A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, a multiple-input multiple-output (MIMO) technique for indoor optical wireless (OW) communication is proposed. The technique is referred to as \emph{optical spatial modulation (OSM)}. The key concept is based on spatial modulation (SM). At any given time instant, only one transmitter is active and the others are inactive. A transmitter in space is considered as a spatial constellation point which is assigned a unique bit sequence. Consequently, transmitters are turned on and off depending on the incoming data bits, similar to the activation of constellation points in traditional digital modulation schemes. Hence, a data rate of the base two logarithm of the number of transmit units is achieved. The active transmitter radiates a certain intensity level at a particular time instant. At the receiver side, the optimal SM detector is slightly modified and used to estimate the spatial constellation point. The estimated spatial constellation point is used to arrive at the original bit stream via de-mapping. The upper bound bit-error-ratio (BER) of OSM is analyzed for a MIMO configuration consisting of four transmit units (light emitting diodes (LEDs)) and four receive units (photo diodes (PDs)) in a room. The BER performance is determined for different transmitter and receiver separation distances and different transmitter half power semiangles. It is shown that the proposed OSM technique achieves twice and four times the data rate as compared to OOK (on-off keying) and PPM (pulse-position modulation), respectively. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, we study the performance of Spatial Modulation (SM) applied to optical wireless communications (OWC) in indoor environments with line-of-sight (LOS) characteristics. To this end, we consider setup scenarios with different numbers of optical transmitters and receivers which are arranged within a room. SM is compared to Repetition Coding (RC). Because RC is known to achieve very good performance in OWC systems due to the use of intensity modulation and the resulting constructive superposition of the power signals. The results show that SM can outperform RC when high spectral efficiencies are desirable, e.g. 4 bit/s/Hz and greater, since it can operate with reduced signal modulation orders by conveying additional data bits in the spatial domain. We also demonstrate that SM benefits from receive-diversity to a larger extent while at the same time requiring less computational complexity. Furthermore, we give a general framework to numerically approximate the average bit error probability of both SM and RC. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> This letter proposes significant enhancement in optical spatial modulation (OSM) performance by aligning the transmit and receive units. OSM is a recently proposed pulsed modulation technique for indoor optical wireless (OW) communication . In OSM, multiple transmitters are considered where only one transmitter is active at a time and the others are turned off. The incoming bit sequence activates one of the transmit units, i.e. the transmit units are considered as a spatial constellation points and each unique sequence of incoming bits is mapped to one of the constellation points. It is shown that the proposed transmit-receive unit alignments for OSM enhances the performance by more than 14 dB in signal to noise ratio (SNR). In addition, the resultant scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying (OOK), pulse position modulation (PPM), and pulse amplitude modulation (PAM). <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Recently, rapid increase of mobile devices pushed the radio frequency (RF)-based wireless technologies to their limits. Free-space-optical (FSO), a.k.a. optical wireless, communication has been considered as one of the viable solutions to respond to the ever-increasing wireless capacity demand. Particularly, Visible Light Communication (VLC) which uses light emitting diode (LED) based smart lighting technology provides an opportunity and infrastructure for the high-speed low-cost wireless communication. Though stemming from the same core technology, the smart lighting and FSO communication have inherent tradeoffs amongst each other. In this paper, we present a tutorial and survey of advances in these two technologies and explore the potential for integration of the two as a single field of study: LIGHTNETs. We focus our survey to the context of mobile communications given the recent pressing needs in mobile wireless networking. We deliberate on key challenges involved in designing technologies jointly performing the two functions simultaneously: LIGHTing and NETworking. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, we compare the performance of multiple-input-multiple-output (MIMO) techniques applied to indoor optical wireless communications (OWC) assuming line-ofsight (LOS) channel conditions. Specifically, several 4 × 4 setups with different transmitter spacings and different positions of the receiver array are considered. The following MIMO algorithms are considered: Repetition Coding (RC), Spatial Multiplexing (SMP) and Spatial Modulation (SM). Particularly, we develop a framework to analytically approximate the bit error ratios (BERs) of these schemes and verify the theoretical bounds by simulations. The results show that due to diversity gains, RC is robust to various transmitter-receiver alignments. However, as RC does not provide spatial multiplexing gains, it requires large signal constellation sizes