Technical & Performance
FiRa is offering flexibility to address a wide range of use cases to allow for interoperability where pre-shared keys don't exist, or in cases where battery-driven devices demand low-energy modes, etc.
UWB-based products can reach up to 100 meters of range under line-of-sight conditions.
However, as with any radio technology, the maximum real-world range of UWB depends on several factors, including channel frequency, antenna design, power levels, and complexity of the propagation environment (which can be influenced by in-band interference and the materials and objects present in the environment). Like other RF technologies, UWB does not go through metal but does pass through other materials, such as wood, plaster, and even brick. The more dense the material, the shorter the range.
Unlike Bluetooth® LE, which only operates at 2.4 GHz, UWB can operate on different frequencies between 6.5 and 10 GHz. Generally speaking, the higher the frequency, the shorter the range, but this can be mitigated using a number of techniques.
FiRa supports the use of high-rate pulse (HRP) repetition frequency in UWB-enabled mobile devices because HRP enables lower latency and a higher density of UWB devices in a given venue, resulting in superior overall performance.
UWB is designed for scalability and has already been successfully deployed in factory and office-building settings that employ hundreds of anchors and thousands of tags. UWB is able to support large-scale, high-density networks of anchors and devices/tags because it uses very short packets and highly accurate time synchronization, making it possible to build efficient TDMA schemes with fine synchronization.
Several UWB features combine to ensure reliable operations, even as the number of UWB installations, on smartphones and in the infrastructure continues to grow. UWB’s use of impulse radio technology, with very short packets, reduces the probability of collisions. The collision rate is also kept low by the MAC, which can schedule ranging sessions with multiple devices. The MAC can still range with other, uncoordinated systems if a collision does occur. Another factor that adds to UWB’s reliability is the PHY, which is very robust and can recover quickly in noisy environments.
The UWB technique itself is not limited by temperature, but there are specified temperature ranges for semiconductors and the applications they support. For example, there are UWB chipsets that are designed and tested for the industrial temperature range (-40 to +85 °C), and some for the automotive-grade temperature range (-40 to +105 °C). Other ranges may be made available based on application needs.
UWB Compared to Other Technologies
The way UWB works gives it an advantage in energy efficiency. Unlike Bluetooth® LE and Wi-Fi, UWB is an impulse radio. Its modulation is ideal for location applications because it supports very short packets that use very little energy to compile a distance measurement. Fast data transfers, of up to 27/31 Mbps as specified by the IEEE 802.15.4z standard, also contribute to power savings because UWB needs less time (and energy) than Bluetooth® LE to transfer the same amount of data. When operating in transmit-only mode (like a beacon) or synchronized two-way communication modes, UWB can use less power than Bluetooth® LE.
Because UWB systems only require one or a few measurements to compute a single distance or position, each calculation uses less energy. Bluetooth® LE and Wi-Fi solutions, on the other hand, require many more samples and post-processing calculations to compute each distance or position, and this extra work uses extra energy.
Bluetooth® LE remains the most energy-efficient solution when the application is not time-synchronized. This is why UWB and Bluetooth® LE are often paired together, using Bluetooth® LE as a low-power discovery technology and waking UWB only when its secure, fine-ranging capabilities are needed.
Positioning with UWB is exceptionally accurate in all operating environments – not just best-case scenarios. UWB delivers accuracy down to a few centimeters with a reliability of 99.9% under normal operating conditions and, in challenging environments such as the factory floor, is accurate to approximately 30 cm with 95% reliability.
Compare this to Wi-Fi and Bluetooth® LE, which have been shown to deliver good results, but only under ideal conditions. Recent tests published by Cisco, for example, demonstrate Wi-Fi and Bluetooth® LE accuracy in the 2 to 3 meters range with 95% reliability in a strictly controlled environment. However, these results quickly degrade when conditions are less than perfect. Similarly, while it’s true that some Bluetooth® LE systems can achieve sub-meter accuracy, these results are under very specific conditions, including a very high infrastructure density and clear line of sight. Real-world operating environments rarely match the laboratory conditions used for testing, meaning day-to-day operation is unlikely to achieve the same level of accuracy with a sufficient degree of reliability.
UWB’s advantage in positioning is due, in large part, to physics. UWB’s unique pulse signal, operating over 500 MHz of bandwidth, increases the accuracy of Time of Flight (ToF) calculations, which determine distance by measuring the travel time of a radio wave and multiplying that time by the speed of light. UWB’s very fast transmission of steep and narrow pulses makes it possible to mark signal timing with a higher degree of certainty. The UWB pulse signal maintains its accuracy even as the distance between the devices increases and displays excellent resilience in non-Line-of-Sight (non-LoS) scenarios.
The UWB ToF calculation is more accurate than the Receiver Signal Strength Indication (RSSI) technique used by Bluetooth®, Bluetooth® LE, and Wi-Fi. RSSI measurements are more susceptible to environmental factors, such as obstructions and interference from other radios, and this reduces accuracy. An obstruction can result in severe attenuation of signal power, leading to errors that can be off by multiple meters.
