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An intelligent antenna synthesis method is proposed to automatically select suitable antenna type and provide optimal geometric parameters according to the requirement of antenna performance. The performance characteristics of different antennas are analyzed, and a smart antenna selection model is established to recommend the appropriate antenna by using support vector machine (SVM). Then, the stacking ensemble model is built by combining five primary learners to give full play to the advantages of each type of learners and, finally, the geometric parameters of the antenna are provided. Microstrip patch antenna, spiral antenna, and horn antenna are used to demonstrate the accuracy and efficiency of the model. The system shows a great ability of antenna classification with accuracy over 99% and parameter prediction with a mean absolute percentage error (MAPE) of less than 6%. Moreover, the results are compared with the traditional data-driven model, and the key parameters of the model are comprehensively discussed. The proposed method could be widely used in intelligent antenna design in practice. [ABSTRACT FROM AUTHOR]

This communication presents a concept of a sub-6 GHz antenna-on-display (AoD) that can eventually be integrated into the transparent area of a display panel of various wireless devices for the first time in the literature. The transparency of the proposed microwave AoD is realized using metal mesh conductive film and features optical transparency, which is compatible with high-resolution liquid crystal display (LCD)/organic light-emitting diode (OLED) display panel requirements. To maximize the radiation efficiency despite the extremely thin substrate ($0.0048\lambda _{0}$), a traveling-wave antenna topology is inspired and further modified to incorporate the inherent structural limitations of modern-day high-resolution display panels. Eventually designed to operate in a leaky-wave mode, a novella dedicated feeding mechanism is introduced to minimize undesired coupling between the antenna structure and the display panel. The composite right-/left-handed (CRLH) unit cell employs a single shunt inductor topology to maximize the radiation efficiency. The measured 6 dB impedance bandwidth of the proposed microwave AoD is from 2.36 to 6.17 GHz, which is consistent with the fast wave region of the proposed unit cell. The measured realized gain of the microwave AoD consisting of 13 unit cells is 2.68 dBi at 5.5 GHz with a radiation efficiency of 62.5%. This is the first demonstration to ascertain that an AoD topology can be applicable at microwave applications while reducing the antenna-to-ground distance by approximately a factor of 20 compared to previous studies. [ABSTRACT FROM AUTHOR]

In this article, we propose using new machine learning (ML)-based optimization methods as an alternative to traditional optimization methods, for complex antenna designs. This is an efficient methodology to tackle computational challenges, as it is capable of handling a large number of design parameters and is more efficient as well as informative. The proposed technique is applied for modeling the gain performance in the principal plane of a monopole antenna when its radiation properties are modified by placing spatially dependent dielectric material around it. Using the proposed methodology, the dielectric constant values are mapped to the gain pattern of the design. We use two ML techniques for this purpose, namely Gaussian process (GP) regression and artificial neural network (ANN). Once each of these models is obtained, they are further used for estimating the dielectric constant values that can suggest optimal directions to modify gain patterns for single-beam and multiple-beam patterns rather than the conventional omnidirectional pattern of a monopole antenna. The performance of this technique is compared with heuristic optimization techniques, such as genetic algorithms (GAs). The proposed method proves to be quite accurate in spite of being a high-dimensional nonlinear problem. A prototype of a monopole design with three-beam gain pattern is fabricated and tested. The measurement results agree well with the simulation results. The proposed methodology can provide useful and scalable optimization tools for computationally intensive antenna design problems. [ABSTRACT FROM AUTHOR]

In this communication, two composite right-/left-handed transmission line (CRLH-TL)-based reconfigurable antennas with multiple-parameter reconfiguration capability have been presented. In antenna I, the polarization is switched between circular polarization and linear polarization. In antenna II, a split-ring resonator (SRR) is introduced that is connected with the ground through another p-i-n diode D2. In the D2 OFF-state, the metamaterial behavior of the SRR establishes. Due to negative permeability at the frequency of operation, it produces magnetic coupling with the antenna and the antenna starts radiating at a new band (5.2 GHz), forming dual-band characteristics with circular polarization. Antenna II is capable of providing band/frequency and polarization/band, frequency, and polarization reconfiguration using different ON/OFF combination states of diodes D1 and D2. The antennas are suitable for 2.4/5.2 GHz WLAN and 3.5/3.6 GHz WiMAX applications. [ABSTRACT FROM AUTHOR]

A dual-circular polarization (CP) textile antenna is investigated for wearable applications at 3.5 GHz WiMAX and 5.8 GHz industrial, scientific, and medical bands. The proposed antenna is composed of a dual-band monopole antenna and a polarization rotation artificial magnetic conductor (PRAMC). Through the PRAMC, the dual-CP radiation is enabled and the backward radiation is alleviated, in which the left-handed CP is generated in the lower band and the right-handed CP is realized in the upper band. Notably, dyadic reflection coefficient analysis is employed to understand the operating mechanism. Both monopole and PRAMC are printed on textile substrate, achieving conformability and comfortability. In addition, numerical results indicate that the performance of the antenna is robust to lossy human body and structural deformations. For verification, the prototype of the antenna was fabricated by two types of manufacturing process (i.e., laser cutting and screen printing), and the advantages and drawbacks of each fabricating approach are discussed for referring. The antenna made by laser cutting was tested on the phantom with the −10 dB impedance bandwidths of 11.7% and 9.1%, the 3 dB axial ratio bandwidths of 2.0% and 8.2%, and the peak gains of 6.6 and 7.2 dBic, in dual bands, respectively. [ABSTRACT FROM AUTHOR]

Capital expenditures and indoor challenges are two of the main obstacles toward equal access positioning services worldwide. Global Navigation Satellite Systems (GNSS) do not function well indoors and in some challenging outdoor scenarios, such as dense forest canopies or hilly terrains rich in vegetation due, for example, to multipaths and low carrier-to-noise ratios. Terrestrial solutions nowadays can be used to complement GNSS, but they are typically costly to deploy with high coverage and do not offer equal access, for example in some low-revenue countries, in regions forbidding wireless 5G access due to health concerns, or in areas hard to reach with terrestrial infrastructure, such as deep jungle, desert areas with sandy dunes, and deep valleys/deep canyons. As many low Earth orbit (LEO) mega-constellations are emerging and their satellites are significantly closer to Earth than GNSS satellites, solutions based on LEO could complement GNSS. LEO-based communications are expected to be widespread in the next decade, and they will offer a global and easy-to-access infrastructure, with the main costs to the end user coming from the receiver equipment. It is our assumption that future wireless receivers will support the integration of terrestrial and satellite infrastructure, and thus, the LEO-based positioning tasks could be mainly implemented as software add-ons on existing future receivers. Nevertheless, closer proximity to Earth does not automatically mean stronger received signals or acceptable positioning accuracy, especially when the carrier frequencies of the new LEO signals are higher than those in GNSS. Here, we present a feasibility study of LEO-based equal access localization by looking at the current opportunities, benefits, and challenges of LEO megaconstellations used as signals of opportunities. We show that there is an unharnessed potential of future LEO megaconstellations for equal access localization, although several challenges are still to be overcome. [ABSTRACT FROM AUTHOR]

