Rotatable antennas (RAs) expand the spatial degrees of freedom of multiple-input multiple-output (MIMO) systems beyond conventional fixed-panel arrays. However, existing evaluations often model rotation merely as a scalar gain adjustment and overlook three hardware-critical effects: 1) the phase carried by the antenna pattern, 2) rotation-induced changes in the polarization, and 3) orientation-dependent mutual coupling variations. In this context, we develop a unified modeling-evaluation-optimization framework that explicitly incorporates phase, polarization, and mutual coupling effects through a rotation-explicit complex vector element pattern (CVEP). Polarization coupling and mismatch are captured by embedding the rotated CVEPs into a$2\times 2$per-ray polarization structure, while mutual coupling variation is modeled via power-consistent interpolation of embedded radiation patterns under joint orientation states. Additionally, a compact RA base-station (RA-BS) element and a$6\times 3$RA-BS prototype supporting ±60° mechanical rotation with a high front-to-back ratio are designed, assembled, and measured. The simulation and measurement results validate that the proposed electromagnetic (EM)-consistent RA system model accurately characterizes rotation-induced variations in gain, polarization, and radiation patterns. Furthermore, an alternating feasible-direction optimization algorithm, tailored to the jointly programmable BS- and subarray-level rotations, is developed to maximize the downlink sum-rate in multi-user MIMO deployments. Our simulations demonstrate that the proposed rotation-aware RA-BS architecture significantly outperforms conventional gain-only and mutual-coupling-neglected baselines. These findings highlight the necessity of incorporating phase, polarization, and mutual coupling effects into RA modeling and optimization to ensure robust performance under uniform user distributions and maximize achievable throughput in hotspot deployments.

As the backbone of the fifth-generation (5G) cellular network, massive multiple-input multiple-output (MIMO) encounters a significant challenge in practical applications: how to deploy a large number of antenna elements within limited spaces. Recently, holographic communication has emerged as a potential solution to this issue. It employs dense antenna arrays and provides a tractable model. Nevertheless, some challenges must be addressed to actualize this innovative concept. One is the mutual coupling among antenna elements within an array. When the element spacing is small, near-field coupling becomes the dominant factor that strongly restricts the array performance. Another is the polarization of electromagnetic waves. As an intrinsic property, it was not fully considered in the previous channel modeling of holographic communication. The third is the lack of real-world experiments to show the potential and possible defects of a holographic communication system. In this paper, we propose an electromagnetic channel model based on the characteristics of electromagnetic waves. This model encompasses the impact of mutual coupling in the transceiver sides and the depolarization in the propagation environment. Furthermore, by approximating an infinite array, the performance restrictions of large-scale dense antenna arrays are also studied theoretically to exploit the potential of the proposed channel. In addition, numerical simulations and a channel measurement experiment are conducted. The findings reveal that within limited spaces, the coupling effect, particularly for element spacing smaller than half of the wavelength, is the primary factor leading to the inflection point for the performance of holographic communications.

In this paper, the channel of an indoor holographic multiple-input multiple-output (MIMO) system is measured. It is demonstrated through experiments for the first time that the spatial oversampling of holographic MIMO systems is able to increase the capacity of a wireless communication system significantly. However, the antenna efficiency is the most crucial challenge preventing us from getting the capacity improvement. An extended EM-compliant channel model is also proposed for holographic MIMO systems, which is able to take the non-isotropic characteristics of the propagation environment, the antenna pattern distortion, the antenna efficiency, and the polarization characteristics into consideration.

Extremely large-scale multiple-input multiple-output (XL-MIMO) system providing more degrees of freedom and beamforming gain, can effectively increase the capacity and coverage of wireless networks, which has become one of the key technologies for 6G. However, the near-field and non-stationary effects will appear as the array aperture expands. Therefore, existing channel models such as COST 2100 are extended to model these propagation effects. Considering the actual deployment of extremely large-scale antennas, this paper further extends the COST 2100 channel, including a) extending BS VR to 3D modeling to support the non-stationary characteristics of large-scale arrays in vertical and horizontal dimensions; b) extending the distribution of MS VR in vertical height to support user equipments (UEs) which are distributed on floors at different heights; c) extending models to support spatially consistent propagation characteristics between multi-TRPs. Finally, we show that our modeling method is reasonable through parameter tuning and simulation, and it can be used to evaluate the system performance of large-scale MIMO with different deployment morphologies.

Facing the worldwide explosive growth of the wireless devices, the future wireless network is required to provide seamless access for the users with diverse Quality-of-Service (QoS) requirements. In this article, a novel multiple access scheme based on the principle of multidomain index modulation is proposed to address the downlink multiple access problem for users with diverse QoS requirements, including the Internet-of-Things (IoT) devices and the smart electronic devices. Unlike the conventional nonorthogonal multiple access (NOMA) schemes which utilize power-domain diversities to realize multiple access, in the proposed scheme, information for different users is conveyed by different domains of the transmitted signals, including the constellation domain, frequency domain, time domain, and spatial domain. As a result, the intracluster interference among users is alleviated and the successive interference cancellation is avoided to reduce the computational complexity of signal detection at the receiver side, which is well suited for the IoT devices. The closed form lower bounds and approximations of the achievable rate of the proposed scheme are further derived to provide accurate estimation of the achievable rate of the communication system. Simulation results validate the superior performance of the proposed scheme over the conventional orthogonal and NOMA schemes.

