40,462 research outputs found
The Effect of Macrodiversity on the Performance of Maximal Ratio Combining in Flat Rayleigh Fading
The performance of maximal ratio combining (MRC) in Rayleigh channels with
co-channel interference (CCI) is well-known for receive arrays which are
co-located. Recent work in network MIMO, edge-excited cells and base station
collaboration is increasing interest in macrodiversity systems. Hence, in this
paper we consider the effect of macrodiversity on MRC performance in Rayleigh
fading channels with CCI. We consider the uncoded symbol error rate (SER) as
our performance measure of interest and investigate how different
macrodiversity power profiles affect SER performance. This is the first
analytical work in this area. We derive approximate and exact symbol error rate
results for M-QAM/BPSK modulations and use the analysis to provide a simple
power metric. Numerical results, verified by simulations, are used in
conjunction with the analysis to gain insight into the effects of the link
powers on performance.Comment: 10 pages, 5 figures; IEEE Transaction of Communication, 2012
Corrected typo
Performance Analysis of Dual-User Macrodiversity MIMO Systems with Linear Receivers in Flat Rayleigh Fading
The performance of linear receivers in the presence of co-channel
interference in Rayleigh channels is a fundamental problem in wireless
communications. Performance evaluation for these systems is well-known for
receive arrays where the antennas are close enough to experience equal average
SNRs from a source. In contrast, almost no analytical results are available for
macrodiversity systems where both the sources and receive antennas are widely
separated. Here, receive antennas experience unequal average SNRs from a source
and a single receive antenna receives a different average SNR from each source.
Although this is an extremely difficult problem, progress is possible for the
two-user scenario. In this paper, we derive closed form results for the
probability density function (pdf) and cumulative distribution function (cdf)
of the output signal to interference plus noise ratio (SINR) and signal to
noise ratio (SNR) of minimum mean squared error (MMSE) and zero forcing (ZF)
receivers in independent Rayleigh channels with arbitrary numbers of receive
antennas. The results are verified by Monte Carlo simulations and high SNR
approximations are also derived. The results enable further system analysis
such as the evaluation of outage probability, bit error rate (BER) and
capacity.Comment: 24 pages, 7 figures; IEEE Transaction of Wireless Communication 2012
Corrected typo
OPEN ACCESS AND MISSING MARKETS IN ARTISANAL FISHING
This paper combines a model of open access fisheries exploitation with a distance-based approach to missing labor and product markets. The model generates predictions about the circumstances under which exploitation increases or decreases with distance. An econometric model is estimated with survey data from artisanal fishing households in Minahasa, Indonesia. The results can be used to assess the impacts of improved transportation infrastructure on fishery exploitation.Marketing,
Discovery of a Spin-Down State Change in the LMC Pulsar B0540-69
We report the discovery of a large, sudden, and persistent increase in the
spin-down rate of B0540-69, a young pulsar in the Large Magellanic Cloud, using
observations from the Swift and RXTE satellites. The relative increase in the
spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in
the spin rate is seen, and no change is seen in the pulsed X-ray emission from
B0540-69 following the change in the spin-down rate. Such large relative
changes in the spin-down rate are seen in the recently discovered class of
'intermittent pulsars', and we compare the properties of B0540-69 to such
pulsars. We consider possible changes in the magnetosphere of the pulsar that
could cause such a large change in the spin-down rate.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
Staircase to Higher-Order Topological Phase Transitions
We find a series of topological phase transitions of increasing order, beyond
the more standard second-order phase transition in a one-dimensional
topological superconductor. The jumps in the order of the transitions depend on
the range of the pairing interaction, which is parametrized by an algebraic
decay with exponent . Remarkably, in the limit the order
of the topological transition becomes infinite. We compute the critical
exponents for the series of higher-order transitions in exact form and find
that they fulfill the hyperscaling relation. We also study the critical
behaviour at the boundary of the system and discuss potential experimental
platforms of magnetic atoms in superconductors.Comment: 5+5pages, 7 figures. Accepted as a Rapid Communicatio
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Dealing with propositional ambiguity in business process improvement
If it is true that people express their views about organisational issues in ambiguous terms then one needs to address this ambiguity instead of the ‘problems’ to find an appropriate methodological approach to resolving or dissolving problem situations in the organisation. This paper highlights and discusses those issues, which therefore relate to ambiguityin relation to decision making tasks within organisations, and the related Soft Systems Methodology / Systems Thinking school of thought, which traditionally constrains such ambiguities. A model of these issues is presented in terms of the Business Process Improvement (BPI) task to highlight these interdependencies
Development and Testing of a 2-D Transfer CCD
This paper describes the development, operation,
and characterization of charge-coupled devices (CCDs) that feature an electrode structure that allows the transfer of charge both horizontally and vertically through the image area. Such devices have been termed two-dimensional (2-D) transfer CCDs (2DT CCDs), as opposed to the conventional devices, which might be called one-dimensional transfer CCDs, but in other respects are the same as conventional CCD devices. Batches of two different 2DT CCD test devices, featuring different electrode structures but with identical clocking operation in each case, were produced and
tested. The methodology of 2-D charge transfer in each of the device types is described, followed by a presentation of test results from the new CCDs. The ability of both 2DT CCD transfer electrode schemes to successfully transfer charge in both horizontal and vertical directions in the image section of the devices has been proven, opening up potential new applications for 2DT CCD use
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Free atmospheric CO2 enrichment increased above ground biomass but did not affect symbiotic N2-fixation and soil carbon dynamics in a mixed deciduous stand in Wales
Through increases in net primary production (NPP), elevated CO2 is hypothesizes to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE) experiment near Bangor, Wales, 4 ambient CO2 and 4 FACE plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. Four years after establishment, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by FACE. We observed a decrease of leaf N content in Betula and Alnus under FACE, while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by FACE. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated CO2 at this site
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