A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Spatial modulation (SM) is a recently developed transmission technique that uses multiple antennas. The basic idea is to map a block of information bits to two information carrying units: 1) a symbol that was chosen from a constellation diagram and 2) a unique transmit antenna number that was chosen from a set of transmit antennas. The use of the transmit antenna number as an information-bearing unit increases the overall spectral efficiency by the base-two logarithm of the number of transmit antennas. At the receiver, a maximum receive ratio combining algorithm is used to retrieve the transmitted block of information bits. Here, we apply SM to orthogonal frequency division multiplexing (OFDM) transmission. We develop an analytical approach for symbol error ratio (SER) analysis of the SM algorithm in independent identically distributed (i.i.d.) Rayleigh channels. The analytical and simulation results closely match. The performance and the receiver complexity of the SM-OFDM technique are compared to those of the vertical Bell Labs layered space-time (V-BLAST-OFDM) and Alamouti-OFDM algorithms. V-BLAST uses minimum mean square error (MMSE) detection with ordered successive interference cancellation. The combined effect of spatial correlation, mutual antenna coupling, and Rician fading on both coded and uncoded systems are presented. It is shown that, for the same spectral efficiency, SM results in a reduction of around 90% in receiver complexity as compared to V-BLAST and nearly the same receiver complexity as Alamouti. In addition, we show that SM achieves better performance in all studied channel conditions, as compared with other techniques. It is also shown to efficiently work for any configuration of transmit and receive antennas, even for the case of fewer receive antennas than transmit antennas. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> A fundamental component of spatial modulation (SM), termed generalized space shift keying (GSSK), is presented. GSSK modulation inherently exploits fading in wireless communication to provide better performance over conventional amplitude/phase modulation (APM) techniques. In GSSK, only the antenna indices, and not the symbols themselves (as in the case of SM and APM), relay information. We exploit GSSKpsilas degrees of freedom to achieve better performance, which is done by formulating its constellation in an optimal manner. To support our results, we also derive upper bounds on GSSKpsilas bit error probability, where the source of GSSKpsilas strength is made clear. Analytical and simulation results show performance gains (1.5-3 dB) over popular multiple antenna APM systems (including Bell Laboratories layered space time (BLAST) and maximum ratio combining (MRC) schemes), making GSSK an excellent candidate for future wireless applications. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we present space shift keying (SSK) as a new modulation scheme, which is based on spatial modulation (SM) concepts. Fading is exploited for multiple-input multiple-output(MIMO) channels to provide better performance over conventional amplitude/phase modulation (APM) techniques. In SSK, it is the antenna index used during transmission that relays information, rather than the transmitted symbols themselves. This absence of symbol information eliminates the transceiver elements necessary for APM transmission and detection (such as coherent detectors). As well, the simplicity involved in modulation reduces the detection complexity compared to that of SM, while achieving almost identical performance gains. Throughout the paper, we illustrate SSK's strength by studying its interaction with the fading channel. We obtain tight upper bounds on bit error probability, and discuss SSK's performance under some non-ideal channel conditions (estimation error and spatial correlation). Analytical and simulation results show performance gains over APM systems (3 dB at a bit error rate of 10-5), making SSK an interesting candidate for future wireless applications. We then extend SSK concepts to incorporate channel coding, where in particular, we consider a bit interleaved coded modulation (BICM) system using iterative decoding for both convolutional and turbo codes. Capacity results are derived, and improvements over APM are illustrated (up to 1 bits/s/Hz), with performance gains of up to 5 dB. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> A new transmission approach, referred to as subcarrier-index modulation (SIM) is proposed to be integrated with the orthogonal frequency division multiplexing (OFDM) systems. More specifically, it relates to adding an additional dimension to the conventional two-dimensional (2-D) amplitude/phase modulation (APM) techniques, i.e. amplitude shift keying (ASK) and quadrature amplitude modulation (QAM). The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Analytical and simulation results show error probability performance gain of 4 dB over 4-QAM OFDM systems for both coded and uncoded data without power saving policy. Alternatively, power saving policy retains an average gain of 1 dB while using 3 dB less transmit power per OFDM symbol. