Bluetooth® positioning and distance measurements

Bluetooth® positioning and distance measurements

Direction finding and high-accuracy distance measurements (HADM)

Bluetooth® location services

Location-based services and applications have become commonplace in today’s electronic devices, such as smartphones, cars and wearables. Sometimes, satellite (GNSS) or cellular networks fall short due to insufficient coverage or accuracy. This is especially true for indoor applications. Therefore, it is common to use short-range technologies like Wi-Fi, UWB or Bluetooth® to support proximity, secure ranging, tracking and navigation functionalities within indoor environments.

Today’s Bluetooth® location service applications offer proximity and ranging capabilities based on link availability and path loss estimation. They also incorporate direction finding through angle of arrival (AoA) or angle of departure (AoD) estimation. The ongoing evolution of Bluetooth® LE will further enhance these capabilities by introducing a phase ranging technology called Bluetooth® Channel Sounding to support secure ranging applications.

A few well-known applications that use Bluetooth® location services are:

  • Asset tracking
  • Proximity detection
  • Contact tracing
  • Secure access applications

Bluetooth® Low Energy proximity and tracing services

Bluetooth® Low Energy (LE) proximity and tracing services utilize link status and estimated pathloss to identify nearby peers and determine the distance to a peer. This is done using a received signal strength indicator (RSSI), which reflects the signal strength at the receiver’s end to estimate the distance between devices.

However, an RSSI-based ranging method offers limited accuracy with high uncertainty, due to the dependencies on actual radio channel behavior. It has also been observed that RSSI-based ranging can be manipulated without great difficulty. This poses a potential risk, especially in security applications such as digital keys. Recognizing these limitations, the Bluetooth® Special Interest Group (SIG) is actively developing the technology to introduce high-accuracy distance measurements (HADM) with built-in security features.

Bluetooth® positioning and direction finding

A Bluetooth® LE direction finding (DF) feature was defined in Bluetooth® 5.1 to enhance the capabilities of Bluetooth® positioning services. This feature supports two methods for determining the direction of a Bluetooth® signal:

  • Angle of arrival (AoA) estimation: A Bluetooth® transmitter with a single antenna sends a specialized direction-finding signal. The receiving peer device, equipped with an antenna array, measures the phase difference to estimate the relative signal direction. This method is commonly employed for asset tracking.
  • Angle of departure (AoD) estimation: A stationary Bluetooth® transmitter uses a switched antenna array to transmit direction-finding-enabled packets. The receiving device, equipped with a single antenna, captures the signals and measures the phase differences to estimate the relative signal direction. This method is suitable for applications that require precise directional information in dynamic scenarios.

The precision of AoA/AoD estimation for direction finding relies heavily on:

  • Number of antennas
  • Stable transmit power
  • Low frequency offset
  • Drift of DF signal (LE 1M or LE 2M) transmitting device
  • Capability of receiving device to accurately sample I/Q data from received signals

To ensure robust performance, the Bluetooth® SIG has specified various test cases with distinct setups. The R&S®CMW wireless communications test platform supports these test cases with an automated test solution.

HADM with Bluetooth® Channel Sounding

Bluetooth® Channel Sounding uses phase-based ranging (PBR) to enable HADM between two Bluetooth® LE devices; it uses the phase shift between the received and transmitted radio signals of different channels. By utilizing two or more signals with different frequencies, the measured phase difference (Δθ) between these signals serves as a precise indicator for estimating distance.

  • One device acts as the initiator, transmitting a packet with a constant tone extension (CTE).
  • The second device functions as the reflector, responding to the first device by sending a packet back with the same phase as the received signal.

This process ensures accurate and reliable distance estimation between the Bluetooth® devices. Typical HADM applications include keyless entry systems, indoor navigation and asset tracking, with new use cases on the horizon.

