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COMMUNICATION 2016 Projects

Category Archives

Low-cost On-demand C-RAN based Mobile Small-cells

Abstract

          Although 4G networks are vastly being deployed around the world, the exponential growth of mobile traffic and the requirements of upcoming services are further pushing the limits on current mobile networks; hence worldwide research interests have shifted towards 5G paradigm. But 5G networks are not to be deployed till 2020; hence there is a need for solutions to address increasing demands of current networks, without incurring huge costs on operators. In this paper, we discuss low cost innovative networking scenario, which can be built using available 4G technologies, yet continue to exist within the 5G paradigm when deployed. The paper proposes on-demand deployment of mobile small cells, using either user mobile handsets or remote radio units (RRUs). The front-hauling from the core network to the small cells exploit disruptive technology trends, which are expected to play roles within the 5G paradigms, including cloud-based radio access network (C-RAN), and self-organizing networking. The paper discusses the envisioned scenario, shows how it can be built on expected 5G technologies trends, presents preliminary results that show the benefits gained from such deployment and finally details the foreseen open research challenges that need to be addressed.


A Survey on Wireless Security: Technical Challenges, Recent Advances, and Future Trends

Abstract

      Due to the broadcast nature of radio propagation, the wireless air interface is open and accessible to both authorized and illegitimate users. This completely differs from a wired network, where communicating devices are physically connected through cables and a node without direct association is unable to access the network for illicit activities. The open communications environment makes wireless transmissions more vulnerable than wired communications to malicious attacks, including both the passive eavesdropping for data interception and the active jamming for disrupting legitimate transmissions. Therefore, this paper is motivated to examine the security vulnerabilities and threats imposed by the inherent open nature of wireless communications and to devise efficient defense mechanisms for improving the wireless network security. We first summarize the security requirements of wireless networks, including their authenticity, confidentiality, integrity, and availability issues. Next, a comprehensive overview of security attacks encountered in wireless networks is presented in view of the network protocol architecture, where the potential security threats are discussed at each protocol layer. We also provide a survey of the existing security protocols and algorithms that are adopted in the existing wireless network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term evolution (LTE) systems. Then, we discuss the state of the art in physical-layer security, which is an emerging technique of securing the open communications environment against eavesdropping attacks at the physical layer. Several physical-layer security techniques are reviewed and compared, including information-theoretic security, artificial-noise-aided security, security-oriented beamforming, diversity-assisted security, and physical-layer key generation approaches. Since a jammer emitting radio signals can readily interfere with the legitimate wireless users, we also introduce the family of various jamming attacks and their countermeasures, including the constant jammer, intermittent jammer, reactive jammer, adaptive jammer, and intelligent jammer. Additionally, we discuss the integration of physical-layer security into existing authentication and cryptography mechanisms for further securing wireless networks. Finally, some technical challenges which remain unresolved at the time of writing are summarized and the future trends in wireless security are discussed.


Hybrid Positioning Aided Amorphous-Cell Assisted User-Centric Visible Light Downlink Techniques

Abstract

         Visible Light Communications (VLC) has attracted significant attention in recent years, where the novel concept of User-Centric (UC) VLC based on Amorphous cells (A-Cells) exhibits extra benefits compared to conventional circular cells. The construction of A-Cells relies on the knowledge of the users’ positions, hence the intrinsic amalgamation of VLC and positioning becomes important. Therefore we propose a novel hybrid positioning technique by beneficially combining the lowcomplexity of triangulation based positioning and the high accuracy of fingerprinting, in order to support A-Cell assisted UC VLC under practical LED linearity constraints with clipping distortion and noise. Our simulation results demonstrate that the proposed technique is capable of achieving a much higher positioning accuracy than triangulation at a lower complexity than fingerprinting, where the resultant system throughput is similar to that of perfect positioning.


A 0.6–3.8 GHz GaN Power Amplifier Designed Through a Simple Strategy

Abstract

          This letter presents the design strategy for an ultrawideband, high-efficiency hybrid power amplifier based on a commercial GaN-HEMT. The measurement results demonstrate a state-of-the-art fractional bandwidth of 145.5%, with saturated output power higher than 10 W from 0.6 to 3.8 GHz and power added efficiency exceeding 46% in the whole band, thus covering most of the mobile frequencies and making this device suitable for small-base station applications. The simple design approach exploits a N-section transformer, and allows for a priori estimation of the bandwidth: in the proposed case, a good agreement between estimated and measured bandwidth is obtained.


Network Architecture of Bi-directional Visible Light Communication and Passive Optical Network

 Abstract

      Network architectures for combined the fiber network outside the 11 building and the visible light communication (VLC) access network inside the 12 building are important for effectively distributing the high capacity data to different 13 users. In this work, we propose a bi-directional network combining the VLC access 14 network and the time-wavelength-division-multiplexed passive optical network 15 (TWDM-PON). Orthogonal frequency division multiplexed (OFDM) modulation is 16 used since it offers high spectral efficiency for both the TWDM-PON and the VLC 17 access network. Low-cost phosphor-based white-light light emitting diodes (LEDs) 18 are used; hence the VLC access network can combine with the lighting systems.


