Grant-Free Random Access (GFRA) is a key enabler for massive Machine-Type Communications (mMTC) and ultrareliable low-latency communication (URLLC) in 5G and beyond. Traditional methods for user activity detection often rely on prior knowledge of Large Scale Fading Coefficients (LSFC) and the number of active users, which limits their practical applicability. In this paper, we propose a novel manifold-based activity detection method that utilizes the covariance structure of received signals to efficiently identify active users without requiring LSFC or prior knowledge of the number of active users. The proposed method integrates Riemannian distance metrics with machine learning techniques, including logistic regression, Gaussian modeling, and k-means clustering, to enhance detection accuracy. We evaluate three variants: (1) a threshold-based approach trained using logistic regression, (2) an adaptive Gaussian modeling technique for real-time threshold determination, and (3) a k-means clustering method, which proves to be the most effective among the three. Simulation results demonstrate that the manifold-based method outperforms the Multiple Measurement Vector (MMV) approach in detection accuracy while maintaining significantly lower computational complexity. Our findings establish the proposed manifold-based framework as a promising solution for scalable, low-latency activity detection in next-generation wireless networks.

In this paper, we propose a simultaneously transmitting and reflecting intelligent reflecting surface (STAR-IRS) assisted multi-user communication system in the terahertz (THz) band. To overcome the potential blockage of direct links from the base station (BS) towards users or the possibility of users located out of the reach of the BS, the STAR-IRS assisted link can help enhancing the performance of the system. We derive closed-form expressions for the signal-to-noise ratio (SNR) outage probability for optimal and non-optimal STAR-IRS phase shifts with considering the users' statistical distribution within the service area. We conduct our analysis assuming the combined$\alpha-\mu$distribution, pointing errors, and molecular absorption that are inherent in THz transmission. The derived expressions are validated through Monte Carlo simulations and the effect of various system parameters on the outage probability is studied. Results show that the proposed system can achieve acceptable outage performance even with the existence of phase shift errors. Moreover, the performance can be further enhanced with increasing the number of STAR-IRS elements, which is practical in the THz band due to the very small wavelength.

Adaptive video streaming in cellular networks faces challenges due to the dynamic nature of network conditions, particularly in environments with varying mobility patterns. This study introduces a novel multi-stage mobility-aware throughput prediction engine (MATH-P) designed to enhance the Quality of Experience (QoE) in adaptive bitrate (ABR) streaming. MATH-P integrates a classification-driven model selection mechanism that dynamically adjusts to different mobility scenarios, such as stationary, vehicular, and high-speed mobility, allowing for precise throughput predictions. By replacing the conventional throughput estimation module in existing ABR systems with MATH-P, our experiments demonstrate significant improvements across key QoE models and streaming performance metrics across different mobility scenarios. The results highlight MATH-P's ability to deliver smoother video playback, reduced interruptions, and better overall streaming quality. The comprehensive evaluation shows that MATH-P outperforms traditional estimation methods, making it a robust solution for enhancing video streaming in mobility-rich environments.

We consider intermittently connected vehicular networks (ICVNs) in which base stations (BSs) are installed along the highway to connect moving vehicles with internet. Due to the deployment cost, it is hard to cover the entire highway with BSs. To minimize the outage time in the uncovered area (UA), several cooperative store-carry-forward (CSCF) schemes have been proposed in which a vehicle is selected to act as a relay by buffering data to be relayed to a target vehicle in the UA. In this paper, we propose an energy-efficient full-duplex (FD) CSCF scheme that exploits the relay ability to receive and transmit simultaneously to improve the effective communication time, Te, between the relay and the target vehicle. Accordingly, it can minimize the outage time and deliver more data to the the target vehicle. In addition, the power allocation that minimizes the transmission cost (TC) under the required rates constraints is found. The problem is formulated as a geometric program (GP) and globally solved using the interior-point method. As compared to the half-duplex CSCF scheme, simulation results show that the proposed FD scheme offers more effective time, more successfully delivered data in the UA and lower TC.

