A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> A novel multiple-input multiple-output (MIMO) transmission scheme, called space-time block coded spatial modulation (STBC-SM), is proposed. It combines spatial modulation (SM) and space-time block coding (STBC) to take advantage of the benefits of both while avoiding their drawbacks. In the STBC-SM scheme, the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain which corresponds to the on/off status of the transmit antennas available at the space domain, and therefore both core STBC and antenna indices carry information. A general technique is presented for the design of the STBC-SM scheme for any number of transmit antennas. Besides the high spectral efficiency advantage provided by the antenna domain, the proposed scheme is also optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme which profits from the orthogonality of the core STBC. The performance advantages of the STBC-SM over simple SM and over V-BLAST are shown by simulation results for various spectral efficiencies and are supported by the derivation of a closed form expression for the union bound on the bit error probability. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> A key challenge of future mobile communication research is to strike an attractive compromise between wire- less network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, espe- cially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless commu- nications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communica- tions, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Further- more, it has received sufficient research attention to be im- plemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> This paper proposes a multiple-input multiple-output (MIMO) transmission scheme for M-ary modulations, called Spatially Modulated Orthogonal Space-Time Block Coding (SM-OSTBC), based on the concept of Spatial Constellation (SC) codewords introduced by Le at el. . In the proposed scheme, transmit codeword matrices are generated by multiplying SC matrices with codewords constructed from Orthogonal Space-time Block Codes (O-STBC). The maximum spectral efficiency of the proposed scheme is equal to (n_T-2+ log_2 M) bpcu, where n_T is the number of transmit antennas and M is the modulation order. The SC matrices provide a means of carrying information bits together with the O-STBC codewords and allow the SM-OSTBC scheme to achieve second-order transmit diversity by satisfying the non-vanishing determinant property. A systematic method to design the SC codewords for an even number of transmit antennas greater than 3 is presented. A single-stream maximum-likelihood (ML) decoder, which requires a low computational complexity thanks to the structure of the SM-OSTBC codewords and to the orthogonality of the O-STBCs, and a sphere decoder with further reduced signal processing complexity are developed. The bit error rate (BER) performance of the proposed scheme is studied by using both theoretical union bound analysis and computer simulations. Finally, simulation results are presented in order to compare BER performance, energy efficiency and decoding complexity of the proposed scheme with those of several existing MIMO transmission schemes. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> A high rate space-time block coded spatial modulation scheme with cyclic structure (STBC-CSM) is presented in this letter. In the proposed STBC-CSM scheme, a pair of transmit antennas are chosen out of the total transmit antennas to send Alamouti's STBC, whose two signal symbols are drawn from two different constellations, and the antenna pairs activated in different codewords are moving cyclically along the total transmit antenna array. To exploit the diversity advantage of Alamouti's STBC, the optimization of STBC-CSM is given by maximizing its coding gain. Moreover, the proposed scheme allows for a low-complexity maximum-likelihood (ML) detector due to the orthogonality of Alamouti's STBC. The simulation results verify our theoretical analysis and demonstrate the performance advantages of our proposed STBC-CSM over the existing schemes such as STBC-SM, H-STBC-SM, CIOD-SM-H and SM. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> A spatial modulation (SM) scheme based on multi-strata space-time coding (MSSTC), called MSSTC-SM, is proposed. We allow two layers of MSSTC to be assigned unequal transmit power and phase, and codebooks composing the code set of MSSTC-SM to be assigned different rotation angles. Power and phase allocation as well as rotation angles are jointly optimized by differential evolution algorithm to maximize the minimum coding gain distance of the resultant MSSTC-SM. It is observed that the proposed MSSTC-SM outperforms other conventional transmission schemes in view of spectral efficiency and bit error probability with a comparable or lower detection complexity. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> This paper proposes a new multiple-input–multiple-output (MIMO) technique called quadrature spatial modulation (QSM). QSM enhances the overall throughput of conventional SM systems by using an extra modulation spatial dimension. The current SM technique uses only the real part of the SM constellation, and the proposed method in this paper extends this to in-phase and quadrature dimensions. It is shown that significant performance enhancements can be achieved at the expense of synchronizing the transmit antennas. Additionally, a closed-form expression for the pairwise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. Moreover, a simple and general asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results corroborate the accuracy of the conducted analysis and show the significant enhancements of the proposed QSM scheme. