911 research outputs found
A Genetic Algorithm Based Finger Selection Scheme for UWB MMSE Rake Receivers
Due to a large number of multipath components in a typical ultra wideband
(UWB) system, selective Rake (SRake) receivers, which combine energy from a
subset of multipath components, are commonly employed. In order to optimize
system performance, an optimal selection of multipath components to be employed
at fingers of an SRake receiver needs to be considered. In this paper, this
finger selection problem is investigated for a minimum mean square error (MMSE)
UWB SRake receiver. Since the optimal solution is NP hard, a genetic algorithm
(GA) based iterative scheme is proposed, which can achieve near-optimal
performance after a reasonable number of iterations. Simulation results are
presented to compare the performance of the proposed finger selection algorithm
with those of the conventional and optimal schemes.Comment: To appear in the Proc. IEEE International Conference on Ultrawideband
(ICU-2005
Auction-Based Distributed Resource Allocation for Cooperation Transmission in Wireless Networks
Cooperative transmission can greatly improve communication system performance
by taking advantage of the broadcast nature of wireless channels. Most previous
work on resource allocation for cooperation transmission is based on
centralized control. In this paper, we propose two share auction mechanisms,
the SNR auction and the power auction, to distributively coordinate the
resource allocation among users. We prove the existence, uniqueness and
effectiveness of the auction results. In particular, the SNR auction leads to a
fair resource allocation among users, and the power auction achieves a solution
that is close to the efficient allocation.Comment: To appear in the Proceedings of the IEEE IEEE Global Communications
Conference (GLOBECOM), Washington, DC, November 26 - 30, 200
Auction-based Resource Allocation for Multi-relay Asynchronous Cooperative Networks
Resource allocation is considered for cooperative transmissions in
multiple-relay wireless networks. Two auction mechanisms, SNR auctions and
power auctions, are proposed to distributively coordinate the allocation of
power among multiple relays. In the SNR auction, a user chooses the relay with
the lowest weighted price. In the power auction, a user may choose to use
multiple relays simultaneously, depending on the network topology and the
relays' prices. Sufficient conditions for the existence (in both auctions) and
uniqueness (in the SNR auction) of the Nash equilibrium are given. The fairness
of the SNR auction and efficiency of the power auction are further discussed.
It is also proven that users can achieve the unique Nash equilibrium
distributively via best response updates in a completely asynchronous manner.Comment: To appear in the Proceedings of the 2008 IEEE International
Conference on Acoustics, Speech and Signal Processing, Las Vegas, NV, March
30 to April 4, 200
Optimal and Suboptimal Finger Selection Algorithms for MMSE Rake Receivers in Impulse Radio Ultra-Wideband Systems
Convex relaxations of the optimal finger selection algorithm are proposed for
a minimum mean square error (MMSE) Rake receiver in an impulse radio
ultra-wideband system. First, the optimal finger selection problem is
formulated as an integer programming problem with a non-convex objective
function. Then, the objective function is approximated by a convex function and
the integer programming problem is solved by means of constraint relaxation
techniques. The proposed algorithms are suboptimal due to the approximate
objective function and the constraint relaxation steps. However, they can be
used in conjunction with the conventional finger selection algorithm, which is
suboptimal on its own since it ignores the correlation between multipath
components, to obtain performances reasonably close to that of the optimal
scheme that cannot be implemented in practice due to its complexity. The
proposed algorithms leverage convexity of the optimization problem
formulations, which is the watershed between `easy' and `difficult'
optimization problems.Comment: To appear in IEEE Wireless Communications and Networking Conference
(WCNC 2005), New Orleans, LA, March 13-17, 200
A Non-Cooperative Power Control Game for Multi-Carrier CDMA Systems
In this work, a non-cooperative power control game for multi-carrier CDMA
systems is proposed. In the proposed game, each user needs to decide how much
power to transmit over each carrier to maximize its overall utility. The
utility function considered here measures the number of reliable bits
transmitted per joule of energy consumed. It is shown that the user's utility
is maximized when the user transmits only on the carrier with the best
"effective channel". The existence and uniqueness of Nash equilibrium for the
proposed game are investigated and the properties of equilibrium are studied.
Also, an iterative and distributed algorithm for reaching the equilibrium (if
it exists) is presented. It is shown that the proposed approach results in a
significant improvement in the total utility achieved at equilibrium compared
to the case in which each user maximizes its utility over each carrier
independently.Comment: To appear in Proceedings of the 2005 IEEE Wireless Communications and
Networking Conference, New Orleans, LA, March 13 - 17, 200
Lepton Flavor Violating Decays of Neutral Higgses in Extended Mirror Fermion Model
We perform the one-loop induced charged lepton flavor violating decays of the
neutral Higgses in an extended mirror fermion model with non-sterile
electroweak-scale right-handed neutrinos and a horizontal symmetry in the
lepton sector. We demonstrate that for the 125 GeV scalar there is tension
between the recent LHC result 1% and the
stringent limits on the rare processes and
or from low energy experiments.Comment: 23 pages, 3 figures. Added some of referenc
MODIS On-orbit Calibration Uncertainty Assessment
MODIS has 20 reflective solar bands (RSB) and 16 thermal emissive bands (TEB). Compared to its heritage sensors, MODIS was developed with very stringent calibration uncertainty requirements. As a result, MODIS was designed and built with a set of on-board calibrators (OBC), which allow key sensor performance parameters and on-orbit calibration coefficients to be monitored and updated. In terms of its calibration traceability, MODIS RSB calibration is reflectance based using an on-board solar diffuser (SD) and the TEB calibration is radiance based using an on-board blackbody (BB). In addition to on-orbit calibration coefficients derived from its OBC, calibration parameters determined from sensor pre-launch calibration and characterization are used in both the RSB and TEB calibration and retrieval algorithms. This paper provides a brief description of MODIS calibration methodologies and an in-depth analysis of its on-orbit calibration uncertainties. Also discussed in this paper are uncertainty contributions from individual components and differences due to Terra and Aqua MODIS instrument characteristics and on-orbit performance
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