Secret key rates and optimization of BB84 and decoy state protocols over time-varying free-space optical channels

Abstract

       We optimize secret key rates (SKRs) of weak coherent pulse (WCP)-based QKD over time-varying free-space optical (FSO) channels affected by atmospheric turbulence. The random irradiance fluctuation due to scintillation degrades the SKR performance of WCP-based QKD, and to improve the SKR performance we propose an adaptive scheme in which transmit power is changed in accordance with the channel state information. We first optimize BB84 and decoy state-based QKD protocols for different channel transmittances. We then present our adaptation method, to overcome scintillation effects, of changing the source intensity based on channel state predictions from a linear autoregressive (AR) model, while ensuring the security against the eavesdropper. By simulation, we demonstrate that by making the source adaptive to the time-varying channel conditions, SKRs of WCP-based QKD can be improved up to over 20%.


Energy profiling in practical sensor networks: Identifying hidden consumers

Abstract

        Reducing energy consumption of wireless sensor nodes extends battery life and / or enables the use of energy harvesting and thus makes feasible many applications that might otherwise be impossible, too costly or require constant maintenance. However, theoretical approaches proposed to date that minimise WSN energy needs generally lead to less than expected savings in practice. We examine experiences of tuning the energy profile for two near-production wireless sensor systems and demonstrate the need for (a) microbenchmark-based energy consumption profiling, (b) examining start-up costs, and (c) monitoring the nodes during long-term deployments. The tuning exercise resulted in reductions in energy consumption of a) 93% for a multihop Telos-based system(average power 0.029 mW) b) 94.7% for a single hop Ti- 8051-based system during startup, and c) 39% for a Ti- 8051 system post start-up. The work reported shows that reducing the energy consumption of a node requires a whole system view, not just measurement of a “typical” sensing cycle. We give both generic lessons and specific application examples that provide guidance for practical WSN design and deployment.


Simultaneous Wireless Information and Power Transfer in K-tier Heterogeneous Cellular Networks

Abstract

       In this paper, we develop a tractable model for joint downlink (DL) and uplink (UL) transmission of K-tier heterogeneous cellular networks (HCNs) with simultaneous wireless information and power transfer (SWIPT) for efficient spectrum and energy utilization. In the DL, the mobile users (MUs) with power splitting receiver architecture decode information and harvest energy based on SWIPT. While in the UL, the MUs utilize the harvested energy for information transmission. Since cell association greatly affects the energy harvesting in the DL and the performance of wireless powered HCNs in the UL, we compare the DL and the UL performance of a random MU in HCNs with nearest base station (NBS) cell association to that with maximum received power (MRP) cell association. We first derive the DL average received power for the MU with the NBS and the MRP cell associations. To evaluate the system performance, we then derive the outage probability and the average ergodic rate in the DL and the UL of a random MU in HCNs with the NBS and the MRP cell associations. Our results show that increasing the small cell base station (BS) density, the BS transmit power, the time allocation factor, and the energy conversion efficiency, weakly affect the DL and UL performance of both cell associations. However, the UL performance of both cell associations can be improved by increasing the fraction of the DL received power used for energy harvesting.


Theoretical Analysis of Hybrid Buffer–Aided Cooperative Protocol Based on Max–Max and Max–Link Relay Selections

Abstract

          Motivated by the recent max–link protocol as well as the max–max protocol, both of which were developed for a simple dual-hop buffer-aided cooperative network, we present a novel hybrid buffer-aided cooperative protocol that attains the benefits of a high reliability and a reduced packet delay. More specifically, we incorporate a two-stage relay selection strategy, which is capable attaining a low outage probability comparable to the max–link protocol. Also, the proposed protocol maintains a beneficial end-to-end packet delay, which is lower than that of the max–link protocol in the realistic scenario supporting finite source packet transmissions. Furthermore, by introducing a periodic Markov-chain model, we derive the theoretical outage probability of our hybrid buffer-aided scheme under the realistic assumption of finite-buffer relays. Our analytical and simulation results demonstrate that the proposed protocol benefits from the above-mentioned high-diversity reliable performance as well as the reduced end-to-end packet delay.


Novel Non-contact Control System for Medical Healthcare of Disabled Patients

Abstract

          When limb-disabled patients want to activate the nurse emergency call system, adjust the temperature on air-conditioners, switch on or off lights, watch television, or have other urgent needs and require assistance from other people, their needs cannot be readily met if there is no one around. All above devices need to be operated manually or with a remote control. Thus disabled patients cannot operate by themselves, and this also increases the burden of the nursing assistants. In order to improve the above issue, a novel non-contact control system is designed to allow disabled patients activating the nurse emergency call system and adjusting other appliances. Disabled patients can stare at the control icons of a visual stimulus generator, which accompanies a wearable electroencephalogram (EEG) acquisition device with non-contact dry electrode for monitoring patients’ EEG signals and converting the EEG signals into relevant control commands via the signal processing system, to achieve the function of nurse calling and the effect of controlling the devices in a hospital. The result shows that the proposed system could effectively monitor and convert EEG signals and achieve the control effects for which disabled a patient desires in a hospital. Therefore, the non-contact control system provides a new control framework for the facilities in a hospital, which significantly assist patients with limb disability.


