2,578 research outputs found
Error Rate Analysis for Coded Multicarrier Systems over Quasi-Static Fading Channels
This paper presents two methods for approximating the performance of coded
multicarrier systems operating over frequency-selective, quasi-static fading
channels with non-ideal interleaving. The first method is based on
approximating the performance of the system over each realization of the
channel, and is suitable for obtaining the outage performance of this type of
system. The second method is based on knowledge of the correlation matrix of
the frequency-domain channel gains and can be used to directly obtain the
average performance. Both of the methods are applicable for
convolutionally-coded interleaved systems employing Quadrature Amplitude
Modulation (QAM). As examples, both methods are used to study the performance
of the Multiband Orthogonal Frequency Division Multiplexing (OFDM) proposal for
high data-rate Ultra-Wideband (UWB) communication.Comment: 5 pages, 3 figures, 2 tables. Submitted to Globecom 200
Performance Analysis and Enhancement of Multiband OFDM for UWB Communications
In this paper, we analyze the frequency-hopping orthogonal frequency-division
multiplexing (OFDM) system known as Multiband OFDM for high-rate wireless
personal area networks (WPANs) based on ultra-wideband (UWB) transmission.
Besides considering the standard, we also propose and study system performance
enhancements through the application of Turbo and Repeat-Accumulate (RA) codes,
as well as OFDM bit-loading. Our methodology consists of (a) a study of the
channel model developed under IEEE 802.15 for UWB from a frequency-domain
perspective suited for OFDM transmission, (b) development and quantification of
appropriate information-theoretic performance measures, (c) comparison of these
measures with simulation results for the Multiband OFDM standard proposal as
well as our proposed extensions, and (d) the consideration of the influence of
practical, imperfect channel estimation on the performance. We find that the
current Multiband OFDM standard sufficiently exploits the frequency selectivity
of the UWB channel, and that the system performs in the vicinity of the channel
cutoff rate. Turbo codes and a reduced-complexity clustered bit-loading
algorithm improve the system power efficiency by over 6 dB at a data rate of
480 Mbps.Comment: 32 pages, 10 figures, 1 table. Submitted to the IEEE Transactions on
Wireless Communications (Sep. 28, 2005). Minor revisions based on reviewers'
comments (June 23, 2006
Sexual behaviour among people with HIV according to self-reported antiretroviral treatment and viral load status
OBJECTIVE: To assess, among people with HIV, the association of self-reported antiretroviral treatment (ART) and viral load status with condomless sex with an HIV-serodifferent partner (CLS-D). DESIGN: Cross-sectional study of 3258 HIV-diagnosed adults in the United Kingdom, 2011–2012. METHODS: CLS-D in the past 3 months and self-reported ART/viral load were ascertained by questionnaire. Clinic-recorded viral load was documented. HIV-transmission risk sex (CLS-D-HIV-risk) was defined as CLS-D together with either not on ART or clinic-recorded viral load more than 50 copies/ml. RESULTS: Of 3178 participants diagnosed more than 3 months ago, 2746 (87.9%) were on ART, of whom self-reported viral load was ‘50 copies/ml/ or less/undetectable’ for 78.4%; ‘more than 50 copies/ml/detectable’ for 8.3%; ‘do not know/missing’ for 13.3%. CLS-D prevalence was 14.9% (326/2189), 6.4% (23/360) and 10.7% (67/629) among men who have sex with men, heterosexual men and women, respectively. Among men who have sex with men, CLS-D prevalence was 18.8% among those not on ART; 15.2% among those on ART with undetectable self-reported viral load; 9.8% among those on ART without undetectable self-reported viral load. Compared with ‘on ART with undetectable self-reported viral load’, prevalence ratios (95% confidence interval) adjusted for demographic/HIV-related factors were: 0.66 (0.45, 0.95) for ‘on ART without undetectable self-reported viral load’, and 1.08 (0.78, 1.49) for ‘not on ART’ (global P = 0.021). Among heterosexual men and women (combined), ART/self-reported viral load was not associated with CLS-D [corresponding adjusted prevalence ratios: 1.14 (0.73, 1.79) for ‘on ART without undetectable self-reported viral load’; 0.88 (0.44, 1.77) for ‘not on ART’, P = 0.77]. CLS-D-HIV-risk prevalence was 3.2% among all participants; 16.1% for ‘not on ART’; 0.6% for ‘on ART with undetectable self-reported viral load; 4.2% for ‘on ART without undetectable self-reported viral load.’ CONCLUSION: Use of ART was not associated with increased prevalence of CLS-D, and was associated with greatly reduced prevalence of HIV-transmission risk sex
Investigation of charge coupled device correlation techniques
Analog Charge Transfer Devices (CTD's) offer unique advantages to signal processing systems, which often have large development costs, making it desirable to define those devices which can be developed for general system's use. Such devices are best identified and developed early to give system's designers some interchangeable subsystem blocks, not requiring additional individual development for each new signal processing system. The objective of this work is to describe a discrete analog signal processing device with a reasonably broad system use and to implement its design, fabrication, and testing
Cosmological Implications of the Tetron Model of Elementary Particles
Based on a possible solution to the tetron spin problem, a modification of
the standard Big Bang scenario is suggested, where the advent of a spacetime
manifold is connected to the appearance of tetronic bound states. The metric
tensor is constructed from tetron constituents and the reason for cosmic
inflation is elucidated. Furthermore, there are natural dark matter candidates
in the tetron model. The ratio of ordinary to dark matter in the universe is
calculated to be 1:5.Comment: 23 page
Attitudinal Differences Between Male And Female Auditors, With Special Emphasis On Turnover Trends
Cholesterol and coronary heart disease: screening and treatment
Coronary heart disease (CHD) is a major cause of morbidity and mortality in the United Kingdom, accounting for just under one quarter of all deaths in 1995: 27% among men and 21% among women.1 Although many CHD deaths occur among elderly people, CHD accounts for 31% of male and 13% of female deaths within the 45–64 age group
An Empirical Comparison of Project Delivery Method Performance for Highway Construction Projects
The intent of this study was to provide an empirical analysis of project performance between the traditional design-bid-build (DBB) method and alternative design-build (DB) method of project delivery for highways. The study examined five major performance metrics: cost growth, schedule growth by notice to proceed, schedule growth by construction start date, award growth and construction engineering inspection cost factor. The data were collected from six selected state departments of transportation (DOT): Florida, Indiana, Oregon, North Carolina, Ohio, and Utah. These six DOTs have significant experience on using the DB project delivery method. Totally, more than 15,000 projects were mined and analyzed. To create a comparable pair between DBB and DB projects, six contract size bins were defined: projects under 2M - 5M - 10M - 20M - 50M. Performance data were collected from the six states by direct DOT official interviews and were mapped to the exploratory metrics. Three rounds of mining were conducted to accomplish the comparable sets of projects: missing data point removal, outlier removal, and project pairing by the bin-sampling method. Projects were matched one-to-one between DBB and DB at +/- 15% of contract award amount and +/- 1 year of respective project construction start date. The results of analysis showed that on average, the cost growth for DB projects is higher than the cost growth for DBB projects for smaller project ranges and lower than DBB projects for larger project ranges. The schedule growth based on notice to proceed dates and construction start dates on DB was found less than that for DBB projects across all sampled states and for all project sizes. DBB produced more negative award growth than DB for all contract size bins. For CEI factor, DBB showed higher mean values than DB for five out of the six contract size ranges
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