UWB or Bluetooth CS for positioning solutions

Positioning is achieved with various wireless technologies, with UWB, BLE, and Wi-Fi being the most prominent. UWB has gained market attention for its centimeter-level accuracy, low latency, and strong security, while BLE remains popular due to its low power use, affordability, and broad adoption. The new BLE version, Bluetooth Low Energy CS, uses channel sounding (CS) to significantly boost accuracy.

This article helps designers understand UWB and BLE features for choosing the best technology for applications like indoor positioning, asset tracking, and secure building access.

An overview of ultra-wideband (UWB)

Initially developed for military use, ultra-wideband (UWB) enables precise, secure, real-time measurement of location, distance, and direction. Commercial applications emerged in the early 2000s, and mass market adoption was confirmed with the 2019 iPhone 11 featuring Apple’s UWB U1 chip. UWB is now recognised as a versatile technology used for presence detection, gesture recognition, vital signs monitoring, and positioning.

Figure 1: UWB application scenarios

UWB operates in the 3.1–10.6GHz range, transmitting short data ~2 nanosecond pulse bursts across a 500MHz bandwidth. This wide bandwidth allows for highly accurate spatial and directional data (down to 10cm). UWB also benefits from operating in a less crowded frequency range than Bluetooth and Wi-Fi, which share the 2.4GHz band. Its enhanced security stems from a physical layer (PHY) that uses cryptography and random number generation to prevent attacks.

UWB measures distance using Time of Flight (ToF), calculating the round-trip time of a pulse between two devices, such as an anchor and a tag.

Figure 2: UWB time-of-flight used to range between two devices

Unlike amplitude or frequency-modulated signals (Figure 3), its impulses allow for precise arrival time measurement and greater immunity to interference and multipath effects.

Figure 3: Comparison of UWB impulse radio with reflected signal and Bluetooth LE narrowband signal

UWB supports different positioning techniques, including two-way ranging (TWR), time difference of arrival (TDoA), and phase difference of arrival (PDoA). Each method offers trade-offs in power consumption, scalability, and cost, allowing UWB to range between two devices, thousands of devices, or operate without fixed anchors.

Bluetooth and Bluetooth LE Channel Sounding (BLE CS)

Launched in 2004, BLE is a key part of the IoT ecosystem, known for its low power use, 40-channel data transmission in the 2.4GHz band, and mesh networking. BLE positioning relies on beacons and two main techniques: Trilateration and Triangulation. Trilateration, the most common, uses at least two beacons and measures distance via the Receive Signal Strength Indicator (RSSI). Triangulation uses two or three beacons, with known distances between them, and measures Angle-of-Attack (AoA) or Angle-of-Departure (AoD) to determine distance and direction.

Figure 4: Bluetooth LE trilateration and triangulation-based location estimation scenarios

In November 2022, the Bluetooth Technology Alliance (SIG) introduced the Bluetooth Low Energy Channel Sounding (BLE CS) specification, significantly improving distance measurement compared to previous BLE versions. Set to release in 2024–2025, BLE CS adds a new physical layer with amplitude-shift keying modulation over 72 channels, up from the traditional 40.

BLE CS uses phase-based ranging (PBR) and round-trip time (RTT) to measure the distance between devices. Device A sends a signal to Device B, which verifies the phase and retransmits it. Device A then compares the phases of the sent and received signals to calculate distance, repeating this over various frequencies for accurate measurement.

Figure 5: Bluetooth LE channel sounding, phased-based ranging

BLE CS can use PBR and RTT together to enhance accuracy, range, and security. It is gaining strong industry support and is expected to become the leading Bluetooth positioning solution due to its improved accuracy and stability over RSSI. Importantly, BLE CS doesn't require extra hardware like antenna arrays and can be implemented with existing Bluetooth chipsets, leveraging the extensive Bluetooth ecosystem.

UWB or BLE CS?

Ultimately, the end application's specific requirements and operating environment drive the choice of solution. UWB and BLE CS are both suitable positioning technologies and though BLE CS is integrated into an extensive spectrum of devices, UWB is rapidly catching up. Range, data rate, power consumption, and cost are key evaluation criteria, with security and deployment costs also important for positioning technologies. In Table 1, you’ll see an overview of the pros and cons of UWB and the variants of BLE discussed. These areas are discussed in more detail below.

