Cellular Transmissions Research Articles

Coping with Spatial Unfairness and Overloading Problem in Mobile Networks via D2D Relaying

Device-to-device (D2D) relaying is able to increase the network capacity, enhance the network coverage, or mitigate the interference to legacy cellular transmissions. These benefits are even emphasized if a proper incentives are offered to the users to motivate them to act as relays. We first survey the stateof- the-art incentives to show that despite a proper incentivization, the benefits from relaying are enjoyed typically only by the users directly involved in relaying, i.e., either those in favorable locations to act as relays or those exploiting such relays to improve their performance. Nevertheless, many users, who are not satisfied with their quality of service (QoS), may not profit from D2D relaying due to their unfavorable locations. Besides, the current incentive mechanisms are not able to alleviate the overloading of the base station (BS) without violating QoS of already admitted users. Thus, to cope with the spatial unfairness and the overloading of BSs, we propose resource allocation framework extending D2D relaying benefits also to the users not directly involved in the relaying process. The proposed framework enables efficient reuse of radio resources and takes inspiration from economy concept of taxes. Moreover, it gives an opportunity to the users distributing spared radio resources to increase their virtual monetary gain, reputation, or even helping other users depending on mutual social relationships. The simulations demonstrate that the proposed concept improves the ratio of satisfied users and/or maximizes the number of newly admitted users for which the BS would not have radio resources otherwise.

Multiple Access Design for Symbiotic Radios: Facilitating Massive IoT Connections With Cellular Networks

Symbiotic radio (SR) has emerged as a spectrum-and energy-efficient paradigm to support massive Internet of Things (IoT) connections. Two multiple access schemes are proposed in this paper to facilitate massive IoT connections using the cellular network based on the SR technique, namely, the simultaneous access (SA) scheme and the selection diversity access (SDA) scheme. In the SA scheme, the base station (BS) transmits information to the receiver while multiple IoT devices transmit their information simultaneously by passively backscattering the BS signal to the receiver, while in the SDA scheme, only the IoT device with the strongest backscatter link transmits information. In both of the schemes, the receiver jointly decodes the information from the BS and IoT devices. To evaluate the above two schemes, the closed-form expressions of the ergodic rates in high signal-to-noise ratio (SNR) regimes and outage probabilities for cellular and IoT transmissions are derived by using extreme value theory, generalized-K distribution approximation and Gaussian-Chebyshev quadrature methods. Finally, numerical results are provided to verify the theoretical analysis and compare the proposed multiple access schemes. When the number of IoT devices is small, the SDA scheme is more appealing since it can significantly reduce the computational complexity while achieving equivalent performance to the SA scheme. When the number of IoT devices is large, the SA scheme is preferable since it guarantees a significantly better rate performance and a lower outage probability.

Cellular Network Enabled Energy-Harvesting Secure Communications for Full-Duplex D2D Links

This article investigates the secure transmissions for a wireless powered full-duplex (FD) device-to-device (D2D) overlay system. To coordinate the cellular downlink transmissions and the D2D transmissions, we propose a two-phase transmission protocol, where the first phase is dedicated to the transmissions of information and energy from the base station (BS) to its users and the devices, respectively, and the second phase is dedicated to information exchanging between the two devices over an FD link overheard by either active or passive eavesdroppers. In the case of active eavesdroppers, perfect channel state information (CSI) is assumed to be available, whereas for passive eavesdroppers, only statistic CSI is available. Both self-interference (SI) mitigation and BS-aided cooperative jamming are considered for the D2D secure transmissions. For system design, nonconvex power minimization problems under transmission rate constraints are formulated and convex approximated for efficiently obtaining numerical solutions. Simulation results show that the proposed scheme can well coordinate the cellular transmissions and the FD-D2D secure transmissions, while the cooperative jamming strategy can enhance the D2D transmission security, especially in the case of passive eavesdroppers.

Energy Efficiency Optimization in Adaptive Transmit Antenna Selection Systems With Limited Feedback

We investigate the energy efficiency (EE) of cellular downlink transmissions with limited feedback, where the channel state information (CSI) assumed to be available at the destination is quantized and fed back to the multiantenna base station for transmitting precoding purposes. Typically, the employment of antennas with poor channel quality marginally enhances system performance but substantially consumes energy resources such as circuit power. Thus, we propose an adaptive transmit antenna selection (ATAS) scheme via setting a channel gain threshold to select transmit antennas with relatively good channel condition for reducing power resource consumption. Meanwhile, the conventional single transmit antenna (STAS) scheme is considered as a baseline. In order to improve EE while considering the impact of feedback overhead, we conduct the effective EE analysis for both ATAS and STAS schemes and show that a maximal effective EE of the proposed ATAS scheme can be achieved by jointly adjusting the channel gain threshold and transmit power. As a consequence, we propose the ergodic effective EE optimization of ATAS (eEEEO-ATAS) scheme to maximize the effective EE. Numerical simulation results demonstrate that the proposed ATAS scheme performs better than the STAS scheme in terms of effective EE.

