This paper presents a novel generalized quadrature spatial modulation (GQSM) transmission scheme using antenna grouping. The proposed GQSM scheme combines QSM and conventional spatial multiplexing (SMux) techniques in order to improve the spectral efficiency (SE) of the system. Analytical and simulation results show that the proposed transmission scheme has minimal losses in terms of the average bit error probability along with the advantage of an increased SE compared with previous SM and QSM schemes. For the case studies, this advantage represents a reduction of up to 81% in terms of the number of required transmit antennas compared with QSM. In addition, a detection architecture based on the ordered successive interference cancellation scheme and the QR decomposition is presented. The proposed QRD‐M adaptive algorithm showed a near‐maximum‐likelihood performance with a complexity reduction of approximately 90%.

The prevailing approach for characterizing the Doppler shift (DS) of mobile radio channels assumes the transmission of an unmodulated carrier. This consideration is valid for the analysis of narrowband channels, but its pertinence is questionable in regards to the modeling of wideband channels. In this correspondence, we redefine the DS from a time-frequency analysis perspective that does not depend on the aforementioned assumption. We systematically demonstrate that the DS can be characterized by the instantaneous frequency of the channel transfer function. This generic definition makes evident a fundamental aspect of the DS that is seldom acknowledged, namely, the DS is a frequency-varying quantity. We show that the second-order statistics of wideband mobile radio channels are non-stationary due to the DS's frequency variations. In addition, we present numerical results of a case study showing that such non-stationarities can cause significant system performance degradations.

This paper investigates the cognitive stimulation experienced by players engaging in virtual reality (VR) puzzle games through the analysis of electroencephalography (EEG) data. The study employs magnitude-square coherence (MSC) and spectral entropy (SpEn) metrics to quantify neural activity patterns associated with problem-solving processes during gameplay. Results reveal unique coherence and entropy profiles across different VR gaming tasks, with Tetris gameplay eliciting heightened coherence and entropy values compared to other games. Specifically, Tetris demonstrates increased coherence between frontal and temporal brain regions, indicative of enhanced visuospatial processing and decision making. These findings underscore the importance of considering both spectral coherence and entropy when assessing the cognitive effects of video game tasks on brain activity. Insights from this study may inform the design of serious VR games aimed at promoting cognitive development and problem-solving skills in players.

Measurement campaigns carried out in different propagation scenarios around the world have shown that the statistical properties of vehicular multipath radio channels are strongly non-stationary. However, in spite of its practical relevance, the impact of the channel's non-stationarities on the performance of the vehicular communication systems (VCS) has barely been investigated, and is therefore not fully understood. To increase the knowledge on such important subject, we present in this paper a comparative performance analysis of six channel estimation techniques for VCS based on the IEEE 802.11p Standard, namely, the Least Squares (LS), Spectral-Temporal Averaging (STA), Modified STA (MSTA), Constructed Data Pilots (CDP), Frequency Linear-Averaged Data Pilot (FLDP), and Time-Domain Reliable Frequency-Domain Interpolation (TRFI) estimation techniques. Using a novel simulation framework, we evaluate the estimators' performance in terms of their bit error rate (BER) for the case when the propagation channel fulfills the wide-sense stationary uncorrelated scattering (WSSUS) condition, and also for the case when such condition is not met. The obtained results show that the estimation techniques that apply a joint time-frequency interpolation (STA, FLDP, and TRFI) are considerably more sensible to the channel's non-stationarities than the techniques that only interpolate in the time domain (MSTA and CDP).

In this article, a comparison of the absorption properties of 7 common agricultural waste materials from the state of Colima in Mexico is performed. The study carried out at X‐band frequencies finds that the highest absorption levels were mainly from 8 to 10.5 GHz. The experiment, based on a WR‐90 waveguide with samples inserted in holders in the middle of it, shows that papaya peel and lemon peel had the highest absorption levels in the aforementioned frequency range. This study is relevant because of the vast amount of agricultural waste generated in such state of Mexico, that can be used as absorbers in the microwave regime, and not managed as garbage. In this work, the feasibility of using these eco‐friendly and nontoxic materials as microwave absorbers instead of typical commercial synthetic materials is evaluated.