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Characterization and linearization of RF power amplifiers (PAs) are key issues of fifth-generation wireless communication systems, especially when high peak-to-average ratio waveforms are introduced. Recently, deep learning methods have achieved great success in numerous domains including wireless physical-layer. However, there has been limited work in using deep learning for PAs behavioral modeling and linearization. In this paper, we make a bridge between memory effects of the nonlinear PAs and memory of bidirectional long short-term memory (BiLSTM) neural networks. We then build a BiLSTM-based behavioral modeling architecture and its accompanying digital predistortion (DPD) model by reconciling a non causality concern. Next, an additional model is proposed in this paper to mitigate uncertainty of the tested PA when transforming phases. The experimental results demonstrate the effectiveness of the proposed scheme, in which the adequately trained networks are capable of characterizing the PA, and the artificial intelligence-based DPD shows promising linearization performance when considering the tested PAs inherent unpredictability. [ABSTRACT FROM AUTHOR]

This paper analyzes the efficacy of decoupled wireless access in a two-tier heterogeneous network. The decoupled wireless access and its performance benefits have been studied in different scenarios recently. In this paper, an in-depth analysis on its efficacy from spectral efficiency perspective is provided. To achieve this task, (i) new closed-form expressions for probability of association of user equipment with different tiers employing different frequency bands (i.e., microwave and millimeter wave) with different pathloss exponents are derived using univariate Fox's H-functions; (ii) Distributions of the distance to the serving base stations are also derived; (iii) Exact expressions of spectral efficiency for different association cases are further obtained using bivariate Fox's H-functions. Furthermore, rigorous simulation results are provided which validate the aforementioned analytical results. In addition to that, a detailed discussion on the decoupling gain of decoupled wireless access and its efficacy is also provided. Finally, despite the improvement provided by the decoupled wireless access, which is evident from the results presented in this paper, a few questions are raised on its pragmatic value. [ABSTRACT FROM AUTHOR]

Next-generation wireless networks will give rise to heterogeneous networks by integrating multiple wireless access technologies to provide seamless mobility to mobile users with high-speed wireless connectivity. Device-to-device (D2D) communication has proven to be a promising technology that can increase the capacity and coverage of wireless networks. The D2D communication was first introduced in long-term evolution advanced (LTE-A) and has gained immense popularity for the offloading traffic using the licensed and unlicensed band. Challenges arise from resource allocation, provision of quality-of-service (QoS), and the quantification of capacity in an unlicensed band due to the distributed nature of Wi-Fi. In this paper, we propose an analytical performance model for the scalable MAC protocol (SC-MP) in which a resource allocation mechanism is based on the IEEE 802.11 point coordinated function to access the Wi-Fi channel for voice and video/multimedia traffic. In the SC-MP, D2D communication is applied to further offload the video/multimedia traffic. In particular, this paper establishes a three-state semi-Markovian model to derive a closed-form expression of effective capacity in terms of transmission rate and quality-of-service. Further, the SC-MP is analytically modeled using the four-state traditional Markov model to derive the saturation throughput. The analytical results are validated through simulations, hence, proving the appropriateness of the model. [ABSTRACT FROM AUTHOR]

