Low Latency Broadcast Scheduling for Battery-Free Wireless Networks Without Predetermined Structures

Broadcasting is a fundamental networking service where the source node tries to disseminate the message to the whole network. The problem of Minimum Latency Broadcast Scheduling (MLBS) which seeks a fast and collision-free broadcast schedule has been well studied when nodes are energy-abundant. However, in battery-free wireless networks, node can only receive or transmit packets after it has harvested enough energy. In such networks, it is of great importance to exploit the harvested energy smartly to reduce broadcast latency. Unfortunately, the existing works rely on predetermined structures may greatly increase the latency by choosing a node with large charging latency as the backbone node. In addition, they assume each node can only transmit once which may result in much waiting latency. To address the above issues, we investigate the MLBS problem in battery-free wireless networks without predetermined structures in this paper. Firstly, to make use of the harvested energy smartly, we intertwine the construction of broadcast tree and the computation of an energy-satisfied and collision-free schedule. Secondly, a Delayed Broadcasting technique is proposed for each node to tradeoff between the number of transmissions and its waiting latency. By considering residual energy and transmitting time, two latency and energy aware scheduling algorithms are proposed, in which the broadcast tree can be constructed adaptively according to nodes' energy status. Finally, the theoretical analysis and simulation results verify that the proposed algorithms have high performance in terms of broadcast latency.