22,629 research outputs found
Amplified biochemical oscillations in cellular systems
We describe a mechanism for pronounced biochemical oscillations, relevant to
microscopic systems, such as the intracellular environment. This mechanism
operates for reaction schemes which, when modeled using deterministic rate
equations, fail to exhibit oscillations for any values of rate constants. The
mechanism relies on amplification of the underlying stochasticity of reaction
kinetics within a narrow window of frequencies. This amplification allows
fluctuations to beat the central limit theorem, having a dominant effect even
though the number of molecules in the system is relatively large. The mechanism
is quantitatively studied within simple models of self-regulatory gene
expression, and glycolytic oscillations.Comment: 35 pages, 6 figure
Fairness Evaluation in Cooperative Hybrid Cellular Systems
Many method has been applied previously to improve the fairness of a wireless communication system. In this paper, we propose using hybrid schemes, where more than one transmission scheme are used in one system, to achieve this objective. These schemes consist of cooperative transmission schemes, maximal ratio transmission and interference alignment, and non-cooperative schemes, orthogonal and non-orthogonal schemes used alongside and in combinations in the same system to improve the fairness. We provide different weight calculation methods to vary the output of the fairness problem. We show the solution of the radio resource allocation problem for the transmission schemes used. Finally, simulation results is provided to show fairness achieved, in terms of Jain's fairness index, by applying the hybrid schemes proposed and the different weight calculation methods at different inter-site distances
Modeling multi-cellular systems using sub-cellular elements
We introduce a model for describing the dynamics of large numbers of
interacting cells. The fundamental dynamical variables in the model are
sub-cellular elements, which interact with each other through phenomenological
intra- and inter-cellular potentials. Advantages of the model include i)
adaptive cell-shape dynamics, ii) flexible accommodation of additional
intra-cellular biology, and iii) the absence of an underlying grid. We present
here a detailed description of the model, and use successive mean-field
approximations to connect it to more coarse-grained approaches, such as
discrete cell-based algorithms and coupled partial differential equations. We
also discuss efficient algorithms for encoding the model, and give an example
of a simulation of an epithelial sheet. Given the biological flexibility of the
model, we propose that it can be used effectively for modeling a range of
multi-cellular processes, such as tumor dynamics and embryogenesis.Comment: 20 pages, 4 figure
Performance limits for FDMA cellular systems described by hypergraphs
The authors present some preliminary material about hypergraphs, including a discussion of what they call random hypergraph multicolorings, a notion which is central to the analysis of frequency-assignment algorithms. They show that for any frequency-assignment algorithm, the carried traffic function must satisfy T(r)⩽T_0(r), where T_0(r) is a simple function that can be computed by linear programming. They give an asymptotic analysis of a class of 'fixed' frequency-assignment algorithms, and show that in the limit as n→∞, these algorithms achieve carried traffic functions that are at least as large as T_1( r), another simple function that can be computed by linear programming. They show that T_0(r)=T_1(r). This common value, denoted by T_(H,p)(r) is the function referred to above. They also describe some of the most important properties of the function TH,p(r), and identify the 'most favorable' traffic patterns for a given hypergraph H
milliProxy: a TCP Proxy Architecture for 5G mmWave Cellular Systems
TCP is the most widely used transport protocol in the internet. However, it
offers suboptimal performance when operating over high bandwidth mmWave links.
The main issues introduced by communications at such high frequencies are (i)
the sensitivity to blockage and (ii) the high bandwidth fluctuations due to
Line of Sight (LOS) to Non Line of Sight (NLOS) transitions and vice versa. In
particular, TCP has an abstract view of the end-to-end connection, which does
not properly capture the dynamics of the wireless mmWave link. The consequence
is a suboptimal utilization of the available resources. In this paper we
propose a TCP proxy architecture that improves the performance of TCP flows
without any modification at the remote sender side. The proxy is installed in
the Radio Access Network, and exploits information available at the gNB in
order to maximize throughput and minimize latency.Comment: 7 pages, 6 figures, 2 tables, presented at the 2017 51st Asilomar
Conference on Signals, Systems and Computers, Pacific Grove, CA, 201
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
Two-Stage Subspace Constrained Precoding in Massive MIMO Cellular Systems
We propose a subspace constrained precoding scheme that exploits the spatial
channel correlation structure in massive MIMO cellular systems to fully unleash
the tremendous gain provided by massive antenna array with reduced channel
state information (CSI) signaling overhead. The MIMO precoder at each base
station (BS) is partitioned into an inner precoder and a Transmit (Tx) subspace
control matrix. The inner precoder is adaptive to the local CSI at each BS for
spatial multiplexing gain. The Tx subspace control is adaptive to the channel
statistics for inter-cell interference mitigation and Quality of Service (QoS)
optimization. Specifically, the Tx subspace control is formulated as a QoS
optimization problem which involves an SINR chance constraint where the
probability of each user's SINR not satisfying a service requirement must not
exceed a given outage probability. Such chance constraint cannot be handled by
the existing methods due to the two stage precoding structure. To tackle this,
we propose a bi-convex approximation approach, which consists of three key
ingredients: random matrix theory, chance constrained optimization and
semidefinite relaxation. Then we propose an efficient algorithm to find the
optimal solution of the resulting bi-convex approximation problem. Simulations
show that the proposed design has significant gain over various baselines.Comment: 13 pages, accepted by IEEE Transactions on Wireless Communication
- …