The exploitation of millimeter wave (mmWave) and sub-Terahertz (sub-THz) bands is expected to be one of the main pillars for the development of future cellular networks due to the high available bandwidth they provide. The existence of Line-of-Sight (LOS) link between a user equipment (UE) and an access point (AP) is a prerequisite for connection establishment in these networks, as the wireless links in these bands are very sensitive to blockage effects. This can be achieved by densifying APs within a network area. An arising challenge is the efficient exploitation of the available bandwidth of a given network. In this paper, the maximization of the number of served UEs in modern mmWave and sub-THz cellular networks is investigated and achieved by deploying a Maximum Flow Algorithm for UE-AP association (MFUA) to optimize bandwidth allocation, assuming that every AP will have a finite and predefined amount of bandwidth which they can share among UEs. MFUA determines the maximum flow between two given nodes of a graph corresponding to a specific network, where the capacity of its edges is known. An extensive simulation campaign was carried out revealing that the use of MFUA utilizes bandwidth more effectively compared to the reference method and improves the system performance, leading to the maximization of number of served UEs. The examined test cases include static and time-evolving scenarios.

This work presents accurate closed-form approximations for the probability density function (PDF) of the sum of independent and identically distributed (i.i.d.) fading envelopes and square fading envelopes, experienced by indoor and outdoor channels operating in the D-band. In order to provide a simple yet accurate analytical expression for these PDFs, we propose the use of the Pearson family of distributions, which are mainly characterized by their skewness and kurtosis. Our analysis has demonstrated that among the seven types of Pearson distributions, the type I Pearson distribution provides the most accurate fit to the exact PDF of envelopes and squared envelopes, for a diverse range of indoor and outdoor wireless propagation scenarios. The distribution parameters are estimated using moments-matching techniques, while the requisite moments are obtained through a measurement campaign conducted in indoor as well as outdoor environments. Specifically, with regard to the indoor scenarios, the following locations have been considered: A mall, an airport, and an entrance hall. With regard to the outdoor scenarios, the following locations have been selected: A university campus, a residential area, and a city center. Our results are further applied to analyze the average bit error rate performance and the ergodic capacity of equal-gain combining (EGC) and maximal-ratio combining (MRC) receivers, the sum rate of rate splitting multiple access (RSMA) systems with EGC diversity reception, as well as the coverage probability of wireless systems employing intelligent reflecting surfaces (IRS). Our analysis is supported by extensive numerical results and Monte Carlo simulations.

As the demands of users increase continuously over time, especially in 5G and beyond 5G era, accurate performance evaluation is essential for design and optimization of cellular networks. To this end, stochastic geometry and specifically, uniform Poisson Point Processes (PPPs) have been employed in the past for the performance analysis of such networks, due to their mathematical tractability and adequate accuracy they provide. The distribution of the distance between a user node and its tagged access point (AP) is an important metric, which is derived from the statistical properties of PPPs. However, the presence of obstacles within the network's deployment area, has not attracted much attention from the research community. In this paper, we study the distribution of the distance between a user node and its tagged AP in areas with obstacles, where network nodes are distributed according to a PPP. Numerical results accompanied with simulations, are presented to verify the proposed analysis.

This paper presents novel moment generating function (MGF)- and characteristic function (CHF)-based frameworks for the EC performance analysis of a generic Lp-norm diversity combining scheme under adaptive transmission policies. The considered system operates over generalized fading channels, a maximum delay constraint and under various channel state information (CSI) conditions. Depending upon the operational CSI, four policies are studied, namely: i) Constant power with optimal rate adaptation (ORA); ii) Optimal power and rate adaptation (OPRA); iii) Channel inversion with fixed rate (CIFR); and iv) Truncated CIFR (TIFR). The Lp-norm diversity is a generic diversity structure which includes as special cases various well-known diversity schemes, such as equal gain combining (EGC), maximal ratio combining (MRC) and amplify-and-forward (AF) relaying. Under the ORA and OPRA policies, we derive single integral expressions for evaluating the EC of Lp-norm diversity reception directly from the MGF or the incomplete MGF of the Signal-to-Noise-Ratio (SNR) at the receiver, respectively. For the EC performance evaluation of the EGC and AF relaying systems operating under the OPRA policy, a CHF-based approach, which is computationally more efficient as compared to the MGF-based approach, is further presented. It is shown that the EC for the CIFR and TIFR policies can be directly evaluated from the MGF or the CHF of the SNR at the receiver, respectively. For the ORA policy, a novel analytical approach for the asymptotic EC performance analysis is also developed and evaluated, revealing how important system operation parameters affect the overall system performance. The mathematical formalism is validated with selected numerical and equivalent simulation performance evaluation results, thus confirming the correctness of the proposed analytical methodology.