Adaptive Optimization of Quantized Perturbation Coefficients for Fiber Nonlinearity Compensation

Abstract

       In perturbation based nonlinearity compensation (PB-NLC) technique, quantization of perturbation coefficients is employed for reduction of computational and implementation complexity. In this work, we propose and experimentally verify the adoption of a decision directed least mean square (DD-LMS) algorithm for optimization and complexity reduction of PB-NLC equalizer. We show that for 32 GBaud dual polarization (DP) 16-QAM after 2560 km of single mode fiber (SMF), the proposed scheme further reduces the computational term by 46% compared to that of conventional PB-NLC with uniform quantization of perturbation coefficients for the same Q-factor improvement.


A Mobile Offloading Game Against Smart Attacks

Abstract

        Mobile devices such as smartphones can offload applications and data to the cloud via access points or base stations to reduce energy consumption and improve user experience. However, mobile offloading is vulnerable to smart attackers that use smart and programmable radio devices such as universal software radio peripherals to perform multiple types of attacks, such as spoofing and jamming, based on the radio environments and offloading transmissions. In this paper, a mobile offloading game is investigated that consists of three players: a mobile device that chooses its offloading rate, a smart attacker that determines its attack mode, and a security agent that decides whether or not to initiate full protection for the serving access point during the offloading. Nash and Stackelberg equilibria of the offloading game are derived and their existence conditions are discussed. A Q-learning based mobile offloading strategy is proposed for mobile devices that are unaware of system parameters such as the channel conditions in dynamic radio environments. Simulation results show that the proposed offloading strategy can improve the utility of the mobile device and reduce the attack rate of smart attackers.


Multiuser Diversity over Parallel and Hybrid FSO/RF Links and Its Performance Analysis

Abstract

          Hybrid free-space optical (FSO)/radio-frequency (RF) communication has emerged as an effective solution for high data rate wireless transmission. In this paper, multiuser diversity over parallel and hybrid FSO/RF links is discussed. We present and analyze a hybrid FSO/RF point to multi-points system which consists of a hybrid access point (HAP), multiple FSO users and multiple RF users. Either a FSO user or a RF user is scheduled to communicate with HAP at each transmission block. We propose link quality scheduling strategy. The statistical characterizations of the proposed strategy are derived. Based on these characterizations, the outage probability and the average bit-error rate are also analyzed. Novel asymptotic closed-form expressions at high SNR are derived. The multiuser diversity gain and diversity order for this scheduling strategy are further discussed. Numerical results are given to validate all the analytical results.


Polarization-Independent Phase-Sensitive Amplification

Abstract

       We throughly analyze the requirements on the signal and idler state of polarizations (SOPs) for achieving maximum amplification in phase-sensitive amplifiers (PSAs). These requirements are described using a Jones-space description as well as Stokes-space description. Our analysis includes the cases of polarization-diverse and vector PSAs, and in each type of PSA we also consider the signal-degenerate and the non-degenerate schemes.We observe that the relation between the signal and idler SOPs to achieve maximum phase-sensitive (PS) amplification can be described similarly in polarization-diverse and in vector PSAs. Moreover, both types of PSAs are polarization-dependent, which means that PSAs do require polarization-tracking schemes when being implemented in a realistic optical-transmission scenario. We therefore evaluate how polarization tracking of the signal and the idler SOPs can overcome the theoretical polarization dependence of both polarization-diverse and vector PSAs. We find that only one polarization tracker for either the signal or idler SOP is necessary for achieving polarization-independent PS amplification when considering the general case of a dualpolarization (DP) modulated signals. This polarization tracker requires the control of three degrees of freedom which describe a general polarization rotation. For single-polarization (SP) modulated signals, the polarization tracker can rotate both the signal and the idler SOPs simultaneously which eliminates the need for splitting the signal and the idler before the PSA. Moreover, only two degrees of freedom for the polarization tracker are necessary in this case. When considering degenerate schemes, a polarization tracker with two degrees of freedom is sufficient to achieve maximum PS amplification of DP binary phase-shift keying (BPSK) signals in both vector and polarization diverse PSAs. For the case of SP-BPSK signals, a polarization-diverse PSA can amplify polarization-independently by controlling the relative phase between the pumps, whereas a polarization tracker with only one degree of freedom is necessary in the case of vector PSAs.


