This paper focuses on maximizing the sum secrecy rate in secure multi-user MISO communication systems that use stacked intelligent metasurfaces (SIM). SIM technology manipulates electromagnetic waves and improves secure communication by combining several metasurface layers with discrete phase-shifting capabilities. We propose a methodology for optimizing beamforming vectors at the base station and phase shifts across metasurface layers, with the goal of maximizing the sum secrecy rate while adhering to practical power constraints. The non-convex optimization problem, induced by discrete phase shifts and coupled design beamforming parameters, is dealt by using an alternating optimization (AO) method. This method employs successive convex approximation for beamforming and projected gradient ascent for phase shift adjustment, resulting in convergence to locally optimal solutions. The proposed approach is thoroughly assessed in simulated scenarios to discover how it performs under various system configurations. The findings reveal that increasing the number of metasurface layers and meta-atoms significantly increases the sum secrecy rate by improving spatial control, lowering interference, and effectively repelling eavesdropping threats. Furthermore, the AO algorithm demonstrates rapid convergence and computational efficiency, making it appropriate for practical use. The framework demonstrates strong flexibility to changes in transmit power, antenna design, and user densities while retaining stable and scalable performance. This research emphasizes the potential of SIM-assisted systems in improving security in wireless communications by enhancing spatial architecture and beamforming, which can complement existing security strategies.

Energy consumption (EC) represents a significant challenge for 5 G and 6 G mobile networks, necessitating a primary focus on optimizing energy savings (ES). This paper illustrates the practical benefits of a user-centric deep reinforcement learning (DRL) models in achieving a green cellular network. The primary objective is to optimize energy usage in a heterogeneous network (HetNet). The optimization of power consumption (PC) in such networks is a non-convex and NP-hard problem. To address this challenge, we propose using reinforcement learning (RL). Due to the extensive state and action space, classical RL approaches are unsuitable. Therefore, the adoption of DRL methods, notably the deep Q-network (DQN) and deep deterministic policy gradient (DDPG) methods, is necessary. The proposed approach entails a user-centric connection establishment, whereby small base stations (SBSs) are switched to anonmode. The mode switching determined by the DRL methods is controlled by an anti-abrupt transition mechanism, which prevents unnecessary oscillations in the network. The results are benchmarked against existing approaches, specifically genetic algorithm (GA) and particle swarm optimization (PSO) for ES. The proposed methods outperform both GA and PSO optimization techniques in terms of ES and significantly reduce time consumption, enhancing its practical implementation feasibility.

In this paper, we utilize a graph neural network to perform joint user association and access point activation/deactivation to optimize network blockage. Instead of using theoretical models to characterize the distribution of network traffic, we use a real-world network traffic dataset. In order to train the graph neural network, our method leverages reinforcement learning, specifically employing the deep deterministic policy gradient (DDPG) algorithm. This approach allows us to benefit from the advantages of both value-based and policy-based reinforcement learning methods. A simple but flexible reward function is defined to capture the trade-off between the fraction of active access points and network blockage. The graph neural network's awareness of the network topology gives the proposed method a clear performance advantage over the commonly used greedy heuristic optimization method, reducing blockage by up to more than 50% on real-world network traffic data while also reducing computational complexity from$\mathcal {O}(N^{3})$to$\mathcal {O}(N)$. The proposed user association and access point activation method is not limited by the network architecture or technology, and can be applied to different generations of cellular networks.

