What is index modulation (IM)? This is an interesting question that we have started to hear more and more frequently over the past few years. The aim of this paper is to answer this question in a comprehensive manner by covering not only the basic principles and emerging variants of IM, but also reviewing the most recent as well as promising advances in this field toward the application scenarios foreseen in next-generation wireless networks. More specifically, we investigate three forms of IM: spatial modulation, channel modulation and orthogonal frequency division multiplexing (OFDM) with IM, which consider the transmit antennas of a multiple-input multiple-output system, the radio frequency mirrors (parasitic elements) mounted at a transmit antenna and the subcarriers of an OFDM system for IM techniques, respectively. We present the up-to-date advances in these three promising frontiers and discuss possible future research directions for IM-based schemes toward low-complexity, spectrum- and energy-efficient next-generation wireless networks.

Index Modulation Techniques for Next-Generation Wireless Networks

A key challenge of future mobile communication research is to strike an attractive compromise between wire- less network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, espe- cially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless commu- nications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communica- tions, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Further- more, it has received sufficient research attention to be im- plemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field.

Spatial Modulation for Generalized MIMO: Challenges, Opportunities, and Implementation This tutorial paper offers a comprehensive overview of the state of the art in spatial modulation for generalized multiple-input-multiple-output (MIMO) technologies.

In this paper, a novel orthogonal frequency division multiplexing (OFDM) scheme, which is called OFDM with index modulation (OFDM-IM), is proposed for frequency-selective fading channels. In this scheme, inspiring from the recently introduced spatial modulation concept for multiple-input multiple-output (MIMO) channels, the information is conveyed not only by M-ary signal constellations as in classical OFDM, but also by the indices of the subcarriers, which are activated according to the incoming bit stream. Different transceiver structures are proposed and a theoretical error performance analysis is provided for the new scheme. It is shown via computer simulations that the proposed scheme achieves significantly better error performance than classical OFDM due to the information bits carried in the spatial domain by the indices of OFDM subcarriers.

/pdf/orthogonal-frequency-division-multiplexing-with-index-2aqyfejdxw.pdf

Orthogonal frequency division multiplexing with index modulation

A new class of low-complexity, yet energy-efficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely, the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO), has emerged. These systems are capable of exploiting the spatial dimensions (i.e., the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication while relying on a single-Radio Frequency (RF) chain. Moreover, SM may be also viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/cooperative protocol design issues, and on their meritorious variants.

/pdf/design-guidelines-for-spatial-modulation-4di7fcwiu9.pdf

Design Guidelines for Spatial Modulation

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

http://www.homepages.ed.ac.uk/hxh/Li-Fi_PAPERS/13_fath_1.pdf

Performance Comparison of MIMO Techniques for Optical Wireless Communications in Indoor Environments

A novel multiple-input multiple-output (MIMO) transmission scheme, called space-time block coded spatial modulation (STBC-SM), is proposed. It combines spatial modulation (SM) and space-time block coding (STBC) to take advantage of the benefits of both while avoiding their drawbacks. In the STBCSM scheme, the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain which corresponds to the on/off status of the transmit antennas available at the space domain, and therefore both core STBC and antenna indices carry information. A general technique is presented for the design of the STBC-SM scheme for any number of transmits antennas. Besides the high spectral efficiency advantage provided by the antenna domain, the proposed scheme is also optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme which profits from the orthogonality of the core STBC. The performance advantages of the STBC-SM over simple SM and over V-BLAST are shown by simulation results for various spectral efficiencies and are supported by the derivation of a closed form expression for the union bound on the bit error probability.

Space-Time Block Coded Spatial Modulation

In literature many authors reported that in multiple input multiple output (MIMO) detection methods sphere-decoding (SD) is one of the efficient detection technique. In general, Euclidean norm is used for traversing a tree in sphere detection. By using the proposed method circuit complexity can be reduced with negligible performance loss. This is due to the reduction in the number of nodes visited in the critical path of the search tree. This paper presents the performance of complexity of 4x4 MIMO with 16-QAM modulation. The performance is compared with maximum likelihood detection (MLD) and L2 norm with the help of MATLAB simulation results. It was observed that the complexity is reduced when mean of real multiplications and mean of real additions are calculated. Proposed L∞ sphere detection shows better performance as the number of transmitting antennas increased. The tree pruning behavior of proposed SD is aggressive than the previously reported ones. Proposed L∞ sphere detector follows new approach of radius selection for reducing the computational complexity as compared to the L2 sphere de-coding algorithm and with the ideal ML decoder. It was also observed that using the infinity-norm reduces the hardware complexity of sphere detector considerably at only a minor performance loss.

V. Ramakrishna

Papers

Space-Time Block Coded Spatial Modulation

Low Complexity And High Performance Sphere Detection Technique For MIMO Communication Systems