Gen2‐Based Tag Anti‐collision Algorithms Using Chebyshev's Inequality and Adjustable Frame Size

Arbitration of tag collision is a significant issue for fast tag identification in RFID systems. A good tag anti‐collision algorithm can reduce collisions and increase the efficiency of tag identification. EPCglobal Generation‐2 (Gen2) for passive RFID systems uses probabilistic slotted ALOHA with a Q algorithm, which is a kind of dynamic framed slotted ALOHA (DFSA), as the tag anti‐collision algorithm. In this paper, we analyze the performance of the Q algorithm used in Gen2, and analyze the methods for estimating the number of slots and tags for DFSA. To increase the efficiency of tag identification, we propose new tag anti‐collision algorithms, namely, Chebyshev's inequality, fixed adjustable framed Q, adaptive adjustable framed Q, and hybrid Q. The simulation results show that all the proposed algorithms outperform the conventional Q algorithm used in Gen2. Of all the proposed algorithms, AAFQ provides the best performance in terms of identification time and collision ratio and maximizes throughput and system efficiency. However, there is a tradeoff of complexity and performance between the CHI and AAFQ algorithms.     

A Time‐Optimal Anti‐collision Algorithm for FSA‐Based RFID Systems

With the introduction of the new generation RFID technology, EPCglobal Class‐1 Generation‐2, there is considerable interest in improving the performance of the framed slotted Aloha (FSA)‐based tag collision arbitration protocol. We suggest a novel time‐optimal anti‐collision algorithm for the FSA protocol. Our performance evaluation demonstrates that our algorithm outperforms other tag collision arbitration schemes.     

OFDM‐Based STBC with Low End‐to‐End Delay for Full‐Duplex Asynchronous Cooperative Systems

We propose a new space‐time block coding (STBC) for asynchronous cooperative systems in full‐duplex mode. The orthogonal frequency division multiplexing (OFDM) transmission technique is used to combat the timing errors from the relay nodes. At the relay nodes, only one OFDM time slot is required to delay for a pair‐wise symbol swap operation. The decoding complexity is lower for this new STBC than for the traditional quasi‐orthogonal STBC. Simulation results show that the proposed scheme achieves excellent performances.     

On the security of an RFID‐based parking lot management system

Radio Frequency Identification (RFID)‐based parking management systems provide facilities to control parking lot systems within easy access and secure inspection. Chen and Chong have presented a scheme to prevent car thefts for parking lot management systems, which is based on EPC C1‐G2 RFID standard. They claimed that their protocol is resistant against well‐known RFID attacks. In this paper, we prove that Chen and Chong's scheme is not resistant against secret disclosure and impersonation attacks. Therefore, in Chen and Chong parking lot system, a car may be stolen without having a valid tag. In this paper, we also show that the proposed impersonation attack works for any length of cyclic redundancy check and the secret disclosure attack costs at most 2¹⁶ evaluations of the used pseudo random number generator. The success probability of both attacks is 1 while their complexity is only 2 runs of the protocol. Finally, we present an improved protocol and formally and informally prove that the improved protocol provides the desired level of security and privacy.     

Performance analysis of Doppler shift effects on OFDM‐based and MC‐CDMA‐based cognitive radios

The present development of high data rate wireless applications has led to extra bandwidth demands. However, finding a new spectrum bandwidth to accommodate these applications and services is a challenging task because of the scarcity of spectrum resources. In fact, the spectrum is utilized inefficiently for conventional spectrum allocation, so Federal Communications Commission has proposed dynamic spectrum access mechanism in cognitive radio, where unlicensed users can opportunistically borrow unused licensed spectrum, which is a challenge to obtain contiguous frequency spectrum block. This also has a significant impact on multicarrier transmission systems such as orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA). As a solution, this paper develops non‐contiguous OFDM (NC‐OFDM) and non‐contiguous MC‐CDMA (NC‐MC‐CDMA) cognitive system. The implementation of NC‐OFDM and NC‐MC‐CDMA systems provides high data rate via a large number of non‐contiguous subcarriers without interfering with the existing transmissions. The system performance evaluates NC‐OFDM and NC‐MC‐CDMA for mobile scenario where each propagation path will experience Doppler frequency shift because of the relative motion between the transmitter and receiver. The simulation results of this paper proved that NC‐OFDM system is a superior candidate than NC‐MC‐CDMA system considering the mobility for cognitive users. Copyright © 2013 John Wiley & Sons, Ltd.     

