The Future of UWB: Reconciling Sensing with Low Energy Consumption and High Bitrates
Among a growing number of wireless communications options like Wi-Fi, Bluetooth and NFC, an increasing number of applications are using ultra-wideband (UWB) technology’s secure and fine-ranging capabilities to do their magic. This magic is enabling many applications. Hands-free entry solutions leverage UWB’s ability to track approaching people and the technology can be used to automatically unlock doors in a car or a building. Asset tracking and location-based services harness the power of UWB, especially at indoor locations where it is hard to acquire or maintain a stable GPS signal. Use cases include locating assets in warehouses, hospitals or factories with centimeter accuracy and helping people navigate large spaces such as airports and shopping malls.
Acknowledging the technology’s growth potential, market research firm Data Bridge expects UWB’s global market value to increase from $1.16 billion in 2021 to $1.84 billion by 2029.1 This trend is confirmed by ABI Research, which sees annual device shipments of UWB technology in applications like smartphones, vehicles and IoT devices reaching 1.5 billion by 2026, up from 500 million in 2022.2 It is an evolution that goes hand in hand with the proliferation of new UWB applications that combine the need for sensing with low energy consumption, high interference resilience and high bitrates.
IEEE 802.15.4Z AND STRONG INDUSTRY SUPPORT PROPELS UWB INTO THE MAINSTREAM
Today’s impulse radio (IR) UWB systems vastly outperform narrowband radios in terms of ranging accuracy. Enhancements to the UWB physical layer as part of the adoption of the IEEE 802.15.4z amendment in August 2020 have been instrumental in enabling the technology’s secure-ranging capabilities. Industrial ecosystems like the fine-ranging (FiRa) and car connectivity (CCC) consortiums have standardized UWB-enabled use cases across the automotive, smart industry, smart home and smart building markets.
While UWB systems have clear technical advantages and their adoption is growing, these systems do present challenges. UWB uses more expensive circuits and systems are more complex. The wideband performance of the systems also results in higher power dissipation than narrowband technologies such as Bluetooth. These challenges jeopardize the long-term operation of battery-powered UWB applications and have impeded broader adoption of the technology.
A BREAKTHROUGH: A SUB-5 MW, IEEE 802.15.4Z ULTRA-WIDEBAND TRANSMITTER CHIP
In response to the power dissipation challenge, imec introduced a sub-5 mW, IEEE 802.15.4z wideband transmitter chip at the 2021 ISSCC conference. This transmitter chip featured a power budget 10x lower than the UWB state-of-the-art at that time. Fabricated in 28 nm CMOS, with an occupied core area of only 0.15 mm2, the chip was built to support cost-effective, small form factor UWB deployments. It comes with a power consumption of 4.9 mW in standard-compliant operation while adhering to UWB’s stringent spectral emission regulations.
The chip leverages the digital polar transmitter architecture shown in Figure 1 to reduce the IC’s power consumption significantly. This architecture differs from conventional IR-UWB transmitters that typically use an IQ mixer to up-convert the output of a baseband pulse-shaping filter to an RF frequency, which is then amplified by a linear power amplifier (PA) before transmission. This traditional approach results in higher power dissipation and this limits battery lifetime, restricting the IR-UWB applications.
A polar transmitter can employ a non-linear PA with higher efficiency. However, the Cartesian to polar transformation results in bandwidth expansion, which can lead to a digital PA (DPA) clock rate that may be four to 10x higher than the chip rate. This results in high power dissipation for the overall system.
In a contribution to the IEEE Journal of Solid-State Circuits, imec proposed an asynchronous polar transmitter employing a pulse-shaper that consists of a finite-impulse response (FIR) filter employing current-starved inverter-based delay taps resulting in a good power/performance trade-off.3 Additionally, injection-locked ring oscillator (ILRO) technology achieves even greater power savings by enabling fast-duty cycling between the IR-UWB transmitter’s signal bursts within a packet. This allows sections of the transmitter to be turned off between pulses. The proposed transmitter is compatible with the IEEE 802.15.4z standard, supporting coherent operation while lowering the standard for power dissipation. The IR-UWB transmitter chip also complies with stringent spectrum regulations that dictate the frequencies the UWB transmitter can emit to avoid interference with other wireless services. The chip’s asynchronous pulse-shaping design meets worldwide spectral emission regulations while allowing the transmitter to operate close to the maximum power spectral density (PSD).
