Reducing the energy consumption of the friendship mechanism in Bluetooth mesh
Abstract This paper addresses new challenges arising from the emergence of Bluetooth mesh and its rapid adoption in Internet of Things (IoT) and Industrial IoT. One of the main problems associated with Bluetooth mesh is the power consumption of the mesh nodes, since the network needs to be scanned constantly to receive and relay messages. In order to reduce the energy consumption in the nodes where possible, the friendship mechanism is provided as a solution by the Bluetooth mesh specification. The friendship mechanism enables Low Power Nodes (LPNs) to spend most of their lifetime in sleep mode without losing the messages addressed to them. For this purpose, a node that is constantly in scan mode, called friend node (FN), stores these messages, sending them on request. This mechanism works with a stop-and-wait protocol, resulting in inefficient channel utilisation. However, to the best of our knowledge, there are no proposals for the improvement of this mechanism, likely due to its novelty. This paper studies different approaches for the improvement of the friendship mechanism: improving the Bearer Layer, improving time synchronisation and improving advertising channel utilisation. The results of this study reveal that each of the proposals presents a limitation that makes its final implementation unfeasible, and thus the challenge arises of developing a proposal for its optimisation. Accordingly, this work presents a proposal to improve the friendship mechanism with Burst Transmissions and Listen Before Transmit (BTLBT), which has been evaluated and validated in real hardware platforms. The results obtained for 4 LPNs show a reduction in the time required to receive the FN messages, as well as a 66.65% reduction in the time required to scan for each message. Finally, a consumption study is presented, where the results show that our proposal achieves a 19.81% improvement in lifetime compared to the standard friendship mechanism.