In this study, the authors revisit energy detection‐based spectrum sensing cognitive radio systems operating over generalised fading channels. In particular, they derive closed‐form exact expressions as well as low‐ and high‐signal‐to‐noise ratio asymptotic expansions for the misdetection probability over the Fox's H ‐function fading channel. The closed‐form expression is given in terms of the bivariate Fox's H ‐function and subsumes most of the expressions previously presented in the literature. Also, the obtained asymptotic expressions are very easy to compute and can be used to get various performance insights. We verified, theoretically and numerically, the validity of the exact expression for important special cases previously reported in the literature, namely the Nakagami‐ m and the extended generalised‐ K fading distributions. Numerical results also demonstrate the high accuracy of the asymptotic expansions.

In single carrier frequency division multiple access (SC‐FDMA) systems, frequency domain equalisers suffer performance degradation due to several channel impairments such as inter‐symbol interference, inter‐carrier interference (ICI), especially in multiple access/multiple input multiple output (MIMO) systems. This study presents a joint complex regularised zero forcing (JCRZF) equaliser that is able to compensate the channel impairments and to mitigate the ICI induced by the carrier frequency offset (CFO) in mobile channel environments. JCRZF equaliser is also able to eliminate the inter antenna interference resulting from the MIMO channel coupling by transforming the MIMO channel into equivalent SISO channels. Simulation results show that the JCRZF equaliser outperforms ZF based equalisers in terms of bit error rate while preserving their potential complexity and appropriate robustness to CFO estimation errors.

Device-to-device communication (D2D) is an emerging technology aiming at enhancing the performance of next generation wireless communication systems. D2D communication enables two mobile stations to communicate directly without traversing the Base Station (BS). Smart techniques should be applied to manage the interference between the BS and the D2D communicating devices. In this paper, we investigate the problem of BS precoder design and Power Allocation (PA) to deploy D2D communication in a single-cell network. We assume that the BS uses a very large number of antennas, referred to as Massive Multiple-Input-Multiple-Output (MIMO). We propose solution algorithms to maximize the sum of the achievable data rates of the D2D pairs, or their minimum, while maintaining some Quality of Service (QoS) constraints on the Cellular User Equipments (CUEs) which communicate with the BS. Simulation results show that the proposed solutions are superior to the conventional power allocation schemes.

This work presents an analytical framework for characterizing the performance of cooperative and non-cooperative spectrum sensing schemes by figuring out the tradeoff between the achieved diversity and coding gains in each scheme. Based on this analysis, we try to answer the fundamental question: can we dispense with SUs cooperation and still achieve an arbitrary diversity gain? It is shown that this is indeed possible via a novel technique that can offer diversity gain for a single SU using a single antenna. The technique is based on the usage of a reconfigurable antenna that changes its propagation characteristics over time, thus creating an artificial temporal diversity. It is shown that the usage of reconfigurable antennas outperforms cooperative as well as non-cooperative schemes at low and high Signal-to-Noise Ratios (SNRs). Moreover, if the channel state information is available at the SU, an additional SNR gain can also be achieved.

Relaying in OFDMA-based networks is an effective mechanism for enhancing the cell-edge capacity, extending the coverage and utilizing the bandwidth efficiently through spatial reuse. To harness the benefits of relaying, efficient resource allocation schemes should be used, which are aware of the highly dynamic nature of interference in OFDMA relay-enhanced cells (RECs). This paper tackles the joint Power Allocation (PA) and Resource Block Assignment (RBA) problem in a single-cell OFDMA REC. Fair allocation of resources is achieved by assuming a max-min fair objective for the problem and a novel solution technique is proposed, which is capable of obtaining a local optimum for this complex problem. Comparison with other similar works shows the effectiveness of our proposed technique. Simulation results show increase in the 10%tile capacity by a factor of 6.6 compared to previous solution techniques. Moreover, using Jain's fairness index, we show that this technique guarantees more fairness among users.

Spectrum Sensing (SS) plays a very critical role in Cognitive Radio (CR) systems. Among the techniques used for SS is energy detection, which is very popular because of its simplicity and the fact that it does not require information about the primary signal. However, due to its poor performance over fading channels, cooperation between multiple cognitive devices has been proposed to overcome this disadvantage. In this paper, a simple multi-stage cooperative sensing algorithm is presented. The proposed algorithm combines the local decision at each CR along with a group decision received from a fusion center through a simple rule to produce a collective decision. Performance under non-ideal channel conditions, from CR devices to the fusion center and vice-versa, is studied analytically and via simulations. Results show that the proposed algorithm outperforms the conventional hard decisions-based technique and exhibits a comparable performance to the soft decisions-based one at a much lower complexity. In particular, we show that the proposed algorithm improves the detection probability while keeping the false alarm probability almost the same. In addition, we show that it enjoys more robustness against feedback channel errors than the conventional hard decisions-based algorithm.

