Ultra-wideband (UWB) is a technology for the transmission of data using techniques that spread radio energy over a very wide frequency and with a very low power spectral density. The low power spectral density limits the interference potential with conventional radio systems, and the high bandwidth can allow high data throughput for communication devices or precision for location and imaging devices.
UWB as a short-range wireless communication protocol is often compared to Wi-Fi or Bluetooth, but it uses radio waves of short pulses over a spectrum of frequencies ranging from 3.1 to 10.5 GHz in unlicensed applications. UWB has been compared with, and could be thought of, as continuously scanning radar that can precisely lock onto an object in order to provide the object's location and communicate with that object.
There are two different approaches for data transmission in UWB: ultra-short pulses in the picosecond range, which covers all frequencies, or subdividing the total UWB bandwidth into a set of broadband Orthogonal Frequency Division Multiplexing (OFDM) channels. The first approach is more common, as it is cost-effective, although this is at the expense of a degraded signal-to-noise ratio. The second approach exploits the spectrum more efficiently and can offer better performance and data throughput at the expense of increased complexity and power consumption. Often the application of UWB drives the approach taken.
In the case of the short pulses, a UWB transmitter can send billions of those pulses across a wide spectrum frequency with a corresponding receiver translating the pulses into data by listening for a familiar pulse sequence sent by the transmitter. By sending pulses in patterns, UWB can encode information. It can take between 32 and 128 pulses to encode a bit of data, but given how fast the bits arrive, that enables data rates of 7 to 27 megabits per second.
Some of the advantages of UWB include its low power consumption, its high precision, its lack of signal interference, and its speed. UWB is able to offer a low power consumption, with a sensor sending a pulse once per second—capable of working for seven years off a single coin battery.
For precision, rather than depending on signal strength, UWB uses different calculations, such as time of flight (ToF), two way ranging (TWR), time difference of arrival (TDoA), angle of arrival (AoA), and related techniques to determine the distance from another device. With multiple antennas, UWB can also measure the angle the signal is arriving from and provide an object to a location in space.
UWB uses 3.1-10.6 GHz frequency so there is limited probability of any signal interference, which is often a case with Bluetooth and Wi-Fi. And for speed, Bluetooth-based location sensing takes at least two seconds, while UWB is thousands of times faster and means there is no discernible lag to provide a seamless user experience.
The history of UWB stretches back to the first man-made radio when Marconi used spark-gap (short electrical pulses) transmitters for wireless communication. In 1920, UWB signals were banned from commercial use and the technology was restricted to defense applications under classified programs for secure communication. It was 1992 when UWB started receiving attention in the scientific community.
This followed developments in microprocessors, and fast switching techniques made UWB viable for short-range, low-cost communication. Early applications included radar systems, communication, consumer electronics, wireless personal area networks, localization, and medical electronics. In 2002, the U.S. Federal Communication Commission (FCC) was the first organization to release UWB regulations allowing unlicensed use of the allocated spectrum, but with a very low power limit to avoid interference with other technologies that operate in this frequency band, such as Wi-Fi and Bluetooth.
UWB, while being used in various industries or its use being researched in various industries, such as IoT, radar, and medical imaging, the adoption and interest in the use of UWB in consumer electronics when Apple put UWB in their iPhone 11. Other companies, such as Samsung, followed suit, and this allowed for user devices to use this technology for greater tracking and finding devices. It has been used for sports monitoring and tracking for athletes. And NXP and Volkswagen have explored the possibility of using UWB for more secure, convenient, and safe vehicle experiences.
Ultra-wideband has advantages in precision and security over other wireless and data transmission technologies, such as Bluetooth, Wi-Fi, and NFC, and that can be used for various different use applications such as hands free control, location-based services, and device-to-device applications. The applications of the technology include radar systems, medical imaging, and communications.