A Collaborative Caching-Transmission Method for Heterogeneous Video Services in Cache-Enabled Terahertz Heterogeneous Networks

To mitigate the impact of the dramatic growth of wireless video traffic and provide users with heterogeneous video services, a collaborative caching-transmission method in cache-enabled terahertz (THz) heterogeneous networks is studied in this paper. We propose a novel scalable video coding (SVC)-based two-tier cooperative caching strategy that can provide video services with different perceptual qualities. In addition, we propose a hierarchical hybrid transmission scheme where users obtain the requested layer files through the cooperative cellular multicast-D2D and THz transmissions. A base layer-based multicast group aggregation process is presented to improve resource utilization, while an efficient multicast transmission resource scheduling scheme can make better use of the spatial reusability. We derive the expressions for the average offloading capacity gain and average energy consumption, and formulate an efficiency function optimization problem. The problem is efficiently solved by the greedy strategy-gradient descent based caching solution and long tail distribution based heuristic caching solution. Simulation results validate the two solutions and demonstrate that the proposed caching-transmission method can achieve quasi-optimal performance compared with other contrasting schemes.

Reconfigurable Intelligent Surface Assisted Spatial Modulation for Symbiotic Radio

Reconfigurable intelligent surface (RIS) is a key enabler for future paradigm-shifting communication technologies. In a cellular network, an RIS can be used to simultaneously assist the communication of a cellular link and transmit additional data for various Internet of Things (IoT) applications. This coincides with the concept of symbiotic radio (SR). In this paper, we investigate this RIS-assisted SR system. We introduce the new idea of symbiotic modulation: the modulation constellation design allows a receiver to simultaneously detect the data transmitted in the RIS-assisted cellular link and the additional IoT data transmitted by the RIS. We propose three specific modulation schemes all having the feature of receive-antenna index modulation, and hence, called symbiotic spatial modulation (SSM). The first scheme is a coherent SSM scheme with a star-QAM (quadrature amplitude modulation) constellation. Its detection performance is analyzed using either an optimal maximum likelihood detector or a suboptimal successive greedy detector. We then extend the design to two noncoherent SSM schemes and analytically derive their detection performances as well. Simulation results corroborate the analysis and illustrate good detection performance of the proposed SSM schemes for both the cellular and IoT data transmissions in the considered SR system.

Spectrum-Aware Energy Efficiency Analysis in K-tier 5G HetNets

In future multi-tier cellular networks, cognitive radio (CR) compatible with device-to-device (D2D) communication can be an aid to enhance system spectral efficiency (SE) and energy efficiency (EE). Users in proximity can establish a direct connection with D2D communication and bypass the base stations (BSs), thereby offloading the network infrastructure and providing EE improvement. We use stochastic geometry to model and analyze cognitive D2D communication underlying a multi-tier/multi-channel cellular network where the D2D transmitters are capable of harvesting RF energy from ambient interference resulting from simultaneous cellular downlink transmissions. For further improvement in EE, small cells (SCs) can be put into a power-saving mode by specifying a load-dependent transmission power coefficient (TPC) for SC BSs. In addition, to consider practical D2D communication scenarios, we propose a wireless video sharing framework where cache-enabled users can store and exchange popular video files through D2D communication. We investigate the potential effects of the TPC and the introduced D2D layer on the network EE and SE. We will also observe that the energy-harvesting CR-based D2D communication network design will not only ease the spectrum shortage problem but will also result in a greener network thanks to its reliance on ambient energies.

Hopf Bifurcation and Stability Switches Induced by Humoral Immune Delay in Hepatitis C

The role of humoral immune delay on the dynamics of HCV infection incorporating both the modes of infection transmission, namely, viral and cellular transmissions with a non-cytolytic cure of infected hepatocytes is studied. The local and global asymptotic stability of the boundary equilibria, namely, infection-free and immune-free equilibrium are analyzed theoretically as well as numerically under the conditions on the basic reproduction number and the humoral immune reproduction number. The existence of Hopf bifurcation and consequent occurrence of bifurcating periodic orbits around the humoral immune activated equilibrium are illustrated. The findings show that Hopf bifurcation and stability switches occur under certain conditions as the bifurcation parameter crosses the critical values. Furthermore, the dynamical effect of the development rate of B cells is investigated numerically. The results obtained show that the system becomes unstable from stable and regains stability from instability depending on the development rate of B cells for a fixed delay value. Further, the results suggest that a high antigenic stimulation in humoral immunity is beneficial for uninfected hepatocytes with a significant reduction in virions density.

