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In this paper, the physical layer security aspects of a wireless framework over α − κ − μ shadowed (AKMS) fading channel are examined by acquiring closed-form novel expressions of average secrecy capacity, secure outage probability (SOP), and strictly positive secrecy capacity. The lower bound of SOP is derived along with the asymptotic expression of SOP at the high signal-to-noise ratio regime in order to achieve secrecy diversity gain. Capitalizing on these expressions, the consequences due to the simultaneous occurrence of fading and shadowing are quantified. Finally, Monte-Carlo simulations are demonstrated to assess the correctness of the expressions.

In this work, we provide a framework analysis of dual-hop hybrid Millimeter Wave Radio Frequency (RF)/Free Space Optical (FSO) MIMO relaying system. The source is equipped with multiple antennas and employs conjugate beamforming while the destination consists of multiple apertures with selection combining. The system also consists of a relay operating at amplify-and-forward mode. The RF channels are subject to Nakagami-m fading while the optical links experience the M\'alaga distribution. In addition, we introduce the impairments to the relay and receiver. In fact, the relay is impaired by the High Power Amplifier (HPA) nonlinearities while the receiver suffers from the In phase and Quadrature Imbalance. Moreover, we assume two types of HPA nonlinearities impairments called Soft Envelope Limiter (SEL) and Traveling Wave Tube Amplifier (TWTA). Closed-forms of the outage probability, the bit error probability, and the ergodic capacity are derived. Capitalizing on these performances, we derive the high SNR asymptotes to unpack insightful metrics such as the diversity gain. We also address the impacts of some key factors on the system performance such as the impairments, the interferers, the number of antennas and apertures and the pointing errors, etc. Finally, the analytical expressions are confirmed by Monte Carlo simulation.

Quadrature spatial modulation (QSM) multiple-input multiple-output system attracted substantial research interests lately driven by the several promised advantages. As well, cooperative communication is well-known to enhance the diversity gain and the overall system performance. In this paper, the theoretical capacity of amplify and forward (AF)-QSM system is derived and analyzed. In particular, the mutual information is first obtained and used to obtain the capacity. Derived formulas are corroborated through Monte Carlo simulation results over wide range of system and channel parameters. Besides, the impact of various parameters on the capacity and the mutual information of the studied system is investigated. The performance of AF-QSM is compared with AF-spatial modulation system and superior gains are reported. It is revealed that the capacity of AF-QSM is independent of the channel fading distribution where Rayleigh, Rician and Nakagami-m fading channels are considered. It is also reported that increasing the number of transmit antennas enhances the performance whereas increasing the number of relays degrades the performance.

In this paper, the concept of computation diversity is proposed by employing generalized hybrid carrier (GHC) system. The signal is backed up by transform-domain computation to enhance the anti-fading capability. Theoretical analysis is presented to demonstrate the superiority of the proposed method. Numerical simulations in doubly-selective fading channels are provided to verify the results. The bit error rate (BER) performance is guaranteed with a small computational complexity increment. The proposed method not only extends the new diversity dimension, but also improves the diversity gain of the system without occupying additional wireless resources. Moreover, the proposed method shows good adaptability with single carrier modulation and improves diversity performance. As the simulation results shown, time-domain dual component computation diversity (TDC-CD) has 1dB BER gain and 0.1 diversity gain at high signal-to-noise ratio, and single carrier system with TDC-CD achieves 2dB BER gain at 10−4.

Complementary coded multicarrier code-division multiple access (CC MC-CDMA) has a strong potential to offer frequency diversity gain in frequency selective fading channels due to its ideal correlation characteristics. However, in uplink transmissions the use of single-user detection techniques will reduce the diversity gain achievable with complementary codes (CCs). Multiuser detection schemes such as successive interference cancellation (SIC) has a strong potential to overcome multiple access interference (MAI) in near-far environments. In this paper, SIC is analyzed in the context of improving the error rate performance of CC MC-CDMA operating under asynchronous uplink environments. The probability of error (POE) analysis for M-branch diversity system using alternate form of Q-function is derived and its performance is verified using SIC with maximal ratio combining (MRC) and minimum mean square error (MMSE) combining. The analysis of CC MC-CDMA systems under equal and unequal power variations is performed in asynchronous channel conditions and it was shown that considerable improvement in system capacity is achieved through multiuser detection.

Free space optical (FSO) communication systems are subject to turbulence-induced fading as a result of fluctuations in the refractive index. Gamma-Gamma (GG) distribution is commonly used in the literature to characterize moderate-to-strong turbulence conditions. The performance of FSO systems is further degraded by pointing error-induced fading as a result of building sways. While the asymptotic analysis presented in earlier works is important to understand the maximum diversity gains of FSO systems attainable over fading channels, such gains might not be available in practical range of signal-to-noise ratio (SNR). Furthermore, different systems with the same asymptotic slope may have different slopes in the range of finite SNR values. In this paper, we consider a multiple-input multiple-output (MIMO) FSO system with intensity modulation and direct detection (IM/DD). We derive approximate expression for the finite-SNR diversity order over GG turbulence channels in the presence of pointing errors. We also investigate convergence speed to full diversity. We provide numerical results to demonstrate the accuracy of our derivations and corroborate on our analytical findings.

