1,721,168 research outputs found
Performance Improvement by Moving Cell Concept in Urban Fiber-Optic Microcellular Systems
No full textKinematic analysis and design of a six DOF 3-PRPS in-parallel manipulator
No full textThis paper presents a kinematic analysis and design characteristics of an in-parallel manipulator developed for the probing task application that requires high precision, active compliance, and high control bandwidth. The developed manipulator is a class of six-degree-of-freedom in-parallel platforms with 3 PRPS (prismatic-revolute-prismatic-spherical joints) chain geometry. The main advantages of this manipulator, compared with the typical Stewart platform type, are the capability of pure rotation generation and the easy prediction of the moving platform motion. The purpose of this paper is to develop an efficient kinematic model which can be used for real-time control and to propose systematic methods to design the manipulator considering workspace, manipulability, resistivity, singularity, and the existence conditions of the forward kinematic solution. Particularly, we propose a new method for checking the singularity of the parallel manipulator using the translational and rotational resistivity measures. A series of simulation are carried out to show kinematic characteristics and performance of the manipulator mechanism. A prototype manipulator was built based on the kinematic analysis results
Invited paper : Optical interconnection using micro-optic components and waveguide-embedded optical PCBs
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Optical interconnection using 45˚ degree-ended connection rods in an electro-optical printed circuit board.
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A simple method for calculating coupling efficiency in optical interconnection system involving various misalignment parameters
No full textA simple method is presented to approximate the coupling efficiency in optical interconnection systems, which are affected by alignment parameters of various optical elements. The method considers geometric effects of alignment parameters, not considering the material-dependent losses which are insensitive to the misalignment parameters. To indicate the independent contribution of a given alignment parameter, we define a partial coupling efficiency (PCE) that reflects the effect of only one parameter on a local coupling efficiency at an optical element. The total coupling efficiency (TCE) in the whole system is approximated by multiplications of the PCEs calculated for each parameter and normalization factors. For an interconnection scheme using a 45degrees-ended waveguide, we demonstrate by considering many misalignment parameters simultaneously that our approximation is well matched to the results of the simulated TCE. (C) 2004 Elsevier Ltd. All rights reserved
High reuse efficiency of radio resources in urban microcellular systems
No full textA new microcell configuration scheme in urban areas is proposed in order to increase the reuse efficiency of radio resources. Multiple directional-beam antennas lined up along a street form a cigar-shaped cell. Antennas are located at intersection and are directed along the intersecting streets. Two antennas facing each other Form a microzone and, therefore, a cigar-shaped cell consists of multiple microzones in a line. Each microzone is protected against cochannel interference from neighboring microzones by confinement of transmitted signals to a microzone using down-tilting of antenna beams. Therefore, a radio channel which is occupied in one microzone can be used in adjacent microzones. An increase in system rapacity is achieved by the high reuse efficiency of radio resources. The proposed system increases system capacity up to 560% with a call blocking probability of 1% when compared with a conventional system. In addition, a macrodiversity scheme using two antennas in a microzone improves call quality on reverse link
Four-sector cross-shaped urban microcellular systems with intelligent switched-beam antennas
No full textA four-sector cross-shaped urban microcellular system with intelligent switched-beam antennas is proposed. Each sector covers a street block with a base station located at an intersection, and an intelligent beam-switching scheme is used to locate mobile users in the most suitable beam coverage. Due to directional narrow-beam patterns and waveguide effects of tall buildings, radio signals along vertical and horizontal streets do not interfere with each other. Therefore, a channel can be reused simultaneously in multiple neighboring cells as long as cochannels do not encounter each other along the line of sight. The proposed scheme has a channel reuse efficiency of 0.95 for a traffic load of 0.02 [new-call arrivals/s/cell]. The system also increases system capacity more than three times with a blocking probability of 1% and considerably reduces handoff traffic when compared with a conventional cross-shaped microcellular system with an omnidirectional beam pattern
Moving elevator-cell system in indoor buildings
No full textTo plan efficient future PCS networks, indoor environments as well as outdoor environments must be considered. Users typically exhibit vertical motion through elevators and horizontal motion on building floors in indoor environments. A user on the way into or out of an elevator may experience difficulty in communicating with a base station (BS) due to large signal attenuation caused by the metal structure of the elevator, especially the door. The user also may suffer From handoffs as the user passes several floors during the course of a call as the elevator moves. It is necessary to overcome these problems related to elevators for indoor cell planning, In this paper, a nonmoving and two moving elevator-cell systems for a building are considered. The undesirable inter-floor handoffs while the user Is inside the elevator of the nonmoving elevator-cell system (N-system) are eliminated by introduction of two moving elevator-cell systems: a simple moving elevator-cell system (S-system) and a proposed moving elevator-cell system (P-system), The S-system does not seamlessly maintain calls between an elevator and adjacent floors due to insufficient time when the elevator is open to complete the handoff, while the P-system seamlessly maintains calls using a macro diversity with a distributed antenna scheme. The movements of an elevator and users are modeled and the P-system is compared with the S-system in terms of the required number of channels. The P-system reduces the total required number of channels compared with the S-system under heavy traffic conditions. The elevator-cell system and modeling results can be used in the design of future indoor wireless systems
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