777 research outputs found
Symbol Synchronization for Diffusive Molecular Communication Systems
Symbol synchronization refers to the estimation of the start of a symbol
interval and is needed for reliable detection. In this paper, we develop a
symbol synchronization framework for molecular communication (MC) systems where
we consider some practical challenges which have not been addressed in the
literature yet. In particular, we take into account that in MC systems, the
transmitter may not be equipped with an internal clock and may not be able to
emit molecules with a fixed release frequency. Such restrictions hold for
practical nanotransmitters, e.g. modified cells, where the lengths of the
symbol intervals may vary due to the inherent randomness in the availability of
food and energy for molecule generation, the process for molecule production,
and the release process. To address this issue, we propose to employ two types
of molecules, one for synchronization and one for data transmission. We derive
the optimal maximum likelihood (ML) symbol synchronization scheme as a
performance upper bound. Since ML synchronization entails high complexity, we
also propose two low-complexity synchronization schemes, namely a peak
observation-based scheme and a threshold-trigger scheme, which are suitable for
MC systems with limited computational capabilities. Our simulation results
reveal the effectiveness of the proposed synchronization~schemes and suggest
that the end-to-end performance of MC systems significantly depends on the
accuracy of symbol synchronization.Comment: This paper has been accepted for presentation at IEEE International
Conference on Communications (ICC) 201
Diffusive Molecular Communications with Reactive Signaling
This paper focuses on molecular communication (MC) systems where the
signaling molecules may participate in a reversible bimolecular reaction in the
channel. The motivation for studying these MC systems is that they can realize
the concept of constructive and destructive signal superposition, which leads
to favorable properties such as inter-symbol interference (ISI) reduction and
avoiding environmental contamination due to continuous release of molecules
into the channel. This work first derives the maximum likelihood (ML) detector
for a binary MC system with reactive signaling molecules under the assumption
that the detector has perfect knowledge of the ISI. The performance of this
genie-aided ML detector yields an upper bound on the performance of any
practical detector. In addition, two suboptimal detectors of different
complexity are proposed. The proposed ML detector as well as one of the
suboptimal detectors require the channel response (CR) of the considered MC
system. Moreover, the CR is needed for the performance evaluation of all
proposed detectors. However, analyzing MC with reactive signaling is
challenging since the underlying partial differential equations that describe
the reaction-diffusion mechanism are coupled and non-linear. Therefore, an
algorithm is developed in this paper for efficient computation of the CR to any
arbitrary transmit symbol sequence. The accuracy of this algorithm is validated
via particle-based simulation. Simulation results using the developed CR
algorithm show that the performance of the proposed suboptimal detectors can
approach that of the genie- aided ML detector. Moreover, these results show
that MC systems with reactive signaling have superior performance relative to
those with non-reactive signaling due to the reduction of ISI enabled by the
chemical reactions.Comment: This paper has been submitted to IEEE International Conference on
Communications (ICC) 201
Diffusive Mobile Molecular Communications Over Time-Variant Channels
This letter introduces a formalism for modeling time-variant channels for
diffusive molecular communication systems. In particular, we consider a fluid
environment where one transmitter nano-machine and one receiver nano-machine
are subjected to Brownian motion in addition to the diffusive motion of the
information molecules used for communication. Due to the stochastic movements
of the transmitter and receiver nano-machines, the statistics of the channel
impulse response change over time. We show that the time-variant behaviour of
the channel can be accurately captured by appropriately modifying the diffusion
coefficient of the information molecules. Furthermore, we derive an analytical
expression for evaluation of the expected error probability of a simple
detector for the considered system. The accuracy of the proposed analytical
expression is verified via particle-based simulation of the Brownian motion.Comment: 4 pages, 3 figures, 1 table. Accepted for publication in IEEE
Communications Letters (Author's comment: Manuscript submitted Jan. 19, 2017;
revised Feb. 20, 2017; accepted Feb. 22, 2017
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