The $${\kappa -\mu /}$$ Inverse Gamma (KMIG) and $${\eta -\mu /}$$ Inverse Gamma (EMIG) are recently introduced composite fading distributions for the precise design of the wireless systems, where multipath fading and shadowing occur concomitantly. Further, these composite fading models are competent to be employed in the performance investigation of the digital communication system as their mathematical formulations are quite tractable. Average symbol error probability (SEP) and channel capacity analysis are important parameters to investigate the performance of a digital communication system. The applicability of these fading models is illustrated by analysing the performance matrices of the digital communication channels in the present work. Various performance matrices such as the average SEP, the channel capacity under different adaptive schemes namely, optimum rate adaptation (ORA), channel inversion with fixed rate (CIFR) and truncated CIFR are derived. The asymptotic analysis of KMIG and EMIG composite fading models over average SEP performance matrices with coding gain and diversity gain is also carried out in this work. The simplified high and low signal-to-noise-ratio solutions to channel capacity are also provided as a by-product. In addition, approximate analysis to ORA and CIFR capacity are provided under realistic environmental conditions. The accuracy of the derived numerical formulations is validated with the use of Monte–Carlo simulation. The results of present work will be advantageous in the modelling and designing of popular wireless services such as vehicle-to-vehicle communication, wearable communication and wireless power transfer related technologies.

The deployment of the Millimeter-Wave (mm-Wave) band in 5G and beyond wireless communications networks is one of the emerging fields owing to its potential of providing extensive bandwidth. Frequency Hopping (FH) has a high potential for use in wireless networks due to its key advantages of spreading the interference over wide bandwidth and of providing diversity gain in counteracting frequency-selective fading. Furthermore, Fast Frequency Hopping (FFH) intrinsically amalgamated with directional Beamforming (BF) may overcome the impairments because of the path-loss of mm-Wave communications. Thus, we propose FFH assisted base-band precoding aided BF for mitigating the mm-wave channel impairments imposed by both fading as well as path loss, whilst relying on a minimal range of radio frequency chains. The mathematical analysis and simulation results demonstrate that hybrid precoded FFH is indeed a promising high-capacity technique of attaining both time- and frequency-domain diversity gains for the mm-Wave communications.

In industrial Internet-of-Things (IoT) applications including smart factories, railway/aircraft operating and control systems, and so on, it is expected to deliver a bundle of packets with a delay constraint. In this paper, we study delay-constrained transmissions where a user or device is to send a bundle of short-length packets within a certain time limit through radio resource blocks shared with others. We first derive a closed-form expression for (a tight upper-bound on) the probability of decoding error when a short-length packet is transmitted through multiple channels (for a high diversity gain under fading). Using the expression, we then study the performance in terms of delivery delay for a bundle of packets using the notion of queuing systems. It is shown that the derived expressions agree with simulation results, which demonstrates that those can be used to design delay-constrained transmission systems to support industrial IoT applications where a bundle of packets has to be delivered within a certain short time limit with high reliability.

In this paper, we analyze the average symbol error rate (ASER) of single-input multiple-output (SIMO) networks for rectangular quadrature amplitude modulation (RQAM) and cross-QAM (XQAM) subject to Rayleigh fading. Then, we investigate the performance of RQAM for a SIMO system under κ-μ fading conditions. And also, we consider a multiple-input multiple-output with single transmit antenna selection and maximal ratio combining over Rayleigh fading environments. To analyze the key parameters on the network performances, we propose the analytical expressions of ASER for the considered networks. Assuming flat fading, the obtained exact and approximate expressions for ASER based on the probability density function approach. Furthermore, we present asymptotic expressions of RQAM and XQAM schemes for a SIMO system over Rayleigh fading at the high signal to noise ratio to evaluate the network performance in terms of diversity gain. Finally, simulations are ensured to confirm the correctness of our frameworks in this study.

This paper investigates the diversity gain of a distributed cyclic delay diversity (dCDD) scheme for cyclic-prefixed single carrier systems in non-identical fading channels. Non-identical small-scale fading is assumed in the environment, in which non-identical line-of-sight and non-line-of-sight fading coexist. A condition for dCDD resulting in intersymbol interference free reception at the receiver, is extended to this new channel environment. For an overpopulated system setup, a generalized performance analysis, is not available from existing works, is conducted after developing closed-form expressions for the distribution of the signal-to-noise ratio (SNR) realized at the receiver. Since the order statistics are involved in the statistical properties of the SNR, the corresponding spacing statistics are utilized to derive feasible closed-form expressions. The finalized closed-form expressions are shown to provide very reliable outage probability and spectral efficiency of dCDD for underpopulated and overpopulated systems. An asymptotic performance analysis verifies the maximum achievable diversity of the dCDD even in the overpopulated case within the considered channel environment. Link-level simulations are conducted and these verify the maximum achievable diversity gain.

Free space optical (FSO) communication systems provide high bandwidth in unregulated spectrum and act as a powerful line-of-sight wireless connectivity solution. The performance of FSO systems can be seriously impaired by fading as a result of atmospheric turbulence and/or pointing errors due to misalignment. In the context of FSO systems, relaying was proposed as an effective fading mitigation technique due to the fact that the variance is distance-dependent in turbulence channels. In this article, we present a unified performance analysis of multi-hop FSO systems over Double Generalized Gamma (DGG) turbulence channels with pointing error impairments. We assume amplify-and-forward relaying and consider both heterodyne detection and intensity modulation with direct detection. We derive tight closed-form expressions for the outage probability and bit error probability of both fixed-gain and channel state information (CSI)-assisted relaying in terms of the bivariate Fox-H functions and Fox-H functions, respectively. We further analyze asymptotic behavior of the outage probability in terms of simple elementary functions and obtain the achievable diversity orders. Diversity gain is found to be a function of atmospheric turbulence parameters, pointing error, detection type and the number of hops. Monte Carlo simulation results are further provided to verify the accuracy of the derived expressions.

