ABSTRACT Directional modulation (DM) has been widely studied as a promising technique for enhancing physical layer security (PLS). In particular, DM combined with frequency diverse arrays (FDA) enables directional transmission on the two‐dimensional plane. However, the inevitable presence of sidelobes in FDA patterns still poses a risk of information leakage to eavesdroppers. To address this limitation, we propose an artificial‐noise‐aided DM scheme based on a multilog frequency diverse array (AN‐DM‐MFDA). Unlike conventiona methods that uniformly transmit artificial noise (AN), the proposed scheme strategically allocates AN to the leakage sidelobes, thereby reducing their vulnerability to interception. Furthermore, we derive the theoretical expressions for the average bit error rate (BER) and the secrecy capacity of the developed system. Simulation results confirm that the proposed scheme achieves stronger secrecy protection while maintaining reliable detection performance for the legitimate user, outperforming existing AN‐aided DM approaches.

Recent advances in reconfigurable antennas have led to the new concept of the fluid antenna system (FAS) for shape and position flexibility, as another degree of freedom for wireless communication enhancement. This paper explores the integration of a transmit FAS array for hybrid beamforming (HBF) into a reconfigurable intelligent surface (RIS)-assisted communication architecture for multiuser communications in the downlink, corresponding to the downlink RIS-assisted multiuser multiple-input single-output (MISO) FAS model (Tx RIS-assisted-MISO-FAS). By considering Rician channel fading, we formulate a sum-rate maximization optimization problem to alternately optimize the HBF matrix, the RIS phase-shift matrix, and the FAS position. Due to the strong coupling of multiple optimization variables, the multi-fractional summation in the sum-rate expression, the modulus-1 limitation of analog phase shifters and RIS, and the antenna position variables appearing in the exponent, this problem is highly non-convex, which is addressed through the block coordinate descent (BCD) framework in conjunction with semidefinite relaxation (SDR) and majorization-minimization (MM) methods. To reduce the computational complexity, we then propose a low-complexity grating-lobe (GL)-based telescopic-FA (TFA) system with multiple delicately deployed RISs under the sub-connected HBF architecture and the line-of-sight (LoS)-dominant channel condition, to allow closed-form solutions for the HBF and TFA position. Our simulation results illustrate that the former optimization scheme significantly enhances the achievable rate of the proposed system, while the GL-based TFA scheme also provides a considerable gain over conventional fixed-position antenna (FPA) systems, requiring statistical channel state information (CSI) only and with low computational complexity.

Artificial noise (AN) has been recognized as an effective physical-layer security scheme impairing the eavesdropper (Eve). Recently, artificial noise elimination (ANE) has emerged as a promising strategy to mitigate the impact of AN at Eves. However, conventional ANE schemes rely on prior knowledge, such as legitimate channel state information (CSI) or classification information, which may limit their practical applicability. To address these practical challenges, we propose an ANE scheme beyond prior knowledge (BPK) by leveraging machine learning algorithms. Firstly, a coarse projection is applied to partially eliminate the impact of AN using maximum likelihood estimation on the equivalent AN matrix. Secondly, a density clustering algorithm is introduced to obtain classification information based on the coarsely-projected observed vectors. Thirdly, a generalized principal component analysis (PCA)-based ANE algorithm is developed to effectively mitigate the residual AN using the obtained classification information. Furthermore, the artificial-noise-to-signal ratio (ANSR) and computational complexity are analyzed for performance revaluation, and a redefinition of several AN design principles is provided for scenarios involving a powerful Eve equipped with the BPK-ANE scheme by deriving the validity boundary. Finally, numerical results reveal key insights into four principles of AN: 1) Allocating less power to AN; 2) Reducing the randomness of AN; 3) Increasing the number of transmit antennas; and 4) Increasing the modulation order.