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> In this letter, we propose temporal modulation as a new dimension to enhance the performance of spatially modulated space-time block codes (STBCs). We efficiently integrate a cyclic spatially modulated codebook with temporal permutations over four consecutive time slots. To ensure a full transmit diversity order for the designed codebook, we assume that two distinct pairs from the available transmit antennas are activated over two consecutive time slots to construct a 2×2 STBC transmission matrix. We design a rotated version of the orthogonal full-diversity Alamouti STBC as a building block of our proposed codebook. Our numerical results confirm the reduced error rate of the proposed transmission scheme over the state-of-the-art schemes at the same spectral efficiency. <s> BIB007 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> In this paper, a novel multiple-input multiple-output (MIMO) transmission scheme termed space-time block coded differential spatial modulation (STBC-DSM) is proposed. It employs the hybrid concept of differential spatial modulation (DSM) and space-time block coding (STBC) to exploit the diversity benefits of STBC without the channel state information (CSI). In the STBC-DSM scheme, information bits are conveyed via the antenna matrix (AM) indices, as well as STBC blocks. Specifically, a novel AM set is first designed such that the transmitter requires only sparse (one or two) frequency radio (RF) chains. Then, the proposed STBC-DSM scheme is extended to the large-scale MIMO scenarios, and a low-complexity near-optimal detection algorithm is developed. Finally, an upper bound for the average bit error probability of the proposed scheme is derived. Both analytical and simulation results have shown that the proposed scheme is capable of achieving considerable performance gains over the existing DSM and differential Alamouti schemes. <s> BIB008 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Transmit-Diversity Enhanced SM <s> In this paper, motivated by the recent concept of quadrature spatial modulation (QSM), we propose a diversity-achieving QSM (DA-QSM) transmission scheme. In the proposed scheme, two sets of dispersion matrices are employed, and $P$ out of $Q$ dispersion matrices are activated in each set. Then the two groups of $P$ selected dispersion matrices are linearly combined with the real and imaginary parts of $P$ phase-shift keying/quadratic-amplitude modulation constellation symbols, respectively. Due to employing an extra combination of dispersion matrices indices, the proposed DA-QSM scheme provides higher spectral efficiency than the existing DA SM schemes, such as space-time block coded SM (STBC-SM) and spatially modulated orthogonal STBC (SM-OSTBC). Also, a simple and systematic method to construct the dispersion matrices is presented, which guarantees that the DA-QSM scheme can achieve the transmit diversity order of two except for two configurations of $P=Q$ and $P=\frac{Q}{2}$ , and DA-QSM can be applied to an arbitrary number of transmit antennas larger than 3. Furthermore, the performance analysis is conducted and the simulation results are presented to show the performance improvement of the proposed DA-QSM scheme. <s> BIB009
It has been reported in BIB002 that no transmit-diversity gain can be achieved by SM transmission even though the transmitter is equipped with multiple antennas. Hence, many researchers tried to develop transmit-diversity techniques with encoding mechanisms to overcome the lack of transmit-diversity inherent in SM. In BIB001 , the Alamouti code is exploited as the STBC to integrate with SM, which reaps the second-order transmitdiversity and enjoys the system simplicity by activating a pair of transmit antennas. Moreover, owing to the orthogonality of the Alamouti STBC on a spatial-constellation diagram, an optimal detector is further developed for the STBC-SM system with linear complexity. By resorting to the non-vanishing determinant property, the orthogonal STBC is embedded into the spatial constellation to achieve the transmit-diversity order of two BIB003 . However, although the orthogonal STBC based SM scheme in BIB003 achieves higher spectral efficiency without the rotation phase optimization involved in BIB001 , it is limited by its antenna configuration, which requires that the number of transmit antennas should be even and not less than four. To overcome the spectral efficiency degradation in the STBC-SM system of BIB001 , an enhanced STBC-SM making use of the cyclic structure and signal constellation rotation is developed in BIB004 , which improves the spectral efficiency without scarifying the transmit-diversity. By optimizing the power and phase allocation, a SM scheme based on modified multi-strata STBC is also proposed to further improve the spectral efficiency while maintaining the same transmit-diversity order BIB005 . In BIB007 , temporal permutations are introduced as a new dimension to improve the performance of spatially modulated STBCs and ensure a full transmit diversity order. To enjoy the high transmit-diversity order while avoiding channel estimation, the STBC is also integrated into the (D)SM, which reaps the diversity order without the requirement of CSI at the receiver BIB008 . Inspired by the QSM proposed in BIB006 , the in-phase and quadrature parts of the constellation symbols are linearly multiplexed by a pair sets of dispersion matrices in BIB009 to obtain the diversity-achieving QSM transmission mechanism, which achieves the second-order transmit-diversity and improves the spectral efficiency by using additional spatial information embedded in a dispersion matrix associated with the quadrature part.