In this paper, we propose the Adaptive Power-Controlled Energy-Efficient Depth-Based Routing (APC-EEDBR) protocol. This protocol is designed to address the challenges posed by complex environments and limited resources in underwater-sensor networks. Employing a dual-weight adjustment mechanism and adaptive power control enables the protocol to achieve energy-efficient relay selection and enhance the link stability. The protocol adopts a cluster-free, hop-by-hop communication strategy and a cross-layer design to improve path stability and forwarding efficiency while mitigating hotspot issues in data aggregation areas. The simulation results demonstrate that the APC-EEDBR protocol effectively reduces energy consumption and communication overhead by approximately 16%, and significantly prolongs the network lifetime by about 39% compared with EEDBR.

In recent years, research on modulation signal recognition using deep learning (DL) has achieved significant success. However, the complex environment of underwater channels presents substantial challenges for modulation recognition. To address this issue, this paper proposes a multi-scale feature fusion hybrid model (HM) based on Gram angle field, Markov transition field, and recurrence plot (GMR). The hybrid model is used to fuse time domain and frequency domain features and integrate multi-scale features into low-dimensional features. Results from lake trials in Qiandao Lake demonstrate that the network achieves a recognition accuracy of 94.31% under real underwater acoustic channel conditions. Comparative experiments with other methods further prove the superiority of the proposed method across multiple evaluation metrics.

In underwater acoustic communication (UWA), there is a significant presence of multipath and Doppler spread. The integration of orthogonal frequency division multiplexing (OFDM) with index modulation (IM), utilizing subcarrier index modulation to enhance system performance underwater, has garnered considerable interest from researchers. Multiple mode modulation can enhance utilization by transmitting symbols of different modes on different subcarriers. Inspired by the concepts of index modulation and multiple mode modulation, this paper proposes a method that combines multiple mode indexing with the filter bank multicarrier system (MM-FBMC-IM), enabling the transmission of different modulation orders on each subcarrier to increase system flexibility. Simulations demonstrate that under the same spectral efficiency, multiple mode indexing FBMC offers superior bit error rate (BER) performance compared to conventional FBMC and index modulation FBMC.

Underwater acoustic target recognition (UATR) technology plays a significant role in marine exploration, resource development, and national defense security. To address the limitations of existing methods in computational efficiency and recognition performance, this paper proposes an improved WS-ViT model based on Vision Transformers (ViTs). By introducing the Wavelet Transform Convolution (WTConv) module and the Simplified Linear Attention (SLAttention) module, WS-ViT can effectively extract spatiotemporal complex features, enhance classification accuracy, and significantly reduce computational costs. The model is validated using the ShipsEar dataset, and the results demonstrate that WS-ViT significantly outperforms ResNet18, VGG16, and the classical ViT model in classification accuracy, with improvements of 7.3%, 4.9%, and 2.1%, respectively. Additionally, its training efficiency is improved by 28.4% compared to ViT. This study demonstrates that WS-ViT not only enhances UATR performance but also maintains computational efficiency, providing an innovative solution for efficient and accurate underwater acoustic signal processing.

Considering that multi-band interference often leads to a significant increase in the bit error rate at the system receiver end in actual underwater acoustic communication environments, this paper proposes a subcarrier silence anti-interference technology scheme based on filter bank multi-carrier (FBMC) with index modulation (IM). First, it is analyzed that, under three different underwater acoustic channels and without added interference, the underwater acoustic filter bank multi-carrier with index modulation (FBMC-IM) communication system outperforms traditional FBMC systems in terms of bit error rate performance. Subsequently, targeting the frequency distribution characteristics of multi-band interference, this paper designs an adaptive subcarrier silence mechanism. Through notch detection, interference band information is fed back to the transmitter, and subcarriers within the communication band that overlap with the interference signal spectrum are silenced, while unaffected subcarriers continue to carry communication information, thereby achieving multi-band partitioning to avoid interference effects. Additionally, to further enhance system performance, the paper integrates Virtual Time Reversal Mirror (VTRM) channel equalization technology, which leverages the time-focusing characteristics of multipath signals to effectively suppress multipath interference and delay spread in the acoustic channel. Simulation and field test results demonstrate that the proposed subcarrier-silence-based FBMC-IM anti-interference scheme significantly improves system reliability under multi-narrowband interference conditions. In the simulated underwater acoustic channel, the BER is reduced by approximately 65–80% at a signal-to-noise ratio of 0 dB; in the 5 km test channel in the Bohai Sea, the BER is reduced by 70–85% compared to the traditional FBMC system; in the test channel near Dalian with strong multipath spread, the BER is improved by more than one order of magnitude at a signal-to-noise ratio of 30 dB, with a BER reduction exceeding 90% under the configuration of Q = 4, k = 1. These results fully validate the superior anti-interference capability and communication robustness of the proposed scheme in interfering underwater acoustic environments.