Convey Information Bits Research Articles

Performance enhanced dual-mode index modulation OFDM with OCT precoding in VLC systems

In this paper, dual-mode index modulation orthogonal frequency division multiplexing (DMIM-OFDM) enabled by orthogonal circulant matrix transform (OCT) precoding is proposed and experimentally demonstrated in visible light communication (VLC) systems. Since all available subcarriers are active to convey information bits, DMIM-OFDM can achieve higher spectral efficiency (SE) and energy efficiency (EE) than index modulation OFDM (IM-OFDM). In addition, to mitigate the uneven frequency-selective fading between different subblocks, channel-independent OCT precoding is applied to all subblocks to equalize the overall signal-to-noise ratio (SNR). The experimental results show that the DMIM-OFDM with OCT precoding outperforms the traditional IM-OFDM, DMIM-OFDM without precoding, and with DFT precoding at different SEs. For DMIM-OFDM VLC system with SE of 4.5 bit/s/Hz, by using OCT precoding, the receiver sensitivity improvement of 3 dB can be achieved at the bit error rate (BER) of 3.8e−3 after 3.5-m free-space transmission.

Generalized 3-D Spatial Scattering Modulation

Three-dimensional (3-D) massive multiple-input-and-multiple-output (MIMO) systems, which explore degrees of freedom in both the vertical and the horizontal dimensions, are a promising technology to enhance spectral efficiency in the next-generation communication systems. As an emerging modulation technology with millimetre wave (mm-wave) communication in massive MIMO systems with limited radio-frequency (RF) chains, the spatial scattering modulation (SSM) makes use of beamspace domain resources to further improve the spectral efficiency. However, most published works on the SSM only focus on two-dimensional (2-D) MIMO systems. In this paper, we generalize the SSM system to 3-D space. First, we design a novel generalized 3-D SSM system by considering both vertical and horizontal angles to determine scattering paths, which are selected to convey information bits. Then, we propose a whitening filter based optimal detection algorithm to detect the received symbols with correlated noise, where the correlation is generated by the combination of the received signals from the large-scale planar receiving antenna array. Next, we design a 2-D fast Fourier transform (FFT) based transceiving approach to improve the hardware friendliness. After that, we propose a low-complexity detector based on the linear minimum mean square error (MMSE) detection algorithm. Moreover, we derive the union upper bound on average bit error probability (ABEP) in a closed form and the asymptotic performance expression for the generalized 3-D SSM system. Finally, we analyse the impact of transmission environment on the ABEP performance. Numerical results show that the generalized 3-D SSM system outperforms the conventional 2-D SSM system, which reduces the ABEP by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\times $ </tex-math></inline-formula> with the same signal-to-noise ratio (SNR) level under the typical indoor environment.

Cluster Index Modulation for mmWave Communication Systems

In this study, a novel cluster index modulation (CIM) scheme, which is based on indexing the available clusters in the environment, is proposed for future mmWave communication systems. Exploiting the fact that the available clusters in the system are well separated in terms of their angular distribution, we selected the best path for each of them and then performed IM in an algorithmic manner to convey information bits. It is shown that by means of large antenna arrays and analog RF beamforming with the indexed clusters, the destructive effect of inter-beam/cluster interference can be remarkably mitigated. Also, we designed a hybrid beamforming architecture at the transmitter to further reduce the effect of residual inter-beam/cluster interference, where the analog RF beamformer is followed by a digital baseband precoder using the zero-forcing technique. Computer simulations reveal that the proposed scheme can provide better error performance than traditional mmWave communication, and the proposed hybrid architecture outperforms beam index modulation (BIM) for a point-to-point scenario. Semi-analytical derivations and closed-form unconditional pairwise error probability (UPEP) expressions are derived for both analog and hybrid architectures, which confirm the validity and superiority of our proposed scheme.

Successive-Coded Spatial Shift Keying Modulation for MIMO Wireless Communications

Spatial domain modulation employs spatial degree of freedom to convey information bits. Traditional spatial domain modulation schemes include spatial modulation, spatial shift keying (SSK), and variations of these two schemes. To fully make use of the spatial degree of freedom and improve the achievable data rate of traditional spatial domain modulation schemes, we propose a successive-coded SSK (SC-SSK) modulation scheme. The core of the proposed SC-SSK scheme is a multiple step coded modulation strategy, in which different information bits are mapped to the designed pattern in each step. The constellation of the transmit signals is designed. A QR decomposition based successive detection algorithm is proposed for this particular coded modulation strategy. The achievable rate, the error rate performance, and the computational complexity of the proposed SC-SSK scheme are analyzed in detail. Simulations are carried out to compare the proposed the SC-SSK scheme with the reference spatial domain modulation schemes, and reveal the advantages of the proposed SC-SSK scheme.

