Online lifetime-centric multicast routing for ad hoc networks with directional antennas

We consider a wireless ad hoc network where each node employs a single-beam directional antenna and is provisioned with limited energy. We are interested in an online multicast routing algorithm for successive multicast communication requests with the aim of maximizing network lifetime. The beamforming property associated with single-beam directional antenna introduces some unique problems that do not exist for omnidirectional antennas and therefore significantly increases the design space for routing algorithms. The contributions of this paper are twofold. First, we provide some important theoretical understanding on various multicast problems and deduce that even an offline version of this problem is NP-hard. Second, we develop a highly competitive online heuristic algorithm that takes network lifetime consideration directly into iterative calculations and show that an algorithm designed under this methodology provides consistently better performance than the current state-of-the-art algorithm that takes remaining energy into iterative calculations. The theoretical results and heuristic algorithm in this paper offer some important insights on algorithmic design for energy-constrained wireless ad hoc networks with directional antennas.