, which makes the solution for the whole cabin more complex. For instance, one vehicle monitoring solution currently available on the market has six UWB anchors: two interior and four exterior.

Security risks

The only point of access for 60 GHz FMCW radar systems is the interior ECU (electronic control unit). To break into the system, the attacker would have to physically access the ECU in the car’s interior, which makes it resistant to hacker attacks.

UWB phone-as-a-key systems use Bluetooth technology, most commonly Bluetooth Low Energy (BLE) based proximity authentication that unlocks the vehicle when the owner’s phone is nearby. This solution is vulnerable to various cybersecurity threats like relay and rolling-PWN attacks that attempt to open the car door or even start the engine. Solving these security issues requires additional infrastructure, which adds to the complexity and price of the final solution.

Cost comparison

One of the main disadvantages of UWB sensors is their high price. A 60 GHz FMCW solution covering the whole vehicle costs around $35, compared to around $100 for a UWB solution with the same features. The steep price, nearly three times the cost of a 60 GHz radar system, is one of the main obstacles for UWB.

Adoption rate prediction

As mentioned above, the cost of UWB-based solutions is currently much higher than other technologies, and it is expected not to drop significantly in the near future. There is also a concern regarding the security vulnerabilities of this technology, along with privacy concerns like unauthorized people monitoring and tracking. As there are no current regulations for UWB technology in this area, it is a valid point to consider.

Overview

Conclusion

Taking into account all the advantages and disadvantages of the two radar technologies, the high cost, slow adoption rate, security vulnerabilities, and other factors limiting UWB potential for mass production, NOVELIC sees 60 GHz FMCW radar as the optimal solution for automotive applications, namely child presence detection compliant with all Euro NCAP requirements and seat occupancy detection.