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, a generalised technique for spatial modulation (SM) is presented. Generalised spatial modulation (GSM) overcomes in a novel fashion the constraint in SM that the number of transmit antennas has to be a power of two. In GSM, a block of information bits is mapped to a constellation symbol and a spatial symbol. The spatial symbol is a combination of transmit antennas activated at each instance. The actual combination of active transmit antennas depends on the random incoming data stream. This is unlike SM where only a single transmit antenna is activated at each instance. GSM increases the overall spectral efficiency by base-two logarithm of the number of antenna combinations. This reduces the number of transmit antennas needed for the same spectral efficiency. The performance of GSM is analysed in this paper, and an upper bound on the bit-error-ratio (BER) performance is derived. In addition, an algorithm to optimise the antenna combination selection is proposed. Finally, the performance of GSM is validated through Monte Carlo simulations. The results are compared with traditional SM. It is shown that for the same spectral efficiency GSM performs nearly the same as SM, but with a significant reduction in the number of transmit antennas. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results demonstrate a close match. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, a novel orthogonal frequency division multiplexing (OFDM) scheme, which is called OFDM with index modulation (OFDM-IM), is proposed for frequency-selective fading channels. In this scheme, inspiring from the recently introduced spatial modulation concept for multiple-input multiple-output (MIMO) channels, the information is conveyed not only by M-ary signal constellations as in classical OFDM, but also by the indices of the subcarriers, which are activated according to the incoming bit stream. Different transceiver structures are proposed and a theoretical error performance analysis is provided for the new scheme. It is shown via computer simulations that the proposed scheme achieves significantly better error performance than classical OFDM due to the information bits carried in the spatial domain by the indices of OFDM subcarriers. <s> BIB007 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <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> BIB008 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> A novel variant of orthogonal frequency division multiplexing (OFDM) techniques, which carries additional information bits through the index domain including in-phase and quadrature dimensions, is recently proposed. For its nature, we refer to this technique as OFDM with in-phase/quadrature index modulation (OFDM-I/Q-IM) . In this letter, we propose a novel low-complexity detector based on the maximum-likelihood (ML) criterion for OFDM-I/Q-IM, which does not need to know the variance of the noise and the possible realizations of the active subcarrier indices. With the proposed ML detector, the asymptotic average bit error probability (ABEP) and the exact coding gain achieved by OFDM-I/Q-IM are also derived. <s> BIB009 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Recently, orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) was proposed. By selecting a fixed number of subcarriers as active subcarriers to carry constellation symbols, the indices of these active subcarriers may carry additional bits of information. In this paper, we propose two generalization schemes of OFDM-IM, named OFDM with generalized index modulation 1 (OFDM-GIM1) and OFDM-GIM2, respectively. In OFDM-GIM1, the number of active subcarriers in an OFDM subblock is no longer fixed. Dependent on the input binary string, different numbers of active subcarriers are assigned to carry constellation symbols. In OFDM-GIM2, independent index modulation is performed on the in-phase and quadrature component per subcarrier. Through such ways, a higher spectral efficiency than that of OFDM-IM may be achieved. Since both generalization schemes proposed suffer from BER performance loss in low SNR region, an interleaving technique is proposed to tackle this problem. Finally, noting that the two generalization schemes are compatible with each other, the combination of these two schemes, named OFDM-GIM3, has also been investigated. Computer simulation results clearly show our proposed scheme's superiority in both spectral efficiency and BER performance compared to existing works. <s> BIB010 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Orthogonal frequency division multiplexing with index modulation (OFDM-IM), which uses the indices of the active subcarriers to transmit data, is a recently proposed multicarrier transmission technique. In this letter, we propose coordinate interleaved OFDM-IM (CI-OFDM-IM) by combining OFDM-IM and space-time block codes with coordinate interleaving. In this scheme, the real and imaginary parts of the data symbols are transmitted over different active subcarriers to achieve an additional diversity gain. The average bit error probability (ABEP) of the proposed scheme is derived and its superiority over the reference systems is shown via computer simulations. <s> BIB011 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a novel