In this paper, we present a comprehensive framework for the performance analysis of dual-hop relaying communications with variable gain amplify-and-forward (AF) relays and operating in the presence of both multipath fading and shadowing, modeled by the Fisher-Snedecor F-distribution. Novel closed-form expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) of the considered system subject to hardware impairments are first derived. Single-integral expressions for the numerical evaluation of the n-th moment of the end-to-end SNR, the outage probability (OP), the ergodic capacity under different adaptive transmission schemes, the effective capacity and the average bit error rate (ABER) of M-ary modulation schemes are further presented. The proposed analytical expressions are valid for most of the well-known fading distributions, provided that the moment generating function (MGF) of the inverse SNR of each hop is readily available. For the special case of ideal hardware, it is shown that the above performance metrics can be expressed in closed-form. It is worth pointing out that the proposed analysis is valid even when the destination node is equipped with multiple antennas and maximal ratio combining (MRC) is employed. The correctness of the proposed mathematical analysis is validated through extensive numerically evaluated results accompanied with Monte-Carlo simulations.

The effective capacity (EC) has been introduced as a performance metric that takes into account the delay constraints imposed by real-time emerging applications. This paper develops a novel moment generating function (MGF)-based approach for the effective capacity analysis of equal gain combining (EGC) diversity receivers over generalized fading channels under a maximum delay constraint. Selected numerical and simulation performance evaluation results are presented, verifying the validity of the proposed unified approach.

The frequency scarcity imposed by fast growing demand for mobile data service requires promising spectrum aggregation systems. The so-called higher order statistics (HOS) of the channel capacity is a suitable metric on the system performance. While prior relevant works have improved our knowledge on the HOS characterization of spectrum aggregation systems, an analytical framework encompassing generalized fading models of interest is not yet available. In this paper, we pursue a detailed HOS analysis of κ-μ and κ-μ shadowed fading channels by deriving novel and exact expressions. Furthermore, the simplified HOS expressions for the asymptotically low and high signal-tonoise regimes are derived. Several important statistical measures, such as amount of fading, amount of dispersion, reliability, skewness, and kurtosis, are obtained by using the HOS results. More importantly, the useful implications of system and fading parameters on spectrum aggregation systems are investigated for channel selection. Finally, all derived expressions are validated via Monte Carlo simulations.

In this paper, we investigate the performance of spatial modulation (SM) for vehicle-to- infrastructure (V2I) and vehicle-to-vehicle (V2V) communications over a generalized multiple scattering channel. This channel model provides a realistic statistical description of an intervehicular communication environment and includes as special cases the Rician, Rayleigh, and double-Rayleigh channels. We derive an accurate closed form expression for the pairwise error probability of SM, which is used to obtain the error rate performances of SM over various propagation scenarios. The performance analysis reveals the impact of the number of receive antennas on the error rate performance of SM transmission over multiple scattering channels. Various numerically evaluated results are presented to demonstrate the correctness of the proposed analysis.

