MC-CDMA aided multi-user space-time shift keying in wideband channels

In this paper, we propose multi-carrier code division multiple access (MC-CDMA)-aided space-time shift keying (STSK) for mitigating the performance erosion of the classic STSK scheme in dispersive channels, while supporting multiple users. The codewords generated by the STSK scheme are appropriately spread in frequency-domain (FD) and transmitted over a number of parallel frequency-?at subchannels. We propose a new receiver architecture amalgamating the single-stream maximum-likelihood (ML) detector of the STSK system and the multiuser detector (MUD) of the MC-CDMA system. The performance of the proposed scheme is evaluated for transmission over frequency-selective channels in both uncoded and channel-coded scenarios. The results of our simulations demonstrate that the proposed scheme overcomes the channel impairments imposed by wideband channels and exhibits near-capacity performance in a channel-coded scenario

Multi-user steered multi-set space-time shift-keying for millimeter-wave communications

The recently proposed concept of multiset space-time shift keying (MS-STSK) is intrinsically amalgamated with the multiple-input multiple-output (MIMO) philosophy for the sake of enhancing the attainable system throughput. Explicitly, we propose a multiuser steered MS-STSK (MU-SMS-STSK) scheme for the downlink of millimeter-wave (mmWave) communications, which is combined with analogue beamforming (BF) that relies on phase shifters and power amplifiers to overcome the high attenuation of mmWaves. Hence, our MU-SMS-STSK system combines the concepts of MU-MIMO, MS-STSK, BF, and orthogonal frequency-division multiplexing for communicating with multiple users relying on the same time and frequency resources

Design guidelines for spatial modulation

A new class of low-complexity, yet energyefficient 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 whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be 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

Multi-set space-time shift keying and space-frequency space-time shift keying for millimeter-wave communications

In this paper, we introduce a novel OFDM-aided multifunctional multiple-input multiple-output scheme based on multi-set space-time shift keying (MS-STSK), where the information transmitted over each subcarrier is divided into two parts: STSK codeword and the implicit antenna combination (AC) index. In MS-STSK, a unique combination of antennas can be activated at each subcarrier to convey extra information over the AC index while additionally transmitting the STSK codeword. Furthermore, inspired by the MS-STSK concept, this scheme is extended also to the frequency domain in the novel context of our multi-space-frequency STSK (MSF-STSK), where the total number of subcarriers is partitioned into blocks to implicitly carry the block's frequency index. The proposed MSF-STSK scheme benefits from the huge bandwidths available at mmWaves for partitioning the total number of OFDM subcarriers into blocks to convey more information over the frequency domain. Both proposed systems use STSK codewords as the basic transmission block, and they can achieve higher data throughput and better BER performance than STSK. Moreover, given that the system is meant to operate at mmWaves, antenna arrays relying on several antenna elements are employed at both the transmitter and receiver for analogue beamforming with the aid of phase shifters and power amplifiers to overcome the effect of high path loss

Multidimensional Index Modulation for 5G and Beyond Wireless Networks

This study examines the flexible utilization of existing IM techniques in a comprehensive manner to satisfy the challenging and diverse requirements of 5G and beyond services. After spatial modulation (SM), which transmits information bits through antenna indices, application of IM to orthogonal frequency division multiplexing (OFDM) subcarriers has opened the door for the extension of IM into different dimensions, such as radio frequency (RF) mirrors, time slots, codes, and dispersion matrices. Recent studies have introduced the concept of multidimensional IM by various combinations of one-dimensional IM techniques to provide higher spectral efficiency (SE) and better bit error rate (BER) performance at the expense of higher transmitter (Tx) and receiver (Rx) complexity. Despite the ongoing research on the design of new IM techniques and their implementation challenges, proper use of the available IM techniques to address different requirements of 5G and beyond networks is an open research area in the literature. For this reason, we first provide the dimensional-based categorization of available IM domains and review the existing IM types regarding this categorization. Then, we develop a framework that investigates the efficient utilization of these techniques and establishes a link between the IM schemes and 5G services, namely enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communication (URLLC). Additionally, this work defines key performance indicators (KPIs) to quantify the advantages and disadvantages of IM techniques in time, frequency, space, and code dimensions. Finally, future recommendations are given regarding the design of flexible IM-based communication systems for 5G and beyond wireless networks.Comment: This work has been submitted to Proceedings of the IEEE for possible publicatio

OFDMA/SC-FDMA aided space-time shift keying for dispersive multi-user scenarios

Motivated by the recent concept of Space-Time Shift Keying (STSK) developed for achieving a flexible diversity versus multiplexing gain trade-off, we propose a novel Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier Frequency Division Multiple Access (SC-FDMA) aided multi-user STSK scheme for frequency-selective channels. The proposed OFDMA/SC-FDMA STSK scheme is capable of providing an improved performance in dispersive channels, while supporting multiple users in a multiple antenna aided wireless system. Furthermore, the scheme has the inherent potential of benefitting from the low-complexity single-stream Maximum-likelihood (ML) detector. Both an uncoded and a sophisticated near-capacity coded OFDMA/SC-FDMA STSK scheme were studied and their performances were compared in multiuser wideband Multiple-Input Multiple-Output (MIMO) scenarios. Explicitly, OFDMA/SC-FDMA aided STSK exhibits an excellent performance even in the presence of channel impairments due to the frequency-selectivity of wideband channels and proves to be a beneficial choice for high capacity multi-user MIMO systems