Orthogonal frequency division multiplexing with index modulation by using multiple constellation sets

AbstractIn this article, a new transmission method named enhanced orthogonal frequency division multiplexing (E‐OFDM) is proposed to increase the spectral efficiency (SE) of the OFDM. The proposed method conveys information bits not only by the M‐ary symbols but also by the multiple different constellation sets. In the proposed method, we build the sub‐blocks by splitting the whole OFDM into pieces. Then, we use different constellation sets in each sub‐block and we assign the extra bits to them to increase the SE of the OFDM systems. Consequently, at the same modulation level, the proposed method has higher SE than the conventional OFDM system. The simulation results also show that the proposed method achieves better bit error rate (BER) performance than the conventional OFDM system with tolerable complexity. For example, the proposed method with a sub‐block size 2 doubles the SE of the conventional OFDM method with BPSK modulation, and also it has approximately 1.6 dB better BER performance than the conventional OFDM at BER =10−4. New constellation designs and receiver algorithm for the detection of additional bits are also presented.

Index and Constellation Order Lowering for OFDM With Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a promising variant of OFDM where indices of symbol carrying sub-carriers also convey information bits besides the complex symbols themselves. Recently, a lower order modulation variant has been proposed for OFDM-IM, where the baseband constellation is lowered with appropriate rotations and index reuse, so as to lower the number of sub-blocks whose pairwise error probability is inversely related to the signal to noise ratio (SNR). In this work, we demonstrate that the number of symbol carrying sub-carriers and hence the number of used indices can also be lowered along with modulation order lowering. This reduces the aforementioned number of worst case sub-block pairs even further. The resulting unused sub-carriers can now be used to enhance the spectral efficiency as well. Numerical results reveal SNR gains up to 5dB for uncoded systems and 2dB for coded systems.

On the Phase Sequences and Permutation Functions in the SLM Scheme for OFDM-IM Systems

In orthogonal frequency division multiplexing with index modulation (OFDM-IM), the active subcarriers can convey information bits by modulated symbols as well as their indices. OFDM-IM has attracted a great deal of attention from researchers by virtue of high energy efficiency. Unfortunately, OFDM-IM has inherited large peak-to-average power ratio (PAPR) of the classical OFDM signal, but there are few works dealing with it. Selected mapping (SLM) is a promising PAPR reduction technique that is distortionless, has good PAPR reducing capability, and can be easily adapted in OFDM-IM systems. In SLM for OFDM-IM systems, the phase sequences rotate the OFDM-IM block in the frequency domain before the inverse fast Fourier transform (IFFT) is applied. Also, permutation in the frequency domain can be easily introduced before multiplication of phase sequences in SLM. In this paper, we investigate the phase sequence set (PSS) and permutation functions in the SLM scheme for OFDM-IM systems; First, the efficiency of the permutation is analyzed as a function of the number of active subcarriers. Second, the optimal conditions for the PSS and permutation functions are derived, which is verified through simulations.

Message Passing Receivers for Generalized Media-Based Modulation Signals

We consider generalized media-based modulation (GMBM), where transmit antennas and radio frequency (RF) mirrors (which are parasitic elements placed near the transmit antennas as digitally controlled scatterers) are indexed simultaneously to convey information bits. We develop low complexity receiver algorithms for the detection of high-rate, large-dimension GMBM signals. Message passing-based detection is a promising low-complexity approach. The elements in a GMBM transmit vector are interdependent. Message passing with a multi-layering approach is proposed to take care of this dependency. The proposed multi-layering approach decouples the dependencies through the addition of new layers and constraints that account for the antenna activation and RF mirror activation patterns. The proposed message passing detection with multi-layering, termed as multi-layered message passing detection , is shown to outperform message passing detection without multi-layering and constraints. In addition to exploiting multi-layering, the channel hardening property of large MIMO channels is exploited for GMBM signal detection and channel estimation. The algorithm based on this approach is termed as multi-layered channel hardening-exploiting message passing algorithm . The proposed algorithms scale well in complexity and achieve good bit error performance in high-rate, large-dimension GMBM systems.

