In Part 2, we discussed the second false-start of Ultra-WideBand (UWB) leveraging over-engineered orthogonal frequency-division multiplexing (OFDM) transceivers, launching at the dawn of the great recession and surpassed by a new generation of Wi-Fi transceivers. These circumstances signed the end of the proposed applications – short-range very high data-rate (i.e., few hundred Mbps) wireless link – not of the technology. In fact, the history of UWB is a little bit more complex: by the time the high speed wireless UWB proposal was starting to fade, other UWB applications were thriving.
Starting in World-War II, the rapid development of microwave systems paved the way to the development of UWB systems. In the 1960’s the Lawrence Livermore National Laboratory (LLNL) and the Los Alamos National Laboratory (LANL) were working on pulse transmitters, receivers and antennas. These research projects were not pure academic research; there was indeed high incentive to develop impulse systems: UWB could provide ultra-high resolution, which could then be used for object positioning, characterization and identification. By the 1970’s UWB radars were developed mainly for military application. As research continued to progress, other applications were found and, at the end of 1990’s, multiple UWB radars were used for a wide range of applications: forestry applications, through-wall detection in urban areas, imaging for search and rescue operations and obstacle avoidance.
In order to really understand the appeal of UWB, we first have to grasp the time-frequency duality, well encapsulated by the Fourier Transform. In simple terms, this duality states that if you have an infinitely long periodic time signal, it will have an infinitely small bandwidth. On the other hand, if you have an infinitely short impulse signal, it will have an infinitely large bandwidth. In other terms, it means you can trade time for bandwidth. Why would you what to do that? There are multiple reasons for it but a very important one is to enable ultra-high-resolution positioning.
There are two basic ways to determine the distance between RF devices: you can either use the Received Signal Strength (RSS) or the Time of Flight (ToF) of the signal. RSS is a very simple technique to implement and can be used by any wireless transceiver, which explains why it is so widely used. However, it is severely limited in its accuracy: the perceived distance between two immobile objects will change according to obstacles in their direct path. As an example, if you have two devices placed 10 meters apart but separated by a brick wall, which provides 12 dB of attenuation, you would think that both devices are 40 meters away. ToF solves this issue. By measuring the time it takes to travel from one device to the other, you can precisely extract the distance between both objects. In our previous example, the speed of light will indeed be reduced inside the brick wall, but this will only induce an error of about 10 cm (due to the slight reduction in the speed of light in the brick).
ToF is clearly the way to go in order to accurately position objects in space. One drawback however is that you need to deal with the speed of light, which is pretty fast to say the least. In fact, the light takes only 333 picoseconds to travel 10 cm. If one wants to measure distances between objects with centimeter precision, sub-nanosecond accuracy will be needed in the system. The easiest way to achieve this accuracy is to send a signal that is very short in time, which requires, thanks to the time-frequency duality, an UWB signal.
The possibility of accurately measuring the distance with ToF explains to a large extent the resurgence of the UWB in the last few years. The market for accurate positioning is rapidly growing in multiple sectors and should continue to see a double-digit growth in the next years. Multiple companies are now jumping into the UWB bandwagon, the latest being Apple which equipped its iPhone 11 with an UWB chip, the U1, seemingly its own design. With the capability to implement Real-Time Location Systems (RTLS), UWB enables a wealth of new applications in a wide variety of markets: Industry 4.0, IoT, and vehicular.
As we saw in this article, time can be traded for bandwidth, which can advantageously be used to do positioning. But it can also provide other advantages. In Part 4, we will explore another key advantage to UWB in many wireless applications: very low latency.
About Frederic Nabki
Dr. Frederic Nabki is cofounder and CTO of SPARK Microsystems, a wireless start-up bringing a new ultra low-power and low-latency UWB wireless connectivity technology to the market. He directs the technological innovations that SPARK Microsystems is introducing to market. He has 17 years of experience in research and development of RFICs and MEMS. He obtained his Ph.D. in Electrical Engineering from McGill University in 2010. Dr. Nabki has contributed to setting the direction of the technological roadmap for start-up companies, coordinated the development of advanced technologies and participated in product development efforts. His technical expertise includes analog, RF, and mixed-signal integrated circuits and MEMS sensors and actuators. He is a professor of electrical engineering at the École de Technologie Supérieure in Montreal, Canada. He has published several scientific publications, and he holds multiple patents on novel devices and technologies touching on microsystems and integrated circuits.
About Dominic Deslandes
Dr. Dominic Deslandes is cofounder and CSO of SPARK Microsystems, a wireless start-up bringing a new ultra low-power and low-latency UWB wireless connectivity technology to the market. He leads SPARK Microsystems’s long-term technology vision. Dominic has 20 years of experience in the design of RF systems. In the course of his career, he managed several research and development projects in the field of antenna design, RF system integration and interconnections, sensor networks and UWB communication systems. He has collaborated with several companies to develop innovative solutions for microwave sub-systems. Dr. Deslandes holds a doctorate in electrical engineering and a Master of Science in electrical engineering for Ecole Polytechnique of Montreal, where his research focused on high frequency system integration. He is a professor of electrical engineering at the École de Technologie Supérieure in Montreal, Canada.