Rich scattering of ultraviolet signals enables the non-line-of-sight outdoor wireless connectivity and eliminates the line-of-sight requirement of free-space optical links. Besides scattering losses, ultraviolet signals also suffer from the atmospheric turbulence-induced fading. One of the strong fading mitigation techniques is the spatial diversity, which has been extensively studied in the context of wireless radio frequency and infrared networks. In this study, spatial diversity techniques for non-line-of-sight ultraviolet communication links are considered. In particular, multiple-input-single-output (MISO), single-input-multiple-output (SIMO), and multiple-input-multiple-output (MIMO) non-line-of-sight ultraviolet communication systems are derived. The BER performance of the single-input-single-output (SISO) link is also derived as a benchmark. The accuracy of the derivations is confirmed through Monte Carlo simulations. The results demonstrate the significant performance improvements in spatial diversity schemes over SISO counterparts. The authors further investigate the effect of spatial correlation on the performance of non-line-of-sight ultraviolet links with spatial diversity. They demonstrate that the spatial correlation degrades the performance significantly, and efficient separation between apertures is crucial to achieve the maximum diversity gain.

A joint data and interference transmission scheme based on a new distributed asynchronous cyclic delay diversity (dACDD) technique is proposed for cooperative communication systems. Without any perfect channel state information from a legitimate user (LU) and an eavesdropping user (EU), joint remote radio head (RRH) selection for the data and jamming signal transmissions is proposed for dACDD to achieve the maximum diversity gain at the LU, while degrading the receive signal-to-interference-plus-noise ratio at the EU. The proposed dACDD is the extension of distributed cyclic delay diversity, which requires a tight synchronization among the central control unit and RRHs. Thus, processing at each RRH causing no intersymbol interference at the LU is developed. Then, the selection scheme for a data RRH is proposed, which selects a single RRH connected with the channel having the greatest channel magnitude as the data RRH to transmit a desired confidential message and controls the remaining RRHs to transmit an artificial interference sequence to the LU and EU. For the proposed distributed system, the marginal secrecy outage probability and marginal probability of non-zero achievable secrecy rate are analyzed by deriving closed-form expressions, whose correctness is verified via link-level simulations over non-identically distributed frequency selective fading channels.

This paper proposes a new time–space diversity scheme for data transmission through flat fading channels. Extended pulses are used to shape the modulated symbols at different time slots. The proposed transmitter does not change the transmission rate of the modulated symbols after the shaping process. One transmitting antenna is used to transmit the shaped symbols. Multiple antennas are used in the receiver to collect the transmitted symbols. The diversity gain in the proposed system is the product of the numbers of time slots through which the modulated symbol is transmitted and the number of receiving antennas. The proposed transmitter uses neither space–time codes nor spreading codes. The received signal suffers from intentional inter-symbol interference due to the correlation between the shaped symbols. Instead of using equalizers to remove this interference, multi-symbols detectors are used to exploit this interference to achieve the desired diversity gain. Buffers store the replicas of the desired symbol after the multi-symbols detector during its diverse period. Two-dimensional maximal ratio combiner adds these replicas in one decision variable. The proposed system achieves high diversity gain in flat fading channels with one transmitting antenna, and without affecting the used communication resources.

Real-time communication is affected by practical constraints such as node mobility and imperfect channel state information. Most technical contributions in the area of cooperative communication neglect these practical constraints, thus, assumes ideal propagation scenarios. Such approximations make sense in low-rate systems, but can lead to very false results when examining future high data rate systems. In this work, closed-form expression of pairwise error probability (PEP) is derived for dual hop and multiple hop selective decode-and-forward relaying network over time-selective Nakagami-m fading links. Space–time block code is used in combination with multiple-input multiple-output to achieve the diversity gain along with cooperative diversity. To obtain the optimal source-relay power allocation factors, a mathematical framework has been proposed to improve the performance of the system in the power-constraint situation. Simulation results have been presented for various values of fading severity parameter and channel variance. Results for different node-mobility scenarios are also provided. Results show that the system performance improves by increasing the fading severity parameter and relay-to-destination (RD) channel gain. It is noted that the relaying network’s diversity order (DO) is the same as the non-cooperative network’s DO in a scenario when both source node (SN) and destination nodes (DNs) are static, and relay node (RN) is mobile. Also, if the RN and DN are static and the SN is mobile, DO will be equivalent to zero. At high signal-to-noise ratio (SNR), system performance with equal and optimal energy distribution can be seen approaching an asymptotic floor limit, because system performance independent of the power of the noise components. The effect of mobility of the DN on the average per-block PEP output is less important compared to the mobility of the SN. The scheme is restricted by an asymptotic error floor with a greater SNR regime for other node-mobility situations. The analytical results are verified by Monte Carlo simulations for M-ary signaling maximal ratio combiner cooperative system.

Layered transmission is studied in this paper to accommodate various device capabilities and channel conditions. The problem of efficiently broadcasting a common set of layer-encoded data from a single base station to multiple users over quasi-static fading channels is examined. Considering the maximum tolerable delay, a block-level utility is defined in terms of average probability of successful reception of each layer. Based on non-orthogonal multiple access scheme, we propose a complete algorithm to jointly optimize power allocation and transmission rates. By utilizing the idea of opportunistic scheduling, we first derive the success probability of one single layer in homogeneous scenarios, then extend the results to heterogeneous scenarios where users are subject to different channel statistics. The multi-layer optimization is realized by iteratively repeating the single-layer operations. Starting from the base layer, we first choose an optimal subset of users as the corresponding target group, then apply the single-layer allocation process until no power resources are left. Computer simulation and discussion confirm that our method maximizes the block-level utility at the same time balances the tradeoff between multiuser diversity gain and multicast gain.