AN IR-UWB 802.15.4Z TRANSCEIVER TO SUPPORT THE NEXT GENERATION OF UWB APPLICATIONS
Supporting the growing adoption of UWB requires more than a low-power transmitter. The industry requires an optimized UWB transceiver that includes high performance ranging, direction-finding and localization algorithms. Researchers at imec have addressed these issues in a paper at ESSCIRC 2022.4 In this paper, researchers presented a very low-power IR-UWB 802.15.4z transceiver that strikes a balance between cost-efficient silicon layout, low energy consumption and accurate localization measurements.
The proposed design is implemented in 28 nm CMOS occupying an area of 1.06 mm2. The chip’s reduced power consumption results from a highly optimized, low-power and interference-resilient receiver (Rx) architecture coupled with an innovative digital polar transmitter architecture. A distributed, two-stage digital PLL allows for further reduction of the chip’s power consumption and contributes to a reduced measurement time of localization.
The transceiver’s system architecture is shown in Figure 2. It contains a system clock generator, along with an energy-efficient polar transmitter (Tx) and three Rxs with self-contained PLLs. The Rx consists of a two-stage low noise transconductance amplifier, passive mixer, TIA (transimpedance amplifier), lowpass filter and analog-digital converter (ADC). All amplifiers in the Rx consist of unit inverter-based gm cells regulated by a self-biased current regulator. The ADC is a 2 GSps 6-bit 2x time-interleaved (TI) ADC, which is a trade-off between TI complexity and slice sample rate. The transceiver consumes 8.9 mW in Tx mode and 21.5 mW per channel in Rx mode while achieving -33 dBm out-of-band (OOB) blocker tolerance.
UWB’S NEXT BIG THING?
While ultra-wideband technology continues to be refined, the industry is exploring the viability of several new UWB applications beyond the typical secure and fine-ranging applications being pursued by the FiRa and CCC consortiums. The technology’s large bandwidth makes it possible to build UWB radar systems that extract information in much greater resolution and detail than narrowband technologies. With the short RF pulse properties, the technology could be useful in presence detection systems and it could detect breathing patterns or a person’s heartbeat. There are ongoing efforts to create cost-effective UWB radar-on-chip systems that are highly energy-efficient and the size of a fingernail.
This technology could become an enabler in automotive applications. High-end vehicles already contain UWB anchors for secure keyless entry. Instead of adding additional mmWave radar sensors, vehicle manufacturers are exploring the possibility of leveraging the installed UWB sensors for passive presence detection applications. Some of these applications include detecting whether a child or a pet is left unattended in a car or monitoring a driver’s physical parameters. In addition to saving on component and installation costs, the power consumption of UWB radar sensors is significantly lower due to their lower carrier frequencies. Auto manufacturers are actively investigating equipping their vehicles with child detection systems. From the 2023 model year, only vehicles with this feature will be able to get the highest Euro NCAP (New Car Assessment Programme) safety rating.
INCREASING THE DATA RATES OF UWB TECHNOLOGY
Increasing the battery life in UWB applications is an important enabler for the future adoption of the technology. There is a significant development effort in this area, but pushing the boundaries of UWB extends beyond the challenge of energy consumption. Researchers at imec are investigating how the technology can also support very high bitrate applications while maintaining low-power consumption.
Fabricated in 28 nm CMOS and occupying a surface area of 0.155 mm2, the chip shown in Figure 3 accommodates data transfer rates up to 1.66 Gb/s for in-body and short-range applications. This is more than 50x faster than what is possible using the current IEEE 802.15.4z standard. Despite these record-setting bitrates, the transmitter has a power consumption of less than 10 mW. We believe that the 5.8 pJ/b energy efficiency is at least an order of magnitude improvement over Wi-Fi.
The chip uses sophisticated modulation schemes that build on all-digital phase-locked loops (ADPLLs) and digitally-controlled power amplifiers to achieve the reported data transfer rates. The architecture uses an energy-efficient, low jitter ring oscillator in combination with a low-power polar transmitter to enable those hybrid impulse modulation schemes in the smallest possible footprint. Figure 3, originally published in IEEE’s Journal of Solid-State Circuits, shows the proposed low-power polar-based IR-UWB Tx capable of performing 3D hybrid impulse modulation for supporting higher data rates. The amplitude and the phase modulation can be performed independently by the polar architecture. Unlike previously presented carrier-less topologies, the proposed Tx modulates the pulse delay independently from the carrier phase.
