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The efficiency of link adaptation in wireless communications relies greatly on the accuracy of channel knowledge and transmission mode selection. In this paper, a novel deep learning based link adaptation framework is proposed for the orthogonal frequency-division multiplexing (OFDM) systems with compressed-sensing-assisted index modulation, termed as OFDM-CSIM, communicating over millimeter-wave (mmWave) channels. To achieve link adaptation, a novel multi-layer sparse Bayesian learning (SBL) algorithm is proposed for accurately and instantaneously providing the required channel state information. Meanwhile, a deep neural networks (DNN)-assisted adaptive modulation algorithm is proposed to choose the best possible transmission mode to maximize the achievable throughput. Simulation results show that the proposed multi-layer SBL algorithm enables more accurate channel estimation than the conventional techniques. The DNN-based adaptive modulator is capable of achieving a higher throughput than the learning-assisted solution based on the $k$ nearest neighbor ($k$ -NN) algorithm, and also the classic average signal-to-noise ratio (SNR)-based solutions. Moreover, analysis shows that both the multi-layer SBL algorithm and the DNN-assisted adaptive modulator achieve better performance than their respective conventional counterparts while at a significantly lower computational complexity cost. [ABSTRACT FROM AUTHOR]

Index modulation (IM) is a recently proposed multi-carrier transmission scheme, which conveys information both by conventional symbols as well as by the specific subcarrier activation patterns conveying them. However, an impediment of IM is that it lacks transmit diversity gain. In this paper, we circumvent this limitation by proposing a limited-feedback assisted IM transmission scheme. Specifically, Euclidean distance based subcarrier subset selection (ED-SSS) is proposed and its attainable transmit diversity order is shown to be $N_c-N_{IM}+1$ , where $N_c$ is the total number of subcarriers in an IM block and $N_{IM}$ is the number of subcarriers used for IM. Furthermore, the ED-SSS is shown to be amenable to low-complexity implementation owing to the orthogonality of its subcarriers. In order to attain the maximum transmit diversity order of $N_c$ , ED-SSS is further extended with the aid of transmit precoding and its transmit diversity order is quantified. The proposed precoding assisted ED-SSS is shown to subsume several of the existing precoding aided IM transmission schemes. Simulation studies are conducted for validating our theoretical claims and also for quantifying the attainable performance gains of the proposed schemes. Specifically, at a BER of $10^{-3}$ an SNR gain as high as 8 dB is observed in case of precoding when compared to its counterpart operating without precoding. [ABSTRACT FROM AUTHOR]

A large-scale differential-detection aided generalized spatial modulation (GSM) system is proposed, which relies on a novel Gram–Schmidt basis set and an adaptive low-complexity detector, and is evidently suitable for high-mobility millimeter-wave (mmWave) channels. We consider nonstationary time-varying mmWave channels and assume that the beam-angles remain relatively fixed, while the channel coefficients vary rapidly. In this scenario, it is a challenging task to find the accurate estimates of channel coefficients for digital beamforming, which becomes an even more severe problem, as the numbers of subarrays and subcarriers increase. Our analog-beamforming-aided nonsquare differentially detected scheme achieves a higher transmission rate than the conventional coherent multiple-input multiple-output schemes because the pilot overhead and the complex-valued feedback are eliminated. Our simulation results following the IEEE 802.11ad specifications show that the performance of our proposed nonsquare differential GSM improved upon increasing the number of subarrays, where the maximum transmission rate of 16 b/s/Hz was considered. [ABSTRACT FROM AUTHOR]