A novel low-profile wideband antenna is proposed with high-gain, high-isolated, and dual-polarized properties. It consists of two mutually-orthogonal bowtie-shaped dipole radiators, four rectangular parasitic elements, and a cylindrical artificial magnetic conductor (AMC) cavity. By introducing parasitic elements, additional resonance is generated, and the bandwidth is widened. The gain is mainly improved by the cylindrical metallic wall and wideband AMC of the cavity. The AMC operates in ±90o reflection phase band-gap bandwidth of 2.35-4.25 GHz, and its equivalent circuit model is developed to understand the working mechanism. The orthogonal placement of two dipole radiators ensures polarization diversity and high isolation. The impacts of various environmental conditions on antenna performance are investigated. To verify the concept of design and demonstrate its excellent performance features, a prototype is fabricated and measured. The proposed wideband antenna has a height of 0.18 wavelength at the center frequency. The measured -10-dB impedance bandwidth is from 2.16 to 3.96 GHz, where the realized gain is 8.34-10.96 dBi and the radiation efficiency is more than 81.8%. High isolation of > 28.65 dB and low envelop correlation coefficient (ECC) of < 2.74 × 10-3 are also achieved between antenna elements. It can be used in the base station for intelligent Internet of Vehicle (IoV) applications, covering the bands of WLAN, WiMAX, Bluetooth, LTE, and 5G sub-6 GHz. [ABSTRACT FROM AUTHOR]

With the prevalence of orthogonal frequency-division multiplexing (OFDM) in many standards, e.g., IEEE 802.11, IEEE 802.16, DVB-T, and DVB-T2, a number of variant modulation schemes based on OFDM have been proposed, which resort to signal sparsity to further enhance spectral efficiency and mitigate the high peak-to-average ratio (PAPR) problem. Among these variants, OFDM with subcarrier number modulation (OFDM-SNM) has been proven to be efficient for simple communication systems with low constellation modulation orders and limited decoding capability. To rigorously verify the performance advantages of OFDM-SNM, we present the study of OFDM-SNM in this paper from the information-theoretic perspective. In particular, we determine an upper bound on the mutual information of OFDM-SNM in closed form by using the log sum inequality. Also, we analyze the optimal pattern utilization probabilities (PUPs) for OFDM-SNM by channel-dependent coding and propose an easy-to-implement iterative algorithm to approach the optimal PUPs. Moreover, considering the practical achievability, we propose a Huffman coding based achievable PUP vector construction scheme to obtain the achievable PUPs and the corresponding achievable rate. We carry out numerical simulations to verify the effectiveness of this study and illustrate the efficiency of the obtained PUPs in comparison with several benchmarks. [ABSTRACT FROM AUTHOR]

This article introduces a novel method of laser ablation patterning-based additive manufacturing (AM) to develop a broadband planar antenna for sub-6 GHz wireless communications applications. The presented technique consists of fused deposition modeling (FDM) and the laser ablation cutting-based metal patterning. The metal layer is transferred to a thermoplastic-based ABS substrate without any postprocessing. FDM and metal patterning are independent operations in our procedure and therefore the proposed prototyping is time-efficient compared to the current AM techniques. The 3-D printed antenna is in the form of the single-layer ABS substrate–metal radiator fed by a coplanar waveguide (CPW). The antenna is also printed on an FR-4 substrate using printed circuit board (PCB) technology, and the radiation skills of the 3-D printed antenna are benchmarked with its PCB counterpart. The numerical results obtained with a full-wave analysis tool are verified by the experimental results. The proposed antenna operates on a broadband covering 2.54–5.84-GHz band with the peak gain around 4 dBi and meets the requirements of the Worldwide Interoperability for Microwave Access (WiMAX) and wireless local area network (WLAN) band applications. The fabricated 3D-printed antenna is loaded to human body, and the reflection coefficients are measured for off-body communication links. The calculated electromagnetic power density profiles on the human phantom are demonstrated for various operating frequencies. [ABSTRACT FROM AUTHOR]

The fifth-generation (5G) network is a fast-growing technology that impacts personal devices for both society and the economy. With the widespread Internet of Things (IoT) devices in such networks, powering and exploring energy to operate them is vital in the 5G era. Therefore, projecting and forecasting how to power IoT devices in the 5G network have already begun, with an aspiration to provide self-powered and green future communication services. Here, we provide a vision for energy harvesting technologies for IoT devices (e.g., emerging wearable and implantable devices employed in healthcare and consumer technologies) that can aid the research line in the 5G era. We propose that various power harvesting and management techniques at the circuit, device, and system levels will be the most crucial segment of IoT devices. Thus, self-power and sustainability should be key features of IoT devices in the 5G network, and ought to be given close attention by electronics and communications communities. To envision this concept, we provide a systematic outline in which prospective power harvesting scenarios of IoT devices in the 5G network are expected. We successively describe vital potential landscapes of 5G and evaluate the energy harvesting and power management requirements. We additionally investigate the challenges beyond energy technologies that could impede the 5G enhancement. [ABSTRACT FROM AUTHOR]

In this study, a novel single-fed low-profile circularly polarized (CP) antenna with a bandpass filtering response is proposed. It is based on a planar substrate integrated waveguide (SIW) dual-mode (TE102/TE201) cavity. When the vias on the edge become sparse, the electromagnetic wave leaks out while maintaining a good dual-mode filtering response. The antenna is folded in order to reduce the aperture size to form an un-splitted radiation beam with small side lobes. Owing to a rotated dual-mode operation, the fields escaping from four sets of sparse vias are approximately of equal amplitude with a progressive phase difference of 90° in sequence. CP radiation is thus achieved when the four orthogonal half-mode radiation patches are excited by the leaking field. By adopting a single feeding with two pairs of asymmetrical shorting pins, the peak gain is improved significantly and a 3 dB axial ratio (AR) response with two minima is obtained simultaneously. Long metal walls and rectangular slots are introduced to fold the current flow and change the wave direction. Consequently, sidelobe level is significantly reduced and the antenna directivity is enhanced. To verify this novel design idea, an antenna prototype with a height of 0.036 λ0 has been fabricated using the multilayer PCB process and measured in a near-field microwave chamber. Measured results are well consistent with the simulation, demonstrating CP radiation with a flat/high gain and good filtering performance. [ABSTRACT FROM AUTHOR]