In this paper, a novel index modulation aided non-orthogonal multiple access (NOMA) scheme is proposed for visible light communication (VLC). Unlike the conventional NOMA schemes, the proposed scheme conveys information for different users through both the index-domain and constellation-domain symbols with the aid of index modulation, which is able to cancel the intra-cluster interference completely and avoid the use of successive interference cancellation to decrease computational complexity. The achievable multi-user sum rate of the proposed scheme is analyzed and a closed-form expression of the lower bound is derived. Then, an approximation is further obtained to realize accurate prediction of the achievable multi-user sum rate. Simulation results validate the accuracy of the approximation of the achievable sum rate and the superior performance of the proposed scheme.

Recently, the index modulation technique is introduced into the visible light communication (VLC) system to convey information bits in a more energy-efficient and spectral-efficient way. However, in practice, the index modulation aided VLC system should be carefully designed to be compatible with dimming control. In this paper, a novel hybrid dimming scheme is proposed for the index modulation aided VLC system, which combines the frequency-domain and time-domain dimming strategies to maximize the channel capacity and maintain the desired illumination level. Simulation results validate the superior performance of the proposed hybrid dimming scheme.

Visible light communication (VLC) is regarded as one of the promising candidate to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously. Recently, VLC is combined with generalized spatial modulation (GenSM) technology to improve spectral and energy efficiencies. In order to provide high speed communication and flexible dimming control simultaneously, in this paper, a spectral-efficient GenSM based hybrid dimming scheme, which combines the spatial-domain and time- domain dimming strategies, is proposed for VLC. The channel capacity of the proposed scheme is analyzed and a closed-form expression of the upper bound of the channel capacity is derived. According to the required illumination level, the spatial-domain and time-domain strategies are realized based on the maximization of the channel capacity. Simulation results substantiate the superior performance of the proposed dimming scheme over state-of-art dimming schemes.

Recently, mobile social networks (MSNs) has been playing an increasingly large proportion in people's daily life, and consequently attracted enormous amount of researches in this area, including network data collection, user behavior analysis and so on. Many of them are based on the community structure of the MSNs, the detection of which has attracted academic attention. In this paper, we propose an inter-community detection scheme under the framework of the emerging compressive sensing (CS) over graphs. Firstly, we extract the social structure among users by calculating the probability of two users encountering with each other. Then, the proposed scheme utilizes the encounter probability and the edge-clustering coefficient to define a novel additive property to make the CS algorithm applicable. Simulation results demonstrate that the proposed detection scheme can detect inter- community links more accurately than the conventional random walk based method.

As a cluster between Internet of Things (IoT) and mobile social networks (MSNs), social IoT allows close interaction between humans and things. Many applications of IoT and MSN are based on the community structure to realize efficient services, and thus the detection of the community structure has become a key problem and attracted much academic attention. In this paper, a compressive sensing (CS) over graphs-based intercommunity detection scheme is proposed for the social IoT. By exploiting the probability of two nodes encountering each other, the encounter probability and the edge-clustering coefficient are utilized to define a novel metric for each connection and construct the measurement matrix. Then a CS-based detection algorithm is proposed to detect the intercommunity links. Moreover, the edge-clustering coefficient is exploited as the prior information to further improve accuracy and reduce complexity. Simulations show that the proposed detection scheme outperforms the conventional random walk-based scheme in the social IoT.

In spatial modulation (SM) systems, the distribution of amplitude-phase modulation (APM) symbol causes the tradeoff of detection performance between APM symbol and active antenna, which infers the overall capacity of SM system. In this paper, the APM constellation and symbol labeling of SM system is investigated. The optimized APM constellation is designed to maximize the system coded modulation average mutual information (CM-AMI). The symbol labeling of SM system is optimized with binary switching algorithm (BSA) using the symbol detection pairwise error probability (PEP) criteria. Moreover, the proposed APM constellation and symbol labeling are applied in a coded spatial modulation (SM) system with the bit-interleaved coded modulation and iterative demapping (BICM-ID). Simulation result shows the BICM-ID SM system with proposed constellation and symbol labeling has a signal-to-noise ratio (SNR) gain compared to conventional constellation system and independent demapping system.

The non-orthogonal multiple access (NOMA) technology has been proposed and regarded as one of the potential promising technologies for the future 5G network. The extension of generalized spatial modulation multiple-input multiple-output (MIMO) to NOMA system improves both the spectral and energy efficiencies of the system, while maintaining the massive connectivity and low latency advantages, but it puts forward challenges for the multi-user and signal detection as well. In this paper, we propose a joint user activity and signal detection scheme based on the block-sparse compressive sensing (BS-CS) method in the uplink NOMA system, in which the generalized spatial modulation MIMO technology is used. By exploiting the structure and sparsity of the multi-user generalized spatial modulation signals, we formulate the detection problem into a block-sparse recovery problem. Then a BS-CS based detection algorithm, enhanced structured block-sparse compressive sampling matching pursuit (ESB-CoSaMP), is proposed to detect the active users and transmitted data efficiently. Moreover, the information of active antennas at each user is exploited in ESB-CoSaMP to further improve the accuracy. Simulations show that the proposed detection scheme outperforms the conventional CS and BS-CS based schemes.