Single antenna deployed in mobile terminals suffers multipath fading and thereby not only reduces the operating bandwidth but also the efficiency of the antenna. Multiple Input Multiple Output (MIMO) technology thus plays a key role in the modern wireless communication system due to the fact that it not only increases the capacity of the channel but also increases data rate in a fading environment. The design of the MIMO antenna is carried out on different diversity techniques, namely polarization, frequency, pattern diversity, and quasi-self-complimentary method. Also, from the design aspect, isolation between the identical elements is a bigger challenge to encounter. Different methods have been used for both 2 × 2/4 × 4 MIMO antenna configuration to achieve better isolation

Free space optical (FSO) communication has emerged to provide line of sight connectivity and higher throughput over unlicensed optical spectrums. Cognitive radio (CR), on the other hand, can utilize the radio frequency (RF) spectrum and allow a secondary user (SU) to share the same spectrum with the primary user (PU) as long as the SU does not impose interference on the PU. Owing to the potential of these emerging technologies, to provide full spectrum efficiency, this paper focuses on the mixed CR RF-FSO transmission scheme, where RF communication is employed at one hop followed by the FSO transmission on the other hop in a dual-hop decode-and-forward (DF) configuration. To quantify the performance of the proposed scheme, closed form error probability is derived over Rayleigh/Exponentiated Weibull (EW) fading distributions by considering the statistical and instantaneous feedback channel of the primary network. We also employed an asymptotic analysis to illustrate the diversity gain of the overall system. We believe that the proposed scheme can be applicable to the 5G+ networks where an unlicensed university student connects to the home computer with the aid of an FSO path.

Multipath due to reflections of the sea surface, seabed, and obstacles, as well as inhomogeneity within the ocean, is an important characteristic of underwater acoustic channels. Mutual interference among multiple paths causes severe amplitude fading and frequency selective fading. The guard interval is an effective anti-multipath method, but an excessively long guard interval will reduce the data rate of multi-carrier underwater acoustic communication. In this paper, we propose a new anti-multipath multi-carrier communication method based on orthogonal chirp division multiplexing (OCDM) that uses chirp signals for carrier modulation. As OCDM exploits the multipath components for diversity gain, the system robustness is improved. The new method also adds a data pick-based rake receiver for maintaining good communication performance, even at short guard intervals. We detail the implementation and parameter selection of the anti-multipath OCDM system and compare its performance with the traditional orthogonal frequency division multiplexing (OFDM) scheme using simulations; under a severe multipath simulation condition (the delay spread is longer than the guard interval), the anti-multipath OCDM achieves a bit error rate (BER) of $10^{-6}$ , while the OFDM has a BER floor of $10^{-3}$ . The simulation results verify the feasibility of the proposed method and the superiority of its anti-multipath performance.

Satellite communication plays an important role in future wireless network. In this article, we investigate the outage performance of the integrated satellite-terrestrial relay network (ISTRN) with relay selection based adaptive decode-and-forward (RSADF), where the relay selection is based on outdated channel state information (CSI), and the multiple-antenna relays conduct maximum-ratio receiving and transmitting for decoding and forwarding, respectively. Particularly, we first obtain a novel closed-form expression for the outage probability of the considered ISTRN with RSADF. Furthermore, to get further insights of the effect of key system parameters, e.g., the number of relays, the number of antennas, the CSI outdating level, and the channel fading characteristics, on the system performance, we conduct asymptotic analysis for three typical high average signal-to-noise-ratio (SNR) scenarios, i.e., 1) all satellite and terrestrial links are with high average SNR, 2) the satellite-to-relay link and the relay-to-user link are with high average SNR, and 3) only the relay-to-user link is with high average SNR. The derived high SNR approximations of outage probability explicitly reveal the impact of key system parameters in the form of diversity gain and coding gain. Finally, numerical simulations are presented to validate the analytical results.

In this paper, we investigate the wireless powered multi-user multi-relay communication network, in which only relay nodes need energy harvesting with power splitting-based simultaneous wireless information and power transfer architecture. A low-complexity practical scheme, in which the best user selection and partial Nth best relay selection are adopted, is proposed and analyzed under the impact of outdated channel state information (CSI). The exact and lower bound closed-form expressions for the outage probability are derived over independent but not necessarily identical distributed (i.n.i.d) Rayleigh fading channel, and its asymptotic analysis is also given. The asymptotic analysis reveals that the diversity gain can achieve 2, which is different from the system without outdated CSI. The correctness of analytical result is validated by Monte Carlo simulations, and simulation results provide insights into the effect of system parameters, i.e., the impact of outdated CSI, the number of relays and users, average channel fading power, energy harvesting coefficient and power-splitting ratio, on the outage performance. At last, simulation results show that the outdated CSI and the number of relays also affect the optimal value of the power-splitting ratio.

In this paper, we consider Mt×M system (Mt > M), where Mt and M are the numbers of antennas at the transmitter and receiver, respectively. We select M out of Mt transmit antennas using two different antenna selection schemes. In scheme 1, we select the subset of M antennas out of total $$(\begin{array}{l}{M_{t}} \\{M}\end{array})$$ subsets. In the selected subset, the minimum SNR is maximum compared to minimum SNR of all the remaining subsets. In scheme 2, Mt available transmit antennas are divided into Mtg disjoint groups of successive antennas, where Mtg = Mt/N. It means that there are N antennas in each group, where N ≤ M. Further both Mt and M are divisible by N and the total possible combinations of available groups are given $$(\begin{array}{l}{M_{tg}} \\{C}\end{array})$$ Then we select the subset of M antennas out of total $$(\begin{array}{l}{M_{tg}} \\{C}\end{array})$$ subsets. In the selected subset, the minimum SNR is maximum compared to minimum SNR of all the remaining subsets. In this scheme, N and C are chosen to meet the requirements of M selected antennas for transmission. After antenna selection, the resulting system will be M×M. We use Minimum Mean Square Error (MMSE) Vertical Bell Laboratories Layered Space Time (VBLAST) detection at the receiver for both the antenna selection schemes. We present MIMO Symbol Error Rate (SER) versus MIMO Symbol SNR using simulations for M-QAM constellations with Rayleigh fading channels. We have compared the performance of the considered systems with prevailing high complexity schemes ML and MMSE Improved VBLAST. The considered scheme 1 with MMSE VBLAST outperforms the prevailing schemes while scheme 2 with MMSE VBLAST provides similar performance in a wide range of SNR compared to prevailing schemes. However, the number of feedback bits used in scheme 2 is less as compared to scheme 1. There is a tradeoff between the SER performance and the number of required feedback bits. As N decreases, scheme 2 performance starts moving towards the performance of scheme 1. Both the systems provide the diversity gain in the fading channel.