Compact high-gain wideband antenna systems for through-the-wall imaging and wireless communications, featuring 160% fractional bandwidth, are presented. Each radiating system, consisting of two orthogonal Vivaldi antennas forming a cross-shaped configuration so as to excite linear (horizontal/vertical) and circular polarization (CP), is equipped with a top-mount spherical–axicon dielectric lens. The optimized shaping of the lens and of the outer edge Vivaldi arms allow achieving gain levels exceeding 15 dBi with good front-to-back-ratio. The proposed antenna features a broadside gain diagram with stable radiation pattern and wideband impedance matching in the frequency range between 650 MHz and 6 GHz. CST Microwave Studio, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna and to guide its physical realization. Two-port equivalent circuits were developed to characterize parasitic coupling effects between the Vivaldi antennas ports, while a full-wave analysis allowed characterizing their frequency- and time-domain behaviors. The numerical results concerning the antennas parameters, illustrating the suitability of the proposed antennas to support narrow and ultra-wideband signal waveforms, are found to be in good agreement with the experimental measurements performed on an antenna prototype. [ABSTRACT FROM AUTHOR]

This article describes a fast microwave tomography reconstruction algorithm based on the 2-D discrete dipole approximation (DDA). Synthetic data from a finite-element-based solver and experimental data from a microwave imaging system are used to reconstruct images and to validate the algorithm. The microwave measurement system consists of 16 monopole antennas immersed in a tank filled with lossy coupling liquid and a vector network analyzer. The low-profile antennas and lossy nature of the system make the DDA an ideal forward solver in image reconstructions. The results show that the algorithm can readily reconstruct a 2-D plane of a cylindrical phantom. The proposed forward solver combined with the nodal adjoint method for computing the Jacobian matrix enables the algorithm to reconstruct an image within 6 s. This implementation provides significant time savings and reduced memory requirements and is a dramatic improvement over previous implementations. [ABSTRACT FROM AUTHOR]

A wideband high-power dual-branch helical reflectarray antenna (RAA) is presented. The reflecting element consists of two metal helical branches, and the variable rotation angles enable full 360° phase adjustment. An X-band RAA prototype with $9 \times 9$ rectangular grid is simulated and measured. Full-wave simulations show that the maximum gain of 23.7 dB is achieved with the beam focused at ($\theta = 20{{^{\circ }}}$ , $\varphi = 0{{^{\circ }}}$) direction at center frequency of 9.3 GHz and the 1 dB gain bandwidth is over 24.2%. The measured reflection coefficient is lower than −16.3 dB in the whole band. From 8.4 to 10.8 GHz, the tested axial ratio is less than 2.3 dB. At center frequency, the tested gain is 23.4 dB and the corresponding aperture efficiency is 50.6%. The beam-scanning performance of the RAA is tested within 30° angular in two orthogonal planes with the scan loss of less than 1.5 dB and the axial ratios of lower than 1.4 dB. Taking the flat-topped beam as an example, the beam-forming capability of the RAA is verified. The measured results demonstrate the feasibility of the proposed design. The simulated results show that the power-handling capacity of the RAA is about 358 MW under vacuum condition. [ABSTRACT FROM AUTHOR]

Microwave selective/localized heating has been widely used in special areas, e.g., medical treatment and food processing, but the control of selective/localized heating in restricted space, e.g., microwave ovens, is difficult to accomplish. In this article, a Giuseppe Peano fractal phased-array antenna is designed, and the phase of each radiator is derived to achieve the arbitrary spatial division of the electromagnetic field in a cavity based on the superposition principle of waves. Then, a multiphysics model of microwave heating is established by coupling the electromagnetic field and heat transfer to simulate the directional control of microwave heating in a cavity. An experimental system is built, and the heating results are measured using an infrared thermal imager to verify the temperature distribution in different spatial regions. Finally, the feasibility of the model for different heating targets is discussed. [ABSTRACT FROM AUTHOR]

Based on multigap loop (MGL) antenna and low-noise norm detector, a novel nano-second (ns)-level transient magnetic-field (${H}$ -field) sensor is proposed in this article. The direct measurement result of the MGL antenna is the differential signal of the ${H}$ -field, which is capable to be digitized for storage by the norm detector. The original ${H}$ -field can be restored using the software integral method. The developed ns-level ${H}$ -field sensor exhibits two major advantages. First, it can measure the ${H}$ -field in the substation or the coupled ${H}$ -field inside the hermetically sealed cavities, such as the cockpit of vehicles or aircrafts, which is because the need for the transmission line is removed. Second, its sensitivity is significantly higher than the measurement system with the hardware passive integrator, and the integral error can also be effectively reduced by the low-noise norm detector. In this article, the realization of the ns-level transient ${H}$ -field sensor will be detailed. The simulated upper cutoff frequency of the designed MGL antenna is about 1.9 GHz. The sampling rate of the norm detector is 2 GS/s as the maximum. The dynamic range of the detector is about 42 dB and the operation bandwidth ranges from 0.3 kHz to 500 MHz by calibration. The total storage space of 128 kB can record as long as $64~\mu \text{s}$ at 2 GS/s and is extendable. Test results show that the developed sensor can measure the ns-level ${H}$ -field accurately. [ABSTRACT FROM AUTHOR]

Fuses are commonly used to provide medium voltage (MV) protection to distribution transformers. Unfortunately, there are certain deficiencies introduced when primary-side fuses are used. In paper mill power systems, given the unique organization of the paper mill loads around individual feeders to facilitate load shedding, it may be advantageous to provide transformer differential relay protection from the primary of the transformer to the load side of the main secondary breaker instead of primary fuse protection. This protection can then trip either a primary-side grounding switch (with fuses) or a primary-side feeder circuit breaker using a fiber or a WiMAX (Worldwide Interoperability for Microwave Access) connection. Protection against overload is provided by a secondary main circuit breaker and by design. [ABSTRACT FROM AUTHOR]

The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. [ABSTRACT FROM AUTHOR]