In order to take the advantages of spatial modulation (SM) and support the multiple-access (MA) communications requiring high connectivity, we integrate the SM with DS-CDMA to propose a SM/DS-CDMA scheme, which is in favor of attaining both antenna diversity and frequency diversity. Associated with the SM/DS-CDMA scheme, a range of linear and nonlinear multiuser detectors (MUDs) are proposed and studied. Specifically, for linear MUDs, both minimum mean-square-error-aided joint spatial demodulation (MMSE-JSD) and MMSE-aided separate spatial demodulation (MMSE-SSD) are introduced. For nonlinear MUDs, we first present the joint maximum-likelihood MUD (JML-MUD) for demonstrating the potential of the SM-/DS-CDMA systems. Then, the MMSE-relied iterative interference cancellation (MMSE-IIC) is suggested, and the associated two types of low-complexity high-efficiency reliability measurement schemes are proposed. In this paper, we mathematically analyze both the single-user average bit error rate (ABER) of the SM/DS-CDMA systems employing joint spatial demodulation (JSD) and the approximate ABER of the SM/DS-CDMA systems employing the MMSE-JSD. We investigate and compare the ABER performance of the SM/DS-CDMA systems with various detection schemes and also with some legacy schemes. Our studies and performance results show that the SM/DS-CDMA systems in conjunction with appropriate MUD schemes are capable of providing a desirable tradeoff among the number of users supportable, implementation complexity, and the ABER performance. [ABSTRACT FROM AUTHOR]

In this paper, we propose an energy-efficient spatial modulation-based molecular communication (SM-MC) scheme, in which a transmitted symbol is composed of two parts, i.e., a space derived symbol and a concentration derived symbol. The space symbol is transmitted by embedding the information into the index of a single activated transmitter nanomachine. The concentration symbol is drawn according to the conventional concentration shift keying (CSK) constellation. Benefiting from a single active transmitter during each symbol period, SM-MC can avoid the inter-link interference problem existing in the current multiple-input multiple-output (MIMO) based MC schemes, which hence enables low-complexity symbol detection and performance improvement. Correspondingly, we propose a low-complexity scheme, which first detects the space symbol by energy comparison, and then detects the concentration symbol by the maximum ratio combining assisted CSK demodulation. In this paper, we analyze the symbol error rate (SER) of the SM-MC and of its special case, namely the space shift keying-based MC (SSK-MC), where only space symbol is transmitted and no CSK modulation is invoked. Finally, the analytical results are validated by computer simulations. Our studies demonstrate that both the SSK-MC and SM-MC are capable of achieving better SER performance than the conventional MIMO-MC and single-input single-output-based MC, when given the same symbol rate. [ABSTRACT FROM AUTHOR]

The existing literature on transmit antenna selection (TAS) aided spatial modulation (SM) systems extensively deals with the Euclidean distance (ED) based TAS owing to its high transmit diversity gain. In this paper, we consider the ED-TAS aided generalized spatial modulation (GSM) system that transmits multiple symbols in each channel use and characterize its attainable diversity gain. Second, we show that the minimum ED of the received constellation does not grow beyond a certain point when the size of the signal set is sufficiently large, which facilitates low-complexity implementations of the ED-TAS aided SM system. Our numerical studies revealed that a signal-to-noise gain of about 8 dB is achievable by employing ED-TAS in the GSM system compared to its counterpart dispensing with ED-TAS. [ABSTRACT FROM AUTHOR]

Index modulation (IM) is an attractive concept for next generation communication systems. However, as an emerging technique, there are still some challenges need to be tackled in this frontier. In this paper, we consider two aspects of IM, which are diversity and detection complexity. Specifically, we propose a linear precoding assisted index modulation (LPIM) scheme for orthogonal frequency division multiplexing (OFDM) systems. We commence by analyzing the diversity and coding gains of the proposed scheme. Moreover, a detailed codebook design criterion is proposed. Then, our LPIM codebook is designed based on the maximum diversity and coding gain criteria. In contrast to the signaling model of the existing full diversity precoder designed for OFDM, we introduce a modeling method to link the zero-valued IM symbols to the origin of a Lattice for implementing our full diversity precoder designed for OFDM-IM. Both analytical and computer simulation results are provided for characterizing the attainable performance of OFDM-LPIM, demonstrating that it is capable of achieving full diversity as well as an attractive coding gain. However, the maximum-likelihood (ML) detection complexity of OFDM-LPIM is excessive, hence a low-complexity generalized iterative residual check detector (GIRCD) is proposed, which is inspired by the existing sparse recovery algorithms. Finally, computer simulation results are provided for demonstrating that GIRCD can provide a beneficial trade-off between bit error ratio performance and complexity. [ABSTRACT FROM AUTHOR]

