MUPACK—A Multiuser Packed ARQ Protocol for JANUS-Based Underwater Acoustic Networks

As the first standardized underwater acoustic communication protocol, JANUS aims to become the reference means of communication between underwater devices. Its specification focuses on the physical aspects of transmission for compatibility across multiple manufacturers and ease of implementation. Currently, JANUS does not include specification of any layers above Medium Access Control (MAC). Therefore, reliable communication in JANUS-based Underwater Acoustic Networks (UANs) can only be enabled by developing protocols, such as Automatic Repeat reQuest (ARQ), on top of the JANUS standard. This paper proposes a novel JANUS-compatible ARQ protocol featuring Multi-User Packed ACKnowledgment (MUPACK), bitfield-based selective retransmissions and header loss recovery to improve the reliability of UANs powered by JANUS.Our proposed ARQ protocol addresses the challenges of high roundtrip latency and low throughput associated with underwater acoustic communication. Through implementation and simulation, we demonstrate that the proposed ARQ scheme, combined with a Carrier Sense Multiple Access (CSMA)-based MAC protocol, vastly outperforms Stop-and-Wait (SW) and Selective Repeat (SR) ARQ in throughput and latency while maintaining compliance with the JANUS specification, thus making it wellsuited for practical deployment in UANs.