In this paper, we consider a switch-and-examine combining (SEC) diversity scheme operating over independent and identically distributed (i.i.d) branches assuming an α-μ fading channel. We derive expressions for the average symbol error rate (ASER) for a class of coherent modulation techniques considering this fading model as well as expressions for the ergodic capacity under the same assumptions. The results for the ASER and the ergodic capacity are shown to reduce to those previously reported in the literature for other channel models such as the Weibull model as a special case, which confirms the validity of the obtained expressions. Different aspects are studied including the effect of fading severity, the number of branches and the modulation scheme used. Also, insights on the optimal choice of the switching threshold are provided.

In this paper, we present two novel Resource Allocation (RA) strategies based on the Signal-to-Leakage-plus-Noise-Ratio (SLNR) for the downlink (DL) of Coordinated Multi Point (CoMP) transmission in LTE-Advanced (LTE-A) system. The proposed RA strategies select the UEs that can efficiently share the same Resource Block (RB) without degrading the overall throughput by using the SLNR metric. In addition, we compare the proposed strategies to the RA based on the more common Signal-to-Interference-plus-Noise-Ratio (SINR) strategy. The SLNR-based RA is shown to provide significant gains in the overall system throughout that reach up to 80% and is shown to have even less complexity than the typical SINR-based RA, which makes it a very attractive choice for the implementation of CoMP in practical cellular systems.

Spectrally-efficient and low-latency support of local media services is expected to be provided by enabling underlay direct Device-to-Device (D2D) communication mode in future cellular networks. Interference Alignment (IA) can enhance the capacity of a wireless network by providing more degrees of freedom. In this paper, we propose using IA techniques in a D2D underlay network to enhance spectral efficiency. We compare IA transmission and traditional point-to-point (P2P) transmission from the Bit-Error-Rate (BER) and sum-rate points of view. Furthermore, we propose three grouping schemes for the D2D users into groups of 3-pairs such that IA can be applied using a limited number of signal extensions. Results demonstrate that although traditional P2P transmission can achieve better BER performance; IA transmission is still able to achieve gains in the sum rate. Also, system simulations show that the cell total D2D sum rate can be improved using IA. A gain of up to 31.8% is shown to be attainable at a reasonable transmit signal power level.

One of the main problems in LTE-A networks is the small rates achieved by cell-edge users. This is due to the adoption of a frequency reuse factor of 1, which aims at increasing the overall capacity. This occurs, however, at the expense of increasing the interference level for cell-edge users. Cooperative communication through the use of relays is an efficient technique to solve this problem. However, careful placement of the relays is a crucial factor in determining the expected capacity gain. In this paper, the relay placement problem in an LTE-A network is studied, taking into consideration the effect of co-channel interference. An optimization framework is proposed to maximize either the total cell capacity or the total cell-edge capacity. Simulation results show a capacity gain factor of 8.027 for cell-edge users due to relay deployment, under 100% cell load in center cell and adjacent cells.

The sum and harmonic mean of random variables (RVs) appear frequently in performance evaluation studies of wireless communications systems. In particular, the sum appears in the performance evaluation of maximal ratio combining (MRC) and equal gain combining (EGC) diversity receivers whereas the harmonic mean is encountered in performance evaluation studies of cooperative diversity networks with non-regenerative relays. In this study, the authors propose highly accurate finite-series approximations for the cumulative distribution function (CDF) of the sum and harmonic mean of two α−μ distributed RVs. The proposed approximations do not require neither a look-up table nor solving complicated transcendental equations, as is typically the case in the literature. The results reveal that the proposed approximations are very accurate over the typical range of interest when compared with the exact CDFs computed using numerical integration methods.

