22,390 research outputs found
Information Rates of ASK-Based Molecular Communication in Fluid Media
This paper studies the capacity of molecular communications in fluid media,
where the information is encoded in the number of transmitted molecules in a
time-slot (amplitude shift keying). The propagation of molecules is governed by
random Brownian motion and the communication is in general subject to
inter-symbol interference (ISI). We first consider the case where ISI is
negligible and analyze the capacity and the capacity per unit cost of the
resulting discrete memoryless molecular channel and the effect of possible
practical constraints, such as limitations on peak and/or average number of
transmitted molecules per transmission. In the case with a constrained peak
molecular emission, we show that as the time-slot duration increases, the input
distribution achieving the capacity per channel use transitions from binary
inputs to a discrete uniform distribution. In this paper, we also analyze the
impact of ISI. Crucially, we account for the correlation that ISI induces
between channel output symbols. We derive an upper bound and two lower bounds
on the capacity in this setting. Using the input distribution obtained by an
extended Blahut-Arimoto algorithm, we maximize the lower bounds. Our results
show that, over a wide range of parameter values, the bounds are close.Comment: 31 pages, 8 figures, Accepted for publication on IEEE Transactions on
Molecular, Biological, and Multi-Scale Communication
Bounds on the Capacity of ASK Molecular Communication Channels with ISI
There are now several works on the use of the additive inverse Gaussian noise
(AIGN) model for the random transit time in molecular communication~(MC)
channels. The randomness invariably causes inter-symbol interference (ISI) in
MC, an issue largely ignored or simplified. In this paper we derive an upper
bound and two lower bounds for MC based on amplitude shift keying (ASK) in
presence of ISI. The Blahut-Arimoto algorithm~(BAA) is modified to find the
input distribution of transmitted symbols to maximize the lower bounds. Our
results show that over wide parameter values the bounds are close.Comment: 7 pages, 4 figures, Accepted in IEEE GLOBECOM 201
Capacity of Molecular Channels with Imperfect Particle-Intensity Modulation and Detection
This work introduces the particle-intensity channel (PIC) as a model for
molecular communication systems and characterizes the properties of the optimal
input distribution and the capacity limits for this system. In the PIC, the
transmitter encodes information, in symbols of a given duration, based on the
number of particles released, and the receiver detects and decodes the message
based on the number of particles detected during the symbol interval. In this
channel, the transmitter may be unable to control precisely the number of
particles released, and the receiver may not detect all the particles that
arrive. We demonstrate that the optimal input distribution for this channel
always has mass points at zero and the maximum number of particles that can be
released. We then consider diffusive particle transport, derive the capacity
expression when the input distribution is binary, and show conditions under
which the binary input is capacity-achieving. In particular, we demonstrate
that when the transmitter cannot generate particles at a high rate, the optimal
input distribution is binary.Comment: Accepted at IEEE International Symposium on Information Theory (ISIT
Adaptive Molecule Transmission Rate for Diffusion Based Molecular Communication
In this paper, a simple memory limited transmitter for molecular
communication is proposed, in which information is encoded in the diffusion
rate of the molecules. Taking advantage of memory, the proposed transmitter
reduces the ISI problem by properly adjusting its diffusion rate. The error
probability of the proposed scheme is derived and the result is compared with
the lower bound on error probability of the optimum transmitter. It is shown
that the performance of introduced transmitter is near optimal (under certain
simplifications). Simplicity is the key feature of the presented communication
system: the transmitter follows a simple rule, the receiver is a simple
threshold decoder and only one type of molecule is used to convey the
information
Microgravity: A Teacher's Guide With Activities in Science, Mathematics, and Technology
The purpose of this curriculum supplement guide is to define and explain microgravity and show how microgravity can help us learn about the phenomena of our world. The front section of the guide is designed to provide teachers of science, mathematics, and technology at many levels with a foundation in microgravity science and applications. It begins with background information for the teacher on what microgravity is and how it is created. This is followed with information on the domains of microgravity science research; biotechnology, combustion science, fluid physics, fundamental physics, materials science, and microgravity research geared toward exploration. The background section concludes with a history of microgravity research and the expectations microgravity scientists have for research on the International Space Station. Finally, the guide concludes with a suggested reading list, NASA educational resources including electronic resources, and an evaluation questionnaire
The impact of an intervention to introduce malaria rapid diagnostic tests on fever case management in a high transmission setting in Uganda: A mixed-methods cluster-randomized trial (PRIME).
Rapid diagnostic tests for malaria (mRDTs) have been scaled-up widely across Africa. The PRIME study evaluated an intervention aiming to improve fever case management using mRDTs at public health centers in Uganda. A cluster-randomized trial was conducted from 2010-13 in Tororo, a high malaria transmission setting. Twenty public health centers were randomized in a 1:1 ratio to intervention or control. The intervention included training in health center management, fever case management with mRDTs, and patient-centered services; plus provision of mRDTs and artemether-lumefantrine (AL) when stocks ran low. Three rounds of Interviews were conducted with caregivers of children under five years of age as they exited health centers (N = 1400); reference mRDTs were done in children with fever (N = 1336). Health worker perspectives on mRDTs were elicited through semi-structured questionnaires (N = 49) and in-depth interviews (N = 10). The primary outcome was inappropriate treatment of malaria, defined as the proportion of febrile children who were not treated according to guidelines based on the reference mRDT. There was no difference in inappropriate treatment of malaria between the intervention and control arms (24.0% versus 29.7%, adjusted risk ratio 0.81 95\% CI: 0.56, 1.17 p = 0.24). Most children (76.0\%) tested positive by reference mRDT, but many were not prescribed AL (22.5\% intervention versus 25.9\% control, p = 0.53). Inappropriate treatment of children testing negative by reference mRDT with AL was also common (31.3\% invention vs 42.4\% control, p = 0.29). Health workers appreciated mRDTs but felt that integrating testing into practice was challenging given constraints on time and infrastructure. The PRIME intervention did not have the desired impact on inappropriate treatment of malaria for children under five. In this high transmission setting, use of mRDTs did not lead to the reductions in antimalarial prescribing seen elsewhere. Broader investment in health systems, including infrastructure and staffing, will be required to improve fever case management
Receivers for Diffusion-Based Molecular Communication: Exploiting Memory and Sampling Rate
In this paper, a diffusion-based molecular communication channel between two
nano-machines is considered. The effect of the amount of memory on performance
is characterized, and a simple memory-limited decoder is proposed and its
performance is shown to be close to that of the best possible imaginable
decoder (without any restriction on the computational complexity or its
functional form), using Genie-aided upper bounds. This effect is specialized
for the case of Molecular Concentration Shift Keying; it is shown that a
four-bits memory achieved nearly the same performance as infinite memory. Then
a general class of threshold decoders is considered and shown not to be optimal
for Poisson channel with memory, unless SNR is higher than a value specified in
the paper. Another contribution is to show that receiver sampling at a rate
higher than the transmission rate, i.e., a multi-read system, can significantly
improve the performance. The associated decision rule for this system is shown
to be a weighted sum of the samples during each symbol interval. The
performance of the system is analyzed using the saddle point approximation. The
best performance gains are achieved for an oversampling factor of three.Comment: Submitted to JSA
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