Conventional Spatial Modulation Research Articles

Transmit antenna selection for multi-user VASM systems: Simplicity and fairness

Variable Active Antenna Spatial Modulation (VASM) systems have been shown to offer higher spectral efficiency and greater flexibility than conventional spatial modulation systems. In VASM systems, since a part of the information is carried on the indices of activated antennas, the transmit antenna selection (TAS) problem significantly impacts the systems’ quality. In this article, we propose two new TAS methods for multi-user VASM systems, namely, Hi-TAS and ObO-TAS. Specifically, Hi-TAS aims to reduce the system’s computational complexity, which is a hierarchical combination of two popular TAS methods, i.e., channel gain-based TAS (CG-TAS) and Euclidean distance-based TAS (ED-TAS). Meanwhile, the ObO-TAS alternately chooses each transmit antenna one by one for every user to ensure fairness among them. In addition, we propose the idea of reusable TAs to improve the quality of the system. The calculation and simulation results show that the proposed Hi-TAS has a computational complexity of only 7.74% compared to ED-TAS while achieving better average bit error rate performance for the system than ED-TAS. The proposed ObO-TAS also demonstrates the advantage of ensuring fairness among users, namely that the difference in bit error rate among users is very small compared to other TAS methods.

Low complexity deep neural network based transmit antenna selection and signal detection in SM-MIMO system

In this paper, with the investigation of the conventional Euclidean distance based transmit antenna selection (ED-AS) and the maximum likelihood detection (MLD) in spatial modulation (SM) multiple-input multiple-output (MIMO) system, we propose the deep neural network (DNN) based transmit antenna selection (DNN-AS) and signal detection (DNN-SD), respectively, to effectively balance the system performance and the complexity. For the proposed DNN-AS, we transform the existing problem of AS into a prediction problem and design a low dimension multi-output classifier to achieve the low complexity solution of AS. For the DNN-SD, we present two sub-DNNs to recover the transmitted SM signal. Numerical results reveal that the proposed DNN-AS scheme gets a better average bit error rate (ABER) performance than the typical AS schemes in SM-MIMO system with lower complexity. In contrast to the ED-AS approach, it attains the optimal and suboptimal ABER performance at low-and-moderate signal-to-noise ratio (SNR) region and high SNR region, respectively. The proposed DNN-AS scheme achieves obvious SNR gains compared with the conventional SM system and gets about 3.5 dB gains over the typical maximum-norm based AS (Norm-AS) algorithm. Furthermore, the proposed DNN-SD scheme obtains a superior detection performance compared with the conventional linear detection methods and provides the same ABER performance as the optimum MLD scheme in the presence of correlated noise.

High mobility enabled spatial and media‐based modulated orthogonal frequency division multiplexing systems for beyond 5G wireless communications

SummaryThis paper introduces the concept of spatial and media‐based modulated (SMBM) orthogonal frequency division multiplexing (OFDM) as a potential candidate for highly mobile next generation beyond 5G (B5G) wireless communications. The proposed SMBM‐OFDM technique utilizes not only the transmit antenna and channel state indices but also OFDM subcarriers to improve the system performance under high mobility. In addition, this study sheds light on challenging fast time‐varying channel estimation problem of MBM‐based systems by using the linear minimum mean square error (LMMSE) approach due to its optimality to investigate the achievable system performance with the aid of basis expansion modeling. The minimum lower bound on the channel estimation error (Bayesian Cramer–Rao bound) is derived theoretically and shown to be attainable by the considered LMMSE estimator. Moreover, symbol detection performance is provided for different modulation types and higher mobile velocities. Simulation results demonstrate that SMBM‐OFDM system under high mobility is able to provide around 12‐dB performance gains in terms of both channel estimation and symbol detection error compared to conventional spatial modulation (SM)‐OFDM systems without MBM. The presented framework is important due to addressing the high mobility support of SMBM‐OFDM systems for B5G wireless communications in terms of achievable channel estimation and data detection performance.

