Shinya Sugiura

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

A key challenge of future mobile communication research is to strike an attractive compromise between wireless networks 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 worlds first experimental activities in this vibrant research field.

Single-Carrier SM-MIMO: A Promising Design for Broadband Large-Scale Antenna Systems

The main limitations of employing large-scale antenna (LSA) architectures for broadband frequency-selective channels include, but are not limited to their complexity, power consumption, and the high cost of multiple radio frequency (RF) chains. Promising solutions can be found in the recently proposed family of single-carrier (SC) spatial modulation (SM) transmission techniques. Since the SM schemes transmit antenna (TA) activation process is carried out in the context of a SC-SM architecture, the benefits of a low-complexity and low-cost single-RF transmitter are maintained, while a high MIMO multiplexing gain can be attained. Moreover, owing to its inherent SC structure, the transmit signals of SC-SM have attractive peak power characteristics and a high robustness to RF hardware impairments, such as the RF carrier frequency offset (CFO) and phase noise. In this paper, we present a comprehensive overview of the latest research achievements of SC-SM, which has recently attracted considerable attention. We outline the associated transceiver design, the benefits and potential tradeoffs, the LSA aided multiuser (MU) transmission developments, the relevant open research issues as well as the potential solutions of this appealing transmission technique.

Frequency-Domain Equalization of Faster-than-Nyquist Signaling

In this letter, motivated by the recent rediscovery of faster-than-Nyquist (FTN) signaling transmissions, we conceive a frequency-domain equalization (FDE)-assisted FTN receiver architecture, which is capable of attaining a low demodulating complexity. The proposed scheme is especially beneficial for a long channel tap FTN scenario. More specifically, in our scheme the resultant inter-symbol interference imposed by FTN signaling is approximated by a finite-tap circulant matrix structure, which allows us to employ an efficient fast Fourier transform operation and a low-complexity channel-inverse-based minimum mean-square error detection algorithm. Our simulation results demonstrate that the proposed scheme is capable of attaining a near-optimal error-rate performance without imposing any substantial demodulating complexity as well as power penalty.

Subcarrier-Index Modulation Aided OFDM - Will It Work?

The achievable performance of subcarrier-index modulation (SIM) is analyzed in terms of its minimum Euclidean distance, constrained and unconstrained average mutual information, as well as its peak-to-average power ratio (PAPR). Our performance investigations identify the beneficial operating region of the SIM scheme over its conventional orthogonal frequency-division multiplexing (OFDM) counterpart, hence providing general design guidelines for the SIM parameters. More specifically, an SIM scheme is shown to be beneficial for the scenario of a relatively low transmission rate below 2 b/s/Hz. In addition, we demonstrate that the PAPR of the SIM scheme is comparable with that of its OFDM counterpart under the idealized simplifying assumption of having Gaussian input symbols.

Frequency-Domain-Equalization-Aided Iterative Detection of Faster-than-Nyquist Signaling

A reduced-complexity three-stage-concatenated faster-than-Nyquist signaling (FTNS)-based transceiver architecture is proposed, which operates with the aid of soft decision (SoD) frequency-domain equalization (FDE) at the receiver. More specifically, the decoding algorithm conceived allows us to attain near-capacity performance as an explicit benefit of iterative detection, which is capable of eliminating the intersymbol interference imposed by FTNS. The proposed SoD FDE-aided FTNS detector has low decoding complexity that linearly increases upon increasing the FTNS block length and, hence, is particularly beneficial for practical long-dispersion scenarios. Furthermore, extrinsic information transfer charts are utilized for designing a near-capacity three-stage-concatenated turbo FTNS system, which exhibits an explicit turbo cliff in the low-signal-to-noise-ratio region, hence outperforming its conventional two-stage-concatenated FTNS counterpart.