Cellular-Assisted Device-to-Device Communications for Healthcare Monitoring Wireless Body Area Networks

We envisage each person will wear an individual wireless body area network (WBAN) for healthcare monitoring. Two WBANs in proximity may collide. Such WBAN collisions can significantly degrade communication quality of service (QoS), in terms of throughput and latency of healthcare applications. To avoid collisions, we propose to use cellular-assisted device-to-device (D2D) communications to connect on-body sensors to a hub within WBAN. These D2D transmissions are performed concurrently with cellular transmissions and thus, interference is imposed on each other. A radio resource allocation scheme has been developed to manage the interference. The scheme uses a combination of difference of convex optimization and Hungarian algorithm to control transmit power and to assign communication channel to both cellular and D2D transmissions. The objective is to maximize the sum of cellular throughput while avoiding collisions among co-located WBANs and satisfying QoS requirements of healthcare applications. Evaluation results confirm that WBAN collisions can be avoided at a crowded pedestrian walkway, even when there are as many as 6 pedestrian arrivals per second.

Numerical investigation of self-sustaining modes of 2D planar detonations under concentration gradients in hydrogen–oxygen mixtures

Self-sustaining modes of detonations in non-uniform mixtures for hydrogen and oxygen are numerically studied. Concentration gradients are set vertical to the direction of detonation propagation, with equivalence ratios decreasing from rich values to lean ones. High-resolution codes based on the fifth-order weighted essentially non-oscillatory (WENO) scheme in spatial discretization and the 3rd-order Additive Runge-Kutta (ARK) schemes in time discretization, with detailed chemical kinetics model, are developed. Two-dimensional (2D) numerical simulations are conducted in a 2D planar geometry, non-uniform distributions are then precisely controlled as a function of width. The cellular structures and transmissions, failure and re-initiation mechanisms of detonation fronts are characterized. Results show that the low concentration gradient produces the multi-head mode of detonation with continuous adaptation of velocities and multicellular structures to local concentration. The high concentration gradient generates single-head mode with detonation re-initiation at channel walls produced by reflected transverse Mach waves. Specially, the intermediate distribution between the low and high concentration gradients induces an alternation mode between singe-head and multi-head detonations.

Performance of UAV-Assisted D2D Networks in the Finite Block-Length Regime

We develop a comprehensive framework to characterize and optimize the performance of a unmanned aerial vehicle (UAV)-assisted D2D network, where D2D transmissions underlay cellular transmissions. Different from conventional non-line-of-sight (NLoS) terrestrial transmissions, aerial transmissions are highly likely to experience line-of-sight (LoS). As such, characterizing the performance of mixed aerial-terrestrial networks with accurate fading models is critical to precise network performance characterization and resource optimization. We first characterize closed-form expressions for a variety of performance metrics such as frame decoding error probability (referred to as reliability), outage probability, and ergodic capacity of users. The terrestrial and aerial transmissions may experience either LoS Rician fading or NLoS Nakagami-m fading with a certain probability. Based on the derived expressions, we formulate a hierarchical bi-objective mixed-integer-nonlinear-programming (MINLP) problem to minimize the total transmit power of all users and maximize the aggregate throughput of D2D users subject to quality-of-service (QoS) measures (i.e., reliability and ergodic capacity) of cellular users. We model the proposed problem as a bi-partite one-to-many matching game. To solve this problem, we first obtain the optimal closed-form power allocations for each D2D and cellular user on any possible subchannel, and then incorporate them to devise efficient subchannel and power allocation algorithms. Complexity analysis of the proposed algorithms is presented. Numerical results verify the accuracy of our derived expressions and reveal the significance of aerial relays compared to ground relays in increasing the throughput of D2D pairs especially for distant D2D pairs.

Battery-less internet of things –A survey

Traditional wireless communication technologies such as Bluetooth and Wi-Fi are used extensively over the last two decades. They offer various advantages like higher data connection rates, good coverage, mobility, expandability, ease of use, etc. However, these traditional wireless communication solutions are expensive and also drain the battery life of devices connected to it. Internet-of-Things (IoT), demands devices that consume very little power and are less bulky. A solution to this is newly emerging passive technology called Ambient Backscatter Communication System. It is a cutting edge primitive that allows wireless communication between the devices by leveraging ambient radio frequency (RF) signals of TV and cellular transmissions. Its competency in consuming very low power during communication brings us closer to the world of IoT and its applications. In this paper, we present a detailed survey of backscatter communication systems. In particular, the fundamentals, architecture and the challenges involved are discussed. Using the multilevel classification framework, we review the major experimental and theoretical work carried out in literature.