Cell-free Massive multiple-input multiple-output (CF-mMIMO) is one of the most promising technologies. It is crucial to examine the performance of CF-mMIMO systems in real-world scenarios, particularly the hardware impairments caused by nonlinear power amplifiers (PAs). This paper’s main objective is to thoroughly examine CF-mMIMO under PA non-linearity at user equipment (UE), focusing on power allocation performance. We provide closed-form expressions for uplink achievable data rates while accounting for the nonlinear behavior of the PA. We extensively examine power control strategies. Initially, we explore full power transmission and Channel Inversion. Then, we address the non-convex problem of maximizing both the sum rate (MSR) and the minimum rate (MMR) of users using the single condensation method (SCM) and successive convex approximation (SCA) algorithm. We propose iterative algorithms to optimize the ultimate geometric programming (GP) problem and find the optimal power control coefficients. Results confirm that the proposed nonlinearity-aware power control yields substantial enhancements in net throughput compared to conventional algorithms. This underscores the superiority of integrating the nonlinearity of PAs into the power allocation strategy. The proposed MSR algorithm not only enhances the sum throughput but also increases the minimum net throughput and Jain’s fairness index of net throughput.

In this paper, we investigate the effect of power amplifier (PA) nonlinearity on a multi user multiple-input multiple-output orthogonal frequency division multiplexing (MU-MIMO-OFDM) system where the base station (BS) uses linear precoding to transmit data for single antenna users through a correlated channel. The signal to distortion, interference and noise ratio is derived for any order of PA nonlinearity. Our analysis shows that a correlated channel can result in correlated distortions at the output of PAs which increase the received distortion power of users. Approximations for the ergodic achievable rate of the users are provided when the BS transmits data through a correlated channel using maximum ratio transmission or zero forcing precodings and number of BS antennas and users are large. Also, closed form approximations for the ergodic achievable sum rate of the system are provided when the channel is not correlated. The simulation results agree with the derived approximations even when the number of transmit antennas and users are relatively small. The approximations can be used to find the achievable sum rate maximizing number of users or transmit power of the system.

In this paper, we examine the secrecy performance of two-way relaying between a large-scale multiple antenna base station (BS) and a single antenna mobile user (MU) in the presence of a multiple antenna external jammer. We consider the untrusted relaying scenario, where an amplify-and-forward relay is both a necessary helper and a potential eavesdropper to the BS and MU transmissions. With the aim of maximizing the instantaneous secrecy sum rate, we derive new closed-form solutions for the optimal power allocation (OPA) under the following three scenarios: 1) without jamming (WoJ) where the jammer is not activated; 2) friendly jamming (FJ) where the jamming signal is known a priori at the BS and MU; and 3) Gaussian noise jamming (GNJ) where the jamming signal is unknown at the BS and MU. Based on our OPA solutions, new closed-form expressions are derived for the ergodic secrecy sum rate (ESSR) with Rayleigh fading channels. Furthermore, we characterize the high signal-to-noise ratio slope and power offset of the ESSR to provide a fundamental comparison of the WoJ, FJ, and GNJ scenarios. Based on our analysis, we propose a simple relay selection criterion for the scenario when the BS and MU are assisted by multiple untrusted relays. Numerical examples are presented to demonstrate the impact of the jammer's location, number of antennas and the advantage of the proposed relay selection criterion on the secrecy performance. Our findings highlight that similar to the trusted relaying scenario, the ESSR of all three secure transmission scenarios improve as the number of untrusted relays increases. Moreover, we highlight an interesting insight that the OPA for the GNJ scenario results in the same ESSR performance as the OPA for the WoJ scenario.

In this paper, a joint relay selection and power allocation (JRP) scheme is proposed to enhance the physical layer security of a cooperative network, where a multiple antennas source communicates with a single-antenna destination in the presence of untrusted relays and passive eavesdroppers (Eves). The objective is to protect the data confidentially while concurrently relying on the untrusted relays as potential Eves to improve both the security and reliability of the network. To realize this objective, we consider cooperative jamming performed by the destination while the JRP scheme is implemented. With the aim of maximizing the instantaneous secrecy rate, we derive a new closed-form solution for the optimal power allocation and propose a simple relay selection criterion under two scenarios of non-colluding Eves (NCE) and colluding Eves (CE). For the proposed scheme, a new closed-form expression is derived for the ergodic secrecy rate (ESR) and the secrecy outage probability as security metrics, and a new closed-form expression is presented for the average symbol error rate as a reliability measure over Rayleigh fading channels. We further explicitly characterize the high signal-to-noise ratio slope and power offset of the ESR to highlight the impacts of system parameters on the ESR. In addition, we examine the diversity order of the proposed scheme to reveal the achievable secrecy performance advantage. Finally, the secrecy and reliability diversity-multiplexing tradeoff of the optimized network are provided. Numerical results highlight that the ESR performance of the proposed JRP scheme for NCE and CE cases is increased with respect to the number of untrustworthy relays.