Performance Analysis of Full-Duplex Decode-and-Forward Relaying With Media-Based Modulation

In this paper, we introduce and analyze the performance of a two-hop three-node full-duplex (FD) relay network, where the source and relay nodes transmit using media-based modulation (MBM). An MBM is a promising new modulation scheme that conveys information bits by digitally controlling the parasitic elements (known as radio frequency mirrors) placed near the transmit antenna. The relay uses decode-and-forward relaying protocol. We refer to this system as FD relaying system with MBM (FDR-MBM). We first derive an upper bound on the end-to-end average bit error probability of FDR-MBM with maximum-likelihood detection at the relay and destination nodes. The bound is increasingly tight with increasing signal-to-noise ratios. Numerical results show that, for the same spectral efficiency, FDR-MBM can perform better than FD relaying using conventional modulation schemes. We then derive the diversity order achieved in FDR-MBM. The analytically predicted diversity orders are validated through simulations. Finally, we derive lower and upper bounds on the achievable rate in FDR-MBM.

Media-Based Modulation for the Uplink in Massive MIMO Systems

Media-based modulation (MBM) is an attractive modulation scheme, which can achieve high data rates using multiple radio frequency (RF) mirrors (parasitic elements) and fewer transmit antennas/RF chains. In this paper, we consider MBM for the uplink in a massive multiple input multiple output (MIMO) system consisting of tens of users and tens to hundreds of base station receive antennas. Each user employs MBM with one transmit antenna and multiple RF mirrors placed near it. The on / off status of the RF mirrors conveys information bits in addition to the bits conveyed through conventional modulation symbols. We show that the multiuser MBM (MU-MBM) system achieves very good bit error performance compared to other conventional multiuser MIMO systems. We propose two types of low-complexity detection algorithms for massive MU-MBM systems. The first type is based on compressive sensing that exploits the inherent sparse nature of the MBM transmit vectors. The second type is based on message passing that performs both detection and channel estimation at low computational complexity. To do this, it exploits the “channel hardening” phenomenon that occurs in large MIMO channels. It is shown that the proposed algorithms are not only computationally less complex, but also provide very good bit error performance in massive MU-MBM systems.

Low-Complexity LLR Calculation for OFDM With Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a promising multicarrier transmission technique. In OFDM-IM, only a subset of subcarriers are activated to transmit modulated symbols and the indices of the activated subcarriers are used to convey information bits implicitly. In the coded OFDM-IM system, we need to calculate the log likelihood ratio (LLR) value of each bit, whose computational complexity is extremely high due to the dependence between the subcarriers caused by the subcarrier-index modulation. In this letter, we propose a novel simplified LLR calculation algorithm for OFDM-IM. Simulation results show that the proposed algorithm achieves near-optimal coded bit error rate performance with considerably low computational complexity.

Design guidelines on beam index modulation enabled wireless communications

A new wireless transmission scheme, named by authors as beam index modulation (BIM), is proposed. It exploits radiation beam indices at the transmitter sides to convey information bits, in addition to the information transmitted by modulating radio frequency carriers, i.e. the classical means of wireless transmission. Favourably, only a single RF chain is required at both transmitter and receiver sides. When compared with traditional beamforming, the proposed BIM system exhibits improved bit error rate performance in sparse non-line-of-sight wireless propagation channels. A parametric study is conducted, from which the design guidelines are provided and experimentally validated.

Noncoherent OFDM-IM and Its Performance Analysis

In conventional orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM), the active subcarriers can convey information bits by modulated symbols as well as their indices. To detect modulated symbols, coherent detection is usually considered, which requires the channel state information (CSI) estimation for all subcarriers at a receiver. In OFDM-IM, however, since only a fraction of subcarriers are active, the overhead for pilot transmissions through all subcarriers to allow the receiver to estimate the CSI could be excessive, in particular, under a fast fading environment. To avoid this difficulty, we consider noncoherent OFDM-IM, where only the indices of active subcarriers are used to convey information bits. For a better performance, a transmit diversity scheme is also studied. We derive a closed-form expression for the probability of index error when no transmit diversity is considered under frequency-selective Rayleigh fading. We also derive an upper-bound when the transmit diversity scheme is employed. From the upper-bound, the diversity order is also clearly shown.