An Effective Spatial Modulation Based Scheme for Indoor VLC Systems

We propose an enhanced spatial modulation (SM)-based scheme for indoor visible light communication systems. This scheme enhances the achievable throughput of conventional SM schemes by transmitting higher order complex modulation symbol, which is decomposed into three different parts. These parts carry the amplitude, phase, and quadrant components of the complex symbol, which are then represented by unipolar pulse amplitude modulation (PAM) symbols. Superposition coding is exploited to allocate a fraction of the total power to each part before they are all multiplexed and transmitted simultaneously, exploiting the entire available bandwidth. At the receiver, a two-step decoding process is proposed to decode the active light emitting diode index before the complex symbol is retrieved. It is shown that at higher spectral efficiency values, the proposed modulation scheme outperforms conventional SM schemes with PAM symbols in terms of average symbol error rate (ASER), and hence, enhancing the system throughput. Furthermore, since the performance of the proposed modulation scheme is sensitive to the power allocation factors, we formulated an ASER optimization problem and propose a sub-optimal solution using successive convex programming (SCP). Notably, the proposed algorithm converges after only few iterations, whilst the performance with the optimized power allocation coefficients outperforms both random and fixed power allocation.

Spatiotemporal Fourier transform with femtosecond pulses for on-chip devices

On-chip manipulation of the spatiotemporal characteristics of optical signals is important in the transmission and processing of information. However, the simultaneous modulation of on-chip optical pulses, both spatially at the nano-scale and temporally over ultra-fast intervals, is challenging. Here, we propose a spatiotemporal Fourier transform method for on-chip control of the propagation of femtosecond optical pulses and verify this method employing surface plasmon polariton (SPP) pulses on metal surface. An analytical model is built for the method and proved by numerical simulations. By varying space- and frequency-dependent parameters, we demonstrate that the traditional SPP focal spot may be bent into a ring shape, and that the direction of propagation of a curved SPP-Airy beam may be reversed at certain moments to create an S-shaped path. Compared with conventional spatial modulation of SPPs, this method offers potentially a variety of extraordinary effects in SPP modulation especially associated with the temporal domain, thereby providing a new platform for on-chip spatiotemporal manipulation of optical pulses with applications including ultrafast on-chip photonic information processing, ultrafast pulse/beam shaping, and optical computing.

Filter-Enhanced Spatial Modulation and Multiplexing in Indoor Optical Wireless Systems

Optical wireless communication (OWC) systems have been widely studied to provide high-speed connections in indoor environments. In this paper, we propose a filter-enhanced indoor OWC system with hybrid spatial modulation (SM) and spatial multiplexing (SMUX) to further increase the data rate. The filter-enhanced SM enables extra information be transmitted via the spatial indices of OWC transmitters, and the SMUX further increases the data rate via the parallel transmission of multiple signals even under highly-similar channels. The proposed scheme is experimentally demonstrated. Up to 35 Gb/s data rate can be achieved with 2.5 GBaud/s symbol rate and four transmitters. Compared with the filter-enhanced SM scheme, the achievable data rate can be increased by 100%. Compared with the conventional SM and SMUX, the bit-error-rate (BER) is improved by over two orders-of-magnitude.

RIS-Assisted Advanced Spatial Modulation Techniques for Ambient Backscattering Communications

The dynamic control of wireless channels is a trending field of research which has been made possible by the advent of metamaterial-based reconfigurable intelligent surfaces (RIS). Moreover, for future applications in 5G and beyond, the device size constraints and power supply issues also need to be resolved before RIS can be deployed at large scale. Keeping these problems in mind, we propose RIS-assisted ambient backscattering (ABSc) communication framework utilizing advanced spatial modulation (ASM) techniques for spectral- and energy-efficient communication. Here, ABSc technique is leveraged for harnessing the power from ambient RF waves, while ASM techniques are deployed to ensure high spectral efficiencies by activating more than one but not the full set of antennas for transmission. Extensive performance analysis of ASM techniques are carried out, and upper-bounds on the ensuing error rates are derived. We corroborate the error rate upper-bound results with Monte-Carlo simulation results, and also provide comparative results to reveal the benefits of the proposed framework. In particular, it is shown that the ASM technique of improved quadrature spatial modulation (IQSM) can achieve the highest spectral efficiency. All the ASM techniques can perform better than the conventional spatial modulation technique by offering signal-to-noise power ratio gains of more than 2 dB. Additionally, RIS-assisted ASM techniques with ABSc perform better than the conventional frameworks without RIS.

Differential Transmission Schemes for Generalized Spatial Modulation

Differential modulation schemes are very relevant in receivers having power and processing limitations, as these schemes dispense with the need for knowledge of channel coefficients for symbol detection. Spatial modulation (SM) is a scheme used in multi-antenna transmission scenarios where the data is transmitted in the amplitude, phase and spatial domains through selected antennas. In the coherent domain, generalized SM (GSM) employs multiple antennas in combination during every time slot to enhance the spectral efficiency (SE). In this paper, we propose two differential schemes which activate two or more antennas at a time to transmit the modulated symbol. These schemes achieve higher SE using a lesser number of antennas and lower order modulation schemes instead of the higher number of antennas required for conventional SM schemes based on differential modulation. Simulation studies reveal that the proposed schemes have better bit error rate performance than traditional differential SM schemes. We also derive the analytical union bound for the proposed schemes and is satisfied from medium to high signal-to-noise ratio (SNR) ranges.

