140 research outputs found
On the BER of Multiple-Input Multiple-Output Underwater Wireless Optical Communication Systems
In this paper we analyze and investigate the bit error rate (BER) performance
of multiple-input multiple-output underwater wireless optical communication
(MIMO-UWOC) systems. In addition to exact BER expressions, we also obtain an
upper bound on the system BER. To effectively estimate the BER expressions, we
use Gauss-Hermite quadrature formula as well as approximation to the sum of
log-normal random variables. We confirm the accuracy of our analytical
expressions by evaluating the BER through photon-counting approach. Our
simulation results show that MIMO technique can mitigate the channel
turbulence-induced fading and consequently, can partially extend the viable
communication range, especially for channels with stronger turbulence
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
Feedback-Aware Precoding for Millimeter Wave Massive MIMO Systems
Millimeter wave (mmWave) communication is a promising solution for coping
with the ever-increasing mobile data traffic because of its large bandwidth. To
enable a sufficient link margin, a large antenna array employing directional
beamforming, which is enabled by the availability of channel state information
at the transmitter (CSIT), is required. However, CSIT acquisition for mmWave
channels introduces a huge feedback overhead due to the typically large number
of transmit and receive antennas. Leveraging properties of mmWave channels,
this paper proposes a precoding strategy which enables a flexible adjustment of
the feedback overhead. In particular, the optimal unconstrained precoder is
approximated by selecting a variable number of elements from a basis that is
constructed as a function of the transmitter array response, where the number
of selected basis elements can be chosen according to the feedback constraint.
Simulation results show that the proposed precoding scheme can provide a
near-optimal solution if a higher feedback overhead can be afforded. For a low
overhead, it can still provide a good approximation of the optimal precoder.Comment: 7 pages, 5 figures, to appear at the IEEE International Symposium on
Personal, Indoor and Mobile Radio Communications (PIMRC) 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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