Improved acoustic underwater communication with orthogonal Kasami-based sequences for multi-user communication

Wireless acoustic underwater communication systems have a limited energy resource and require an energetic consideration of all design decisions, including communication protocols. Besides reducing the power consumption is a robust detection of signals in the doubly spread channel, which varies in time and frequency, the main focus of wake-up and detection signals. Due to the challenging properties of the underwater channel, like the multipath propagation and the Doppler effects, correlation-based methods with fixed sequences only lead to the desired success under good to perfect conditions without signal-, symbol- and timing-reconstruction. This work presents a Kasami-based approach for reducing the overhead using a cross-layer adapted frame structure for the RTS/CTS hand-shaking protocol. It reduces the power consumption up to 88.3 % with an increased payload of 3.8 %, a possible collision detection till -4 dB, a supported relative speed of +/-20 m/s with a detection and decoding rate of up to 100 % using Kasami code-based sequences, related to predefined IDs and frame types for optimized cross-layer functionality of the handshake-based MAC protocol.