Enhanced Orthogonal Frequency Division Multiplexing With Index Modulation

Index modulation concept has attracted considerable research interest in the past few years. As a realization of index modulation in the frequency domain, orthogonal frequency division multiplexing with index modulation (OFDM-IM) has recently been proposed, which conveys information bits through both the subcarrier activation patterns and the amplitude phase modulation constellation points. This paper proposes two enhanced OFDM-IM schemes aimed at achieving higher spectral efficiency and diversity gain, respectively. The first one, termed OFDM with hybrid in-phase/quadrature index modulation (OFDM-HIQ-IM), explores the I- and Q- dimensions jointly for index modulation, allowing transmission of more index modulation bits in each subcarrier group. The second one, termed linear constellation precoded OFDM-IQ-IM (LP-OFDM-IQ-IM), spreads information symbols across two adjacent active subcarriers through linear constellation precoding to harvest additional diversity gain. By maximizing the minimum squared Euclidean distance, two different realizations of LP-OFDM-IQ-IM are derived, which leads to a rotated and a diamond-shaped constellation, respectively. The proposed OFDM-HIQ-IM and LP-OFDM-IQ-IM, as revealed by both theoretical analyses and computer simulations, enable low-complexity detection and exhibit superior error rate performance over the existing OFDM-IM schemes.

Generalized 3-D Constellation Design for Spatial Modulation

Spatial modulation (SM) conveys information bits by utilizing both the antenna index and complex symbols to form a 3-D constellation. Similar to 2-D modulation, the structure of 3-D constellation could greatly affect the transmission reliability. In this paper, a generalized 3-D constellation design is proposed to optimize the constellation diagram used for each antenna, i.e., to optimize the complex symbols and their total number for each antenna and finally to enhance the transmission reliability. The optimal design method with exhaustive search algorithm may cause prohibitive computational complexity, especially when the cardinality of 3-D constellation is large. To overcome this issue, a recursive design algorithm is proposed with a computational complexity increasing polynomially with the cardinality of 3-D constellation. Extensions of the proposed methods to the SM constellation design for massive multiple-input multiple-output transmission, generalized spatial modulation (GSM) constellation design, and the SM constellation design with transmit antenna correlation are also discussed. Simulations are done to validate those theoretical analysis, and results show that the proposed 3-D constellation design is a generalized design scheme and can be adopted in any SM/GSM systems without constraints on the number of transceiver antennas. It is also shown that the proposed approach offers better symbol-error-rate performance than other solutions.

Hybrid Spatial Modulation Beamforming for mmWave Railway Communication Systems

Using higher frequency bands [e.g., millimeter wave (mmWave)] is the most effective and straightforward way to alleviate the bands scarcity at lower frequency bands (e.g., microwave) while simultaneously supporting the ever-growing data rate demands for future cellular networks. Cellular-networks-based high-speed railway (HSR) wireless communication systems also need to be evolved to satisfy the requirements of train-ground data transmission by using higher frequency bands. An essential characteristic of HSR propagation channels is the strong line of sight, which results in high channel correlation. Therefore, the conventional multiple input multiple output (MIMO, e.g., VBLAST, STBC) is less effective under the HSR scenario. Moreover, the high complexity of the conventional MIMO makes it hard to achieve multiple antenna gain. Spatial modulation (SM) is a low complexity and high spectral efficiency multiple antenna technology that has emerged in recent years. The properties of SM imply that it may be a potential technique for improving the performance of HSR wireless communication systems. In this paper, a hybrid SM beamforming scheme operating at mmWave frequency bands is proposed for future 5G HSR wireless communication systems. The proposed scheme is designed in both analog and digital domains. In digital domain, SM is used to activate antenna array (AA) indices to convey information bits. RF beams are predefined and the optimal beams are selected to transmit modulation symbols in analog domain. Theoretical analysis and numerical results indicate that the proposed scheme achieves a good compromise between performance and complexity. Multiple antenna gain, which is difficult to achieve by the conventional MIMO, can be almost achieved by the proposed scheme due to analog beamforming. Numerical results further show that the performance of the proposed scheme is not sensitive to the number of predefined RF beams, but it is to some extent sensitive to both AAs at base station and antenna elements in an AA on the train.

