Message authentication using tag embedding has been widely adopted for Internet of Things (IoT) networks due to its efficient performance and lower resource consumption compared to other tag appending approaches. Specifically, in tag embedding, the authentication tag and the message are superimposed in one signal to save time, energy, and spectral resources, making it an ideal alternative for networks with limited resources, such as IoT networks. However, due to the lower power allocated to the tag symbols (compared to the message symbols) in the conventional scheme, the received tag experiences higher transmission errors, increasing the authentication failure rate (AFR). Moreover, an Eve might be able to capture either the message, the tag or both as they are transmitted unprotected in the conventional scheme. In this work, a novel message authentication scheme is proposed to enhance the performance of the tag embedding scheme. Specifically, the proposed scheme involves precoding the tag signal prior to being superimposed with the message signal and emitted over the channel. The conducted analysis and evaluation reveal that the proposed scheme can significantly reduce both the tag error rate (TER) and the message error rate (MER), which should be directly reflected in improving the AFR. In addition, the performance at the eavesdropper is shown to be degraded due to the precoding of the tag signal induced in the proposed scheme. The included analysis and explored results investigate the impact of power allocation at the transmitter between the tag and message signals to minimize MER, TER or AFR.

The growing demand for spectrum resources necessitates the urgent need for innovative physical-layer solutions that maximize spectral efficiency. Over the past decades, multiple access (MA) schemes have been extensively developed to improve spectral utilization and support more users. However, existing standards are based solely on orthogonal multiple access (OMA) schemes, which restrict multiple users from sharing the same channel, inherently limiting overall spectral efficiency. Although recent research has proposed various non-orthogonal multiple access (NOMA) alternatives, these approaches face significant practical challenges, including receiver complexity, fairness issues, and scalability concerns, which cast doubt on their short-term feasibility. To address these limitations, a new uplink MA framework, termed cooperative modulation (CoM), is introduced. The scheme enables simultaneous multiuser transmission over a single channel through user-side channel pre-equalization combined with a deterministic phase-rotation design. In CoM, users transmit precoded modulated symbols that cooperatively form a structured composite constellation at the receiver. This precoding requires no information exchange among users; each user independently applies channel pre-equalization and a fixed phase shift prior to transmission. Unlike existing rotation-based or NOMA schemes, the phase-rotation optimization in CoM is rendered channel-independent due to pre-equalization, allowing the design to scale to arbitrary numbers of users and modulation orders through offline lookup tables. It is also noted that practical limits on the number of users arise from computational complexity and the minimum Euclidean distance of the composite constellation rather than from theoretical constraints. Unlike conventional NOMA, CoM avoids iterative decoding and successive interference cancellation, making it more suitable for practical large-scale deployments. The phase-shift design is identified as a critical performance factor and is examined in detail. Through theoretical analysis and extensive simulations, including the impact of imperfect CSI across a wide range of SNR values and user densities, substantial gains in error performance, spectral efficiency, and computational complexity are demonstrated relative to OMA, NOMA, and recent index-modulated MA schemes. These results position CoM as a promising approach for future spectrally efficient uplink communication systems.

This article proposes a two-fold triple system (TFTS)-based obfuscation scheme as a structured physical-layer transmission technique for multiple-input multiple-output (MIMO) systems. TFTS is a class of combinatorial block designs that enables index-based spatial signaling without cryptographic keys or additional computational overhead. The proposed scheme constructs a space-modulation matrix derived from a TFTS of orderv, where each row corresponds to a unique antenna activation pattern transmitting unmodulated carriers. The TFTS combinatorial space is generated by merging two non-isomorphic Steiner triple systems, yielding a mapping space that grows super-exponentially withv. This growth becomes extreme even for moderate dimensions; for example, atv= 40, the number of valid TFTS realizations exceeds 1010258, rendering exhaustive reconstruction computationally infeasible. The TFTS constellation matrix is assumed to be pre-shared and securely stored at the legitimate transceivers, while an eavesdropper is modeled as a fully informed and computationally unbounded adversary that lacks the correct TFTS mapping and therefore operates under mismatched decoding. Under this adversary model, Eve’s demodulation decisions degrade to random guesses, resulting in an average bit error rate (ABER) approaching 0.5 and negligible exploitable information. Accordingly, the proposed framework is explicitly positioned as a physical-layer obfuscation mechanism rather than a secrecy-capacity or cryptographic security scheme. The obfuscation strength of the system is evaluated through information-leakage analysis, quantifying the mutual information between transmitted indices and Eve’s observations, as well as detectability analysis based on hypothesis testing. Simulation results demonstrate that the proposed TFTS-obfuscation scheme preserves strong performance for the intended receiver in terms of ABER, mutual information, and achievable rate, while maintaining minimal information leakage and low detectability at the eavesdropper.

This article presents a novel low-complexity deep learning model for physical-layer secret key generation (PSKG), specifically designed to enhance wireless security in the Internet of Things (IoT). PSKG typically generates cryptographic keys by exploiting the reciprocal nature of wireless channels; however, this reciprocity is frequently compromised in time-division duplex (TDD) systems due to hardware imperfections and noise, which significantly complicate the key generation process. To effectively address these challenges, the proposed deep neural network (DNN) is developed to efficiently learn and enhance reciprocity features, even in the presence of imperfect channel state information (CSI). Furthermore, the study introduces a DNN-based PSKG method that strategically leverages the phase of channel frequency responses for key extraction. The results conclusively demonstrate that the proposed model substantially reduces the key disagreement ratio (KDR) and enhances randomness, thus providing a robust and practical solution for securing wireless communications in IoT environments.

Physical Layer Secret Key Generation (PSKG) exploits wireless channel reciprocity to establish cryptographic keys between legitimate users, providing a promising solution for securing IoT networks. However, reciprocity in time-division duplex (TDD) systems is often compromised by hardware imperfections and channel noise, posing significant challenges for reliable key generation. To address these issues, this paper proposes an autoencoder-based noise augmentation (AE-NA) model that operates in an unsupervised manner. Specifically, the proposed model integrates dynamic Gaussian noise augmentation directly into the autoencoder architecture. This approach enhances feature extraction capabilities and improves noise robustness, enabling the network to learn noise-invariant representations effectively from noisy channel estimates. Furthermore, we present a comprehensive PSKG framework that incorporates the proposed AE-NA model. Reported results demonstrate that the AE-NA-based PSKG significantly reduces the key disagreement ratio (KDR) while enhancing key randomness, thereby providing a scalable and effective solution for secure key generation in dynamic IoT environments.