A concurrently dual-polarized, simultaneous transmit and receive (STAR) antenna system with high transmit (TX)-receive (RX) isolation is presented. The STAR antenna consists of four dual-polarized patches, two for TX and two for RX. The radiators are fed using a network consisting of four 90° hybrids and four 180° hybrids. The input ports of the feed network constitute the inputs/outputs of the STAR antenna system. The system supports concurrent transmission and reception of waves with both right- and left-hand circular polarization. Due to the phase cancellation and geometrical symmetry of the antenna, the TX/RX coupling between ports with the same polarization is canceled using the feed network. In addition, four right-angle slots are inserted in the ground plane and a cross-shaped, high-impedance surface is inserted between the radiating patches to further suppress the coupling between the differently polarized TX and RX ports. Simulation and measurement results of a fabricated prototype show good agreement and demonstrate TX/RX isolation levels greater than 38 dB for all polarization combinations over a 6.5% bandwidth (6.0–6.4 GHz). Moreover, the fabricated prototype provides broadside axial ratios below 2.5 dB and realized gains above 7.8 dBic for all TX and RX modes, demonstrating good, concurrent-dual-polarization performance. [ABSTRACT FROM AUTHOR]

A simple conformal ultrawideband (UWB) antenna with monopole-like radiation patterns is proposed in this communication. To achieve the wide bandwidth, two rings are arranged concentrically around the main annular-ring circular patch antenna, in which two rectangular slots are added. The antenna has monopole-like radiation patterns generated by combining four propagation modes of TM01, TM02, TM03, and TM04 throughout the operating bands. To enhance the flexibility and robustness, the proposed antenna is fabricated using conductive fabric embedded into polydimethylsiloxane (PDMS) polymer. To our knowledge, this is the first flexible UWB antenna with monopole-like radiation patterns reported in the open literature. The measured results show that the antenna achieves a 10 dB return loss bandwidth from 2.85 to 8.6 GHz. Monopole-like radiation patterns are maintained throughout the frequency band, agreeing well with simulated results. This has been validated through the measured mean realized gain (MRG) pattern from 2.85 to 8.6 GHz. The fabricated antenna was bent and tested at various curvatures to verify its conformability. To evaluate suitability for UWB communications, the system-fidelity factors of the antenna are investigated using full-wave analysis in CST Microwave Studio, in both flat and bent conditions, validating its potential for UWB pulse transmission. [ABSTRACT FROM AUTHOR]

This article details the experimental work conducted at the Electromagnetic Compatibility and Wireless Laboratory, U.S. Food and Drug Administration, to investigate the use of Licensed Assisted Access (LAA) signals for wireless coexistence testing. A software-defined radio platform was deployed to generate realistic LAA signals and measure the wireless coexistence impact on the LAA communication link. The equipment under test (EUT) used IEEE 802.11ac as an example of incumbent technology in the 5-GHz band. The standardized radiated anechoic chamber method was used for testing. Results highlight the mutual coexistence impact of LAA in the 5-GHz band and suggest that selecting an LAA signal with the maximum possible channel time occupancy and the highest possible modulation and coding scheme yields the most impactful coexistence situation on both the EUT and the LAA system. Additionally, an analysis of the internal LAA system states during coexistence testing is presented to document the inverse relationship between LAA transmit and wait times during coexistence and the adverse impact of challenging coexistence scenarios on successful channel access. Finally, the risk management process of wireless coexistence for medical devices is summarized and associated with coexistence testing. [ABSTRACT FROM AUTHOR]

This article presents a novel dual-polarized millimeter-wave (mm-Wave) patch antenna with bandpass filtering response. The proposed antenna consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches. The combination of the stacked patches and the driven patch can be equivalent to a bandstop filtering circuit for generating a radiation null at the upper band edge. Besides, four additional shorted patches are added beside the cross-shaped driven patch to introduce another radiation null at the lower band edge. Moreover, by embedding a cross-shaped strip between these four stacked patches, the third radiation null is generated to further suppress the upper stopband. As a result, a quasi-elliptic bandpass response is realized without requiring extra filtering circuit. For demonstration, a prototype was fabricated with standard PCB process and measured. The prototype operates in the 5G band (24.25–29.5 GHz) and it has an impedance bandwidth of 20%. The out-of-band gain drops over 15 dB at 23 and 32.5 GHz, respectively, which exhibits high selectivity. These merits make the proposed antenna a good element candidate for the 5G mm-Wave massive MIMO applications to reduce the requirements of the filters in the mm-Wave RF front ends. [ABSTRACT FROM AUTHOR]

This article presents an efficient analysis method for a novel continuous transverse stub (CTS) antenna. As opposed to state-of-the-art CTS antenna designs, the proposed architecture achieves circular polarization using a single CTS array and without any polarization converter. The structure consists of long radiating slots/stubs fed by over-moded parallel-plate waveguides. More precisely, the transverse electromagnetic (TEM) mode and the first transverse electric (TE1) mode of the feeding waveguides are used to generate a circularly polarized field. The array is analyzed using a spectral mode-matching method. First, the active reflection coefficient of the infinite array is derived in closed form. A windowing approach is then adopted to compute the radiation patterns of finite-size arrays. Numerical results obtained with this method are in excellent agreement with full-wave simulations, carried out with a commercial software. The performance of this class of CTS antennas has been investigated using the developed model. It is theoretically demonstrated that the proposed array can be designed to attain an axial ratio (AR) lower than 3 dB over a 52.9% relative bandwidth at broadside. Furthermore, the active input reflection coefficient is lower than −10 dB over a 40.8% relative bandwidth, when the array steers its main beam at $\theta _{0}=45^\circ $. This solution is an attractive candidate for next generation satellite communication terminals. [ABSTRACT FROM AUTHOR]

Operating LTE networks in unlicensed bands together with legacy WiFi systems is deemed as a promising technique to support explosively growing mobile traffic. In conventional LTE/WiFi spectrum sharing schemes, LTE systems need to know WiFi traffic demands for optimizing system parameters to protect WiFi systems, for which the two systems are required to cooperate with each other via signallings exchanges. However, it is difficult to establish a dedicated channel among the two independent systems for exchanging signallings. Hence, in this paper, we propose an intelligent duty-cycle medium access control protocol to realize the effective and fair spectrum sharing between LTE and WiFi systems without requiring signalling exchanges. Specifically, we first design a duty-cycle spectrum sharing framework, which allows an LTE system to share the spectrum with a WiFi system by using time sharing. After that, we develop deep reinforcement learning (DRL)-based algorithms to learn WiFi traffic demands by analyzing WiFi channel activity, e.g., the idleness/business of WiFi channels, which can be observed by the LTE system via monitoring WiFi channels. Based on the learnt knowledge, the LTE system can adaptively optimize LTE transmission time to maximize its own throughput and meanwhile to provide sufficient protection to the WiFi system. Simulation results show that, in terms of LTE throughput and WiFi protection, the performance of the proposed intelligent scheme can approach that of the genie-aided exhaustive search algorithm, which needs the perfect knowledge of WiFi traffic demands through massive signalling exchanges and is of high computational complexity. [ABSTRACT FROM AUTHOR]