Operationalizing Engagement with Multimedia as User Coherence with Context

Abstract

          Traditional approaches for assessing user engagement within multimedia environments rely on methods that are removed from the human computer interaction itself, such as surveys, interviews and baselined physiology. We propose a context coherence approach that operationalizes engagement as the amount of independent user variation that covaries in time with multimedia contextual events during unscripted interactions. This can address questions about the features of multimedia users are most engaged and how engaged users are without the need for prescribed interactions or baselining. We assessed the validity of this approach in a psycho physiological study. 40 participants played interactive video games. Intake and post stimulus questionnaires collected subjective engagement reports that provided convergent and divergent validity criteria to evaluate our approach. Estimates of coherence between physiological variation and in-game contextual events predicted subjective engagement and added information beyond physiological metrics computed from baselines taken outside of the multimedia context. Our coherence metric accounted for task-dependent engagement, independent of predispositions; this was not true of a baselined physiological approach that was used for comparison. Our findings show compelling evidence that a context-sensitive approach to measuring engagement overcomes shortcomings of traditional methods by making best use of contextual information sampled from multimedia in time-series analyses.


Design, Modeling, and Performance Analysis of Multi-Antenna Heterogeneous Cellular Networks

Abstract

       This paper presents a stochastic geometry-based framework for the design and analysis of downlink multiuser multiple-input multiple-output (MIMO) heterogeneous cellular networks (HetNets) with linear zero-forcing (ZF) transmit precoding and receive combining, assuming Rayleigh fading channels and perfect channel state information (CSI). The generalized tiers of base stations (BSs) may differ in terms of their Poisson point process (PPP) spatial density, number of transmit antennas, transmit power, artificial-biasing weight, and number of user equipments (UEs) served per resource block. The spectral efficiency of a typical user equipped with multiple receive antennas is characterized using a non-direct momentgenerating- function (MGF)-based methodology with closed-form expressions of the useful received signal and aggregate network interference statistics systematically derived. In addition, the area spectral efficiency is formulated under different space-division multiple-access (SDMA) and single-user beamforming (SUBF) transmission schemes. We examine the impact of different cellular network deployments, propagation conditions, antenna configurations, and MIMO setups on the achievable performance through theoretical and simulation studies. Based on state-of-theart system parameters, the results highlight the inherent limitations of baseline single-input single-output (SISO) transmission and conventional sparse macro-cell deployment, as well as the promising potential of multi-antenna communications and smallcell solution in interference-limited cellular environments.


Advanced Eigenvalue Tracking of Characteristic Modes

 Abstract

         Eigenvalue tracking is a serious issue in the calculation of characteristic modes over a wide frequency range. Two commonly used algorithms in this regard are investigated and the drawbacks that typically occur during eigenvalue tracking are explained. We discuss the effect of the degraded modes in detail. A new algorithm is presented, which overcomes these drawbacks in an innovative way. The new algorithm is explained in detail and investigated with respect to its numeric stability. A rectangular plate is used as a generic example to evaluate the tracking algorithms. Finally, a fractal antenna is evaluated as an advanced example.


Software Calibration of a Frequency-Diverse, Multistatic, Computational Imaging System

Abstract

        We demonstrate a technique for calibrating a frequency-diverse, multistatic, computational imaging system. A frequency-diverse aperture enables an image to be reconstructed primarily from a set of scattered field measurements taken over a band of frequencies, avoiding mechanical scanning and active components. Since computational imaging systems crucially rely on the accuracy of a forward model that relates the measured and transmitted fields, deviations of the actual system from that model will rapidly degrade imaging performance. Here, we study the performance of a computational imaging system at microwave frequencies based on a set of frequency-diverse aperture antennas, or panels. We propose a calibration scheme that compares the measured versus simulated scattered field from a cylinder, and calculates a compensating phase difference to be applied at each of the panels comprising the system. The calibration of the entire system needs be performed only once, avoiding a more laborious manual calibration step for each transmitting and receiving path. Imaging measurements performed using the system confirm the efficacy and importance of the calibration step.


Energy-Efficient Resource Allocation for Massive MIMO Amplify-and-Forward Relay Systems

Abstract

       Energy-efficient resource allocation is investigated for multi-pair massive MIMO amplify-and-forward relay systems, where a dedicated relay assists pair-wise information exchange among many pieces of single-antenna user equipment (UEs). The system energy efficiency (EE) is theoretically analyzed by employing large system analysis and random matrix theory. This analytical result provides excellent approximation for the system with a moderate number of antennas, and it also enables several efficient algorithms, working with different knowledge of channel state information (CSI), to maximize the system EE by scheduling the optimal numbers of relay antennas and UE pairs as well as the corresponding relay transmission power. In contrast to conventional resource allocation schemes, the proposed algorithms avoid complicated matrix calculations and the instantaneous CSI of small-scale fading; therefore they are computationally efficient with low CSI overhead. The proposed optimization framework sheds light on the optimized system configurations, and it also offers an efficient way to achieve EEoriented resource allocation for the multi-pair massive MIMO relay systems.