Secrecy capacity is a fundamental information-theoretic performance metric to predict the maximum data rate of reliable communication, while the intended message is not revealed to the eavesdropper. Motivated by this consideration in this paper, a unified communication-theoretic framework for the analysis of the probability of nonzero secrecy capacity, the secrecy outage probability, and the secrecy capacity of multiple-antenna systems over fading channels is proposed. Specifically, a powerful frequency-domain approach is first developed in which the integrals involved in the evaluation of the probability of nonzero secrecy capacity and secrecy outage probability are transformed into the frequency domain, by employing Parseval's theorem. A generic approach for the evaluation of the asymptotic secrecy outage probability at high signal-to-noise ratio (SNR) region is also introduced, thus providing useful insight as to the parameters affecting the secrecy performance. Finally, a unified numerical approach for computing the average secrecy capacity of multiple-antenna systems under arbitrary fading environments is developed. The proposed framework is general enough to accommodate any well-known multiantenna transmission technique and fading model. Finally, the secrecy performance of several multiple-antenna system setups is assessed, in the presence of generalized fading conditions and arbitrary antenna correlation, while various numerical and computer simulation results are shown and compared to substantiate the proposed mathematical analysis.

In this paper, we investigate the performance of space shift keying (SSK) transmission over a generalized multiple scattering channel. This channel model provides a realistic statistical description of an intervehicular communication environment and includes as special cases the Rician, Rayleigh, and double-Rayleigh channels. We derive an accurate closed-form expression for the pairwise error probability of SSK, which is used to obtain the uncoded and coded error rate performances of SSK over various propagation scenarios. An asymptotic analysis for high values of the signal-to-noise ratio is carried out to determine the diversity and coding gains of the proposed system. The performance analysis reveals the impact of the number of receive antennas and the use of soft and hard decision decoding on the error rate performance of the SSK transmission over multiple scattering channels. Various numerically evaluated results accompanied by Monte Carlo simulations are presented to demonstrate the correctness of the proposed analysis.

The analytical evaluation of the average bit error rate (ABER) performance of a digital multihop transmission system operating in the presence of co-channel interference and Rayleigh fading is presented. It is assumed that the number of interferers at each relay node and the destination is a binomial random variable that belongs to a binomial point process. Analytical expressions for the ABER of Amplify-and-Forward and Decode-and-Forward relaying in terms of a single integral that can be easily evaluated numerically, are derived. An asymptotic analysis is employed to obtain simple ABER approximations and optimize the power allocation and location of the relays. Finally, the analytical results are validated with computer simulations.

This study presents a comprehensive performance analysis of an energy detector over Gamma‐shadowed Rician fading channels, namely Rician fading channels with the fluctuating line‐of‐sight components following the Gamma distribution. This composite multi‐path/shadowing model has been shown to provide a remarkably accurate fading characterisation while leading to closed‐form expressions for important channel statistics. Rapidly convergent infinite series representations are firstly derived for the average probability of detection and the area under the receiver operating characteristic curve for the no‐diversity reception case. These results are then extended to the case of maximal ratio, equal gain and selection diversity. To this end, novel analytical expressions for the statistics of the end‐to‐end signal‐to‐noise ratio of equal gain and selection diversity receivers, operating over Gamma‐shadowed Rician fading channels are derived. Analytical results are substantiated by Monte Carlo simulation, as well as by extensive numerically evaluated results.

Hierarchical Quadrature Amplitude Modulation is considered to enhance the aggregate Spectral Efficiency (SE) in broadcast systems operating under fading conditions. Closed-form and series representations for SE are derived assuming that the user terminals are uniformly distributed as to their distance from the Base Station and employ Maximum Likelihood detection. The modulation parameters are adjusted to optimize system performance. Numerical results and Monte Carlo simulations show that by adjusting the constellation diagram of the Hierarchical Modulation scheme, the SE performance may be significantly enhanced, especially under fading conditions.

In this paper, we analyze the performance of an energy detector operating over Gamma shadowed Rice fading channels, namely Rice fading channels with the fluctuating line-of-sight components following the Gamma distribution. This composite multi-path/shadowing model has been shown to provide remarkably accurate fading characterization while leading to closed-form expressions for important channel statistics. For the considered system, we first derive analytical expressions for the average probability of detection, using either the probability density function method or the moments generating function method. The application of the former method, yields a rapidly convergent infinite series representation for the average probability of detection. The latter method is based on a contour integral representation for the Marcum Q-function. Finally, an infinite series representation for the area under the receiver operating characteristic curve is derived. Extensive numerically evaluated results, accompanied with Monte-Carlo simulations, are presented to corroborate the proposed analysis, for composite multi-path/shadowing scenarios of practical interest.