multicarrier transmission technique which has been proposed as an alternative to classical OFDM. The main idea of OFDM-IM is the use of the indices of the active subcarriers in an OFDM system as an additional source of information. In this work, we propose multiple-input multiple-output OFDM-IM (MIMO-OFDM-IM) scheme by combining OFDM-IM and MIMO transmission techniques. The low complexity transceiver structure of the MIMO-OFDM-IM scheme is developed and it is shown via computer simulations that the proposed MIMO-OFDM-IM scheme achieves significantly better error performance than classical MIMO-OFDM for several different system configurations. <s> BIB012 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> A new scheme, called code index modulation-spread spectrum (CIM-SS), is presented in this paper. This scheme is based on direct sequence-spread spectrum (DS-SS) modulation and can achieve higher data rate than the conventional DS-SS with lower energy consumption. At the transmitter, the bit stream is divided into blocks of two bits each. For each block, only the first bit is spread by one of two spreading codes while the second bit selects the code to be used. The receiver estimates both the code and the transmitted bit. The performance of the CIM-SS is analyzed and compared to the conventional DS-SS systems. <s> BIB013 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we introduce a new spatial modulation (SM) technique using one or two active antennas and multiple signal constellations. The proposed technique, which we refer to as Enhanced SM or ESM, conveys information bits not only by the index(es) of the active antenna(s), but also by the constellations transmitted from each of them. The main feature of ESM is that it uses a primary signal constellation during the single active antenna periods and some other secondary constellations during the periods with two active transmit antennas. The secondary signal constellations are derived from the primary constellation by means of geometric interpolation in the signal space. We give design examples using two and four transmit antennas and QPSK, 16QAM, and 64QAM as primary modulations. The proposed technique is compared to conventional SM as well as to spatial multiplexing (SMX), and the results indicate that in most cases, ESM provides a substantial performance gain over conventional SM and SMX while reducing the maximum-likelihood (ML) decoder complexity. <s> BIB014 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this work, we use the concept of the new emerging technology of reconfigurable antennas (RAs) in an effort to improve the performance of space shift keying (SSK). Indeed, the reconfigurable properties of RAs can be used as additional degrees of freedom to enhance the performance of SSK in terms of throughput, system complexity, and error performance. In this context, considering correlated and nonidentically distributed Rician fading channels, we propose a number of SSK-RA schemes using SSK with antenna-state selection while taking advantage of the effect of RAs on the multipath propagation channel. More specifically, based on the variation of the Rician $K$ -factor and the correlation coefficients with different antenna states, the proposed schemes jointly optimize the fading and correlation parameters to enhance SSK’s performance. In this paper, we analyze the performance of the proposed SSK-RA schemes over Rician fading channels in terms of average spectral efficiency (ASE) and bit error rate (BER). We also provide several simulation examples through which we corroborate these analytical results. The proposed schemes are shown to enhance the performance of SSK both in terms of ASE and BER. For the same ASE, compared to that of SSK, not only do the proposed SSK-RA schemes provide much better error performance, they also reduce the implementation cost and the overall system complexity considerably. <s> BIB015 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Generalized frequency division multiplexing (GFDM) is a promising non-orthogonal multicarrier transmission scheme which has recently received a great deal of attention towards future fifth generation (5G) wireless networks. It overcomes the limitations of orthogonal frequency division multiplexing (OFDM) while preserving most of the advantages of it. On the other hand, index modulation (IM) has the potential to provide a flexible system design with adjustable number of active subcarriers as well as significant bit error rate (BER) performance improvement for multicarrier systems. In this paper, we propose the combined application of GFDM and IM techniques. We present the GFDM-IM system model and evaluate its error performance by comparing to classical GFDM and OFDM-IM for Rayleigh multipath fading channels. It is shown via computer simulations that the GFDM-IM system achieves signicantly better error performance than classical GFDM due to the information bits carried in the spatial domain by the indices of active GFDM subcarriers. <s> BIB016 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we propose a generalized code index modulation (CIM) technique for direct-sequence spread spectrum (DSSS) communication. In particular, at the transmitter, the bit stream is divided