By taking a variety of realistic hardware imperfections into consideration, we propose an optimal power allocation (OPA) strategy to maximize the instantaneous secrecy rate of a cooperative wireless network comprised of a source, a destination, and an untrusted amplify-and-forward relay. We assume that either the source or the destination is equipped with a large-scale multiple antennas' system, while the rest are equipped with a single antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-based cooperative jamming. Given this system model, novel closed-form expressions are presented in the high signal-to-noise ratio regime for the ergodic secrecy rate and the secrecy outage probability. We further improve the secrecy performance of the system by optimizing the associated hardware design. The results reveal that by beneficially distributing the tolerable hardware imperfections across the transmission and reception radio-frequency front ends of each node, the system's secrecy rate may be improved. The engineering insight is that equally sharing the total imperfections at the relay between the transmitter and the receiver provides the best secrecy performance. Numerical results illustrate that the proposed OPA together with the most appropriate hardware design significantly increases the secrecy rate.

In this paper, we examine the secrecy performance of two-way relaying between a multiple antenna base station (BS) and a single antenna mobile user (MU) in the presence of a multiple antenna friendly jammer (FJ). We consider the untrusted relaying scenario where an amplify-and-forward relay is both a necessary helper and a potential eavesdropper. To maximize the instantaneous secrecy sum rate, we derive new closed-form solutions for the optimal power allocation (OPA) between the BS and MU under the scenario of relaying with friendly jamming (WFJ). Based on the OPA solution, new closed-form expressions are derived for the ergodic secrecy sum rate (ESSR) with Rayleigh fading channel. Furthermore, we explicitly determine the high signal-to-noise ratio slope and power offset of the ESSR to highlight the benefits of friendly jamming. Numerical examples are provided to demonstrate the impact of the FJ's location and number of antennas on the secrecy performance.

In this paper, we propose a self-dependent two-way secure communication where two sources exchange confidential messages via a wireless powered untrusted amplify-and-forward (AF) relay and friendly jammer (FJ). By adopting the time switching (TS) architecture at the relay, the data transmission is accomplished in three phases: Phase I) Energy harvesting by the untrusted relay and the FJ through non-information transmissions from the sources, Phase II) Information transmission by the sources and jamming transmissions from the FJ to reduce information leakage to the untrusted relay; and Phase III) Forwarding the scaled version of the received signal from the untrusted relay to the sources. For the proposed system, we derive a new closed-form lower bound expression for the ergodic secrecy sum rate (ESSR). Numerical examples are provided to demonstrate the impacts of different system parameters such as energy harvesting time, transmit signal-to-noise ratio (SNR) and the relay/FJ location on the secrecy performance. The numerical results illustrate that the proposed network with friendly jamming (WFJ) outperforms traditional one-way communication and the two-way without friendly jamming (WoFJ) policy.

In this paper we investigate the joint power and channel allocation problem in two-tier OFDMA femtocell networks using a multiobjective approach with focus on energy efficiency. Three main objectives are considered in our problem formulations namely, energy efficiency, spectral efficiency, and power consumption. To solve the muliobjective problems, we have utilized a non- dominated sorting genetic algorithm (NSGA-II) and an algorithm have been proposed to perform the resource allocation procedures. In this investigation, to preserve the quality service of users, we have applied a minimum data rate threshold for all users. Furthermore, we impose an interference threshold limit on each subchannel to protect the macrocell user quality of service. Finally, the simulation results figure out that we can achieve 30% better energy efficiency by trading the throughput by about 20%.

