Dynamic Orthogonal Frequency Division Multiple Access resource management for downlink interference avoidance in two‐tier networks

In two‐tier networks, which consist of macrocells and femtocells, femtocells can offload the traffic from macrocells thereby improving indoor signal coverage. However, the dynamic deployment feature of femtocells may result in signal interference due to limited frequency spectrum. The tradeoff between broad signal coverage and increased signal interference deserves further exploration for practical network operation. In this paper, dynamic frequency resource management is proposed to avoid both co‐tier and cross‐tier Orthogonal Frequency Division Multiple Access downlink interference and increase frequency channel utilization under co‐channel deployment. A graph‐based non‐conflict group discovery algorithm is proposed to discover the disjoint interference‐free groups among femtocells in order to avoid the co‐tier interference. A macrocell uses the femtocell gateway for frequency resource allocation among femtocells to avoid cross‐tier interference. We formulate the optimized frequency resource assignment as a fractional knapsack problem and solve the problem by using a greedy method. The simulation results show that the average data transfer rate can be increased from 21% to 60%, whereas idle rate and blocking rate are decreased in the range of and , respectively, as compared with conventional graph coloring and graph‐based dynamic frequency reuse schemes. Copyright © 2013 John Wiley & Sons, Ltd.     

Axial ratio bandwidth improvement of compact planar monopole antenna with dual-band and dual-sense

A small size, dual-band and dual-sense monopole antenna is proposed to improve the axial ratio bandwidth (ARBW). The proposed antenna is considered on a low-cost lossy FR4 substrate with parasitic strips (PSs) and partial ground plane of half guided wavelength dimensions. The dimension of the antenna in terms of wavelength is $\mathbf{0.27}{\mathit{\lambda }}_{\mathbf{0}}\mathit{\times }\mathbf{0.29}{\mathit{\lambda }}_{\mathbf{0}}\mathit{\times }\mathbf{0.02}{\mathit{\lambda }}_{\mathbf{0}}$, where ${\mathit{\lambda }}_{\mathbf{0}}$ is the wavelength at the lowest resonant frequency. The circularly polarized (CP) mode is created for strong orthogonal electric fields ${\mathit{E}}_{\mathit{X}}$ and ${\mathit{E}}_{\mathit{Y}}$. The obtained phase difference (PD) between two electric fields ${\mathit{E}}_{\mathit{X}}$ and ${\mathit{E}}_{\mathit{Y}}$ is varied from ${\mathbf{86}}^{°}$ to ${\mathbf{96}}^{°}$ under ARBW. The achieved ARBW is 3.68–3.8 GHz, 4.84–12.58 GHz, and impedance bandwidth (IBW) is 3.51–3.82 GHz and 4.28–15 GHz. The applications of the proposed antenna are International Telecommunication Union (ITU) for 5G, C-band IEEE 802.11a wireless local area network (WLAN) at 5 GHz (5.15–5.825 GHz) and X-band wireless systems.     

Inter‐annual variability,risk and confidence intervals associated with propagation statistics. Part II: parameterization and applications

This set of two companion papers aims at providing a model for the inter‐annual variability of earth‐space propagation statistics and for the inherent risk and CIs. In part I, it was proposed to model the yearly variance σ² of empirical complementary CDFs so that where is the variance of estimation, the inter‐annual climatic variance and p the long‐term probability. Particularly, an analytical formulation of was derived and parameterized from synthetic rain attenuation data. Considering the statistical framework developed in part I, this part II is specifically devoted to the parameterization of the variance of estimation from experimental data of rain attenuation and rainfall rate. Then, a methodology to model and parameterize worldwide the inter‐annual climatic variance is presented. The model of yearly variance of the empirical complementary CDFs is finally compared against yearly experimental variances derived from data collected worldwide. The knowledge of this variability is very useful for system design as it allows the risk on a required availability and associated with a given propagation margin to be quantified. Copyright © 2013 John Wiley & Sons, Ltd.     

Successive relaying for large MIMO amplify‐and‐forward relay networks

In this paper, we consider a large relay network with one source, K relays and M users, where the source and relays are equipped with W and N antennas, respectively. We propose an amplify‐and‐forward successive relaying protocol in which the relays are divided into 2 groups to successively help transmission to M users. Achievable sum rate of the proposed protocol is derived and found to scale as when N and M are fixed and K→∞ . On the other hand, when M and K are fixed and N→∞, the achievable sum rate scales as . Therefore, the scaling law of the achievable sum rate coincides with the capacity scaling law of the considered network. Then, both precoding at the source and grouping of the relay nodes are jointly optimized to further improve the proposed protocol. Numerical results show that the proposed successive relaying protocol can outperform the conventional 2‐slot relaying protocol and the proposed joint optimization scheme for source precoding and relay grouping bring considerable rate gain.     