A Survey of the Challenges, Opportunities and Use of Multiple Antennas in Current and Future 5G Small Cell Base Stations

 Abstract

 Small cell base stations (SBSs) and multiple antennas are seen as fundamental technologies in the emergence of the next generation (i.e., 5th generation, 5G) of cellular wireless technology. This article provides a comprehensive survey of literature relating to the applications and challenges associated with using multiple antennas in SBSs. The use of multiple antenna techniques in conventional wireless base stations has undergone much study and is widespread. With heterogeneity in current networks and a furthering of this theme together with greater densification expected in 5G systems, their use in SBSs is at an evolutionary stage. In this article, unique design challenges associated with size, cost and performance in SBSs are presented. We present a clear understanding of this increasingly important research area, identifying a clear classification of use and design guidelines. We present a state-of-the-art review of the literature to show how researchers are using and considering the use of multiple antennas in small cells. Attention is given to current generation networks; and with SBSs being a dominant technology necessary for 5G, we also provide insights into the design challenges in such possible future networks.


A Novel Digital Phantom Using an Optical Non-contact Measurement System

Abstract

Digital phantoms are vital for various biomedical researches. Traditional phantoms include theoretical models and voxel models reconstructed from medical images. It has been demonstrated that the homogeneous phantom filled with uniform tissue is accurate enough for wearable antenna design, body-centric channel modelling, etc. Therefore, it is interesting and necessary to investigate the novel approach of generating digital phantoms using an optical non-contact measurement system. In this paper, the point cloud data are first obtained; then, they are simplified via principal components analysis; finally, by applying surface reconstruction and mesh simplification techniques, a digital Chinese phantom is established. To verify the usability of the phantom, numerical calculation is performed to check E-fields at different positions on the body. Results sufficiently prove the feasibility of the train of thought presented in this paper.


An Accurate Edge Extension Formula for Calculating Resonant Frequency of Electrically Thin and Thick Rectangular PatchAntennas with and without Air Gaps

Abstract

         A new and accurate edge extension formula based on the Taguchi method is proposed to calculate the resonant frequency of electrically thin and thick rectangular patch antennas with and without an air gap. Based on 3205 antennas datum random distribution in the electrical substrate thickness h/λd range from 0.001 to 0.2 and the dielectric constant range from 1.0 to 10.2, the edge extension formula is created with the Taguchi method. The resonant frequencies predicted by using the proposed formula are a better agreement with simulated and measured results than those calculated with the existing formulae in other literatures, especially for electrically thick substrates. Furthermore, experimental results for the rectangular patch antennas with an air gap (RPAAG) are given, which shows that h/λd should be less than 0.13 in the design of a capacitively-fed RPAAG.


Reconfigurable Antennas Based on Self-Morphing Liquid Crystalline Elastomers

Abstract

          Pattern- and frequency-reconfigurable antennas are developed using metalized liquid crystalline elastomers (LCEs) that can change their geometries from flat to helical shapes. The pitch angle and number of turns in this transformation are controlled by temperature. An external heat source is applied to reshape the geometry of these antennas, thereby reconfiguring their performance. The antennas are characterized using simulations and measurements.


Sub-THz Wireless over Fibre for Frequency Band 220 GHz – 280 GHz

 Abstract

       Higher capacity wireless access networks are required to serve the growing demands for mobile traffic and multimedia services. The use of sub-THz carrier frequencies is a potential solution for the increased data demands. This paper proposes and demonstrates experimentally the photonic generation of a multiband signal for sub-THz wireless-over-fibre transmission at up to 100 Gb/s (20 Gb/s in each band) using the full spectrum 220 – 280 GHz for downlink wireless transmission and an uplink with 10 Gb/s on-off keying (OOK). By using an optical frequency comb generator (OFCG), 5 optical tones spaced by 15 GHz are selected and split into odd and even optical subcarriers modulated separately using 10 Gbaud quadrature phase shift keying (QPSK) with Nyquist bandwidth achieved by using root raised cosine (RRC) filtering with 0.01 roll off factor. These optical subcarriers are combined and transmitted over 10 km of fibre to the remote antenna unit (RAU). The optical bands are then filtered and transmitted separately at the RAU in a wireless channel. The received sub-THz band is down-converted to the IF frequency and digital signal processing is employed at the receiver to measure the bit error ratio (BER). The performance is also evaluated to investigate the impact of the uplink on the downlink optical transmission. The receiver link budget and wireless distance for acceptable BER are also explored. The proposed system aims to distribute sub-band THz signals for short range indoor mobile units. The overall transmission capacity is increased by transmitting it as a multiband, which also reduces the bandwidth requirements on opto-electronic devices.


Spatial Modulation via 3-D Mapping

Abstract

This letter proposes a jointly mapped spatial modulation (JM-SM) scheme to break through the constraint on the number of transmit antennas in traditional SM systems. It is realized via jointly mapping the transmit information bits to 3-D constellation points. A 3-D constellation design scheme for JMSM is analyzed and established by minimizing the system average bit error probability (ABEP). In addition, the extension of the joint 3-D mapping to GSM is discussed. Simulation results show that the proposed schemes can be adopted to MIMO systems with arbitrary number of transmit antennas and offer better ABEP performance than those existing schemes.