into blocks in which each block is divided into two subblocks: mapped and modulated subblocks. Thereafter, the bits within the mapped subblock are used to select one of the predefined spreading codes, which is then used to spread the modulated bits of the second subblock. In this design, using the spreading code index as an information-bearing unit increases the overall spectral efficiency of this system. At the receiver side, the spreading code index is first estimated, thus resulting in a direct estimation of mapped subblock bits. Consequently, the corresponding spreading code to this estimated index is used to despread the modulated symbol of the modulated subblock. Subsequently, mathematical expressions for bit error rate (BER), symbol error rate (SER), throughput, energy efficiency, and the system complexity are derived to analyze the system performance. Finally, simulation results show that the proposed modulation scheme can achieve a higher data rate than the conventional DSSS system, with lower energy consumption and complexity. <s> BIB017 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> The emerging market of the Internet of Things (IoT) requires new energy-efficient and low-complexity Multiple-Input-Multiple-Output (MIMO-) aided radio access technologies. This trend will have a profound impact on both the theory and practice of future communication networks, which will not be purely optimized for approaching the attainable capacity anymore, but will explicitly include the energy efficiency for the design and optimization of the entire protocol stack. In this paper, we discuss a recently introduced modulation scheme for IoT applications, which leverages the concepts of Reconfigurable Antennas (RecAnts) and Spatial Modulation (SM). RecAnt-SM constitutes a promising new air interface in the context of MIMO-aided transmission, which can be beneficially invoked for the design of medium-throughput, low-complexity and energy-efficient communication systems by relying on a limited number of RF chains and the flexibility of simple RecAnt designs. <s> BIB018 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, for the first time, visual demonstrations of new signal processing candidate techniques for the future fifth generation of mobile networks and the internet of things, called Transmit Spatial Modulation and Receive Spatial Modulation, respectively, are described. These techniques exploit multiple antennas to boost the spectral efficiency of the wireless link. However, compared to multiple-antenna systems, they use less Radio-Frequency modules, and they are expected to be lower in cost, size and energy consumption. They are thus promising to provide high data rate to/from small connected objects. In Transmit Spatial Modulation, the receiver, (a base station for instance), additionally to conventional demodulation, detects "where, in space, the signal comes from" to get additional data bits. In Receive Spatial Modulation, the receiver (a connected object for instance), additionally to conventional demodulation, detects "where, in space, the signal is arriving at" to get additional bits. Thanks to a new device called the Radio Waves Display and our spatial modulation test bed, for the first time, we visualize, in real time, the spatial repartition of the signal around and on the receiver. This enables even the general public to perform a spatial demodulation, in a visual manner, and understand intuitively, the concept. <s> BIB019 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we introduce the concept of space-time channel modulation (STCM), which extends the classical space-time block codes into a third dimension: channel states (transmission media) dimension. Three novel STCM schemes, which provide interesting tradeoffs among decoding complexity, error performance, and data rate by combining space-time block coding and media-based modulation (MBM) principles, are proposed. It is shown via computer simulations that the proposed STCM schemes achieve considerably better error performance than the existing MBM and classical systems. <s> BIB020 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM), which provides a flexible trade-off between spectral efficiency and error performance, is recently proposed as a promising transmission technique for energy-efficient 5G wireless communication systems. However, due to the dependence of subcarrier symbols within each subblock and the strong interchannel interference, it is challenging to detect the transmitted data effectively while imposing low computational burden to the receiver. In this paper, we propose a low-complexity detector based on the sequential Monte Carlo (SMC) theory for the detection of MIMO-OFDM-IM signals. The proposed detector, which draws samples based on the importance weights at the subblock level, achieves near-optimal error performance with considerably reduced computational complexity. Simulation and numerical results in terms of bit error rate (BER) and number of complex multiplications (NCM) corroborate the superiority of the proposed detector. <s> BIB021 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Motivated by the recent index modulation (IM) concept in the spatial, frequency, and space-time domains, we propose