In this study, the effect of introducing cochannel interference (CCI) on the performance of diversity receivers operating over the Weibull fading channel is thoroughly investigated. More specifically, the authors derive novel bit error rate (BER) expressions for the dual-branch selection combining (SC) and post-detection equal gain combining (EGC) diversity M-PSK receivers with possibly correlated branches operating over Weibull fading channels in presence of CCI. A characteristic function (CF)-based approach is used to achieve this goal. For the EGC correlated branches case, because of lack of existence of a closed-form expression for the CF of the sum of two Weibull random variables (RVs), the authors revert to using the Padé approximation (PA) technique to approximate this CF by a rational function and hence an approximate BER expression is obtained. Various results pertaining to the effect of fading severity of both the desired signal and the interferers, the effect of the number of interferers and the effect of correlation between diversity branches for different M-PSK modulations are presented. The obtained results are verified by comparison with Monte Carlo simulations and excellent agreement is observed.

The performance of binary phase shift keying in a Weibull fading environment is analysed in the presence of cochannel interference (CCI) in terms of the bit error rate (BER). We derive an exact expression for the BER in this case on the basis of a characteristic function approach. Furthermore, since it is difficult to obtain the distribution of the CCI and because of the complexity of the obtained exact BER expression, we derive an approximate expression for the BER by invoking the central limit theorem. The validity of the exact expression and the accuracy of the approximate one are verified by comparing their results with those obtained via Monte Carlo simulations. The effect of such factors as the number of interferers and the fading severity of both the desired as well as the interfering signals on performance is also investigated.

Abstract In this paper, we propose a combined analytical and simulation framework for performance evaluation of the forward link in the cdma2000 evolution for data only (1xEV‐DO) cellular systems with throughput and spectral efficiency being used as performance metrics. A closed form expression for the aggregate average throughput is derived in terms of system‐dependent parameters and a discrete random process that reflects the stochastic behavior of the transmission channel. The random process is expressed in terms of the cumulative distribution function (CDF) of the users signal‐to‐interference‐plus‐noise ratio (SINR). Quantitative results for throughput and spectral efficiency are presented for a variety of users distribution models, base station antenna types and frequency reuse factors for the cases of sectorized and non‐sectorized cells. Furthermore, we study the impact of the cell radius on the system performance. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, we evaluate the performance of two dual-branch diversity techniques operating over the Weibull fading channel in the presence of a dominant co-channel interferer with a minimum desired signal power constraint. These two diversity schemes are selection combining (SC) and switch-and- stay combining (SSC). We derive expressions for the outage probability in both cases, which are very simple to calculate numerically and reduce to closed-form ones in many special cases. Also, our expressions reduce to previously published well-known ones for the Rayleigh fading channel as a special case. We present a set of numerical results which show the effect of fading severity of both the desired signal and the interferer on the performance.

In this paper, we conduct a comprehensive study on the performance of dual-branch diversity M-PSK receivers with possibly correlated branches operating over Weibull fading channels in presence of cochannel interference (CCI). We use a characteristic function (CF) based approach to derive exact expressions for the bit error rate (BER) under such conditions assuming both selection combining (SC) and post-detection equal gain combining (EGC) diversity schemes. For the EGC correlated branches case, due to the lack of existence of a closed-form expression for the CF of the sum of two correlated Weibull random variables (RVs), we revert to using the Padé approximation (PA) technique to approximate this CF by a rational function and hence, an approximate BER expression is obtained. Various results pertaining to the effect of fading severity of both the desired signal and the interferers, and the effect of correlation between diversity branches for different M-PSK modulations are presented. Our results are verified by comparison with Monte Carlo simulations and excellent agreement is observed.

In this paper, we analyze the performance of binary phase shift keying (BPSK) in a Weibull fading channel in presence of cochannel interference (CCI). The performance is quantified in terms of the bit error rate (BER). Two expressions are derived for the BER in this case, the first is an exact expression based on a characteristic function (CF) approach, while the second is an approximate expression based on the use of the central limit theorem (CLT). The exact expression reduces to well-known previously obtained expressions for the special case of Rayleigh fading. The validity of the exact expression is further confirmed by comparing its results to those obtained via Monte Carlo simulations. We investigate the effect of such factors as the number of interferers and the fading severity of both the desired as well as the interfering signals on performance.

