3,590 research outputs found
Distributed Space-Time Message Relaying for Uncoded/Coded Wireless Cooperative Communications
During wireless communications, nodes can overhear other transmissions through the wireless medium, suggested by the broadcast nature of plane wave propagation, and may help to provide extra observations of the source signals to the destination. Modern research in wireless communications pays more attention to these extra observations which were formerly neglected within networks. Cooperative communication processes this abundant information existing at the surrounding nodes and retransmits towards the destination in various forms to create spatial and/or coding diversity, thereby to obtain higher throughput and reliability. The aim of this work is to design cooperative communication systems with distributed space-time block codes (DSTBC) in different relaying protocols and theoretically derive the BER performance for each scenario. The amplify-and-forward (AF) protocol is one of the most commonly used protocols at the relays. It has a low implementation complexity but with a drawback of amplifying the noise as well. We establish the derivation of the exact one-integral expression of the average BER performance of this system, folloby a novel approximation method based on the series expansion. An emerging technology, soft decode-and-forward (SDF), has been presented to combine the desired features of AF and DF: soft signal representation in AF and channel coding gain in DF. In the SDF protocol, after decoding, relays transmit the soft-information, which represents the reliability of symbols passed by the decoder, to the destination. Instead of keeping the source node idling when the relays transmit as in the traditional SDF system, we let the source transmit hard information and cooperate with the relays using DSTBC. By theoretically deriving the detection performance at the destination by either using or not using the DSTBC, we make comparisons among three SDF systems. Interesting results have been shown, together with Monte-Carlo simulations, to illustrate that our proposed one-relay and two-relay SDF & DSTBC systems outperform traditional soft relaying for most of the cases. Finally, these analytic results also provide a way to implement the optimal power allocation between the source and the relay or between relays, which is illustrated in the line model
Importance of non-flow in mixed-harmonic multi-particle correlations in small collision systems
Recently CMS Collaboration measured mixed-harmonic four-particle azimuthal
correlations, known as symmetric cumulants SC(n,m), in pp and pPb collisions,
and interpreted the non-zero SC(n,m) as evidence for long-range collectivity in
these small collision systems. Using the PYTHIA and HIJING models which do not
have genuine long-range collectivity, we show that the CMS results, obtained
with standard cumulant method, could be dominated by non-flow effects
associated with jet and dijets, especially in collisions. We show that the
non-flow effects are largely suppressed using the recently proposed subevent
cumulant methods by requiring azimuthal correlation between two or more
pseudorapidity ranges. We argue that the reanalysis of SC(n,m) using the
subevent method in experiments is necessary before they can used to provide
further evidences for a long-range multi-particle collectivity and constraints
on theoretical models in small collision systems.Comment: 7 pages and 6 figures, replace with published versio
Sorting and separation of microparticles by surface properties using liquid crystal-enabled electro-osmosis
Sorting and separation of microparticles is a challenging problem of
interdisciplinary nature. Existing technologies can differentiate
microparticles by their bulk properties, such as size, density, electric
polarizability, etc. The next level of challenge is to separate particles that
show identical bulk properties and differ only in subtle surface features, such
as functionalization with ligands. In this work, we propose a technique to sort
and separate particles and fluid droplets that differ in surface properties. As
a dispersive medium, we use a nematic liquid crystal (LC) rather than an
isotropic fluid, which allows us to amplify the difference in surface
properties through distinct perturbations of LC order around the dispersed
particles. The particles are placed in a LC cell with spatially distorted
molecular orientation subject to an alternating current electric field. The
gradients of the molecular orientation perform two functions. First, elastic
interactions between these pre-imposed gradients and distortions around the
particles separate the particles with different surface properties in space.
Second, these pre-imposed patterns create electro-osmotic flows powered by the
electric field that transport the sorted particles to different locations thus
separating them. The demonstrated unique sorting and separation capability
opens opportunities in lab-on-a-chip, cell sorting and bio-sensing
applications
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