In this study, the physical layer resource allocation in orthogonal frequency‐division multiple access (OFDMA) systems is studied by considering the non‐linear effects of power amplifier (PA). The non‐linearity produces cross‐correlation among the subcarriers and results in deteriorating the OFDMA subcarriers orthogonality. Hence, the signal‐to‐interference ratio (SIR) of the output signal of PA for OFDMA signal with different power scaling factors for subcarriers is derived. Then, the theoretical SIR is verified by simulation result. Next, the optimisation problem is designed to maximise the total achievable downlink rate of all users by assigning subcarriers and power scaling factors. This non‐convex problem is solved by comprehensive learning particle swarm optimisation. The simulation results show that when PA is non‐linear, better total rate is achieved by considering non‐linearity in resource allocation compared with the conventional resource allocation techniques.

Here, the authors investigate the optimum power allocation to increase the ergodic capacity in cloud radio access network (C‐RAN). At first, some closed‐form expressions are derived to calculate the ergodic capacity in downlink transmission of C‐RAN. This is followed by using these expressions to optimise the power sharing among remote radio heads (RRHs), where this process is coordinated in a baseband unit. Then a sparse power allocation (SPA) strategy is proposed for coordination multipoint joint transmission (CoMP‐JT). By applying SPA in C‐RAN, the power allocations for RRHs can be managed to achieve higher capacity. The improvement in capacity is more satisfied in low signal‐to‐noise ratio region. It is shown that the proposed method can improve the ergodic capacity and meanwhile reduces the network power consumption. Simulation results show that using SPA strategy for CoMP‐JT increases the ergodic capacity by 4 bits/s/Hz in 8‐RRHs C‐RAN compared with equal power allocation technique.

We study the performance of device-to-device (D2D) communication underlaying cellular wireless network in terms of the meta distribution of the signal-to-interference ratio (SIR), which is the distribution of the conditional SIR distribution given the locations of the wireless nodes. Modeling D2D transmitters and base stations as Poisson point processes (PPPs), moments of the conditional SIR distribution are derived in order to calculate analytical expressions for the meta distribution and the mean local delay of the typical D2D receiver and cellular downlink user. It turns out that for D2D users, the total interference from the D2D interferers and base stations is equal in distribution to that of a single PPP, while for downlink users, the effect of the interference from the D2D network is more complicated. We also derive the region of transmit probabilities for the D2D users and base stations that result in a finite mean local delay and give a simple inner bound on that region. Finally, the impact of increasing the base station density on the mean local delay, the meta distribution, and the density of users reliably served is investigated with numerical results.

In this study, the authors propose a low‐complexity method for symbol synchronisation in the third generation partnership project long term evolution (LTE) downlink system. The authors introduce the lowest sampling frequency of a receiver for synchronisation purposes. Using a low sampling frequency at the receiver means that the digital signal is decimated and a lower number of processing samples is needed. This results in reducing the computational complexity. It is also shown that this advantage comes at the cost of signal‐to‐noise ratio degradation and insertion of a systematic error in synchronisation that can be avoided by choosing a proper decimation factor. A thorough analysis is also conducted for all possible sampling frequencies that reduce the computational complexity of LTE cell search. To show the validity of the authors’ method, they implemented an LTE primary synchroniser in C++ using GNU Radio libraries and prepared a software‐based radio modem, tested in different conditions. Some Monte‐Carlo simulations are carried out to compare the proposed method with other low‐complexity methods. These comparisons show the suggested method is faster than available techniques in literatures.

In this study, the authors study the problem of secure transmission in two‐hop amplify‐and‐forward systems with an untrusted relay. To prevent the untrusted relay from intercepting the source message and to achieve positive secrecy rate, the destination‐based cooperative jamming technique is used. In this method, the destination sends an intended jamming signal to the relay. This jamming signal helps protecting the source message from being captured reliably at the untrusted relay, while the destination cancels itself intended jamming signal. The optimal power allocation (OPA) strategy is considered for the proposed system. They observe that the objective function is a quasi‐concave function at high signal‐to‐noise‐ratio regimes. Based on this OPA strategy, in the first step, the outage probability of the system is investigated. It is investigated for three cases. In the two cases, either of the source or the destination node is equipped with large‐scale antennas, and in the third case, both of them are equipped with large‐scale antenna arrays. In all the cases, the closed‐form expressions are derived. In the second step, they investigate the ergodic secrecy rate and present the closed‐form solutions for all the mentioned cases. Finally, simulation results indicate the accuracy of the derived equations.