Transient Analysis of Lumped Circuit Networks Loaded Thin Wires By DGTD Method

Abstract

       With the purpose of avoiding very fine mesh cells in the proximity of a thin wire, the modified telegrapher’s equations (MTEs) are employed to describe the thin wire voltage and current distributions, which consequently results in reduced number of unknowns and augmented Courant-Friedrichs-Lewy (CFL) number. As hyperbolic systems, both the MTEs and the Maxwell’s equations are solved by the discontinuous Galerkin time-domain (DGTD) method. In realistic situations, the thin wires could be either driven or loaded by circuit networks. The thin wire-circuit interface performs as a boundary condition for the thin wire solver, where the thin wire voltage and current used for the incoming flux evaluation involved in the DGTD analyzed MTEs are not available. To obtain this voltage and current, an auxiliary current flowing through the thin wire-circuit interface is introduced at each interface. Corresponding auxiliary equations derived from the invariable property of characteristic variable for hyperbolic systems are developed and solved together with the circuit equations established by the modified nodal analysis (MNA) modality. Furthermore, in order to characterize the field and thin wire interactions, a weighted electric field and a volume current density are added into the MTEs and Maxwell-Ampere’s law equation, respectively. To validate the proposed algorithm, three representative examples are presented.


Compact Multi Mode Multi Element Antenna for Indoor UWB Massive MIMO

 Abstract

In this paper we present a concept for a compact ultra wideband multi element antenna for massive MIMO indoor base stations. The antenna concept is based on the simultaneous excitation of different Characteristic Modes on each element of the multi element antenna. This enables an effective 484 port antenna using only 121 physical antenna elements. Thereby a size reduction of 54 % compared to a generic multi element antenna based on crossed dipoles is achieved. The antenna operates in the ultra-wide frequency band of 6 GHz – 8.5 GHz with a reflection coefficient of sii < -10dB and the inter element and intra element mutual coupling of the antenna ports is sji ≤ -20 dB.


Constellation-Randomization Achieves Transmit Diversity for Single-RF Spatial Modulation

Abstract

The performance of spatial modulation (SM) is known to be dominated by the minimum Euclidean distance (MED) in the received SM constellation. In this paper, a symbol scaling technique is proposed for SM in the multiple-inputmultiple- output (MIMO) channel that enhances the MED to improve the performance of SM. This is achieved by forming fixed sets of candidate pre-scaling factors for the transmit antennas, which are randomly generated and are known at both the transmitter and receiver. For a given channel realization, the transmitter chooses the specific set of factors that maximizes the MED. Given the channel state information readily available at the receiver for detection, the receiver independently chooses the same set of pre-scaling factors and uses them for the detection of both the antenna index and the symbol of interest. We analytically calculate the attainable gains of the proposed technique in terms of its transmit diversity order based on both the distribution of the MED and on the theory of classical order statistics. Furthermore, we show that the proposed scheme offers a scalable performance-complexity tradeoff for SM by varying the number of candidate sets of pre-scaling factors, with significant performance improvements compared to conventional SM.


ENERGY EFFICIENT USER ASSOCIATION FOR CLOUD RADIO ACCESS NETWORKS

Abstract

         Cloud radio access network (C-RAN) and massive multiple-input multiple-output (MIMO) are recognized as two key technologies for the fifth-generation (5G) mobile networks. In this paper, we consider the energy efficiency-based user association problem in massive MIMO empowered C-RAN, where multiple antennas are clustered at each remote radio head (RRH). We first obtain the deterministic equivalent expression of the energy efficiency, and then propose three user association algorithms, named nearest-based user association (NBUA), single- candidate RRH user association (SCRUA), and multi-candidate RRHs user association (MCRUA), respectively. In NBUA and SCRUA, each user is associated with only one RRH, and in MCRUA, multiple RRHs can serve the same user. In our algorithms, the impact of power consumption of fronthaul links and antennas are considered by allowing inefficient RRHs to be turned into sleep mode. We provide numerical comparisons of the proposed algorithms and a state-of-the-art baseline which associates each user with the nearest RRH. The results show that our proposed algorithms achieve higher energy efficiency than the baseline algorithm. The proposed MCRUA algorithm achieves a good balance between spectral and energy efficiency, and the performance gain is more significant when the number of users is large.


Gradient-based Coverage Optimization Strategy for Mobile Sensor Networks

Abstract

A Voronoi-based strategy is proposed to maximize the sensing coverage in a mobile sensor network. Each sensor is moved to a point inside its Voronoi cell  using a coverage improvement scheme. To this end, a gradient-based nonlinear optimization approach is utilized to find a target point for each sensor such that the local coverage increases as much as possible, if the sensor moves to this point. The algorithm is implemented in a distributed fashion using local information exchange among sensors. Analytical results are first developed for the single sensor case, and are subsequently extended to a network of mobile sensors, where it is desired to maximize network-wide coverage with fast convergence. It is shown that under some mild conditions the positions of the sensors converge to a stationary point of the objective function, which is the overall weighted coverage of the sensors. Simulations demonstrate the effectiveness of the proposed strategy.