Cooperative Adaptive Cruise Control (CACC) is considered as a key enabling technology to automatically regulate the inter-vehicle distances in a vehicle string, and improve the traffic throughput efficiency. In the existing CACC systems, the coupling between wireless communication uncertainty, and system states is not well modeled. In this paper, we integrate the jamming attacks, and wireless channel fading effects into the CACC state space equations such that it effectively captures the coupling impact. Then, we propose a novel time domain approach to analyze the mean string stability (MSS) of such a model. Based on the proposed model, we analyze the impact of the jammer's location on the string stability. We derive a sufficient condition for the packet successful delivery probability which indicates that the jammer has a higher probability to destabilize the string when it is closer to the first vehicle following the lead vehicle. We also propose a methodology to compute the upper, and lower bounds of the inter-vehicle distance trajectories between the lead vehicle, and its follower. Furthermore, string safety is investigated by numerically estimating the collision probability across the string. We conduct comprehensive Monte Carlo simulations to evaluate the stability, and safety of the string in various scenarios. We identify that string stability, and safety are highly influenced by the jamming attacks signal, and jammer's location. We show the consistency between the main results achieved by MSS analysis, and the Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In evolved multimedia broadcast/multicast service (eMBMS), service continuity enables users move from one cell to another without interrupting eMBMS service. Unlike traditional handover in unicast transmission, an user equipment can receive eMBMS service in either unicast or multicast mode. In this paper, we point out a new handover failure problem in eMBMS due to the miss of rekeying information. We first take a close look at the new handover scenarios. We then investigate the problem by using comprehensive mathematical models. Our models provide insights on the new handover problem and introduce theoretical guidelines for mobile operators to design and optimize their networks without wide deployment to save cost and time. Moreover, we propose a solution to combat against the handover failure. Both the simulation and analytical results demonstrate that the impacts of the eMBMS handover failure are reduced significantly. In this paper, we present a systematic way to investigate the handover failure problem in eMBMS. [ABSTRACT FROM AUTHOR]

With the rapid development of high-speed train (HST), the HST wireless communication systems have been attracting an increasing amount of attention. For the design, optimization, and evaluation of HST communication systems, it is vital to have an accurate channel model that can mimic the non-stationary characteristics of HST communication links. In this paper, we propose a new geometry-based stochastic channel model (GSCM) for rural macrocell scenarios by exploiting the sum-of-frequency-modulated signals method. The time-variant (TV) theoretical autocorrelation function (ACF) and Doppler power spectrum density of the proposed GSCM under von-Mises scattering environments are also derived by employing the Wigner distribution function. Moreover, a new simulation method is developed to reproduce the proposed GSCM. To reconstruct the non-stationary characteristic precisely, we also develop a low complexity parameter computation approach with linear variation. Finally, the simulation results demonstrate that the TV train's velocity leads to the non-stationary characteristic in the channel model. Meanwhile, the simulated ACF agrees well with the theoretical and measured ones, showing the correctness of the theoretical derivation and the simulation method. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) based offloading stands out as a promising approach to mitigate the pressure over cellular networks. From the perspectives of both operators and users, an ideal solution is expected to maximize the offloading efficiency (ratio) while guaranteeing the quality-of-service (QoS) of users. However, existing approaches seldom jointly take into consideration offloading efficiency optimization and QoS guarantee. In this paper, we study how to maximize the percentage of total offloaded traffic of mobile content downloading via D2D, while guaranteeing the user minimum throughput under limited buffer size. The major challenge is how to incorporate all potential D2D opportunities to maximize the offloading performance. We propose a spatial–temporal dynamic graph (STDG) to capture all possible D2D opportunities in D2D-based traffic offloading. Based on STDG, we mathematically formulate an optimization problem of maximizing the offloading efficiency, subject to throughput requirement and buffer size constraint. The formulated problem is a linear-fractional problem and can be transformed into an equivalent linear program, whose solution reveals the maximum offloading ability that D2D achieves under QoS satisfaction. Trace-based simulations validate the superiority of our approach over three benchmark approaches. [ABSTRACT FROM AUTHOR]

With the increasing demand for high-data mobile traffic and applications, Device-to-Device (D2D) communication has emerged as a promising technique for next generation of cellular networks to increase the network capacity. In this paper, to offload traffic from network backhaul, we investigate the problem of relaying data through multihop nodes, using D2D communication, for a set of transmitter-receiver pairs, by sharing cellular resource blocks. Furthermore, the problem is extended to schedule the transmission links within a maximum time frame to obey a delay constraint. If the transmission path could not be scheduled within the maximum time frame for any D2D communication pair, the communication is redirected through the base station similar to cellular mode. Our problem aims at minimizing the overall D2D transmission power by giving priority to maximizing the number of paths that go through D2D relaying. We mathematically formulate the above problem and find optimal solutions for small networks. We show the NP-hardness of the problem, and owing to its complexity, we propose an algorithmic method for more extensive networks. Through numerical results, the performance of our mathematical optimization model and algorithm is compared and the efficiency of the proposed algorithmic method is shown. [ABSTRACT FROM AUTHOR]