To protect data communication from eavesdropper nodes, different techniques have been developed to improve the physical‐layer security (PLS) of communications systems. Destination‐based cooperative signalling (DBCS) is one of such techniques where the destination sends an intended artificial noise to the untrusted listeners helping to protect the source message from being captured reliably at eavesdroppers. In this study, the authors investigate the application of DBCS to improve the PLS, and as a consequence the secrecy performance of a two‐hop amplify‐and‐forward cooperative system with an untrusted relay. To get the best performance out of DBCS, the transmit power of the source's signal as well as the artificial noise should be carefully adjusted. To address this, they have introduced the optimal power allocation to maximise the secrecy rate of the system under a sum‐power constraint at the network nodes. For a system with large‐scale antenna arrays at the base station, then then find the closed‐form solution for the secrecy outage probability and the ergodic secrecy rate of the optimised system for both uplink and downlink. The presented simulation results validate the authors’ theoretical analysis and reveal that the proposed DBCS with optimal power allocation significantly improves the secrecy performance of the system.

In this study, the authors study the diversity‐multiplexing trade‐off (DMT) of multi‐input–multi‐output (MIMO) systems in which linear dispersion (LD) codes are used. They first focus on an LD‐coded 2 × 2 MIMO systems at the high signal‐to‐noise ratio (SNR) regime. By using the joint eigenvalue density, the outage probability is presented in a very compact expression, which establishes the DMT framework at this regime. Simulation results show that the derived expression for the outage probability is sufficiently accurate at high SNR regimes but less accurate in the transition region. Finally, for the special case of multi‐input–single‐output, they derive both the outage probability and the DMT framework inexact and closed form formulas at all SNRs, including finite SNRs.

Spurious intermodulation components have recently been identified as a major problem in carrier aggregation mobile transmitters with multi-band power amplifiers (PAs). This article presents novel adaptive digital predistortion (DPD) solutions with reduced complexity in both the predistortion processing and the feedback paths, to tackle this problem. Compared with conventional DPDs which aim to linearize the whole transmit bandwidth, the proposed technique aims at mitigating only those intermodulation components which are most problematic from the spurious emission limit perspective. The proposed technique is verified with extensive simulations in various 3GPP LTE-A carrier aggregation scenarios, showing that the intermodulation spurs can be efficiently mitigated below the spurious emission limit with relatively small back-offs.

In this study, two relay selection methods in the half‐duplex decode‐and‐forward relaying for cooperative multiple‐input multiple‐output‐orthogonal frequency division multiplexing (MIMO‐OFDM) systems have been introduced. The relay selections are implemented using the symbol‐based and subcarrier‐based methods. By considering different number of antennas for source, each relay, and destination, the authors have derived closed‐form outage expressions for these proposed methods. The MIMO channel model for each subcarrier, between source–relay and relay–destination is considered as a MIMO Rician fading channel with independent but not necessary identically distributed. Moreover, the outage expressions for MIMO independent and identically distributed Rician and Rayleigh fading channels are derived as special cases. Furthermore, the correlation among the OFDM subchannels is analysed. In addition, the implementation issues of both relay selection methods are also investigated. Monte Carlo simulations are performed to validate the outage analysis where the excellent agreement between the analytical and simulation results is observed.

