An MC-CDMA-Based MAC Protocol for Efficient Concurrent Communication in Mobile Underwater Acoustic Networks

Mobile Underwater Acoustic Networks (UANs) leverage Autonomous Underwater Vehicles (AUVs) to enhance flexibility and mobility, playing an essential role in ocean research. Similar to static UANs, the Medium Access Control (MAC) protocol is still critical for mobile UANs to achieve efficient communication. However, mobile UANs are delay-sensitive and suffer from low Signal-to-Noise Ratio (SNR), which presents significant challenges for the design of MAC protocols. As a hybrid technology combining spread spectrum and multi-carrier modulation, Multi-Carrier Code Division Multiple Access (MC-CDMA) offers simple multi-path channel equalization and flexible multi-user access, aiding the MAC protocol in achieving robust communication in mobile UANs. Along this line, we propose an MC-CDMA-based MAC (MC-MAC) protocol, which considers both characteristics of mobile UANs and MC-CDMA to achieve efficient concurrent communication. Specifically, to adequately utilize the limited underwater communication resources, we design an adaptive node clustering algorithm, classifying nodes based on propagation distance, relative mobile velocity, data size, and data grade. Meanwhile, the algorithm determines non-random initial center nodes and adaptively decides the optimal number of clusters to decrease the computational complexity. Based on the clustering results, we present a many-objective optimization algorithm, which jointly allocates specific spreading code length, spreading code number, subcarrier range, and transmission power to optimize throughput, delay, and energy consumption in mobile UANs. Extensive simulation results demonstrate that MC-MAC fully leverages the advantages of MC-CDMA, providing efficient concurrent communication with lower energy consumption for mobile UANs compared to state-of-the-art protocols.