A ticket dispenser (TD) is used to assist customers with the waiting process in, e.g., a restaurant. This paper deploys a mobile TD system (MTDS) with waiting time prediction to enhance the user experience while waiting. For example, the MTDS for a restaurant allows a customer to remotely draw a ticket for a meal order anywhere through a smartphone before she/he arrives at the restaurant and therefore reduces her/his waiting time. The developed MTDS system can dynamically adjust the predicted waiting time. We propose two output indicators and develop a discrete-event simulation model to investigate the performance of the predicted time adjustment (PTA) mechanism for the MTDS. With a proper frequency of recalculation for the predicted waiting times, this paper indicates that the waiting times can be more accurately predicted without consuming more wireless network resources and power of mobile devices. [ABSTRACT FROM PUBLISHER]

The heterogeneous networks (HetNets) performance is highly dependent on the interference coordination among cells since both macrocells and small cells share the same spectrum. This paper focuses on the configuration of eICIC parameters: almost blank subframe ratio and cell range expansion bias defined for LTE-A. We propose an online learning mechanism based on a big data-driven framework and multiarmed bandit algorithms that retrieves data from the network to learn efficient configurations of eICIC parameters without requiring any previous knowledge about the network (e.g., traffic load, topology, scheduling algorithm). Our numerical results show that our approach attains a significant improvement with respect to the state of the art of online learning algorithms in networks under stationary and variable conditions (e.g., number of small cells, traffic load). [ABSTRACT FROM AUTHOR]

A flexible, automatic, reliable, and safe charging and discharging system for electric vehicles (EVs) and hybrid EVs is crucial in vehicle-to-grid (V2G) operation. The bidirectional inductive wireless power transfer system (BIWPTS) is an ideal solution in this situation. With authentic power-flow models for the BIWPTS in hand, designers and operators can predict, optimize, and analyze the interaction performance between the EV and the grid. Thus, this paper presents a harmonics-based theoretical power-flow model for BIWPTS for charging and discharging EVs in V2G applications. The proposed model provides accurate estimation for the active and reactive power flow during V2G and grid-to-vehicle modes. Moreover, the impact of the circuit losses and harmonics, due to the high-frequency power inverters, on the power-flow performance is investigated. This effect is stated mathematically by four novel power-flow criteria formulas. New conditions for achieving maximum active and reactive power, and unity and zero power-factor system operation, are also developed. The sensitivity of the circuit performance to the variation of its parameters has been studied. For validation purposes, a computer-based model and experimental platform of BIWPTS for EV applications are developed and tested. The comparison between the theoretical, simulation, and experimental results verified the proposed models and analysis. [ABSTRACT FROM PUBLISHER]

In this paper, a new mathematical approach for the analysis and optimization of cellular-enabled low-energy mobile devices with simultaneous wireless information and power transfer capabilities is introduced. The proposed methodology relies on modeling the locations of the base stations as points of a spatial Poisson point process, and it leverages stochastic geometry for system-level analysis. The tradeoffs emerging from simultaneous wireless information and power transfer transmission are characterized through the concept of “feasibility regions” and are quantified through the joint cumulative distribution function of harvested power and rate. To gain insight on the achievable performance, in addition, an upper bound is proposed, and its accuracy is discussed. The system model encompasses a realistic channel model that accounts for line-of-sight (LOS) and non-LOS (NLOS) links, different cell association criteria, practical receivers based on time switching and power splitting schemes, and directional beamforming. The analysis shows that optimal values for the time switching and power splitting ratios exist and that directional beamforming and network densification are capable of enhancing system performance. More specifically, high directional antennas lead cellular networks to operate in the noise-limited regime, which is proved to provide optimal performance, and because of the existence of LOS and NLOS links, an optimal deployment density for the base stations is proven to exist for typical system setups. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a new transmission scheme, called integer forcing-and-forward (IFF), for communications among multipair multiple-antenna users in which each pair exchanges their messages with the help of a single multiple-antenna relay in the multiple-access and broadcast phases. The proposed scheme utilizes integer forcing linear receiver (IFLR) at the relay, which uses equations, i.e., linear integer combinations of messages, to harness intrapair interference. Accordingly, we propose the design of a mean square error (MSE)-based transceiver, including precoder and projection matrices for the relay and users, assuming that perfect channel state information (CSI) is available. In this regard, in the multiple-access phase, we introduce two new MSE criteria for the related precoding and filter designs, i.e., the sum of the equations MSE (Sum-Equation MSE) and the maximum of the equations MSE (Max-Equation MSE), to exploit the equations in the relay. In addition, the convergence of the proposed criteria is proven as well. Moreover, in the broadcast phase, we use the two traditional MSE criteria, i.e., the sum of the users% mean square errors (Sum MSE) and the maximum of the users% mean square errors (Max MSE), to design the related precoding and filters for recovering the relay%s equations by the users. Then, we consider a more practical scenario with imperfect CSI. For this case, the IFLR receiver is modified, and another transceiver design is proposed, which takes into account the effect of channel estimation error. We evaluate the performance of our proposed strategy and compare the results with the conventional amplify-and-forward (AF) and denoise-and-forward (DF) strategies for the same scenario. The results indicate the substantial superiority of the proposed strategy in terms of outage probability and sum rate. [ABSTRACT FROM PUBLISHER]