Performance Analysis of Spectrally Efficient Adaptive Spatial Modulation in MIMO System by using QAM

Abstract: In this article, we proposed a multiple input multiple outputs (MIMO) technique such as spectrally efficient adaptive quadrature spatial modulation (SEAQSM) which is based on space modulation techniques (SMTs). SMTs are logarithmically proportional to transmitting antenna & this technique fulfills the requirement of high data rate in the MIMO system. The Spatial position of the transmitting antenna improves the performance of the MIMO system. In space modulation technique spectral efficiency is logarithmically proportional to transmit antenna, if we increase the antenna at the transmitter end then the bandwidth efficiency significantly improved. We have to improve the performance MIMO system, minimize the latency and low power consumption. The proposed technique performance is explored over Rayleigh fading channel for a particular MIMO. These techniques underestimate the transmit antennas with less RF chain. In this paper, we analyzed the performance of our proposed scheme with conventional SM and QSM by using MONTE CARLO Simulation in term of BER with distinct order of QAM symbol. SE acquired for varying SNR at a BER of 10−3are obtained for uncorrelated Rayleigh channel. Keywords: Spatial Modulation(SM), MIMO, Spectral efficiency, Energy efficiency, Quadrature Spatial Modulation (QAM), Maximum Likelihood (ML) detector.

Virtual Spatial Channel Number and Index Modulation

This paper proposes a novel precoding-aided and efficient data transmission scheme called virtual spatial channel number and index modulation (VS-CNIM), which conveys extra data by changing both the number and index of active virtual parallel channels of multiple-input multiple-output (MIMO) channels, obtained through the singular value decomposition (SVD) in each time slot. Unlike the conventional virtual spatial modulation (VSM), where extra data bits are transmitted only using index of active virtual parallel channels, the VS-CNIM scheme, depending on incoming information bits, transmits extra bits utilizing both the number and indices of active parallel channels along the bits carried by M -ary constellation symbols. Therefore, VS-CNIM provides significantly superior spectral efficiency (SE) compared to VSM. Considering the influence of imperfect channel estimation, a closed-form upper bound is derived on average bit error probability (ABEP). The asymptotic performance is also analyzed, which gives the coding gain and diversity order and describes error floor under the consideration of perfect and imperfect channel estimation, respectively. Monte Carlo simulations exhibit that the VS-CNIM scheme achieves considerably better error performance and high SE than precoding-aided SM (PSM) and VSM schemes.

Highly stable measurement for nanoparticle extinction cross section by analyzing aperture-edge blurriness.

In order to stabilize the extinction cross section measurement of a single nanoparticle, we propose to analyze the blurriness parameter of aperture edge images in real time, which provides a feedback to lock the sample position. Unlike the conventional spatial modulation spectroscopy (SMS) technique, a probe beam experiences both the spatial modulation by a piezo stage and the temporal modulation by a chopper. We experimentally demonstrate that the measurement uncertainty is one order magnitude less than that in the previous report. The proposed method can be readily implemented in conventional SMS systems and can help to achieve high stability for sensing based on light extinction by a single nanoparticle, which alleviate the impact from laboratory environment and increase the experimental sensitivity.

Multi-Antenna Selection for Double Spatial Modulation

In this paper, to exploit the spatial domain of transmit antennas (TAs) for the transmit diversity gain in the double spatial modulation (DSM) system, a new scheme of multi-antenna selection for DSM (MAS-DSM) is designed. In the MAS-DSM system, the number of TAs are grouped into n groups, each of which corresponds to an sub-system of DSM. More specifically, a transmitted spatial vector is constructed by two spatial vectors (SVs). For the achievability of transmit diversity gain, one of the two SVs is obtained by using n antenna index (AI) vectors to modulate a data symbol, another of them is obtained by multiplying with a rotation angle after another n AI vectors to modulate another data symbol. Finally, the spectral efficiency and the average bit error ratio (BER) are analyzed. Simulation results by using Monte Carlo demonstrate that the proposed MAS-DSM system has better BER performance compared with the conventional spatial modulation schemes in wireless communication network.

