A Set of Simplified Scheduling Constraints for Underwater Acoustic MAC Scheduling

The acoustic propagation speed under water poses significant challenges to the design of underwater sensor networks and their medium access control protocols. Similar to the air, scheduling transmissions under water have significant impacts on throughput, energy consumption, and reliability. Although the conflict scenarios and required scheduling constraints for deriving a collision-free schedule have been identified in the past, applying them in a scheduling algorithm is by no means easy. In this paper, we derive a set of simplified scheduling constraints and propose two scheduling algorithms with relatively low complexity for both known and unknown orders of transmissions. Our experimental results show that scheduling without slots is on average 22% better than scheduling with slots for large packet sizes, while for small packet sizes scheduling without slots is about 40% better. We also compare our "smallest delay first" heuristic algorithm with the "highest transmission load first" heuristic of ST-MAC and show that our heuristic algorithm performs on average 13% better.