This paper develops efficient compute-and-forward (CMF) schemes in multiuser multirelay networks. To solve the rank failure problem in CMF setups and to achieve full diversity of the network, we introduce two novel CMF methods, namely, extended CMF and successive CMF. The former, having low complexity, is based on recovering multiple equations at relays. The latter utilizes successive interference cancelation (SIC) to enhance system performance compared with the state-of-the-art schemes. Both methods can be utilized in a network with different number of users, relays, and relay antennas, with negligible feedback channels or signaling overhead. We derive new concise formulations and explicit framework for the successive CMF method, as well as an approach to reduce its computational complexity. Our theoretical analysis and computer simulations demonstrate the superior performance of our proposed CMF methods over the conventional schemes. Furthermore, based on our simulation results, the successive CMF method yields additional signal-to-noise ratio (SNR) gains and shows considerable robustness against channel estimation error (CEE), compared with the extended CMF method. [ABSTRACT FROM PUBLISHER]

In this paper, novel closed-form expressions for the level crossing rate and average fade duration of $\kappa-\mu$ shadowed fading channels are derived. The new equations provide the capability of modeling the correlation between the time derivative of the shadowed dominant and multipath components of the $\kappa-\mu$ shadowed fading envelope. Verification of the new equations is performed by reduction to a number of known special cases. It is shown that as the shadowing of the resultant dominant component decreases, the signal crosses lower threshold levels at a reduced rate. Furthermore, the impact of increasing correlation between the slope of the shadowed dominant and multipath components similarly acts to reduce crossings at lower signal levels. The new expressions for the second-order statistics are also compared with field measurements obtained for cellular device-to-device and body-centric communication channels, which are known to be susceptible to shadowed fading. [ABSTRACT FROM PUBLISHER]

This paper discusses the energy- and spectral-efficient transmissions for delay-constrained wireless communication systems utilizing hybrid automatic repeat request (HARQ). Three design metrics are considered: 1) the energy efficiency (EE) measured by the average energy required to successfully deliver one information bit from a source to its destination; 2) the spectral efficiency (SE) defined as the average data rate per unit bandwidth; and 3) the average energy per bit normalized by the SE. Optimum system designs with respect to different metrics are developed by analytically identifying the sequence of transmission energy that should be employed at different retransmissions. The optimum energy distributions are calculated with a new backward sequential calculation method, where the energy at each retransmission round is expressed as a closed-form expression of a wide range of practical system parameters, such as circuit power and channel coding in the physical layer and frame length and protocol overhead in the media access control layer. Reducing the SE-normalized energy per bit yields a balanced tradeoff between EE and SE. Numerical results demonstrate that reducing the SE-normalized energy per bit achieves a 26.7% SE gain over the system that minimizes the average energy per bit; yet, the EE of the two systems is almost identical. [ABSTRACT FROM AUTHOR]