to enable high spectral efficiencies. In contrast, SMP enables high data rates by exploiting multiplexing gains. In order to provide these gains, SMP needs sufficiently low channel correlation. SM is a combined MIMO and digital modulation technique. We show that SM is more robust to high channel correlation compared to SMP, while enabling larger spectral efficiency compared to RC. Moreover, we investigate the effect of induced power imbalance between the multiple transmitters. It is found that power imbalance can substantially improve the performance of both SMP and SM as it reduces channel correlation. In this context, we also show that blocking some of the links is an acceptable method to reduce channel correlation. Even though the blocking diminishes the received energy, it outweighs this degradation by providing improved channel conditions for SMP and SM. For example, blocking 4 of the 16 links of the 4 × 4 setup improves the BER performance of SMP by more than 20 dB, while the effective signal to noise ratio (SNR) is reduced by about 2 dB due to the blocking. Therefore, MIMO techniques can provide gains even under LOS conditions which provide only little channel differences. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper the error performance analysis of a low complexity, multiple transmitter generalised space shift keying (GSSK) signalling technique for short range indoor visible light communications is presented. In an N_t transmitter system, this signalling technique is capable of achieving a spectral efficiency of N_t bits/s/Hz. The GSSK system has a higher spectral efficiency than the conventional on-off keying (OOK) and pulse position modulation (PPM) techniques. The GSSK transmitter is much simpler than that of an equivalent regular pulse amplitude modulation (PAM) system with similar spectral efficiency. An analytical expression for the symbol error rate (SER) is presented and verified using simulations. The receiver is based on the maximum likelihood criterion and using multiple photodetectors (PDs) in the receiver improves the error performance. Within the room and the transmitter-receiver configuration under consideration, with four PDs, a gain of 6 dB is attainable over the single PD system for the case of 2 and 3 bits/s/Hz. Considering a fixed link range with N_t = 2 and at a symbol error rate of 10-6, using wide half angle LEDs with Φ1/2= 60° requires about 12 dB less in electrical signal-to-noise ratio compared with Φ1/2 = 30°. The beam directivity is however of much lower effect when the room under consideration is equiped with sufficient LEDs to provide full coverage. The GSSK technique can also support dimming control by using different pulse widths. This, however, is at a price of reduced spectral efficiency. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> This paper demonstrates the merit and de-merit of a low complexity, multiple transmitter generalised space shift keying (GSSK) signalling technique for short range indoor visible light communications. To illustrate the high spectral efficiency credential of GSSK, an array of $N_{{\rm t}}$ white light emitting diodes (LEDs) is used to demonstrate $N_{{\rm t}}$ bits/symbol transmission by exploiting the natural differences in the channel gains of the spatially separated LED array. With two low power white LEDs each having a $\hbox{3}$ dB modulation bandwidth of $\hbox{8}$ MHz, data transmission of up to $\hbox{40}$ Mbits/s ( $\hbox{20}$ Mbaud) is demonstrated. For an average received electrical signal power of ${-12.5}$ dBm and $2\times 10^{4}$ data symbols, the measured symbol error rate at $\hbox{20}$ Mbaud is $7 \times 10^{-2}$ and $5 \times 10^{-5}$ at $\hbox{10}$ Mbaud ( $\hbox{20}$ Mbits/s) without any error control coding. The GSSK technique is experimentally shown to be most suitable for a fixed configuration as its performance is quite sensitive to receiver mobility. <s> BIB007 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, we investigate the performance of generalized spatial modulation (GSM) in indoor wireless visible light communication (VLC) systems. GSM uses $N_t$ light emitting diodes (LED), but activates only $N_a$ of them at a given time. Spatial modulation and spatial multiplexing are special cases of GSM with $N_{a}=1$ and $N_{a}=N_t$, respectively. We first derive an analytical upper bound on the bit error rate (BER) for maximum likelihood (ML) detection of GSM in VLC systems. Analysis and simulation results show that the derived upper bound is very tight at medium to high signal-to-noise ratios (SNR). The channel gains and channel correlations influence the GSM performance such that the best BER is achieved at an optimum LED spacing. Also, for a fixed transmission efficiency, the performance of GSM in VLC improves as the half-power semi-angle of the LEDs is decreased. We then compare the performance of GSM in VLC systems with those of other MIMO schemes such as spatial multiplexing (SMP), space shift keying (SSK), generalized space shift keying (GSSK), and spatial modulation (SM). Analysis and simulation results show that GSM in VLC outperforms the other considered MIMO schemes at moderate to high SNRs; for example, for 8 bits per channel use, GSM outperforms SMP and GSSK by about 21 dB, and SM by about 10 dB at $10^{-4}$ BER. <s> BIB008 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> We present a novel multiple-input multiple-output (MIMO) optical modulation method combining antenna shift keying with joint pulse position and amplitude modulations. The proposed approach, denoted optical spatial