1,721,067 research outputs found
Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing
Full text linkOrthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E-b/I-O values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCRM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E-b/I-O value decrease.This work was supported in part by MIC, Korea, under the BrOMA
Information Technology Research Center (ITRC) support program supervised
by Institute of Information Technology Assessment (IITA)
Performance Evaluation of 1X-EV-DO rev.A with a Per-User Throughput Based Scheduling Algorithm
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Simulator on the WCDMA High Speed Downlink Packet Access System and Performance Evaluation of a Multiplexing Scheme with Hybrid Schedulers
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Selective hydrogenation of 1,3-butadiene on TiO2-modified Pd/SiO2 catalysts
No full textThe properties of Pd/SiO2 catalysts modified with titanium oxide were examined by determining their activity with respect to the partial hydrogenation of 1,3-butadiene included in an excess amount of butenes and by characterizing their surfaces using infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), H-2 chemisorption, and temperature-programmed desorption (TPD). The TiO2-modified catalysts had an improved selectivity for the conversion of 1,3-butadiene to 1-butene, particularly when the catalysts were reduced at high temperatures, e.g., 500 degreesC. IR and chemisorption results suggest that, when the catalyst is reduced at 500 degreesC, the Pd surface is decorated with partially-reduced TiOx similar to the case of TiO2-supported catalysts, which show strong metal-support interaction (SMSI). XPS and TPD results indicate that the I'd surface is also modified electronically, in that the charge is transferred from the Ti species to Pd and the adsorption of I-butene to the Pd surface becomes weaker. It can be concluded that the strong interaction between the Pd surface and partially reduced TiO2 is responsible for the improved selectivity of the catalyst for the conversion of 1,3-butadiene to 1-butene. (C) 2002 Elsevier Science B.V. All rights reserved
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