Developed from the recently emerged generalized pre-coding aided spatial modulation (GPSM) concept, a novel non-linear GPSM scheme based on the powerful vector perturbation philosophy is proposed, where a particular subset of receive antennas is activated and the specific activation pattern itself conveys useful implicit information in addition to the conventional modulated and perturbed symbols. Explicitly, both the infinite and finite alphabet capacities are derived for the proposed non-linear GPSM scheme. The associated complexity, energy efficiency, and error probability are also investigated. Our numerical results show that, as the only known non-linear realization within the spatial modulation family, the proposed scheme constitutes an attractive solution to the flexible design of green transceivers, since it is capable of striking a compelling compromise amongst the key performance indicators of throughput, energy consumption, complexity, and performance. In particular, in the challenging full-rank scenario, conveying information through receive antenna indices exhibits a lower complexity, a higher energy efficiency, and a better error resilience than that of the conventional arrangement. [ABSTRACT FROM PUBLISHER]

Precoding-aided spatial modulation (PSM), which conveys information partially by the indices of receive antennas, has some advantages over conventional spatial modulation (SM) using the indices of transmit antennas. In PSM, the precoder may be optimized for different purposes. In this paper, we study the transmitter design in the PSM systems, which motivates to provide secrecy communications. Specifically, we consider a pair of communication terminals overheard by an eavesdropper. The precoder is optimized by jointly minimizing the power received by the eavesdropper and maximizing the power received by the desired terminal. Both the error performance and the ergodic secrecy rate achievable are studied when assuming communications over independent Rayleigh fading channels. Our studies show that positive secrecy rate and low-complexity detection can be attainable simultaneously for the desired receiver even when the eavesdropper employs more receive antennas than the desired receiver. [ABSTRACT FROM PUBLISHER]

In multihop diversity (MHD) aided multihop links, the nodes are assumed to have buffers for temporarily storing their received packets for further transmission at instances of good channel quality. Since adaptive modulation is employed, the number of packets in each time slot (TS) is affected both by the channel quality and the buffer fullness. During each time-slot (TS), the criterion used for activating a specific hop is that of transmitting the highest number of packets. When more than one hop is capable of transmitting the same number of packets, the particular hop having the highest channel quality (reliability) is activated. Hence, we refer to this regime as the maximum throughput adaptive rate transmission (MTART) scheme. The bit error ratio (BER), the outage probability, the throughput as well as the bandwidth-efficiency of the MTART scheme is analyzed. Our results demonstrate that our MTART regime has the potential of significantly outperforming conventional adaptive modulation. Naturally, the BER is improved by the buffering scheme advocated at the cost of an increased delay. Hence, the distribution of the end-to-end packet delay will also be characterized. [ABSTRACT FROM PUBLISHER]

In this letter, the precoding-aided spatial modulation (PSM) is generalized to a secret PSM (SPSM) scheme, which has the capability to resist malicious eavesdropping from an eavesdropper that is unknown to the transmitter. We design a time-varying precoder for the SPSM so that it can retain all the PSM's advantages at the desired receiver while producing time-varying interference to the eavesdropper. The secrecy capacity of our proposed SPSM is studied, and the optimal power allocation between signal and interference transmission is investigated. Our studies and performance results demonstrate that our SPSM can significantly improve the secrecy performance of the PSM, particularly in a high-signal-to-noise-ratio region. Furthermore, the SPSM is capable of achieving a nonzero secrecy rate even when the eavesdropper has more antennas than the desired receiver. [ABSTRACT FROM PUBLISHER]