In wireless sensor networks, multi-way relaying is a very common network configuration, where multiple nodes exchange information via a single relay over uncorrelated fading channels. In such configuration, node pair-wise communication together with physical-layer network coding (PNC) at the relay node provides a good trade-off between spectral efficiency and error performance. A joint channel decoding-PNC algorithm employed at the relay can further improve the bit error rate performance. This study proposes an improved joint channel decoding-PNC algorithm for M-ary phase shift keying modulated multi-way wireless relay systems. The proposed algorithm can achieve an additional diversity gain by exchanging bit-level or symbol-level soft information between the constitute decoders decoding different information pairs. Moreover, several schemes are proposed for exchange of the soft information between the parallely operating channel decoders. Simulation results demonstrate improved error and convergence performance of the proposed algorithm over the existing algorithms at the expense of non-significant increase in computational complexity.

In this paper, we investigate the problem of downlink non-orthogonal multiple access (NOMA) over block fading channels. For the single antenna case, we propose a class of NOMA schemes where all the users' signals are mapped into $n$-dimensional constellations corresponding to the same algebraic lattices from a number field, allowing every user attains full diversity gain with single-user decoding, i.e., no successive interference cancellation (SIC). The minimum product distances of the proposed scheme with arbitrary power allocation factor are analyzed and their upper bounds are derived. Within the proposed class of schemes, we also identify a special family of NOMA schemes based on lattice partitions of the underlying ideal lattices, whose minimum product distances can be easily controlled. Our analysis shows that among the proposed schemes, the lattice-partition-based schemes achieve the largest minimum product distances of the superimposed constellations, which are closely related to the symbol error rates for receivers with single-user decoding. Simulation results are presented to verify our analysis and to show the effectiveness of the proposed schemes as compared to benchmark NOMA schemes. Extensions of our design to the multi-antenna case are also considered where similar analysis and results are presented., 15 pages, 8 figures, accepted by IEEE Transactions on Wireless Communications

The fact that cyclic delay diversity (CDD)-based single-carrier (SC) scheme increases the frequency diversity without entailing the receiver to be aware of the transmission strategy makes it to be a good candidate for achieving full diversity gain in cooperative systems. In this letter, we scrutinize the impact of CDD-SC scheme in the cognitive radio network (CRN) with a great aim of overcoming the channel estimation challenge as well as the signaling overhead in the CRN. More specifically, in virtue of order statistics, the closed-form expressions for outage probability and symbol error rate are derived under independent and identical distributed (i.i.d.) frequency-selective fading channel model. Our results divulge the diversity order of the proposed system to be mainly affected by the number of multipath components available in the CRN.

In this paper, we consider a flat fading noncoherent wireless communication system with double transmitter antennas and massive multiple receiver antennas, in which the channel coherence time is divided into four orthogonal time slots, and these are used within a complete transmission cycle. For such a system, we systematically design a family of noncoherent unitary space–time codes. Then, within this family and with the noncoherent maximum likelihood (ML) detector, we propose the design of an optimal unitary space-time code that minimizes the worst-case pairwise error probability (PEP) subject to a constraint on total transmission bits. A closed-form optimal solution is attained by first characterizing the optimal structure for any fixed bits on each parameter space and then finding an optimal bit assignment that further minimizes the worst-case PEP. Also, asymptotic PEP performance analysis on such an optimal code further shows that it enables full receiver-diversity gain when the number of the receiver antennas goes to infinity, with the increasing rate of the coding gain in terms of signal-to-noise ratio (SNR) being the number of the transmitter antennas. In other words, it also provides full diversity gain, i.e., the product of the number of the receiver antennas and the number of the transmitter antennas, when SNR goes to infinity. Therefore, we call such a code double full diversity code. One of the significant advantages of the proposed optimal design for our considered massive multiple-input multiple-output system is that it has no error floor with SNR increasing. Another significant advantage is that it enables a fast ML detector.

In this article, we analyze the bit error rate (BER) performance of the multiple-input multiple-output (MIMO) based free-space optical (FSO) link by adopting Gamma–Gamma (GG) distribution with atmospheric turbulences (ATs) and pointing errors (PEs). By expanding the GG distribution, the complexity is high due to Meijer-G function with MIMO. To reduce the complexity, we proposed a mathematically tractable power series based probability density function of the GG fading with PEs and ATs. Based on the proposed power series PDF, the exact BER is derived, allowing to analyze the BER performance for single-input single-output (SISO), Single Input Multiple Output (SIMO) and extended to MIMO link for three combining schemes with M-ary Phase Shift Keying (M-PSK). The derived BER expression also helps to derive the Asymptotic Bit Error Rate (ABER), diversity gain, combining gain and cross-validated for SISO, SIMO and MIMO/FSO links. The effect of PEs over the performance of the FSO link is analyzed and observed that PEs degrades the BER and gain of the FSO link rapidly. The deduced MRC provides high SNR gain at-least 3.5 dB over EGC and 8 dB gain over SC for negligible PEs ξ = 11.23 at BER 10−6 and for BER 10−3, the SNR gain for MRC over EGC is 1.5 dB and approximately above 3 dB over SC for severe PEs ξ = 1.23. The proposed power series based PDF offers high gain and power efficiency of the MIMO/FSO link over SISO and SIMO link. This article identifies the crucial factors affecting the FSO link and helps in mitigating them to design an optimal system and opens for wide range of applications like fifth-generation (5G) networks, smart city applications etc.