The relevance of vehicle communications in next-generation networks entails the necessity of studying their performance in the framework of upcoming massive architectures. In this regard, a study of the wireless channel between a hybrid massive MIMO BS and a vehicular platform is proposed. Adequate metrics and methodology are provided for the assessment of such scenarios. The impact of different multi-antenna geometries and MIMO architectures in both vehicle and BS is modeled based on a numerical simulation of a realistic urban area. We compare several massive hybrid BS configurations with distinct multi-antenna vehicular rooftop solutions. This paper studies the channel eigenvalues and capacities for sub-6 GHz (3.6 GHz) and millimeter-wave (mmWave) (26 GHz) bands under different propagation conditions. The results suggest that the use of hybrid massive configurations increase the channel capacity by subdividing the massive BS into two or four logical radio channels. It is also shown that the greater available bandwidth at mmWave band can compensate the larger attenuation of radio channels in small size cells. The use of adequate metrics to measure the temporal coherence of the channel is also discussed for the beam switching update. [ABSTRACT FROM AUTHOR]

A multistage collaborative machine learning (MS-CoML) method that can be applied to efficient multiobjective antenna modeling and optimization is proposed. Machine learning methods, including single-output Gaussian process regression (SOGPR) and symmetric and asymmetric multioutput GPR (MOGPR) methods, are introduced to collaboratively build highly accurate multitask surrogate models for antennas. Variable-fidelity electromagnetic (EM) models are simulated, with their responses utilized to build separate MOGPR surrogate models. By combining the three machine-learning methods in a multistage framework, mappings between the same and different responses of the EM models with variable fidelity are learned, therein helping to substantially reduce the computational effort under a negligible loss of predictive power. Three antenna designs aiming at single-band, broadband, and multiband applications are selected as examples. And, for illustrating the applicability and superiority of the proposed MS-CoML method, a reference point-based multiobjective antenna optimization algorithm is used to optimize these three antennas. Simulation results show that using the MS-CoML method can significantly reduce the total optimization time without compromising modeling accuracy and optimized performance. [ABSTRACT FROM AUTHOR]

One of the greatest challenges in applying compressive sensing (CS) signal processing techniques to electromagnetic imaging applications is designing a sensing matrix that has good reconstruction capabilities. Compressive reflector antennas (CRAs) are a class of antennas that have been shown to provide enhanced image reconstruction performance over traditional reflector antennas (TRAs) when CS techniques are employed. In this article, we present a unified CRA design method, which considers both the sensing capacity and efficiency of the antenna and can be used for both compressive imaging and multiple-input multiple-output (MIMO) communication applications. The unified design method is assessed for a CRA configuration in which dielectric scatterers are added to the surface of a TRA. The design results demonstrate the ability of the unified design method to enhance the CS reconstruction capabilities of the CRA. [ABSTRACT FROM AUTHOR]

This article presents a graphene-based, dynamically reconfigurable antenna with a voltage-controlled, far-field radiation pattern in the microwave frequency band. The proposed antenna consists of two radiating patches and a planar feed network mainly composed of a graphene-based attenuator and a power divider with a hybrid graphene–metal phase shifter. The output phase of the phase shifter changes by a bias voltage on the graphene. The antenna has two operating states with different beam directions when the bias voltage is between 0.7 and 5 V. The equivalent circuit model is employed to analyze the phase shift characteristic of the graphene–metal phase shifter. Then the prototype of the reconfigurable antenna is fabricated and tested. The experimental results are in good agreement with the simulated ones. This article demonstrates that in the microwave frequency band, by proper design, the graphene–metal structure can be used to realize the new type of the reconfigurable antenna, in which this kind of graphene-based tuning structure can be easily stacked with other circuits by a simple pasting technique than soldering. This feature has potential applications in flexible radio frequency system in future. [ABSTRACT FROM AUTHOR]

In this work, a novel miniaturized meandered slot-line-based quad-band multiple-input-multiple-output (MIMO) antenna system is presented. The proposed design consists of two-antenna elements meandered in an H-shaped configurations. The miniaturization techniques of meandered slot-line and reactive loading are implemented to operate the antenna in sub-1 GHz bands with compact structure which results in an antenna size of $0.08\lambda _{o}$ corresponding to its lowest operating band. The frequency reconfigurability in the design is achieved by reactively loading the slots using varactor diodes. Covering most of the modern communication standards, the antenna operates in 0.665–1.13 GHz, 1.415–2.005 GHz, 2.42–3.09 GHz, and 3.18–3.89 GHz bands. Furthermore, complete analysis of frequency reconfigurability and design procedure is provided as a guideline for designing such an antenna system for any desired band of operation. The proposed two-element design is realized on a board dimensions of $60\times 120\times0.76$ mm3 using an RO4350 substrate. The proposed design is well-suited for wireless terminals with second generation cognitive radio (CR) capabilities for radio-frequency (RF) front-end applications. [ABSTRACT FROM AUTHOR]

Recent developments and the ubiquitous availability of wireless technologies and inter-vehicle communication systems are anticipated to lead to the evolution of heterogeneous wireless networks. Based on standards such as the IEEE 802.11, 5G and WiMax, coupled with mobile IP for the content delivery of road safety and infotainment services to drivers over the new generation of vehicular networks. However, the performance of traditional mobility management protocols over vehicular networks is affected by network topology changes and vehicles’ high mobility. Therefore, efficient mobility management solution that mitigates the challenges of vehicles’ mobility is needed. In this paper, we present an adaptive mobility management protocol for predictive hierarchical mobile IPv6 in vehicular networks. We develop a dynamic Mobility Anchor Point (MAP) discovery and selection scheme that adjusts the network topology structure to fit the vehicles’ mobility environment better. Moreover, the predictive handover scheme is based on a multi-observation hidden Markov model, which utilizes the vehicles’ movement projections to estimate the subsequent point of access. The performance of our proposed protocol has been tested using NS-2 and several real and synthetic mobility traces. The results indicate that our protocol exhibits better performance results when compared to well-known handover protocols in reducing the handover latency and packet loss. [ABSTRACT FROM AUTHOR]

