Since the early 2000s, ultra-wideband (UWB) technology has been increasingly applied in various commercial sectors requiring secure and accurate ranging capabilities. Well-known examples include contactless access control systems for cars and buildings, asset positioning in warehouses, hospitals, and factories, and navigation support in large venues such as airports and shopping malls.

UWB wireless signal transmission is characterized by the transmission of extremely short pulses in the time domain. This characteristic is maximized in pulse radio (IR) UWB technology, transmitting pulses in the nanosecond or even picosecond range. Therefore, in the frequency domain, it occupies a much larger bandwidth than wireless "narrowband" communication technologies such as Wi-Fi and Bluetooth.

UWB technology operates over a wide frequency range (typically 6 to 10 GHz), with channel bandwidths of approximately 500 MHz or even higher. As a result, its ranging accuracy is far superior to narrowband technologies. Today, UWB technology can provide centimeter-level or even millimeter-level positioning information between a transmitter (TX) and a receiver (RX), typically at a distance of 10 to 15 meters.

In addition, the enhancements to the UWB physical layer (as part of the amendments to the IEEE 802.15.4z low-rate wireless network standard) have played a crucial role in enabling secure ranging functionality.

Over the years, imec has made significant contributions to advancing UWB technology and overcoming the challenges that hinder its widespread adoption: reducing power consumption, increasing bit rate, improving ranging accuracy, making receiver chips more resistant to interference from other wireless technologies operating in the same frequency band, and enabling cost-effective CMOS silicon chip implementation.

Introduction from Imec

Imec researchers have developed multiple generations of ultra-wideband (UWB) radio chips compliant with the IEEE 802.15.4z standard for ranging and communication. Imec's transmitter circuitry employs innovative pulse shaping and modulation techniques, combined with an advanced polarized transmitter, digital phase-locked loop (PLL), and ring oscillator architecture, achieving millimeter-level ranging accuracy with low power consumption.

On the receiver side, innovative circuit design gives the device excellent interference immunity while minimizing power consumption. Each generation of UWB prototype transmitter and transceiver chips is manufactured using cost-effective CMOS-compatible processes and features small-area silicon wafers.Inspired by the outstanding performance of ultra-wideband (UWB) technology, experts have long claimed that UWB's potential extends far beyond "precise and secure ranging." They see radar-like application opportunities, which, unlike ranging, use a single device to transmit UWB pulses and analyze the reflected signals to detect "passive" objects.

Combined with the precise ranging capabilities of Ultra-Wideband (UWB), this technology can be applied to the automotive industry, such as detecting the presence of occupants and monitoring their gestures and breathing to improve occupant safety. In smart homes, UWB radar sensors can automatically adjust lighting based on the presence of people. In nursing homes, this technology can be used to detect falls and issue alarms without the need for intrusive camera surveillance.

IEEE 802.15.4ab

IEEE 802.15.4ab, a next-generation wireless technology standard expected to be officially released in early 2026, will facilitate the realization of such UWB applications. 802.15.4ab will provide several enhancements, including the implementation of radar functionality in IR-UWB devices, transforming them into sensing devices.

At the VLSI Technology and Circuits Symposium 2025 (VLSI 2025), imec showcased its fourth-generation UWB transceiver, conforming to the radar sensing baseline defined in the initial version of 802.15.4ab.

Its key features include enhanced modulation and high data rate support. Furthermore, imec's UWB radar sensing technology achieves unique enhanced radar sensing capabilities (such as longer detection ranges) and data rates up to 124.8 Mb/s—all integrated into a system-on-a-chip (SoC). This new radio module also complies with the current 802.15.4z standard and combines radar sensing capabilities with communication and secure ranging functions.

A unique feature of the imec infrared ultra-wideband radar sensing system is its 2x2 MIMO architecture, which employs a full-duplex configuration with two transmitters and two receivers. In this configuration, a duplexer controls the operating mode of the transceivers (transmit or receive mode). Furthermore, the transmitters and receivers are paired via duplexers (TX1-RX1, TX1-RX2, and TX2-RX2). This allows the radar to operate simultaneously in transmit and receive modes without the need for an RF switch to change modes.

This operating method reduces the radar's effective operating range—previously, the effective operating range was limited by the switching time between the two modes. Imec's full-duplex radar can operate within a range of 30 cm to 3 meters, a groundbreaking achievement. In this full-duplex MIMO configuration, the effective operating range is limited only by the radar's 500 MHz bandwidth.

This infrared ultra-wideband dual-receiver radar (IR-UWB 2TRX) physically employs two antenna elements, each shared by one transmitter (TX) and one receiver (RX). However, its 2x2 MIMO full-duplex configuration actually allows for the use of three antenna arrays, significantly improving the radar's angular resolution and reducing its footprint. Compared to state-of-the-art single-input single-output (SISO) radars, this radar has a 1.7x smaller footprint and 2.5 fewer antennas, making it a high-performance, compact, and cost-effective solution. The radar employs advanced technology to isolate transmitted and received signals, achieving >30dB isolation within a 500MHz bandwidth.