In this paper, we investigate the performance of a wireless transmission system that employs amplify-and-forward (AF) relays and operates in an interference-limited environment. We consider a multi-hop network in which the co-channel interferers are scattered according to a spatial Poisson process and the desired and interfering signals at each relay and the destination experience Nakagami-m fading. Exact expressions for the average bit error probability and the average channel capacity of the considered system are obtained as single integrals that can be reliably evaluated numerically. In addition, the diversity and coding gains per hop are obtained. The novel expressions can be used to show the impact of system and interference model parameters such as the number of hops and the transmit power, path loss exponent, and spatial density of interferers, respectively, on the performance of multi-hop systems. Simulation results are further provided to demonstrate the accuracy of the analytical expressions.

The authors present an alternative moments-based approach for the performance analysis of dual-hop relaying communications systems over generalised fading channels. A unified analytical approach for the computation of the nth moment of the harmonic mean of N≥2 arbitrarily distributed random variables (RVs) is proposed. On the basis of this statistical result, we analyse the outage and the average error rate performance of dual-hop cooperative wireless systems employing amplify-and-forward (AF) relays. Moreover, our newly derived results can be applied to evaluate the average sum rate of AF relaying systems. Extensive numerical and simulation results are presented to substantiate the proposed analysis.

ABSTRACT In this paper, a study on the end‐to‐end performance of multi‐hop non‐regenerative relaying networks over independent generalized‐gamma (GG) fading channels is presented. Using an upper bound for the end‐to‐end signal‐to‐noise ratio (SNR), novel closed‐form expressions for the probability density function, the moments, and the moments‐generating function of the end‐to‐end SNR are presented. Based on these derived formulas, lower bounds for the outage and the average bit error probability (ABEP) are derived in closed form. Special attention is given to the low‐ and high‐SNR regions having practical interest as well as to the Nakagami fading scenario. Moreover, the performance of the considered system when employing adaptive square‐quadrature amplitude modulation is further analyzed in terms of the average spectral efficiency, the bit error outage, and the ABEP. Computer simulation results verify the tightness and the accuracy of the proposed bounds. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, highly accurate closed-form approximations to the probability density function of the sum of independent identically distributed (i.i.d.) generalised-K fading envelopes are derived. These approximations are valid for a wide range of values of the distribution parameters and number of summands. Based on the previously derived formulas, simple precise approximations for the outage probability and the average bit error probability of equal-gain combining receivers operating on i.i.d. generalised-K fading channels are proposed. Extensive numerically evaluating and computer simulation results are presented to demonstrate the proposed analysis.

The authors study the performance of a dual-hop plus a direct link multiple-input multiple-output (MIMO) wireless communication system using orthogonal space–time block codes. The system under consideration is based on the decode-and-forward relaying protocol and operates over spatially correlated Nakagami-m fading channels. The proposed analysis is generic enough to account for any MIMO correlation model either from measurements or having theoretical and analytical justification. Analytical expressions for the system end-to-end outage and average symbol error probability are obtained, while critical parameters of the MIMO channel are taken into consideration such as the angle of arrival, the antenna array configuration, the wavelength and non-isotropic scattering conditions. Various numerical and computer simulation results demonstrate the proposed mathematical analysis and the impact of the above parameters to the system performance.

An analysis for the Shannon channel capacity of digital receivers operating over η–μ fading channels is presented under four adaptive policies: constant power with optimal rate adaptation, optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate. In this context, useful formulae for the average channel capacity for maximal-ratio combining receivers with not necessarily identically distributed branches are derived. The analysis also includes the performance of single-branch receivers. These expressions provide an effective tool to assess the spectral efficiency of the aforementioned adaptive transmission techniques over practical fading channels. Our newly derived expressions include several special cases that arise from the η–μ distribution, namely the Nakagami-m and the Hoyt distribution. Extensive numerical and computer simulation results are also presented that illustrate the proposed mathematical analysis.