A simple and accurate statistical model (SASM) for a high‐power amplifier (HPA) with memory in multi‐input multi‐output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is proposed. This model is statistically equivalent to the more complex generalised memory polynomial (GMP) model, which is one of the most accurate models. The HPA distortion is modelled using stationary white Gaussian noise sources that pass through finite impulse response (FIR) filters. The filter coefficients and the variance of noise sources are derived analytically from the GMP model parameters by spectral decomposition of the GMP noise power spectrum. The number of FIR filters is equal to the memory length of the GMP model. The HPA effect on the OFDM signal, considered as frequency‐dependent attenuation coefficients, is modelled using another FIR filter. These FIR filters with small lengths make the model computationally inexpensive and mathematically tractable. The main characteristics of this model are identical bit error rate (BER) and error vector magnitude of subcarriers with those in the GMP model. The proposed model is the simplest representation of a HPA with memory effects. An excellent agreement between the simulation results of the SASM and GMP model is observed. This verifies the accuracy and efficiency of the proposed method.

A novel technique is presented to design efficient full‐rate space–time block codes (STBCs) over correlated Rician fading channels. The authors first derive a formula for the achievable information rate of a linear dispersion coded multi‐input single‐output system as a function of correlation at the transmitter in a Rician fading channel. In addition, the authors obtain the bit‐error‐rate (BER) equations for this system, when multiple phase shift keying and multiple quadrature amplitude modulation schemes are used at the transmitter. Therefore with regard to derived formulae and using a genetic algorithm, a method is presented to construct STBCs over correlated Rician fading channels. The efficient designed STBCs for two and four transmit antennas enjoy full‐rate, simple structure, simple processing at the receiver, better BER performance than associated orthogonal STBCs at practical signal‐to‐noise ratios (SNRs) and higher achievable information rate than them at all SNRs.

The nonlinear behavior of power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM)-based cognitive radio (CR) system introduces in-band and adjacent channel interferences. The power in the adjacent channels is an important issue in the CR because it can act as interference to primary users. In this paper, we derive a closed-form expression for the leakage power at adjacent channels when CR devices use OFDM modulation. Moreover, the PA nonlinearity creates in-band distortion that produces intercarrier interference and reduces the secondary system capacity. To control this effect, we derive the optimum power scaling factor for the input signal that maximizes the secondary user rate. The optimization process is executed by considering nonlinear effects on signal-to-interference-and-noise ratio under the constraints of the powers in the adjacent channels. The power in the adjacent channels should not exceed the interference temperature limit. The analytical results are verified by simulation studies.

The interference to the primary receiver (PR) is a critical issue in the resource allocation of cognitive radio (CR) networks. For instance, the nonlinearity of the power amplifier (PA) causes nonlinear interference to the PRs. This paper studies the power allocation in cognitive radio networks by considering the nonlinear effects of the PA on the received signal-to-noise ratio (SNR) at the secondary receiver (SR) and the adjacent channel interference (ACI) to the PRs. A nonlinear PA with limited dynamic range and a lower limit on the transmit power is assumed for the secondary transmitter (ST). To control the resulting ACI from the ST to the PRs, the PA needs to be turned off in some fading blocks. To investigate the throughput, an analytical expression for the probability of data transmission between the secondary users is derived as a function of the interference temperature limits of the PRs. All analyses are performed for both peak and average ACI power constraints. Through theoretical analysis and simulation studies, maximum achievable average SNR at the SR is investigated. Moreover, the throughput degradation is studied and it is observed that the average ACI power constraints result in the better performance than the peak ones.

In this paper, the effects of nonlinear High Power Amplifier (HPA) with memory on Multi-Input Multi-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system are analyzed and a theoretical framework is proposed. The memory effects are represented by Generalized Memory Polynomial (GMP) model. Moreover, we derive an analytical formulation with infinite nonlinearity order and infinite memory length. The channel is assumed MIMO frequency selective and it is modeled as a linear dispersive channel with uniform power profile. We show that the decision variables of the nonlinearity distortion can be modeled by the complex attenuation and zero mean additive noise model. The analytical expressions for complex attenuation, mean and variance of nonlinear noise are derived and SER of MIMO-OFDM system using HPA with memory is presented. Excellent agreement between the analytical results and numerical simulations is observed that verifies the accuracy and efficiency of the proposed method.