Signal transmission employs a hybrid analog/digital polarization transmitter, introducing filtering effects in the analog domain for signal modulation. This results in a clear transmitted signal spectrum, ensuring good performance and low-power operation of the ultra-wideband radar sensor.

Finally, in addition to the MIMO-based analog/RF section, the UWB radar sensor is equipped with an advanced digital baseband (or modem) for signal processing. This component extracts relevant information, such as the distance between the radar and the target and estimates of the angle of arrival.

The characteristics of radar based on infrared ultra-wideband (IR-UWB) MIMO technology are highly attractive in automotive applications. Ultra-wideband radar can not only detect the presence of people inside a vehicle (e.g., children), but also map occupant distribution and monitor vital signs such as breathing. Currently, many automotive OEMs and Tier 1 suppliers have included this functionality in their R&D plans. However, currently, no radar technology can achieve these functions with the required accuracy. A particularly challenging aspect is achieving sufficient angular resolution to detect two targets at the same (close) distance from the radar. Furthermore, for breathing monitoring, it is essential to be able to detect minute movements of the target within seconds.

At the IEEE International Symposium on Personal, Indoor and Mobile Wireless Communications 2025 (IEEE PIMRC 2025), researchers at imec demonstrated their first proof-of-concept, proving that imec's latest infrared ultra-wideband MIMO radar system can perform two in-vehicle perception tasks: occupant detection and breathing frequency estimation. 

The in-vehicle measurements were conducted inside a small car. The ultra-wideband platform was positioned in the center of the roof, in front of two self-developed antenna arrays near the rearview mirrors. The antennas were 55 cm from the center of the driver and front passenger seats. Experimental results confirmed that the system can estimate angle of arrival and breathing frequency with high accuracy. For example, with both the passenger and driver seats occupied, imec's UWB radar system achieved standard deviations of less than 1.90 degrees and 2.95 bpm for angle of arrival and breathing frequency estimation, respectively.

Among their contributions, the authors of imec highlighted another benefit of using UWB technology for in-vehicle monitoring: the TRX architecture, already used in some cars for keyless entry, can be reused for radar applications, thereby reducing overall costs.

IR-UWB transceiver

In addition to its superior radar sensing capabilities, imec's latest IR-UWB transceiver boasts another feature that distinguishes it from existing UWB solutions: it offers data rates up to 124.8 Mb/s—the highest data rate currently compatible with the upcoming 802.15.4ab standard. This is approximately 20 times higher than the 6.8 Mb/s data rate used in current ranging and communication applications, thanks to optimizations to the analog front-end and digital baseband. The high data rate also results in extremely low power consumption per bit - far lower than that of Wi-Fi, for example - especially at the transmitting end.

These features will open up new application areas for audio and video data streaming. Potential applications include next-generation smart glasses or VR/AR devices, and the compact size of the UWB TRX is a significant advantage.

The IEEE 802.15.4ab standard also supports another feature: advanced ranging. This feature will improve the link budget for signal transmission, increasing ranging distance by four times—up to 100 meters in unobstructed line-of-sight conditions. This feature is expected to significantly enhance the user experience of keyless entry solutions for automobiles and smart buildings. It not only increases the effective working distance but also better handles various complex environments, such as when the signal is obstructed by objects (like people).

imec's fifth-generation UWB technology introduces a new narrowband (NB) transceiver, enabling advanced ranging capabilities. This transceiver architecture supports NB-assisted UWB operation, increasing the actual working range of UWB by up to four times compared to previous generations.

Over the past two decades, ultra-wideband (UWB) technology compliant with the IEEE 802.15.4z standard has proven its ability to support secure ranging and positioning deployments in large-scale markets and is widely used in automotive, smart industry, smart homes, and smart buildings. With the upcoming release of the IEEE 802.15.4ab standard, emerging UWB devices can now also be equipped with radar capabilities.

imec's fourth-generation IR-UWB technology is the first (publicly reported) radar sensing device compliant with the 802.15.4ab standard, demonstrating superior radar sensing capabilities suitable for applications such as automotive and smart homes. Record-breaking high data rates also indicate the potential of UWB technology to open up new markets: for example, providing low-power data streaming for smart glasses or AR/VR devices.

The narrowband (NB) transceiver architecture introduced in the fifth-generation product not only unlocks advanced ranging capabilities but is also designed with scalability in mind. While its primary function is to implement narrowband-assisted ultra-wideband (UWB) according to the IEEE 802.15.4ab standard, it also lays the foundation for supporting emerging standards such as Bluetooth high-frequency bands, thus paving the way for unified, multi-band, multi-standard low-power wireless solutions.

The future of UWB technology is bright. Not only are technological advancements rapid, but ongoing standardization efforts are also helping to shape current and future UWB applications.

Source: Compiled from imec

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