The seminal works in (Foschini & Gans, 1998) and (Telatar, 1999) on multiple antenna elements at the transmitter and the receiver show a huge increase in the throughput of this pointto-point channel referred to also as multiple input multiple output (MIMO) system. These promising results of high spectral efficiency and enhanced reliability shifted the focus of research on multi antenna communications and motivated the introduction of multiple antenna elements in the future communication systems. Researchers persist to strive for finding space time codes (STC) with reduced decoding complexity. These codes take into account both the spatial and temporal dimensions of the MIMO channel. Orthogonal Space-Time Block Codes (OSTBCs) (Larsson & Stoica, 2003) are widely used because they are easy to encode and decode. For the case of two transmit antennas, the OSTBC is known as Alamouti code (Alamouti, 1998). OSTBCs are repetition codes that only provide diversity gain. In order to approach the capacity limit they have to be used in concatenation with an outer code. Remarkable coding gains can be obtained if a capacity achieving temporal encoder, such as turbo or Low-Density Parity Check (LDPC) code is used in concatenation with a STC (Gonzalez-Lopez et al., 2006). Recently it has been shown for the ergodic channels that the complex concatenation of the STC and the outer codes can be replaced with temporally coded and spatially multiplexed streams (coded spatial streams) for nearing capacity (Ghaffar & Knopp, 2008a). Each spatial stream can also be independently coded using temporal encoders as convolutional, turbo or LDPC codes whereas at the receiver, standard off-the-shelf decoders are used after the demodulator. To combat the frequency selectivity of MIMO wireless channels with low complexity equalization at the receivers, MIMO OFDM is the appropriate alternative. To contest the inherent fading of MIMO OFDM wireless channels, improved code diversity of bit interleaved coded modulation (BICM) for fading channels is rendering it the preferred option. Consequently the future wireless systems shall be based on BICM MIMO OFDM systems. However the requisite antenna spacing combined with the complexity constraints at the receiver are restricting the future MIMO based communication systems to the maximum of 4 spatial streams whereas it is reduced to 2 spatial streams in most scenarios. The existing and forthcoming standards as IEEE 802.11n (802.11n, 2006), IEEE 802.16m (802.16m, 2007) and Third Generation Partnership Project Long Term Evolution (3GPP LTE) (LTE, 2006) substantiate this argument. This chapter therefore focuses on low dimensional spatially multiplexed time coded BICM MIMO OFDM systems with first part being devoted to the transmission strategies and corresponding receiver structures for such systems in the broadcast scenario while second part 10

The traditional differential chaotic keying (DCSK) system is a kind of low-power and low-complexity system. However, in order to meet the demand of high throughput of low-power network, like wireless body area network (WBAN), the DCSK system must be redesigned. A multicarrier M-ary differential chaos shift keying system(MC-MDCSK) has been proposed, where good diversity gain and high throughput have been achieved. Analytical bit-error-rate expressions are derived and verified by simulations over additive white Gaussian noise and multi-path fading channels.

This paper focuses on the outage performance of a downlink integrated satellite-terrestrial relay network (ISTRN), which includes a satellite (S) transmitting messages to a user (D) with the help of K relays ({R k , k =1,⋯,K}) using a threshold-based decode-and-forward (DF) transmission protocol. In addition, we consider the case of relay selection based on out-dated channel state information (CSI) to better reflect the actual scenario. The shadowed-Rician (SR) fading and Nakagami-m fading are considered for the channel model of the S-R k links and R k -D links, respectively. In order to reveal the impact of the parameters on the performance of the considered network, the outage probability is adopted as a performance criterion and the corresponding exact closed-form expressions are derived. Further, in order to investigate the influence of system parameters more intuitively, asymptotic outage probabilities are considered for the two cases: 1) high average SNR for S-R k link and R k -D link; 2) high average SNR for R k -D link. The asymptotic analysis results exactly reveal the influence of the relevant system parameters on the decoding gain and the diversity gain. Finally, simulation and numerical results verify the correctness of the analysis.

Opportunistic relay selection (ORS) has been recognized as a simple but efficient method for mobile nodes to achieve cooperative diversity in slow fading channels. However, the wrong selection of the best relay arising from outdated channel state information (CSI) in fast time-varying channels substantially degrades its performance. With the proliferation of high-mobility applications and the adoption of higher frequency bands in 5G and beyond systems, the problem of outdated CSI will become more serious. Therefore, the design of a novel cooperative method that is applicable to not only slow fading but also fast fading is increasingly of importance. To this end, we develop and analyze a deep-learning-aided cooperative method coined predictive relay selection (PRS) in this article. It can remarkably improve the quality of CSI through fading channel prediction while retaining the simplicity of ORS by selecting a single opportunistic relay so as to avoid the complexity of multi-relay coordination and synchronization. Information-theoretic analysis and numerical results in terms of outage probability and channel capacity reveal that PRS achieves full diversity gain in slow fading wireless environments and substantially outperforms the existing schemes in fast fading channels., Comment: arXiv admin note: text overlap with arXiv:2102.03325