In this article, a compact low-profile antenna for octa-band unbroken metal-rimmed smartphone applications is proposed. The antenna consists of a capacitive coupling rectangular vertical plate and two new-type extended ground branches. For lower frequency, the LTE700, GSM850, and GSM900 bands are provided by the bezel mode which is generated through capacitive coupling excitation of a rectangular vertical plate to the bezel. For upper frequency, the DCS, PCS, UMTS, LTE2300 and LTE2500 bands are covered by the multiple modes of two ground branches. With the proposed structure, the operating bands can be expanded and optimized simply. All the mentioned bands are achieved in the size of ($70 \times 7 + 20 \times 2$) $\times $ (1.5 + 0.8) mm3 on the 130 mm $\times \,\, 70$ mm system board. The antenna is fabricated and measured to verify this proposal. The tested results include reflection coefficient, radiation patterns, efficiency, and gain. [ABSTRACT FROM AUTHOR]

A compact and wideband folded dipole antenna with multi-resonant modes is presented in this paper. Three resonant modes are obtained by using a modified planar folded dipole and its coupled feeding structure. Incorporating the shorting pins and parasitic patches, multiple resonant modes in the antenna are manipulated, shifted, and then combined to increase the impedance bandwidth. Using this concept, a prototype of a multi-mode folded dipole is designed, fabricated, and measured. The experimental results show that the proposed antenna achieves a bandwidth of 80% from 1.57 to 3.68 GHz, while occupying a compact size of $0.3\lambda _{0}\times 0.15\lambda _{0}\times 0.05\lambda _{0}$ ($\lambda _{0}$ is the wavelength in free space at the lowest operating frequency). Furthermore, a simple and effective design to achieve good omnidirectional radiation performance is developed by placing two proposed folded dipoles back to back. The antenna exhibits a flat gain variation of less than 1.27 dB over a broad bandwidth (82%) in the horizontal plane. Such a compact, wideband, planar antenna is a promising candidate for indoor signal coverage, wireless access points, and micro base stations in 2G/3G/4G/5G and WLAN/WiMAX wireless communication systems. [ABSTRACT FROM AUTHOR]

An arm-implantable rectenna, supported by a compact planar inverted F-antenna (PIFA) and a rectifier, is proposed for wireless data telemetry and power transfer in the Medical Device Radiocommunications Service (401–406 MHz) and industrial, scientific, and medical (ISM) (902.8–928 MHz) bands. The rectifier is integrated into the system by using the antenna’s ground plane delivering, thus, a robust solution for the implanted devices. Each development stage is theoretically analyzed first and then experimentally tested. The antenna size is $16 \times 14 \times 1.27$ mm3. The slit/slot loading techniques applied onto the radiator offer the antenna size reduction and the dual-band operation. PIFA’s resonance stability is shown and its radiation and safety responses are addressed. Further, an arm-attached matching layer (ML) is proposed to enhance the wireless power link. Then, an analysis of rectifier circuits is conducted in order to obtain optimum conversion efficiency at low input powers. By following an attentive design process, the final system (rectenna) is built and tested in whole; the measurements verify our approach. [ABSTRACT FROM AUTHOR]

In medical microwave imaging (MMWI), the antennas usually operate at close distance from the body and are required to pick up weak echoes from the inside that are masked by high skin reflection. The near-field antenna behavior strongly determines how the received signals affect the effectiveness of the imaging algorithms. However, these usually simply assume the usual antenna far-field radiation characteristics. Here, we discuss three antenna effects that can deteriorate the overall imaging performance but are rarely addressed in the literature: antenna internal reflections, angular dispersion of the “near-field phase center,” and antenna frequency dispersive electric length. We propose dedicated methods to characterize these factors and present mitigation strategies to be integrated into the inversion algorithms. We demonstrate these effects for three frequently used broadband antennas, using signals from an experimental breast imaging lab setup. In fact, the antenna study and design cannot ignore that it operates in the near field of breast and interacts with its boundary. The methods and conclusions can be extended to other MMWI applications. To the best of our knowledge, this is the first systematic study of the above antenna factors in the context of MMWI. [ABSTRACT FROM AUTHOR]

Safe and reliable operation of future autonomous vehicles requires ultra-low latency vehicle-to-vehicle (V2V) networking. However, due to scalability issues of purely ad hoc network, vehicle-to-infrastructure (V2I) communication is still in demand. To avoid interference between V2V and V2I communications, conventional network association such as handover may generate a large amount of control and signaling overhead, especially in environments with high-speed mobility and small-coverage access points. Taking the additional latency caused by the overhead into consideration, a vehicle-centric approach is proposed to guarantee the low-latency requirements of the V2V networks. Different from solely optimizing the latency performance, the proposed approach focuses on effectively operating the network association and resources re-allocation. This avoids the massive exchange of control information and signaling and reduces its impact on latency. The proposed framework for V2V networking can underlay different virtual cells with a constrained network association rate and we can derive the corresponding upper bound of the latency performance. Analysis and simulation results indicate that our scheme successfully guarantees the upper bound of the latency and simultaneously constrains the network association rate, thus limiting the additional control exchange and signaling overhead. [ABSTRACT FROM AUTHOR]

The Cucker–Smale flocking model is designed to analyze the velocity and position-control mechanisms in a group of living individuals, such as a flock of birds. In this model, each agent (a bird or fish) adjusts its velocity according to its own velocity and the weighted mean of the relative velocities of the other members of the flock. We herein focus on the simple, distributed, and autonomous nature of the flocking model and apply its operating principles to fair resource allocation for vehicle-mounted mobile relays (VMRs) by considering their need for distributed fair resource allocation in various network topologies. By adaptively adjusting the VMR transmission power, the proposed method effectively alleviates the interference between users in vehicles and users directly connected to the base station. We evaluate the performance of the proposed method in the context of the IEEE 802.16j based system. The achievable bandwidth performance of the proposed method is evaluated relative to that of both the fixed power allocation (FPA) method and the signal-to-interference plus noise ratio (SINR)-based transmit power control method. The result shows that the proposed method adjusts to various network topologies and provides better achievable bandwidth than both the SINR-based method and the FPA method. [ABSTRACT FROM AUTHOR]