In this paper, we employ an analytical method to evaluate the route bit-error-rate (BER) performance of a wireless ad hoc network which exploits minimum distance routing. First, we estimate the average source-destination distance. Then, we derive an analytical formula to estimate the average number of hops in routes. Finally, we derive the average Route BER based on (1) the transmit power of nodes, (2) the network bandwidth, and (3) the angular view of minimum distance routing. We show that increasing node density leads to a reduction in average route BER until the average interference power overpowers the average received power. The analytical derivations have been validated using simulation studies.

A design technique to realise a low-complexity multiple-input multiple-output (MIMO) receiver using a time-multiplexed single front-end receiver is introduced. The architecture uses a simple front-end receiver where it delivers radio frequency signals to baseband section. The theory behind this architecture is analysed and the diversity gain of the proposed receiver is investigated. This simple MIMO receiver can provide the same diversity gain as the diversity gain of the multiple front-end. Moreover, the experimental studies are conducted to evaluate the diversity gain of the proposed architecture. Excellent agreement between the simulated and measurement results is obtained. The proposed architecture provides a new receiver design technique with lower complexity, power consumption and cost in MIMO systems.

In this article, the authors develop an ‘analytical closed-form expression’ for the outage capacity of a wireless ad hoc network. First, a series of practical modulation schemes including binary phase shift keying (BPSK) and quadrature amplitude modulation (QAM) are considered. Then, a proper formulation for the total network capacity is presented based on the cumulative distribution function (CDF) of the signal to interference power ratio (SIR). A closed-form expression for this CDF is also analytically derived. Subsequently, the outage capacity of the network is examined. By investigating the effect of the outage threshold, it is shown that an optimum threshold value exists that maximises the outage capacity. This optimum value is obtained in the networks with different number of nodes. The analytical results are verified by conducting simulation studies.

This study presents an exact analysis of circuit non-linearity and phase noise effects on orthogonal frequency division multiplexing (OFDM) communication systems. Using an analytical approach, the degradation effects of these impairments on the performance of OFDM systems are studied. A truncated power series is used to represent the third-order non-linear behaviour of a radio frequency circuit. The phase noise is modelled with Lorentzian power density function. Then, by use of an expression for interferences and intermodulation terms, a closed-form signal-to-noise degradation relation is theoretically extracted. The analytical results are compared with simulation outcomes. The comparison shows that bit error rate of the analytical results closely matches with simulation results of the OFDM system.

The effects of phase noise on the adaptive modulation multiple-input multiple-output (MIMO) wireless system are investigated. A variable-rate variable-power adaptive modulation (AM) technique with perfect channel state information (P-CSI) at both transmitter and receiver is considered. Phase noise (PN) is modeled as a zero-mean, stationary, finite-power random process. The analytical results are extracted and the simulation studies are performed. These studies show the performance degradation of MIMO wireless systems due to phase noise effects. The degradation values are obtained based on phase noise variances in adaptive modulation MIMO systems. Moreover, the experimental studies to evaluate the accuracy of analytical and simulation results are conducted using a MIMO test bed. The excellent agreements among these results are obtained. These results can effectively be used to design and to performance study of practical MIMO wireless systems with adaptive modulation, e.g. IEEE802.16, and Wimax.

The authors employ a statistical method to characterise the wireless ad hoc network capacity problem. The channel parameters such as path loss and fading are considered in the analysis. Moreover, a simulation method based on the probability density function of signal-to-interference-plus-noise power-ratio is introduced. In both analysis and simulation, two receiving methods, matched filter (MF) and minimum-mean-square-error (MMSE) detector, are considered. After establishing the accuracy of the analytic approximation and comparing its results with simulation results, the scalability of a random network is studied. Moreover, the outage and ergodic capacities are determined for various network and channel parameters. It is shown that when MMSE detector is used in the network, the capacity is higher than when MF is used. When number of the nodes increases the total ergodic capacity raises, but per node capacity reduces when using both MF and MMSE detectors. It is shown that the total outage capacity reaches a maximum. This leads to the conclusion that an optimum value for the number of nodes in the network exists, which maximises the outage capacity.

