All about Ultra-Wideband #2: What Makes its RF Behavior Unique?
For a technology that inherently involves transmissions with very wide bandwidths, it might be counterintuitive to learn that its transmissions are brief and latency can be so low. We’ll explain why.
Published on December 1, 2023
Wide Bandwidth, Low Frequency
In our last UWB blog post, we discussed the accuracy that Ultra-Wideband (UWB) is able to provide – at least 20x more accurate than technologies like Wi-Fi and Bluetooth alone. UWB achieves location accuracy down to a 10cm margin of error, which is a massive improvement with serious implications for location tracking where it’s most critical, such as in industrial, medical, warehousing, and other applications.
For those unfamiliar with the physics of RF behavior, it might seem counterintuitive that a UWB tag like our Sera NX040 communicates across a whopping 500 MHz in session (with 7 GHz of total UWB spectrum available) and yet can do so with minimal power consumption and very low latency. In this post we’ll explain a principle that makes this and other characteristics of UWB possible.
Little Pulse, Big Reach: The Inverse Relationship Between Pulse Length and Spectral Bandwidth
Ultra-Low latency is certainly one of UWB’s key features, along with its uniquely broad bandwidth (it’s in the name, after all). Interestingly, these two characteristics exist not despite each other, but because of each other. This has to do with a principle in RF behavior that is described as the time and frequency domain relationship.
For the sake of simplicity, we’ll focus on what this relationship is, and not how it works. But the effect is straightforward: the shorter an RF pulse is, the broader its bandwidth is. Extremely short RF pulses have much wider bandwidths than pulses of a longer duration.
What this means is that UWB’s usage of extremely brief RF pulses has multiple effects that lead to its characteristic differentiation. In our Sera NX040, pulses that are less than 2 nanoseconds in duration, which enables higher data rates. This shorter duration also means that power usage is lower since the radio spends less time actively transmitting.
When you look at it this way, UWB’s defining characteristics aren’t counterintuitive, they make perfect sense. Low latency, low power consumption, and wide bandwidth are all created by this unique relationship between pulses and frequency.
A Secondary Effect: Coexistence with Neighboring Technologies
Short time over the air, as we’ve demonstrated, has very particular results for the power usage on a UWB device. However, there is an important secondary effect here, which is that the wide frequency bandwidth allows UWB to communicate with other UWB devices in the same space without competing in frequency bands that other technologies use.
This is because UWB’s short pulses generate a signal with a very wide bandwidth that is very low in spectral density. One analogy might be to imagine UWB’s radiation as a light in a room, which blankets the room in a low but even amount of light. This means the light is low in density, but wide in its area of coverage. By contrast, other wireless technologies like Wi-Fi or Bluetooth might be likened to a spotlight: a small, concentrated area of the same amount of light, but focused in a particular area. These technologies occupy specific ranges of the 2.5, 5, or 6 GHz frequency range, but do so with a higher intensity on the particular channels and frequencies that they operate in.
UWB is able to communicate in brief, wide ranging pulses that are non-destructive and non-interfering with these other technologies, while remaining perfectly “audible” to each other. This is part of why UWB can be such a helpful technology for location in environments that are already dense with other wireless devices. This low-density characteristic makes UWB truly non-competing with existing implementations, giving operators a new tool that does not require retrofitting legacy equipment for coexistence.
Coming Next: The Many Types of UWB Topologies and Their Effect On Throughput, Power, and Location Accuracy
This post is focused on the RF characteristics that enable UWB’s particular behavior. In our next post, we’ll look at how these characteristics are used in the protocol to facilitate real time location data. Obviously, low latency is critical to keeping location current and up to date, and as we’ve said previously, location information is only as accurate as it is current.
However, UWB’s throughput, power consumption, and location accuracy are heavily influenced by the particular network architecture and implementation used. As we’ll discuss, UWB traditionally functions with two device classes: tags, which are mobile, and anchors, which are stationary. But it’s also possible to use fixed tags as anchors, and in various numbers as well. And the specific implementation and number of UWB tags, anchors, or tags-as-anchors has significant effects on the power usage of tags, the throughput of tags, the difficulty of integration, and the types of location or range that can be achieved.
Watch our blog for more on UWB at: www.lairdconnect.com/resources/blog
About Our UWB Modules
Our lineup of innovative new UWB modules seamlessly integrates cutting edge UWB silicon from NXP, with the processing and Bluetooth Low Energy (LE) capabilities of Nordic Semiconductor’s nRF52 SoC. The combination of the two enables significant advancements in granularity of location that improves existing Bluetooth LE beaconing and RSSI-based ranging. They’re optimized for battery-powered implementations and integrate additional memory, crystals and components to simplify your overall BOM and drive down the cost of integration.
This comprehensive hardware approach is complimented by a range of added value software, Python scripting capabilities, and desktop and mobile tools. Whether your application is hosted or hostless, we have options to suit your application’s needs, as well as your engineering team’s capabilities. All of this is then backed by our industry leading technical support, design services, and test services to to help you simply implement UWB in your next project.
Our innovative integration of the best wireless silicon from NXP and Nordic Semiconductor has produced the secure, flexible Sera NX040 range. The series features tightly integrated hardware and RF designs, all optimized for low power operation and reducing the need for external clocks, filters and components. Already using Bluetooth LE for basic beaconing or RSSI-based ranging? Now, easily advance to the next level with NFC and UWB for more granular locationing and positioning. This granularity yields much higher accuracy compared to RSSI-only proximity applications in industrial environments.
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