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Spatial modulation (SM) and space shift keying (SSK) techniques have the unique advantages of their single-radio-frequency (RF) structures compared with conventional multiple-input-multiple-output (MIMO) techniques. However, the transmission rates of these techniques are decided by the maximal switching frequency or by the minimal switching time between the RF chain and transmit antennas, which has been a bottleneck for their applications in future broadband wireless communications. To alleviate this problem, we propose a class of novel offset SM (OSM) and offset SSK (OSSK) schemes, with the aid of channel state information (CSI) at the transmitter. Compared with conventional SM and SSK, the proposed OSM and OSSK schemes can reduce the switching frequency of the RF chain, by introducing an offset between the connected RF chain and the index of the spatial modulated antenna. In extreme conditions, the proposed OSM and OSSK can work without RF switching while maintaining the single-RF advantage of conventional SM and SSK schemes. Through theoretical analysis, we also develop the bit-error rate (BER) performance bounds for the proposed two schemes. Finally, our simulation results demonstrate that the proposed OSM and OSSK outperform their counterparts, including conventional SM, SSK, CSI-aided SM, and CSI-aided SSK, while having a simplified RF-switching structure. [ABSTRACT FROM AUTHOR]

This letter presents the measurement of photoconductive semiconductor switch (PCSS) based on semi-insulating (SI) GaAs in its linear mode, through which output voltage saturation and sublinear current–voltage characteristics were obtained. The measurements of its dark-state characteristics were also taken to explore the underlying physical mechanism. Both the resistance and free-carrier concentration of ON-state and dark-state PCSS were extracted and analyzed. Remarkable contrasts between the resistance characteristics and obvious parallels for the features of free-carrier density indicate that the sublinear current–voltage characteristics of PCSS are related to the negative differential mobility and the native defect EL2 levels of SI GaAs. The sublinear current–voltage characteristics and the saturation of output voltage exhibited in terahertz pulse generator based on GaAs PCSS are ascribed to the intrinsic characteristics of PCSS. [ABSTRACT FROM PUBLISHER]