Directional modulation (DM) is a physical layer security (PLS) technique implemented at the transmitter, leveraging antenna arrays to ensure secure communications. Through a process of spatial precoding between transceivers to transmit signals in specific directions, DM is capable of disrupting communications in unintended directions to prevent eavesdropping. In general, recent progress in the development of multiple-input multiple-output (MIMO) systems, including advanced radio frequency (RF), antenna technologies, along with innovative precoding algorithms, has enhanced the capabilities of DM techniques, leading to a multitude of robust DM variants. Hence, this survey aims to offer a comprehensive overview of DM, covering its fundamentals, promising variants, applications, hardware implementations, and future trends. Initially, the basic principle of DM is outlined in a general manner for subsequent comprehension. Subsequently, the large family of DM techniques is categorized into distinct variants based on the types of transmitting arrays. Next, we give a comprehensive survey of DM in common wireless scenarios, including multi-user (MU), relay, Internet of Things (IoT), and non-orthogonal access (NOMA) networks. Furthermore, we provide an illustration of DM system implementations, encompassing foundational architectures and cost-effective hardware realizations. Finally, concerning the unresolved challenges and current research focal points in DM, we present future research directions that merit further exploration and reference.

In pursuit of real-time sensing within ultra-short duration, conventional sensing algorithms are gradually failing to fulfill the stringent latency demands. Specifically, traditional subspace-based methods such as multiple signal classification (MUSIC) are hindered by their need for an extensive number of snapshots to accumulate the rank of the spatial covariance matrix (SCM), resulting in poor real-time performance. Moreover, advanced techniques like compressed sensing and machine learning are constrained by requirements for high signal sparsity or suffer from limited generality. To handle these challenges, this paper proposes an innovative extension of subspace theory tailored to insufficient-snapshot scenarios, leveraging the concept of spatio-temporal exchangeability. Based on the defined spatio-temporal correlation predicated on the space translation invariance characteristic of uniform linear arrays, we engineer a pseudo SCM that inherently possesses sufficient rank. This methodology not only resolves the rank-deficiency issue but also fully exploits the array aperture and significantly reduces the noise level. Simulation results are presented, substantiating the feasibility and enhanced performance of the proposed algorithms, marking a significant advancement over existing methodologies.

Directional modulation (DM), as a multi-antenna-based physical layer security (PLS) technology toward millimeter wave (mmWave) scenarios, is capable of guaranteeing effective and secure transmissions by simultaneously performing beamforming and artificial noise (AN). Over the past decade, the DM architecture has changed from a fully analog (FA) one to a fully digital (FD) one. Additionally, the hybrid architecture, which effectively balances both performance and hardware considerations, has unfortunately received limited attention regarding the integration of DM within its framework. In this paper, we intend to give a detailed study of DM technology under the still imperfect FA and more effective hybrid architectures. Specifically, for a single-user (SU) multiple-input single-output (MISO) FA-DM systems, considering the constant modulus constraint (CMC) of phase shifters (PSs) as well as the power allocation issue, we propose a low-complexity DM precoder with closed-form solutions by maximizing the entropy of precoder (EoP). On the other hand, optimization problems are cast and discussed under different RF chain number configurations for SU multiple-input multiple-output (MIMO) hybrid-DM systems. Specifically, as the RF chain count decreases from twice the data stream number to match it, we all use optimization to achieve the corresponding optimal or near-optimal solutions. Finally, simulation results verify our aforementioned analysis and demonstrate the superiority of the proposed FA and hybrid-DM algorithms in terms of secrecy rate and bit error rate (BER) compared to the counterparts when PSs with low resolution are used.

Recently, stacked intelligent metasurfaces (SIMs) have aroused widespread discussions as an innovative technology for directly processing electromagnetic (EM) wave signals. By stacking multiple programmable metasurface layers, an SIM has the ability to provide additional spatial degrees of freedom without the introduction of expensive radio-frequency chains, which may outperform reconfigurable intelligent surfaces (RISs) with single-layer structures. For the sake of alleviating information leakage risks in wireless communications, artificial noise (AN) has arisen as a physical-layer security technology with severe hardware constraints, which is impracticable in single-input single-output (SISO) systems. Therefore, we deploy an SIM at the transmitter (Alice) to accomplish joint modulation, beamforming, and AN in SISO systems. As such, an artificial neural network structured SIM aims to convert an input carrier signal into a desired output signal. Subsequently, we formulate the fitting problem between the actual output signal and the desired signal. Moreover, we introduce a regularization parameter to improve the energy efficiency. In order to tackle this resultant non-convex problem, we provide an alternating optimization algorithm to iteratively determine each variable. For the sake of reducing the computational complexity, we derive closed-form expressions for each phase shift and transmit power. Furthermore, we theoretically analyze the secrecy rate and computational complexity. By considering the signal deviation introduced by SIM, we derive upper and lower bounds of the secrecy rate to provide fundamental insights. Finally, simulation results demonstrate that the SIM-aided SISO system is capable of realizing secure communications efficiently, while the introduced power regularization parameter saved over 2 dB transmit power for a 5-layer SIM without amplifying the fitting error.

