262 research outputs found
Multiuser Switched Diversity Scheduling Schemes
Multiuser switched-diversity scheduling schemes were recently proposed in
order to overcome the heavy feedback requirements of conventional opportunistic
scheduling schemes by applying a threshold-based, distributed, and ordered
scheduling mechanism. The main idea behind these schemes is that slight
reduction in the prospected multiuser diversity gains is an acceptable
trade-off for great savings in terms of required channel-state-information
feedback messages. In this work, we characterize the achievable rate region of
multiuser switched diversity systems and compare it with the rate region of
full feedback multiuser diversity systems. We propose also a novel proportional
fair multiuser switched-based scheduling scheme and we demonstrate that it can
be optimized using a practical and distributed method to obtain the feedback
thresholds. We finally demonstrate by numerical examples that
switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the
ultimate network capacity of full feedback systems in Rayleigh fading
conditions.Comment: Accepted at IEEE Transactions on Communications, to appear 2012,
funded by NPRP grant 08-577-2-241 from QNR
Polymer Maximum Drag Reduction: A Unique Transitional State
The upper bound of polymer drag reduction is identified as a unique
transitional state between laminar and turbulent flow corresponding to the
onset of the nonlinear breakdown of flow instabilities
Joint Power and Resource Allocation for Block-Fading Relay-Assisted Broadcast Channels
We provide the solution for optimizing the power and resource allocation over
block-fading relay-assisted broadcast channels in order to maximize the long
term average achievable rates region of the users. The problem formulation
assumes regenerative (repetition coding) decode-and-forward (DF) relaying
strategy, long-term average total transmitted power constraint, orthogonal
multiplexing of the users messages within the channel blocks, possibility to
use a direct transmission (DT) mode from the base station to the user terminal
directly or a relaying (DF) transmission mode, and partial channel state
information. We show that our optimization problem can be transformed into an
equivalent "no-relaying" broadcast channel optimization problem with each
actual user substituted by two virtual users having different channel qualities
and multiplexing weights. The proposed power and resource allocation strategies
are expressed in closed-form that can be applied practically in centralized
relay-assisted wireless networks. Furthermore, we show by numerical examples
that our scheme enlarges the achievable rates region significantly.Comment: IEEE Transactions on Wireless Communications, June 201
Thresholds Optimization for One-Bit Feedback Multi-User Scheduling
We propose a new one-bit feedback scheme with scheduling decision based on
the maximum expected weighted rate. We show the concavity of the -user case
and provide the optimal solution which achieves the maximum weighted rate of
the users. For the general asymmetric M-user case, we provide a heuristic
method to achieve the maximum expected weighted rate. We show that the sum rate
of our proposed scheme is very close to the sum rate of the full channel state
information case, which is the upper bound performance
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