a novel broadband single-carrier (SC)-based IM (SC-IM) scheme as well as its low-complexity frequency-domain equalization (FDE) algorithm. The proposed FDE-aided SC-IM scheme outperforms the conventional FDE-aided SC scheme, while achieving a comparable low level of detection complexity. In addition, in order to reduce the inter-channel correlation arising from the activated symbol indices, we propose a symbol mapping algorithm, which further improves the achievable error-rate performance of the SC-IM scheme. Our simulation results demonstrate the performance advantage of the proposed FDE-aided SC-IM scheme over the conventional FDE-aided SC scheme. <s> BIB022 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Index modulation has become a promising technique in the context of orthogonal frequency division multiplexing (OFDM), whereby the specific activation of the frequency domain subcarriers is used for implicitly conveying extra information, hence improving the achievable throughput at a given bit error ratio (BER) performance. In this paper, a dual-mode OFDM technique (DM-OFDM) is proposed, which is combined with index modulation and enhances the attainable throughput of conventional index-modulation-based OFDM. In particular, the subcarriers are divided into several subblocks, and in each subblock, all the subcarriers are partitioned into two groups, modulated by a pair of distinguishable modem-mode constellations, respectively. Hence, the information bits are conveyed not only by the classic constellation symbols, but also implicitly by the specific activated subcarrier indices, representing the subcarriers’ constellation mode. At the receiver, a maximum likelihood (ML) detector and a reduced-complexity near optimal log-likelihood ratio-based detector are invoked for demodulation. The minimum distance between the different legitimate realizations of the OFDM subblocks is calculated for characterizing the performance of DM-OFDM. Then, the associated theoretical analysis based on the pairwise error probability is carried out for estimating the BER of DM-OFDM. Furthermore, the simulation results confirm that at a given throughput, DM-OFDM achieves a considerably better BER performance than other OFDM systems using index modulation, while imposing the same or lower computational complexity. The results also demonstrate that the performance of the proposed low-complexity detector is indistinguishable from that of the ML detector, provided that the system’s signal to noise ratio is sufficiently high. <s> BIB023 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> Orthogonal frequency division multiplexing with index modulation (OFDM-IM) performs transmission by considering two modes over OFDM subcarriers, which are the null and the conventional $M$ -ary signal constellation. The spectral efficiency (SE) of the system, however, is limited, since the null mode itself does not carry any information and the number of subcarrier activation patterns increases combinatorially. In this paper, a novel IM scheme, called multiple-mode OFDM-IM (MM-OFDM-IM), is proposed for OFDM systems to improve the SE by conveying information through multiple distinguishable modes and their full permutations. A practical and efficient mode selection strategy, which is constrained on the phase shift keying/quadrature amplitude modulation constellations, is designed. Two efficient detectors that provide different tradeoffs between the error performance and detection complexity are also proposed. The principle of MM-OFDM-IM is further extended to the in-phase and quadrature components of OFDM signals, and the method of generating multiple modes from the $M$ -ary pulse amplitude modulation constellation for this modified scheme is also introduced. Bit error rate (BER) analyses are provided for the proposed schemes. Monte Carlo simulations on BER corroborate the analyses and show that the proposed schemes appear as promising multi-carrier transmission alternatives by outperforming the existing OFDM-IM counterparts. <s> BIB024 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> The single-radio-frequency (RF) multiple-input-multiple-output (MIMO) system has been proposed to pursue a high spectral efficiency while keeping a low hardware cost and complexity. Recently, the available degrees of freedom (DoF) in the polarization domain has been exploited to reduce the size of the transmit antenna array and provide 1 bit per channel use (bpcu) multiplexing gain for the single-RF MIMO system. Nevertheless, the polarization domain resource still has the potential to provide a higher multiplexing gain in the polarized single-RF MIMO system. In this paper, we propose a generalized polarization shift keying (PolarSK) modulation scheme that uses polarization states in the dual-polarized transmit antenna as an information-bearing unit to increase the overall spectral efficiency. At the receiver, the optimum maximum likelihood (ML) detector is employed to investigate the ultimate performance limit of the PolarSK. A closed-form union upper bound on the average bit error probability (ABEP) of the PolarSK with the optimum ML receiver is derived. Inspired by the analytic ABEP, a constellation diagram optimization algorithm is proposed. To reduce