This article presents a complete system model implementation of a digital communication system using Universal software radio peripheral (USRP) and Matlab. In particular, a software defined radio (SDR)-transceiver is implemented in Matlab and configured on the USRP, where several tests and measurements are performed. The deployed system allows investigating the impact of wireless channel impairments including amplitude attenuation, phase shift, time delay, and frequency offset on the overall system performance. As well, synchronization algorithms for symbol synchronization, carrier synchronization, and frame synchronization are presented and evaluated. Reported results reveal accurate implementation and robust design of variant digital communication systems. Results for 16, 64, and 256-quadrature amplitude modulation (QAM) are presented and discussed. As well, reported measurement for the bit error rate (BER) reveal accurate matching with theoretical results over Rician fading channel with a Rician K-factor of 10. Besides, the impact of the pulse shaping parameters and over sampling ratio on the overall system performance is illustrated and discussed.

This article proposes two low complexity decoders for non coherent differential space shift keying (DSSK) multiple input multiple output (MIMO) system by representing the detection problem as a hierarchical tree structure. Such presentation enables yielding the optimal maximum likelihood (ML) performance but with a massive reduction in computational complexity. Attained reduction is accomplished through 1) utilizing the error-repetitive property of DSSK detection to reduce the number of computed error terms and 2) developing two efficient searching strategies that avoid searching the entire alphabet as in ML detectors. These searching strategies enable a trade–off between performance and complexity. Unlike existing sparse recovery (SR) decoders, which require a projection phase to ensure the closure property (i.e., only single transmit antenna is active at each particular time instant and the multiplication of a constellation matrix with another one will produce a matrix from within the set), the new algorithms, inherently, maintain the closure property of DSSK system without additional procedures. Reported results reveal that optimal ML performance is obtained with a huge reduction in complexity by proper adjustment of parameters. It is also shown that the proposed algorithm performs better than state of the art SR algorithms, and the feasibility of massive MIMO configurations with low complexity is demonstrated.

Very recently, signed quadrature spatial modulation (sQSM) is developed as a competent technique that expands the spatial constellation diagram of QSM system by adding a bipolar dimension. Despite the enhanced spectral efficiency, the existing optimal maximum likelihood (ML) presents a serious computational challenge for large scale sQSM systems. Therefore, developing a reduced complexity detector for sQSM schemes is of significant importance to enable implementing and enjoying the inherent advantages of this promising system. Toward this end, a Tree Search (TS) optimal low complexity detector, calledTSopt, for sQSM Multiple Input Multiple Output (MIMO) system is proposed and analyzed in this paper. The proposed detector expands the computationally complex ML detector for sQSM into a tree-structure representation. The idea of the suggested algorithm is to employ an efficient searching strategy that can expeditiously find the branch corresponding to the minimum error without tracing the entire nodes as in the ML case. It is reported that the proposed TSopt algorithm achieves the exact error performance as ML detector but with substantial reduction in computational complexity. Besides, complexity analysis in terms of the number of visited nodes of the TSopt algorithm is analyzed and a closed-form expression for the expected complexity at high SNR values is derived. Reported results disclose agreement between simulation and expected analytical complexity with substantial gains of around 60–80% in complexity reduction for different system parameters.

Space modulation techniques (SMTs) are multiple-input multiple-output (MIMO) transmitter system implementations that have shown to achieve favorable properties compared to existing MIMO technologies. This includes properties such as lower power consumption, cost, and enhanced error performance. As modern wireless standards have come to demand also more reliability and less latency, in recent work analyzing the reliability of SMTs, it was shown that existing SMT implementations do not effectively perform under degraded system conditions. Essentially, under certain failure conditions, parts of SMT systems become unusable although still effectively operational. As a result, affecting the best achievable spectral efficiency, and thus system data rate of the system. In this work, novel SMT implementations are presented and referred to as hybrid SMTs (HSMTs). HSMTs are designed to degrade in a manner that keeps use of operational hardware and maintains a higher spectral efficiency for longer duration. Four different HSMTs are presented namely; hybrid space shift keying (HSSK), hybrid spatial modulation (HSM), hybrid quadrature space shift keying (HQSSK), and hybrid quadrature spatial modulation (HQSM). Additionally, a reliability analysis framework for HSMTs is presented using two different analytical tools and all introduced models are comparatively studied.

Space modulation techniques (SMTs) have emerged as a family of multiple-input multiple-output (MIMO) transmitter designs that require a maximum of a single RF-chain. SMTs have been analyzed in the context of cost, power, and error performance in past studies and have shown to exert favorable advantages over traditional implementations such as spatial multiplexing (SMX). However, given future application requirements, analysis of the hardware also in the context of reliability becomes essential. In this work, an SMT hardware reliability analysis framework is devised using two quantitative analysis tools consisting of reliability block diagrams (RBDs) and Markov Chains. In addition, a comparative study using commercial component failure rates is performed to analyze how SMTs compare to each other.

This paper proposes a combination between quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system and orthogonal frequency division multiplexing (OFDM) aiming to benefit from their superior inherent advantages. The proposed system uses multiple transmit antennas and applies QSM technique on the different OFDM sub-carriers transmitted from the multiple antennas. Therefore, at each frequency sub-carrier, one antenna will be transmitting a real part of the modulated symbol and another or the same antenna will be transmitting the imaginary part of that symbol. As such, many of the transmitted sub-carriers in one OFDM symbol will be un-modulated and transmitting no data, which promises major reduction in the peak to average power ratio (PAPR). Typical OFDM systems generally suffer from high PAPR, which causes major performance degradation in the presence of high power amplifier (HPA) nonlinearities. It is revealed, in this paper, that the proposed system achieves superior performance as compared to it's spatial modulation and spatial multiplexing counterpart systems. Analytical analysis on the overall bit error probability is provided and corroborated through Monte Carlo simulation results.

Receive space modulation relies on channel knowledge at the transmitter and precoding to spatially modulate the receive antennas. This results in reduced complexity and more efficient receiver implementations. Receive space modulation techniques (RSMTs) in particular are a recently introduced family of hardware implementations that leverage receive space modulation. As with any RF hardware implementation, RSMTs will suffer from the effects of RF impairments due to non-ideal behavior of components. Particularly, the I/Q modulator is an essential component in most transmitter implementations which suffers from phase and amplitude imbalance that have an adverse effect on transmitted signals. In this paper, the impact of I/Q amplitude and phase imbalance on the performance of RSMTs is analyzed an studied. It is revealed through the acquired results that amplitude imbalance has the most adverse effect on the different systems, in particular when a high modulation order of an arbitrary constellation is leveraged.

Acousto optical modulator (AOM) is proposed recently to externally modulate the laser beam in free space optical (FSO) system. The idea is to control the laser beam diffraction angle by a sequence of incoming bits, which controls the frequency of the acoustic wave propagating inside the Bragg cell. At the receiver, multiple photo diodes (PDs) are installed, where each is aligned to one of the pre-designed diffracted angles [1]. Superior performance are already reported over lognormal and negative exponential fading channels. In this study, the performance of AOM-FSO system is analyzed over Gamma-Gamma (GG) turbulent channel. Closed form expression of the average bit error rate is obtained in terms of Meijer's G function and analytical results are corroborated through Monte Carlo simulation results. In addition, the impact of atmospheric turbulence, separation distance between PDs and link range are studied.

