164 research outputs found
Instantly Decodable Network Coding for Real-Time Scalable Video Broadcast over Wireless Networks
In this paper, we study a real-time scalable video broadcast over wireless
networks in instantly decodable network coded (IDNC) systems. Such real-time
scalable video has a hard deadline and imposes a decoding order on the video
layers.We first derive the upper bound on the probability that the individual
completion times of all receivers meet the deadline. Using this probability, we
design two prioritized IDNC algorithms, namely the expanding window IDNC
(EW-IDNC) algorithm and the non-overlapping window IDNC (NOW-IDNC) algorithm.
These algorithms provide a high level of protection to the most important video
layer before considering additional video layers in coding decisions. Moreover,
in these algorithms, we select an appropriate packet combination over a given
number of video layers so that these video layers are decoded by the maximum
number of receivers before the deadline. We formulate this packet selection
problem as a two-stage maximal clique selection problem over an IDNC graph.
Simulation results over a real scalable video stream show that our proposed
EW-IDNC and NOW-IDNC algorithms improve the received video quality compared to
the existing IDNC algorithms
Delivery Time Reduction for Order-Constrained Applications using Binary Network Codes
Consider a radio access network wherein a base-station is required to deliver
a set of order-constrained messages to a set of users over independent erasure
channels. This paper studies the delivery time reduction problem using
instantly decodable network coding (IDNC). Motivated by time-critical and
order-constrained applications, the delivery time is defined, at each
transmission, as the number of undelivered messages. The delivery time
minimization problem being computationally intractable, most of the existing
literature on IDNC propose sub-optimal online solutions. This paper suggests a
novel method for solving the problem by introducing the delivery delay as a
measure of distance to optimality. An expression characterizing the delivery
time using the delivery delay is derived, allowing the approximation of the
delivery time minimization problem by an optimization problem involving the
delivery delay. The problem is, then, formulated as a maximum weight clique
selection problem over the IDNC graph wherein the weight of each vertex
reflects its corresponding user and message's delay. Simulation results suggest
that the proposed solution achieves lower delivery and completion times as
compared to the best-known heuristics for delivery time reduction
Throughput Maximization in Cloud Radio Access Networks using Network Coding
This paper is interested in maximizing the total throughput of cloud radio
access networks (CRANs) in which multiple radio remote heads (RRHs) are
connected to a central computing unit known as the cloud. The transmit frame of
each RRH consists of multiple radio resources blocks (RRBs), and the cloud is
responsible for synchronizing these RRBS and scheduling them to users. Unlike
previous works that consider allocating each RRB to only a single user at each
time instance, this paper proposes to mix the flows of multiple users in each
RRB using instantly decodable network coding (IDNC). The proposed scheme is
thus designed to jointly schedule the users to different RRBs, choose the
encoded file sent in each of them, and the rate at which each of them is
transmitted. Hence, the paper maximizes the throughput which is defined as the
number of correctly received bits. To jointly fulfill this objective, we design
a graph in which each vertex represents a possible user-RRB association,
encoded file, and transmission rate. By appropriately choosing the weights of
vertices, the scheduling problem is shown to be equivalent to a maximum weight
clique problem over the newly introduced graph. Simulation results illustrate
the significant gains of the proposed scheme compared to classical coding and
uncoded solutions.Comment: 7 pages, 7 figure
Bearing Capacity of Driven Open-Ended Pipe Piles in Weak Soil Formations
Steel pipe piles have been increasingly used as deep foundations for offshore or onshore structures in weak soil formations. These piles are usually open-ended and installed to their final level using suitable hammers or vibrators relying on the subsurface conditions. Simultaneously, the soil plug (SP) forms inside the employed pipe pile during driving or installation. Moreover, it affects bearing behavior and total pile resistance. The experimental tests have been performed on a single tube pile. All tube piles were tested using the well-graded sand collected from the Egyptian desert, and the sand was prepared at medium density using a raining technique. The outcomes of the model pile tests showed that the value of plug resistance in open-ended pipe pile (OEPP) is typically on the order of 50% to 70% of the total pile load of OEPP, and it is influenced by pile thickness, pile diameter, pile length, and submerged state. Simultaneously, the plugging influence of OEPP increased with increasing pile thickness and embedded pile length. However, the plugging influence decreased with increasing pile diameter. The total pile load of OEPP increased with increasing the embedded pile length. It must be noted that the influence of pile length on the total pile load is greater than the influence of pile diameter; this refers to the pile length having a significant effect on the total pile load. This is due to an increase in the influence of SP
Prediction and Verification of the Conditions Governing the Synthesis of Tailored Zeolite a for Heavy Metals Removal
Numerous experimental trials, exhaustive analytical and testing procedures are usually undertaken, to reach the appropriate conditions for synthesis of “Zeolite A”. However, it is possible to come-up with a semi quantitative approach, through modeling and optimization techniques, to define the approximate range of
initial conditions governing the preparation of a tailored zeolite with specific characteristics including silica
to alumina ratio, particle size, and cation exchange capacity to be used for the removal of heavy metals. This paper is an attempt to adopt an engineering approach essentially comprising the formulation of a mathematical model relating the characteristics of zeolite A to the synthesis conditions based on numerous
experimental published results, optimization to define the synthesis conditions required to produce specific
zeolite A , verification of this proposed approach with experimental results for preparation of tailored zeolite
A conducted at our laboratories and the assessment of its efficiency for separation of chromium (III). The
composition of the synthesized zeolite A has been as anticipated and the removal of chromium (III) has been
in agreement with the developed model. These results indicate that is possible to adopt this approach in a
generic manner to select the optimum synthesis conditions for the preparation of zeolites having specific
performance characteristics
Pattern selection in the absolutely unstable regime as a nonlinear eigenvalue problem: Taylor vortices in axial flow
A unique pattern selection in the absolutely unstable regime of a driven,
nonlinear, open-flow system is analyzed: The spatiotemporal structures of
rotationally symmetric vortices that propagate downstream in the annulus of the
rotating Taylor-Couette system due to an externally imposed axial through-flow
are investigated for two different axial boundary conditions at the in- and
outlet. Unlike the stationary patterns in systems without through-flow the
spatiotemporal structures of propagating vortices are independent of parameter
history, initial conditions, and system's length. They do, however, depend on
the axial boundary conditions, the driving rate of the inner cylinder and the
through-flow rate. Our analysis of the amplitude equation shows that the
pattern selection can be described by a nonlinear eigenvalue problem with the
frequency being the eigenvalue. Approaching the border between absolute and
convective instability the eigenvalue problem becomes effectively linear and
the selection mechanism approaches that one of linear front propagation.
PACS:47.54.+r,47.20.Ky,47.32.-y,47.20.FtComment: 15 pages (LateX-file), 8 figures (Postscript
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