Detect and interpret movements or positions with high reliability, even in complex environments.
Ultra-wideband (UWB) is a short-range wireless communication technology that was once intended for military applications. In 2002, the U.S. Federal Communications Commission (FCC) exempted its license and made it available for public use. Since then, UWB technology has evolved over time, transforming the way devices interact by offering secure ranging and precision sensing capabilities.
With its unmatched precision in device-to-device communication and high-speed data transfer, this technology enables fast and reliable data transfer. This feature has expanded its applications in various non-military fields, such as telecommunications, remote sensing, medical, and space exploration. UWB, which is being used in various devices, including wearables, automotive, tags, and smartphones, enables precise location tracking and facilitates high-speed data exchange.
This blog post will explore the intricacies of UWB radar, examining its underlying principles, diverse applications, and inherent advantages. Before delving into the specifics of radar, it is essential to grasp the fundamentals of Ultra-Wideband technology and its operational mechanisms.
Ultra-wideband (UWB) is an advanced wireless communication technology that operates across a wide frequency spectrum ranging from 3.1 GHz to 10.6 GHz. Their broad frequency range allows them to function in a part of the radio spectrum that is distinct from the industrial, scientific, and medical (ISM) bands. Therefore, UWB can coexist seamlessly with other popular wireless technologies, such as Bluetooth Low Energy (BLE), GPS, and Wi-Fi (see Figure 1).
UWB is defined as a radio frequency technology that transmits data across a wide bandwidth — either 500 MHz or more, or at least 20% of the arithmetic center frequency. This large bandwidth enables the transmission of very short, narrow pulses in the time domain, following the formula BW × T ≥ 4/π, which describes the relationship between bandwidth (BW) and pulse duration (T).
For example, traditional communication technologies like Wi-Fi are limited to bandwidths of 20 MHz, resulting in pulse widths larger than 4 nanoseconds. In contrast, UWB systems operating at 500 MHz achieve pulse widths as short as 2 nanoseconds. This exceptional timing resolution allows UWB to distinguish between incoming signals and their reflections with great precision, making it highly suitable for radar applications.
Due to its large bandwidth, UWB was originally proposed as an ideal solution for applications requiring precise timing and location capabilities.
Fig. 1: UWB operational frequency.
UWB achieves precise distance measurement through a method called Time-of-Flight (ToF), which calculates the distance between two devices by measuring the time it takes for a radio signal to travel from one device to another and then back. The measured time is then multiplied with the speed of light to determine the distance.
In real world applications, the above-explained process is straightforward. When a UWB-enabled device, such as a smartphone, wristband, or smart key, comes into range of another UWB device, the two devices initiate a “ranging” process. This involves exchanging challenge/response packets and measuring the roundtrip time of these signals, which is the foundation of ToF.
Depending on the application, such as asset tracking or indoor navigation, either the mobile device or the fixed UWB device calculates the precise location. For example, in indoor navigation, the mobile device determines its position relative to fixed UWB anchors and pinpoints its location on a map. UWB’s ability to deliver high accuracy stems from its use of very large channel bandwidth (500 MHz) and extremely short pulses — each lasting just 2 nanoseconds. These short pulses enable precise timing measurements, allowing the mobile device’s movements to be tracked in real time with exceptional accuracy.
The technology uses an impulse-radio principle, transmitting up to 1,000 impulses per millisecond. These short, well-defined signals in the time domain ensure high accuracy ranging, as they can be easily decoded by the receiver.
One of the key challenges in wireless communication is the multipath effect, where signals reflect off objects and reach the receiver at different times, causing distortion. UWB addresses this issue effectively by using short pulses and wide bandwidth to distinguish between direct and reflected signals. This capability ensures accurate ranging and positioning, even in complex environments.
UWB device enables precise positioning through advanced techniques like Two-Way Ranging (TWR), Time-Difference of Arrival (TDoA), and Angle of Arrival (AoA). These methods leverage UWB’s unique capabilities to deliver accurate location and spatial orientation for a wide range of applications.