This paper addresses the implementation and performance analysis of sparse code multiple access (SCMA)-multiple-input multiple-output (MIMO) systems. SCMA is a promising technology to accommodate the ever-increasing number of users as well as spectral and bandwidth efficiency enhancements for next generations wireless systems. Also, MIMO techniques promise significant enhancements in reliability and spectral efficiency of wireless systems. In this study, spatial modulation (SM) and spatial multiplexing (SMX) MIMO techniques are considered along with SCMA. The analytical average bit error ratio (ABER) bound over Rayleigh fading channels is derived and shown to be accurate for a wide range of system parameters. Derived analytical formulas are corroborated through Monte Carlo simulation results and the impact of variant system and channel parameters on the performance of both SCMA-SMX and SCMA-SM systems are thoroughly investigated.

Receive space modulation techniques (RSMTs) are a recently introduced family of hardware implementation multiple-input multiple-output (MIMO) models. RSMTs allow for efficient implementations at the receiver side where either a single or no radio frequency (RF) chain is required. Quadrature based RSMTs, in particular, allow for increasing the spectral efficiency by adding a quadrature dimension to the transmitted signal. Yet, the number of receive antennas in RSMTs must be a power of two integer. To relax this requirement, and allow for arbitrary number of receive antennas, generalized hardware implementation models for two quadrature based RSMTs are presented in this paper. Namely, Generalized Receive Quadrature Space Shift Keying (GRQSSK) and Generalized Receive Quadrature Spatial Modulation (GRQSM) are designed and analyzed. A comparative study is conducted to compare the bit error rate, cost, and power consumption when deploying such systems.

Capacity analysis of space modulation techniques (SMTs) multiple-input multiple-output (MIMO) systems were recently derived and significant enhancements were reported assuming perfect channel knowledge at the receiver. It was illustrated that SMTs achieve higher theoretical capacity than spatial multiplexing (SMX) MIMO system, which can be attained through designing signal symbols such that their distribution multiplied by the channel distribution leads to complex Gaussian distribution. Yet, perfect channel knowledge is impractical and channel estimation techniques must be considered, which cause channel estimation errors (CSE). Such errors are shown in previous literature to severely impact the performance of SMX MIMO system and prevent achieving the theoretical capacity of these systems. Therefore, the impact of CSE on the capacity of SMTs are studied in this paper. It is shown that Space modulation techniques (SMTs), and unlike SMX, can achieve the capacity in the presence of CSE and the conditions under which this can be obtained are derived over variant fading channels. Also, the impact of CSE on the overall capacity is discoursed. Validating the derived theoretical capacity formula through Monte Carlo simulation of the mutual information are presented over wide range of system and channel parameters.

Index Modulation (IM) concept is exploited to propose a novel uplink multiple access technique called, IM-multiple access (IMMA). In IMMA, part of the transmitted block for each user is used to modulate a complex symbol that is transmitted on a specific time slot determined by the remaining bits in that block. Concurrent transmissions from different users are probable in IMMA since the operating time slot for each user is individually selected and the scheme can be considered as a non-orthogonal multiple access (NOMA) technique. Yet, it is revealed that the error rate at the centralized receiver is better than other orthogonal multiple access schemes. Adopting a maximum likelihood detector to jointly decode all the transmitted blocks from various users is shown to be computationally complex. Hence, a reduced-complexity detection scheme is proposed where a substantial reduction in computational complexity of more than 50% is attained with a marginal performance penalty. Besides, an analytical upper bound of the average bit error rate (BER) and the probability of collision are derived in a closed form expression. It is also disclosed through simulation results that a significant enhancement in the BER is achieved for the proposed IMMA scheme as compared with the conventional TDMA system and to sparse code multiple access NOMA scheme.

In this paper, three non-coherent index modulation (IM) schemes are proposed and analyzed. All schemes are based on subcarrier index modulation (SIM) in which an OFDM symbol is divided to groups of subcarriers and part of the subcarriers within each group are only active. The first scheme is called differential subcarrier index shift keying (DSISK). In DSISK, the index of the active subcarrier within a group is the only source of information and no modulated data symbol is transmitted. The second scheme is named differential subcarrier index modulation (DSIM), which transmits a modulated symbols on the active subcarriers and data bits are conveyed in both the index of the active subcarriers and the transmitted data symbols. The last scheme named as differential subcarrier index quadrature modulation (DSIQM) enhances the data rate of DSIM by activating two subcarrier indexes. One subcarrier will transmit the real part of the modulated symbol, whereas the second active subcarrier modulates the quadrature component of the active subcarrier. A unified upper bound formula for computing the average bit error probability is derived for all presented schemes. Analytical results are corroborated through Monte Carlo simulation results, where a close match is reported at pragmatic signal-to noise ratio (SNR) values.

The recently proposed quadrature spatial modulation (QSM) has drawn an increasing attention due to its high spectral efficiency compared with the previous space modulation schemes. In this study, the performance of QSM in two‐way decode‐and‐forward relaying cooperative networks is investigated. In two‐way relaying cooperative networks, two source nodes are allowed to simultaneously transmit data on the same time slot to a relay node. The relay node decodes the transmitted data from both transmitting nodes and retransmits them in the next time slot. Using network coding techniques, each node is able to decode the data of the other node upon accomplishing the second time slot. Considering QSM as the adopted modulation at all nodes, the average bit error rates at the source nodes and the relay are formulated in a closed form expression. Obtained results reveal that QSM‐based two‐way relaying can achieve better error performance than other related scenarios.

Quadrature spatial modulation (QSM) is a recent multiple input multiple output transmission scheme that attracted significant research interest. QSM expands the spatial constellation diagram of spatial modulation (SM) to enhance the overall spectral efficiency while retaining all SM inherent advantages. In this paper, differential QSM (DQSM) is proposed to alleviate the requirement of channel knowledge at the receiver side. Receiver channel knowledge is crucial in QSM as part of the data are encoded in the Euclidean difference among different channel paths. Time dimension and orthogonal in-phase and quadrature spatial dimensions of QSM are exploited to facilitate differential modulation and demodulation while maintaining single RF-chain transmitters. In addition, a systematic design of the transmission blocks is provided for arbitrary number of transmit and receive antennas. Besides, a novel analytical framework for analyzing the performance of DQSM is derived and shown to predict accurate performance for differential SM and differential space shift keying systems as well. Analytical and simulation results are shown to match closely over a wide range of signal to noise ratios and for different system parameters.

