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Recently, reconfigurable intelligent surface (RIS), which operates with the aim to manipulate multi-path signals, has been widely considered for wireless communications. In this letter, we extend the employment of RIS to indoor positioning, with the aid of ultra-wideband (UWB) technique. Moreover, the Cramér-Rao lower bound of the developed positioning scheme is quantified. Both theoretical analysis and simulation results demonstrate that RIS has the potential to realize accurate positioning with a single access point, due to its ability to mark the channel and replace traditional active positioning anchors. Moreover, it is also depicted that when the number of receive antennas is limited, time-of-arrival based positioning has a higher accuracy than that based on angle-of-arrival, due to the high multipath resolution of UWB signals. [ABSTRACT FROM AUTHOR]

In this letter, the idea of transmit antenna selection is combined with the offset spatial modulation (OSM) technique. Specifically, two novel transmit antenna selection schemes, termed as antenna selection based on grouped Euclidean distance (AS-GED) and channel coefficient (AS-CC), are developed toward a flexible tradeoff between system performance and computational complexity. Simulation results show that the proposed antenna selection schemes achieve significant performance improvement compared to traditional OSM systems. [ABSTRACT FROM AUTHOR]

To support interference-free quasi-synchronous code-division multiple-access (QS-CDMA) communication with low spectral density profile in a cognitive radio (CR) network, it is desirable to design a set of CDMA spreading sequences with zero-correlation zone (ZCZ) property. However, traditional ZCZ sequences (which assume the availability of the entire spectral band) cannot be used because their orthogonality will be destroyed by the spectrum hole constraint in a CR channel. To date, analytical construction of ZCZ CR sequences remains open. Taking advantage of the Kronecker sequence property, a novel family of sequences (called "quasi-ZCZ" CR sequences) which displays zero cross-correlation and near-zero auto-correlation zone property under arbitrary spectrum hole constraint is presented in this paper. Furthermore, a novel algorithm is proposed to jointly optimize the peak-to-average power ratio (PAPR) and the periodic auto-correlations of the proposed quasi-ZCZ CR sequences. Simulations show that they give rise to single-user bit-error-rate performance in CR-CDMA systems which outperform traditional non-contiguous multicarrier CDMA and transform domain communication systems; they also lead to CR-CDMA systems which are more resilient than non-contiguous OFDM systems to spectrum sensing mismatch, due to the wideband spreading. [ABSTRACT FROM AUTHOR]