6,086 research outputs found
Cooperative Interference Control for Spectrum Sharing in OFDMA Cellular Systems
This paper studies cooperative schemes for the inter-cell interference
control in orthogonal-frequency-divisionmultiple- access (OFDMA) cellular
systems. The downlink transmission in a simplified two-cell system is examined,
where both cells simultaneously access the same frequency band using OFDMA. The
joint power and subcarrier allocation over the two cells is investigated for
maximizing their sum throughput with both centralized and decentralized
implementations. Particularly, the decentralized allocation is achieved via a
new cooperative interference control approach, whereby the two cells
independently implement resource allocation to maximize individual throughput
in an iterative manner, subject to a set of mutual interference power
constraints. Simulation results show that the proposed decentralized resource
allocation schemes achieve the system throughput close to that by the
centralized scheme, and provide substantial throughput gains over existing
schemes.Comment: To appear in ICC201
Exploiting Interference Alignment in Multi-Cell Cooperative OFDMA Resource Allocation
This paper studies interference alignment (IA) based multi-cell cooperative
resource allocation for the downlink OFDMA with universal frequency reuse.
Unlike the traditional scheme that treats subcarriers as separate dimensions
for resource allocation, the IA technique is utilized to enable
frequency-domain precoding over parallel subcarriers. In this paper, the joint
optimization of frequency-domain precoding via IA, subcarrier user selection
and power allocation is investigated for a cooperative three-cell OFDMA system
to maximize the downlink throughput. Numerical results for a simplified
symmetric channel setup reveal that the IA-based scheme achieves notable
throughput gains over the traditional scheme only when the inter-cell
interference link has a comparable strength as the direct link, and the
receiver SNR is sufficiently large. Motivated by this observation, a practical
hybrid scheme is proposed for cellular systems with heterogenous channel
conditions, where the total spectrum is divided into two subbands, over which
the IAbased scheme and the traditional scheme are applied for resource
allocation to users located in the cell-intersection region and cellnon-
intersection region, respectively. It is shown that this hybrid resource
allocation scheme flexibly exploits the downlink IA gains for OFDMA-based
cellular systems.Comment: 5 pages, 5 figures, GC2011 conferenc
A multi-phenotypic cancer model with cell plasticity
The conventional cancer stem cell (CSC) theory indicates a hierarchy of CSCs
and non-stem cancer cells (NSCCs), that is, CSCs can differentiate into NSCCs
but not vice versa. However, an alternative paradigm of CSC theory with
reversible cell plasticity among cancer cells has received much attention very
recently. Here we present a generalized multi-phenotypic cancer model by
integrating cell plasticity with the conventional hierarchical structure of
cancer cells. We prove that under very weak assumption, the nonlinear dynamics
of multi-phenotypic proportions in our model has only one stable steady state
and no stable limit cycle. This result theoretically explains the phenotypic
equilibrium phenomena reported in various cancer cell lines. Furthermore,
according to the transient analysis of our model, it is found that cancer cell
plasticity plays an essential role in maintaining the phenotypic diversity in
cancer especially during the transient dynamics. Two biological examples with
experimental data show that the phenotypic conversions from NCSSs to CSCs
greatly contribute to the transient growth of CSCs proportion shortly after the
drastic reduction of it. In particular, an interesting overshooting phenomenon
of CSCs proportion arises in three-phenotypic example. Our work may pave the
way for modeling and analyzing the multi-phenotypic cell population dynamics
with cell plasticity.Comment: 29 pages,6 figure
MICROMANIPULATOR-RESONATOR SYSTEM FOR SELECTIVE WEIGHING OF INDIVIDUAL MICROPARTICLES
Over the past decade, MEMS-based cantilever sensors have been widely used in the detection of biomolecules, environmental pollutants, chemicals and pathogens. Cantilever-based sensors rely on attachment of target entities on their surface. The attachment causes either change in surface stress or resonance frequency of the cantilever, which is detected using various schemes that range from optical to piezoelectric. The majority of these sensors rely on probabilistic attachment of multiple target entities to the sensor surface. This introduces uncertainties since the location of the adsorbed target entity can modify the signal generated by the sensor. In addition, it does not allow the measurement of individually selected target entities. The goal of this dissertation is to exploit the cantilever-based sensors\u27 mass sensing capability to develop a supermarket weight scale for the micro world: a scheme that can enable the user to pick an individual target entity and weigh only that particular entity by precisely positioning it on a micro- weight scale
- …