Space modulation techniques (SMTs), in which some or all of the data bits modulate a block of spatial constellation symbol, are promising candidates for future 5G wireless systems. They promise data rate enhancements while maintaining low energy consumption, hardware cost, and computational complexity. As such, they attracted significant research interest in the past few years. One of the major assets of SMTs is the assumption that they can operate with a single RF chain at the transmitter even though multiple antennas might be activated at one time instant. Thus far, this claim is anticipated in several research articles but the transmitter designs of the different SMTs with a single RF chain are not addressed yet in the literature. SMTs include different system configurations, such as spatial modulation, space shift keying, quadrature spatial modulation, and quadrature space shift keying. The required hardware components to implement a transmitter for each of these systems with the minimum number of RF-chains are discussed in this paper. In addition, hardware limitations and the impact of different hardware blocks on the overall system performance are discussed. Besides, a comparison among different schemes along with conventional spatial multiplexing algorithm in terms of power consumption, hardware cost, probability of error, and receiver computational complexity is presented. It is shown that some of these techniques can operate without any RF-chain while a single-RF chain is sufficient for other systems. Moreover, these schemes can be traded off in terms of energy savings, complexity, performance, and cost.

Capacity analysis for millimeter-wave (mmWave) quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system is presented in this paper. QSM is a new MIMO technique proposed to enhance the performance of conventional spatial modulation (SM) while retaining almost all its inherent advantages. Furthermore, mmWave utilizes a wide-bandwidth spectrum and is a very promising candidate for future wireless systems. Detailed and novel analysis of the mutual information and the achievable capacity for mmWave-QSM system using a 3-D statistical channel model for outdoor mmWave communications are presented in this paper. Monte Carlo simulation results are provided to corroborate derived formulas. Obtained results reveal that the 3-D mmWave channel model can be closely approximated by a log-normal fading channel. The conditions under which capacity can be achieved are derived and discussed. It is shown that the capacity of QSM system can be achieved, by carefully designing the constellation symbols for each specific channel model.

In this paper, we analyze multiple-input multiple-output quadrature spatial modulation (QSM-MIMO) systems that operate under imperfect channel information over correlated α-μ fading channels. A simple and closed-form expression for the pairwise error probability (PEP) is provided. Based on the obtained PEP, a closed-form upper bound expression for the average bit error probability (BEP) is obtained. The obtained results clearly show the effect of the fading parameters on the average BEP. In case of the α-μ fading channels, increasing a has larger negative impact on the average BEP compared to increasing μ. In addition, the results demonstrate that the correlation coefficient of the transmit-antennas significantly deteriorates the average BEP when compared to the correlation coefficient of the receive-antennas.

Quadrature spatial modulation (QSM) in cognitive radio (CR) is a new spectral efficient multiple-input multiple-output (MIMO) digital modulation technique. In QSM, the spatial constellation diagram of conventional spatial modulation (SM) system is extended to include both in-phase and quadrature components of the data symbol. As such, QSM combined with CR techniques achieve significant improvement in the overall spectral efficiency while the advantages of SM are retained. In this paper, we study the performance of QSM-MIMO-CR systems in the presence of mutual primary-secondary co-channel interference. A closed-form expression for the average pair-wise error probability (PEP) of the secondary system is derived and used to calculate a tight upper bound of the average bit error rate (ABER) over Rayleigh fading. In addition, a simple asymptotic expression is derived and analyzed. Simulation results, which corroborate the numerical ones, show the importance of QSM in improving the overall secondary performance.

Quadrature spatial modulation (QSM) is proposed recently as an efficient multiple‐input–multiple‐output wireless communication technique. In QSM, spatial multiplexing gain is achieved through modulating a two‐dimensional spatial constellation diagram in addition to conventional signal modulation. It was demonstrated that QSM can be designed with single in‐phase and quadrature (IQ) transmitter. However, the impact of IQ modulator imperfections, which degrade signal fidelity and overall system performance, has not been studied in the literature. In this study, typical IQ modulator/demodulator is considered for QSM system and the performance of the system is analysed and discussed. In particular, IQ imbalance channel modelling, pair‐wise error probability, and average bit error ratio are discussed. Results reveal that IQ imbalance can lead to significant performance degradation of QSM system and should be carefully addressed for any future deployment.

In this paper, we present a comprehensive framework for quadrature spatial modulation (QSM) in generalized fading channels. In particular, the performance analysis of QSM systems in the presence of imperfect channel knowledge and under correlated fading channels is presented. A simple and closed-form expression for the pairwise error probability (PEP) is provided. Based on the obtained PEP, a closed-form upper bound expression for the average bit error probability (BEP) is obtained. The analysis is unified in the sense that it is applicable for any fading channel once its envelope and phase distributions are available. As such, different generalized fading distribution models, namely, η-μ, κ-μ, and α-μ distributions, are considered. The obtained results clearly show the influence of the fading parameters on the average BEP. In the case of the α-μ fading channels, increasing α has larger negative impact on the average BEP compared with increasing μ. For the κ-μ channels, increasing μ results in increasing the average BEP dramatically when compared with increasing κ. In the same context, in η-μ fading channels, as μ increases the average BEP degrades whereas increasing η slightly improves the average BEP. In addition, it is demonstrated that transmit-antenna correlation significantly deteriorate the average BEP when compared with receive-antenna correlation.

Space modulation techniques, such as spatial modulation (SM) and space shift keying (SSK), are spatial multiplexing MIMO techniques that use multiple transmit- and receive-antenna in a new and resourceful fashion to enhance the overall spectral efficiency of wireless communication systems. In this paper, the performance of space modulations over the generalized κ-μ fading channels under imperfect channel state information (CSI) is analyzed. In particular, a generalized, simple and exact closed-form expression for the pairwise error probability (PEP) of SM- and SSK-MIMO systems that operate over the generalized κ - μ fading channels is derived and evaluated. The PEP expression jointly considers the envelope-phase distribution of the fading channel. Based on the derived PEP and the union bound technique, a closed-form expression for the average bit error rate (BER) is obtained. The system performance is analyzed and discussed through representative numerical examples over a wide range of the fading parameters (κ and μ) and under the channel estimation error. The numerical results are corroborated with Monte-Carlo simulations to validate our analytical results.

Quadrature spatial modulation (QSM) is a new multiple-input multiple-output (MIMO) transmission technique that enhances the overall spectral efficiency of conventional spatial modulation (SM). QSM extends the single dimension spatial constellation to another dimension by considering the inphase and the quadrature components of the data symbol. It has been shown that spectral efficiency can be significantly increased while most inherent advantages of SM are retained. In this paper, the impact of Gaussian imperfect channel estimation on the performance of QSM system is studied. A closed-form expression for the pair-wise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the Average Bit Error Probability (ABEP) over Rayleigh fading. Also, simple asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results highlight the accuracy of the conducted analysis.

