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Electric vehicles (EVs) and unmanned aerial vehicles (UAVs) show great potential in modern transportation and communication networks, respectively. However, with growing demands for such technologies, the limited energy infrastructure becomes the bottleneck for their future growth. It might be of high cost and low energy efficiency for all the operators to each have their own dedicated energy infrastructure, such as charging stations. In this paper, we analyze a wireless charging infrastructure sharing strategy in UAV and EV-involved networks. We consider a scenario where UAVs can charge in EV charging stations and pay for the sharing fee. On the EVs' side, sharing infrastructure can earn extra profit but their service quality, such as waiting time, might slightly reduce. On the UAVs' side, if renting EV charging stations can achieve an acceptable system performance, say high coverage probability, while considering the cost, they may not need to build their dedicated charging stations. In this case, we use tools from stochastic geometry to model the locations and propose an optimization problem that captures the aforementioned trade-offs between cost or profit and quality of service. Our numerical results show that sharing infrastructure slightly increases the waiting time of EVs, say within $5$ min, but dramatically decreases the waiting time of drones, say more than $50$ min, and deploying more charging stations do achieve better performances, but all these better performances are expected to cost more.

Electric vehicles (EVs) are being actively adopted as a solution to sustainable transportation. However, a bottleneck remains with charging, where two of the main problems are the long charging time and the range anxiety of EV drivers. In this research, we investigate the deployment of dynamic charging systems, i.e., electrified roads that wirelessly charge EVs on the go, with a view to accelerating EVs adoption rate. We propose a traffic-based deployment strategy, statistically quantify its impact, and apply the strategy to two case studies of real traffic in New York City (USA) and Xi'an (China). We find that our analytical estimates not only closely match the real data, but they also suggest that dynamic charging considerably extends the driving range of popular EV models in urban mobility. For example, when only 5% of the existing roads in New York City are equipped with this technology, an EV model such as the Nissan Leaf will approximately maintain its battery level without stopping to recharge. If the percentage of charging roads is increased to 10%, then the Leaf will gain nearly 10% of its battery after every 40 kilometers of driving. Our framework provides a solution to public and private organizations that support and facilitate vehicle electrification through charging infrastructure., Comment: 14 pages, accepted to IEEE Transactions on Vehicular Technology

This paper investigates the full-duplex (FD)-enabled unmanned aerial vehicles (UAVs) communication system designed to improve spectrum utilization and coverage issues in the suburban environment. The reliability analysis of the considered system is analyzed in terms of block error rate (BLER) under ultra-reliable and low-latency communication constraints. With the assumption of the combined effect of fading and shadowing, the closed-form expressions for BLER and system goodput are obtained over Rician shadowed fading channels considering various shadowing scenarios, inter-UAV interference, and self-interference (SI) cancellation capabilities at FD node. The obtained results over Rician shadowed fading for FD-enabled UAV system are also compared with it's half-duplex counterpart over Rician fading channels. It was concluded that strong SI suppression capabilities at FD GS can results in almost 85% of performance gain at low shadowing severity conditions. The numerical results reveal important observations related to the impact of shadowing severity in the suburban areas, SI cancellation capabilities, blocklength and channel uses on the reliability performance of the FD-enabled multi-UAV system.

In this article, we study the energy efficiency (EE) of orthogonal frequency-division multiple access (OFDMA) cellular networks under the 5 G requirement of EE enhancement. We aim to present a power allocation scheme maximizing the EE of downlink cellular communications while avoiding numerical methods such as fractional programming. We focus on two EE forms; global EE and weighted sum EE. Therefore, we propose a novel explicit expression of the optimal power allocation related to each subcarrier. We also present the power control with limited power budget or/and minimal transmission rate constraint in both base station and subcarrier perspectives. As a result, we notice the occurrence of some transmission outage events depending on the constraints’ parameters. From another side, we extend our study to analyze the effect of the channel state information (CSI) unavailability on our proposed power scheme. In the numerical results, we show that our proposed power control improves the EE, especially at high power budget regime and low minimal rate regime. We also show that having more subcarriers enhances the OFDMA EE. Finally, we show that EE degradation due to CSI unavailability is very small showing the robustness of the proposed scheme against CSI imperfectness.1

