Environment–aware LMA-based TDMA topology optimization

To address the high latency and related performance limitations of conventional Time Division Multiple Access (TDMA) protocols in underwater acoustic sensor networks, this paper proposes an integrated optimization scheme that combines environment-aware link modeling with Local Mean Algorithm (LMA)-based topology control, adopting a cross-layer collaborative optimization framework spanning physical-layer channel modeling, topology control, and MAC-layer time slot scheduling. First, a link quality distribution map is constructed based on a ray acoustic model and the physical-layer communication scheme by incorporating sound speed profiles, multipath propagation, sea surface and seabed reflections, and ambient noise, so that the spatial distribution of packet error rate accurately characterizes the differences in channel communication conditions across different spatial positions and breaks through the limitations of the traditional ideal disk model. Subsequently, LMA is introduced as the core control mechanism, in which each node adjusts its transmit power dynamically using only one-hop neighbor information: when the number of neighbor nodes exceeds the local mean, the node reduces its power to prune redundant links and lower interference, whereas otherwise it increases its power to maintain network connectivity, with convergence analysis determining the feasible range of the learning rate to ensure that the topology progressively approaches a local equilibrium. On this basis, building on the locally optimized topology obtained through LMA, a low-conflict distributed greedy time slot allocation algorithm based on neighbor count is designed, in which nodes with a higher number of neighbors are given priority in competition and select the smallest time slot number that does not conflict with their neighbors, reducing the number of time slots in the frame structure from the global node count to the local mean, thereby shortening the frame length and lowering scheduling waiting latency, while a mobility margin is reserved in the guard interval to cope with ocean current drift and enhance robustness. Simulation results show that, compared with the conventional TDMA protocol, the proposed method increases the packet delivery ratio from 28% to 70% under a low transmission interval, an improvement of approximately 42 percentage points; raises throughput from 7.3 bit/s to 18.3 bit/s, an increase of about 150.7%; and reduces end-to-end latency from 898 s to 158 s, a decrease of approximately 82.4%; meanwhile, the number of topology links is significantly reduced, effectively lowering the probability of signal collisions within the channel. These results verify that the LMA-centered integrated strategy can effectively address the spatial heterogeneity challenges of underwater acoustic channels, significantly improve the comprehensive performance of dense underwater networks in terms of transmission reliability and latency, and provide a feasible path for the design of future intelligent and highly reliable underwater acoustic network protocols.