Norm-based user selection algorithm for single-RF space modulation techniques with geometric mean decomposition based precoding scheme

Joint user selection algorithm and fully digital geometric mean decomposition (GMD)-based precoding scheme is considered in this paper for single radio frequency (RF) space modulation techniques (SMTs), namely, spatial modulation (SM) and space shift keying (SSK) schemes. The objective is to jointly perform the Frobenius norm-based user selection algorithm and design GMD-based precoded SMTs with single-RF chain in order to reduce the cost and the power consumption in multiple input multiple output (MIMO) systems, and to avoid the complicated bit-allocation problem of singular value decomposition (SVD)-based precoding technique. Based on these schemes, the GMD-based precoding transmission carried out in the context of a single-user SMTs can readily be extended to the multi-user (MU) case. Simulation results demonstrate that single-RF SMTs with GMD-based precoding scheme is capable of outperforming SMTs with SVD-based precoding technique. Meanwhile, MU-SMTs with GMD-based precoding scheme provide significant performance gains over the conventional SM- and SSK-MIMO counterparts and single-user SMTs with GMD-based precoding algorithm, which increase the energy efficiency and the reachability using these schemes. Furthermore, better error performance in MU-SMTs with fully digital GMD-based precoding technique is obtained by selecting any number of users. Therefore, MU-SMTs with GMD-based precoding scheme can be effectively used in various 5G wireless networks.

Joint Power Allocation Scheme for Distributed Secure Spatial Modulation in High-Speed Railway

In this article, a distributed secure spatial modulation (DSSM) is proposed to improve the secrecy performance of transmission system in high-speed railway (HSR) scenario. N-remote antenna units are connected with central processing unit to build a cooperative DSSM system. Considering the influences of correlated shadow fading, spatial-temporal correlated fading and Doppler shift, the expressions of secrecy capacity (SC) and bit error rate (BER) are derived. Based on the design of artificial noise, two power allocation algorithms are jointly proposed as security schemes in HSR scenario. At first, a joint optimal secrecy capacity algorithm (JOSCA) is proposed to maximize SC. Another Lagrange constraint extreme algorithm (LCEA) is proposed to maximize inhibition of eavesdropper's BER performance. The numerical results show that compared to conventional spatial modulation, the proposed DSSM with JOSCA brings higher SC and keeps a high value of cooperative SC as the advance of train. Moreover, the proposed LCEA brings better BER performance of legitimate receiver while greatly limiting that of eavesdropper. In terms of the tradeoff between SC and BER, the DSSM gets better balance at the viaduct of high-speed railway scenario.

Covert Information Embedded Spatial Modulation

In this letter, we propose a new convert information embedded spatial modulation (SM) system for secure communications, in which the transmitter tries to send covert information to the specific receiver while keeping the unintended receiver unaware of the transmission. In the proposed system, the covert information bits are conveyed via the activated antenna index while the common information bits are via the modulation symbols. Specifically, the convert information modulation is achieved by carefully designing the space-time mapping principle so that it is disguised as a conventional SM antenna index. Furthermore, an efficient detection scheme is designed for the proposed system. The simulation results show that the proposed scheme with the developed receiver can offer nearly the same performance gain as conventional SM, whereas the unintended receiver can hardly detect the information correctly. Moreover, the average bit error rate (BER) is analyzed, which also validates our simulation results.

Performance analysis of M‐APSK generalised spatial modulation with constellation reassignment

SummaryGeneralised spatial modulation (GSM) is a recently developed multiple‐input multiple‐output (MIMO) technique aimed at improving data rates over conventional spatial modulation (SM) systems. However, for identical antenna array size and configurations (AASC), the bit error rate (BER) of GSM systems in comparison with SM systems is degraded. Recently, a GSM system with constellation reassignment (GSM‐CR) was proposed in order to improve the BER of traditional GSM systems. However, this study focused on M‐ary quadrature amplitude modulation (M‐QAM) schemes. The focus of this paper is the application of a circular constellations scheme, in particular, amplitude phase shift keying (APSK) modulation, to GSM and GSM‐CR systems. An analytical bound for the average BER of the proposed M‐APSK GSM and M‐APSK GSM‐CR systems over fading channels is derived. The accuracy of this bound is verified using Monte Carlo simulation results. A 4 × 4 16‐APSK GSM‐CR system achieves a gain of 2.5 dB at BER of 10−5 over the traditional 16‐APSK GSM system with similar AASC. Similarly, a 6 × 4 32‐APSK GSM‐CR system achieves a gain of 2 dB at BER of 10−5 over equivalent 32‐APSK GSM system.

Design and performance analysis of indoor cooperative IHDAF protocol-based spatial modulation-index modulation visible light communication system.