modulation (OSM), offers better power and spectral efficiencies than conventional MIMO optical modulation methods. We also provide a theoretical analysis framework for the performance of both uncoded and coded OSM in free space optical communication channels with weak-to-moderate and moderate-to-strong atmospheric turbulence. Theoretical derivations are validated with simulations, which illustrate the feasibility of the proposed transceiver in key design metrics, such as spectral efficiency, error performance, and robustness against scintillation effects. <s> BIB009 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> The use of optical spatial modulation (OSM), which has been recently emerged as a power and bandwidth efficient pulsed modulation technique for indoor optical wireless communication, is proposed as a simple, low-complexity means of achieving spatial diversity in coherent free space optical (FSO) communication systems. In doing so, this paper makes several novel contributions as follows. It presents a generic analytical framework for obtaining the Average Bit Error Probability (ABEP) of uncoded OSM with coherent detection in the presence of turbulence-induced fading. Although the framework is general enough to accommodate any type of models based on turbulence scattering, the focus in this paper is the H-K distribution. Although this distribution represents a very general scattering model valid over a wide range of atmospheric conditions, it is has not been considered in the past in conjunction with FSO systems possibly because of its mathematical complexity. The proposed analytical framework yields exact performance evaluation results for MIMO systems with two transmit- and an arbitrary number of receive apertures. In addition, tight upper bounds are derived for the error probability for OSM systems with an arbitrary number of transmit apertures as well as for convolutionally encoded signals. The performance of OSM is compared to that of well established coherent FSO schemes, employing spatial diversity at the transmitter or the receiver only. Specifically, it is shown that OSM can offer comparable performance with conventional coherent FSO schemes while outperforming the latter in terms of spectral efficiency and hardware complexity. Various numerical performance evaluation results are also presented and compared with equivalent results obtained by Monte Carlo simulations which verify the accuracy of the derived analytical expressions. <s> BIB010 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, we present a constellation optimization technique that can be invoked for optical spatial modulation (OSM) multiple-input multiple-output (MIMO) systems within the context of optical wireless (OW) systems that is designed to negate the high channel correlation imposed on conventional OSM schemes. More specifically, the proposed unified OSM architecture relies on power-imbalanced (PI) multiple transmit light sources. Furthermore, we formulate the constrained capacity of the proposed PI-OSM scheme, and then provide the design guidelines of our OSM scheme's PI constellation, in which the parameters have been optimized to ensure the associated constrained capacity is maximized. Our simulation results demonstrate that our proposed scheme is capable of outperforming conventional OSM and OW-MIMO schemes over a wide range of signal-to-noise ratios. <s> BIB011 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented. <s> BIB012 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> This letter focuses on a spatial modulation (SM)-based multiple input single output optical wireless communication system. In the system, both input-dependent noise and finite alphabet are employed. Based on information theory, the theoretical expressions of the mutual information and its lower bound are derived. By maximizing the minimum distance, an optimization problem for precoding design is formulated. Then, an interior point method-based iteration algorithm is proposed to solve the problem. Numerical results show that the performance of the proposed SM scheme outperforms that of the conventional, choosing the best-gain channel scheme. Moreover, the proposed precoding scheme can provide better system performance than the scheme without precoding. <s> BIB013 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> This paper reports the effect of data modulation on the emitted light quality of phosphor converted white LEDs. The results showed that provided the expected average current driving the LEDs remains unchanged then the emitted light quality will stay the same. For a dc-balanced modulating signal, with a nonvarying average value, any fluctuations in the instantaneous driving current due to data modulation do not have any significant impact on the measured light quality metrics. For visible light communication applications therefore, a dc-balanced signalling becomes a prerequisite if the expected quality of light emitted by the LEDs is to be preserved. The findings are premised on adequate thermal management for the LEDs under test. <s> BIB014 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Massive multi-input multi-output (MIMO) has great potential to improve transmission rate of visible light communication (VLC) systems. However, high inter-channel interference (ICI) is the main factor that seriously influences the transmission performance. In this letter, with the channel state information (CSI) known at the transmitters, a general criterion of balancing the spectral efficiency and the error performance is established