As mobile networks progress towards a unified framework for integrated sensing and communication (ISAC), it is foreseeable to introduce new privacy concerns, particularly the potential exposure of position information to unintended receivers. In other words, the scope of physical-layer security (PLS) needs to be expanded to encompass both communication and sensing privacy. Therefore, in contrast to conventional PLS schemes that focus predominantly on preventing eavesdropping, this paper proposes a novel physical-layer privacy (PLP) design within ISAC frameworks, in order to guarantee the secrecy of data transmission while obscuring transmitter’s directional information. Specifically, we introduce a metric termed angular-domain peak-to-average ratio (ADPAR) to assess sensing resistance (SR) performance. Subsequently, three fundamental optimization problems are formulated under such ADPAR constraints to enhance communication secrecy, depending upon the integrity of illegitimate channel state information. These problems are then tackled using advanced strategies such as null-space projection and the cooperation with artificial noise. Additionally, closed-form solutions are further derived in a few specific cases by leveraging singular value decomposition (SVD) and generalized SVD. Finally, simulation results affirm the effectiveness of our design in safeguarding the twofold privacy within ISAC networks.

In addressing the challenges posed by high-mobility communication channels, orthogonal time frequency space (OTFS) emerges as an efficient waveform, heralding considerable performance enhancements. This work delves into the realm of index modulation (IM)-aided OTFS frameworks, with a spotlight on delay-IM with OTFS (DeIM-OTFS) for its exceptional mitigation of inter-symbol interference. Specifically, we introduce a cutting-edge multi-layer message passing detection (MLMPD) algorithm and its streamlined variant for DeIM-OTFS, capitalizing on genuine a priori information to accelerate convergence and enhance bit error rate (BER) performance. Through meticulous simulation, our MLMPD algorithm demonstrates BER performance improvement while substantially reducing complexity, setting a new benchmark for robust, efficient communication in future-oriented scenarios.

Recently, the reconfigurable intelligent surface (RIS), capable of adjusting the phase shifts (PSs) of the reflecting signals through its low-cost elements, has emerged as a promising technology for next-generation wireless communications. However, the RIS may be manipulated by an illegal passive attacker (Wyn) due to the shared nature of wireless channels. In this paper, a Wyn-controlled RIS is considered to attack multiple-input single-output (MISO) communications via passive beamforming based on existing localization and Rician factor estimation techniques. Specifically, we propose an alignment cancellation (AC) scheme to minimize the achievable rate (AR), where the closed-form expressions for location, reflecting element number, and PSs are derived. Furthermore, the computational complexity is quantified to evaluate the low-cost characteristics of this algorithm. Simulation results demonstrate that the proposed AC scheme outperforms other benchmark schemes in degrading the AR with efficient and low-complexity designs.

Reconfigurable intelligent surface (RIS), a large array of passive scattering elements, is able to control the properties of electromagnetic waves, thereby enhancing the channel capacity, reducing the bit error rate, and enabling novel signal modulation methods. However, the promising gain of RIS depends on the precision of channel estimation. In this paper, we propose a three-step channel reconstruction framework to improve the channel estimation accuracy inspired by the concept of integrated sensing and communication scenario. Firstly, based on the coarse channel state information (CSI), the proposed dual one-dimensional multiple signal classification (D1D-MUSIC) algorithm improves the localization precision with a reduced complexity. Secondly, expectation maximization-based refined estimation (EMRE) algorithms are proposed to refine the CSI and estimate channel statistical properties (CSP), i.e., the shadow fading, the power of line-of-sight paths, and that of non-line-of-sight components. Thirdly, a gradient descent-based pilot optimization (GDPO) algorithm is further derived to improve the channel estimation precision on the basis of estimated CSPs. Finally, simulation results demonstrate that the developed D1D-MUSIC algorithm has lower localization error and complexity compared with conventional two-dimensional MUSIC algorithm. Moreover, the EMRE algorithms achieve the identical normalized mean square error (NMSE) performances as the ideal minimum mean square error estimator, while possessing robust resistance to the channel model mismatch. Furthermore, the developed GDPO technique is capable of providing an over 11 dB signal-to-noise ratio gain for channel estimation performance at NMSE$\bf = 10^{-2}$.