A versatile fading distribution that generalises many commonly used models for multi-path and shadow fading is the so-called generalised-K (KG) distribution. By considering the product of N independent but not necessarily identically distributed (n.i.d.) squared KG random variables (RVs), we derive exact closed-form expressions for the moment generating function, probability density function, cumulative distribution function and the moments of the cascaded KG fading channel. Expressions for the ergodic capacity and the error performance of different digital modulation schemes are also obtained. Based on the above mentioned formulas, we analyse the performance of orthogonal space-time block codes over multiple-input multiple-output keyhole KG fading channels. Various performance evaluation results demonstrate the proposed mathematical analysis.

In this paper, new expressions for the probability density function (pdf) of the sum of non-identical independent squared η-μ random variables are derived. Based on our newly derived results, we provide a pdf-based approach for the performance analysis of 1-D and 2-D RAKE receivers in the context of an asynchronous direct sequence code division multiple access system operating over η-μ fading channels. For the considered system, useful performance metrics such as the outage probability, the channel capacity and the average bit error probability are investigated. Extensive numerical and computer simulation results are presented that illustrate the proposed mathematical analysis.

This paper deals with a trivariate Nakagami-m distribution derived from the diagonal elements of a Wishart matrix. For this distribution, infinite series representations for its probability density and cumulative distribution functions are derived having an arbitrary covariance matrix and integer-order fading parameters. Moreover, upper bounds on the error resulting from truncating the infinite series are obtained. Based on the derived formulas, the performance of triple-branch generalized selection combining (GSC) receivers is analyzed. For this type of receivers, the outage and the average bit error probability for a variety of modulation schemes are analytically obtained. The performance of GSC receivers is compared to that of conventional selection and maximal-ratio diversity schemes. In order to check the accuracy and convergence of the derived formulas, various performance evaluation results are presented and compared to equivalent simulation ones.

This paper provides exact-form expressions for the average symbol error probability (ASEP) of various digital modulation schemes with maximal ratio combining (MRC) diversity over L independent, not necessarily identically distributed (n.i.d.) eta-mu fading channels. The derived expressions are given in terms of the Lauricella and Appell hypergeometric functions and include several others available in the literature such as those for Nakagami-m and Hoyt. General asymptotic ASEP expressions are also derived for all the considered modulation schemes which provide useful insights regarding the factors affecting the performance of the considered system.

In this paper the impact of the position of user's hand holding a multiple-input-multiple-output (MIMO) terminal on system performance and more specifically on channel capacity is investigated. We consider a 4times4 MIMO system with a personal digital assistant (PDA) equipped with a compact array of 4 patch elements. Radiation field patterns of the antenna elements in the presence of the other elements as well as in the presence of a user's hand are simulated. Different positions of the user's hand are taken into account. The covariance matrix of the receiving antennas is evaluated by means of the obtained patterns. A correlation-based channel model is considered, where the antenna patterns are incorporated. Extensive simulations showed that the performance of the MIMO systems varies significantly with the position of the user's hand.

Future wireless communication systems are expected to provide seamless inter-working between existing and 3G radio networks providing the user with a wide variety of services, while maintaining a large area of coverage and minimum user QoS requirements. In this paper, a new mechanism that implements interoperability between HSDPA and WLAN systems is proposed. The proposed interoperability mechanism is activated via the optimization of a suitably defined cost function, which takes into account all the appropriate system level parameters that trigger the interoperability process. The performance evaluation of the proposed scheme is assessed by means of a software - based simulation platform. A number of simulations have been carried out in order to demonstrate the performance enhancements achieved by the proposed mechanism in terms of user throughput, handovers statistics, and system throughput.

In this paper the system level performance of an HSDPA (high speed downlink packet access) MIMO network, which combats the effects of antenna correlation by applying novel reconfigurable techniques is investigated. Reconfigurability is achieved at the link level by applying a linear precoding scheme at the transmitter space-time block encoder. An appropriate link to system interface has been developed, taking into account the linear precoding technique. The system level performance metrics of interest are the average system throughput and the number of satisfied users. Simulation results are presented in order to demonstrate the performance enhancements achieved by the application of reconfigurable techniques compared to the conventional ones.