In this paper, we consider multiple-input single-output (MISO) and single-input multiple-output (SIMO) systems, and study the diversity-multiplexing tradeoff (DMT) for them at finite signal to noise ratio (SNR). To characterize the tradeoff, the outage probability versus SNR is extracted. The diversity gain is defined as the slope at a particular SNR of the outage probability versus SNR curve and the multiplexing gain is measured as the ratio of the system spectral efficiency to the capacity of an additive white Gaussian noise (AWGN) channel. This paper provides a useful tool to examine the DMT of MISO/SIMO systems in practical (finite SNR) situation.

The capacity estimation of ad hoc networks is a challenging performance analysis issue. In this paper we employ a statistical method based on the probability density function of Signal-to-Interference-plus-Noise-Ratio (SINR) to characterize the capacity problem. The channel parameters as path loss, shadowing, fading, etc. are considered in this method. We first establish the accuracy of the method with comparison its results with the previous works. Then, using this method an exact value for the capacity of the ad hoc and mesh networks are presented according to the allocated resources to the network. The network scalability problem is examined and the accuracy and efficiency of the presented technique are discussed.

We describe a novel architecture for direct conversion receivers based on sixport configuration. The analytical and simulation results show that the introduced multi-port direct receiver is capable to perform MQAM and MPSK demodulations. Moreover, this demodulator can be easily designed for broadband applications. A main advantage of this design is to reduce six ports to five ports. The proposed receiver is very suitable for software radio applications.

In this work we develop a computer-aided tool for propagation prediction of wireless channels based on a modified shooting and bouncing ray (SBR) method that is combined with GTD/UTD (geometrical theory of diffraction/uniform theory of diffraction). Our simulation results show that the new algorithm reduces the computation time while the accuracy of the algorithm is preserved. In this paper we also investigate the effects of receiver antenna height and antenna beamwidth on path loss and channel parameters for LMDS systems.

This paper discusses various challenges to realize a fixed wireless ATM network and provides solutions to these challenges. The capacity allocation in wireless ATM, wireless link impact on ATM traffic, and optimum utilisation of the wireless network resources for a LOS wireless ATM link are studied. An adaptive MQAM modulator is introduced to provide an optimum solution to these problems. The modulator level is adjusted using a unique QoS metric in a wireless ATM network. The metric, termed modified effective bandwidth, takes into account the bandwidth demand, QoS requirements, and outage conditions of the wireless ATM link. A performance study using VBR MPEG-1 video traffic in a fixed wireless channel (Ricean channel) demonstrates the advantages of the proposed system.

A phase locked loop based architecture is proposed for generation and frequency stabilization of direct Gaussian minimum shift keying (GMSK) at microwave and millimeterwave frequencies. A continuous phase frequency shift keyed (CPFSK) signal with a modulation index of 0.5 is produced at the desired output frequency using a full 360 degree linear continuous phase modulator that is controlled by the integrated baseband information signal. This modulated signal is used as the reference signal for a phase locked high power voltage controlled oscillator. The phase locked loop facilitates reference signal frequency tracking and provides Gaussian spectral shaping to the modulated output signal. Phase locked loop imperfections and their effect on the modulated output signal are considered and simulation results are presented.

The concept of effective bandwidth has been recently introduced to analyze the call admission, congestion control, and resource management in ATM networks. In this paper, the effective bandwidth is proposed as a metric of quality of service for wired and radio ATM. Using traditional and self-similar models of traffic sources, the effective bandwidth for an ideal channel is computed. The results are extended to random error and burst error channels by computing cell loss ratio. Using a modified fluid flow model, analytical approaches are examined using an ATM-simulator with different buffer sizes and Hurst parameters. The results can be used by the ATM system designer when dealing with bandwidth restricted channels, e.g., radio ATM.