This paper analyzes the performance of space modulation techniques over generalized fading channels with imperfect channel estimation. In particular, a unified approach for calculating the pairwise error probability (PEP) of spatial modulation (SM) and space shift keying (SSK) modulation techniques for multiple-input multiple-output (MIMO) wireless communication systems is presented. A new, simple, and exact closed-form expression for the PEP over generalized α-μ fading channels under imperfect channel state information (CSI) is derived. The PEP expression considers the joint distributions of the envelope and the phase of the fading channel. Furthermore, the derived PEP and the union bound technique are used to obtain a closed-form expression for the average bit error rate (BER). The influence of the fading parameters α and μ and the channel estimation error on the system performance is analyzed and discussed through representative numerical examples. The correctness of our derivations is validated by means of MonteCarlo simulations.

Spatial modulation (SM) is a relatively new multiple-input multiple-output (MIMO) technology that can provide high data rate with reasonable spectral efficiency. In this paper, the bit error rate (BER) performance of SM systems under vehicle-to-vehicle (V2V) channel models is investigated. The theoretical BER expression is given. The impact of some V2V channel model parameters on the underlying space-time correlation function (STCF) and the BER performance of SM systems are also studied. Simulation results indicate that modulation schemes, maximum Doppler frequency, the distance between the transmitter (Tx) and receiver (Rx), and antenna element spacings can affect the performance of SM systems.

A high spectral efficiency multiple-input multiple- output (MIMO) technique called Quadrature Spatial Modulation (QSM) is proposed in this work. QSM enhances the overall spectral-efficiency of conventional SM systems by using an extra spatial modulation dimension. The conventional SM technique uses only the real part of the spatial modulation constellation and QSM extends this to in-phase and quadrature dimensions. It is shown that significant performance enhancements as compared to conventional SM can be achieved without any extra cost. Also, a closed-form expression for the pair-wise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the Average Bit Error Probability (ABEP) over Rayleigh fading channels. Additionally, simple and general asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results corroborate the accuracy of the conducted analysis and demonstrate the significant enhancements of the QSM scheme.

This paper investigates the bit error rate (BER) performance of spatial diversity free-space optical (FSO) communication systems using on-off keying modulation. The study considers correlated log-normal FSO channels as well as path losses due to weather effects using intensity modulation and direct detection schemes. An approximated moment generating functions (MGF) for the joint probability density function of correlated log-normal channels are considered. Using MGF approximation, BER expressions for repetition codes (RCs) and orthogonal space time block codes (OSTBCs) in correlated lognormal channels are derived. Results show that RCs outperform OSTBCs in correlated channel conditions. In addition, the effect of different weather conditions (e.g., haze, rain and fog) on the BER performance of the FSO links are studied. Monte Carlo simulation results are further provided to demonstrate the validity of the proposed mathematical analysis.

A high spectral efficiency cooperative communication system is proposed in this paper. The concept of signal space diversity (SSD) is utilized to double the spectral efficiency of opportunistic cooperative communication networks. SSD rotates the transmitted symbols by a certain angle at the source, before transmission, such that each in-phase and quadrature component of the rotated symbol contains enough information to retrieve the entire original data symbol. As such, parts of the rotated symbols are transmitted by the source and the other parts are transmitted by a relay. In opportunistic relaying, the best relay among all relays that decode the source signals correctly participates in forwarding a message to the destination. Optimum receiver along with detailed performance analysis are presented in this paper. Also, asymptotic analysis and optimum power allocations at the source and the active relay are given. It is shown that the proposed technique enhances the performance by about 2dB over the conventional opportunistic relaying. As well, optimum power allocation is shown to further enhance the error probability performance.

Performance analysis of multi‐hop wireless networks with non‐regenerative relays over Nakagami‐ m fading channels in the presence of co‐channel interference is presented in this paper. In the analysis, an arbitrary number of independent and identically distributed Nakagami‐ m interferers will be considered. Closed‐form expression for the cumulative distribution function (CDF) of the upper bounded end‐to‐end signal‐to‐interference‐plus‐noise ratio (SINR) at the destination is given. The obtained CDF is then considered to study the average bit error probability (ABEP). Furthermore, an approximate expression for the CDF of the instantaneous end‐to‐end SINR is derived, based on which simple and general asymptotic expression for the error probability is presented and discussed. The derived asymptotic equation is shown to reduce to the already published equation in Rayleigh fading, which corroborate the exactness of the derived analysis. Besides, analytical comparison between amplify‐and‐forward and decode‐and‐forward multi‐hop systems in terms of ABEP is provided. Optimisation of the power allocation at the network's transmit nodes and the positioning of the relays are studied as well. It is shown that optimum power allocation achieves only coding gain, whereas optimising relay locations yields diversity gains as well as coding gain.

Generative models, which can generate bursty error sequences with similar burst error statistics to those of descriptive models, have an immense impact on the wireless communications industry as they can significantly reduce the computational time of simulating wireless communication links. Adaptive generative models aim to produce any error sequences with any given signal-to-noise ratios (SNRs) by using only two reference error sequences obtained from a reference transmission system with two different SNRs. Compared with traditional generative models, this adaptive technique can further considerably reduce the computational load of generating new error sequences as there is no need to simulate the whole reference transmission system again. In this paper, reference error sequences are provided by computer simulations of a long term evolution (LTE) system. Adaptive generative models are developed from three widely used generative models, namely, the simplified Fritchman model (SFM), the Baum-Welch based hidden Markov model (BWHMM), and the deterministic process based generative model (DPBGM). It is demonstrated that the adaptive DPBGM can provide accurate burst error statistics and bit error rate (BER) performance of the LTE system, while the adaptive SFM and adaptive BWHMM fail to do so.

Hybrid Automatic Retransmission reQuest (HARQ) is an effective technique to improve the reliability of wireless communication systems by detecting, correcting, and retransmitting the erroneous packets. Packet-level error sequences obtained from physical layer wireless communication systems are important for the design and performance evaluation of high layer protocols, e.g., HARQ. In this paper, we utilize the open source Vienna long-term evolution (LTE) simulator to study the impact of HARQ on the burst error statistics of packet-level error sequences. Moreover, we propose a generative model that can generate packet-level error sequences with predicted burst error statistics similar to those of error sequences obtained from wireless systems with HARQ. Simulation results demonstrate that the proposed generative model is accurate and efficient in predicting the behavior of HARQ in terms of a set of burst error statistics rather than predicting the packet error rate (PER) only.

In this paper, we analyze and evaluate the performance of spatial modulation (SM) systems that operate over independent and identically distributed (i.i.d) η - μ fading channels. More specifically, a closed-form expression in terms of Appell's hypergeometric function for the pairwise error probability (PEP) is derived. Furthermore, simplifications for some special fading distributions such as Nakagami-m, Rayleigh, and Nakagami-q (Hoyt) are then presented. The derived expressions are valid for integer, as well as for non-integer values of μ. Simulation results demonstrate that the average bit error rate (BER) improves when η and μ increase, whilst the effect of μ is more pronounced than that of η.

