Spatial Modulation Scheme Research Articles

Adaptive Spatial Modulation for Indoor Visible Light Communications

Visible light communication (VLC) exhibits rapid development tendency in recent years since it has many attractive features such as its low cost, electromagnetic interference-free and license-free spectrum. In this work, we consider the indoor VLC system with single mobile user. Due to mobility, the distance between the activated light-emitting diode (LED) and receive photodiode (PD) is varied. Under the assumption of random direction (RD) mobility model, we derive the probability density function (PDF) and the cumulative distribution function (CDF) of received electrical signal-to-noise ratio (SNR) for the mobile user. The adaptive spatial modulation (ASM) scheme with two adaptive mechanisms is developed where the modulation size can be dynamically changed based on the derived CDF and pre-specified switching threshold. Simulation results demonstrate that the proposed scheme can balance the trade-off in terms of spectral efficiency and link robustness.

Differential optical spatial modulation with pulse position modulation over atmospheric turbulence

Optical spatial modulation (OSM), a recent optical multiple-input multiple-output transmission scheme in wireless optical communication, has aroused great research interests. OSM scheme requires accurate channel state information (CSI) during transmitter and receiver sides, but it is difficult to accurately estimate CSI in OSM scheme. Therefore, a scheme named differential optical spatial modulation scheme with pulse position modulation (DOSM-PPM) based on the space-time mapping block of orthogonal design is proposed in order to completely avoid CSI estimation. The bit error rate (BER) performance of DOSM-PPM is analyzed under log-normal turbulent channel model and simulated using Monte Carlo method. The results show that the transmission rate of DOSM-PPM is improved effectively. Meantime, the proposed DOSM-PPM scheme outperforms DOSM scheme with spatial pulse amplitude modulation by 1 dB at 1 × 10 − 3 BER with the same spectrum efficiency.

Variable-Block-Length Joint Channel Estimation and Data Detection for Spatial Modulation Over Time-Varying Channels

We propose novel variable-block-length joint channel estimation and data detection for spatial modulation over time-varying channels, where the data frame is divided into multiple blocks, and channel state information (CSI) is estimated in a block-by-block manner. More specifically, in each block maximum-likelihood-based data detection and channel estimation are iteratively carried out, where the detected data block is used as a long pilot sequence to update CSI. Our simulation results demonstrate that the performance of the proposed scheme is capable of approaching that of a perfect-CSI scenario. Moreover, the proposed scheme outperforms the recent rectangular differential spatial modulation scheme, without any substantial cost in terms of the preamble overhead and detection complexity.

Indoor optical wireless communication system with filters-enhanced generalized spatial modulation and carrierless amplitude and phase (CAP) modulation.

The spatial modulation principle has been widely studied in indoor optical wireless communication (OWC) systems to provide high-speed connections to users by encoding part of data in the spatial domain. To further increase the speed and to eliminate the requirements of accurate channel state information (CSI) and low channel correlation, in this Letter we propose and demonstrate an indoor OWC system with a filters-enhanced generalized spatial modulation (FE-GSM) scheme and 16-carrierless amplitude and phase (16-CAP) modulation. The 16-CAP increases the data rate in symbol domain, and the FE-GSM scheme allows activating multiple transmitters simultaneously to increase data rate in the spatial domain. Experimental results show that using a 2.5 GBaud/s indoor OWC system with three transmitters, 15 Gb/s data rate is achieved even under identical channels without pre-known CSI. The demonstrated scheme provides a promising solution to increase data rate in indoor OWC systems.

Differentially-Encoded Rectangular Spatial Modulation Approaches the Performance of Its Coherent Counterpart

A simplified rectangular differential spatial modulation (S-RDSM) scheme is conceived for massive multiple-input multiple-output (MIMO) systems dispensing with the channel state information (CSI). In the proposed S-RDSM scheme, the information bits are first mapped to a conventional SM symbol and then rectangular differential encoding is invoked between a pair of SM symbols. Then a non-coherent detector relying on a forgetting factor is developed, which requires no CSI at the receiver. Explicitly, a low-complexity hard limited maximum likelihood (HL-ML) detector is conceived for our generalized S-RDSM scheme, which is characterized by our theoretical analysis. Furthermore, we derive the optimal forgetting factor in closed form, which is capable of significantly reducing the complexity of the associated optimization. Finally, the upper bounds of the average bit error probability (ABEP) are derived using the moment generating function (MGF), and are validated by our simulation results. Both the theoretical and simulation results have shown that the proposed S-RDSM system outperforms the existing non-coherent schemes, despite operating at 10% of the benchmarker’s complexity, whilst approaching the performance of its coherent SM counterpart at a comparable complexity.

