Low-Complexity Beamforming Design for a Cooperative Reconfigurable Intelligent Surface-Aided Cell-Free Network.

Cell-free (CF) networks are proposed to suppress the interference among collocated cells by deploying several BSs without cell boundaries. Nevertheless, as installing several base stations (BSs) may require high power consumption, cooperative CF networks integrated with a reconfigurable intelligent surface (RIS)/metasurface can avoid this problem. In such cooperative RIS-aided MIMO networks, efficient beamforming schemes are essential to boost their spectral and energy efficiency. However, most of the existing available beamforming schemes to maximize spectral and energy efficiency are complex and entail high complexity due to the matrix inversions. To this end, in this work we present a computationally efficient stochastic optimization-based particle swarm optimization (PSO) algorithm to amplify the spectral efficiency of the cooperative RIS-aided CF MIMO system. In the proposed PSO algorithm, several swarms are generated, while the direction of each swarm is tuned in each iteration based on the sum-rate performance to obtain the best solution. Our simulation results show that our proposed scheme can approximate the performance of the existing solutions for both the performance metrics, i.e., spectral and energy efficiency, at a very low complexity.

Wide field-of-view optical broadcasting for bi-directional indoor optical wireless communications employing PAM-4 modulation.

We present wide field-of-view (FOV) bi-directional point-to-multipoint indoor optical wireless communications operating over a range of 4 m. The system is designed to integrate with fiber-to-the-home/building networks realized by a passive optical network. A phase-only spatial light modulator (SLM)-based beam steering base station with a ±30° FOV broadcasts downstream transmissions to two nomadic user terminals that use mirror-based beam steering to provide a ±50° FOV. At the base station, a composite phase mask is constructed on the SLM not only to perform optical broadcasting, but also to steer upstream optical transmissions from user terminals at a different wavelength. Successful upstream and downstream data transmission of 25 Gbit/s PAM4 is achieved.