In this paper, spatial modulation (SM) is considered in a cooperative communication system and the effect of imperfect channel estimation on the overall system performance is analyzed. SM is a multiple-input multiple-output (MIMO) technique that considers the multiple transmit antennas as an added constellation points and utilizes them to boost the spectral efficiency. In our analysis, a wireless communication system, where a source communicating with a destination through a direct link and multiple decode and forward (DF) relays, is considered. Imperfect channel knowledge is assumed at each relay and at the destination node. In cooperative mode, only the relays that correctly decode the source signal forward the decoded message to the destination. A closed form expression of the pair wise error probability (PEP) is obtained for a system consisting of two transmit antennas, multiple DF relays and single receive antenna and a tight upper bound is given for the average error probability. As well, asymptotic expression for the PEP at high signal to noise ratio (SNR) is derived.

In this paper, performance and optimization study of multi-hop wireless system with amplify and forward (AF) relays over Nakagami-m fading channels and in the presence of co-channel interference is considered. Arbitrary number of independent and identically distributed Nakagami-m interferers is assumed in the analysis. The cumulative distribution function (CDF) of the upper bounded end-to-end signal-to-interference-plus-noise ratio (SINR) at the destination is calculated in closed-form. The obtained CDF is then used to study the end-to-end average bit error probability (ABEP). As well, approximate expression for the CDF of the instantaneous end-to-end SINR is derived. Based on this, simple and general asymptotic expression for the error probability is presented and discussed. Finally, optimizing power allocation at the transmit nodes and the positioning of the relays are studied. Obtained results revealed that optimum power allocation slightly enhances the performance, whereas optimizing relay locations yields significant performance enhancement. Further improvement is shown to be achieved through joint power and positions optimization.

In this paper, Sphere Decoding (SD) algorithms for Spatial Modulation (SM) are developed to reduce the computational complexity of Maximum—Likelihood (ML) detectors. Two SDs specifically designed for SM are proposed and analysed in terms of Bit Error Ratio (BER) and computational complexity. Using Monte Carlo simulations and mathematical analysis, it is shown that by carefully choosing the initial radius the proposed sphere decoder algorithms offer the same BER as ML detection, with a significant reduction in the computational complexity. A tight closed form expression for the BER performance of SM—SD is derived in the paper, along with an algorithm for choosing the initial radius which provides near to optimum performance. Also, it is shown that none of the proposed SDs are always superior to the others, but the best SD to use depends on the target spectral efficiency. The computational complexity trade—off offered by the proposed solutions is studied via analysis and simulation, and is shown to validate our findings. Finally, the performance of SM—SDs are compared to Spatial Multiplexing (SMX) applying ML decoder and applying SD. It is shown that for the same spectral efficiency, SM—SD offers up to 84% reduction in complexity compared to SMX—SD, with up to 1 dB better BER performance than SMX—ML decoder.

Space modulation techniques, such as spatial modulation (SM) and space shift keying (SSK), are efficient low complexity implementation of multiple input multiple output (MIMO) systems. In such techniques, a single transmit-antenna is activated during each time instant and the activated antenna index is used to convey information. Due to the novel method of conveying information, a major criticism arises on the practicality of such techniques in the presence of real-time imperfections such as channel estimation errors. Therefore, the aim of this paper is to shed light on this issue. The performance of such systems are analyzed in the presence of Gaussian imperfect channel estimations. More specifically, the performance of SSK system consisting of Nttransmit and Nrreceive antennas with maximum-likelihood (ML) detection and imperfect channel state information (CSI) at the receiver is studied. The exact average bit error probability (ABEP) over Rayleigh fading channels is obtained in closed-form for Nt= 2 and arbitrary Nr; while union upper bound is used to compute the ABEP when Nt>; 2 and arbitrary Nr. Furthermore, simple and general asymptotic expression for the ABEP is derived and analyzed. Besides, the effect of imperfect CSI on the performance of SM, Alamouti and SSK schemes considering different number of channel estimation pilots are studied and compared via numerical Monte Carlo simulations. It is shown that, on the contrary to the raised criticism, space modulation techniques are more robust to channel estimation errors than Alamouti since the probability of error is determined by the differences between channels associated with the different transmit antennas rather than the actual channel realization.

In this paper, the performance of indoor OFDM (orthogonal frequency division multiplexing) optical wireless (OW) communication systems in the presence of LED (light emitting diode) clipping distortions is analyzed. Two indoor OW OFDM techniques are considered. An ACO-OFDM (asymmetrically clipped optical OFDM) system produces half-wave symmetry time signal at the output of the OFDM modulator by special assignment of subcarriers. Therefore, bipolar-unipolar conversion is achieved by clipping the signal at the zero level at the expense of data rate reduction. The second technique, called DCO-OFDM (DC-biased optical OFDM), assigns data to all possible subcarriers to increase the data rate. However, half-wave symmetry signals cannot be achieved and a DC bias is needed to convert the bipolar signal to a unipolar signal before modulating the LED intensity. The performance of these systems, in terms of average electrical OFDM signal power versus bit-error-ratio (BER), DC power consumption, and transmitted optical power in the presence of additive white Gaussian noise (AWGN) channel and considering a practical LED model, are studied. Analytical results are validated through Monte Carlo simulation results and the results demonstrate close match. The results clearly highlight that LED clipping has significant impact on the performance of these systems and system design should consider optimizing the OFDM signal power, DC bias point, and LED dynamic range.

In this paper, single amplify and forward (AF) relay is placed between the source and the destination in space shift keying (SSK) multiple-input single output (MISO) system. In SSK, transmit-antenna indices form a spatial constellation diagram where each group of base two logarithm of the input data bits are mapped to one spatial constellation point. Hence, at each time instant, only single transmit antenna is active, which transmits certain energy that contains no data symbol, and all other antennas are off. The receiver, with single receive antenna, decodes the received signal from the single antenna AF relay and estimates the index of the active transmit-antenna to retrieve the transmitted information bits. Closed-form bit error ratio (BER) is derived for the considered system in correlated and uncorrelated channels assuming a transmitter with two transmit antennas. The analytical framework is generalized for an arbitrary number of transmit antennas and a tight upper bound on the BER performance is derived. Additionally, asymptotic analysis are carried out to investigate the effect of the different system parameters on the overall system performance. The analytical results are validated through Monte-Carlo simulation results.

In this paper, we study the performance of Spatial Modulation (SM) applied to optical wireless communications (OWC) in indoor environments with line-of-sight (LOS) characteristics. To this end, we consider setup scenarios with different numbers of optical transmitters and receivers which are arranged within a room. SM is compared to Repetition Coding (RC). Because RC is known to achieve very good performance in OWC systems due to the use of intensity modulation and the resulting constructive superposition of the power signals. The results show that SM can outperform RC when high spectral efficiencies are desirable, e.g. 4 bit/s/Hz and greater, since it can operate with reduced signal modulation orders by conveying additional data bits in the spatial domain. We also demonstrate that SM benefits from receive-diversity to a larger extent while at the same time requiring less computational complexity. Furthermore, we give a general framework to numerically approximate the average bit error probability of both SM and RC.