Modeling and Performance Analysis for Ambient Backscattering Underlaying Cellular Networks

Ambient backscatter is an intriguing technology that enables ultra-low-power devices to communicate with each other by reflecting and modulating the existing pervasive RF signals, e.g., TV signals, WIFI signals, cellular signals, etc. This paper works on the mathematical modeling and performance analysis of ambient backscatter communications (AmBackComs) underlying cellular networks for Internet of Things applications. Based on the time switching (TS) and power splitting (PS) receiver architectures, two operating schemes are employed to enable energy harvesting and ambient backscattering at the ambient backscatter (AB) transmitter. In order to maximize the outage capacity for the AB transmitters, we formulate two optimization problems optimizing the TS and PS ratios. Two schemes with low complexity are proposed to obtain the near-optimal outage performance. Considering the coexistence of the AmBackComs and cellular downlink transmissions, successful transmission probabilities for AB transmitters and cellular downlink transmissions are both derived for the TS and PS schemes and provide insights on how various system parameters, such as the TS ratio, the PS ratio, the density of base stations (BSs)/AB transmitters, etc., impact the system performance. Numerical results show that the outage capacity for AmBackComs can be significantly improved by selecting a proper TS/PS ratio and our proposed schemes can achieve near-optimal outage capacities. The study also shows that many more ultra-low-power devices users can be connected via the proposed scheme at a cost of a slightly reduced overall network capacity.

Multicell D2D Communications for Hierarchical Control of Microgrid System

In microgrid, hierarchical control requires an advanced communication network. In order to meet stringent communication latency requirement, we use cellular-assisted underlay device-to-device (D2D) communications to connect control devices directly to central controller. Compared to the literature, this scenario is unique because control devices and central controller are not located within a same cell. Thus, a D2D link may span across multiple cells, and a single D2D transmission may impose interference on multiple cellular transmissions in different cells. This article aims to guarantee a minimum throughput to each control unit over D2D link to satisfy its latency requirement, while maximizing the spectral efficiency, which is measured in term of sum-rate of all cellular users. A 2-tier resource allocation scheme has been proposed. Tier-1 assigns channels to static control units. Tier-2 operates more frequently in assigning channels to mobile cellular users and control transmit power for both cellular and D2D nodes. Tier-1 optimization has been solved using the Hungarian algorithm. Tier-2 optimization is originally a complex nonconvex problem, and has been transformed into a combination of convex optimization and linear assignment problem. The proposed scheme has been evaluated through extensive simulations, and comparisons with a benchmark scheme that assigns communication channels randomly. Results have confirmed the efficiency and superiority of the proposed scheme, as well as its ability in finding the smallest D2D transmit power necessary in fulfilling a given latency requirement.

Energy Minimization of Multi-Cell Cognitive Capacity Harvesting Networks With Neighbor Resource Sharing

In this paper, we investigate the energy minimization problem for a cognitive capacity harvesting network (CCHN), where secondary users (SUs) without cognitive radio (CR) capability communicate with CR routers via device-to-device (D2D) transmissions, and CR routers connect with base stations (BSs) via CR links. Different from traditional D2D networks that D2D transmissions share the resource of cellular transmissions in the same cell, we consider the scenario that D2D transmissions share the uplink cellular frequency bands (CFBs) of neighbor cells. To ensure that the transmissions from SUs do not affect the transmissions for the cellular users (CUs) in the neighbor cells, an inter-cell handshake process is proposed. We formulate the energy minimization problem for SUs as a mixed integer non-linear programming (MINLP). To solve this problem, we decompose it into two nested subproblems: a transmit power optimization subproblem and a CR router and uplink CFB selection subproblem. For the first subproblem, it is proved to be convex, and thus can be efficiently solved. For the second subproblem, we propose a two-level nested game theoretic approach to finding its solution. Simulation results show that the proposed algorithms can significantly improve the performance. With the help of CR routers/the neighbor resource sharing, the energy consumption for SUs can be saved around 30%-37% on average.