C‐MRC–based cooperative spatial modulation with antenna selection

SummaryA new high‐performance low‐complexity cooperative maximal ratio combining (C‐MRC)‐based cooperative relaying scheme, which is called antenna selection‐aided cooperative spatial modulation scheme with C‐MRC (AS‐CSM), is proposed for decode and forward (DF)‐based cooperative relaying networks operating over independent but non‐identically distributed (i.n.d.) Rayleigh fading channels. The AS‐CSM scheme is formed with the combination of cooperative SM with the high‐performance low‐complexity coherent demodulator C‐MRC and antenna selection techniques. In the AS‐CSM scheme, the information is transmitted from the source terminal (ST) to the relay terminal (RT) and the destination terminal (DT) in the form of not only modulated symbols but also antenna indices, which carry additional information bits in the spatial domain. Therefore, a high spectral efficiency is obtained by the proposed scheme for cooperative relaying networks. In this scheme, first, the index of the activated antenna of ST is estimated, and the best antenna selection at RT is investigated considering the received instantaneous equivalent to signal‐to‐noise values acquired at DT. The transmitted symbols are estimated with low‐complexity coherent demodulator C‐MRC at DT by using the noisy signals from ST and RT. An exact closed‐form expression for the bit error probability (BEP) of the AS‐CSM scheme is derived, and the theoretical results are validated with Monte‐Carlo simulation results.

Generalized Space Time Block Coded Spatial Modulation for Open-Loop Massive MIMO Downlink Communication Systems

In this paper, we propose a generalized space-time block coded spatial modulation (GSTBC-SM) scheme for open-loop massive multiple-input and multiple-output (MIMO) downlink communication systems. Specifically, we firstly partition the information bits into multiple groups with each group modulated by the spatial modulation (SM), where the SM symbols are invoked for orthogonal STBC (OSTBC) and quasi-orthogonal STBC (Q-OSTBC) structures. Then, message passing (MP) and block minimum mean square equalization (B-MMSE) detectors are designed for our GSTBC-SM systems, to achieve near-optimal performance with significantly reduced complexity in massive MIMO configurations. Finally, we derive the theoretical average bit error probability (ABEP) of the proposed scheme. The main contribution is that the propose scheme achieves high transmission rate and diversity gain even with small number of radio frequency (RF) chains at the transmitter. Simulation results verify the theoretical derivations and show that the proposed GSTBC-SM scheme provides near 20 dB gain over the conventional GSTBC scheme under massive MIMO configurations.

Secure transmission via random quadrature spatial modulation

AbstractIn this article, we propose a random quadrature spatial modulation (RQSM) scheme to achieve secure transmission in multiple‐input multiple‐output multiantenna eavesdropper channels. We consider the case in which the eavesdropper has more antennas than that of the legitimate receiver, leading to a strong wiretap channel. In this case, the conventional secure quadrature spatial modulation schemes based on the artificially interfering signals are vulnerable to eavesdropping. On the contrary, the proposed RQSM scheme is able to achieve the physical‐layer security without transmitting artificial noises. Specifically, the bits‐to‐symbol mapping of the proposed RQSM is randomized according to the instantaneous channel state information of the legitimate link. Since in a rich scattering environment, the legitimate and the wiretap channels are generally independent of each other due to the spatial decorrelation property. Thus, the eavesdropper can be considered ignorant of the legitimate channel and cannot decode the confidential messages correctly. We derive the ergodic secrecy rate of the proposed RQSM scheme and show that the secrecy performance does not degrade as the number of antennas at the eavesdropper increases, which also outperforms the conventional jamming strategies. In addition, the bit error rate of the RQSM is also analyzed, which shows that security is achieved without sacrificing the system's reliability. Numerical results validate the theoretical derivations and demonstrate the effectiveness of the proposed RQSM scheme.

Design and Performance Analysis of LED-Grouping Based Spatial Modulation in the Visible Light Communication System

In this paper, a light emitting diode grouping based spatial modulation (LGSM) scheme is investigated for the indoor visible light communication (VLC) system for a better symbol error rate (SER) performance with the aid of characteristics of the spatial modulation. In consideration of the high channel correlation property of the visible light communication, the multiple transmitting LEDs are separated into different groups with the purpose of alleviating the channel correlation among each group. Owing to the proposed grouping scheme, the spatial information and channel correlation property can be perfectly utilized to improve the system performance of SER, which implies a higher transmission capability by the proposed LGSM scheme. Meanwhile, the mathematical derivation of SER for the proposed LGSM scheme is also provided by considering the maximal likelihood detection. Both of the simulated and theoretical results have proved that a better SER performance can be obtained via the proposed LGSM scheme compared with the common spatial modulation VLC system. Furthermore, the influence of the elevation angle of the receive photo detector in the LGSM VLC system is also investigated.

