being determined transmits the signal using multiple antennas in an array and the receiving device has a single antenna. The receiving device uses multiple signals to determine the IQ data and estimate its position. AoA is often used for tracking the position of assets, while AoD is the preferred technique to enable robots to determine where they are in a facility with good accuracy and low latency. The basic concept for AoA-based RTLS tracking is straightforward: Θ = arccos x ((phase difference x wavelength) / (2 π x distance between the antennas)) (Figure 2). Real-world implementations are more complicated and need to account for signal propagation delays caused by environmental variables, multipath signals, varying signal polarization, and other factors. In addition, when antennas are used in an array, they can experience mutual coupling and affect each other’s responses. Finally, it can be quite challenging to develop the algorithms needed to take all of these variables into account and efficiently implement them in a time-critical solution in a resource-constrained embedded environment. Fortunately for developers, complete Bluetooth AoA and AoD solutions include IQ data collection and preprocessing, multipath components suppression, compensation for environmental factors, and mutual coupling between antennas.
Figure 1: Antenna arrays form the basis for Bluetooth AoA and AoD RTLS implementations. Image source: Silicon Labs
radio core with low active and sleep currents and an integrated power amplifier with up to 6-decibel meters (dBm) transmit (TX) power in a 4 × 4 × 0.85 millimeter (mm) QFN32 package (Figure 3). They include secure boot with root of trust and secure loader (RTSL). Additional security features include hardware cryptographic acceleration for AES128/256, SHA- 1, SHA-2 (up to 256-bit), ECC (up to 256-bit), ECDSA, and ECDH, and a true random number generator
SoCs for Bluetooth AoA and AoD
Developers can turn to SoCs such as the
EFR32BG22C222F352GN32-C from Silicon Labs to implement Bluetooth 5.2 networking and AoA and AoD. This SoC is part of the EFR32BG22 Wireless Gecko family that includes a 32-bit Arm Cortex-M33 core with 76.8 MHz maximum operating frequency plus a 2.4 GHz energy-efficient
Figure 2: The equation for determining the AoA (top right) uses the phase difference of the arriving signals, the signal wavelength, and the distance between adjacent antennas. Image source: u-blox
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