This paper investigates the use of a reconfigurable intelligent surface (RIS) to aid point-to-point multi-data-stream multiple-input multiple-output (MIMO) wireless communications. With practical finite alphabet input, the reflecting elements at the RIS and the precoder at the transmitter are alternatively optimized to minimize the symbol error rate (MSER). In the reflecting optimization with a fixed precoder, two reflecting design methods are developed, referred as eMSER-Reflecting and vMSER-Reflecting. In the optimization of the precoding matrix with a fixed reflecting pattern, the matrix optimization is transformed to be a vector optimization problem and two methods are proposed to solve it, which are referred as MSER-Precoding and MMED-Precoding. The superiority of the proposed designs is investigated by simulations. Simulation results demonstrate that the proposed reflecting and precoding designs can offer a lower SER than existing designs with the assumption of complex Gaussian input.Moreover, we compare RIS with a full-duplex Amplify-and-Forward (AF) relay system in terms of SER to show the advantage of RIS.

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Recently, a camera or an image sensor receiver based optical wireless communications (OWC) techniques have attracted particular interest in areas such as the internet of things, indoor localization, motion capture, and intelligent transportation systems. As a supplementary technique of high-speed OWC based on photo-detectors, communications hinging on image sensors as receivers do not need much modification to the current infrastructure, such that the implementation complexity and cost are quite low. Therefore, in this paper, we present a comprehensive survey of optical camera communication (OCC) techniques, and their use in localization, navigation, and motion capture. This survey is distinguishable from the existing reviews on this topic by covering multiple aspects of OCC and its various applications. The first part of the paper focuses on the standardization, channel characterization, modulation, coding, synchronization, and signal processing techniques for OCC systems while the second part of the article presents the literature on OCC based localization, navigation, motion capture, and intelligent transportation systems. Finally, in the last part of the paper, we present the challenges and future research directions of OCC.(OCC) [5]. FSO communication systems consist of a laser diode (LD) transmitter and a photodiode (PD) receiver. It typically relies on UV or visible bands, offers high rate transmission in a long distance, and can be used for a backhaul of communication networks. However, FSO communications need a strict alignment, and consequently, their cost at transceivers is high. Also, FSO communication systems suffer from atmospheric turbulence which can be mitigated by using different statistical channel models [6,7,8,9,10], robust modulation techniques [11,12], and accurate pointing and tracking methods [13,14,15]. On the other hand, VLC hinging on visible bands is an LD or light emitting diode (LED) transmitter and PD receiver-based medium-range communication technology. VLC is capable of offering high data rate within a range of tens of meters but does not consider multiple user access. The advancement of VLC systems has also led to enable various location aware indoor applications. Recently, several indoor localization systems based on VLC are proposed [16,17,18,19,20]. Interested readers are referred to [21,22], and the references therein for VLC based indoor localization and tracking methods. Nevertheless, the VLC technology suffers from both limited coverage and interference. Increasing the field of view of the LEDs improves the coverage; however, it increases the interference at the receiver. Signal-to-interference ratio based methods can be used to analyze the coverage and interference problems in VLC systems [23]. Different from VLC, Li-Fi is an LED transmitter based light networking technology that involves multiple user access, bidirectional communications, multi-cell handover, etc. The emerging Li-Fi supports mobile communica-

This paper investigates generic signal shaping methods for multiple-data-stream generalized spatial modulation (GenSM) and generalized quadrature spatial modulation (Gen-QSM) based on the maximizing the minimum Euclidean distance (MMED) criterion. Three cases with different channel state information at the transmitter (CSIT) are considered, including no CSIT, statistical CSIT and perfect CSIT. A unified optimization problem is formulated to find the optimal transmit vector set under size, power and sparsity constraints. We propose an optimization-based signal shaping (OBSS) approach by solving the formulated problem directly and a codebook-based signal shaping (CBSS) approach by finding sub-optimal solutions in discrete space. In the OBSS approach, we reformulate the original problem to optimize the signal constellations used for each transmit antenna combination (TAC). Both the size and entry of all signal constellations are optimized. Specifically, we suggest the use of a recursive design for size optimization. The entry optimization is formulated as a non-convex large-scale quadratically constrained quadratic programming (QCQP) problem and can be solved by existing optimization techniques with rather high complexity. To reduce the complexity, we propose the CBSS approach using a codebook generated by quadrature amplitude modulation (QAM) symbols and a low-complexity selection algorithm to choose the optimal transmit vector set. Simulation results show that the OBSS approach exhibits the optimal performance in comparison with existing benchmarks. However, the OBSS approach is impractical for large-size signal shaping and adaptive signal shaping with instantaneous CSIT due to the demand of high computational complexity. As a lowcomplexity approach, CBSS shows comparable performance and can be easily implemented in large-size systems.

This letter proposes a jointly mapped spatial modulation (JM-SM) scheme to break through the constraint on the number of transmit antennas in traditional SM systems. It is realized via jointly mapping the transmit information bits to 3-D constellation points. A 3-D constellation design scheme for JM-SM is analyzed and established by minimizing the system average bit error probability (ABEP). In addition, the extension of the joint 3-D mapping to GSM is discussed. Simulation results show that the proposed schemes can be adopted to MIMO systems with arbitrary number of transmit antennas and offer better ABEP performance than those existing schemes.

Media-Based Modulation (MBM) is regarded as a promising technique for future massive machine-type communications (mMTC) due to its high energy/spectral efficiency, good error performance and low-complexity radio frequency hardware implementation. In this paper, we consider both sparsity nature of user activity and sparsity nature of MBM signals in the uplink MBM-enabled mMTC system. According to the static user activation or the dynamic user activation in a coherent time, we classify the transmission schemes into two types and propose corresponding improved compressive sensing (CS)-based joint user identification and data detection with/without prior information of channel state information (CSI). The simulation results demonstrate the performance advantages of our proposed algorithms over the state-of-the-art CS-based user detection methods or CS-based symbol detection methods and evaluate the performance with different system parameters. INDEX TERMS Massive machine-type communications (mMTC), media-based modulation (MBM), compressive sensing.

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