6 Table 1: Comparison of UWB and Bluetooth LE location-based technologies

Range

Multiple factors can impact achievable range – operating frequency, data rates, antenna design, and so on – while the application environment is also key, especially indoors, where multipath signal reflections are present.

UWB outperforms BLE in typical line-of-sight (LOS) conditions and requires fewer anchors (Figure 6) than BLE for the same coverage, reducing infrastructure, deployment, and maintenance costs. While Bluetooth LE CS can improve accuracy and range, there’s a trade-off between the two, with sub-meter accuracy limited to shorter distances. Accuracy will typically degrade at the edge of the coverage area, especially in multipath environments.

7 Figure 6: Comparison of UWB and Bluetooth LE coverage scenarios

Security

Cyber security is critical in developing positioning solutions since any wirelessly connected device represents a potential attack surface to a malicious agent. The BLE CS standard incorporates several security features. However, as the technology is still in its infancy, these measures still need to be proven, and it will take time before the technology is adopted for use cases, such as digital car keys.

UWB, on the other hand, is already known for its robust security features, with many UWB devices already meeting the Security Evaluation Standard for IoT Platforms (SESIP) level-3 certification. Based on the IEEE 802.15.4z standard, UWB incorporates added security enhancements at the physical layer (PHY), including cryptography, random number generation, and other techniques – essentially employing the Advanced Encryption Standard (AES) protocol, an encryption specification widely adopted by the US federal government, at its core.

Scalability and design challenges

UWB is now integrated into most major smartphones and is widely used for locating personal items, unlocking cars, and indoor navigation. It can scale to hundreds or thousands of devices for indoor asset tracking. With Uplink-TDoA (UL-TDoA), UWB tags send signals to a network of time-synchronised anchors, which relay the information to a central gateway to calculate their position. This system can also combine with Downlink-TDoA (DL-TDoA) for tasks like locating and navigating to asset tags in warehouses using mobile devices.

BLE CS, however, has limitations for large-scale applications. It lacks broadcast features, requiring devices to range sequentially, which increases measurement times and reduces scalability. The complex CS procedure further slows down the process, limiting its use to smaller applications like peer-to-peer communication or basic proximity detection. Large-scale environments, like manufacturing plants, won't tolerate these delays.

In smartphones, BLE CS faces another challenge. It requires multiple antennas to reduce multipath effects, which is difficult in current devices already packed with radios and antennas (5G, Wi-Fi, Bluetooth, NFC, UWB). For BLE AoA, two antennas would need to be spaced 62.5mm apart, compared to just 18.8mm for UWB. This antenna spacing makes BLE CS harder to integrate, though future Bluetooth LE chipsets may address this issue.

Despite these challenges, BLE CS and UWB can complement each other. In scenarios like tracking assets up to 50 meters in a warehouse, BLE CS can provide coarse positioning (within 500cm), while UWB offers finer accuracy (within 10cm). Many UWB systems already use Bluetooth LE for device discovery and authentication before switching to UWB for precise ranging. BLE CS could improve performance in these situations by offering better distance measurements.

Leveraging the ecosystem

Most wireless technologies can be used to implement positioning and ranging services. Developers must carefully consider the requirements of the end application before selecting the right one for the job.

UWB has become popular in recent years based on its precision and resilience to interference. It is widely adopted in applications requiring high accuracy and security, such as asset tracking and access control. Bluetooth LE, however, has the benefit of being a foundational technology in the IoT ecosystem, with extensive infrastructure and device deployment, and advancements like direction-finding and channel-sounding techniques are set to enhance its positioning.

When selecting the optimal solution technology, developers can increasingly benefit from comprehensive supply-chain ecosystems to ensure the correct technology choice and accelerate market time. Innovators such as Qorvo, while offering comprehensive portfolios of devices, turnkey modules, and software stacks, can also leverage established partnerships to help customers from proof of concept to production design.