As a benefit of their inherent rateless nature, fountain codes constitute a favorable choice for protecting packet-based transmissions in the physical layer for wireless channels having varying quality. However, previous research has revealed that the performance of fountain codes substantially degrades as their block length is reduced. Three structural phenomena of the Tanner graph were identified by Mackay in the hard decoding of fountain codes on binary erasure channels (BECs), which may be referred to as having “no degree-one check nodes (CNs),” “no emerging degree-one CNs,” and “uncovered variable nodes (VNs).” In this paper, we explicitly analyzed how these structural phenomena influence their soft decoding algorithm. Furthermore, these phenomena are shown to be responsible for the high error floors when fountain codes are transmitted over noisy fading channels, particularly for the transmissions of short blocks. To eliminate the influence of these structural phenomena, we conceived a technique of generating a few specifically encoded bits with the aid of the associated Tanner graph. Simulation results have demonstrated that our improved Raptor (IRaptor) codes significantly reduce the packet loss ratio (PLR) of conventional fountain codes, despite imposing reduced low complexity. Finally, we conceive a novel adaptive hybrid automatic repeat request (HARQ) scheme based on a lookup table (LUT)-aided technique, which may adapt its coding rate for each transmission. Our simulation results demonstrated that the proposed IRaptor HARQ achieves a similar performance to the Long-Term Evolution (LTE) turbo-coded HARQ scheme or even outperforms the LTE arrangement for block length in excess of 1000 bits. [ABSTRACT FROM PUBLISHER]

In a vehicular ad hoc network (VANET), the performance of the communication protocol is heavily influenced by the vehicular density dynamics. However, most of the previous works on VANET performance modeling paid little attention to vehicle distribution or simply assumed homogeneous car distribution. It is obvious that vehicles are distributed nonhomogeneously along a road segment due to traffic signals and speed limits at different portions of the road, as well as vehicle interactions that are significant on busy streets. In light of the inadequacy, in this paper, we present an original methodology to study the broadcasting performance of 802.11p VANETs with practical vehicle distribution in urban environments. First, we adopt the empirically verified stochastic traffic models, which incorporate the effect of urban settings (such as traffic lights and vehicle interactions) on car distribution and generate practical vehicular density profiles. Corresponding 802.11p protocol and performance models are then developed. When coupled with the traffic models, they can predict broadcasting efficiency, delay, and throughput performances of 802.11p VANETs based on the knowledge of car density at each location on the road. Extensive simulation is conducted to verify the accuracy of the developed mathematical models with the consideration of vehicle interaction. In general, our results demonstrate the applicability of the proposed methodology on modeling protocol performance in practical signalized road networks and shed insights into the design and development of future communication protocols and networking functions for VANETs. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel tractable approach for accurately analyzing both the coverage probability and the achievable throughput of cellular networks. Specifically, we derive a new procedure referred to as the equivalent uniform-density plane-entity (EUDPE) method for evaluating the other-cell interference. Furthermore, we demonstrate that our EUDPE method provides a universal and effective means to carry out the lower bound analysis of both the coverage probability and the average throughput for various base-station distribution models that can be found in practice, including the stochastic Poisson point process (PPP) model, a uniformly and randomly distributed model, and a deterministic grid-based model. The lower bounds of coverage probability and average throughput calculated by our proposed method agree with the simulated coverage probability and average throughput results and those obtained by the existing PPP-based analysis, if not better. Moreover, based on our new definition of cell edge boundary, we show that the cellular topology with randomly distributed base stations (BSs) only tends toward the Voronoi tessellation when the path-loss exponent is sufficiently high, which reveals the limitation of this popular network topology. [ABSTRACT FROM PUBLISHER]

In this paper, we propose generalized moment-based estimators of the Gamma-Gamma fading distribution. Specifically, the moment-based estimators are defined by using the $k$ -th, the $(k+1)$-th, the $l$-th, and the $(l+1)$-th order moments. Hence, the new moment-based estimators, which can choose lower order moments, have more degrees of freedom than existing estimators. In order to compare their performance, the normalized mean square error is taken into account. We validate, by Monte Carlo simulations, that the new moment-based estimators with lower order moments are superior to the existing estimators over various channel conditions. [ABSTRACT FROM PUBLISHER]