基于CDMA2000 1x移动台的一种捕获方案及其性能分析

针对CDMA2000的物理层协议．根据并行结构的快速捕获．以及自适应门限控制的方法．提出了一种移动台系统中实用的捕获方案，并对此方案在瑞利衰落信道中的性能进行理论分析。     

超高频RFID标签的数字电路设计

在研究读写器和射频标签通信过程的基础上,结合EPC C1G2协议以及ISO/IEC18000-6协议,采用VHDL语言设计出一种应用于超高频段的射频标签数字电路.对电路的系统结构和模块具体实现方法进行了描述.基于0.18 μm CMOS工艺标准单元库,采用EDA工具对电路进行了前端综合和后端物理实现.给出的仿真结果表明该电路符合协议要求,综合后的电路规模约为11000门,功耗约为35 μW.该电路可应用于超高频段的各种RFID标签的数字部分.     

Enhanced Omnidirectional Photovoltaic Performance of Solar Cells Using Multiple‐Discrete‐Layer Tailored‐ and Low‐Refractive Index Anti‐Reflection Coatings

An optimized four‐layer tailored‐ and low‐refractive index anti‐reflection (AR) coating on an inverted metamorphic (IMM) triple‐junction solar cell device is demonstrated. Due to an excellent refractive index matching with the ambient air by using tailored‐ and low‐refractive index nanoporous SiO₂ layers and owing to a multiple‐discrete‐layer design of the AR coating optimized by a genetic algorithm, such a four‐layer AR coating shows excellent broadband and omnidirectional AR characteristics and significantly enhances the omnidirectional photovoltaic performance of IMM solar cell devices. Comparing the photovoltaic performance of an IMM solar cell device with the four‐layer AR coating and an IMM solar cell with the conventional SiO₂/TiO₂ double layer AR coating, the four‐layer AR coating achieves an angle‐of‐incidence (AOI) averaged short‐circuit current density, J_SC, enhancement of 34.4%, whereas the conventional double layer AR coating only achieves an AOI‐averaged J_SC enhancement of 25.3%. The measured reflectance reduction and omnidirectional photovoltaic performance enhancement of the four‐layer AR coating are to our knowledge, the largest ever reported in the literature of solar cell devices.     

Performance of wavelet based Multi‐Chip Rate DS‐CDMA signals over multi‐path Nakagami‐m fading channels

Multi‐Chip Rate/Direct Sequence‐Code Division Multiple Access (MCR/DS‐CDMA) technique using scaled chip waveforms has been designed as an alternative to multi‐data rate DS‐CDMA techniques having constant chip rates. In this work, the probability of error (P_e) expression for MCR/DS‐CDMA signals is derived over multi‐path Nakagami‐m fading channels to investigate the effects of chip waveforms on it. This paper also proposes the use of orthogonal wavelets as chip waveforms of MCR/DS‐CDMA signals over the considered channel. For numerical calculations, Daubechies‐22 (D₂₂) wavelet is used because its side lobes are 40 dB below its main lobe in frequency domain. D₂₂ is compared with a Square Root Raised Cosine (SRRC) chip waveform. In the numerical calculations, only first four scales of the chip waveforms relating to four different chip/data rates are considered. The results for the P_e performance and the capacity (the number of user per Hertz for a same P_e level) show that D₂₂ significantly outperforms the SRRC chip waveform at all data rates, due to low cross correlations among different scales of orthogonal wavelets. Besides, by increasing the number of scales, the advantage of the use of orthogonal wavelets will increase furthermore. Copyright © 2007 John Wiley & Sons, Ltd.     

Full‐Color Delayed Fluorescence Materials Based on Wedge‐Shaped Phthalonitriles and Dicyanopyrazines: Systematic Design,Tunable Photophysical Properties,and OLED Performance

Purely organic light‐emitting materials, which can harvest both singlet and triplet excited states to offer high electron‐to‐photon conversion efficiencies, are essential for the realization of high‐performance organic light‐emitting diodes (OLEDs) without using precious metal elements. Donor–acceptor architectures with an intramolecular charge‐transfer excited state have been proved to be a promising system for achieving these requirements through a mechanism of thermally activated delayed fluorescence (TADF). Here, luminescent wedge‐shaped molecules, which comprise a central phthalonitrile or 2,3‐dicyanopyrazine acceptor core coupled with various donor units, are reported as TADF emitters. This set of materials allows systematic fine‐tuning of the band gap and exhibits TADF emissions that cover the entire visible range from blue to red. Full‐color TADF‐OLEDs with high maximum external electroluminescence quantum efficiencies of up to 18.9% have been demonstrated by using these phthalonitrile and 2,3‐dicyanopyrazine‐based TADF emitters.     