Surface Micromachined Pressure Sensor with Internal Substrate Vacuum Cavity

A surface micromachined piezoresistive pressure sensor with a novel internal substrate vacuum cavity was developed. The proposed internal substrate vacuum cavity is formed by selectively etching the silicon substrate under the sensing diaphragm. For the proposed cavity, a new fabrication process including a cavity side‐wall formation, dry isotropic cavity etching, and cavity vacuum sealing was developed that is fully CMOS‐compatible, low in cost, and reliable. The sensitivity of the fabricated pressure sensors is 2.80 mV/V/bar and 3.46 mV/V/bar for a rectangular and circular diaphragm, respectively, and the linearity is and for these two diaphragms. The temperature coefficient of the resistances of the polysilicon piezoresistor is to per degree of Celsius according to the sensor design. The temperature coefficient of the offset voltage at 1 atm is 0.0019 mV and 0.0051 mV per degree of Celsius for a rectangular and circular diaphragm, respectively. The measurement results demonstrate the feasibility of the proposed pressure sensor as a highly sensitive circuit‐integrated pressure sensor.     

New Time‐Domain Decoder for Correcting both Errors and Erasures of Reed‐Solomon Codes

A new time‐domain decoder for Reed‐Solomon (RS) codes is proposed. Because this decoder can correct both errors and erasures without computing the erasure locator, errata locator, or errata evaluator polynomials, the computational complexity can be substantially reduced. Herein, to demonstrate this benefit, complexity comparisons between the proposed decoder and the Truong‐Jeng‐Hung and Lin‐Costello decoders are presented. These comparisons show that the proposed decoder consistently has lower computational requirements when correcting all combinations of ν errors and μ erasures than both of the related decoders under the condition of , where d_min denotes the minimum distance of the RS code. Finally, the (255, 223) and (63, 39) RS codes are used as examples for complexity comparisons under the upper bounded condition of . To decode the two RS codes, the new decoder can save about 40% additions and multiplications when as compared with the two related decoders. Furthermore, it can also save 50% of the required inverses for .     

Supercapacitive Properties of Composite Electrode Consisting of Activated Carbon and Di(1‐aminopyrene)quinone

Di(1‐aminopyrene)quinone (DAQ) as a quinone‐containing conducting additive is synthesized from a solution reaction of 1‐aminopyrene and hydroquinone. To utilize the conductive property of DAQ and its compatibility with activated carbon, a composite electrode for a supercapacitor is also prepared by blending activated carbon and DAQ (3:1 w/w), and its supercapacitive properties are characterized based on the cyclic voltammetry and galvanostatic charge/discharge. As a result, the composite electrode adopting DAQ exhibits superior electrochemical properties, such as a higher specific capacitance of up to at , an excellent high‐rate capability of up to , and a higher cycling stability with a capacitance retention ratio of 82% for the 1,000th cycle.     

Real‐Time Locomotion Mode Recognition Employing Correlation Feature Analysis Using EMG Pattern

This paper presents a new locomotion mode recognition method based on a transformed correlation feature analysis using an electromyography (EMG) pattern. Each movement is recognized using six weighted subcorrelation filters, which are applied to the correlation feature analysis through the use of six time‐domain features. The proposed method has a high recognition rate because it reflects the importance of the different features according to the movements and thereby enables one to recognize real‐time EMG patterns, owing to the rapid execution of the correlation feature analysis. The experiment results show that the discriminating power of the proposed method is 85.89% when walking on a level surface, 96.47% when going up stairs, and 96.37% when going down stairs for given normal movement data. This makes its accuracy and stability better than that found for the principal component analysis and linear discriminant analysis methods.     

Adaptive Calibration Method in Multiport Amplifier for K‐Band Payload Applications

This letter proposes a novel calibration method for a multiport amplifier (MPA) to achieve optimum port‐to‐port isolation by correcting both the amplitude and phase of the calibration signals. The proposed architecture allows for the detection of the phase error and amplitude error in each RF signal path simultaneously and can enhance the calibrated resolution by controlling the analog phase shifters and attenuators. The designed and MPAs show isolation characteristics of 30 dB and 27 dB over a frequency range of 19.5 GHz to 22.5 GHz, respectively.     

Non‐resonant Element in Slotted Ground Plane for Multiband Antenna Operation

New ways of achieving small, multiband, multifunctional, and standard solutions for mobile handset antennas are demanded in the current wireless market. A non‐resonant element of , a matching network, and a slotted ground plane are proposed to satisfy mobile market demands that require multiband operation and small antenna solutions. The main advantage of the proposed design is that with only one non‐resonant element of considerably small size (0.015λ, 900 MHz), the handset is capable of providing operation at mobile bands.     

