This letter investigates the impact of multiple shadows for indoor visible light communication (VLC) systems composed of a VLC access point and multiple terminals. The blockage is a crucial problem in the VLC system, which would result in great deterioration of users’ communication quality due to the shadow area caused by the blockage. Considering the room boundaries and overlap between shadows, we derive the mathematical expressions of the shadow area and position. In the simulation part, the effect of multiple shadows on throughput and outage performance is appraised. Furthermore, we also take the effect of the room size into account.

Natural disasters have challenged the survivability of Elastic Optical Inter-DataCenter Networks (EO-DCNs), and it is urgent to establish efficient disaster protection schemes. In this paper, we investigate the disaster-resilient service provisioning problem leveraging cooperative storage system (CSS). Instead of mirrored content backup on a single DC, our proposed CSS partitions a required content into no less than three fragments if possible, each of which is then stored on a DC located in different disaster zones. Accordingly, multi-path routing with the adaptive number of working paths to distinct DCs is employed to serve each request, while a protection path is computed to protect against a disaster failure. Our main objective is to jointly minimize the spectrum usage and maximal occupied frequency slot index (MOFI) subject to disaster resilience. Besides, we also expect to cut the content storage space. To this end, we propose for the first time a CSS-based dedicated end-to-content path protection (CDP), which allows service provisioning through multiple paths with the adaptive number of paths rather than a single path. This consequently reduces at least half of the reserved spectrum on the protection path. To find the optimal CDP strategy, we formulate the studied problem as an integer linear program (ILP) and then propose a fast heuristic algorithm. Observing the trade-off between the spectrum usage and content storage space, we further design a maximum-CDP (M-CDP), which generates the maximum number of working paths to reduce the content storage space. Simulations are conducted to compare the proposed schemes with the traditional protection strategy using mirrored storage and single-path routing. Numerical results demonstrate that the proposed CSS-based protection schemes enable to cut up to 21.6% of the spectrum usage and 15% of the content storage space.

Recently, visible light communication (VLC) based on LEDs has attracted much attention. In order to realize multiusers indoor VLC systems, a reasonable channel model considering random shadowing, which is first proposed to the best of our knowledge, is significant. Taking the nonquantitative obstructions with random movement into account, by introducing the Poisson process and the probability density function, we propose a weighting function and set up a channel model. The expressions of the received optical power, the horizontal illuminance and the impulse responses are given. The verification of the model's feasibility is presented through simulation. Moreover, based on the proposed channel model, the simulation analysis of the effect of random shadowing on communication performance is conducted, and the corresponding simulation optimization is also made.

Automatic modulation classification (AMC) plays an important role in intelligent wireless communications. With the rapid development of deep learning in recent years, neural network-based automatic modulation classification methods have become increasingly mature. However, the high complexity and large number of parameters of neural networks make them difficult to deploy in scenarios and receiver devices with strict requirements for low latency and storage. Therefore, this paper proposes a lightweight neural network-based AMC framework. To improve classification performance, the framework combines complex convolution with residual networks. To achieve a lightweight design, depthwise separable convolution is used. To compensate for any performance loss resulting from a lightweight design, a hybrid data augmentation scheme is proposed. The simulation results demonstrate that the lightweight AMC framework reduces the number of parameters by approximately 83.34% and the FLOPs by approximately 83.77%, without a degradation in performance.

In this letter, we propose a novel adaptive multi-user association strategy for non-orthogonal multiple access (NOMA) in visible light communication (VLC) systems, by which a number of user association (UA) schemes are obtained, in order to improve the multi-user system performance. Moreover, two new concepts called the redundant user and the multi-user association matrix are proposed to indicate UA status and data rates. The system throughput of the proposed strategy is evaluated and compared with the traditional NOMA without UA and NOMA-based pairwise coupling schemes, while the effect of the residual interference is also investigated.