# A Reconfigurable Formation and Disjoint Hierarchical Routing for Reshapeable Bluetooth Networks
###### Abstract
Among them, energy harvesting (EH) technology [8] is very promising, due to the unlimited energy supply provided by power sources such as solar power. Therefore, in order to efficiently forward packets and manage harvesting energy for a rechargeable Bluetooth sensor network, this study proposes a reconfigurable mesh-tree with a disjoint hierarchical routing protocol. In contrast to our prior work [9], the size of the mesh-subnet is fixed and predefined by the constant \(k\) value regardless of the network size. However, the reconfigurable mesh-tree determines the variant \(k\) instead of the constant \(k\) layer in the mesh-subnet for the various sizes of networks. In addition, the reconfigurable mesh-tree can dynamically compute the optimum layer \(k\) when the size of the network changes in the topology maintenance phase. As a result, the reconfigurable mesh-tree constructs a desired mesh-shaped topology in one densely covered area that is extended by several tree-shaped topologies to other sparsely covered areas. Thus far, most scatternet formation methods partition networks by collecting complete topology information [10; 11; 12], thereby introducing considerable computation or communication overheads. To mitigate topology formation overhead, a peak-search method is proposed with partial topology information. The peak-search method designs three blocks: the connection link, the hop length and the optimum decision blocks. The connection link block calculates the total number of links, the hop length block computes the average query hop and the optimum decision block uses a decision-making criterion to locate the desired \(k\) layer for the mesh-subnet. With the packet forwarding in the mesh-tree topology, most of the sensor traffic loads pass through the mesh-subnet to the sink node. From the energy consumption point of view, the nodes nearer the sink forward most of the packets, and deplete their batteries more rapidly than other nodes, and thus become an energy hole in a network. To balance the traffic load and mitigate the energy hole problem in the mesh-subnet, two equal disjoint paths are designed for each node forwarding packets to the sink. The design goal of the routing algorithm is to balance the energy consumption for hot-spot nodes, and to deliver packets from one subnet to all other subnets effectively. Thus, by simultaneously harvesting renewable energy, the network lifetime of the hot-spot nodes can be prolonged by the two equal paths routing design. The remainder of this paper is arranged as follows: Section 2 reviews current Bluetooth scatternet formation and routing protocols. In Section 3, the reconfigurable mesh-tree concept and the formation algorithm are presented. In Section 4, the peak-search method to achieve the desired configuration is described in detail. In Section 5, the hierarchical routing protocol for the reconfigurable mesh-tree topology is presented. In Section 6, computer simulations are used to demonstrate the scatternet, routing and energy performances. Finally, conclusions are offered in Section 7.