In this paper, Sphere Decoding (SD) algorithms for Spatial Modulation (SM) are developed to reduce the computational complexity of Maximum--Likelihood (ML--) optimum detectors, which foresee an exhaustive search of the whole search space and have a complexity that linearly increases with the product of number of transmit--antenna, receive--antenna, and size of the modulation scheme. Three SDs specifically designed for SM are proposed and analyzed in terms of Bit Error Probability (BEP) and computational complexity. By judiciously choosing some key parameters, e.g., the radius of the sphere centered around the received signal, it is shown that the proposed algorithms offer the same BEP as ML--optimum detection, with a significant reduction of the computational complexity. Also, it is shown that none of the proposed SDs is always superior to the others, but the best SD to use depends on the system setup, i.e., the number of transmit--antenna, receive--antenna, and the size of the modulation scheme. The computational complexity trade--off offered by the proposed solutions is studied via analysis and simulation, and numerical results are shown to validate our findings.

Nonlinearities can drastically degrade the performance of OFDM (orthogonal frequency division multiplexing) based optical wireless (OW) communication systems using intensity modulation (IM) of the optical carrier. The light emitting diode (LED) transfer function distorts the signal amplitude and forces the lower signal peaks to be clipped at the LED turn-on voltage (TOV). Additionally, the upper signal peaks can result in optical output degradation. The induced distortion can be controlled by optimizing the bias point (BP) of the LED and/or backing-off the signal power modulating the LED. In this paper, the obtained experimental results using a hardware demonstrator for OW OFDM transmission based on field programmable gate array (FPGA) and off-the-shelf analog components are presented. The conducted measurements for the bit-error performance focus on determining the optimum BP and optimizing the OFDM signal amplitude to obtain best performance. In this context, the experimental bit-error ratio (BER) is obtained as a function of the LED BP and the RMS (root mean square) OFDM signal across the LED.

In this paper a novel detection algorithm for spatial modulation (SM) based on sphere decoder (SD) tree search idea is proposed. The aim is to reduce the receiver complexity of the existing optimal decoder while maintaining an optimum performance. The algorithm performs a maximum likelihood (ML) search, only over those points that lie inside a sphere, centered at the received signal, of given radius. It is shown with the aid of analytical derivations, that for a SNR (signal-to-noise ratio) between 2~dB and 18~dB at least 45% and up to 85% reduction in the number of complex operations can be achieved with a close to optimal bit-error-ratio (BER) performance.

In this paper, a multiple-input multiple-output (MIMO) technique for indoor optical wireless (OW) communication is proposed. The technique is referred to as optical spatial modulation (OSM). The key concept is based on spatial modulation (SM). At any given time instant, only one transmitter is active and the others are inactive. A transmitter in space is considered as a spatial constellation point which is assigned a unique bit sequence. Consequently, transmitters are turned on and off depending on the incoming data bits, similar to the activation of constellation points in traditional digital modulation schemes. Hence, a data rate of the base two logarithm of the number of transmit units is achieved. The active transmitter radiates a certain intensity level at a particular time instant. At the receiver side, the optimal SM detector is slightly modified and used to estimate the spatial constellation point. The estimated spatial constellation point is used to arrive at the original bit stream via de-mapping. The upper bound bit-error-ratio (BER) of OSM is analyzed for a MIMO configuration consisting of four transmit units (light emitting diodes (LEDs)) and four receive units (photo diodes (PDs)) in a room. The BER performance is determined for different transmitter and receiver separation distances and different transmitter half power semiangles (Φ1/2). It is shown that the proposed OSM technique achieves twice and four times the data rate as compared to OOK (on-off keying) and PPM (pulse-position modulation), respectively.

Nonlinearities can drastically degrade the performance of optical communication systems based on intensity modulation (IM) of the optical carrier using the time domain orthogonal frequency division multiplexing (OFDM) electrical signal variations. The light emitting diode (LED) transfer function distorts the signal amplitude and forces the lower signal peaks to be clipped at the LED turn-on voltage (TOV). Additionally, the upper signal peaks are purposely clipped before modulating the LED to avoid chip overheating. The induced distortion can be controlled by optimizing the bias point and/or backing-off the signal power. In this paper, a model that incorporates amplitude distortion and that provides a parameterized upper clipping to control nonlinearity induced distortion is proposed. Through Monte Carlo simulations, the model can be used to determine the optimum bias point and to optimize the signal power to obtain best performance. In this context, an analytical approach to evaluate symbol error probability is proposed. A comparison with Monte Carlo simulation results is carried out to verify the accuracy of this approach.

The performance of hard and soft convolutional channel coding techniques for optical spatial modulation (OSM) are analyzed in this paper. OSM is a recently proposed multiple-input multiple-output (MIMO) technique for indoor optical wireless (OW) communication. In OSM only one transmitter is active at a time and the others are turned off. The spatially separated transmit units are considered as spatial constellation points, i.e. the incoming bit sequence activates one of the transmit units. The active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, optimal detection techniques are used to estimate the active transmitter index and retrieve the original information bits. In this paper, channel coding is applied to OSM and the performance of hard and soft detections are analyzed analytically and validated through Monte Carlo simulations. It is shown that the performance can be significantly enhanced by applying channel coding techniques and a gain in signal-to-noise-ratio (SNR) of about 5 dB and 7 dB at a bit-error-ratio (BER) of 10-4are achieved for hard and soft decisions, respectively.

Trellis Coded Spatial Modulation (TCSM) is a novel transmission technology for Multiple-Input-Multiple-Output (MIMO) systems, which has been recently proposed to improve the performance of Spatial Modulation (SM) over correlated fading channels. The fundamental principle of TCSM is to use convolutional encoding and Maximum-Likelihood Sequence Estimation (MLSE) decoding to increase the free distance between sequences of spatial constellation points, thus improving, especially over spatially correlated fading channels, the end-to-end system performance. In this paper, we propose tight analytical bounds for performance analysis of TCSM over correlated fading channels. In particular, the contributions of this paper are as follows: i) we propose two asymptotically tight (for high Signal-to-Noise-Ratios, SNRs) upper bounds for the analysis of uncoded SM schemes, which offer a better accuracy than already existing frameworks, ii) we propose a simple Chernoff bound for performance analysis of TCSM, which, although weak, can well capture the diversity order of the system, and iii) we propose an asymptotically tight (for high SNRs) true union bound for the accurate performance prediction of TCSM over correlated fading channels. Analytical frameworks and findings will also be substantiated via Monte Carlo simulations.