Space-time line code (STLC) constitutes an attractive multiple-input multiple-output (MIMO) transmission scheme conceived for full diversity gain, while reducing the complexity of the receiver substantially. In this paper, we investigate the influence of imperfect channel estimation to STLC when the channel is modeled by Rayleigh and Rician fading. Furthermore, based on the derived the signal-to-interference-plus-noise ratio (SINR), both the theoretical bit-error-rate (BER) bound and the outage probability of STLC are quantified subject to channel estimation errors. The numerical results finally confirm the reliability of the theoretical analysis.

Orthogonal Time-Frequency-Space (OTFS) modulation has demonstrated superior performances to extend coverage for high-mobility communicatoins. In this paper, we propose a novel OTFS scheme featuring interference self-cancellation achievable with nearly linear complexity. We first apply the repetitive precoding in delay-Doppler domain, and performing negative padding in the time-frequency domain. Additionally, we formulate equivalent coefficients for the TF domain channel to obtain combined gain with point division equalization. Through numerical simulation, compared with the unprocessed OTFS system, the proposed scheme can achieve a significant performance improvement under TF domain point equalization. Finally, through the analysis of computational complexity, our proposed scheme can realize the transceivers design and equalization with approximately linear complexity.

Abstract Offset spatial modulation (OSM) is an attractive variant in the family of spatial modulation technology, which is capable of reducing the frequency of radio frequency chain switching in practical implementations. This paper elaborates on the benefits of adaptive power allocation (PA) conceived for OSM systems. First, a closed‐form solution of the optimal PA algorithm is derived for the case of two transmit antennas, which maximizes the minimum Euclidean distance (ED) between the received signal points. Moreover, based on the above solutions, a low‐complexity iterative PA algorithm is proposed for larger numbers of transmit antennas, by exploiting the EDs of a few dominant error vectors. Furthermore, for striking a flexible trade‐off between the bit error performance and complexity, an iterative convex approximation based PA algorithm is also developed. Finally, simulation results are presented to show that the proposed PA algorithms provide considerable improvements on the original OSM in terms of the bit error rate.

As a revolutionary technology for future wireless communications, reconfigurable intelligent surface (RIS), characterized by an efficient way of manipulating wireless signals, has been widely investigated in recent years toward enhancing signal quality, energy efficiency, throughput, and so on. However, in RIS-assisted Internet of Things (IoT), a new issue as multipath separation emerges, especially, when deploying multiple RISs to assist communication, since the devices may have limited signal processing capabilities. For alleviating this problem, we conceive a novel RIS-enabled code-division multiple access (CDMA) structure, where each RIS holds a specified time-varying coefficient to tag the channel. Moreover, multipath extraction is further considered, including a practical channel estimation approach along with theoretical derivations in terms of Cramér–Rao lower bound, mean-square error, as well as ergodic channel capacity. Simulation results corroborate the feasibility of the conceived RIS-CDMA structure and the effectiveness of the proposed multipath extraction approach.

Recently, communications with the aid of reconfigurable intelligent surface (RIS), which operates with the aim of enhancing the system communication performance, have aroused extensive researches. Furthermore, the use of RIS for positioning has been considered. Therefore, we focus on a practical structure of indoor positioning assisted by distributed RISs through utilizing their ability to manipulate multipath signals, through the developed quasi-static and dynamic modes. Specifically, in the quasi-static mode, for reducing the implementation cost, the reflection coefficients for each RIS are preset and remain constant. In the dynamic mode, the reflection coefficients can be timely updated with a two-step positioning approach toward more accurate positioning performance. Furthermore, the Cramér-Rao lower bound of the developed positioning scheme is quantified through theoretical analysis. Both theoretical analysis and simulation results demonstrate that RIS has the potential to realize accurate positioning even with a single access point, due to its ability to mark the channel and replace traditional active positioning anchors. Meanwhile, we also show that the developed two-step positioning scheme can achieve considerable performance gain in accurate positioning.

