A Spatial TDMA-Based Medium Access Control Protocol for Underwater Acoustic Backscatter Networks

Underwater acoustic backscatter networks (UABN) constitute a promising communication paradigm, where battery-free nodes transmit data by modulating and reflecting a fraction of an incident carrier signal from an acoustic source, removing the network lifetime constraint due to depletion of batteries. Recently, solutions have been proposed for the deployment, coverage and link modeling problems in UABN. However, efficient data collection from the sensing region to multiple receivers further requires medium access control (MAC) among nodes. In this paper, a centralized MAC protocol, called UABN-MAC, is proposed for low-latency and reliable data collection in multistatic UABN. UABN-MAC incorporates source-controlled TDMA and does not require time synchronization among nodes. In order to resolve contention among nodes, the source collects information about total propagation delays between itself and the receivers over all nodes. The delay information is gathered through source transmissions and receiver acknowledgment messages. The source uses the collected network information to group nodes into backscatter clusters for sensor data collection at the receivers. Performance evaluations show that UABN-MAC achieves feasible and scalable UABN operation in terms of slot duration, frame length, delay reduction, channel utilization, throughput, and packet delivery ratio. The analysis results also reveal that the protocol is robust against synchronization errors among the source and receivers.