Intelligent reflecting surface (IRS) has recently emerged as a promising technology for 6G wireless systems, due to its capability to reconfigure the wireless propagation environment. In this paper, we investigate a Rate-Splitting Multiple Access (RSMA) for IRS-assisted downlink system, where the base station (BS) communicates with single-antenna users with the help of an IRS. RSMA relies on rate-splitting (RS) at the BS and successive interference cancellation (SIC) at the users and provides a generalized multiple access framework. We derive a new architecture called IRS-RS that leverages the interplay between RS and IRS. For performance analysis, we utilize an \textit{on-off control technique} to control the passive beamforming vector of the IRS-RS and derive the closed-form expressions for outage probability of cell-edge users and near users. Moreover, we also analyze the outage behavior of cell-edge users for a sufficiently large number of reflecting elements. Additionally, we also analyze the outage performance of cooperative RS based decode-and-forward (DF)-assisted framework called DF-RS. Through simulation results, it is shown that the proposed framework outperforms the corresponding DF-RS, RS without IRS and IRS-assisted conventional non-orthogonal multiple access (NOMA) schemes. Furthermore, the impact of various system's parameters such as the number of IRS reflecting elements and the number of users on the system performance is revealed.

Terahertz (THz) wireless technology is envisioned to enable terabit-per-second (Tbps) and secure transmissions in sixth-generation (6G) communication networks and has attracted attention from academia and industry in recent years. Because the transmission range of THz radios is restricted compared to that of microwave radios, frequency reuses in the THz band become much more flexible and even possible among transceiver pairs in close proximity. However, without appropriate spatial arrangement and coordination, the frequency reuse in the THz band can also lead to severe co-channel interference and result in a low signal-to-interference-plus-noise ratio (SINR) or a signal-to-interference ratio (SIR), which finally degrades signal detection and network reliability. To thoroughly study the co-channel interference in the THz band, we model the co-channel interference by the compound channel model and analyze it in detail. The adopted channel model captures the key features of THz communication, such as, spreading loss, molecular absorption loss, and dynamic shadowing, which is much different and complicated than those used in the low-frequency band. The resulted SINR and SIR are investigated by approximating the sum of co-channel interference as a gamma distribution. The generalized analytical results are also reduced to specialized forms for two special cases, i.e., the single-interferer case and the case of multiple independent and identically distributed (i.i.d.) interferers. Due to the generalized nature of the THz interference model constructed in this paper, the results play a meaningful role in practical implementation and can be easily extended to advanced performance analyses for THz communication systems.

In this paper, we develop the transient performance limits of wireless transmissions for ultra-reliable low-latency communications (URLLC). In particular, we derive the exact statistics of the maximum amount of data that can be delivered during a fixed time duration over fading channels, for both channel state information (CSI) at transmitter side and CSI at receiver side only scenarios. Following a recently proposed data-oriented approach, we then analyze the performance of sample ideal transmission schemes in terms of URLLC support. Selected numerical examples are presented to examine the effect of power adaptation and rateless coding on transient transmission performance over fading channels.

Future Internet of Things (IoT) applications demand highly energy-efficient wireless transmission solutions. In this article, we characterize the energy efficiency (EE) of wireless transmission over fading channels from individual transmission session perspective. Specifically, we apply a statistical EE metric to analyze and optimize ideal continuous rate adaptation (CRA) and continuous power adaptation (CPA) transmission schemes. The resulting statistical characterization establishes an EE performance limit for data transmissions over fading channels and facilitates a direct tradeoff analysis between maximal achievable EE and instantaneous latency requirement.

In this correspondence, we consider a mixed radio-frequency/underwater wireless optical communication (RF-UWOC) system with a fixed-gain amplify-and-forward relay, where the RF link experiences a Generalized- $K$ distribution while the UWOC link undergoes a mixture Exponential-Generalized Gamma distribution. In our analysis, new closed-form expressions for the cumulative distribution function (CDF), and probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR) are derived. Capitalizing on these useful statistics, the performance of the proposed mixed RF-UWOC system is investigated in terms of the outage probability, average bit error rate, and average channel capacity. Our analytical expressions are verified via Monte Carlo simulations results, and insightful discussions are presented.

In this work, the performance of a dual-hop variable gain amplify-and-forward (AF) mixed radio frequency (RF)/free space optics (FSO) system is analyzed in details. As variable gain AF relay network is considered, processing delay results in outdated channel state information (CSI) during amplification at the relay. For general applicability, the RF link is modeled with the generalized Nakagami-m fading. The FSO link is modeled with the Gamma-Gamma distribution which is affected with the atmospheric turbulence and pointing error impairments, and both the intensity modulation with direct detection (IM/DD) and heterodyne detection are employed at the FSO receiver. In this context, analytical expressions of outage probability and ergodic capacity are derived in terms of Meijer-G function and extended generalized bivariate Meijer-G function. For diversity order, asymptotic outage probability expression is also derived. Further, cumulative distribution function based generalized average symbol error rate expressions for various quadrature amplitude modulation (QAM) schemes such as hexagonal QAM, rectangular QAM, and cross QAM are derived in terms of Meijer-G function. Furthermore, a detailed comparative study of various modulation schemes is presented and the impact of pointing error, atmospheric turbulence, outdated CSI, and Nakagami-m parameter are highlighted on the system performance. Finally, all the analytical results are verified through Monte-Carlo simulations.

