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101.
102.
Mobile ad hoc networks (MANETs) have been positioned as one of the most important emerging wireless communication scenarios. Temporally formed by a collection of wireless mobile hosts, a MANET does not require the aid of any centralized administration. From this stems a suite of challenges in achieving an efficient MANET routing and content delivery in order to make the best use of precious resources and reduce the routing overhead at each MANET host. One of the reported approaches for solving the issue is the use of caching, which is expected to minimize the routing overhead by taking advantage of the limited memory at each mobile host. This paper introduces a novel scheme for addressing the above issue, called Reclaim‐Based Caching (RBC) policy, which dynamically utilizes a cache replacement mechanism of reclaiming stale routes to efficiently verify and validate a recoverable caching mechanism in Dynamic Source Routing. The main design purposes of RBC are to reduce the routing control overhead, lower the end‐to‐end routing delay, enhance the packet delivery ratio, and obtain a higher throughput for improving routing performance and accelerating the Route Discovery process due to low temporary link failure and high cache utilization. Hence, we can gather all feasible and historical route information into the cache library to be reclaimed as a threshold of efficient routing control. Consequently, the proposed RBC of this paper can be used in the universal wireless network environment to achieve better routing performance and to provide a more flexible real‐time application. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
103.
Multicast is a scalable solution for group communications. In order to offer security for multicast applications, a group key has to be changed whenever a member joins or leaves the group. This incurs 1-affects-n problem, which is a constraint on scalability. Decentralized approaches solve the scalability problem by dividing a group into several subgroups that use independent group keys. These approaches, however, introduce new challenges: problem of trusting third party and inefficiency of data delivery. Proxy encryption is a good approach to solve the problem of trusting third party. In this paper, we propose a novel secure multicast scheme using the proxy cryptography. The proposed scheme provides not only scalability but also data transmission efficiency by dynamic subgrouping of group members while intermediate data-relaying third parties are not required to be trusted.  相似文献   
104.
We evaluated the limit of scaling bottom electrode contact (BEC) heater size and high resistivity heater to reduce writing current. It was found that the resistivity of heater should be increased for reducing writing current below the heater size of about 50 nm without any undesirable increase of resistance of the crystalline state (SET state, Rset). It was shown in the numerical simulations that the dissipated heat loss through BEC during melting GST was decreased in the increase of resistivity of heater. In addition, we analyzed the resistance components contributing to the total set resistance. It was observed that the undesired sharp increase of Rset as the BEC size decreases below 50 nm was attributed to the resistance component of GST–BEC interface. In the case of high resistivity heater, the contributions of both incomplete crystallization and heater itself were enhanced.  相似文献   
105.
106.
We propose a rigorous 2D approximation technique for the 3D waveguide structures; it can minimize the well‐known approximation errors of the commonly used effective index method. The main concept of the proposed technique is to compensate for the effective cladding index in the equivalent slab model of the original channel waveguide from the modal effective index calculated by the nonuniform 2D finite difference method. With simulations, we used the proposed technique to calculate the coupling characteristics of a directional coupler by the 2D beam propagation method, and the results were almost exactly the same as the results calculated by the 3D beam propagation method.  相似文献   
107.
Substrate removed bulk GaAs-AlGaAs electrooptic modulators with 3.7-V-cm drive voltage at 1.55 mum were realized. The 1.94-mum-thick undoped GaAs-AlGaAs epilayer removed from its substrate behaves as an electrooptic dielectric layer and has electrodes placed directly on both sides. This allows a very strong modulating electric field overlapping very well with the optical mode. The propagation loss in the presence of electrodes is less than 2.9dB/cm. There is very good agreement between the measured and simulated values  相似文献   
108.
This paper presents a new push-push voltage-controlled oscillator (VCO) technique that extracts a second harmonic output signal from a capacitive common node in a negative-gm oscillator topology. The generation of the second harmonics is accounted for by the nonlinear current-voltage characteristic of the emitter-base junction diode causing: 1) significant voltage clipping and 2) different rise and fall times during the switching operation of the core transistors. Comparative investigations show the technique is more power efficient in the high-frequency region than a conventional push-push technique using an emitter common node. A prototype 17-GHz VCO realized in GaInP/GaAs HBT technology produces an output power of -6dBm and a phase noise of -110.4dBc/Hz at 1-MHz offset, which is equivalent to a VCO figure-of-merit of -184.3dBc/Hz, while drawing 4.38 mA from a 3.0-V supply  相似文献   
109.
In this paper, we construct a family of block orthogonal Golay sequences that have low peak-to-mean envelope power ratio (PMEPR) as well as block wise orthogonal properties. We then present an application of the sequences to channel estimation of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. We compare the performance of the proposed algorithm with that of a frequency division multiplexing (FDM) piloting algorithm, and investigate the effect of co-channel interference (CCI) on the channel estimation performance.  相似文献   
110.
Much effort in register transfer level (RTL) design has been devoted to developing "push-button" types of tools. However, given the highly complex nature, and lack of control on RTL design, push-button type synthesis is not accepted by many designers. Interactive design with assistance of algorithms and tools can be more effective if it provides control to the steps of synthesis. In this paper, we propose an interactive RTL design environment which enables designers to control the design steps and to integrate hardware components into a system. Our design environment is targeting a generic RTL processor architecture and supporting pipelining, multicycling, and chaining. Tasks in the RTL design process include clock definition, component allocation, scheduling, binding, and validation. In our interactive environment, the user can control the design process at every stage, observe the effects of design decisions, and manually override synthesis decisions at will. We present a set of experimental results that demonstrate the benefits of our approach. Our combination of automated tools and interactive control by the designer results in quickly generated RTL designs with better performance than fully-automatic results, comparable to fully manually optimized designs.  相似文献   
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