Underwater wireless sensor network (UWSN) is a typical application of wireless network in underwater environment, which mainly uses acoustic communication at present. However, due to the characteristics of high bit error rate, very limited bandwidth and high transmission delay, the data transmission collision of underwater communication is very serious. In order to reduce transmission collision and improve network performance, we propose a collision-free time slot scheduling MAC protocol based on multi-level quorum system for high loaded UWSNs. The proposed protocol can allocate different time slots for nodes in the same collision area, while realize space reuse for nodes in different collision areas. Considering the unbalanced data transmission of each node, a multi-level quorum system algorithm is constructed for fairness, which can allocate time slots on demand according to the data transmission amount of each node. In order to ensure reliable transmission of data, a light weight retransmission mechanism is designed to reduce the impact of long delay on channel duty cycle. Simulation results prove that the proposed MAC protocol can effectively avoid transmission collision, reduce transmission delay, improve system energy efficiency, and have good adaptability for different network topologies.

水下无线传感器网络（UWSN）是无线网络在水下环境中的典型应用，目前主要使用声学通信。然而，由于误码率高，带宽非常有限，传输时延高的特点，水下通信的数据传输冲突非常严重。为了减少传输冲突并提高网络性能，针对高负载的UWSN，提出了一种基于多级仲裁系统的无冲突时隙调度MAC协议。所提出的协议可以为同一碰撞区域内的节点分配不同的时隙，同时为不同碰撞区域内的节点实现空间复用。考虑到每个节点的数据传输不平衡，为公平起见，构造了一个多级仲裁系统算法，可以根据每个节点的数据传输量按需分配时隙。为了确保可靠的数据传输，设计了轻量级重传机制来减少长时间延迟对信道占空比的影响。仿真结果表明，所提出的MAC协议能够有效避免传输冲突，减少传输时延，提高系统能效，对不同的网络拓扑具有良好的适应性。