28,179 research outputs found
Thin-layer chromatography analysis of the crude lipid extract of (Ms), (Ma), and (Mc)
No full text<p><b>Copyright information:</b></p><p>Taken from "Genomics of glycopeptidolipid biosynthesis in and "</p><p>http://www.biomedcentral.com/1471-2164/8/114</p><p>BMC Genomics 2007;8():114-114.</p><p>Published online 9 May 2007</p><p>PMCID:PMC1885439.</p><p></p> Open rectangle, diglycosylated GPLs; closed rectangle, triglycosylated GPLs. MALDI-TOF mass spectra of the crude lipid fractions of (Ms), (Ma), and (Mc). Open rectangle, diglycosylated GPLs; closed rectangle, triglycosylated GPLs
Performance evaluation of carrier interferometry implementations of MC-CDMA over a wideband channel suffering phase noise
Full text linkIn 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
Block-Equidistant Resource Mapping in OFDMA, MC-CDMA, and SS-MC-MA
No full textA resource allocation scheme for next
generation multi-carrier systems is analyzed in this
paper. The mapping scheme is based on a blockequidistant
distribution of the user resources for nonfrequency-
adaptive downlink transmissions. This leads
to benefits of frequency diversity, potential power
savings by user terminal sleep mode, and reduction of
signalling overhead. The mapping scheme is applied
and investigated for different multi-carrier schemes,
namely OFDMA, MC-CDMA, and SS-MC-MA in the
context of the WINNER system
Block-equidistant resource mapping in OFDM, MC-CDMA and SS-MC-MA
No full textA resource allocation scheme for nextgeneration multi-carrier systems is analyzed in thispaper. The mapping scheme is based on a blockequidistantdistribution of the user resources for nonfrequency-adaptive downlink transmissions. This leadsto benefits of frequency diversity, potential powersavings by user terminal sleep mode, and reduction ofsignalling overhead. The mapping scheme is appliedand investigated for different multi-carrier schemes,namely OFDMA, MC-CDMA, and SS-MC-MA in thecontext of the WINNER system
Performance evaluation of channel estimation techniques for a proposed '4G' MC-CDMA based system in a time varying channel
Full text linkThis 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
Optimisation des systèmes MIMO SS-MC-MA dans le contexte UWB
Full text linkDans cet article, nous proposons une forme d'onde de type SS-MC-MA (spread spectrum multi-carrier multiple-access) basée sur la solution MBOA (Multiband OFDM Alliance) pour les applications UWB (ultra-wideband) haut débit, en considérant les contextes UWB européen et américain. Le système proposé est optimisé pour augmenter le débit, la marge ou la portée du système. De plus, une composante MIMO est ajoutée afin de bénéficier de la diversité spatiale. Nous montrons que le système MIMO SS-MC-MA adaptatif peut être avantageusement exploité pour les applications UWB haut débit
Loading Algorithms for Adaptive SS-MC-MA Systems over Wireline Channels: Comparison with DMT
No full textIn this paper, we propose to combine adaptive loading principles with the spread-spectrum multicarrier multiple access (SS-MC-MA) scheme. Such an approach has particular interests in the context of powerline communications (PLC), where the transmitter has not only to exploit robust transmission techniques, but has also to adapt the waveform to the channel response. We introduce finite-granularity loading algorithms that dynamically handle the configuration of the system under power spectral density constraints. The presented algorithms assign subcarriers, spreading codes, bits and energy to each user in order to maximize either the data rate or the noise margin at a given target symbol error rate. These algorithms can actually be viewed as a widening of the classical waterfilling approach in the case of an hybrid spread-spectrum multicarrier system. Simulation results of the new scheme are presented for different measured PLC channels and are compared with those of the classical discrete multitone modulation (DMT) approach. It is shown that the adaptive SS-MC-MA scheme performs significantly better than DMT, due to its natural energy gathering capability. Adaptive SS-MC-MA then leads to a more efficient bits and energies distribution and constitutes a simple solution to reduce the quantification loss induced by the use of finite order modulation
Loading Algorithms for Adaptive SS-MC-MA Systems over Wireline Channels: Comparison with DMT
No full textIn this paper, we propose to combine adaptive loading principles with the spread-spectrum multicarrier multiple access (SS-MC-MA) scheme. Such an approach has particular interests in the context of powerline communications (PLC), where the transmitter has not only to exploit robust transmission techniques, but has also to adapt the waveform to the channel response. We introduce finite-granularity loading algorithms that dynamically handle the configuration of the system under power spectral density constraints. The presented algorithms assign subcarriers, spreading codes, bits and energy to each user in order to maximize either the data rate or the noise margin at a given target symbol error rate. These algorithms can actually be viewed as a widening of the classical waterfilling approach in the case of an hybrid spread-spectrum multicarrier system. Simulation results of the new scheme are presented for different measured PLC channels and are compared with those of the classical discrete multitone modulation (DMT) approach. It is shown that the adaptive SS-MC-MA scheme performs significantly better than DMT, due to its natural energy gathering capability. Adaptive SS-MC-MA then leads to a more efficient bits and energies distribution and constitutes a simple solution to reduce the quantification loss induced by the use of finite order modulation
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
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