Joint-Mapping-Based Variable Active Antenna Spatial Modulation

Spatial modulation (SM) maps information to both spatial dimensions (active antenna indices) and conventional 2D ${M}$ -ary symbols. The existing SM schemes use fixed number of active antennas in each transmit vector as varying them causes detection ambiguity. Motivated by this, we introduce a new joint-mapping based variable active antenna spatial modulation scheme, which varies the number of active antennas in each transmit vector. It alleviates detection ambiguity by jointly mapping information to the complete 3D constellation consisting of active antenna indices (spatial dimension) and the 2D ${M}$ -ary symbols. This is unlike the existing SM schemes which separately map information to the active antenna indices and the 2D symbols. This idea enables us to i) avoid detection ambiguity; and ii) achieve low bit error rate and comparable maximum likelihood detection complexity as that of existing SM schemes.

AF relay assisted multiuser MIMO‐DQSM downlink transmission system

This Letter presents an amplify and forward (AF) relay assisted multiuser multiple input-multiple output (MU-MIMO) downlink transmission system based on a double quadrature spatial modulation (DQSM) scheme. The authors analyse and compared the bit error rate performance of the proposed AF-MU-MIMO-DQSM system with its conventional counterpart AF-MU-MIMO system, which uses quadrature amplitude modulation/phase shift-keying modulation. Results show that the utilised technique can effectively cancel the interference produced by multiple users and multiple relays in the system. The proposed AF-MU-MIMO-DQSM system has up to 2 dB gain compared with the conventional system for the analysed cases.

Multi-User Differential Spatial Modulation scheme for massive MIMO uplink communications

Spatial Modulation (SM) is a Multi-Input Multi-Output (MIMO) transmission technique where only one antenna transmits data in each transmission interval, leading to a reduction in the number of RF chains and transmission power. The application of SM in Massive MIMO systems relies on perfect channel estimation, which is a fundamental challenge in these systems. Differential Spatial Modulation (DSM) is a method proposed to avoid channel estimation challenges. However, the conventional square DSM cannot easily be applied to multi-user communication applications. In this paper, a novel Multi-User Differential Spatial Modulation (MU-DSM) transmission scheme is proposed for multi-user massive MIMO uplink communications. Moreover, for the proposed transmission scheme, a non-coherent MU-DSM detector is presented. As demonstrated in the analytical and simulation results, the proposed MU-DSM scheme performs very close to its coherent counterpart where perfect channel information is available.

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.

Precoding-Aided Secure Time-Domain Index Modulation

In this letter, we propose a generalized precoding-aided secure time-domain index modulation (PSTD-IM) scheme for enhancing the rate and secrecy of the system. Unlike in the conventional time-domain index modulation (TD-IM), where a single (or a set of) Nyquist pulse is activated over multiple symbol periods at the transmitter, in this letter, the pulse (or the set of pulses) is activated at the legitimate receiver, thereby securing the information transfer. In addition, we project artificial noise (AN) onto the null space of the legitimate user and degrade the signal-to-noise-ratio (SNR) at the eavesdropper. In fact, we propose the above-discussed generalized PSTD-IM for a multi-user downlink scenario, where each user is expected to receive an independent TD-IM symbol. We analyze the secrecy rate and derive a closed-form expression for an upper bound on the average bit error rate (ABER) of the proposed scheme. Further, we show that the proposed scheme achieves transmit diversity as opposed to the existing spatial modulation schemes.

Opto-Electron Eng, 2020, 47(3)] Research status and development of optical spatial modulation technology

Optical spatial modulation (OSM), a new optical multiple input multiple output (OMIMO) technique, effectively improves the transmission rate and energy efficiency by using the spatial domain laser index to carry additional information. Meantime, since only one laser is activated per symbol duration to transmit information, the problems of channel interference and synchronization are solved in traditional OMIMO system. This paper firstly introduces several OSM technologies and summarizes their research status both at home and abroad. Nextly, the OSM, optical space shift keying (OSSK), enhanced optical spatial modulation (EOSM) and differential optical spatial modulation (DOSM) schemes are compared and analyzed in terms of transmission rate, spectral efficiency, bit error rate (BER) and complexity. Finally, the key problems and future development direction are pointed out in OSM system.