Channel, Mode and Power Optimization for Non-Orthogonal D2D Communications: A Hybrid Approach

The increasing traffic demand in cellular networks has recently led to the investigation of new strategies to save precious resources like spectrum and energy. Direct device-to-device (D2D) communication becomes a promising solution if the two terminals are located in close proximity. In this case, the D2D communications should coexist with cellular transmissions, so they must be carefully scheduled in order to avoid harmful interference impacts. In this paper, we outline a novel framework encompassing channel allocation, mode selection and power control for D2D communications. Power allocation is done in a distributed and cognitive fashion at the beginning of each time slot, based on local information, while channel/mode selection is performed in a centralized manner only at the beginning of an epoch, a time interval including a series of subsequent time slots. This hybrid approach guarantees an effective tradeoff between overhead and adaptivity. We analyze in depth the distributed power allocation mechanism, and we state a theorem which allows to derive the optimal power allocation strategy and to compute the corresponding throughput. Extensive simulations confirm the benefits granted by our approach, when compared with state-of-the-art distributed schemes, in terms of throughput and fairness.

A delayed HIV-1 model with cell-to-cell spread and virus waning

ABSTRACT In this paper, we propose and analyse a delayed HIV-1 model with both viral and cellular transmissions and virus waning. We obtain the threshold dynamics of the proposed model, characterized by the basic reproduction number . If , the infection-free steady state is globally asymptotically stable; whereas if , the system is uniformly persistent. When the delays are positive, we show that the intracellular delays in both viral and cellular infections may lead to stability switches of the infected steady state. Both analytical and numerical results indicate that if the effect of cell-to-cell transmission is ignored, then the risk of HIV-1 infection will be underestimated. Moreover, the viral load of model without virus waning is higher than the one of model with virus waning. These results highlight the important role of two ways of viral transmission and virus waning on HIV-1 infection.

Generalised uplink model for cellular and D2D transmissions

This study investigates a hybrid wireless communication network consisting of both regular cellular users and device-to-device (D2D) users. A generalised uplink model is developed. The model is based on stochastic geometry and encompasses several new features, including heterogeneous pathloss links, non-singular law, configurable pathloss-compensation, and offset uniform distribution. A set of closed-form solutions is derived for the coverage probability and ergodic capacity. Many recently proposed models can be regarded as special cases of the model presented in this study.

Beam-Sweeping Design Based on Nearest Users Position and Beam in 5G mmWave Networks

The beam sweeping procedure estimates the beamforming directions, or beams, to be used for downlink millimeter-wave cellular transmissions to an incoming user entering the cell. We propose three new approaches for the choice of the sequence by which beams are explored (the beam-search sequence), in order to reduce the average time to find the directions. The proposed methods exploit a) the correlation among angles of departure of the incoming user and its nearest, already connected user, and b) the position of both the incoming and its nearest user. For point a), the nearest-neighbor-beam search method starts from the beam of the nearest user, and then explores other beams, with directions progressively farther away (in the angular domain) from the first beam. In the beam-and-angle search, the beam-search sequence is optimized by exploiting the knowledge of both users' position and the nearest-user beam. We also propose the simplified beam-and-angle search, which still exploits the nearest-user information, although in a suboptimal and simpler fashion. Based on the channel model of the 3rd generation partnership project, we analytically design the optimal beam-and-angle search sequence. We assess the performance of the proposed solutions, in terms of their average discovery time, also in comparison with existing approaches.

Radio Resource Allocation Scheme for Reliable Demand Response Management Using D2D Communications in Smart Grid

Integration of renewable energy into power distribution network is a challenge because renewable output is intermittent. This problem can be tackled through demand response management which controls consumption demand by adjusting energy prices in real-time to match the available time-varying power supply. Such real-time pricing (RTP) requires an advanced communication network to collect data and to disseminate price information. We use cellular-assisted underlay device-to-device (D2D) communications to connect energy management units (EMUs) directly to the RTP control center. Such D2D transmissions can be interfered by concurrent cellular transmissions. This interference can affect reliability of the RTP operation. We quantify the reliability requirements given a tolerable financial loss and a supply-demand gap. The cost in satisfying the reliability requirement appears in the form of a lower sum-rate for all cellular nodes, because cellular rate is a revenue generator for communication service provider. We formulate an optimization problem to allocate radio resources in terms of communication channel and transmit power, to maximize the cellular sum-rate without compromising the RTP reliability requirements. Since the optimization problem is non-convex, we use a pair of iterative algorithms to assign communication channel using the Hungarian algorithm and to control transmit power using the difference of convex (DC) optimization. The effectiveness of the combination of the Hungarian algorithm and the DC optimization has been verified through extensive simulations, with the results compared against a benchmark scheme that randomly assigns communication channels.