In this work, we study the problem of jamming avoidance for ensuring quality-of-service (QoS) in terms of the network lifetime and overhead in wireless sensor networks (WSNs). We propose a mobility model using Single-Leader-Multiple-Followers Stackelberg game theory to avoid the jamming affected region. In the proposed model, the centralized unit (CU) identifies the jamming affected region based on the locations of the affected nodes and acts as the leader. On the other hand, the jamming affected nodes act as followers and decide the mobility pattern, including the angle of movement, while minimizing the energy consumption and delay in packet delivery. A scheme, named M-JAW, for ensuring QoS, while avoiding jammers in WSNs, is proposed using the stated game-theoretic mobility model. Using M-JAW, the energy consumption of the overall network reduces by up to $\text{20.36}\%$ , and the network overload reduces by 44.13– $\text{50.12}\%$ , which, in turn, increases the lifetime of WSNs.

We propose an interference-based wireless powered communication system in which an energy constrained source harvests energy from a single dominant co-channel interferer and then transmits information to a destination equipped with $N$ receive antennas. Assuming interference dominates noise power at the destination and the receive antenna that maximizes the signal-to-interference ratio is selected, we investigate the average throughput for the delay-limited and delay-tolerant transmission modes. In particular, we derive an analytical expression of the average throughput for the delay-limited transmission mode, and a precise lower bound on the average throughput for the delay-tolerant transmission mode. Furthermore, we derive simplified asymptotic expressions of the average throughput for both transmission modes assuming asymptotically large number of receive antennas (i.e., $N \rightarrow \infty$ ). We use the obtained asymptotic expressions to derive insightful closed-form expressions for the optimal energy harvesting time, which maximizes the average throughput, for both transmission modes. We show that the throughput-optimal energy harvesting time for the delay-limited and the delay-tolerant transmission scale like $O (\frac{1}{\sqrt{N}})$ and $ O (\frac{1}{ \log (N)})$ , respectively, for asymptotically large $N$ .

In this paper, the problem of determining the maximum of independent but non-identically distributed (i.n.i.d.) double $\alpha$ - $\mu$ random variables (RVs) is investigated. In particular, we present a novel analysis to calculate the moments of the maximum of i.n.i.d. double $\alpha$ - $\mu$ RVs. To this end, an exact analytical expression for the $n$ -th moment is first derived, which is then used to study the performance of selection combining receivers in terms of channel quality estimation index, average bit error rate, and average (ergodic) channel capacity. The derived analytical results are compared with Monte-Carlo simulations, which validates the analysis and provides useful insights on the influence of fading and shadowing on the system performance.

In this correspondence paper, we consider the performance of a mixed free-space optical and radio frequency (FSO-RF) relaying system with energy harvesting in the existence of both atmospheric turbulence and pointing errors. More specially, we assume that the direct current component of the FSOsignal, which is generally filtered out, can be used for energy harvesting at the relay. We derive the exact closed-form expression for the outage probability of this setup in terms of the bivariate Fox-H function.We also provide the asymptotic analysis to obtain the diversity order. Finally, Monte Carlo simulations are carried out to verify the correctness of our analytical results. National Natural Science Foundation of China;Guangzhou Science and Technology Program key projects;Natural Science Foundation of Hunan Province; Department of Education of Guangdong Province; Fundamental Research Funds for the Central Universities Scopus

This paper proposes a robust beamforming (BF) scheme to enhance the physical layer security (PLS) of a multibeam satellite system operating at Ka band. By considering the effects of beam gain, path loss, and rain attenuation, we first formulate a constrained optimization problem to maximize the minimal achievable secrecy rate of multiuser under the assumption of imperfect eavesdropping channel and the constraint of total transmit power on the satellite. Since the problem is non-convex and mathematically intractable, we exploit the sequential convex approximation approach and S-procedure method to transform the original problem into one with a series of linear matrix inequality and second-order cone constraints, and then propose an iterative scheme to obtain the optimal BF weight vectors. Finally, simulation results showing the effectiveness and superiority of the proposed algorithm are provided.