Recent studies have shown that utilizing a mobile sink (MS) to harvest and carry data from a wireless sensor network (WSN) can enhance network operations and increase the network lifetime. Since a significant portion of sensor nodes' energy is consumed for data transmission to an MS, the specific trajectory has a profound influence on the lifetime of a WSN. In this paper, we study the problem of controlling sink mobility in event-driven applications to achieve maximum network lifetime. In these applications, an MS with limited velocity has to harvest the captured data of events from a group of sensor nodes in a specific time as a reporting time slot. We show that this problem is NP-hard, and then, we propose a convex optimization model inspired by the support vector regression technique to determine an optimal trajectory of an MS without considering predefined structures such as a virtual grid or rendezvous points. The effectiveness of our approach is validated via the extensive number of simulation runs and comparison with other algorithms. [ABSTRACT FROM PUBLISHER]

As the binary sensing model is a coarse approximation of reality, the probabilistic sensing model has been proposed as a more realistic model for characterizing the sensing region. A point is covered by sensor networks under the probabilistic sensing model if the joint sensing probability from multiple sensors is larger than a predefined threshold $\varepsilon$. Existing work has focused on probabilistic point coverage since it is extremely difficult to verify the coverage of a full continuous area (i.e., probabilistic area coverage). In this paper, we tackle such a challenging problem. We first study the sensing probabilities of two points with a distance of $d$ and obtain the fundamental mathematical relationship between them. If the sensing probability of one point is larger than a certain value, the other is covered. Based on such a finding, we transform probabilistic area coverage into probabilistic point coverage, which greatly reduces the problem dimension. Then, we design the $\varepsilon$-full area coverage optimization (FCO) algorithm to select a subset of sensors to provide probabilistic area coverage dynamically so that the network lifetime can be prolonged as much as possible. We also theoretically derive the approximation ratio obtained by FCO to that by the optimal one. Finally, through extensive simulations, we demonstrate that FCO outperforms the state-of-the-art solutions significantly. [ABSTRACT FROM PUBLISHER]

In this paper, we develop a performance modeling technique for analyzing the time-varying network layer queuing behavior of multihop wireless networks with constant bit rate (CBR) traffic. Our approach is a hybrid of a time-varying adjacency matrix and a fluid flow queuing network model. The mobile network topology is modeled using a time-varying adjacency matrix, whereas node queues are modeled using fluid-flow-based differential equations that are solved using numerical methods. Numerical and simulation experiments show that this new approach can provide reasonably accurate results. Moreover, when compared with the computation time required in a standard discrete event simulator, the fluid-flow-based model is shown to be a more scalable tool. Finally, an illustrative example of our modeling technique application is given to show its capability of capturing the time-varying network performance as a function of traffic load, node mobility, and wireless link quality. [ABSTRACT FROM PUBLISHER]

Path loss modeling for both regular and irregular terrains is still gaining significant attention from researchers. A sloped terrain is one specific kind of an irregular terrain that—as far as we are aware—has not been completely studied. Although some results have been published for slope path loss modeling in cellular communication, an adequate model for the case when the transmitter (Tx) and the receiver (Rx) both have low-height antennas and are located on or near a slope does not exist. In this paper, for complete analysis of such conditions, we consider four scenarios: 1) two vehicles are located at opposite ends of the slope; 2) one vehicle is on the slope, and the other vehicle is beyond the slope crest; 3) one vehicle is on the slope, and the other is away from the slope at the bottom; 4) both vehicles are on the slope. For scenarios 1 and 2, we have developed analytical path loss models. We have also made some corroborating measurements for scenario 1. Scenarios 3 and 4 are addressed by models already in the literature. Simulation results for two vehicles traveling toward, on, and then beyond a slope (a sequence of our scenarios) are also shown to illustrate how sloped-terrain path loss varies in contrast to the typical flat-earth condition. Our models for scenarios 1 and 2 add to the literature and can be used to numerically estimate path losses for vehicle-to-vehicle (V2V) communication over a slope. [ABSTRACT FROM PUBLISHER]