by analyzing the special features of MIMO-VLC. Based on the criterion, a channel-adapted spatial modulation (CASM) for massive MIMO-VLC is proposed, so as to find the optimal combinations of active light-emitting diodes under the controlled ICI. Simulation results show that CASM achieves more bit-error-rate gains over optical multi-stream spatial modulation (OMS-SM) with the same spectral efficiency, or even considering 10% reduction in the spectral efficiency of CASM caused by updating the CSI. Moreover, the higher spectral efficiency, the more gains of CASM over OMS-SM. <s> BIB015 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, we propose a generalized light emitting diode (LED) index modulation scheme for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) visible light communications (VLC) systems. The proposed scheme generalizes the LED index modulation concept by using the spatial multiplexing principle to transmit complex OFDM signals through VLC channels by separating these signals into their real-imaginary and positive-negative parts. The maximum a posteriori (MAP) estimator of the proposed scheme, which relies on quadratic programing (QP) problem, is presented for flat VLC channels. It is shown via computer simulations that the proposed scheme achieves considerably better error performance than the existing VLC-MIMO-OFDM systems due to its power efficiency and improved transceiver structure. <s> BIB016 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Recently, optical spatial modulation (OSM) has been proposed for indoor optical wireless communications (OWC), which is considered as a feasible complementary solution for high data rate transmission. This paper investigates the constellation optimization problem for OSM based OWC. An OWC system with multiple transmitters and multiple receivers is considered. By using OSM, only a single transmitter is active at each time instance. Considering the non-negativity and the peak optical intensity constraints, the constellation space for OSM based OWC system is established. By exploiting the channel state information at the transmitter, this paper designs the multi-dimensional constellations by maximizing the minimum Euclidean distance between the received constellation points. Two feasible algorithms are proposed to solve the optimization problem. To evaluate the performance of the proposed algorithms, the symbol error rate is also derived. Simulation results show that the derived constellations using the proposed two algorithms outperform the existing uniformly distributed constellations. <s> BIB017 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> This paper examines the effect of synchronization error on the performance of spatial modulation (SM) technique in optical wireless communication (OWC) systems. SM exploits the deployment of multiple transmitters by encoding user information on their spatial domain. In most works related to SM, a perfect synchronization among these multiple transmitters is assumed. However, synchronization error can result from multipath propagation in OWC channel, and clock jitter and variation in propagation delay of each transmitter. Synchronization error degrades system performance and hence the need to investigate its effect. Using union bound technique, and defining synchronization errors as timing offsets in the received signals, we derive the symbol error rate for space shift keying (SSK), generalized SSK (GSSK), SM, and generalized SM (GSM) schemes, and we validate our analysis with tightly matched simulation results. Results show that degradation in performance increases with synchronization error. While SSK is tolerant for a small range of synchronization error, GSSK, SM, and GSM are significantly impaired. Our results also demonstrate the dependence of SM on channel gain values. We observe that the lower the channel gain of the transmitter in which synchronization error occurs, the lesser the impact of the synchronization error on the system performance. <s> BIB018 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this letter, we propose an active-space, collaborative constellation-based generalized spatial modulation (GSM) multiple-input multiple-output encoding that can enhance the power efficiency of indoor visible-light communication compared with the conventional optical GSM. Simulation results verify that the proposed scheme can also achieve performance improvement compared with both spatial modulation and conventional GSM under the line-of-sight channel condition, particularly for higher values of spectral efficiency. <s> BIB019 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly, real and imaginary components of the complex time-domain OFDM signals are separated first, then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark, we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore, two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system, both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration. <s> BIB020 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, the bit error rate (BER) and the channel capacity of a multiple-input multiple-output (MIMO) system employing optical space shift keying (OSSK) scheme (termed as MIMO-OSSK) are investigated under combined effect of atmospheric turbulence (AT) and pointing errors (PEs). The analysis reveals that the diversity order of MIMO-OSSK remains intact over all AT regimes and under PE severity. This behavior is contrary to traditional pulse-based modulation schemes, where diversity order depends upon AT conditions and PE