Performance Analysis of Massive Spatial Modulation MIMO in High-Speed Railway

For high-speed railway (HSR), an essential characteristic of the propagation channels is the specific spatial–temporal correlation caused by a dominant strong line-of-sight (LOS) component. Multiple-antenna gain is therefore far from being achieved due to this strong channel correlation. However, it is interesting to note that if the resulted intercarrier interference (ICI) is elaborately controlled, high mobility may decrease the channel correlation. Spatial modulation (SM) is one of the promising multiple-antenna technologies for wireless communication systems, which needs only the activation of one transmit antenna to convey information bits implicitly through the index of the active transmit antenna, in addition to conveying information bits through modulation symbols during transmission. In SM, ICI is avoided, which therefore helps in the implementation of the idea of decreasing channel correlation by increasing the velocity in an HSR scenario. In this paper, the performance of massive SM multiple-input multiple-output (MIMO) over a spatial–temporal correlated Rician fading channel is investigated under an HSR scenario. The impacts of velocity, Rician factor K, and signal-to-noise ratio (SNR) are discussed. In addition, the correlation factor and the correlation comparison function are defined as metrics of channel correlation. We theoretically find out that higher velocity makes the impact of temporal correlation more dominant, which weakens the influence of spatial correlation. In other words, spatial correlation can be weakened by high mobility. Our theoretical analysis and simulations further demonstrate that, with an appropriate scheme, massive SM MIMO outperforms Vertical Bell Laboratories Layered Space–Time (VBLAST), except at a lower SNR region with high velocity (usually more than 360 km/h). Consequently, massive SM MIMO is a promising solution within an appropriate range of velocity for HSR wireless communication systems.

New Signal Designs for Enhanced Spatial Modulation

In this paper, we present three new signal designs for enhanced spatial modulation (ESM), which was recently introduced by the present authors. The basic idea of ESM is to convey information bits not only by the index(es) of the active transmit antenna(s) as in conventional SM, but also by the types of the signal constellations used. The original ESM schemes were designed with reference to single-stream SM and involved one or more secondary modulations in addition to the primary modulation. Compared with single-stream SM, they provided either higher throughput or improved signal-to-noise ratio (SNR). In this paper, we focus on multi-stream SM (MSM) and present three new ESM designs leading to increasing SNR gains when they are operated at the same spectral efficiency. The secondary signal constellations used in the first two designs are derived through a single geometric interpolation step in the signal constellation plane, while the third design also makes use of additional constellations derived through a second interpolation step. The new ESM signal designs are described for MIMO systems with four transmit antennas out of which two are active, but we also briefly present extensions to higher numbers of antennas. Theoretical analysis and simulation results indicate that the proposed designs provide a significant SNR gain over MSM.

On the Capacity and Performance of Generalized Spatial Modulation

Generalized spatial modulation (GSM) uses $N$ antenna elements but fewer radio frequency (RF) chains ($R$) at the transmitter. Spatial modulation and spatial multiplexing are special cases of GSM with $R=1$ and $R=N$, respectively. In GSM, apart from conveying information bits through $R$ modulation symbols, information bits are also conveyed through the indices of the $R$ active transmit antennas. In this paper, we derive lower and upper bounds on the the capacity of a ($N,M,R$)-GSM MIMO system, where $M$ is the number of receive antennas. Further, we propose a computationally efficient GSM encoding (i.e., bits-to-signal mapping) method and a message passing based low-complexity detection algorithm suited for large-scale GSM-MIMO systems.

Generalized Space-and-Frequency Index Modulation

Unlike in conventional modulation where information bits are conveyed only through symbols from modulation alphabets defined in the complex plane (e.g., quadrature amplitude modulation (QAM), phase shift keying (PSK)), in index modulation (IM), additional information bits are conveyed through indices of certain transmit entities that get involved in the transmission. Transmit antennas in multi-antenna systems and subcarriers in multi-carrier systems are examples of such transmit entities that can be used to convey additional information bits through indexing. In this paper, we introduce {\em generalized space and frequency index modulation}, where the indices of active transmit antennas and subcarriers convey information bits. We first introduce index modulation in the spatial domain, referred to as generalized spatial index modulation (GSIM). For GSIM, where bits are indexed only in the spatial domain, we derive the expression for achievable rate as well as easy-to-compute upper and lower bounds on this rate. We show that the achievable rate in GSIM can be more than that in spatial multiplexing, and analytically establish the condition under which this can happen. It is noted that GSIM achieves this higher rate using fewer transmit radio frequency (RF) chains compared to spatial multiplexing. We also propose a Gibbs sampling based detection algorithm for GSIM and show that GSIM can achieve better bit error rate (BER) performance than spatial multiplexing. For generalized space-frequency index modulation (GSFIM), where bits are encoded through indexing in both active antennas as well as subcarriers, we derive the achievable rate expression. Numerical results show that GSFIM can achieve higher rates compared to conventional MIMO-OFDM. Also, BER results show the potential for GSFIM performing better than MIMO-OFDM.