Sparse superposition codes are a recent class of codes introduced by Barron and Joseph for efficient communication over the AWGN channel. With an appropriate power allocation, these codes have been shown to be asymptotically capacity-achieving with computationally feasible decoding. However, a direct implementation of the capacity-achieving construction does not give good finite length error performance. In this paper, we consider sparse superposition codes with approximate message passing (AMP) decoding, and describe a variety of techniques to improve their finite length performance. These include an iterative algorithm for SPARC power allocation, guidelines for choosing codebook parameters, and estimating a critical decoding parameter online instead of precomputation. We also show how partial outer codes can be used in conjunction with AMP decoding to obtain a steep waterfall in the error performance curves. We compare the error performance of AMP-decoded sparse superposition codes with coded modulation using LDPC codes from the WiMAX standard. [ABSTRACT FROM PUBLISHER]

A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35–4.98 GHz. The narrowband states are intended to cover communications within the 3.05–4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: 0.235\lambda \textrm {L} \times 0.392\lambda \textrm {L} , where the wavelength \lambda \textrm {L} corresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values. [ABSTRACT FROM AUTHOR]

This paper proposes a linear and efficient transmitter prototype based on pulsed load modulation (PLM) power amplifier (PA). The proposed transmitter setup utilizes the complex delta–sigma (DS) modulation as a signal processing technique instead of the envelope DS modulation for higher linearity performance. Using the complex DS modulation technique reduces the in-band quantization noise significantly at the output of the modulator and consequently, enhances the linearity of the transmitter. To validate the proposed technique, the linearity and efficiency performance of the complex DS modulator (CDSM)-based transmitter are compared with the performance of its envelope DS modulator (EDSM) counterpart in measurement. For this paper, an efficient and linear PLM PA is designed and fabricated using GaAs E-pHEMT transistors. For a Long-Term Evolution (LTE) uplink standard signal with 3-MHz bandwidth and 7-dB peak-to-average power ratio, the CDSM-based transmitter achieves the drain efficiency and power added efficiency of 46% and 42%, respectively, at an average output power of 25.1 dBm. The comparison measurement study of EDSM-based transmitter and the CDSM-based transmitter with the LTE uplink signal shows about 11-dB improvement in the signal-to-noise and distortion ratio of the output signal. The measurement results for LTE signals were able to pass the spectral requirements defined by the standard without applying predistortion techniques. [ABSTRACT FROM AUTHOR]

It is often said that the Internet is ubiquitous in our daily lives, but this holds true only for those who can easily access it. In fact, billions of people are still digitally disconnected, as bringing connectivity to certain zones does not make a good business case. The only solution for these unsatisfied potential users is to directly undertake the building of the infrastructure required to obtaining access to the Internet, typically forming groups in order to share the corresponding cost. This article presents a global classification and a summary of the main characteristics of different Alternative Network deployments that have arisen in recent years with an aim to provide Internet services in places where mainstream network deployments do not exist or are not adequate solutions. The "Global Access to the Internet for All" Research Group of the Internet Research Task Force, where all authors actively participate, is interested in documenting these emerging deployments. As an outcome of this work, a classification has converged by consensus, where five criteria have been identified and, based on them, four different types of Alternative Networks have been identified and described with real-world examples. Such a classification is useful for a deeper understanding of the common characteristics behind existing and emerging Alternative Networks. [ABSTRACT FROM PUBLISHER]

Mobile communications are today widespread and contribute to the development of our society. Every day new devices include some means of wireless transmission, which is becoming ubiquitous with the Internet of Things. These systems are standardized by international organizations such as the IEEE, 3GPP, and ETSI, among others. Even though knowledge of wireless standards is key to the understanding of these systems, wireless communications are quite often taught in engineering degrees in a traditional way, without much emphasis on the standardization. Moreover, strong focus is often placed on the theoretical performance analysis rather than on practical implementation aspects. In contrast, most of the current applications make extensive use of mobile data, and the global users' satisfaction is highly correlated with the mobile data throughput. Thus, modern wireless engineers need to have deep insight on the standards that define the mobile transmission systems, and this knowledge is not acquired following the traditional theoretical teaching schemes. In this article, a new learning approach is described. This novel paradigm is based on a new flexible hardware/software platform (FRAMED-SOFT), which is also detailed. Although the article is focused on two wireless standards, GSM and UMTS, the work discussed in this article can easily be extended to other standards of interest, such as LTE and beyond, WiFi, and WiMAX. [ABSTRACT FROM PUBLISHER]

A novel compact multi-ultrawideband (multi-UWB) and multi-dual-band frequency reconfigurable annular sector slot antenna (FR-ASSA) is presented for wireless applications. Three measured UWB states (3.48–5.5, 5.18–7.35, and 6.06–8.05 GHz) are achieved using six p-i-n diodes employed across a moderately wide slot inserted in a 32 \times 35 mm2 ground plane. Furthermore, 18 dual-band states with independent tuning ability of each band are provided. In dual-band states, the measured frequency tuning ranges are from 2.5 to 3.22 GHz (1.29:1) for the first resonance ( f_{1}) and from 4.36 to 6.58 GHz (1.51:1) for the second resonance ( f_{2})$ . The proposed FR-ASSA can support the standards such as WiMAX lower and middle bands (2.5–28 and 5.2–5.8 GHz), 4G LTE 2500 (2500–2690 MHz), WLAN IEEE 802.11a (5.15–5.825 GHz), and UWB groups #1 (3.4–5 GHz), #2 (5–6.6 GHz), and #3 (6.6–8 GHz) spectrums. [ABSTRACT FROM PUBLISHER]

This article analyzes security vulnerabilities in bandwidth allocation and request mechanisms that are specified in the IEEE 802.16 Standard, and introduces a bandwidth request adversary model called UL-BRA based on these vulnerabilities. The goal of UL-BRA is to abuse the bandwidth request/grant operation of a WiMAX network, resulting in a significant decrease of the overall uplink transmission performance of the network. To overcome the challenge caused by the vulnerabilities of the standard, we propose a security patch incorporating a real-time anomaly detection and restoration (RADR) mechanism, which combines an MCDR scheme with an ATD scheme in order to eliminate the impacts of UL-BRA in real-time. We verify the effectiveness of RADR under UL-BRA threats via simulations, and demonstrate the effectiveness of the proposed patch in mitigating the threats of UL-BRA. [ABSTRACT FROM PUBLISHER]