severity. In addition, the analysis also demonstrates that the MIMO-OSSK utilizes receiver diversity efficiently as compared to existing pulse-based modulations. In order to examine the effect of all ranges of AT along with PE severity on MIMO-OSSK, three different channel models are considered, i.e., log normal, gamma–gamma, and negative exponential. The probability density functions of the sum of squares of difference between two channel coefficients under these channel models are evaluated, to develop analytical expressions of average BER and ergodic channel capacity for the considered setup. On comparing MIMO-OSSK with the same rate MIMO-pulse amplitude modulation (MIMO-PAM) scheme employing repetition coding, it is observed that the MIMO-OSSK scheme outperforms the MIMO-PAM for a spectral efficiency of more than 2 b/s/Hz, provided that the number of receivers is sufficiently large. <s> BIB021 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this paper, the performance of optical spatial modulation (OSM) in the indoor multipath optical wireless channel is investigated. Multipath propagation of the transmitted signal results in the temporal dispersion which causes intersymbol interference (ISI) especially in high-speed communications. The OSM schemes have been investigated in line-of-sight (LOS) channels. However, given the recent trend in Gigabits/s communication, there is a need to investigate the impact of the neglected higher-order reflections. Two variants of OSM are explored as case studies: optical space shift keying and spatial pulse position modulation. The multipath-induced ISI is modeled to account for the spreading of the transmitted signal, and the analytical upper bound on the symbol error rate of both OSM schemes in the multipath channel is derived. The derived analytical bounds are validated by closely matching simulation results. Furthermore, using the spatial distributions of the multipath-induced power penalty, the LOS channel response and the delay spread across the room, we demonstrate how the interaction between these parameters impacts error performance. Multipath-induced ISI has a significant adverse impact on the performance of OSM schemes, particularly on the detection of the activated transmitter as the incurred ISI can alter the channel gain of the received symbol. <s> BIB022 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> In this letter, we propose the computationally efficient constellation design algorithms for single-mode and dual-mode joint generalized spatial modulations (JGSMs) to improve the symbol error rate (SER) performance over highly correlated indoor visible light communication channels. Our simulation results show that the proposed joint and improved dual-mode JGSMs can offer a better SER performance than the proposed single-mode JGSM (SM-JGSM) and the conventional SM-JGSM, which are validated through the analytical bounds. <s> BIB023 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Visible light communication (VLC) is regarded as one of the promising candidates to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously. Recently, VLC is combined with the generalized spatial modulation (GenSM) technology to improve spectral and energy efficiencies. In order to provide high-speed communication and flexible dimming control simultaneously, in this paper, a spectral-efficient GenSM-based hybrid dimming scheme with layered asymmetrically clipped optical OFDM is proposed for VLC, which combines the spatial-domain and time-domain dimming strategies. The channel capacities of the proposed scheme are analyzed and the closed-form expressions of the channel capacity are derived in both the rich scattering scenario and highly correlated scenario. According to the required illumination level, the spatial-domain and time-domain strategies are realized based on the maximization of the channel capacity. Simulation results substantiate the superior performance of the proposed dimming scheme over the state-of-art dimming schemes. <s> BIB024 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> B. SM in Optical Wireless Communications (OWC) <s> Recently, the spatial modulation (SM) technique has been proposed for visible light communication (VLC). This paper investigates the average symbol error rate (SER) for the VLC using adaptive spatial modulation (ASM). In the system, the analysis of the average SER is divided into two aspects: the error probability of the spatial domain and the error probability of the signal domain when the spatial domain is correctly estimated. Based on the two aspects, the theoretical expression of the average SER is derived. To further improve the system performance, an optimization problem is proposed to optimize the modulation orders on the LEDs. The ASM based and the candidate reduction (CR)-ASM based optimization algorithms are proposed to solve the problem, respectively. Numerical results show that the derived theoretical values of the average SER are quite accurate to evaluate the system performance. Moreover, compared with the existing schemes, the proposed two algorithms are better choices for VLC. <s> BIB025
