In this work, a multi-ring tree algorithm is proposed for Bluetooth low-energy networks with non-uniform distribution of devices. In a dense area, a leader root is elected during the leader election phase and a min-path algorithm is introduced to determine the optimal number of rings for various numbers of discoverable roots. According to the optimal configuration, the leader root connects to its one-hop neighboring roots to form the first-tier ring; each new root connects with one downstream

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... ot, and these roots connect together to form the second-tier ring until the desired outermost ring is reached. In sparse areas, each root constructs its own spanning tree subnet, finally creating a multi-ring tree scatternet. To achieve the least route discovery overhead, a multi-hop self-routing protocol is developed to efficiently deliver packets. Computer simulations show that the optimal multi-ring subnet can be determined; the optimal multi-ring tree outperforms conventional dual ring-tree (DRT) and Bluetooth hybrid ring-tree (BlueHRT) in terms of network performance.