A new Multiple Input Multiple Output (MIMO) transmission scheme termed as Generalised Pre-coding aided Spatial Modulation (GPSM) is proposed, where the key idea is that a particular subset of receive antennas is activated and the activation pattern itself conveys useful information. This is in contrast to the previously proposed Spatial Modulation (SM) schemes, which operated by activating a specific subset of transmit antennas. We provide both analytical and numerical results characterizing the GPSM scheme proposed for both conventional as well as for large-dimensional MIMO configurations subject to both realistic imperfect Channel State Information at the Transmitter (CSIT) and to the low-rank approximation invoked for large-dimensional MIMO configurations. We also design a so-called reinforcement matrix for attaining substantial performance improvements for our proposed GPSM scheme. Our investigations show that the GPSM scheme constitutes a flexible alternative to the state-of-the-art MIMO transmission schemes, especially because it is capable of achieving a high throughput. Moreover, the benefits of mapping information to the spatial domain rather than relying on conventional modulation has substantial benefits in the medium to high Signal to Noise Ratio (SNR) region. Quantitatively, GPSM is capable of supporting the same throughput as the conventional full-multiplexing gain based MIMO arrangements at an SNR gain of about 1dB at the same receiver complexity. Furthermore, the reinforcement matrix aided GPSM scheme attains a further 3-4dB performance improvement as compared to the conventional GPSM scheme. [ABSTRACT FROM PUBLISHER]

To take the advantages of the M-ary space-shift keying (MSSK) modulation invented recently, a MSSK fast antenna-hopping space-division multiple-access (MSSK FAH-SDMA) scheme is proposed and studied in this paper. In addition to supporting multiple-access, the FAH is introduced also to achieve transmit diversity by sending every MSSK symbol over several time-slots under the control of a FAH pattern (address). Associated with the MSSK FAH-SDMA, a range of linear and nonlinear detection schemes are studied. Specifically, the linear detection schemes considered include the matched-filtering single-user detector (MF-SUD), zero-forcing multiuser detector (ZF-MUD) and minimum mean-square error (MMSE)-MUD, while the nonlinear detection schemes addressed include the maximum likelihood (ML)-MUD and the receiver multiuser diversity aided multi-stage MMSE (RMD/MS-MMSE) MUD. The single-user pairwise error probability (SU-PEP) and bit error rate (BER) union-bound of the single-user MSSK FAH-SDMA systems employing ML detection are analyzed in detail. Based on the SU-PEP, the minimum transmit diversity order of the MSSK FAH-SDMA systems is specified. For the MSSK FAH-SDMA systems with linear detection, we study two types of MSSK demodulation schemes, which are referred to as the intrauser detections (IUDs), named as the maximum likelihood (ML)-IUD and direct (D)-IUD. For the MSSK FAH-SDMA systems employing the RMD/MS-MMSE MUD, two types of reliability measurement (RM) schemes are proposed, which are the maximum a-posteriori (MAP)-RM and ratio test (RT)-RM. Finally, the BER performance of the MSSK FAH-SDMA systems with various combinations of the proposed techniques is studied, when assuming that the channels from any transmit antennas to any receive antennas experience independent and identically distributed (i.i.d.) Rayleigh fading. [ABSTRACT FROM PUBLISHER]

Space-shift keying (SSK) modulation is a recently proposed multiple-input–multiple-output (MIMO) technique, which activates only a single transmit antenna during each time slot and uses the specific index of the activated transmit antenna to implicitly convey information. Activating a single antenna is beneficial in terms of eliminating the interchannel interference and mitigates the peak-to-mean power ratio while avoiding the need for synchronization among transmit antennas. However, this benefit is achieved at a sacrifice, because the transmit diversity gain potential of the multiple transmit antennas is not fully exploited in existing SSK-assisted systems. Furthermore, a high-SSK throughput requires the transmitter to employ a high number of transmit antennas, which is not always practical. Hence, we propose four algorithms—open-loop space–time space-shift keying (ST-SSK), closed-loop feedback-aided phase rotation, feedback-aided power allocation, and cooperative ST-SSK—to achieve a diversity gain. The performance improvements of the proposed schemes are demonstrated by Monte Carlo simulations for spatially independent Rayleigh fading channels. Their robustness to channel estimation errors is also considered. We advocate the proposed ST-SSK techniques, which can achieve a transmit diversity gain of about 10 dB at a bit error rate (BER) of 10^-5, at the cost of imposing a moderate throughput loss that is dedicated to a modest feedback overhead. Furthermore, our proposed ST-SSK scheme lends itself to efficient communication, because the deleterious effects of deep shadow fading no longer impose spatial correlation on the signals that are received by the antennas, which cannot readily be avoided by colocated antenna elements. [ABSTRACT FROM PUBLISHER]