Half‐Cell and Full‐Cell Applications of Highly Stable and Binder‐Free Sodium Ion Batteries Based on Cu3P Nanowire Anodes

Sodium‐ion battery (SIB) is especially attractive in cost‐effective energy storage device as an alternative to lithium‐ion battery. Particularly, metal phosphides as potential anodes for SIBs have recently been demonstrated owing to their higher specific capacities compared with those of carbonaceous materials. Unfortunately, most reported metal phosphides consist of irregular particles ranged from several hundreds nanometers to tens of micrometers, thus delivering limited cyclic stability. This paper reports the sodium storage properties of additive‐free Cu₃P nanowire (CPNW) anode directly grown on copper current collector via an in situ growth followed by phosphidation method. Therefore, as a result of its structure features, CPNW anode demonstrates highly stable cycling ability with an ≈70% retention in capacity at the 260th cycle, whereas most reported metal phosphides have limited cycle numbers ranged between 30 and 150. Besides, the reaction mechanism between Cu₃P and Na is investigated by examining the intermediate products at different charge/discharge stages using ex situ X‐ray diffraction measurements. Furthermore, to explore the practical application of CPNW anode, a pouch‐type Na⁺ full cell consisting of CPNW anode and Na₃V₂(PO₄)₃ cathode is assembled and characterized. As a demonstration, a 10 cm × 10 cm light‐emmiting diode (LED) screen is successfully powered by the Na⁺ full cell.     

Performance analysis of cellular CDMA high‐speed data services

This paper investigates the forward‐link peak and average data rates, throughput, and coverage of a cellular CDMA system for delivering high‐speed wireless data services. The analysis takes into account major aspects commonly found in the forward data channel and applies the generalized Shannon capacity formula for multi‐element antenna (MEA) systems. The study focuses on the physical layer and is flexible for various propagation environments, antenna configurations, multicode allocations, user distributions, and cell site configurations. Numerical results for various multicode allocations are presented for a system model with two‐tier interfering cells operating under a frequency selective slow fading channel with propagation environments specified in the Recommendation ITU‐R M.1225. Copyright © 2006 John Wiley & Sons, Ltd.     

Scalable Approach to Failure Analysis of High‐Performance Computing Systems

Failure analysis is necessary to clarify the root cause of a failure, predict the next time a failure may occur, and improve the performance and reliability of a system. However, it is not an easy task to analyze and interpret failure data, especially for complex systems. Usually, these data are represented using many attributes, and sometimes they are inconsistent and ambiguous. In this paper, we present a scalable approach for the analysis and interpretation of failure data of high‐performance computing systems. The approach employs rough sets theory (RST) for this task. The application of RST to a large publicly available set of failure data highlights the main attributes responsible for the root cause of a failure. In addition, it is used to analyze other failure characteristics, such as time between failures, repair times, workload running on a failed node, and failure category. Experimental results show the scalability of the presented approach and its ability to reveal dependencies among different failure characteristics.     

A Composite of Carbon‐Wrapped Mo2C Nanoparticle and Carbon Nanotube Formed Directly on Ni Foam as a High‐Performance Binder‐Free Cathode for Li‐O2 Batteries

Cathode design is indispensable for building Li‐O₂ batteries with long cycle life. A composite of carbon‐wrapped Mo₂C nanoparticles and carbon nanotubes is prepared on Ni foam by direct hydrolysis and carbonization of a gel composed of ammonium heptamolybdate tetrahydrate and hydroquinone resin. The Mo₂C nanoparticles with well‐controlled particle size act as a highly active oxygen reduction reactions/oxygen evolution reactions (ORR/OER) catalyst. The carbon coating can prevent the aggregation of the Mo₂C nanoparticles. The even distribution of Mo₂C nanoparticles results in the homogenous formation of discharge products. The skeleton of porous carbon with carbon nanotubes protrudes from the composite, resulting in extra voids when applied as a cathode for Li‐O₂ batteries. The batteries deliver a high discharge capacity of ≈10 400 mAh g^?1 and a low average charge voltage of ≈4.0 V at 200 mA g^?1. With a cutoff capacity of 1000 mAh g^?1, the Li‐O₂ batteries exhibit excellent charge–discharge cycling stability for over 300 cycles. The average potential polarization of discharge/charge gaps is only ≈0.9 V, demonstrating the high ORR and OER activities of these Mo₂C nanoparticles. The excellent cycling stability and low potential polarization provide new insights into the design of highly reversible and efficient cathode materials for Li‐O₂ batteries.     

