CTSMA: Cyclic Time Shift Multiple Access for Underwater Acoustic Networks

Reliable and efficient underwater communication techniques are crucial and urgently needed in the underwater Internet of Things (UW IoT), and it is challenging due to the harsh conditions of the underwater channel. Furthermore, an effective and underwater acoustic-specific Medium Access Control (MAC) layer protocol is necessary for a multi-user network, such as Wireless Sensor Networks (WSN) or fleet of Autonomous Underwater Vehicles (AUVs). To address these challenges, a novel cross-layer scheme has been proposed that integrates the physical layer and the MAC layer, termed Cyclic Time Shift Multiple Access (CTSMA). CTSMA enables multiple users to transmit and receive different data streams within the same network, by using specialized Zero-Correlation-Zone (ZCZ) sequence division. The performance of this framework has been investigated and validated through both emulations and tank experiments with our custom-made underwater IoT devices. The results demonstrate that CTSMA offers superior transmission accuracy than chaotic code-based Code Division Multiple Access (CDMA) under the same coding rate condition.