The impulse waveform is shaped by the digitally-controlled PA (DPA) and a pulse-shaper (PS) that uses eight delay cells to perform FIR filtering in the RF domain. The output of each delay cell enables eight PA cells. The shape and the width of the impulse can be adjusted by the delay of the PS output. An injection-locked ring-based digitally-controlled oscillator (DCO) is adopted to provide low jitter signals for the eight phases of the 8-PSK modulation scheme over a wide frequency range. A 7-bit, 238 Msym/s digital data stream is distributed to PAM, PSK and PPM modulation paths after being synchronized with a 476 MHz system clock (SYS_CLK). The digital PA with 32-unit cells supports up to 4-PAM. The 8-PSK modulation results by selecting one of eight phases from the ILRO using a phase selector (PHMUX).
An application for the architecture shown in Figure 3 is the next generation of smart glasses to enable immersive augmented reality (AR) and virtual reality (VR) experiences. Neuroscientific research could also benefit from high bitrate and miniaturized wireless telemetry modules for intracortical sensing purposes. In each of these cases, UWB could become a strong competing technology to Wi-Fi since Wi-Fi implementations typically involve more complex systems with larger footprints.
CONCLUSION: UWB IS READY TO SUPPORT MASS-MARKET DEPLOYMENTS
While further research and standardization efforts are required to bring UWB technology to maturity, the promising outcome of initial results proves that UWB can support a wide range of new applications that combine the need for high data transfer rates at short distances, very low energy consumption and a small form factor. UWB technology has proven its ability to support mass-market secure-ranging and localization deployments and this is an important takeaway for commercial companies looking at the potential of UWB. The standardization effort that is currently ongoing within the IEEE as well as the supporting regulatory, interoperability and certification discussions will largely determine the future course of UWB technology.
It is exactly at the crossroads of these two efforts that imec operates. imec works with industrial partners to commercialize the technological breakthroughs achieved by our research teams. They are also active participants in standardization bodies and industry consortiums such as IEEE, CCC and ETSI/FCC to help shape current and future UWB applications.
- Data Bridge Market Research, Global Ultra-Wideband (UWB) Market – Industry Trends and Forecast to 2029,” April 2022, Web: https://www.databridgemarketresearch.com/reports/global-ultra-wideband-uwb-market#:~:text=Data%20Bridge%20Market%20Research%20analyses,5.90%25%20during%20the%20forecast%20period.
- ABI Research, “ABI Research’s 2022 Trend Report identifies the one key location technologies market trend that will deliver in 2022—and the one that won’t,” January 2022, Web: https://www.abiresearch.com/press/2022-will-see-uwb-in-rtls-applications-reach-500-million-shipments/.
- G. Singh, E. Allebes, Y. He, E. Tiurin, P. Mateman, J. F. Dijkhuis, G.-J. van Schaik, E. Bechthum, J. van den Heuve, M. El Soussi, A. Breeschoten, H. Korpela, G.-J. Gordebeke, S. Lemey, C. Bachmann and Y.-H. Liu, “An IR-UWB IEEE 802.15.4z Compatible Coherent Asynchronous Polar Transmitter in 28-nm CMOS,” IEEE Journal of Solid-State Circuits, 2021.
- E. Bechthu, M. Song, G. Singh, E. Allebes, C. Basetas, P. Boer, A. Breeschoten, S. Cloudt, J. Dijkhuis, M. Ding, S. Gatchalian, Y. He, J. van den Heuvel, M. Hijdra, P. Mateman, B. Meyer, G.-J.van Schaik, M. El Soussi, B. Thijssen, S. Traferro, E. Turin, P. Vis, N. Winkel, P. Zhang, Y-H Liu and C. Bachmann, “A 3-10 GHz 21.5mW/Channel RX and 8.9mW TX IR-UWB 802.15.4a/z 1T3R Transceiver, IEEE 48th European Solid State Circuits Conference (ESSCIRC),” 2022.
- K. Ramaiah, “In-cabin Radar Can Sense Children in Second- and Third-row Vehicles,” Electronic Products, January 2022, Web: https://www.electronicproducts.com/in-cabin-radar-can-sense-children-in-second-and-third-row-vehicles/.
- M. Song, Y. Huang, H. J. Visser, J. Romme and Y.-H. Liu, “An Energy-Efficient and High-Data-Rate IR-UWB Transmitter for Intracortical Neural Sensing Interfaces,” IEEE Journal of Solid-State Circuits, 2022.