Fluid antenna system (FAS) technology can further improve the performance by changing the antenna position and shape over a given space dynamically. In this paper, a FAS-assisted orbital angular momentum (FAS-OAM) communication system is proposed, in which the base station (BS) transmits OAM signals with multiple modes to a receiver equipped with fluid antennas. In order to analyze the performance of the proposed system accurately, the block-correlation model is employed to construct the channel correlation of FAS with low complexity. Then, the outage probability and ergodic capacity are derived based on the assumption of the non-central chi-square distribution, and the Gauss-Laguerre quadrature method is adopted to obtain closed-form results. Simulation results show that the derived theoretical approximate and closed-form results of outage probability and ergodic capacity are consistent with corresponding simulation results. Compared with the conventional OAM and MIMO systems, the proposed FAS-OAM system exhibits significant performance advantages in terms of outage probability and ergodic capacity, and confirms the effectiveness of FAS-OAM over fading channels.

Orbital angular momentum (OAM) technology can provide an additional degree of freedom in the spatial domain and solve the problem of spectrum shortage in the sixth generation (6G) networks. In this paper, a near-field OAM channel model based on the electromagnetic information (EMI) theory is proposed, in which the dyadic Green’s function approach and discrete Fourier basis functions are utilized to accurately describe the characteristics of near-field channel and OAM signal propagation in practical scenarios, respectively. To improve the performance of misaligned transmission, a near-field OAM misalignment precoding scheme is presented according to the characteristics of the proposed channel model. Specifically, phase errors are compensated and the optimal power is assigned according to the channel condition, which can mitigate the channel capacity loss caused by the the inter-mode interference resulting from the misalignment. Numerical results show that the benefit brought by the polarization along the propagation direction is predominantly significant at short distances, and decreases rapidly to zero as the distance increases. Results also show that the presented scheme outperforms the conventional fixed parameter scheme and effectively reduces the effects of the misalignment in practical scenarios.

The ocean contains vast resources such as biological, mineral, and strategic resources for national defense. Developing underwater wireless sensor networks (UWSNs) to achieve collaborative data collection and transmission is essential for marine exploration activities. The Internet of Things (IoT), enabling real-time data transmission, holds immense potential in its application to UWSNs, known as the underwater Internet of Things (UIoT). Underwater vehicles (UVs), as mobile nodes in UIoT, play an irreplaceable role in enabling dynamic network topology and overcoming static node coverage limitations. However, in the face of massive data generated by UIoT devices, seeking an efficient communication method has become increasingly important. Underwater wireless optical communication (UWOC) technology has attracted extensive attention in underwater communication due to its high-speed data transmission capability and superior transmission capacity. Nevertheless, existing UWOC systems ignore the semantic information of transmitted data, leading to unnecessary communication resource overhead. Furthermore, the spatiotemporally dynamic marine environment presents significant challenges to UWOC technology. This paper integrates semantic communication into the challenging scenario of underwater wireless optical image transmission to further optimize the bandwidth compression efficiency and anti-interference capability of underwater optical wireless communication. In the experimental verification section, the results demonstrate that the communication scheme proposed in this paper can achieve excellent image transmission performance in variable seawater channels, outperforming the traditional source-channel separation communication paradigm in terms of image transmission performance and exhibiting certain robustness.