the computational complexity of the receiver, a linear successive interference cancellation (SIC) detection algorithm and a sphere-decoding (SD) detection algorithm are introduced. Through numerical results, performances of the proposed PolarSK in terms of ABEP and computational complexity are analyzed. Furthermore, the PolarSK is analyzed over measured indoor channels. Numerical and measurement results show that the PolarSK scheme outperforms the state-of-the-art dual-polarized/unipolarized SM schemes. <s> BIB025 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) that uses an antenna array to encode the information symbols into the angle of propagation (and arrival) wave in the wireless channel. At the encoder, the block of information bits is mapped into two symbols: (i) a spatial symbol selecting the direction of arrival of the amplitude and phase modulated carrier signal and (ii) a temporal symbol chosen from the constellation diagram like QAM or PSK. The proposed scheme follows the model for concatenated modulation designs like recently introduced spatial modulation (SM). The use of the transmitted signal angle through antenna array beamforming increases the spectral efficiency of the single-input single-output (SISO) conventional (temporal) modulation by the base-two logarithm of the number of spatial beams that can be resolved (detected) at the receiver. Direction-of-arrival type detection for spatial symbols is developed using a linear array of receive antennas. It is demonstrated that the detection reliability of the spatial symbols in BACM is determined by the number of antennas used at the receiver and the actual angles of signal arrival. <s> BIB026 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we propose an index modulated orthogonal frequency division multiplexing spread spectrum (IM-OFDM-SS) scheme, which combines the techniques of SS and IM under the framework of OFDM. In this scheme, the information bits are jointly conveyed by the indices of spreading codes and the conventional $M$ -ary modulated symbols. A low-complexity maximal ratio combining (MRC) detector is designed, in which the receiver first detects the spreading codes and then de-spreads and demodulates the symbols. The bit error rate (BER) performance of IM-OFDM-SS systems in the presence of channel estimation errors is analyzed. An upper bound and approximate average bit error probability associated with maximum-likelihood and MRC detection, respectively, are derived. Subsequently, we extend the idea of IM-OFDM-SS to multi-code and multi-user scenarios, proposing generalized (G-)IM-OFDM-SS and IM-based multi-carrier code division multiple access (IM-MC-CDMA), respectively. Simulation results verify the analyses and show that the proposed IM/ GIM-OFDM-SS outperforms the existing OFDM-IM and OFDM-SS schemes significantly. In addition, the IM-MC-CDMA exhibits a lower BER than MC-CDMA at the same SEs for either multi-user or single-user detection. <s> BIB027 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> A. Single-Dimension Entity <s> In this paper, we present a novel modulation technique for dual-polarization communication systems, which reduces the error rate compared with the existent schemes. This modulation places the symbols in a 3-D constellation, rather than the classic approach of 2-D. Adjusting the phase of these symbols depending on the information bits, we are able to increase the bit rate. Hence, the proposed scheme conveys information by selecting both polarization state and the phase of radiated electromagnetic wave. We also analyses the performance of the 3-D polarized modulation (PMod) for different constellation sizes and we obtain a curve of rate adaptation. Finally, we compare the proposed 3-D PMod with the other existing schemes, such as single polarization phase shift keying and double polarization vertical Bell Laboratories layer space–time, both carrying the same number of information bits. The results show that the 3-D PMod always outperforms all other schemes, except for low-order modulation. Therefore, we can conclude that the 3-D PMod is an excellent candidate for medium- and high-modulation-order transmissions. <s> BIB028
After the pioneering works in BIB001 and BIB003 , the emergence of SM and SSK schemes has sparked renewed and widespread interest in digital modulation, both of which require a single RF chain only and embed spatial information through the active antenna index. Afterwards, different variants of the SM technology have been developed to accommodate more than one active antennas and further enhance the spectral efficiency, which include (G)SM BIB005 , (G)SSK BIB002 and QSM BIB008 . Besides the spatial entity of antenna, the implementation of SM can also be extended to communication systems deploying RF mirrors and LEDs. As presented in Section V-B, the SM aided VLC, which conveys spatial information through the location of the active LED, is an efficient and inexpensive dual-use technology of illumination and communications BIB006 . Another remarkable implementation of SM in the space domain is the reconfigurable antenna (RA) based system, which controls the ON/OFF states of the RF mirrors surrounding a transmit antenna and further alters the radiation pattern to