Effects of Antenna Switching on Band-Limited Spatial Modulation

In this letter, we investigate the effects of antenna switching on band-limited spatial modulation (SM), where the employment of an SM-specific practical time-limited shaping filter is taken into account. More specifically, we evaluate the SM schemes performance penalty imposed on a bandwidth efficiency, which arises due to the time-limited pulse transmissions. Furthermore, to combat this limitation while maintaining lower RF chains than transmit antenna elements, we propose a multiple-RF antenna switching operation that allows us to exploit a longer pulse shape than that enabled by a single-RF SM scheme. It is demonstrated in our simulations that upon increasing the number of transmit antenna elements, the SM scheme is capable of outperforming the classic MIMO systems, under the assumptions of a low number of RF chains and realistic pulse shaping.

Single-RF Spatial Modulation Requires Single-Carrier Transmission: Frequency-Domain Turbo Equalization for Dispersive Channels

In this paper, we propose a broadband single-carrier (SC) spatial modulation (SM)-based multiple-input-multiple-output (MIMO) architecture relying on a soft decision (SoD) frequency-domain equalization (FDE) receiver. We demonstrate that conventional orthogonal-frequency-division-multiplexing (OFDM)-based broadband transmissions are not readily suitable for the single-radio-frequency-assisted SM-MIMO schemes since this scheme exhibits no substantial performance advantage over single-antenna transmissions. To circumvent this limitation, a low-complexity SoD FDE algorithm based on the minimum mean square error (MMSE) criterion is invoked for our broadband SC-based SM-MIMO scheme, which is capable of operating in a strongly dispersive channel having a long channel impulse response at moderate decoding complexity. Furthermore, our SoD FDE attains a near-capacity performance with the aid of a three-stage concatenated SC-based SM architecture.

Generalized-Spatial-Modulation-Based Reduced-RF-Chain Millimeter-Wave Communications

A generalized spatial modulation (GSM)-based millimeter-wave communications system is proposed. The GSM transmitter is characterized by a lower number of radio frequency (RF) chains than the number of transmit antennas; hence, it is capable of reducing both the transmitter cost and the energy consumption. The antenna array alignment is optimized so as to maximize the rank of the channel matrix encountered. Furthermore, we employ an array of analog beamformers, which allows us to benefit both from the beamforming gain and from the GSM schemes high rate. It is demonstrated that the constrained capacity of the GSM transmitter equipped with as few as two RF chains is capable of approaching the performance of the full-RF spatial multiplexing having eight RF chains.

Unified MIMO-Multicarrier Designs: A Space–Time Shift Keying Approach

A survey and tutorial is provided on the subject of multiple-input-multiple-output (MIMO) multicarrier (MC) systems relying on the space-time shift keying (STSK) concept. We commence with a brief review of the family of MIMO systems, which is followed by the design of STSK systems in the context of MC modulation-based transmissions over dispersive wireless channels. Specifically, the STSK scheme is amalgamated with orthogonal frequency-division multiplexing, MC code-division multiple access, orthogonal frequency-division multiple access (OFDMA), and single-carrier frequency-division multiple access. We also provide a rudimentary introduction to MC differential STSK employing both conventional differential detection and multiple-symbol differential sphere decoding for the sake of dispensing with channel estimation. We conclude with the design recipes of coherent versus noncoherent MC STSK schemes, complemented by a range of future research ideas.

Coherent Versus Non-Coherent Reconfigurable Antenna Aided Virtual MIMO Systems

In this letter, motivated by the recent universal encoding concept of space-time shift keying (STSK), we propose a novel single radio-frequency (RF) based virtual multiple-input multiple-output (VMIMO) architecture, employing a pattern reconfigurable antenna at a transmitter. More specifically, the proposed scheme is based on the concept of pattern-time dispersion matrix activation, which is capable of striking a flexible balance between the transmission rate and the diversity gain, while enabling symbol-based low-complexity detection. Furthermore, we conceive its non-coherently detected counterpart in order to dispense with any channel estimation as well as additional pilot overhead, hence having the potential of outperforming the conventional coherently-detected VMIMO schemes in many practical scenarios.