Improvements to bluetooth low energy and bluetooth mesh towards the new generation of iot-based heterogeneous networks
Hortelano Haro, Diego
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In recent years, the term Internet of Things (IoT) has been gaining momentum, moving from traditional sensor networks in home automation to large networks in different areas, such as smart buildings, smart cities or smart factories. The last of these is having a great impact, with different initiatives arising to facilitate its adaptation, in what is already known as Industry 4.0. The applications of these new trends bring with them new requirements that are challenging the current wireless communication networks. These requirements include transmission reliability (zero fails), total area coverage and sustainability, both in terms of network effciency and network cost. In this context, Bluetooth Low Energy (BLE) technology was developed, maintaining the classic Bluetooth objective of facilitating the connection between devices, but with a minimum power consumption. We opted for research into this particular technology because of the ease with which users can be included in the network, through their smartphone or wearable device, while providing low consumption, ideal for sensor devices. However, after an initial evaluation, we found that the topologies included in the specification did not fulfil the requirements demanded by the latest trends in IoT and Industry 4.0. In order to use BLE technology in these new networks, we proposed a standard compliant mesh network using the broadcast capability of the devices. This network was deployed in a real environment, enabling communication between a wide range of devices, including sensor nodes, tablets, wearable devices and a BLE server. The evaluation carried out showed an excellent percentage of transmissions successfully completed, as well as total coverage of the area. Due to the rising number of applications demanding a new topology and the large number of proposals from both academia and companies, the Bluetooth Special Interest Group (Bluetooth SIG) released a suite of specifications to include mesh topology in BLE. This specification is called Bluetooth mesh, and is built over the lower layers of BLE (the Link Layer and the Physical Layer). Bluetooth mesh uses a controlled flood routing through the broadcast capabilities of the BLE devices. The provisioning procedure stands out in the specification. This procedure enables the devices to receive the network key and other information required to take part in the network in a secure manner. Following its release, we decided to focus on the Bluetooth mesh specification, as well as on the devices which used the early versions of BLE. The Bluetooth SIG advanced that any BLE device capable of sending broadcast messages could be part of a Bluetooth mesh network. However, there were no studies on this, and the available implementations were built on the lower layers of the latest versions of BLE. Therefore, and in order to verify this compatibility, this Doctoral Thesis also includes our implementation of Bluetooth mesh, as well as the provisioning procedure, which is supported by many devices. The evaluation carried out with devices with the first versions of BLE showed their compatibility, although these early versions had more limitations than the later versions. Moreover, after the evaluation of the standard provisioning procedure, a lighter alternative is proposed, specially designed for use on devices with the earlier versions of BLE. Finally, focusing on the Bluetooth mesh specification, it is remarkable for its great power consumption, since the devices need to constantly scan the network to receive the messages, which can be sent at any time. To address this problem, and to enable battery-powered devices to take part in the network, the Bluetooth mesh specification proposes a mechanism called friendship. Thus, one of the devices, called friend node, is constantly scanning the network, receiving and storing the messages sent to the low power node. These messages are sent to the low power node on demand, allowing it to scan the network only at short intervals. However, this friendship mechanism uses data transmissions similar to the stop-and-wait protocol, which is highly inefficient. For this reason, Burst Transmissions and Listen Before Transmit (BTLBT) technique was proposed, which minimises the consumption of these nodes.