8,524 research outputs found
Performance evaluation of carrier interferometry implementations of MC-CDMA over a wideband channel suffering phase noise
No full textIn this paper the performance of Carrier Interferometry (CI) and Pseudo-Orthogonal Carrier Interferometry (PO-CI) [1] implementations of Multi-Carrier Code Division Multiple Access (MC-CDMA) are investigated. Comparisons are made with the performance of traditional MCCDMA (incorporating Hadamard-Walsh spreading codes) [2],[3] and Coded Orthogonal Frequency Division Multiplexing (COFDM) [4]. These systems are simulated over a 20MHz bandwidth, wideband, wide-sense stationary, statistically uncorrelated Rayleigh fading channel suffering additive white Gaussian noise (AWGN) and phase noise. The two channel models employed are consistent with the Model B ‘Indoor and Office’ and Model B ‘Outdoor to Indoor and Pedestrian’ test environment specifications proposed by ETSI for UMTS Terrestrial Radio Access (UTRA) [5]. The BPSK CI system was found to outperform both of the equivalent COFDM and MC-CDMA systems, providing 1dB and 1.5dB performance gains respectively at a bit error rate (BER) of 10-3. The BPSK PO-CI system, shown to offer twice the capacity of the equivalent MC-CDMA, COFDM and CI systems, was found to offer the same performance as MC-CDMA. For higher order modulation schemes, the CI system’s performance was found to equal that of the equivalent MCCDMA system, whilst the performance of PO-CI was found to be very poor. In the presence of phase noise, the CI system was found to outperform the MC-CDMA and COFDM systems, suffering a far lower performance loss for a given level of phase noise and providing a softer fail as this level was increased. This soft fail characteristic was also observed in the PO-CI system
Performance evaluation of channel estimation techniques for a proposed '4G' MC-CDMA based system in a time varying channel
No full textThis paper investigates the performance of channel estimation techniques applied to a proposed fourth generation (4G) multi carrier - code division multiple access (MC-CDMA) system. Coherent detection requires a per-sub band estimation of the channel frequency response for each coded orthogonal frequency division multiplexing (COFDM) symbol. This paper compares the performance of a number of pilot symbol assisted modulation (PSAM) methods for achieving such estimates. Performance results are characterised by bit-error-rate (BER), data throughput (DT) and mean-squared error (MSE) for ETSI UTRA specified channel environments. It is shown that in an indoor environment, FFT filtering provides superior data throughput performance, whereas in a high Doppler vehicular environment, a reduced complexity Wiener filter is able to offer the best performance.This paper investigates the performance of channel estimation techniques applied to a proposed fourth generation (4G) multi carrier - code division multiple access (MC-CDMA) system. Coherent detection requires a per-sub band estimation of the channel frequency response for each coded orthogonal frequency division multiplexing (COFDM) symbol. This paper compares the performance of a number of pilot symbol assisted modulation (PSAM) methods for achieving such estimates. Performance results are characterised by bit-error-rate (BER), data throughput (DT) and mean-squared error (MSE) for ETSI UTRA specified channel environments. It is shown that in an indoor environment, FFT filtering provides superior data throughput performance, whereas in a high Doppler vehicular environment, a reduced complexity Wiener filter is able to offer the best performance
Interactively using Semantic Web knowledge: Creating scalable abstractions with FacetOntology
No full textThe amount of knowledge accessible on the Semantic Web is growing, and there is a need for a scalable solution to facilitate exploring that data. Currently approaches to exploring Semantic Web data either focus on exploring resources individually, following links during exploration, and making little use of collated data, or take the approach of collating and aligning multiple sources into one store for one purpose, and hand-crafting a specific browsing interface onto it. We present an approach that provides a scalable browsing interface, which can browse knowledge from the Semantic Web at will. Our approach creates abstractions of knowledge, collated into facets, which are described using FacetOntology. FacetOntology facilitates describing facets from RDF data, suitable for use in creating datasets for faceted browsing
Growth Morphologies and Mechanisms of Non-Equilibrium Solidified MC Carbide
No full textGrowth morphologies and mechanisms of the carbide of group IVB and VB elements (MC carbide), a typical faceted crystal, were studied with an estimated cooling rate from 102 to 105 K/s. Results showed that although the growth morphologies of the MC carbide vary remarkably with solidification cooling rate, the solid/liquid interface is always atomically smooth, and the growth mechanisms are always lateral growth. The growth mechanism transition from lateral to continuous growth mode, which was predicted by the classic crystal growth theory, was not observed for the TiC type MC carbide within the estimated cooling rate range of 102?105 K/s
Ruth Klüger: la creatività per non “smarrirsi strada facendo”
No full textR. Klüger, a jewish viennese, a US citizen and a germanist, is the Author of two autobiographies “weiter leben”and “unterwegs versore”. Written in a style which alternates between essay and poetry, account and recollection, they are the occasion for the Author to establish a dialogue with the women having as a focus the exchange of experiences and reflections over the status of the feminine emancipation
Eutectic MC Carbide Growth Morphologies of a Laser Clad TiC/FeAl Composite Coating
No full textIn this paper, eutectic MC carbide growth morphology and its evolution with laser scanning speed were studied comprehensively of a laser clad MC carbide reinforced FeAl intermetallic matrix composite coating. As the laser scanning speed increased, the growth morphology of eutectic MC carbide was found to be needle-aligned annulation, butterfly-like and well-developed dendrite
Performance analysis of the MC-CDMA system in frequency selective slow Rayleigh fading channels, DS-CDMA or MC-CDMA?
No full textThis report describes the Bit Error Probability (BEP) performance of Multi-Carrier Code Division Multiple Access (MC-CDMA) system using the RAKE-receiver in frequency selective slow Rayleigh fading channels. The analysis has been carried out by a theoretical approach using the characteristic function method for quadratic form of Gaussian random variables and by computer simulation. The BEP performance of Direct Sequence Code Division Multiple Access (DS-CDMA) system under the same conditions is analysed and compared with the BEP performance of the MC-CDMA system.Electrical Engineering, Mathematics and Computer ScienceTelecommunicatie- en Verkeersbegeleidingssysteme
Dynamics of Network Formation Processes in the Co-Author Model
No full textThis article studies the dynamics in the formation processes of a mutual consent network in game theory setting: the Co-Author Model. In this article, a limited observation is applied and analytical results are derived. Then, 2 parameters are varied: the number of individuals in the network and the initial probability of the links in the network in its initial state. A simulation result shows a finding that is consistent with an analytical result for a state of equilibrium while it also shows different possible equilibria.Dynamics, Network, Game Theory, Model,Simulation, Equilibrium, Complexity
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