417 research outputs found
Performance Analysis of a System with Bursty Traffic and Adjustable Transmission Times
In this work, we consider the case where a source with bursty traffic can
adjust the transmission duration in order to increase the reliability. The
source is equipped with a queue in order to store the arriving packets. We
model the system with a discrete time Markov Chain, and we characterize the
performance in terms of service probability and average delay per packet. The
accuracy of the theoretical results is validated through simulations. This work
serves as an initial step in order to provide a framework for systems with
arbitrary arrivals and variable transmission durations and it can be utilized
for the derivation of the delay distribution and the delay violation
probability.Comment: ISWCS 201
Stable Throughput and Delay Analysis of a Random Access Network With Queue-Aware Transmission
In this work we consider a two-user and a three-user slotted ALOHA network
with multi-packet reception (MPR) capabilities. The nodes can adapt their
transmission probabilities and their transmission parameters based on the
status of the other nodes. Each user has external bursty arrivals that are
stored in their infinite capacity queues. For the two- and the three-user cases
we obtain the stability region of the system. For the two-user case we provide
the conditions where the stability region is a convex set. We perform a
detailed mathematical analysis in order to study the queueing delay by
formulating two boundary value problems (a Dirichlet and a Riemann-Hilbert
boundary value problem), the solution of which provides the generating function
of the joint stationary probability distribution of the queue size at user
nodes. Furthermore, for the two-user symmetric case with MPR we obtain a lower
and an upper bound for the average delay without explicitly computing the
generating function for the stationary joint queue length distribution. The
bounds as it is seen in the numerical results appear to be tight. Explicit
expressions for the average delay are obtained for the symmetrical model with
capture effect which is a subclass of MPR models. We also provide the optimal
transmission probability in closed form expression that minimizes the average
delay in the symmetric capture case. Finally, we evaluate numerically the
presented theoretical results.Comment: Submitted for journal publicatio
Throughput of a Cognitive Radio Network under Congestion Constraints: A Network-Level Study
In this paper we analyze a cognitive radio network with one primary and one
secondary transmitter, in which the primary transmitter has bursty arrivals
while the secondary node is assumed to be saturated (i.e. always has a packet
waiting to be transmitted). The secondary node transmits in a cognitive way
such that it does not impede the performance of the primary node. We assume
that the receivers have multipacket reception (MPR) capabilities and that the
secondary node can take advantage of the MPR capability by transmitting
simultaneously with the primary under certain conditions. We obtain analytical
expressions for the stationary distribution of the primary node queue and we
also provide conditions for its stability. Finally, we provide expressions for
the aggregate throughput of the network as well as for the throughput at the
secondary node.Comment: Presented at CROWNCOM 201
On the preservation of unitarity during black hole evolution and information extraction from its interior
For more than 30 years the discovery that black holes radiate like black
bodies of specific temperature has triggered a multitude of puzzling questions
concerning their nature and the fate of information that goes down the black
hole during its lifetime. The most tricky issue in what is known as information
loss paradox is the apparent violation of unitarity during the
formation/evaporation process of black holes. A new idea is proposed based on
the combination of our knowledge on Hawking radiation as well as the
Einstein-Podolsky-Rosen phenomenon, that could resolve the paradox and spare
physicists from the unpalatable idea that unitarity can ultimately be violated
even under special conditions.Comment: 8 pages, no figure
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