Wireless Technology
The emergence of UWB as a viable positioning technology
By Uros Mali, director segment Smart Sensing & Connectivity, EBV Elektronik M
arket demand for positioning, or ranging technologies is growing, driven by a wide range of applications, including access control, asset
tracking, indoor positioning, ticket validation and tap-free mobile payment. Although ranging can be implemented with most wireless technologies, the optimal choice depends on the specifics of the application’s environment, along with its accuracy, response time and power requirements.
Impulse Radio Ultra-Wideband, commonly referred to as Ultra-Wideband (UWB), has been gaining significant market attention recently as a positioning and ranging technology, with a number of high-profile companies, such as Apple with the iPhone 11, announcing its incorporation into their products. This article examines UWB technology in more detail, explaining the principles of its operation and comparing its ranging capabilities with other wireless technologies. The more popular use cases for UWB are described and the article concludes with a discussion of the main UWB chipsets and modules on the market, along with available hardware and software support.
What is UWB?
Based on the IEEE 802.15.4 standard, UWB is a short-range, wireless communication protocol, operating at very high frequencies in the 6.5 – 9 GHz range. With its ability to use larger channel bandwidth (500 MHz), UWB can capture spatial and directional data with very high levels of accuracy, to less than 10cm. This level of accuracy, along with its immunity to narrowband fading and jamming differentiates UWB from other wireless technologies such as Bluetooth and Wi-Fi which operate in the crowded, 2.4 GHz, ISM band.
Two different positioning techniques are possible with UWB: Two Way Ranging (TWR) and Time Difference of Arrival (TDoA). TDoA operation is based on a system of anchors and tags. The anchors are radio frequency (RF) readers, which are in fixed positions and detect UWB pulses emitted by mobile UWB tags, (Figure 1).
32 July/August 2022
Figure 1: TDoA positioning system
The mobile tag, or initiator, emits data packets which are detected and timestamped by nearby anchors. The timestamp information is forwarded to a location server, which calculates the position of the tag by comparing the difference between timestamps from the anchors, which have a known spacing. Much like a GNSS system, four anchors are required to remove any ambiguities from the localisation calculation and the anchors must all be synchronised to the same clock. With TWR, (Figure 2), two UWB-enabled devices start “ranging” or exchanging radio packets when they are near each other. The distance between the two devices is calculated by multiplying the roundtrip time, or Time-
of-Flight, (ToF), of these radio packets by the speed of light. In Single Sided Two-Way Ranging (SS-TWR) two radio packets are exchanged. Double-Sided Two-Way Ranging (DS-TWR) is more advanced, allowing implicit correction of errors that may exist due to clock offsets between the two devices. In TWR-based positioning systems, (Figure 3), only one anchor is actively involved in a given time slot and the tag and anchor exchange a series of messages which enable the anchor to calculate the ToF of the UWB signal and hence the position of the tag. The infrastructure required for TDoA systems is more complex than for TWR, however they use much less power and
are more scalable. TDoA is therefore more commonly used for indoor navigation and location use cases, for example asset and personnel tracking and safety use cases such as collision avoidance.
How does UWB compare with other technologies?
Although most wireless connectivity technologies, such as Bluetooth and Wi-Fi, can be used for ranging, UWB delivers far superior positioning accuracies and has higher levels of RF security. The high frequency ranging pulses used by UWB operate in the 6.5 to 9 GHz range, well away from the ISM band at around 2.4 GHz. Additionally, UWB signals are extremely
Figure 2: SS-TWR and DS-TWR
Components in Electronics
www.cieonline.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82