Coordinated Day-Ahead Reactive Power Dispatch in Distribution Network Based on Real Power Forecast Errors

Abstract

      Reactive power outputs of DGs are used along with capacitor banks to regulate distribution network voltage. However, reactive power capability of a DG is limited by the inverter ratings and real power outputs of the DG. In order to achieve optimal power flow, minimize power losses, and minimize switching of capacitor banks, a day-ahead coordinated dispatch method of reactive power is proposed. Forecast errors of DG real power in every period are used to estimate the probability distribution of DGs reactive power capacity. Considering different output characteristics and constraints of reactive power sources, a dynamic preliminary-coarse-fine adjustment method is designed to optimize DG and shunt compensator outputs, decrease the switching cost, and reduce loss. The preliminary optimization obtains initial values, and multiple iterations between the coarse and fine optimizations are used to achieve a coordinated result. Simulations studies are performed to verify the proposed method.


Optimal Reactive Power Dispatch for Voltage Regulation in Unbalanced Distribution Systems

Abstract

      In this paper, we propose a method to optimally set the reactive power contributions of distributed energy resources (DERs) present in distribution systems with the goal of regulating bus voltages. For the case when the network is balanced, we use the branch power flow modeling approach for radial power systems to formulate an optimal power flow (OPF) problem. Then, we leverage properties of the system operating conditions to relax certain nonlinear terms of this OPF, which results in a convex quadratic program (QP). To efficiently solve this QP, we propose a distributed algorithm based on the Alternating Direction Method of Multipliers (ADMM). Furthermore, we include the unbalanced three-phase formulation to extend the ideas introduced for the balanced network case. We present several case studies to demonstrate the method in unbalanced three-phase distribution systems.


Energy Efficient Power Allocation Schemes for a Two-User Network-Coded Cooperative Cognitive Radio Network

Abstract

       This paper investigates the outage behavior and power allocation problem in a two-user network-coded cooperative cognitive radio network over Rayleigh fading channels. First, we derive an exact expression for the outage probability of the secondary transmissions, and then we propose an approximate expression whose validity limits are later evaluated. To improve the power efficiency of the secondary network, two power allocation schemes are proposed. In the first scheme, the transmit power is adjusted as a function of the average channel gains and the power control is formulated as a convex optimization problem where the objective is to minimize the total transmit power subject to outage probability constraints. In the second scheme, the transmit power is adjusted as a function of the instantaneous channel gains to guarantee a target signal-to-interference-plus-noise ratio at the receiver. We evaluate the performance of both schemes under cooperative and non-cooperative scenarios considering different network geometries. Our results indicate that the benefits of network coding cooperation are substantial for both power allocation schemes.


PAPR Constrained Power Allocation for Multicarrier Transmission in Multiuser SIMO Communications

Abstract

       Peak-to-average power ratio (PAPR) constrained power allocation for multicarrier transmission in multiuser single-input multiple-output (SIMO) communications is considered in this paper. Reducing the PAPR in any transmission system is beneficial because it allows the use of inexpensive energy-efficient power amplifiers. In this paper, we formulate a power allocation problem for single-carrier (SC) frequency division multiple access (FDMA) and orthogonal FDMA (OFDMA) transmission with instantaneous PAPR constraints. Moreover, a statistical approach is considered in which the power variance of the transmitted waveform is controlled. The constraints for the optimization problems are derived as a function of transmit power allocation and two successive convex approximations (SCAs) are derived for each of the constraints based on a change of variables (COV) and geometric programming (GP). In addition, the optimization problem is constrained by a user-specific quality of service (QoS) constraint. Hence, the proposed power allocation strategy jointly takes into account the channel quality and the PAPR characteristics of the power amplifier. The numerical results show that the proposed power allocation strategy can significantly improve the transmission efficiency of power-limited users. Therefore, it is especially beneficial for improving the performance for cell edge users.


Artificial Noise Aided Secrecy Information and Power Transfer in OFDMA Systems

Abstract

      In this paper, we study simultaneous wireless information and power transfer (SWIPT) in orthogonal frequency division multiple access (OFDMA) systems with the coexistence of information receivers (IRs) and energy receivers (ERs). The IRs are served with best-effort secrecy data and the ERs harvest energy with minimum required harvested power. To enhance the physical layer security for IRs and yet satisfy energy harvesting requirements for ERs, we propose a new frequency-domain artificial noise (AN) aided transmission strategy. With the new strategy, we study the optimal resource allocation for the weighted sum secrecy rate maximization for IRs by power and subcarrier allocation at the transmitter. The studied problem is shown to be a mixed integer programming problem and thus nonconvex, while we propose an efficient algorithm for solving it based on the Lagrange duality method. To further reduce the computational complexity, we also propose a suboptimal algorithm of lower complexity. The simulation results illustrate the effectiveness of proposed algorithms as compared against other heuristic schemes.


