Software-defined acoustic underwater mesh networks

Abstract

While terrestrial IoTs have been extensively explored, both academically and commercially, IoUTs have had significantly fewer developments. The underwater channel presents unique challenges which cause commonly utilized communication methodologies in the RF domain to become nonviable. This thesis presents an underwater mesh network designed to address the challenges faced in the network, data link, and physical layers of the underwater acoustic domain. This underwater mesh network implements a proactive routing protocol for maintaining routing topology, allowing for Dijkstra's algorithm to be utilized as an efficient method of determining the next hop for a data packet. Endpoints across an on-board Ethernet socket will be capable of joining the mesh network, allowing for cross-medium data forwarding. A CRC-32 was implemented as the primary methodology for error detection. Two MAC schemes were implemented for this underwater mesh network: a Pure ALOHA scheme and a repetitive burst retransmission scheme. The routing table discovery process and the implemented MAC schemes were evaluated through testing with hardware in a real-world oceanic environment (located in the Boston harbor). Utilizing a ZP-OFDM communication scheme, the underwater mesh network's discovery process was able to establish topological consensus on the state of the routing table quickly and accurately in this real-world setting. The repetitive retransmission scheme greatly outperformed the Pure ALOHA scheme due to the greater number of collisions (from acknowledgement packets in the shared channel) in the Pure ALOHA scheme. Through real-world testing, the protocols and systems implemented within this underwater mesh networks were shown to be highly successful at establishing and maintaining a network at varying levels of data traffic.