This technique involves bidirectional communication between two devices. During this process, the devices measure the ToF of the UWB radio frequency signals as they travel between them. The distance is calculated by measuring the round-trip time of the signal, multiplying it by the speed of light, and then dividing by two to account for the return journey.
This method provides the separation distance, D, between the two devices. For applications requiring spatial orientation, such as 2D or 3D positioning, triangulation is used. By measuring distances between a mobile tag and multiple fixed anchors, the system calculates the precise location of the tag in 2D or 3D space.
This technique operates similarly to the Global Positioning System (GPS). It relies on a network of time-synchronized anchors distributed across a specific area.
This technique is particularly effective for indoor navigation, where GPS signals are often unavailable or unreliable.
This technique uses an array of antennas to capture incoming UWB signals. By analyzing the phase and amplitude differences across the antennas, the system calculates the angle at which the signal arrives. Advanced signal processing techniques and algorithms further enhance the accuracy of this estimation, enabling precise directional information for a variety of applications.
Ultra-wideband radars utilize ultra-wideband technology to transmit and receive short-duration, low-energy, wideband radio frequency signals reflected from target objects. The duration of a single pulse duration is similar to UWB ranging pulses of 2 ns. However, specific radar pulse shapes are used which have better reflection and sensing properties. In UWB radar, the UWB device emits a signal, which reflects off its surroundings. The same UWB device is concurrently listening on the receiving antenna and can thus analyze the reflected signal, enabling information about objects or devices in its vicinity. This radar principle enables sensing functionalities that can detect and interpret movements or positions with high reliability.
A typical block diagram of a UWB transceiver encompasses both transmitter and receiver sections. The transmitter section includes a pulse generator, power amplifier, modulator, mixer, and transmitting antenna. Conversely, the receiver section comprises a receiving antenna, low noise amplifier (LNA), correlator (which includes an integrator and mixer), and a bandpass filter.
Driven by the oscillator, the pulse generator generates a very narrow pulse width (typically around 2 ns) for transmission. The oscillator provides the pulse generator with a desired waveform, such as a Gaussian envelope, which resembles an impulse signal and defines the pulse repetition frequency (PRF) of the UWB transceiver. PRF denotes the rate at which UWB pulses are transmitted within a given time limit. The generated signal is then amplified by the power amplifier while complying with the low spectral density requirements set by the FCC. This amplified signal is channeled through a feed line to the transmitting antenna, radiating it into space towards the target object.
Fig. 2: UWB radar sensing principle.
Upon reflection from the target, the signal reaches the receiver and is captured by the receiving antenna. Filters are designed to isolate reflections from the target while minimizing interference from other objects. The signal then passes through the LNA, which enhances it by reducing noise levels relative to the received signal. The extent of reflection depends upon the size of the reflecting surface and the distance between the target and the radar. UWB radars can capture reflections from all objects within their field of view (FOV) of the antenna, with the distance to the target corresponding directly to time positioning within the radar frame.
Depending on the antenna configuration (e.g., number of Tx and Rx antennas as well as orientation of the antennas), UWB radar can detect more than movements. Beam forming allows for segmentation and understanding the position of the moving target in the FoV, and/or vital signs, such as the breathing rate, can be detected.
The power consumption of UWB radars is minimal, as they transmit impulses only for short durations. Thanks to their wide bandwidth, they can capture a large amount of information regarding the target compared to conventional narrowband radars. The combination of very narrow pulse widths and advanced signal processing capabilities allows UWB radars to effectively differentiate target reflections from those produced by surrounding objects.
Ultra-wideband technology serves a diverse array of applications across multiple industries, as depicted in Figure 3. In these applications, UWB radar can enhance the value of UWB-based localization, such as providing presence sensing or vital sensing functionality.
Fig. 3: UWB applications.
The potential of UWB to transform secured ranging applications is significant. UWB radar adds an additional functionality that can increase the value of UWB in an application without adding additional BOM. By replacing existing presence sensors, UWB can enhance the overall functionality of a system. At Infineon, we believe that UWB radar is positioned to become a pivotal add-on to UWB ranging technology across diverse sectors. As the UWB technology continues to evolve, we can expect to see innovative applications and widespread adoption emerge.
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