In limited space scenarios, the antennas in the multiantenna cognitive radio (CR) system are closely spaced and often experience correlation among them. In this work, the secrecy performance of correlated multiantenna CR receiver over Nakagami-m fading channels with imperfect channel state information is studied and analyzed. We consider the underlay CR paradigm wherein Alice in the secondary network communicates with Bob while Eve tries to overhear the communication. We also consider that the antennas at Bob and Eve are closely spaced and thus uniformly correlated. To this extent, we derive the analytical expressions for the first and second order secrecy measures like secrecy outage probability, average secrecy outage rate average secrecy outage duration, respectively for the CR receiver. Moreover, in order to gain insights at high SNR, asymptotic analysis of secrecy outage probability is derived, thus obtaining the secrecy diversity gain of order LD (i.e., the number of antennas at Bob). Monte Carlo simulations are carried out to validate the proposed analytical framework. Scopus

International audience; A combinatorial approach was recently proposed for designing multidimensional codebooks for fading channels. Albeit flexible and granting full signal space diversity, it relies on the optimal maximum likelihood detection, which is rather complex. In this work, we propose an alternative low-complexity, list-based detection algorithm for the codebooks under this approach. The detection complexity of the proposed algorithm is analyzed, and simulation results for both detection complexity and error performance are presented. It is concluded that the proposed detection algorithm not only preserves the diversity gain but also presents an excellent performance-complexity trade-off, thus adding value to the combinatorial approach.

In this paper, we analyze the performance of a single-threshold-based switching scheme for hybrid free space optics/ radio frequency (FSO/RF) system over generalized FSO and RF fading channels. The turbulence induced fading in FSO link is modeled using generalized Malaga distribution and the RF channel fading is modeled using recently proposed generalized $\alpha-\eta-\kappa-\mu$ distribution. In addition, the effect of pointing errors and atmospheric attenuation are also taken into consideration to evaluate the system performance assuming heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) techniques. The unified closed-form expression for average symbol error rate (SER) is derived. Further, the asymptotic expression is also derived in closed-form to obtain the diversity gain of the hybrid system. The effect of various FSO and RF channel parameters on the system performance has been investigated and the coding gain obtained due to RF backup link over single-link FSO system has also been reported. Finally, all the derived expressions are validated using Monte-Carlo simulations.

This paper presents a novel ultraviolet (UV) based multiuser indoor wireless communication system. We consider a shot-noise limited photon-counting signal model for a multiple-input single-output (MISO) optical fading channel. The system model is described, considering practical constraints such as transmit power limitations and UV safety exposure limits. We characterize the minimum mean squared error (MMSE) filter to minimize the multiple access interference. The lower bound of the bit error rate (BER) of the proposed system is presented, assuming the channel state information (CSI) at the receiver. A maximum likelihood sequence detection (MLSD) is also developed to efficiently mitigate indoor channel impairments when no CSI is available. It is shown that the performance of the proposed system with MLSD approaches the CSI lower bound performance, even with very short sequences. Simulation results also indicate that the proposed system effectively realizes the diversity gain expected from the MISO configuration.

Unlike orthogonal multiple access schemes, non-orthogonal (NOMA) ones have arisen as an appealing solution to meet the requirements of the upcoming era of massive connectivity. In NOMA schemes, users are allowed to restrainedly interfere. Therefore, NOMA's ability to serve a number of users more than the number of available orthogonal channels has attracted tremendous research efforts in its different performance aspects. However, its error rate performance has not been sufficiently addressed yet. The currently available derived bit error rate (BER) formulas are either assuming ordered users based on their instantaneous channel gains or fit for special cases only. In this paper, assuming that the users are ordered in terms of the average channel gain and considering arbitrary number of users and modulation order, the average pairwise error probability (PEP) of downlink NOMA systems under Nakagami-m fading channels is derived. Both detection rules, maximum likelihood and successive interference cancellation, have been considered. The derived average PEP is then used to obtain the asymptotic diversity gain and an upper bound on BER using union bounding technique. Simulation results validate the accuracy of the derived formulas over different setups. Qatar National Research Fund Scopus

In this paper, we propose a generalized millimeter-Wave (mmWave) reconfigurable antenna multiple-input multiple-output (RA-MIMO) architecture that takes advantage of lens antennas. The considered antennas can generate multiple independent beams simultaneously using a single RF chain. This property, together with RA-MIMO, is used to combat small-scale fading and shadowing in mmWave bands. To this end, first, we derive a channel matrix for RA-MIMO. Then, we use rate-one space-time block codes (STBCs), together with phase-shifters at the receive reconfigurable antennas, to suppress the effect of small-scale fading. We consider two kinds of phase shifters: i) ideal which is error-free and ii) digital which adds quantization error. The goal of phase-shifters is to convert a complex-valued channel matrix into real-valued. Hence, it is possible to use rate-one STBCs for any dimension of RA-MIMO. We investigate diversity gain and derive an upper bound for symbol error rate in cases of ideal and digital phase-shifters. We show that RA-MIMO achieves the full-diversity gain with ideal phase-shifters and the full-diversity gain for digital phase-shifters when the number of quantization bits is higher than one. We investigate RA-MIMO in the presence of shadowing. Our analysis demonstrates that, by increasing the dimension of RA-MIMO, the outage probability decreases which means the effect of shadowing decreases. Numerical results verify our theoretical derivations.