One of the more popular consumer uses of UWB has been position location and tracking, or location-based services, which have also been in one of the more popular developments in UWB. This has been included in a variety of technologies:
- Smart car access—where UWB can be used to unlock a car with a smartphone as a user approaches it for keyless entry and remote start
- Building access—where the use UWB allows for automatic opening of doors to a secure area within a building once a user approaches it
- Asset tracking—where UWB can be used to track various items in consumer and industrial settings
- Sports and fitness tracking—where UWB can be used for tracking players for instant replay animations and other statistics about play
- Indoor navigation—where UWB can be used to provide precise navigation indoor to a gate in the airport or to a product on a shelf
- Warehouse positioning—perhaps a more specific use case of indoor navigation, UWB can be used to track people, machines, and equipment in a warehouse and for accurate positioning in emergency situations
- Smart home—where UWB can be used to turn on or turn off appliances, such as lights or speakers or related connected devices by allowing UWB to sense when a user moves from one room to another
Communication and sensors for UWB can be used for low data rate, where the power spectral density is extremely low and allows UWB systems to operate in the same spectrum with narrowband technology without causing undue interference. This is often used for infrared or ultrasonic approaches and can be affected by shadows and light-related interferences. Other uses in low data rate include use for wireless connection of computer peripherals, such as mouse, monitor, keyboard, joystick, or printer. UWB can allow for multiple devices operating at the same time without interference between devices in the same space. Or, if used for monitoring patients, a network of UWB sensors such as electrocardiogram, oxygen saturation sensors, and electromyography sensors can be combined to develop a proactive and connected healthcare system.
For a high data rate, UWB has the property of being available to fill bandwidth as demands increase. This could be used for something such as streaming video content wirelessly from a video source to a screen. Other uses could be internet access and multimedia, wireless peripheral interfaces, and location-based services.
Using short-pulse UWB techniques have several radar applications. These can include higher range measurement accuracy and range resolution, enhanced target recognition, increased immunity to co-located radar transmissions, increased detection probability for certain classes of targets and ability to detect slow moving or stationary targets. This has been a leading technology candidate for micro air vehicle applications, which offers a capability for high penetration in a wide range of materials such as building materials, concrete block, plastic, and wood.
The use of UWB for radar in the military started in the early 1990s when the U.S. Army Research Laboratory (ARL) developed stationary and mobile ground, foliage, and wall-penetrating radar platforms to detect and identify buried IEDs and hidden adversaries at safe distances. This included systems such as the railSAR, the boomSAR, the SIRE radar, and the SAFIRE radar.
The U.S. ARL also investigated the feasibility of using UWB techniques with Doppler processing to estimate the velocity of a moving target from a stationary platform. And this was also used to monitor the vital signs of the human body, such as heart rate, respiration signals, and human gait analysis and fall detection. For this, UWB could serve as a potential alternative to continuous-wave radar systems since they offer lower power consumption and high-resolution range profile. However, the low signal-to-noise ratio makes it vulnerable to error.
The use of UWB in medical applications has been researched since 1994, where UWB radar was used for an alternate source of remote sensing and imaging. It has been compared against x-ray imaging, as it offers non-ionizing electromagnetic waves which appear to be harmless to the human body and offers a potentially cost-effective method for human body imaging. This is capable in part as UWB can be used to see through obstacles with precision ranging at the centimeter level. Although more comparable to ultrasound than x-ray, it still offers a chance to develop new medical imaging technologies.
UWB has found more acceptance with its capability for location-based and low-data monitoring for patient motion monitoring, where it could be used for remote monitoring for a patient and any motions a patient is using. Further, this could be used for vital sign monitoring, with UWB-enabled sensors that could detect micro-movement inside the human body, similar to the technologies ability to locate objects in a room.
UWB has grown in use and interest for wireless localization. Nevertheless, precise ranging and localization in non-line-of-sight (NLoS) conditions is still an open research topic. Multipath effects, reflections, refractions, and complexity of the indoor radio environment and can introduce a positive bias in the ranging measurement, resulting in inaccurate and unsatisfactory position estimation. The proposed solution for these problems is developing deep learning and graph optimization techniques to achieve effective ranging error mitigation at the edge. Experimentation in this has already shown the benefits of low computational power UWB range error mitigation.
Furthermore, for localization services for IoT, 5G beamforming, and unmanned aerial vehicles, UWB combined with convolutional neural networks have been proposed to use for these technologies. Applications for this technology include home automation, advanced production automation, and unmanned vehicle control.
