This paper introduces metasurface wavefront bending (MWB) to enhance spatial multiplexing in radiative nearfield multi-user multiple-input multiple-output (MU-MIMO) systems. By increasing spherical-wave curvature, MWB strengthens range-dependent phase variations across the receiver array, reduces inter-user channel correlation and improves user separability. The paper develops a curvature-dependent channel analysis, a generalized-sheet-transition-condition (GSTC) synthesisprocedure for MWB and a complete metasurface-assisted MUMIMO channel model. Both a practical common-profile scheme and an ideal user-specific benchmark are evaluated. The results demonstrate that MWB provides substantial improvements in spectral efficiency and effective channel rank. Finally, a threelayer transmissive Huygens metasurface architecture is proposed for physical implementation.
A low-overhead site-specific multi-user multiple-input multiple-output (MU-MIMO) beamforming framework is proposed. Conventional limited-feedback MU-MIMO relies on channel state information reference signal (CSI-RS) transmission and user feedback before grouping and beamforming,…
Channel reciprocity fundamentally limits full-duplex (FD) base stations due to multi-user co-channel interference. We examine the potential of deploying a non-reciprocal dynamic metasurface antenna (NR-DMA) at the base station to overcome this limitation. Our NR-DMA architecture…
This letter analyzes the performance of on-off digital noise (OODN) modulation under multi-user scenarios. While prior works have addressed single-link operation, the impact of co-channel interference remains unexplored. We consider $K$ synchronous OODN interferers over AWGN and…
In frequency-division duplexing systems, the performance gains of pinching-antenna systems (PASS) critically depend on accurate channel state information (CSI) at the base station. However, PASS CSI exhibits structured correlations over the waveguide-antenna grid and pronounced h…
Graph neural network (GNN)-based precoding has demonstrated strong potential for scalable multi-user beamforming in multi-user multiple-input single-output (MU-MISO) systems under space division multiple access (SDMA). However, direct extension to rate-splitting multiple access (…
In 6G, MIMO dimensions continue to scale, yet the increased cost, power consumption, and hardware complexity associated with growing RF chains limit practical deployment. Parasitic antennas offer a promising alternative that can add spatial degrees of freedom and array gain witho…