In this paper, we accurately model the impact of aggregate hardware impairments (HWIs) in communication systems as improper Gaussian signals (IGS), which can describe the asymmetric characteristics of different HWI sources. The proposed model encourages us to adopt the IGS scheme for transmission that represents a general signaling scheme compared with the conventional scheme, proper Gaussian signaling (PGS). First, we express the achievable rate of multiple-input and multiple-output system suffering from various HWIs employing PGS and IGS schemes, when the aggregate effect of HWI is modeled as IGS. Moreover, we tune the transmit IGS statistical characteristics to maximize the achievable rate for the HWI single-input and multiple-output system with two receiver combining schemes. Then, we propose an adaptive scheme to switch between maximal IGS and PGS schemes under certain conditions to improve the system performance with least computational/optimization overhead. Finally, we validate the analytic expressions through numerical and simulation results and quantify the gain reaped from adopting the IGS scheme compared with the PGS scheme.

We investigate the secrecy performance of a multiuser diversity scheme for an interference-limited wireless network with a base station (BS), $N$ legitimate users, and an eavesdropper in the presence of a single dominant interferer. Assuming interference dominates noise power at the eavesdropper and at each legitimate user's receiver, the BS transmits information to the legitimate user with the $k$ th best (highest) signal-to-interference ratio. We derive a closed-form expression for the secrecy outage probability for an arbitrary $N$ and an asymptotic expression for a fixed $k$ and large $N$ . Furthermore, we derive a closed form asymptotic expression for the ergodic secrecy capacity of the $k$ th best user and shows that it scales like $O\left(\log (N)\right)$ for a fixed $k$ and large $N$ .

In this correspondence, we investigate the physical-layer security of a mixed radio frequency/free space optical (RF/FSO) dual-hop communication system for both fixed-and variable-gain relaying schemes. More specifically, we only assume that the eavesdropping happens at the RF link because the optical link has high security. We assume that all RF channels suffer from η-μfading, while the FSO link experiences M-distributed fading. Then, we derive some analytical results for the average secrecy rate and the secrecy outage probability.

In this correspondence, an asymptotic performance analysis for two-way relaying free-space optical (FSO) communication systems with nonzero boresight pointing errors over double-generalized gamma fading channels is presented. Assuming amplify-and-forward (AF) relaying, two nodes having the FSO ability can communicate with each other through the optical links. With this setup, an approximate cumulative distribution function (CDF) expression for the overall signal-to-noise ratio (SNR) is presented. With this statistic distribution, we derive the asymptotic analytical results for the outage probability and average bit error rate. Furthermore, we provide the asymptotic average capacity analysis for high SNR by using the momentsbased method.

This paper considers a secure nonorthogonal multiple access system, where confidential messages are transmitted from a base station to multiple legitimate destinations and wiretapped by multiple illegitimate receivers. It is assumed that all the channels experience a Nakagami- $m$ fading model and all the nodes are equipped with multiple antennas, respectively. Both noncolluding and colluding eavesdroppers are considered, respectively. A max–min (MM) transmit antenna selection (TAS) strategy is adopted to improve the secrecy performance of the target system, in which both users in user paring are considered simultaneously. In particular, closed-form expressions for the cumulative distribution function of the signal-to-interference-noise ratio at the legitimate user are derived first. Then, we obtain the exact and asymptotic analytical results in a closed form for the secrecy outage probability of an MM TAS scheme. Monte Carlo simulation results are presented to corroborate the correctness of the analysis. The results show that the secrecy diversity order is zero and nonzero for fixed and dynamic power allocations, respectively.

We consider a general selection-diversity scheme in which the $k$ th best link is selected from a number of links. We use extreme value theory to derive simple closed-form asymptotic expressions for the average throughput, effective throughput, and average bit error probability for the $k$ th best link over various channel models that are widely used to characterize fading in wireless communication systems. As an application example, we consider the Weibull fading channel model and verify the accuracy of the derived asymptotic expressions through Monte Carlo simulations.

In this correspondence, we investigate the physical layer security for cooperative nonorthogonal multiple access (NOMA) systems, where both amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered. More specifically, some analytical expressions are derived for secrecy outage probability (SOP) and strictly positive secrecy capacity. Results show that AF and DF almost achieve the same secrecy performance. Moreover, asymptotic results demonstrate that the SOP tends to a constant at high signal-to-noise ratio. Finally, our results show that the secrecy performance of considered NOMA systems is independent of the channel conditions between the relay and the poor user.