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Energy-Efficient Opportunistic Packet Scheduling in Mobile Relay Systems

Mobility can potentially increase communication opportunities due to the channel variation it causes. This paper studies a fundamental scheduling problem in a three-node mobile relay system in which data packets are sent from a source to a destination via a mobile relay. Our aim is to fully exploit the communication opportunities brought by relay mobility to minimize the energy consumption under a data throughput constraint. In particular, first, we apply a 2-D finite-state Markov chain (2D-FSMC) channel model to reflect both the large- and small-scale channel fading in the mobile environment. Then, the scheduling problem is formulated as a constrained Markov decision process (C-MDP) and is approximately solved through the Lagrange relaxation approach. Based on this, we proposed a probabilistic algorithm, called the opportunistic packet scheduling (OPS) algorithm, to further reduce energy consumption. The proposed OPS algorithm is proved to be optimal with polynomial complexity. Simulation results show that the proposed algorithm generally outperforms the conventional algorithms in terms of energy consumption. Furthermore, some observations are analyzed for the effect of mobility on the energy-efficient transmission.