Privacy‐friendly weighted‐reputation aggregation protocols against malicious adversaries in cloud services

Reputation systems are used for evaluating trustworthiness of the users based on their feedback (i.e., votes) about each other. Such systems are particularly important for cloud service providers, as they allow them to collect and aggregate feedback on the past behavior of users. Weighted‐reputation aggregation is a protocol, where the vote server has a weight vector for all voters, each voter has a vote score y_i, and they cooperate to compute . We call it ‘privacy‐friendly’, if the respective inputs are kept private. In other words, a privacy‐friendly weighted aggregation protocol is a secure evaluation for functionality . In this work, we propose two privacy‐friendly weighted‐reputation aggregation protocols: one in semi‐honest model and another one in malicious model. The latter protocol uses the cryptographic primitives of homomorphic encryption, verifiable encryption, and the proof of knowledge of a discrete logarithm. Our protocols need only two rounds of communications, which is very efficient in practice. Our protocols are secure against the collusion of at most n ? 2malicious adversaries. Copyright © 2014 John Wiley & Sons, Ltd.     

Biomimetic Bidirectional Switchable Adhesive Inspired by the Gecko

The gecko adhesive system has attracted significant attention since the discovery that van der Waals interactions, which are always present between surfaces, are predominantly responsible for their adhesion. The unique anisotropic frictional–adhesive capabilities of the gecko adhesive system originate from complex hierarchical structures and just as importantly, the anisotropic articulation of the structures. Here, by cleverly engineering asymmetric polymeric microstructures, a reusable switchable gecko‐like adhesive can be fabricated yielding steady high adhesion ( ≈ 1.25 N/cm²) and friction ( ≈ 2.8 N/cm²) forces when actuated for “gripping”, yet release easily with minimal adhesion ( ≈ 0.34 N/cm²) and friction (≈ 0.38 N/cm²) forces during detachment or “releasing”, over multiple attachment/detachment cycles, with a relatively small normal preload of 0.16 N/cm² to initiate the adhesion. These adhesives can also be used to reversibly suspend weights from vertical (e.g., walls), and horizontal (e.g., ceilings) surfaces by simultaneously and judiciously activating anisotropic friction and adhesion forces. This design opens the way for new gecko‐like adhesive surfaces and articulation mechanisms that do not rely on intensive nanofabrication in order to recover the anisotropic tribological property of gecko adhesive pads, albeit with lower adhesive forces compared to geckos.     

Design and Experiment Results of High‐Speed Wireless Link Using Sub‐terahertz Wave Generated by Photonics‐Based Technology

Using a sub‐terahertz (sub‐THz) wave generated using a photonics‐based technology, a high‐speed wireless link operating at up to 10 Gbps is designed and demonstrated for realization of seamless connectivity between wireless and wired networks. The sub‐THz region is focused upon because of the possibility to obtain sufficient bandwidth without interference with the allocated RF bands. To verify the high‐speed wireless link, such dynamic characteristics as the eye diagrams and bit error rate (BER) are measured at up to 10 Gbps for non‐return‐to‐zero pseudorandom binary sequence data. From the measurement results, a receiver sensitivity of –23.5 dBm at is observed without any error corrections when the link distance between the transmitter and receiver is 3 m. Consequently, we hope that our design and experiment results will be helpful in implementing a high‐speed wireless link using a sub‐THz wave.     

Compact Triple‐Band Monopole Antenna for WLAN/WiMAX‐Band USB Dongle Applications

A miniaturized triple‐band antenna suitable for wireless USB dongle applications is proposed and investigated in this paper. The presented antenna, simply consisting of a circular‐arc‐shaped stub, an L‐shaped stub, a microstrip feed line, and a rectangular ground plane has a compact size of and is capable of generating three separate resonant modes with very good impedance matching. The measurement results show that the antenna has several impedance bandwidths for of 260 MHz (2.24 GHz to 2.5 GHz), 320 MHz (3.4 GHz to 3.72 GHz), and 990 MHz (5.1 GHz to 6.09 GHz), which can be applied to both 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. Moreover, nearly‐omni‐directional radiation patterns and stable gain across the operating bands can be obtained.     