Scalable video coding, together with adaptive modulation and coding, is a promising technique for providing real-time video multicast services on mobile stations (MSs) in heterogeneous channel conditions. On the other hand, since MSs are often powered by batteries, reducing the energy consumption of mobile devices is an important concern. In this paper, we study the problem of scalable video multicast scheduling in a mobile worldwide interoperability for microwave access (WiMAX) network with the objective of maximizing the multicast energy throughput. This problem has never been seriously studied when the assumption that different multicast groups may partially overlap is made. We prove that this problem is NP-complete. Our proposed solution, which is called energy-efficient multicast scheduling with adaptive modulation and coding (EEMS-AMC), consists of three modules, namely, online admission control, base-layer data scheduling, and enhancement-layer data scheduling. The admission control rules not only help the base station to admit the maximum number of video streams but ensure that the video data can be delivered to mobile users within the timeliness requirement as well. Moreover, EEMS-AMC adopts the greedy strategy to schedule base-layer data such that even in the worst-case scenario, the average duty cycle of admitted MSs can be within a bounded factor from the theoretical minimum. Finally, EEMS-AMC employs the metric “expected multicast throughput” to derive the proper modulation and coding scheme for each enhancement-layer data and employs the metric “marginal multicast energy throughput” to efficiently derive near-optimal enhancement-layer data scheduling. Simulation results exhibit that EEMS-AMC achieves relatively good performances in terms of multicast energy throughput and normalized total utility. [ABSTRACT FROM AUTHOR]

Transforming traditional single-vehicle-based safety and efficiency control, networked VSC is expected to be a basic element of addressing the challenges for safety and sustainability of road transportation. However, vehicles remain largely as black boxes to researchers and application developers, and open source platforms for evaluating networked VSC solutions at high-fidelity and scale are still lacking. To exploit the potential of networked VSC, we develop the research infrastructure VInsight, which provides basic building blocks for gaining insight into vehicle internals and for enabling high-fidelity, at-scale evaluation of networked VSC solutions. More specifically, VInsight integrates the OpenXC vehicular sensing platform into the Global Environment for Network Innovations (GENI). VInsight deploys a WiMAX research network for integrating high-fidelity real-world vehicular sensing with at-scale ns-3 emulation in the GENI cloud computing facilities, and VInsight develops WiMAX measurement tools for understanding WiMAX link characteristics and driving high-fidelity emulation of networked VSC systems.1 The WiMAX network of VInsight also enables immediate applications such as campus safety patrol; this synergy with opt-in users enables the permanent deployment of VInsight for open innovation in networked VSC systems, thus helping develop solutions to address the grand challenges of road transportation today. [ABSTRACT FROM PUBLISHER]

Small cell networks offer a promising and viable approach to meeting the increasing demand for high-data-rate wireless applications. With the expected increase in the number of small cell deployments, energy efficiency (EE) is a crucial system design parameter that demands consideration from an eco-sustainability perspective. One way to improve EE is to switch off small cell base stations (BSs) or to keep them in energy-saving mode while preserving the quality of service (QoS) experienced by users. With “bits/joule” as the metric, we aim to optimize EE with the introduction of several levels of sleep depths. Using a stochastic geometry-based heterogeneous cellular network (HCN) model, we derive coverage probability, average achievable rate, and EE in heterogeneous $K$-tier wireless networks with different sleep modes for small cells. Then, we try to maximize EE under 1) a random sleeping policy and 2) a strategic sleeping policy, with constraints on both coverage probability and wake-up times. Due to the nonconvexity of EE, we propose an alternative low-complexity near-optimal solution by maximizing the lower bound of EE. We use an alternating iterative approach to solve the resulting multivariable optimization problem. Simulation results confirm the effectiveness of the scheme. With improvements of approximately 30% in EE with random sleeping policy, simulation indicates that instantaneous EE can be further improved by 15% with a strategic sleeping policy. [ABSTRACT FROM AUTHOR]

This communication presents a small, low-profile planar triple-band microstrip antenna for WLAN/WiMAX applications. The goal of this communication is to combine WLAN and WiMAX communication standards simultaneously into a single device by designing a single antenna that can excite triple-band operation. The designed antenna has a compact size of 19 \times 25\;\textmm^2 (0.152 \lambda0\;\times 0.2 \lambda0). The proposed antenna consists of F-shaped slot radiators and a defected ground plane. Since only two F-shaped slots are etched on either sides of the radiator for triple-band operation, the radiator is very compact in size and simple in structure. The antenna shows three distinct bands I from 2.0 to 2.76, II from 3.04 to 4.0, and III from 5.2 to 6.0 GHz, which covers entire WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5) bands. To validate the proposed design, an experimental prototype has been fabricated and tested. Thus, the simulation results along with the measurements show that the antenna can simultaneously operate over WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5 GHz) frequency bands. [ABSTRACT FROM PUBLISHER]

The heterogeneous network (HetNet) is an important concept for next-generation wireless Internet architecture and Internet of Things, where several wireless technologies can coexist, and the users should have the flexibility to select the connectivity based on the environmental condition and application demands. IEEE 802.11 (or WiFi) and IEEE 802.16 (or WiMAX) are the two primary building block technologies for HetNets because of their sustainability, cost effectiveness, well-deployed architectures, and ability to support high-data-rate wireless communications. The existing literature has extensively studied the interoperability between these two technologies, and seamless handover schemes are designed to support WiFi-WiMAX integration in a HetNet environment. However, effective utilization of these two technologies from the end users' point of view is another important research area. We have the following question: When should a user migrate between these two technologies in a HetNet environment? This paper proposes a handover decision mechanism in a WiFi-WiMAX integrated HetNet environment, which supports the “quality of service” and “quality of experience” requirements of the end users. The effectiveness of the proposed scheme is analyzed using simulation results. [ABSTRACT FROM PUBLISHER]

End users increasingly expect ubiquitous connectivity while on the move. With a variety of wireless access technologies available, we expect to always be connected to the technology that best matches our performance goals and price points. Meanwhile, sophisticated onboard units (OBUs) enable geolocation and complex computation in support of handover. In this paper, we present an overview of vertical handover techniques and propose an algorithm empowered by the IEEE 802.21 standard, which considers the particularities of the vehicular networks (VNs), the surrounding context, the application requirements, the user preferences, and the different available wireless networks [i.e., Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX), and Universal Mobile Telecommunications System (UMTS)] to improve users' quality of experience (QoE). Our results demonstrate that our approach, under the considered scenario, is able to meet application requirements while ensuring user preferences are also met. [ABSTRACT FROM PUBLISHER]