embed additional information BIB018 - BIB019 . With the adjustable radiation characteristics of the transmit antenna, RA-SSK is proposed in BIB015 to improve the system performance and reduce the implementation cost in transmit antennas. Moreover, as the changing of radiation pattern results in the variations of the channel characteristics, it can be regarded as the modulation based on the channel state, which is also referred to as channel modulation (CM) schemes BIB020 . Although the SM technology originated in the space domain, SM is not exclusive to the space domain and can be easily transplanted into the frequency/time/code/angle domains. Inspiring by the SM concept, the authors of BIB004 introduce the subcarrier-index modulation (SIM)-OFDM system, which is the first attempt to exploit the subcarrier indices for encoding information and alleviating the high peak-toaverage power ratio issue in OFDM systems. By replacing the transmission of antennas with subcarriers for performing the ON/OFF keying mechanism, orthogonal frequency division multiplexing with index modulation (OFDM-IM) is proposed in BIB007 as a successful and inspiring representative for implementing the SM concept into multi-carrier systems. Inspired by the design of the QSM scheme, OFDM with in-phase/quadrature index modulation (OFDM-I/Q-IM) is proposed in BIB009 to perform the ON/OFF keying mechanism independently in the in-phase and quadrature dimensions, respectively, which further enhances the spectral efficiency and the error performance. In BIB010 , the generalization of OFDM-IM is proposed to further enhance the spectral efficiency and flexibility with a variable number of active subcarriers, which relaxes the constraint of the fixed number of active subcarriers in BIB007 . The concept of SM is also applied to generalized frequency division multiplexing (GFDM) in BIB016 , which yields the GFDM-IM scheme and achieves performance gain over conventional GFDM. To achieve higher diversity gain, a novel coordinate interleaved OFDM-IM (CI-OFDM-IM) scheme is proposed in BIB011 by combining the SM concept and coordinate interleaved STBC in OFDM systems. The combination scheme of OFDM-IM and MIMO, which referred to as MIMO-OFDM-IM, is investigated in BIB012 to achieve higher data rates and better error performance than the traditional MIMO-OFDM scheme, where various low-complexity and near-optimal algorithms are developed for the demodulation of MIMO-OFDM-IM BIB012 - BIB021 . The successful implementation of OFDM-IM has also propelled the spread of the SM concept to the time, code, and angle domains. In BIB022 , a novel single-carrier (SC) based IM (SC-IM) scheme, which activates a subset of symbols in each time-domain subframe to convey additional information, is proposed to enhance the transmission efficiency for broadband systems. A code index modulationspread spectrum (CIM-SS) is proposed in BIB013 to achieve better performance with reduced energy consumption, which carries additional information by choosing one of the two spreading Walsh codes. Moreover, a generalization scheme of CIM-SS (called GCIM-SS) is then proposed in BIB017 to further improve the spectral efficiency, which increases the set size of the spreading Walsh codes to bear more index information. By integrating the SM concept into OFDM spread spectrum (OFDM-SS) systems, the authors of BIB027 propose an index modulated OFDM-SS (IM-OFDM-SS) scheme to harvest the diversity gain and higher spectral efficiency, which embeds the index information through the selection of spreading codes and can be applied to multi-user systems. By enabling the flexibility of activating one or two antennas, an enhanced SM scheme is developed in BIB014 to overcome the compromised spectral efficiency of conventional SM, which jointly select the active antenna(s) and the constellations for embedding more index information. To mitigate the loss in spectral efficiency due to the inactive subcarriers, a dual-mode OFDM (DM-OFDM) is proposed in BIB023 to enhance the data transmission efficiency, in which the originally active subcarriers of OFDM-IM carry the modulated symbols drawn from the primary constellation while those inactive subcarriers of OFDM-IM are reactivated to carry new modulated symbols drawn from a secondary constellation. Furthermore, the generalization scheme of DM-OFDM, which is referred to as multiple-mode OFDM-IM (MM-OFDM-IM) BIB024 and includes more constellation modes, is developed by exploiting the full permutation pattern to carry more index information. By exploiting polarization states for conveying index information through the angle domain, a generalized polarization shift keying (PolarSK) modulation scheme, is proposed for dual-polarization communication systems in BIB025 to achieve high spectral efficiency while retaining a low hardware cost. Moreover, a 3-D polarized modulation (PMod) is developed for dual-polarization communication systems in BIB028 , which selects both polarization state and the radiation phase according to the information bits to achieve better error performance. In BIB026 , a beam angle channel modulation (BACM) scheme is introduced to convey index information in the angle domain, which embeds the information into the AoA of a transmission beam.