Bluetooth Direction Finding

Accurate postitioning with the world's most popular wireless technology

Introduction to the technology

Bluetooth direction finding is the major feature of the Bluetooth 5.1 Core Specification. It is designed to enhance location services where previously only signal strength based technology has been used with Received Signal Strength Indication (RSSI).

Bluetooth direction finding will offer new and improved use case for Real Time Location Systems (RTLS) for asset tracking in a wide range of scenarios from logistics and warehousing to value asset security in hospitals and factories. It also brings added user experiences in proximity-based scenarios for consumer awareness and contextual information.

Bluetooth direction finding can be used to detect location in either 2D or 3D dependent on the complexity of its implementation.


Angle of Arrival (AoA) and Angle of Departure (AoD)
Bluetooth direction finding is based around the two key concepts of Angle of Arrival (AoA) and Angle of Departure (AoD). This makes use of the angular phase-shifts that occur between antennas as they receive (AoA) or transmit (AoD) RF signals.

With the use of antenna arrays at either side of the communication link phase shift data can be determined and from this, location can be calculated.

Direction finding diagram

Which approach to choose?

Whether AoA or AoD is chosen for use depends much on the use case, both can be used effectively, but in certain circumstances one or the other will be more suitable given a range of considerations

AoA allows for use of very simple, low cost tags to act as the source device of which we wish to determine its location. This system would have more complex locator units mounted in an unobstructed manner in location to determine and calculate the position of items that are tagged.

Such scenarios might include:
• Asset tracking in warehouses
• Value asset tracking in hospitals, govt. establishments etc.
• ID location of people and staff


AoD requires more complex tags than AoA from a hardware and software perspective. In this scenario the locator device can be simpler in terms of hardware design but does have software complexity for the determination and calculation of the direction finding functionality.

AoD based direction finding has some strong use cases that include smartphones and wearables. At this time smartphones do not support Bluetooth 5.1 but it is expected they will at some point.

Such scenarios might include:
• Wayfinding in large spaces such as airports, hospitals etc.
• Point of interest assistance in shopping malls, exhibitions etc.
• Search and finding of items such as keys, remote controls etc.


The nRF52811 is a Bluetooth 5.1 ready multiprotocol SoC and is suitable for use as a standalone SoC in AoA-based tags or as a companion connectivity device that adds Bluetooth direction finding capability.

nRF52 Series SoC

Recommended for Direction Finding applications

nRF52811 SoC

Baseline nRF52 Series SoC with comprehensive protocol support, including Bluetooth 5.1 Direction Finding.

64 MHz Cortex-M4
192 KB Flash, 24 KB RAM
2.4 GHz Transceiver
2 Mbps, 1 Mbps, Long Range
Bluetooth 5.1 Direction Finding
ANT, 802.15.4, Thread, Zigbee
+4 dBm TX Power
128-bit AES CCM

UART, SPI, TWI, PDM  
PWM

12-bit ADC