Packet Scheduling for Multihopped Underwater Acoustic Communication Networks

This paper focuses on delay-constrained energy- efficient packet transmission over a static multihop link for underwater acoustic communications, exploiting the underlying distinct channel characteristics, such as the long propagation delays, range-dependent system bandwidths, etc.. Two multihop access modes, namely, TDM and FDM, are investigated. Both modes explicitly incorporate propagation delays, and idling (waiting) periods, which are necessary for efficient channel sharing and co-channel interference avoidance. Optimal offline scheduling (vis-a-vis total transmission energy) of a set of randomly arrived and delay-constrained packets over multihopping is derived. The optimal offline schedule relies on a simple delay budget allocation, which allocates the delay budget to the first hop (from source to the first relaying node) as much as possible. All the relaying nodes simply perform buffer-clearing during any transmission opportunities. The total transmission energy and average packet delay are analyzed and characterized. Performance of energy-efficient scheduling over multihop underwater acoustic communications are further evaluated via simulations. It is demonstrated that, in addition to factors such as multihop resource orthogonalization mode, delay constraints, and SNR operating regimes, energy savings via multihopping for underwater acoustic communications are further dependent on propagation delays, idling periods, and effective transmission bandwidths.