When it comes to location systems, there are two ways to measure responsiveness – hardware latency and application-level latency. Hardware latency is the time it takes the PHY/MAC to complete measurements Application-level latency which, to put it simply, is how quickly the blue dot on the map reacts to your movements. Application-level latency depends on several factors, including the accuracy and reliability of the technology, its data rate, the amount of data being exchanged, and the number of devices sharing airtime in a given place and time.
With UWB, very short packets and the ability to build Time Division Multiple Access (TDMA) systems with fine synchronization give UWB a low hardware-level latency. (The IEEE and the FiRa Consortium define different ranging rounds, so measured delays can vary from a few milliseconds to a few tens of milliseconds.) The high accuracy and reliability of UWB measurements mean only one or a few measurements are needed to determine a precise distance or position. This translates into an application-level latency so low that readings appear instantaneous.
By contrast, Bluetooth® LE and Wi-Fi solutions need many more samples to compute a single distance or position. These additional measurements can take several seconds to collect and then post-process, which is why positioning apps based on these technologies can be sluggish.
UWB components are manufactured using standard CMOS processes similar to those used for Bluetooth® LE, and UWB die sizes are compatible with those of Bluetooth® LE devices. Also, UWB chipsets don’t require specialized or expensive external components. However, because UWB for positioning is still relatively new, it hasn’t reached the same scale of production or deployment as Bluetooth® LE, so it’s currently more expensive than Bluetooth® LE. As with similar radio technologies, though, economies of scale can be expected to bring the cost of UWB components down over time.
Many countries have set aside spectrum for UWB operation. Regulatory guidelines for UWB vary from region to region, but the frequency ranges between 6.490 and 7.987 GHz (UWB bands 5, 6, 8, and 9, using channels 5 and 9) are recommended to achieve global acceptance.
Being able to operate UWB on multiple channels adds capacity because devices can use different channels to co-exist without interfering with each other. On the other hand, some channels are easier to work in than others. Channel 9, for example, offers worldwide coverage, so it can be used in any region, and is not affected by potential interference from Wi-Fi signals present on Channels 5/6. For these reasons, Channel 9 is the only mandatory channel for the FiRa Consortium.
UWB Channel 5 is in the center of the 6-GHz Wi-Fi spectrum, which means there is a chance of interference between the two radios, especially in very dense Wi-Fi environments with high Wi-Fi throughput. Various simulations and empirical data* have shown that radio interference can cause minor UWB packet loss, potentially lengthening the ranging round on an intermittent basis. To enable fully concurrent Wi-Fi and UWB operation without interference, UWB systems can use Channels 8 and 9, which are adjacent to and don’t overlap with the 6-GHz spectrum.
*Understanding and Mitigating the Impact of Wi-Fi 6E Interference on Ultra-Wideband Communications and Ranging, Hannah Brunner, Michael Stocker, Maximilian Schuh, Markus Schuß, Carlo Alberto Boano, and Kay Römer: http://www.carloalbertoboano.com/documents/brunner22uwbwifi.pdf
Several features make UWB an extremely secure positioning technology at the PHY level. Very-low-power transmission is difficult to detect, PHY-level ciphering (defined by the IEEE 802.15.4z standard) protects data transmissions, and Time of Flight (ToF) distance estimations are hard to hack because propagation time and the speed of light are both extremely difficult (if not impossible) to alter. In the Link and higher OS layers, strong PHY-level security is a solid foundation for building other security mechanisms, such as authentication, non-repudiation, and encryption.
Yes, as with other communication technologies, a higher security level is often a tradeoff with the probability of obtaining valid ranging results. Other factors such as receiving implementation, noise and multi-path conditions, and the required security level can also impact ranging results.
FiRa certification programs accommodate products at all defined security levels. The ranging security level is a configuration parameter of the UWB physical layer which can be set to low/medium/high. The component or device security level is a property of the FiRa product/item that vendors choose depending on the targeted market segment. The vendor selects the ranging security level to meet the security needs of the target market segment.
FiRa is in the process of defining security targets for the components specified by FiRa.
STS stands for Scrambled Timestamp Sequence. STS is a ciphered sequence used to ensure the integrity and accuracy of ranging measurement timestamps.
Static STS is an operational mode where the STS is repeated during a session. Provisioned STS and dynamic STS are operational modes where the STS is confidential and never repeated during a ranging session. In dynamic STS mode, the session key used for generating the STS is provided by a separate secure component. In provisioned STS mode this key is provided by the application processor.
In general, UWB is capable of transmitting lots of data quickly at short range. The IEEE 802.15.4z standard and the FiRa additions are focused on impulse radio that incorporates simple modulation schemes while allowing for fine-ranging applications. As of today, the IEEE 802.15.4z standard allows for data communication of small amounts of data; speed is limited to a few tens of Mbps.