Recently, reconfigurable intelligent surface (RIS) has arisen as an excellent technology for assisting wireless communications. In order to handle the intractable non-convex problem for jointly optimizing beamforming and PSs in multiple-input multiple-output (MIMO) transmission, we propose a novel alternating direction (AD) method by maximizing the achievable rate (AR) at the receiver. Specifically, the initial problem is divided into the following two processes: i) optimizing the beamforming vector with fixed PSs, ii) determining a specific PS based on a closed-form solution when the other PSs and beamforming are fixed. Simulation results corroborate that the proposed AD method provides robust attainable performance with reduced computational complexity compared to its traditional counterparts.

Artificial noise elimination (ANE) has arisen as a possible countermeasure for mitigating the influence of artificial noise (AN) at the eavesdropper (Eve). However, conventional ANE schemes require the attainable channel state information (CSI) between the transmitter (Alice) and legitimate receiver (Bob), which reduces the feasibility of this proposal. In this paper, we investigate the issue of ANE without the CSI of Alice-Bob link by minimizing the artificial-noise-to-signal ratio (ANSR). Moreover, the detailed minor component analysis (MCA) algorithm is presented, and the computational complexity is quantified. Simulation results demonstrate that MCA can effectively degrade the influence of AN without the knowledge of CSI.

This paper explores the application of spatial modulation to a cross-media communication system. Specifically, based on the theoretical expression of the mutual information of spatial modulation, an optimization model to maximize the minimum mutual information in the uplink and downlink of the relay is proposed, along with a developed power allocation (PA) scheme. In addition, the simulation is operated under two cross-media communication scenarios to confirm the superiority and robustness of the proposed PA scheme. Finally, the simulation results confirm that the proposed PA scheme has better mutual information performance than that of the average PA scheme.

Abstract Recently, the physical limitation of range‐domain security guarantee for directional modulation with frequency diverse array was disclosed in Ding et al. ( IEEE Access 8, 63302–63309 (2020)). Therefore, to recreate this significant secrecy realisation in both direction and range domain, the authors conceive an artificial noise aided directional modulation scheme via reconfigurable intelligent surface. Specifically, the angle of departure from the reconfigurable intelligent surface to co‐direction receivers varies with distance, which provides the freedom to distinguish users in the range domain. With locations of the active eavesdroppers, an optimisation problem is further formulated to maximise the secrecy rate, which is then solved by applying genetic algorithm and alternating optimisation. On the other hand, when the eavesdroppers are silent, we employ maximum‐ratio transmission precoding and artificial noise to guarantee information security. Finally, simulation results demonstrate that, due to the aid of reconfigurable intelligent surface, the developed directional modulation structure can robustly guarantee the information security in the range domain, whether the information of eavesdroppers is achieved.

Artificial noise (AN), aiming to disturb the eavesdropper while avoiding the influence on the legitimate receiver, has arisen as an excellent technology for improving the physical-layer security of wireless communications. In order to challenge AN, zero-forcing elimination (ZFE) has been introduced as a possible countermeasure to mitigate the AN for the eavesdropper at the cost of more available receive antennas. In this contribution, from the perspective of eavesdroppers, we further conceive a class of efficient null-space elimination (NSE) schemes in order to reduce the number of receive antennas while enhancing the detection quality compared to original ZFE. Furthermore, the performance of secrecy rate as well as bit-error rate (BER) is quantified for both ZFE and NSE schemes through theoretical derivation, while the influence of imperfect channel state information (CSI) is also evaluated. The performance comparison of the above-mentioned schemes illustrates that NSE can provide more robust performance for eavesdroppers over ZFE, with lower hardware requirements as well as moderate complexity increase.