Trellis coded modulation (TCM) is a well known scheme that reduces power requirements without any bandwidth expansion. In TCM, only certain sequences of successive constellation points are allowed (mapping by set partitioning). The novel idea in this paper is to apply the TCM concept to the antenna constellation points of spatial modulation (SM). The aim is to enhance SM performance in correlated channel conditions. SM considers the multiple transmit antennas as additional constellation points and maps a first part of a block of information bits to the transmit antenna indices. Therefore, spatial multiplexing gains are retained and spectral efficiency is boosted. The second part of the block of information bits is mapped to a complex symbol using conventional digital modulation schemes. At any particular time instant, only one antenna is active. The receiver estimates the transmitted symbol and the active antenna index and uses the two estimates to retrieve the original block of data bits. In this paper, TCM partitions the entire set of transmit antennas into sub-sets such that the spacing between antennas within a particular sub-set is maximized. The scheme is called trellis coded spatial modulation (TCSM). Tight analytical performance bounds over correlated fading channels are proposed in this paper. In addition, the performance and complexity of TCSM is compared to the performance of SM, coded V-BLAST (vertical Bell Labs layered space-time) applying near optimum sphere decoder algorithm, and Alamouti scheme combined with TCM. Also, the performance of all schemes with turbo coded modulation is presented. It is shown that under the same spectral efficiency, TCSM exhibits significant performance enhancements in the presence of realistic channel conditions such as Rician fading and spatial correlation (SC). In addition, the complexity of the proposed scheme is shown to be 80% less than the V-BLAST complexity.

In this paper, the infrared optical wireless path loss inside an aircraft cabin is estimated. To this end, a Monte Carlo ray-tracing (MCRT) simulation is performed in a geometric computer-aided design (CAD) cabin model. Position, azimuth (AZ), elevation (EL) and field of view (FOV) properties of transmitters and receivers are defined. Key path loss parameters such as the path loss exponent and the standard deviation of the shadowing component are determined for particular line-of-sight (LOS) and non-line-of-sight (NLOS) cases. A LOS path loss exponent of 1.92 and a shadowing standard deviation of 0.81 dB are obtained. In NLOS conditions, however, the path loss exponent varies depending on the nature of the particular NLOS case considered. The presented scenarios yield NLOS path loss exponent values of 2.26 and 1.28, and shadowing standard deviation values of 1.27 dB and 0.7 dB, respectively.

In this paper, first, path loss models are developed for infrared optical wireless transmission inside an aircraft cabin. Second, a cellular network in the aircraft is considered and signal-to-interference ratio (SIR) maps are determined via simulation. For this purpose, a Monte Carlo ray-tracing (MCRT) simulation is performed in a geometric computer-aided design (CAD) cabin model with defined position, azimuth (AZ), elevation (EL) and field of view (FOV) properties of transmitters and receivers. Mathematical models are developed for line-of-sight (LOS) and non-line-of-sight (NLOS) path losses along particular paths, including estimation of the path loss exponent and the shadowing component. The shadowing is modeled according to a log-normal distribution with zero mean and standard deviation sigma. The validity of this model is confirmed in the paper. It is shown that irradiance distribution under LOS conditions experiences an attenuation with a path loss exponent of 1.92 and a shadowing standard deviation of 0.81 dB. In NLOS conditions, however, the path loss exponent varies, depending on the nature of the NLOS cases considered. The presented NLOS scenarios yield path loss exponent values of 2.26 and 1.28, and shadowing standard deviation values of 1.27 dB and 0.7 dB, respectively. Finally, the cabin is divided into cells and SIR maps are presented for different frequency reuse factors. It is shown that at the edges of the circular cells with diameter of 2.8 m, a SIR of -5.5 dB is achieved in a horizontal cross section of the cabin for frequency reuse of 1, and -2 dB and 3 dB for frequency reuse factors of 2 and 3, respectively. This means that in an aircraft cabin, for reuse factors less than three, viable communication at the cell edges is not feasible without additional interference avoidance or interference mitigation techniques.

In this paper, the effect of channel imperfections on the performance of spatial modulation (SM) and V-BLAST (vertical-Bell Labs layered space-time) combined with OFDM (orthogonal frequency division multiplexing) transmission is presented. Channel imperfections include Rician fading, spatial correlation and mutual antenna coupling. Recently, SM-OFDM is proposed as a multi-antenna transmission approach that results in an increase in spectral efficiency by systematically mapping a block of information bits to a single transmit antenna (out of a set of antennas) and an information symbol. This principle is applied to each subchannel, i.e. for an entire OFDM symbol at any given subchannel and time instant only one antenna is transmitting. For each subchannel this might be a different antenna, though, depending on the sequence of incoming bits. Consequently, inter-channel interference (ICI) at the receiver input is entirely avoided while high spectral efficient is maintained. In this paper, the effect of channel imperfections on SM-OFDM and V-BLAST-OFDM for coded and uncoded systems are studied. For the same spectral efficiency and a BER (bit error ratio) of 10~3, SM-OFDM is shown to perform 4 dB better than V-BLAST-OFDM in the presence of Rician fading and by 7 dB in the presence of all channel imperfections.

White LEDs are set to penetrate many areas of everyday life. An interesting property of these devices (in addition to their lightening capabilities) is that they can be utilised for data transmission. In the past, primarily OOK (on-off keying) has been used for digital data modulation of such devices. OOK imposes limitations on the achievable data rates. Therefore, in this paper OFDM is considered in combination with higher order modulation schemes. A hardware demonstrator with an entire link chain (transmitter and receiver) is developed and measured BER (bit error ratio) results are reported. The system uses pilot sub-carriers to correct frequency synchronisation errors, training sequences for channel estimation and time synchronisation routines. Forward error correction (FEC) coding is used. It is shown that for COFDM (coded OFDM) with QPSK (quadrature phase shift keying) modulation and a single LED, a BER of 2 times 10-5is achieved for a distance of 90 cm between transmitter and receiver.

Interchannel interference (ICI) is the key problem in wireless MIMO (multiple-input multiple-output) transmission. Numerous ICI reduction algorithms are reported in literature. It is common to these ICI reduction algorithms that they require considerable signal processing power. In this paper, a new approach is presented which avoids ICI and, thus, results in low complexity receivers whilst maintaining high spectral efficiency. It is demonstrated that this can be achieved for BPSK (binary phase shift keying) and QPSK (quadrature phase shift keying) modulation by compressing the symbols prior to transmission and by exploiting spatial information at the receiver. The V-BLAST (Vertical Bell Labs Layered Space-Time) algorithm and simple, low complexity MMSE (minimum mean squared error) and zero-forcing (ZF) detection without ICI reduction was used for comparison. It is shown that the new MIMO approach outperforms V-BLAST by about 6.5 dB at a signal-to-noise-ratio (SNR) of 15 dB while it outperforms direct MMSE detection by about 12 dB. In addition, it was found that the spectral efficiency compared to SISO (single-input single-output) is improved by a factor of 4 at about the same bit-error performance