Performing an effective media access control (MAC) protocol suffers from strong dependencies between Underwater Acoustic Networks’ upper and lower layers: 1) the network layer frequently uses geo-routing protocols, which do not provide the specific next-hop for MAC protocols, resulting in serious data collisions and 2) in such scenarios with the unknown next-hop, fixed orthogonal frequency-division multiplexing (OFDM) resource does not adapt to the changing environment, and degrades network performance (OFDM is a mature modulation technology in the physical layer). However, there is scant research on MAC protocols considering the network layer and the physical layer simultaneously, to solve data collisions and resource allocation. To this end, we present a cross-layer MAC protocol to integrate Geo-routing protocols and OFDM technology (GO-MAC) at the same time. GO-MAC employs a handshake scheme to allocate optimal communication resources and select the next-hop concurrently. First, we formulate the OFDM resource allocation as a joint optimization problem based on transmission mode, subcarrier spacing, guard interval, and transmission power, to decrease transmission delay and energy consumption. Then, a Karush–Kuhn–Tucker conditions-based Heuristic algorithm (KKT-H) is proposed to solve this problem. Finally, we consider node congestion and channel quality to assist geo-routing protocols with the next-hop selection, and decrease packet collisions. Simulation results show that our protocol matches geo-routing protocols and OFDM technology better than the state-of-the-art protocols, providing higher end-to-end reliability with lower costs.

中文翻译：

---

一种基于 OFDM 的高效地理路由感知 MAC 协议，用于水声网络

执行有效的媒体访问控制 (MAC) 协议会受到水下声学网络上层和下层之间强依赖性的影响：1) 网络层经常使用地理路由协议，这些协议不为 MAC 协议提供特定的下一跳，导致2）在这种下一跳未知的场景下，固定的正交频分复用（OFDM）资源不适应变化的环境，降低网络性能（OFDM是物理层成熟的调制技术). 然而，同时考虑网络层和物理层以解决数据冲突和资源分配的MAC协议的研究很少。为此，我们提出了一种跨层 MAC 协议，以同时集成 Geo-routing 协议和 OFDM 技术 (GO-MAC)。GO-MAC 采用握手方案来分配最佳通信资源并同时选择下一跳。首先，我们将 OFDM 资源分配制定为基于传输模式、子载波间隔、保护间隔和传输功率的联合优化问题，以减少传输延迟和能量消耗。然后，提出了一种基于 Karush–Kuhn–Tucker 条件的启发式算法 (KKT-H) 来解决该问题。最后，我们考虑节点拥塞和信道质量，以协助地理路由协议进行下一跳选择，并减少数据包冲突。仿真结果表明，我们的协议比最先进的协议更匹配地理路由协议和 OFDM 技术，