Scheduling and Resource Allocation in Downlink Multiuser MIMO-OFDMA Systems

Abstract

 Multiuser MIMO (MU-MIMO) in general, and block diagonalization (BD) in particular, are playing a prominent role toward the achievement of higher spectral efficiencies in modern OFDMA-based wireless networks. The utilization of such techniques necessarily has implications in the scheduling and resource allocation processes taking care of assigning subcarriers, power, and transmission modes to the different users. In this paper, a framework for channel- and queue-aware scheduling and resource allocation for BD-based MU-MIMO-OFDMA wireless networks is introduced. In particular, using an SNR-based abstraction of the physical layer, the proposed design is able to cater for different BD-MU-MIMO processing schemes [co-ordinated Tx-Rx (CTR) or receive antenna selection (RAS)], uniform or adaptive power allocation (UPA/APA), continuous or discrete rate allocation (CRA/DRA), and many different scheduling rules. Additionally, the different strategies are complemented by a new greedy user/stream selection algorithm that is shown to perform very close to the optimal user/stream selection policy at a much lower complexity. Results using system parameters typically found in 4G networks reveal that, in most cases, low-complexity solutions (RAS-, UPA-based) achieve a performance close to the one attained by their more complex counterparts (CTR-, APA-based).


Full-Duplex Wireless Communications: Challenges, Solutions, and Future Research Directions

ABSTRACT

            The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time slots or frequency subbands. Hence, the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyze the main impairments (e.g., phase noise, power amplifier nonlinearity, as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD-based media access control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communications.


Feasibility Study on Aircraft Positioning by Using ISDB-T Signal Delay

Abstract

         This paper is concerned with experimental results of aircraft positioning by using terrestrial digital broadcasting signal delay. Passive Bistatic Radar (PBR) is expected as a conventional primary surveillance radar alternative, and it can also achieve expanding coverage area of the conventional radar. The PBR sensors allow the detection and tracking of noncooperative targets illuminated by transmitters of opportunity such as communication systems (digital terrestrial television broadcasting, AM/FM, 3G/LTE base stations, etc.) or conventional radar system. Especially, the Digital Terrestrial Television Broadcasting (DTTB) signals are the most expected radio waves. In this paper, we show experimental results of aircraft positioning by using the signal delay profile of DTTB whose type is Integrated Services Digital Broadcasting – Terrestrial (ISDB-T) used in Japan. It will be shown that the ISDB-T signal delays are useful surveillance system.


Maximum Lifetime Strategy for Target Monitoring with Controlled Node Mobility in Sensor Networks with Obstacles

Abstract

        Consider a mobile sensor network that is used to monitor a moving target in a field with obstacles. In this paper, an efficient relocation technique that simultaneously maximizes the network lifetime is proposed. The main sources of energy consumption in the network are sensing, communication, and movement of the sensors. To account for this energy consumption, a graph is constructed with edges that are weighted based on the remaining energy of each sensor. This graph is subsequently employed to address the lifetime maximization problem by solving a sequence of shortest path problems. The proposed technique determines a near-optimal relocation strategy for the sensors as well as an energy-efficient route to transfer information from the target to destination. This near-optimal solution is calculated in every time instant using the information obtained through the previous time step. It is shown that by choosing appropriate parameters, sensors’ locations and the communication route from target to destination can be arbitrarily close to their corresponding optimal choices at each time instant. Simulation results confirm the effectiveness of the proposed technique.


Precoding in Multigateway Multibeam Satellite Systems

Abstract

         This paper considers a multigateway multibeam satellite system with multiple feeds per beam. In these systems, each gateway serves a set of beams (cluster) so that the overall data traffic is generated at different geographical areas. Full frequency reuse among beams is considered so that interference mitigation techniques are mandatory. Precisely, this paper aims at designing the precoding scheme which, in contrast to single gateway schemes, entails two main challenges. First, the precoding matrix shall be separated into feed groups assigned to each gateway. Second, complete channel state information (CSI) is required at each gateway, leading to a large communication overhead. In order to solve these problems, a design based on a regularized singular value block decomposition of the channel matrix is presented so that both inter-cluster (i.e. beams of different clusters) and intra-cluster (i.e. beams of the same cluster) interference is minimized. In addition, different gateway cooperative schemes are analysed in order to keep the inter-gateway communication low. Furthermore, the impact of the feeder link interference (i.e. interference between different feeder links) is analysed and it is shown both numerically and analytically that the system performance is reduced severely whenever this interference occurs even though precoding reverts this additional interference. Finally, multicast transmission is also considered. Numerical simulations are shown considering the latest fixed broadband communication standard DVBS2X so that the quantized feedback effect is evaluated. The proposed precoding technique results to achieve a performance close to the single gateway operation even when the cooperation among gateways is low.


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