Reconfigurable intelligent surface (RIS)-assisted wireless communications have been widely investigated toward enhanced signal quality, energy efficiency as well as throughput. The issue of multipath separation and identification via multiple RISs, which, however, remains to be further investigated, is of paramount importance. For alleviating this problem, we conceive a novel RIS-assisted spreading and code division multiple access (CDMA) structure, where each RIS holds a time-varying reflection coefficient sequence for spreading, in order to tag the channel and distinguish each other with the idea of CDMA. Moreover, practical channel estimation and multipath identification are considered, and the ergodic channel capacity is also derived when the receiver employs maximum ratio combining. Simulation results corroborate the feasibility of the proposed RIS-CDMA structure and the effectiveness of the developed channel estimation and multipath combination approaches.

Index modulation (IM) has been developed as an energy-efficient transmission scheme for applications where high data rate is required with a limited energy budget. Meanwhile, multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) have been proved to be promising for the physical layer of wireless systems. Therefore, the concept of combining these three schemes to take all the advantages is emerging and the resulted systems are umbrellaed under the name of space-frequency index modulation (SFIM) systems. However, peak-to-average power ratio (PAPR) poses a challenge for SFIM due to the use of OFDM structure. Clipping is a low-complexity and effective measure to reduce the PAPR, however, it introduces distortions that degrade the system error performance. To address this issue, a hard-decision based cancellation method is proposed for the clipped SFIM system in this paper, which shows significant performance gains by effectively estimating the clipping noise and canceling it from the received signals.

Novel communication technology based on large intelligent surface (LIS) [1] has arisen recently, with the aim to enhance the signal quality at the receiver. In this paper, a practical structure of LIS-based spatial modulation (LIS-SM) is proposed, in order to utilize both transmit and receive antenna indices. Meanwhile, the theoretical average bit error rate (ABER) performance bound of the developed LIS-SM scheme is investigated. For the sake of achieving further spatial diversity gain, we extend its employment to the antenna selection (AS) scenario, and a low-complexity selection algorithm is designed on the basis of minimum squared Euclidian distance and signal-to-leakage-and-noise ratio as well as the idea of greedy elimination algorithm. Performance analysis shows that AS-aided LIS-SM is more robust in terms of ABER compared with conventional LIS-SM. Moreover, complexity analysis also depicts that the proposed fast selection algorithm achieves much lower complexity yet a comparable ABER performance, compared to the traditional exhaustive search.

Artificial noise (AN) is considered as a new physical layer technology to improve the security of wireless systems. In this paper, we investigate secure transmission of AN-aided generalized spatial modulation (GSM), which maintains the same hardware requirements at the transmitter as the conventional GSM. In order to further improve the jamming intensity of conventional AN scheme, we propose an Euclidean distance optimized AN (ED-AN) scheme by minimizing the Euclidean distance between the transmit signal and the jamming signal, which also avoids the power waste of conventional AN scheme. The secrecy capacities of both the AN-GSM and EDAN-GSM schemes are analyzed, and the optimal power allocation of AN-GSM is further investigated by maximizing the secrecy capacity. Furthermore, the upper bounds of the theoretical bit error rates (BERs) of both the legitimate receiver and the illegal eavesdropper over the Rayleigh fading channel are derived. Simulation results validate our derived analysis and demonstrate that the ED-AN scheme offers better secrecy and BER performance.

In this paper, we consider the secure generalised precoding aided spatial modulation (GPSM) scheme, which is combined with artificial noise (AN) to resist unknown malicious eavesdropping. Given a strict power constraint for the transmit signal and a wiretap Rayleigh fading channel, the BER performances of both the desired receiver and malicious eavesdropper are derived. Simulation results validate the accuracy of the theoretical analysis and demonstrate the secrecy performance of the secure GPSM system.

In this paper, a novel scheme dubbed space-time block coded rectangular differential spatial modulation (STBC-RDSM) is proposed for multiple-input and multiple-out (MIMO) systems, which combines space-time block coding (STBC) and rectangular differential spatial modulation (RDSM) to reap their respective benefits while avoiding the drawbacks of conventional differential spatial modulation (DSM) systems. More specifically, in the proposed STBC-RDSM scheme, information bits are conveyed via the rectangular differentially encoded antenna index matrices, as well as the STBC blocks. Furthermore, a low-complexity detection scheme is proposed. Our simulation results demonstrate that STBC-RDSM outperforms its conventional DSM counterparts in various spectral efficiencies. Finally, a closed-form union bound on the bit error rate (BER) is derived and validated by our simulation results.

