A key challenge of future mobile communication research is to strike an attractive compromise between wireless 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, especially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless communications 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 communications, 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. Furthermore, it has received sufficient research attention to be implemented 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.

https://hal-supelec.archives-ouvertes.fr/hal-00840278/document

Spatial Modulation for Generalized MIMO: Challenges, Opportunities, and Implementation

In this paper, a novel orthogonal frequency division multiplexing (OFDM) scheme, called OFDM with index modulation (OFDM-IM), is proposed for operation over frequency-selective and rapidly time-varying fading channels In this scheme, 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 low complexity transceiver structures based on maximum likelihood detection or log-likelihood ratio calculation are proposed and a theoretical error performance analysis is provided for the new scheme operating under ideal channel conditions Then, the proposed scheme is adapted to realistic channel conditions such as imperfect channel state information and very high mobility cases by modifying the receiver structure The approximate pairwise error probability of OFDM-IM is derived under channel estimation errors For the mobility case, several interference unaware/aware detection methods are proposed 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 by the indices of OFDM subcarriers under both ideal and realistic channel conditions

Orthogonal Frequency Division Multiplexing With Index Modulation

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 transmission approach, referred to as subcarrier-index modulation (SIM) is proposed to be integrated with the orthogonal frequency division multiplexing (OFDM) systems. More specifically, it relates to adding an additional dimension to the conventional two-dimensional (2-D) amplitude/phase modulation (APM) techniques, i.e. amplitude shift keying (ASK) and quadrature amplitude modulation (QAM). The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Analytical and simulation results show error probability performance gain of 4 dB over 4-QAM OFDM systems for both coded and uncoded data without power saving policy. Alternatively, power saving policy retains an average gain of 1 dB while using 3 dB less transmit power per OFDM symbol.

Subcarrier-index modulation OFDM

In closed-loop future time division duplex (TDD) wireless systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. However, in TDD interference-limited systems, conventional channel sounding pilots only provide instantaneous channel state information at the transmitter (CSIT), but knowledge about the level of the interference at the receiver cannot be obtained. Therefore, a scheduler cannot optimally exploit the available degree of freedom (DoF) in order to maximize the system capacity (e.g. the downlink (DL) sum capacity). In this paper, a novel interference feedback scheme is proposed to provide the base station (BS) with implicit knowledge about the interference level received by each mobile station (MS). It is proposed to weight the uplink channel sounding pilots by the level of the received interference at each MS. The weighted uplink channel sounding pilots act as a bandwidth-efficient and delay-efficient means for providing the BS with both, CSIT and the level of interference received by each active user. The performance of a system using weighted sounding pilots is compared against a system using non- weighted sounding pilots for both greedy (maximum capacity) as well as fair scheduling criteria such as proportional fair and score based scheduling policies. It is shown that the throughput is increased while fairness is not compromised.

Implicit Pilot-Borne Interference Feedback for Multiuser MIMO TDD Systems

A method and apparatus for communicating information by: dividing the information into at least a first information portion and a second information portion; modulating a plurality of domain resources to encode the first information using an index or grammar; and encoding the second information by modulation of domain resources. Optionally, the plurality of domain resources may be modulated to encode the first information by allocating at least two different modulation types to a plurality of sub-carriers. The modulation type is allocated to domain resources according to the index or grammar, which applies meaning to which modulation type is allocated to which domain resource. The modulation may include encoding part of the first information portion using one or more domain resources of a first domain and another part of the first information portion using one or more domain resources of a second domain.

Inter-carrier modulation

A method and apparatus for communicating information comprising dividing the information into at least a first information portion and a second information portion; modulating a plurality of domain resources to encode the first information using an index or grammar; and encoding the second information by modulation of domain resources. Optionally, the plurality of domain resources may be modulated to encode the first information by allocating at least two different modulation types to a plurality of sub-carriers. The modulation type is allocated to domain resources according to the index or grammar, which applies meaning to which modulation type is allocated to which domain resource. Modulating the plurality of domain resources to encode the first information may comprises encoding part of the first information portion using one or more domain resources of a first domain and another part of the first information portion is encoded using one or more domain resources of a second domain and optionally encoding at least a further part of the first information portion using one or more domain resources of a third domain. The first, second and/or third domains may comprise the frequency, time and/or spatial domains and/or the domain resources comprise sub-channels of a frequency domain, beams arranged in a spatial domain and/or time slots in a time domain. Values are associated with domain resources of at least one domain and at least part of the first information portion is encoded by providing a signal using a domain resource indicative of the value of the portion of the data.

Encoding method by conveying coded bit information on patterns of different modulation schemes on orthogonal resource units

In future time division duplex (TDD) wireless systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co- channel interference (CCI) from adjacent cells in interference- limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. Interference-weighted channel sounding (IWCS) is a spectrally efficient feedback technique that provides the base station (BS) with implicit knowledge about the interference experienced by each active user. The main contribution of this paper is to propose a novel way to make the IWCS pilots usable for improved UL performance. In this context, it is proposed to weight the metric obtained from the IWCS pilots by the interference experienced at the BS. The resultant new metric, which is implicitly dependent on downlink (DL) and UL interference, provides link-protection awareness and is used to jointly improve spectral efficiency in UL as well in DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used.

Rami Abu-alhiga

Papers

Subcarrier-index modulation OFDM

Implicit Pilot-Borne Interference Feedback for Multiuser MIMO TDD Systems

Inter-carrier modulation

Encoding method by conveying coded bit information on patterns of different modulation schemes on orthogonal resource units

Interference-Weighted Channel Sounding for Cellular SDMA-TDD Systems