Successive-relaying-aided decode-and-forward coherent versus noncoherent cooperative multicarrier space–time shift keying

Abstract—Successive-relaying-aided (SR) cooperative multi-carrier (MC) space–time shift keying (STSK) is proposed for frequency-selective channels. We invoke SR to mitigate the typical 50% throughput loss of conventional half-duplex relaying schemes and MC code-division multiple access (MC-CDMA) to circumvent the dispersive effects of wireless channels and to reduce the SR-induced interference. The distributed relay terminals form two virtual antenna arrays (VAAs), and the source node (SN) successively transmits frequency-domain (FD) spread signals to one of the VAAs, in addition to directly transmitting to the destination node (DN). The constituent relay nodes (RNs) of each VAA activate cyclic-redundancy-checking-based (CRC) selective decode-and-forward (DF) relaying. The DN can jointly detect the signals received via the SN-to-DN and VAA-to-DN links using a low-complexity single-stream-based joint maximum-likelihood (ML) detector. We also propose a differentially encoded cooperative MC-CDMA STSK scheme to facilitate communications over hostile dispersive channels without requiring channel estimation (CE). Dispensing with CE is important since the relays cannot be expected to altruistically estimate the SN-to-RN links for simply supporting the source. Furthermore, we propose soft-decision-aided serially concatenated recursive systematic convolutional (RSC) and unity-rate-coded (URC) cooperative MC STSK and investigate its performance in both coherent and noncoherent scenarios

Successive-relaying-aided decode-and-forward coherent versus noncoherent cooperative multicarrier space–time shift keying

Abstract—Successive-relaying-aided (SR) cooperative multi-carrier (MC) space–time shift keying (STSK) is proposed for frequency-selective channels. We invoke SR to mitigate the typical 50% throughput loss of conventional half-duplex relaying schemes and MC code-division multiple access (MC-CDMA) to circumvent the dispersive effects of wireless channels and to reduce the SR-induced interference. The distributed relay terminals form two virtual antenna arrays (VAAs), and the source node (SN) successively transmits frequency-domain (FD) spread signals to one of the VAAs, in addition to directly transmitting to the destination node (DN). The constituent relay nodes (RNs) of each VAA activate cyclic-redundancy-checking-based (CRC) selective decode-and-forward (DF) relaying. The DN can jointly detect the signals received via the SN-to-DN and VAA-to-DN links using a low-complexity single-stream-based joint maximum-likelihood (ML) detector. We also propose a differentially encoded cooperative MC-CDMA STSK scheme to facilitate communications over hostile dispersive channels without requiring channel estimation (CE). Dispensing with CE is important since the relays cannot be expected to altruistically estimate the SN-to-RN links for simply supporting the source. Furthermore, we propose soft-decision-aided serially concatenated recursive systematic convolutional (RSC) and unity-rate-coded (URC) cooperative MC STSK and investigate its performance in both coherent and noncoherent scenarios

Interference-Mitigating Waveform Design for Next-Generation Wireless Systems

A brief historical perspective of the evolution of waveform designs employed in consecutive generations of wireless communications systems is provided, highlighting the range of often conflicting demands on the various waveform characteristics. As the culmination of recent advances in the field the underlying benefits of various Multiple Input Multiple Output (MIMO) schemes are highlighted and exemplified. As an integral part of the appropriate waveform design, cognizance is given to the particular choice of the duplexing scheme used for supporting full-duplex communications and it is demonstrated that Time Division Duplexing (TDD) is substantially outperformed by Frequency Division Duplexing (FDD), unless the TDD scheme is combined with further sophisticated scheduling, MIMOs and/or adaptive modulation/coding. It is also argued that the specific choice of the Direct-Sequence (DS) spreading codes invoked in DS-CDMA predetermines the properties of the system. It is demonstrated that a specifically designed family of spreading codes exhibits a so-called interference-free window (IFW) and hence the resultant system is capable of outperforming its standardised counterpart employing classic Orthogonal Variable Spreading Factor (OVSF) codes under realistic dispersive channel conditions, provided that the interfering multi-user and multipath components arrive within this IFW. This condition may be ensured with the aid of quasisynchronous adaptive timing advance control. However, a limitation of the system is that the number of spreading codes exhibiting a certain IFW is limited, although this problem may be mitigated with the aid of novel code design principles, employing a combination of several spreading sequences in the time-frequency and spatial-domain. The paper is concluded by quantifying the achievable user load of a UTRA-like TDD Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes exhibiting an IFW in comparison to that of its counterpart using OVSF codes. Both system's performance is enhanced using beamforming MIMOs