This paper investigates the maximum coding rate of the multiple-user multiple-input-multiple-output (MU-MIMO) uplink in coherent block-fading channels and with finite blocklength. The backoff of the maximum coding rate from the capacity caused by finite blocklength is precisely characterized by a parameter, called the channel dispersion. In particular, we derive exact analytical and approximation results for a large number of the base station (BS) antennas. By analyzing these results, we observe that even when considering the channel dispersion, the maximum coding rate still increases with respect to the number of BS antennas, whilst the SNR for each user can also improve the performance to a ceiling limited by the inter-user interference. Fast channel dynamics (shorter coherence time) and high diversity gain (large number of blocks) are beneficial for the maximum coding rate under finite blocklength and coherent setting. Moreover, to obtain a certain fraction of the capacity with fixed error probability, the minimum required blocklength (delay) can be reduced by increasing the number of BS antennas. We also show that the channel dispersion will converge to a constant while the minimum required blocklength can approach to zero with massive number of the BS antennas. Hence, from a theoretical viewpoint, deploying a large number of the BS antennas is beneficial for low latency communications.

Wireless communications are affected by several aspects of the multipath fading channel, including clustering, nonlinearity, correlation, scattered waves, and specular components. These aspects have been incorporated into many existing probabilistic fading models. The more aspects are covered, the more complicated is the resulting model. In many cases, the model or the associated system performance or both cannot be obtained in a closed form. As a result, little insight is gained into how each aspect of fading ultimately impacts key metrics such as symbol error rate and outage probability. In this work, we provide a novel asymptotic analysis at high signal-to-noise ratio that yields simple, general, and unified closed-form expressions for the diversity and coding gains of the symbol error rate and outage probability. We cover generalized fading scenarios and all the referred fading aspects. Our results give a handy, yet thorough, characterization of the system performance as impacted by multiple physical aspects of the multipath fading phenomenon. We provide further insights to reveal that all the addressed fading aspects affect the coding gain, whereas only the clustering and nonlinearity affect the diversity gain.

Non-orthogonal multiple access (NOMA) is currently considered as a promising technology for the next-generation wireless networks. In this paper, the error rate performance of NOMA systems is investigated over Nakagami- $m$ fading channels, while considering imperfect successive interference cancelation. In particular, this paper focuses on the pairwise error probability (PEP) analysis, where exact PEP expressions are derived to characterize the performance of all users under different fading conditions. The obtained PEP expressions are then used to derive an exact union bound on the bit error rate (BER). Through the derived PEP expressions, the asymptotic PEP analysis is presented to investigate the maximum achievable diversity gain of NOMA users. Moreover, using the derived BER bound, the power allocation problem for all users in NOMA systems is considered under average power and users BER constraints, which allows realizing the full potential of NOMA. Monte Carlo simulation and numerical results are presented to corroborate the derived analytical expressions and give valuable insights into the error rate performance of each user and the achievable diversity gain.

In this paper, through a mathematical analysis of the overall links capacity equation, we present an efficient partner selection criterion in a cooperative communication scheme with a time-varying fading channel and severe interference on the cooperative links to mitigate the interference effect without the need for additional power consumption to transmit the information signal. For the partner(s) selection, we examine different selection criteria based on minimizing the error rate and maximizing the end-to-end system capacity to collaborate in the delivery process. We prove that in the proposed relay scheme, a simple selection criterion independent of the interference state is a sufficient and efficient criterion for selecting the partners out of terminals suffering from interference. It is found that the use of a simple and efficient selection criterion for assigning multiple cooperating terminals is able to achieve a significant diversity gain, conserve the energy of individual terminals, and improve the error performance with low computational complexity, even in the absence of the interference state information. All of the theoretical findings are verified through simulation studies.

In this correspondence, the physical layer security of wireless systems under generalized $\boldsymbol {\alpha }$ - $\boldsymbol {\kappa }$ - $\boldsymbol {\mu }$ and $\boldsymbol {\alpha }$ - $\boldsymbol {\eta }$ - $\boldsymbol {\mu }$ fading with arbitrary fading parameters is analyzed in terms of the secrecy outage probability (SOP). To this end, novel analytical expressions for the lower bound of the SOP are derived. Moreover, an asymptotic secrecy analysis is investigated for each corresponding SOP to get the secrecy diversity gain. Monte Carlo simulations are provided to assess the accuracy of the proposed analytical framework.

Free-space optical (FSO) links are considered as a cost-efficient way to fill the backhaul/fronthaul connectivity gap between millimeter wave (mmWave) access networks and optical fiber based central networks. In this paper, we investigate the end-to-end performance of dual-hop mixed FSO/mmWave systems to address this combined use. The FSO link is modeled as a Gamma-Gamma fading channel using both heterodyne detection and indirect modulation/direct detection with pointing error impairments, while the mmWave link experiences the fluctuating two-ray fading. Under the assumption of both amplify-and-forward and decode-and-forward relaying, we derive novel closed-form expressions for the outage probability, average bit error probability (BER), ergodic capacity, effective capacity in terms of bivariate Fox's $H$-functions. Additionally, we discuss the diversity gain and provide other important engineering insights based on the high signal-to-noise-ratio analysis of the outage probability and the average BER. Finally, all our analytical results are verified using Monte Carlo simulations., to appear in IEEE OJCOMS

In this paper, the secrecy performance of transmit antenna selection/maximal ratio combining systems in the absence and presence of co-channel interference (CCI) over η-μ fading channels is considered. In particular, closed-form expressions for the secrecy performance are derived. To investigate the secrecy diversity gain, we also provide asymptotic secrecy outage analysis. Results show that the achievable secrecy diversity gain is 2μNT ND regardless of the number antennas of the eavesdropper NE, where NT and ND are the number antennas of the legitimate transmitter and receiver, respectively. Furthermore, it shows that the asymptotic secrecy performance is only dependent on the ratio γE /γD for both the systems with and without CCIs, regardless of the values of PI, where PI is the power of the interference. Finally, we provide some numerical examples to illustrate the presented analytical expressions.