Joint Beamforming and Jamming for Physical Layer Security

In this paper, we consider a joint beamforming and jamming design to enhance physical layer security against potential multiple eavesdroppers in a multiple‐input and single‐output cellular broadcast channel. With perfect channel state information at the base station, we propose various design approaches to improve the secrecy of the target user. Among the proposed approaches, the combined beamforming of maximum ratio transmission and zero‐forcing transmission with a combination of maximum ratio jamming and zero‐forcing jamming ( with ) shows the best security performance because it utilizes the full transmit antenna dimensions for beamforming and jamming with an efficient power allocation. The simulation results show that the secrecy rate of this particular proposed approach is better than the rates of the considered conventional approaches with quality‐of‐service and outage probability constraints.     

Transparent OLED Lighting Panel Design Using Two‐Dimensional OLED Circuit Modeling

In this work, we develop a simulation method to predict a two‐dimensional luminance distribution method using a circuitry simulation. Based on the simulation results, we successfully fabricate large area transparent organic light‐emitting diode panels with high luminance uniformity.     

Accurate Tunable‐Gain 1/x Circuit Using Capacitor Charging Scheme

This paper proposes an accurate tunable‐gain 1/x circuit. The output voltage of the 1/x circuit is generated by using a capacitor charging time that is inversely proportional to the input voltage. The output voltage is independent of the process parameters, because the output voltage depends on the ratios of the capacitors, resistors, and current mirrors. The voltage gain of the 1/x circuit is tuned by a 10‐bit digital code. The 1/x circuit was fabricated using a 0.18 μm CMOS process. Its core area is , and it consumes 278 μW at and . Its error is within 1.7% at to 1 V.     

Implementation of Real‐Time Post‐Processing for High‐Quality Stereo Vision

We propose a novel post‐processing algorithm and its very‐large‐scale integration architecture that simultaneously uses the passive and active stereo vision information to improve the reliability of the three‐dimensional disparity in a hybrid stereo vision system. The proposed architecture consists of four steps — left‐right consistency checking, semi‐2D hole filling, a tiny adaptive variance checking, and a 2D weighted median filter. The experimental results show that the error rate of the proposed algorithm (5.77%) is less than that of a raw disparity (10.12%) for a real‐world camera image having a resolution and maximum disparity of 256. Moreover, for the famous Middlebury stereo image sets, the proposed algorithm's error rate (8.30%) is also less than that of the raw disparity (13.7%). The proposed architecture is implemented on a single commercial field‐programmable gate array using only 13.01% of slice resources, which achieves a rate of 60 fps for stereo images with a disparity range of 256.     

Influence of a Single Grain Boundary on Domain Wall Motion in Ferroelectrics

Epitaxial tetragonal 425 and 611 nm thick Pb(Zr_0.45Ti_0.55)O₃ (PZT) films are deposited by pulsed laser deposition on SrRuO₃‐coated (100) SrTiO₃ 24° tilt angle bicrystal substrates to create a single PZT grain boundary with a well‐defined orientation. On either side of the bicrystal boundary, the films show square hysteresis loops and have dielectric permittivities of 456 and 576, with loss tangents of 0.010 and 0.015, respectively. Using piezoresponse force microscopy (PFM), a decrease in the nonlinear piezoelectric response is observed in the vicinity (720–820 nm) of the grain boundary. This region represents the width over which the extrinsic contributions to the piezoelectric response (e.g., those associated with the domain density/configuration and/or the domain wall mobility) are influenced by the presence of the grain boundary. Transmission electron microscope (TEM) images collected near and far from the grain boundary indicate a strong preference for (101)/(01) type domain walls at the grain boundary, whereas (011)/(01) and (101)/(01) are observed away from this region. It is proposed that the elastic strain field at the grain boundary interacts with the ferro‐electric/elastic domain structure, stabilizing (101)/(01) rather than (011)/(01) type domain walls, which inhibits domain wall motion under applied field and decreases non‐linearity.     

Design Space Exploration for NoC‐Style Bus Networks

With the number of IP cores in a multicore system‐on‐chip increasing to up to tens or hundreds, the role of on‐chip interconnection networks is vital. We propose a networks‐on‐chip‐style bus network as a compromise and redefine the exploration problem to find the best IP tiling patterns and communication path combinations. Before solving the problem, we estimate the time complexity and validate the infeasibility of the solution. To reduce the time complexity, we propose two fast exploration algorithms and develop a program to implement these algorithms. The program is executed for several experiments, and the exploration time is reduced to approximately 1/22 and 7/1,200 at the first and second steps of the exploration process, respectively. However, as a trade‐off for the time saving, the time cost (TC) of the searched architecture is increased to up to and , respectively, at each step compared with that of the architecture obtained through full‐case exploration. The reduction ratio can be decreased to 1/4,000 by simultaneously applying both the algorithms even though the resulting TC is increased to up to when compared with that obtained through full‐case exploration.