###### Abstract  
This paper addresses the challenge of implementing Direction of Arrival (DOA) methods for indoor localization using Internet of Things (IoT) devices, particularly with the recent direction-finding capability of Bluetooth. DOA methods are complex numerical methods that require significant computational resources and can quickly deplete the batteries of small embedded systems typically found in IoT networks. To address this challenge, the paper presents a novel Unitary R-D Root MUSIC for L-shaped arrays that is tailor-made for such devices utilizing a switching protocol defined by Bluetooth. The solution exploits the radio communication system design to speed up execution, and its root-finding method circumvents complex arithmetic despite being used for complex polynomials. The paper carries out experiments on energy consumption, memory footprint, accuracy, and execution time in a commercial constrained embedded IoT device series without operating systems and software layers to prove the viability of the implemented solution. The results demonstrate that the solution achieves good accuracy and attains an execution time of a few milliseconds, making it a viable solution for DOA implementation in IoT devices. Direction of Arrival (DOA); Multiple Signal Classification (MUSIC); Internet of Things (IoT); embedded systems; array signal processing 202323356. [[https://doi.org/10.3390/s23063356](https://doi.org/10.3390/s23063356)]([https://doi.org/10.3390/s23063356](https://doi.org/10.3390/s23063356))  
Footnote †: This paper is an extended version of our paper published in [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON] Implementation of Embedded Multiple Signal Classification 672 Algorithm for Mesh IoT Networks. In Proceedings of the 2022 International Conference on Localization and GNSS (ICL-GNSS), Tampere, Finland, 7-9 June 2022, pp. 1-7. Footnote †: This paper is an extended version of our paper published in [PERSON], [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON] Implementation of Embedded Multiple Signal Classification 672 Algorithm for Mesh IoT Networks. In Proceedings of the 2022 International Conference on Localization and GNSS (ICL-GNSS), Tampere, Finland, 7-9 June 2022, pp. 1-7. Footnote †: This paper is an extended version of our paper published in Torocoli, [PERSON], [PERSON]; [PERSON] [PERSON]; [PERSON], [PERSON], [PERSON]. Most recently, Bluetooth has released a new capability that makes it possible to estimate DOAs [4], unlocking high accuracy as DOA-based positioning is reported to attain sub-meter-level position accuracy [3; 5; 6; 7]. In the direction of arrival version of that new capability, receivers have an array of antennas to make it possible to estimate the azimuth and elevation angles coming from a signal emitted from a BLE tag. By applying, for example, the triangulation method, which employs the cited angles for each receiver and their positions, it is possible to estimate the location of BLE tags. Besides using for DOA estimation, BLE is broadly used for wireless communication of the Internet of Things (IoT). In the IoT terminology, its networks are composed of many nodes that are small battery-powered resource-constrained embedded systems. Particularly, in IoT networks that deploy DOA-based positioning systems, some nodes, called anchor nodes, have an array of antennas that execute DOA methods to estimate the azimuth and elevation of RF signals emitted from BLE tags which are also nodes. Figure 1 depicts an IoT mesh network with the cited positioning systems. In IoT networks, it is important to note that nodes are often constrained embedded systems. These systems typically consist of three distinct subsystems [8], as illustrated in Figure 2. The microcontroller or computing subsystem is responsible for controlling the node's functionalities, and runs instructions on a low-power processor that commonly operates at a few megahertz. It also has flash memory and RAM whose sizes are in order of kilobytes.