The Weibull distribution has recently attracted much attention among the radio community as a statistical model that better describes the fading phenomenon on wireless channels. In this paper, we consider a multiple access system in which each of the desired signal as well as the co-channel interferers are subject to Weibull fading. We analyze the performance of the L-branch maximal ratio combining (MRC) receiver in terms of the outage probability in such scenario in the two cases where the diversity branches are assumed to be independent or correlated. The analysis is also applicable to the cases where the diversity branches and/or the interferers fading amplitudes are non-identically distributed. Due to the difficulty of handling the resulting outage probability expressions numerically using the currently available mathematical software packages, we alternatively propose using Pade approximation (PA) to make the results numerically tractable. We provide numerical results for different number of interferers, different number of diversity branches as well as different degrees of correlation and power unbalancing between diversity branches. All our numerical results are verified by means of Monte-Carlo simulations and excellent agreement between the two sets is noticed

In this letter, we evaluate the performance of the dual-branch maximal ratio combining (MRC) diversity scheme in nonidentical correlated Weibull fading channels with arbitrary parameters. We first use the Pade/spl acute/ approximation (PA) to find closed-form rational expressions for the moment generating function (MGF) of the output signal-to-noise ratio (SNR) of the MRC receiver. Different performance measures, such as the outage probability and the average symbol-error rate for different linear modulations, are then presented using the well-known MGF approach. Furthermore, the effect of the input SNRs unbalancing, the severity of fading, and the degree of correlation on the system performance are also studied. Our results are validated by comparing them with computer simulations, and we show that the PA technique is indeed a convenient tool for such performance evaluation studies.

Summary form only given. In this paper, a comprehensive simulation study is performed for evaluating the performance of the uplink of the wideband code division multiple access (WCDMA) system operating in the time division duplex (TDD) mode. The performance is quantified in terms of the cumulative distribution function (CDF) of the uplink carrier-to-interference-plus-noise ratio (CINR) and the throughput achieved by the users. A number of different practical scenarios are considered in this paper depending on the number of users per cell, the type of the antennas used at the base stations and the value of frequency reuse. Furthermore, we show how techniques like cell sectorization and multi-user detection (MUD) at the base stations can significantly improve the throughput in the system.

We consider the problem of determining the outage probability in cellular systems where each of the links is lognormal-shadowed, Weibull-faded and corrupted by additive noise. We propose two solutions for this problem; a simple lower bound on the outage probability based on the concavity of the logarithmic function and an approximate expression based on the use of the central limit theorem. The approximate expression is slightly more complicated than the lower bound but provides a better accuracy for most of the parameters values. We verify the accuracy of the proposed expressions by comparing them to the outage probability obtained by means of Monte Carlo simulations.

"3G and beyond" cellular networks target a shift from low rate traditional voice services to high rate multimedia communications. Wideband code division multiple access (WCDMA) is a candidate air interface technology for achieving this goal. Usually, throughput and spectral efficiency are two of the most important metrics used in evaluating the performance of such systems. In this paper, we present a pseudo-closed form expression for the average throughput and spectral efficiency of WCDMA in the high speed downlink packet access/frequency division duplex (HSDPA/FDD) mode. The throughput is expressed in terms of system dependent parameters that are analytically defined as well as stochastic parameters that depend on the user received signal-to-interference-plus-noise ratio (SINK). Monte Carlo simulations are used to evaluate those stochastic parameters and several numerical examples are presented. Our results cover a wide variety of practical scenarios in which sectorized/non-sectorized cells, different antenna radiation patterns and different frequency reuse factors are used.

Throughput and spectral efficiency are two important metrics that are used in performance evaluation of next generation cellular systems known as 3G. Wideband code division multiple access (WCDMA) has been adopted as an air interface technology for such systems. Tedious and time consuming Monte Carlo simulation schemes are usually needed to assess the performance of WCDMA in terms of throughput and spectral efficiency. In this paper, we present a simple analytical framework that can be used to evaluate the performance of downlink WCDMA operating in the time division duplex (TDD) mode without using computer simulations. An approximate closed form expression for the cumulative distribution function (CDF) of the user carrier-to-interference-plus-noise ratio (CINR) is first obtained, based on the 3GPP pathloss model, assuming lognormal shadowing and uniform cell loading. The throughput is then expressed in terms of this distribution and other system parameters. Numerical results are presented and show good agreement between both the proposed analytical framework and Monte Carlo simulations.