82,187 research outputs found
Full-Duplex Systems Using Multi-Reconfigurable Antennas
Full-duplex systems are expected to achieve 100% rate improvement over
half-duplex systems if the self-interference signal can be significantly
mitigated. In this paper, we propose the first full-duplex system utilizing
Multi-Reconfigurable Antenna (MRA) with ?90% rate improvement compared to
half-duplex systems. MRA is a dynamically reconfigurable antenna structure,
that is capable of changing its properties according to certain input
configurations. A comprehensive experimental analysis is conducted to
characterize the system performance in typical indoor environments. The
experiments are performed using a fabricated MRA that has 4096 configurable
radiation patterns. The achieved MRA-based passive self-interference
suppression is investigated, with detailed analysis for the MRA training
overhead. In addition, a heuristic-based approach is proposed to reduce the MRA
training overhead. The results show that at 1% training overhead, a total of
95dB self-interference cancellation is achieved in typical indoor environments.
The 95dB self-interference cancellation is experimentally shown to be
sufficient for 90% full-duplex rate improvement compared to half-duplex
systems.Comment: Submitted to IEEE Transactions on Wireless Communication
On the probability distribution function of small scale interplanetary magnetic field fluctuations
In spite of a large number of papers dedicated to study MHD turbulence in the
solar wind there are still some simple questions which have never been
sufficiently addressed like: a)do we really know how the magnetic field vector
orientation fluctuates in space? b) what is the statistics followed by the
orientation of the vector itself? c) does the statistics change as the wind
expands into the interplanetary space? A better understanding of these points
can help us to better characterize the nature of interplanetary fluctuations
and can provide useful hints to investigators who try to numerically simulate
MHD turbulence. This work follows a recent paper presented by the same authors.
This work follows a recent paper presented by some of the authors which shows
that these fluctuations might resemble a sort of random walk governed by a
Truncated Leevy Flight statistics. However, the limited statistics used in that
paper did not allow final conclusions but only speculative hypotheses. In this
work we aim to address the same problem using a more robust statistics which on
one hand forces us not to consider velocity fluctuations but, on the other hand
allows us to establish the nature of the governing statistics of magnetic
fluctuations with more confidence. In addition, we show how features similar to
those found in the present statistical analysis for the fast speed streams of
solar wind, are qualitatively recovered in numerical simulations of the
parametric instability. This might offer an alternative viewpoint for
interpreting the questions raised above.Comment: 25pag, 20 jpg small size figures. In press on "ANnales Geophysicae"
(September 2004
Analytical Model for Outdoor Millimeter Wave Channels using Geometry-Based Stochastic Approach
The severe bandwidth shortage in conventional microwave bands has spurred the
exploration of the millimeter wave (MMW) spectrum for the next revolution in
wireless communications. However, there is still lack of proper channel
modeling for the MMW wireless propagation, especially in the case of outdoor
environments. In this paper, we develop a geometry-based stochastic channel
model to statistically characterize the effect of all the first-order
reflection paths between the transmitter and receiver. These first-order
reflections are generated by the single-bounce of signals reflected from the
walls of randomly distributed buildings. Based on this geometric model, a
closed-form expression for the power delay profile (PDP) contributed by all the
first-order reflection paths is obtained and then used to evaluate their impact
on the MMW outdoor propagation characteristics. Numerical results are provided
to validate the accuracy of the proposed model under various channel parameter
settings. The findings in this paper provide a promising step towards more
complex and practical MMW propagation channel modeling.Comment: Accepted to appear in IEEE Transactions on Vehicular Technolog
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