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.

Precoding-Aided Spatial Modulation With Dual-Polarized Antennas Over Correlated Channels

In this letter, we propose a dual-polarized precoding-aided spatial modulation (DPPSM) scheme, which introduces the polarization dimension into conventional precoding-aided spatial modulation (PSM) to transmit an additional information bit, avoiding the occupation of additional physical space while offering extra transmit diversity. We obtain an upper bound on the average bit error probability (ABEP) of the proposed DPPSM scheme over correlated fading channels. We also derive an approximate upper bound on the ABEP to show the diversity order. Simulation results show that the upper bound is tight for a high signal-to-noise ratio (SNR) range, and the bit error rate (BER) performance of the proposed DPPSM scheme is better than that of the conventional PSM scheme at the same spectral efficiency when equipped with an equal amount of antennas. Furthermore, the proposed DPPSM scheme is more robust to Gaussian channel error when the channel estimation imperfection is considered.

Energy Efficient Transmit-Receive Hybrid Spatial Modulation for Large-Scale MIMO Systems

We consider a point to point large-scale multiple-input multiple-output (MIMO) system operating in the millimeter wave (mmWave) band and an outdoor scenario. Novel transmit and receive spatial modulation (SM) schemes are proposed for uplink (UL) and downlink (DL) data transmission phases based on a novel energy efficient hybrid user terminal architecture. The analog circuitry of the proposed hybrid architecture is divided into two stages: phase shifters and analog switches. The phase shifting stage assures high gain and overcomes the severe path-loss caused by outdoor mmWave propagation. The analog switching stage smartly allocates the antennas to be used at the phase shifting stage and combats the spatial correlation. We provide the analysis of the spectral efficiency $({{SE}})$ of the UL and DL systems. Next, we propose a reduced complexity algorithm that jointly optimizes the analog beamformer and combiner design of the UL and DL circuitry to maximize the energy efficiency $({{EE}})$ . Finally, we compare and evaluate the performance of the proposed algorithm in terms of the ${{SE}}$ and ${{EE}}$ assuming both stochastic and realistic channel models.

Two-Source Asymmetric Turbo-Coded Cooperative Spatial Modulation Scheme with Code Matched Interleaver

This paper proposes, for the first time, a two-source asymmetric turbo-coded-cooperative spatial modulation (SM) scheme over the slow Rayleigh fading channel. As in any coded cooperative communication, the interleaver plays a vital role in mitigating the harsh effect of the wireless channel. Therefore, the code matched interleaver (CMI) is effectively used in the proposed design. The simulated results reveal that the bit error rate (BER) performance of the proposed coded cooperative communication system outperforms the asymmetric turbo-coded non-cooperative scheme under identical conditions. This prominent performance improvement has been made possible due to the joint asymmetric turbo decoding at the destination node. Furthermore, to check the effectiveness of the proposed scheme, we have also developed a two-source asymmetric turbo-coded cooperative scheme based on the vertical bell labs layered space-time (VBLAST), incorporating the CMI as the suitable benchmark. It is observed that the proposed scheme employing SM has a better BER performance than the VBLAST scheme under identical conditions.

Adaptive Spatial Modulation over MmWave Channel with UPA

Spatial modulation (SM) utilizes the transmit antenna index and a quadrature amplitude modulation (QAM) symbol chosen from a constellation diagram to improve spectral efficiency (SE) comparing to conventional modulation scheme. However, in the conventional SM system, the modulation mode applied to the active antenna is fixed, which degrades the bits error rates (BER) and spectral efficiency (SE) performance. Moreover, a large number of researches on SM systems focus on the utilization of the uniform linear array (ULA) for transmission, which only considers the transmission on the horizontal domain while ignoring that on the vertical domain. Therefore, in this paper, we propose an adaptive spatial modulation (ASM) scheme with uniform planar array (UPA) over millimeter wave (mmWave) channels, which combines SM with adaptive modulation (AM) to enhance the performance of SE. To further improve the bits error rates (BER) performance, we develop an UPA-based ASM scheme with transmit antenna selection (TAS). We then analyse the BER and SE performance of both the two ASM scheme and obtain the closed-form expression for SE of the UPA-based ASM scheme with TAS algorithm. The simulations demonstrate that the proposed ASM schemes can achieve a considerable SE and a relatively low BER.