Spatial modulation (SM) has been employed in indoor visible light communication (VLC) systems because of its high data rate and low complexity transmission. However, the activated LED may have poor channel conditions in conventional SM VLC systems, which leads to significant performance degradation. In this paper, a cooperative incremental hybrid decode-amplify-forward (IHDAF) protocol-based SM-index modulation (SM-IM) VLC system is proposed. For the SM-IM scheme, the spatial information and the modulated information are jointly transmitted in one symbol via the optimal VLC channel. The system model and the theoretical outage probability of the proposed IHDAF protocol-based SM-IM VLC system are presented. Numerical results show that the outage probability of the IHDAF protocol-based SM-IM VLC system can be significantly improved compared with the traditional amplify-and-forward and decode-and-forward protocol-based SM VLC systems. Additionally, the power allocation of the proposed scheme is also studied.

Generalized Code Index Modulation and Spatial Modulation for High Rate and Energy-Efficient MIMO Systems on Rayleigh Block-Fading Channel

In this article, a high data rate and energy-efficient multiple-input multiple-output transmission scheme is considered by combining two popular and rational modulation techniques: spatial modulation (SM) and code index modulation-spread spectrum (CIM-SS). Since in the considered system, called generalized CIM-SM (GCIM-SM), incoming information bits determine modulated symbols, activated transmit antenna indices as well as their corresponding spreading code indices, data bits are conveyed not only by modulated symbols but also by the indices of the active antenna and spreading codes. Hence, a GCIM-SM scheme accommodates faster data rates while spending less transmission power and possessing better error performance compared to the conventional direct sequence spread spectrum (DS-SS), SM, quadrature SM (QSM), and CIM-SS systems. The mathematical expressions of the GCIM-SM system for bit error rate, throughput, energy efficiency, and the system complexity are derived to analyze the overall system performance. Besides, it has been shown via computer simulations that the GCIM-SM system has lower transmission energy, faster data transmission rate, and better error performance than DS-SS, SM, QSM, and CIM-SS systems. Performance analysis of the considered system was performed on Rayleigh block-fading channels for quadrature amplitude modulation technique.

Channel correlation relied grouped spatial modulation for massive MIMO systems

Massive multiple-input multiple-output (MIMO) systems with hundreds of correlated antennas at base station are capable of offering abundant spatial resources. When spatial-domain modulation is applied to these systems, the spatial modulation (SM) using only one radiofrequency chain benefits practical implementation, but suffers from significantly reduced multiplexing gain offered by the massive number of antennas. By contrast, the generalised SM (GSM) allows to simultaneously activate multiple transmit antennas, which improves spatial multiplexing gain, but degrades the achievable error performance, as its design pays no attention to the antenna correlation. The authors propose an antenna grouped SM (GrSM) scheme, which is capable of circumventing the shortcomings of both the SM and GSM schemes suffered in massive MIMO scenarios. In the proposed GrSM scheme, transmit antennas are partitioned into multiple groups, where the relatively strongly correlated antennas within individual groups are used to implement component SM schemes, while the relatively weakly correlated antennas in different groups are beneficial to obtain multiplexing gain. In order to further improve the spectral efficiency, adaptive modulation is integrated with GrSM to form the adaptive GrSM (AGrSM). The achievable error and spectral efficiency performance of GrSM and AGrSM systems are investigated based on both mathematical analysis and Monte-Carlo simulations, which are also compared with that of the conventional SM and GSM schemes, when massive MIMO communication scenarios are considered. Their studies and performance results show that GrSM is a promising transmit scheme for massive MIMO, which can outperform both the SM and GSM schemes.

Block-Based Spatial Modulation: Constellation Design and Low-Complexity Detection

Spatial modulation (SM) uses antenna indices to transmit information, along with modulation symbols. The conventional SM scheme fixes the number of active antennas, and consequently the number of transmit symbols, in a transmit vector to avoid detection ambiguity. This work proposes a generalized block-based spatial modulation (GBSM) scheme which varies the number of active antennas in each transmit vector, but fixes their number over a transmission block. The proposed GBSM scheme, which transmits information using the spatial dimensions created over a block of transmit vector, resolves detection ambiguity as the number of transmit symbols over a block remains fixed. It crucially also has a large constellation cardinality, which we exploit by proposing novel low bit error rate (BER) constellation design algorithms. We also propose a novel low-complexity semi-definite relaxation detector, which has similar BER as that of the optimal maximum likelihood detector but with ≈ 85% lower complexity.