Collision-Free Scheduling in Multi-Hop Underwater Acoustic Networks with Local-Traffic Fairness

In this paper, we investigate collision-free transmission scheduling in data-collection-oriented underwater acoustic (UWA) networks with and without physical-layer network coding (PNC). This application-oriented network is usually deployed as a linear multi-hop topology to extend the coverage area and has a funneling effect due to the location-dependent unfairness problem. Moreover, different from terrestrial radio networks, the channel characteristics of UWA networks are featured with high propagation delay and distance-frequency-dependent attenuation. To tackle these problems, two collisionfree scheduling schemes are put forth under a linear multihop topology, which also provides local-traffic fairness among all nodes. Specifically, a successive-link-based scheduling is presented to achieve the upper bound when PNC is not available. Furthermore, PNC is introduced into the scheduling design to obtain the theoretical upper bound. Numerical simulation results indicate that successive-link-based scheduling can achieve the optimal utilization of 3/8 when PNC is not available. In contrast, PNC-aided scheduling is capable of reaching the theoretical upper bound of 1/2. Most important, the two scheduling schemes developed for linear topology are also a fundamental component that can be used in more complex network configurations.