In addition to mmWave communications discussed in the last subsection, OWC is another appealing complement to alleviate the shortage problem of wireless radio resources and achieve high data rate transmission BIB004 , which can be categorized into indoor and outdoor implementations depending on the communication range. For example, by deploying low-cost LEDs for the indoor environment, OWC can provide simultaneous energy-efficient lighting and high throughput transmission. As an efficient and inexpensive dual-use technology of illumination and communications, OWC enjoys a lot of advantages in both indoor and outdoor communications, such as cost efficiency, license-free implementation, large bandwidth, and high reliability. The primitive optical SM is developed in BIB001 for the indoor environment, which can be extended to various scenarios. In BIB009 , an optical SM is developed for outdoor optical communications to achieve a higher spectral efficiency and energy efficiency, where the analytical and simulation results of both uncoded and coded systems are presented under the turbulence induced fading. Based on coherent detection, a theoretical framework for error performance analysis is presented for both uncoded and coded optical SM systems over atmospheric turbulence characterized by HK distribution in BIB010 , which shows enhancement in performance, spectral efficiency and deployment cost. Under the consideration of atmospheric turbulence and pointing error, the error performance and mutual information of the optical SSK are studied over three different optical channel models BIB021 . Considering the inter-symbol interference incurred by delay spread, BIB022 studies the error behavior of the optical SM over indoor multipath optical channels, whose upper bound on error performance is also derived. With CSI available at the transmitter, BIB017 proposes an optical SM based on the constellation optimization, whose minimum Euclidean distance is maximized at the receiver. To deal with the adverse effect on the detection of optical SM incurred by the high channel correlation, an optical SM based on the power imbalance is proposed for OWC in BIB011 , which optimizes the constrained capacity using power allocation. In BIB002 , the error performance of the SM aided OWC system is investigated over the indoor environment characterized by LOS components, which outperforms the repetition coding aided OWC system. In BIB013 , the mutual information and its corresponding lower bound of the SM aided OWC system are theoretically calculated under the MISO and finite input alphabet setting. Based on these theoretical results, the optimal precorder is designed to maximize the minimum Euclidean distance. An enhanced optical SM scheme is proposed for indoor OWC in BIB003 , which aligns multiple transmit-receive units to achieve higher SNR gains. Under the consideration of imperfect synchronization at the transmitter, the theoretical error performance of several variants of optical SM is derived for OWC in BIB018 , which provides some insightful information about the effect of synchronization error. For indoor environments, optical wireless communications can be deployed as VLC for simultaneous luminance and communication. In particular, as one indoor implementation of OWC, VLC is an attractive alternative to apply in some RF-free working environments, e.g., hospital, airplane, and gas station BIB012 , BIB014 . Due to the wide application of LED array comprising a large number of LEDs for sufficient illumination, MIMO technology can be readily integrated into VLC to achieve high transmission rates, where various representative MIMO aided VLC schemes have been investigated and compared in BIB005 . Thanks to its capability of supporting fast switching in LEDs, SM aided VLC can be deployed, which activates a single LED only in the LED array for each channel use to convey index information additionally through the location of the active LED. Moreover, by adjusting the number of active LEDs and the intensities, both (G)SSK and (G)SM provide the flexibility to control the luminance of the LED array and the communication throughput. To attain higher power efficiency, an enhanced optical (G)SM scheme based on the collaborative constellation pattern is developed for indoor VLC in BIB019 - BIB023 . Using the ML-based photodetectors, the theoretical and experimental results of (G)SSK are presented for the short-range indoor VLC in BIB006 and BIB007 . The error performance of (G)SM aided VLC systems is presented with an analytical upper bound on BER in BIB008 . Exploiting available CSI at the transmitter for interchannel interference reduction, an optical SM based on channel adaption is designed to apply in massive MIMO-VLC in BIB015 . Moreover, the combination of optical SM and layered space-time coding is designed for VLC by mapping the spatial information into different space-time coding matrices. To achieve the control flexibility on luminance and the data throughput, a (G)SM aided hybrid dimming strategy using clipped optical OFDM is designed for VLC in BIB024 , whose achievable rate is theoretically analyzed over channels with dense scattering and high correlation, respectively. To achieve a flexible design with an arbitrary number of transmit antennas for SM, a three-domain bit mapping solution based on channel adaptation is suggested in BIB025 , whose lower bound on achievable rate is also obtained in closed-form. Noticing the real and positive constraint on light intensity levels in intensity modulation/direct detection system, the authors of BIB020 and BIB016 successfully apply the (G)SM principle to the optical MIMO-OFDM system, which exploits the advantage of SM based LED to avoid Hermitian symmetry and direct current (DC) bias. Specifically, each complex OFDM signal are split into four components consisting of the real-imaginary and positive-negative parts and then encoded by four LEDs for transmission, which dispenses with DC biasing/asymmetrical clipping BIB020 .