6 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
Optimal Receiver Design for Diffusive Molecular Communication With Flow and Additive Noise
In this paper, we perform receiver design for a diffusive molecular
communication environment. Our model includes flow in any direction, sources of
information molecules in addition to the transmitter, and enzymes in the
propagation environment to mitigate intersymbol interference. We characterize
the mutual information between receiver observations to show how often
independent observations can be made. We derive the maximum likelihood sequence
detector to provide a lower bound on the bit error probability. We propose the
family of weighted sum detectors for more practical implementation and derive
their expected bit error probability. Under certain conditions, the performance
of the optimal weighted sum detector is shown to be equivalent to a matched
filter. Receiver simulation results show the tradeoff in detector complexity
versus achievable bit error probability, and that a slow flow in any direction
can improve the performance of a weighted sum detector.Comment: 14 pages, 7 figures, 1 appendix. To appear in IEEE Transactions on
NanoBioscience (submitted July 31, 2013, revised June 18, 2014, accepted July
7, 2014
Characterizing First Arrival Position Channels: Noise Distribution and Capacity Analysis
This paper addresses two fundamental problems in diffusive molecular
communication: characterizing the first arrival position (FAP) density and
bounding the information transmission capacity of FAP channels. Previous
studies on FAP channel models, mostly captured by the density function of
noise, have been limited to specific spatial dimensions, drift directions, and
receiver geometries. In response, we propose a unified solution for identifying
the FAP density in molecular communication systems with fully-absorbing
receivers. Leveraging stochastic analysis tools, we derive a concise expression
with universal applicability, covering any spatial dimension, drift direction,
and receiver shape. We demonstrate that several existing FAP density formulas
are special cases of this innovative expression. Concurrently, we establish
explicit upper and lower bounds on the capacity of three-dimensional,
vertically-drifted FAP channels, drawing inspiration from vector Gaussian
interference channels. In the course of deriving these bounds, we unravel an
explicit analytical expression for the characteristic function of
vertically-drifted FAP noise distributions, providing a more compact
characterization compared to the density function. Notably, this expression
sheds light on a previously undiscovered weak stability property intrinsic to
vertically-drifted FAP noise distributions.Comment: 30 pages; 3 figures, 1 table; this paper is submitted to IEEE
Transactions on Communication