Overcoming the Unfavorable Kinetics of Na3V2(PO4)2F3//SnPx Full‐Cell Sodium‐Ion Batteries for High Specific Energy and Energy Efficiency

In this work, a full‐cell sodium‐ion battery (SIB) with a high specific energy approaching 300 Wh kg^?1 is realized using a sodium vanadium fluorophosphate (Na₃V₂(PO₄)₂F₃, NVPF) cathode and a tin phosphide (SnP_x) anode, despite both electrode materials having greatly unbalanced specific capacities. The use of a cathode employing an areal loading more than eight times larger than that of the anode can be achieved by designing a nanostructured nanosized NVPF (n‐NVPF) cathode with well‐defined particle size, porosity, and conductivity. Furthermore, the high rate capability and high potential window of the full‐cell can be obtained by tuning the Sn/P ratio (4/3, 1/1, and 1/2) and the nanostructure of an SnP_x/carbon composite anode. As a result, the full‐cell SIBs employing the nanostructured n‐NVPF cathode and the SnP_x/carbon composite anode (Sn/P = 1/1) exhibit outstanding specific energy (≈280 Wh kg^?1_{(cathode+anode)}) and energy efficiency (≈78%); furthermore, the results are comparable to those of state‐of‐the‐art lithium‐ion batteries.     

Performance Analysis of an Adaptive Link Status Update Scheme Based on Link‐Usage Statistics for QoS Routing

In the global Internet, a constraint‐based routing algorithm performs the function of selecting a routing path while satisfying some given constraints rather than selecting the shortest path based on physical topology. It is necessary for constraint‐based routing to disseminate and update link state information. The triggering policy of link state updates significantly affects the volume of update traffic and the quality of services (QoS). In this letter, we propose an adaptive triggering policy based on link‐usage statistics in order to reduce the volume of link state update traffic without deterioration of QoS. Also, we evaluate the performance of the proposed policy via simulations.     

Performance analysis of the forward link cdma2000 1xEV‐DO evolution for multirate services in cellular wireless system

In this paper, we propose a combined analytical and simulation framework for performance evaluation of the forward link in the cdma2000 evolution for data only (1xEV‐DO) cellular systems with throughput and spectral efficiency being used as performance metrics. A closed form expression for the aggregate average throughput is derived in terms of system‐dependent parameters and a discrete random process that reflects the stochastic behavior of the transmission channel. The random process is expressed in terms of the cumulative distribution function (CDF) of the users signal‐to‐interference‐plus‐noise ratio (SINR). Quantitative results for throughput and spectral efficiency are presented for a variety of users distribution models, base station antenna types and frequency reuse factors for the cases of sectorized and non‐sectorized cells. Furthermore, we study the impact of the cell radius on the system performance. Copyright © 2006 John Wiley & Sons, Ltd.     

Large‐Size Growth of Ultrathin SnS2 Nanosheets and High Performance for Phototransistors

2D SnS₂ nanosheets have been attracting intensive attention as one potential candidate for the modern electronic and/or optoelectronic fields. However, the controllable large‐size growth of ultrathin SnS₂ nanosheets still remains a great challenge and the photodetectors based on SnS₂ nanosheets suffer from low responsivity, thus hindering their further applications so far. Herein, an improved chemical vapor deposition route is provided to synthesize large‐size SnS₂ nanosheets, the side length of which can surpass 150 μm. Then, ultrathin SnS₂ nanosheet‐based phototransistors are fabricated, which achieve high photoresponsivities up to 261 A W^?1 (with a fast rising time of 20 ms and a falling time of 16 ms) in air and 722 A W^?1 in vacuum, respectively. Furthermore, the effects of back‐gate voltage and air adsorbates on the optoelectronic properties of the SnS₂ nanosheet have been systematically investigated. In addition, a high‐performance flexible photodetector based on SnS₂ nanosheet is also fabricated with a high responsivity of 34.6 A W^?1.     

Pyrite‐Based Bi‐Functional Layer for Long‐Term Stability and High‐Performance of Organo‐Lead Halide Perovskite Solar Cells

Organo‐lead halide perovskite solar cells (PSCs) have received great attention because of their optimized optical and electrical properties for solar cell applications. Recently, a dramatic increase in the photovoltaic performance of PSCs with organic hole transport materials (HTMs) has been reported. However, as of now, future commercialization can be hampered because the stability of PSCs with organic HTM has not been guaranteed for long periods under conventional working conditions, including moist conditions. Furthermore, conventional organic HTMs are normally expensive because material synthesis and purification are complicated. It is herein reported, for the first time, octadecylamine‐capped pyrite nanoparticles (ODA‐FeS₂ NPs) as a bi‐functional layer (charge extraction layer and moisture‐proof layer) for organo‐lead halide PSCs. FeS₂ is a promising candidate for the HTM of PSCs because of its high conductivity and suitable energy levels for hole extraction. A bi‐functional layer based on ODA‐FeS₂ NPs shows excellent hole transport ability and moisture‐proof performance. Through this approach, the best‐performing device with ODA‐FeS₂ NPs‐based bi‐functional layer shows a power conversion efficiency of 12.6% and maintains stable photovoltaic performance in 50% relative humidity for 1000 h. As a result, this study has the potential to break through the barriers for the commercialization of PSCs.