In this paper, a novel space-time block coded rectangular differential spatial modulation (STBC-RDSM) is proposed for multiple-input and multiple-out (MIMO) system, which combines the space-time block coding (STBC) and rectangular differential spatial modulation (RDSM) to take the advantages of RDSM and STBC systems, while avoiding the drawbacks of conventional differential spatial modulation (DSM) systems. More specifically, in the proposed STBC-RDSM scheme, the information bits are conveyed via the rectangular differential encoded antenna indices matrices, as well as the STBC blocks. Our simulation results demonstrate that STBC-RDSM outperforms the existing DSM systems for various spectral efficiencies.

Spatial-multiplexing aided spatial modulation (SMx-SM) is proposed, which intrinsically amalgamates the concept of vertical bell labs space-time (V-BLAST) and SM to attain a high transmission rate, despite its low number of radio frequency (RF) chains at the transmitter. Specifically, in the SMx-SM scheme, the transmit antennas are partitioned into groups and the SM technique is applied individually to each group. Furthermore, low-complexity threshold-aided compressive sensing-based and message passing-based detectors are derived for our SMx-SM system. Our simulation results show that the proposed SMx-SM system exhibits a better performance despite its lower complexity than the conventional generalized spatial modulation system. More importantly, the proposed SMx-SM system is capable of providing considerable performance gains over the V-BLAST system at the same number of RF chains and throughput. Finally, an upper bound is derived for the average bit error probability, which is confirmed by our simulation results.

In this paper, N-continuous (NC) precoding is first combined with spatial modulation (SM) - orthogonal frequency division multiplexing (OFDM) system for sidelobe suppression, and the bit-error rate (BER) performance of the considered system is analyzed over fading channels. On the one hand, the introduced interference of the NC precoder is modeled and analyzed for SM-OFDM, so as to achieve the theoretical BER performance. On the other hand, we show that the simulation results support the theoretical analysis in different parameter configurations of the considered NC precoded SM-OFDM system.

In this paper, we address the problem of channel estimation in time-variant multi-path environment in Orthogonal frequency division multiplexing systems(OFDM). Based on the assumption that the channel varies in a linear fashion during an OFDM block duration, a novel iterative channel estimation arithmetic with noise and interference suppression using pilot tones is investigated. Through iterative noise and interference suppression to determine the positions of channel taps, then we compute the time averages and slopes of that to get the time domain channel matrix, so such method can improve the precision of the estimation. To increase the spectral efficiency and reduce the computational complexity, assuming the positions of channel taps are not changed in one frame duration, a frame based on such estimation scheme is presented. Along with the channel estimation technique, we also analyze the optimum pilot tones placement. Theoretical analysis and simulation results show that our assumption is reasonable, and the proposed channel estimation arithmetic has a good performance with low computational complexity and high spectral efficiency.

Partial transmit sequence (PTS) with pseudo-random sub-block partition can achieve lower Peak-to-Average Power Ratio (PAPR) performance. Based on the correlation of the candidate signals, we can prove that the performance is uncorrelated with the input signal. In general, the correlation of the candidate signals will increase with the number of candidate signals. As a result, the performance improvement will decrease evidently. In this paper, we provide a novel method to design the phase factor for PTS scheme, so as to achieve quasi orthogonal candidates to get better PAPR reduction performance. Simulation results prove it is more efficient than the traditional one.

This letter presents a class of low complexity partial transmit sequence (LC-PTS) techniques for reducing the peak-to- average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The basic principle is to analyze and utilize the correlation among the candidate signals generated in PTS, so as to simplify the computational complexity. Furthermore, the proposed technique focuses on simplifying the computation for each candidate signal, instead of reducing the total number of candidate signals such as in (Jayalath and Tellambura, 2000). Thus, it can be easily combined with other simplified techniques. Simulation results show that the new technique can effectively reduce the complexity compared with the conventional PTS scheme.