How Bluetooth Channel Sounding works
How Bluetooth® Channel Sounding works

The Bluetooth® SIG is actively specifying test cases focusing on precise measurement and stable frequency and phase generation of channel sounding signals. When antenna areas are utilized, the test cases also address the antenna switching integrity. Given the substantial impact of device design on phase difference and time delay measurements, it is best to conduct over-the-air (OTA) measurements when testing AoA, AoD and Bluetooth® Channel Sounding.

Test solutions for Bluetooth® Channel Sounding and direction finding

Rohde & Schwarz test and measurement solutions offer comprehensive support for Bluetooth® BR, EDR and LE, aligned with the latest Bluetooth® core specifications. A product highlight is the R&S®CMW wireless communications test platform, which sets itself apart by supporting automated testing of Bluetooth® Channel Sounding and direction finding. It adheres to the test cases specified by Bluetooth® SIG for these functionalities, making it a unique solution on the market. This test platform also features in-radio test control for DTM-like testing of Bluetooth® LE devices in an OTA setup, streamlining the test process.

Bluetooth® test functions are integrated into all major Rohde & Schwarz instruments, including signal generators and analyzers. These instruments support not only Bluetooth® but also other non-cellular and cellular standards, consolidating a wide range of test capabilities in a single box.

Want to discuss your specific Bluetooth® test cases with our experts?

Bluetooth® Low Energy channel sounding physical layer verification setup with R&S®CMW and R&S®CMWrun
Bluetooth® Low Energy channel sounding physical layer verification setup with R&S®CMW and R&S®CMWrun

Bluetooth® positioning and distance measurement test solutions

R&S®SMBV100B vector signal generator

New benchmark in its class with up to 1 GHz modulation bandwidth and Bluetooth® support

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R&S®FSV3000 signal and spectrum analyzer

Fast Bluetooth® measurement speeds for high throughput - from R&D to production

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R&S®CMW270 wireless connectivity tester

Non-cellular tester for Bluetooth® BR/EDR/LE - approved by Bluetooth® SIG for RF testing

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R&S®TS8997 regulatory test system for wireless devices

Regulatory testing for wireless devices operating in ISM bands based on ETSI and FCC

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R&S®CMW100 communications manufacturing test set

Ultra-compact non-signaling tester for Bluetooth® - optimized for production lines

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R&S®CMW-Z10 shielded box

Excellent shielding effectiveness - perfect for OTA testing of Bluetooth® devices

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Bluetooth® positioning and distance measurements Knowledge+

Aplication card: Bluetooth® Low Energy channel sounding validation

Read this appcard and learn about comprehensive and fully automated test solutions to verify Bluetooth® Low Energy physical layer functionality.

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Webinar: Redefining testing for Bluetooth® Low Energy

This webinar will give an overview of the latest Bluetooth® LE developments and demonstrate related test solutions.

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Poster: Connecting almost everything with Bluetooth® Low Energy

Overview of Bluetooth® Low Energy technology aspects including physical layer options, direction finding, power control and audio streaming.

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Webinar: Everything you need to know about Bluetooth® Low Energy (LE)

Introduction of latest Bluetooth® features, related test challenges and solutions

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Application card: Ensure accurate Bluetooth® 5.1 direction finding

How to use R&S®CMW to test Bluetooth® direction finding

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White paper: From cable replacement to the IoT – Bluetooth® 5.1

Summary of Bluetooth® technologies with a focus on the physical layer for version 5.1

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Application note: Tests of Bluetooth® Low Energy 5.1 indoor navigation - direction finding

Guide on how to perform BLE 5.1 DF RF tests according to BT 5.1 RF test specification

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Application note: Bluetooth® LE RF test for IoT applications

How to use the R&S®CMW platform to perform measurements for Bluetooth® test specification 5

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Application brochure: Bluetooth® testing with the R&S®CMW wideband radio communication tester

Overview of the R&S®CMW wideband radio communication tester for Bluetooth® applications

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