697 research outputs found
Blind Estimation of Multiple Carrier Frequency Offsets
Multiple carrier-frequency offsets (CFO) arise in a distributed antenna
system, where data are transmitted simultaneously from multiple antennas. In
such systems the received signal contains multiple CFOs due to mismatch between
the local oscillators of transmitters and receiver. This results in a
time-varying rotation of the data constellation, which needs to be compensated
for at the receiver before symbol recovery. This paper proposes a new approach
for blind CFO estimation and symbol recovery. The received base-band signal is
over-sampled, and its polyphase components are used to formulate a virtual
Multiple-Input Multiple-Output (MIMO) problem. By applying blind MIMO system
estimation techniques, the system response is estimated and used to
subsequently transform the multiple CFOs estimation problem into many
independent single CFO estimation problems. Furthermore, an initial estimate of
the CFO is obtained from the phase of the MIMO system response. The Cramer-Rao
Lower bound is also derived, and the large sample performance of the proposed
estimator is compared to the bound.Comment: To appear in the Proceedings of the 18th Annual IEEE International
Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC),
Athens, Greece, September 3-7, 200
Blind identification of possibly under-determined convolutive MIMO systems
Blind identi¯cation of a Linear Time Invariant (LTI) Multiple-Input Multiple-Output (MIMO) system is of great importance in many applications, such as speech processing, multi-access communication, multi-sensor sonar/radar systems, and biomedical applications. The objective of blind identi¯cation for a MIMO system is to identify an unknown system, driven by Ni unobservable inputs, based on the No system outputs. We ¯rst present a novel blind approach for the identi¯cation of a over-determined (No ¸ Ni) MIMO system driven by white, mutually independent unobservable inputs. Samples of the system frequency response are obtained based on Parallel Factorization (PARAFAC) of three- or four-way tensors constructed respectively based on third- or fourth-order cross-spectra of the system outputs. We show that the information available in the higher-order spectra allows for the system response to be identi¯ed up to a constant scaling and permutation ambiguities and a linear phase ambiguity. Important features of the proposed approaches are that they do not require channel length information, need no phase unwrapping, and unlike the majority of existing methods, need no pre-whitening of the system outputs.While several methods have been proposed to blindly identify over-determined convolutive MIMO systems, very scarce results exist for under-determined (No < Ni) case, all of which refer to systems that either have some special structure, or special No, Ni values. We propose a novel approach for blind identi¯cation of under-determined convolutive MIMO systems of general dimensions. As long as min(No;Ni) ¸ 2, we can always ¯nd the appropriate order of statistics that guarantees identi¯ability of the system response within trivial ambiguities. We provide the description of the class of identi¯able MIMO systems for a certain order of statistics K, and an algorithm to reach the solution.Finally we propose a novel approach for blind identi¯cation and symbol recovery of a distributed antenna system with multiple carrier-frequency o®sets (CFO), arising due to mismatch between the oscillators of transmitters and receivers. The received base-band signal is over-sampled, and its polyphase components are used to formulate a virtual MIMO problem. By applying blind MIMO system estimation techniques, the system response is estimated and used to subsequently decouple the users and transform the multiple CFOs estimation problem into a set of independent single CFO estimation problems.Ph.D., Electrical Engineering -- Drexel University, 200
Distinguishing technicolor models via tt-bar productions at polarized photon colliders
We study top quark pair productions at a polarized photon collider from an
e(+)e(-) linear collider (LC) in various improved technicolor model, namely,
the one-family walking technicolor model, the top-color-assisted technicolor
model, and the top-color-assisted multiscale technicolor model. Recent
constraint on the top-pion mass from the precision data of R(b) is considered.
It is shown that, considering only the statistical errors, a polarized photon
collider from a 500 GeV LC with an integrated luminosity of 500 inverse fb is
sufficient for distinguishing the three improved technicolor models
experimentally.Comment: 7 pages, 6 figures, to appear in Physical Review
Blind, MIMO system estimation based on PARAFAC decomposition of higher order output tensors
IEEE Transactions on Signal Processing, 54(11): pp. 4156-4168.We present a novel framework for the identification of
a multiple-input multiple-output (MIMO) system driven by white,
mutually independent unobservable inputs. Samples of the system
frequency response are obtained based on parallel factorization
(PARAFAC) of three- or four-way tensors constructed based on,
respectively, third- or fourth-order cross spectra of the system outputs.
The main difficulties in frequency-domain methods are frequency-
dependent permutation and filtering ambiguities.We show
that the information available in the higher order spectra allows
for the ambiguities to be resolved up to a constant scaling and permutation
ambiguities and a linear phase ambiguity. Important features
of the proposed approach are that it does not require channel
length information, needs no phase unwrapping, and unlike the
majority of existing methods, needs no prewhitening of the system
outputs
Physics Case for the International Linear Collider
We summarize the physics case for the International Linear Collider (ILC). We
review the key motivations for the ILC presented in the literature, updating
the projected measurement uncertainties for the ILC experiments in accord with
the expected schedule of operation of the accelerator and the results of the
most recent simulation studies.Comment: 37 pages, 12 figures, 2 tables; v2 - updates of reference
Implications of the 750 GeV gamma-gamma Resonance as a Case Study for the International Linear Collider
If the gamma-gamma resonance at 750 GeV suggested by 2015 LHC data turns out
to be a real effect, what are the implications for the physics case and upgrade
path of the International Linear Collider? Whether or not the resonance is
confirmed, this question provides an interesting case study testing the
robustness of the ILC physics case. In this note, we address this question with
two points: (1) Almost all models proposed for the new 750 GeV particle require
additional new particles with electroweak couplings. The key elements of the
500 GeV ILC physics program---precision measurements of the Higgs boson, the
top quark, and 4-fermion interactions---will powerfully discriminate among
these models. This information will be important in conjunction with new LHC
data, or alone, if the new particles accompanying the 750 GeV resonance are
beyond the mass reach of the LHC. (2) Over a longer term, the energy upgrade of
the ILC to 1 TeV already discussed in the ILC TDR will enable experiments in
gamma-gamma and e+e- collisions to directly produce and study the 750 GeV
particle from these unique initial states.Comment: 39 pages, 5 figures, 5 tables; v2: some references adde
An electric molecular motor
The computational investigations at California Institute of Technology were supported by National Science Foundation grant no. CBET-2005250 (W.-G.L. and W.A.G.).Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane , in which two cyclobis(paraquat-p-phenylene) (CBPQT4+) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop. The constitution of the loop ensures that both rings undergo highly (85%) unidirectional movement under the guidance of a flashing energy ratchet , whereas the interactions between the two rings give rise to a two-dimensional potential energy surface (PES) similar to that shown by F0F1ATP synthase . The unidirectionality is powered by an oscillating voltage or external modulation of the redox potential . Initially, we focused our attention on the homologous [2]catenane, only to find that the kinetic asymmetry was insufficient to support unidirectional movement of the sole ring. Accordingly, we incorporated a second CBPQT4+ ring to provide further symmetry breaking by interactions between the two mobile rings. This demonstration of electrically driven continual circumrotatory motion of two rings around a loop in a [3]catenane is free from the production of waste products and represents an important step towards surface-bound electric molecular motors.Publisher PDFPeer reviewe
- …