16,099 research outputs found
Two-Way Training for Discriminatory Channel Estimation in Wireless MIMO Systems
This work examines the use of two-way training to efficiently discriminate
the channel estimation performances at a legitimate receiver (LR) and an
unauthorized receiver (UR) in a multiple-input multiple-output (MIMO) wireless
system. This work improves upon the original discriminatory channel estimation
(DCE) scheme proposed by Chang et al where multiple stages of feedback and
retraining were used. While most studies on physical layer secrecy are under
the information-theoretic framework and focus directly on the data transmission
phase, studies on DCE focus on the training phase and aim to provide a
practical signal processing technique to discriminate between the channel
estimation performances at LR and UR. A key feature of DCE designs is the
insertion of artificial noise (AN) in the training signal to degrade the
channel estimation performance at UR. To do so, AN must be placed in a
carefully chosen subspace based on the transmitter's knowledge of LR's channel
in order to minimize its effect on LR. In this paper, we adopt the idea of
two-way training that allows both the transmitter and LR to send training
signals to facilitate channel estimation at both ends. Both reciprocal and
non-reciprocal channels are considered and a two-way DCE scheme is proposed for
each scenario. {For mathematical tractability, we assume that all terminals
employ the linear minimum mean square error criterion for channel estimation.
Based on the mean square error (MSE) of the channel estimates at all
terminals,} we formulate and solve an optimization problem where the optimal
power allocation between the training signal and AN is found by minimizing the
MSE of LR's channel estimate subject to a constraint on the MSE achievable at
UR. Numerical results show that the proposed DCE schemes can effectively
discriminate between the channel estimation and hence the data detection
performances at LR and UR.Comment: 1
On the Evolution of Ion Bunch Profile in the Presence of Longitudinal Coherent Electron Cooling
In the presence of longitudinal coherent electron cooling, the evolution of
the line-density profile of a circulating ion bunch can be described by the 1-D
Fokker-Planck equation. We show that, in the absence of diffusion, the 1-D
equation can be solved analytically for certain dependence of cooling force on
the synchrotron amplitude. For more general cases with arbitrary diffusion, we
solved the 1-D Fokker-Planck equation numerically and the numerical solutions
have been compared with results from macro-particle tracking
Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections
We estimate the decay rates of ,
, and ,
, by taking into account both relativistic and
QCD radiative corrections. The decay amplitudes are derived in the
Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired
interquark potential are used to calculate the wave functions and decay widths
for these states. We find that the relativistic correction to the
ratio is negative and tends to compensate the positive contribution from
the QCD radiative correction. Our estimate gives and ,
which are smaller than their nonrelativistic values. The hadronic widths
and are then indicated accordingly to the first order
QCD radiative correction, if . The decay widths for
states are also estimated. We show that when making the assmption
that the quarks are on their mass shells our expressions for the decay widths
will become identical with that in the NRQCD theory to the next to leading
order of and .Comment: 14 pages LaTex (2 figures included
Detecting Extra Dimension by Helium-like Ions
Considering that gravitational force might deviate from Newton's
inverse-square law and become much stronger in small scale, we present a method
to detect the possible existence of extra dimensions in the ADD model. By
making use of an effective variational wave function, we obtain the
nonrelativistic ground energy of a helium atom and its isoelectronic sequence.
Based on these results, we calculate gravity correction of the ADD model. Our
calculation may provide a rough estimation about the magnitude of the
corresponding frequencies which could be measured in later experiments.Comment: 8 pages, no figures, accepted by Mod. Phys. Lett.
Phenomenology of Dependence of Quarkonium Production in Proton-Nucleus Interactions
We present a phenomenological study of the dependence of quarkonium
production in high energy proton-nucleus collisions. The \xf~dependence of
comover contributions is introduced to account for the observed quarkonium
suppression at low . Combining comover contributions, nuclear shadowing
effect, energy loss mechanism and nuclear absorption together we reproduce the
overall \xf~dependence of E772/E789 data.Comment: 11 pages(Latex), 4 uuencoded figure
Coherent Beam-Beam Tune Shift of Unsymmetrical Beam-Beam Interactions with Large Beam-Beam Parameter
Coherent beam-beam tune shift of unsymmetrical beam-beam interactions was
studied experimentally and numerically in HERA where the lepton beam has a very
large beam-beam parameter (up to ). Unlike the symmetrical case of
beam-beam interactions, the ratio of the coherent and incoherent beam-beam tune
shift in this unsymmetrical case of beam-beam interactions was found to
decrease monotonically with increase of the beam-beam parameter. The results of
self-consistent beam-beam simulation, the linearized Vlasov equation, and the
rigid-beam model were compared with the experimental measurement. It was found
that the coherent beam-beam tune shifts measured in the experiment and
calculated in the simulation agree remarkably well but they are much smaller
than those calculated by the linearized Vlasov equation with the single-mode
approximation or the rigid-beam model. The study indicated that the single-mode
approximation in the linearization of Vlasov equation is not valid in the case
of unsymmetrical beam-beam interactions. The rigid-beam model is valid only
with a small beam-beam parameter in the case of unsymmetrical beam-beam
interactions.Comment: 32 pages, 13 figure
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