The emerging reconfigurable antenna (RA) array technology promises capacity enhancement through dynamic antenna positioning. Traditional approaches enforce half-wavelength or greater spacing among RA elements to avoid mutual coupling, limiting the solution space. Additionally, achieving sufficient spatial channel sampling requires numerous discrete RA positions (ports), while high-frequency scenarios with hybrid processing demand many physical RAs to maintain array gains. This leads to exponential growth in the solution space. In this work, we propose two techniques to address the former challenge: (1) surrounding a limited number of active RAs with passive ones terminated to tunable analog loads to \textit{exploit} mutual coupling and increase array gain, and (2) employing tunable loads on each RA in an all-active design to \textit{eliminate} mutual coupling in the analog domain. Both methods enable arbitrary RA spacing, unlocking the full solution space. Regarding the latter challenge, we develop greedy and meta-heuristic port selection algorithms, alongside low-complexity heuristic variants, that efficiently handle over $10^{20}$ array configurations. Furthermore, we optimize the loading values to maximize the sum-rate in a multiple-input single-output broadcast channel under transmission power constraints, assuming a heuristic linear precoder. In addition, we analyze performance degradation from quantized loads and propose corresponding robust designs. Numerical simulations reveal 20-56\% sum-rate gains over benchmarks and around 60\% performance recovery under quantization errors.

In this paper, we investigate a simultaneous wireless information and power transfer (SWIPT)-assisted vehicular network. By utilizing the concept of SWIPT technology, batteryoperated road-side sensors (RSSs) simultaneously receive control information and harvest energy from cellular base stations (BSs), followed by their communication with vehicles by utilizing the harvested energy. By leveraging stochastic geometry tools, we establish a tractable framework, where the load of BSs and RSSs are taken into account. The analytical expressions for the active probability and average harvested energy of RSSs, as well as the information decoding (ID) success probability of vehicles are derived. The optimal RSSs' density and time splitting factor that maximize ID success probability are illustrated. Additionally, the optimal sensor density within vehicular networks dynamically adjusts in response to varying traffic congestion levels. These results offer invaluable insights for vehicular network design, highlighting the need for adaptive strategies that seamlessly respond to evolving network conditions and traffic patterns.

The concept of fluid antennas (FAs) has emerged as a promising solution to enhance the spectral efficiency of wireless networks, achieved by introducing additional degrees of freedom, including reconfigurability and flexibility. In this paper, we investigate the use of index-modulated (IM) transmissions within the framework of FA systems, where an FA position is activated during each transmission interval. This approach is motivated by the common characteristics exhibited by FAs and IM transmissions, which entails the use of a single radio-frequency chain. From this perspective, we derive a closed-form expression for the bit error rate of IM-FAs considering spatial correlation, demonstrating superior performance compared to conventional IM systems. To enhance the performance of IM-FAs in correlated conditions, channel coding techniques are applied. We first analyze a set partition coding (SPC) scheme for IM-FAs to spatially separate the FA ports, and provide a tight performance bound over correlated channels. Furthermore, the spatial SPC scheme is extended to turbo-coded modulation where the performance is analyzed for low and high signal-to-noise ratios. Our results reveal that through the implementation of channel coding techniques designed for FAs and IM transmission, the performance of coded IM-FAs exhibits notable enhancements, particularly in high correlation scenarios.

In this paper, we present an experimental analysis of far-field wireless power transfer (WPT) using radio frequency (RF) signals. The dual capability of RF signals for power and information transfer drives the integration of WPT and communication systems. The objective is to experimentally validate different waveforms intended for WPT and compare their performance concerning separation distance, transmit power, and output voltage. The experimental analysis conducted involves single and superimposed chirp waveforms, utilizing real-time data for a comparative analysis with conventional fixed-frequency waveforms. Our experimental findings indicate that chirp waveforms significantly enhance the harvested energy, extending the operational range of WPT compared to well-established fixedfrequency waveforms.

In this paper, we investigate the use of index-modulated (IM) transmissions within the framework of fluid antenna (FA) systems, where an FA port is activated during each transmission interval. The adoption of this approach is motivated by the common physical characteristic exhibited by both FAs and IM transmissions, which entails the use of a single radio-frequency (RF) chain. From this perspective, we derive a closed-form expression for the bit error rate (BER) of IM-FA systems in the presence of spatial correlation. Our results demonstrate that IM-FAs outperform conventional IM systems. Since the FA ports are relatively close to each other, we focus on correlation mitigation techniques to improve performance. Specifically, we first investigate two port selection strategies, namely the maximum norm-based and the Euclidean distance-based selection schemes, assuming full channel knowledge. Then, we introduce the concept of spatial set partition coding for IM-FAs to spatially separate the FA ports. Numerical results demonstrate that the performance of IM-FAs is further improved in the case of high correlation whenever we apply the proposed correlation mitigation strategies.

In this paper, we present a non-coherent spatial modulation (SM) detection scheme appropriate for low-cost low-powered devices, where channel knowledge is restricted to the magnitude of the fading gains. We first derive a low-complexity energy detection metric for the multiple receive-antenna case based on the maximum-likelihood criterion. Next, we investigate a biased (non-negative) pulse amplitude modulation design and develop an accurate analytical framework for the symbol error rate at high signal-to-noise ratio. We compare the performance of the proposed scheme with that of the optimal/coherent maximum-likelihood receiver design. Numerical results show that the non-coherent SM outperforms the coherent SM technique for scenarios where non-negative one-dimensional constellations are employed.