6,019 research outputs found
A Queueing Characterization of Information Transmission over Block Fading Rayleigh Channels in the Low SNR
Unlike the AWGN (additive white gaussian noise) channel, fading channels
suffer from random channel gains besides the additive Gaussian noise. As a
result, the instantaneous channel capacity varies randomly along time, which
makes it insufficient to characterize the transmission capability of a fading
channel using data rate only. In this paper, the transmission capability of a
buffer-aided block Rayleigh fading channel is examined by a constant rate input
data stream, and reflected by several parameters such as the average queue
length, stationary queue length distribution, packet delay and overflow
probability. Both infinite-buffer model and finite-buffer model are considered.
Taking advantage of the memoryless property of the service provided by the
channel in each block in the the low SNR (signal-to-noise ratio) regime, the
information transmission over the channel is formulated as a \textit{discrete
time discrete state} queueing problem. The obtained results show that
block fading channels are unable to support a data rate close to their ergodic
capacity, no matter how long the buffer is, even seen from the application
layer. For the finite-buffer model, the overflow probability is derived with
explicit expression, and is shown to decrease exponentially when buffer size is
increased, even when the buffer size is very small.Comment: 29 pages, 11 figures. More details on the proof of Theorem 1 and
proposition 1 can be found in "Queueing analysis for block fading Rayleigh
channels in the low SNR regime ", IEEE WCSP 2013.It has been published by
IEEE Trans. on Veh. Technol. in Feb. 201
Approximate IPA: Trading Unbiasedness for Simplicity
When Perturbation Analysis (PA) yields unbiased sensitivity estimators for
expected-value performance functions in discrete event dynamic systems, it can
be used for performance optimization of those functions. However, when PA is
known to be unbiased, the complexity of its estimators often does not scale
with the system's size. The purpose of this paper is to suggest an alternative
approach to optimization which balances precision with computing efforts by
trading off complicated, unbiased PA estimators for simple, biased approximate
estimators. Furthermore, we provide guidelines for developing such estimators,
that are largely based on the Stochastic Flow Modeling framework. We suggest
that if the relative error (or bias) is not too large, then optimization
algorithms such as stochastic approximation converge to a (local) minimum just
like in the case where no approximation is used. We apply this approach to an
example of balancing loss with buffer-cost in a finite-buffer queue, and prove
a crucial upper bound on the relative error. This paper presents the initial
study of the proposed approach, and we believe that if the idea gains traction
then it may lead to a significant expansion of the scope of PA in optimization
of discrete event systems.Comment: 8 pages, 8 figure
Heavy traffic analysis of open processing networks with complete resource pooling: asymptotic optimality of discrete review policies
We consider a class of open stochastic processing networks, with feedback
routing and overlapping server capabilities, in heavy traffic. The networks we
consider satisfy the so-called complete resource pooling condition and
therefore have one-dimensional approximating Brownian control problems.
We propose a simple discrete review policy for controlling such networks.
Assuming 2+\epsilon moments on the interarrival times and processing times,
we provide a conceptually simple proof of asymptotic optimality of the proposed
policy.Comment: Published at http://dx.doi.org/10.1214/105051604000000495 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Stochastic decomposition in discrete-time queues with generalized vacations and applications
For several specific queueing models with a vacation policy, the stationary system occupancy at the beginning of a rantdom slot is distributed as the sum of two independent random variables. One of these variables is the stationary number of customers in an equivalent queueing system with no vacations. For models in continuous time with Poissonian arrivals, this result is well-known, and referred to as stochastic decomposition, with proof provided by Fuhrmann and Cooper. For models in discrete time, this result received less attention, with no proof available to date. In this paper, we first establish a proof of the decomposition result in discrete time. When compared to the proof in continuous time, conditions for the proof in discrete time are somewhat more general. Second, we explore four different examples: non-preemptive proirity systems, slot-bound priority systems, polling systems, and fiber delay line (FDL) buffer systems. The first two examples are known results from literature that are given here as an illustration. The third is a new example, and the last one (FDL buffer systems) shows new results. It is shown that in some cases the queueing analysis can be considerably simplified using this property
Performance of the sleep-mode mechanism of the new IEEE 802.16m proposal for correlated downlink traffic
There is a considerable interest nowadays in making wireless telecommunication more energy-efficient. The sleep-mode mechanism in WiMAX (IEEE 802.16e) is one of such energy saving measures. Recently, Samsung proposed some modifications on the sleep-mode mechanism, scheduled to appear in the forthcoming IEEE 802.16m standard, aimed at minimizing the signaling overhead. In this work, we present a performance analysis of this proposal and clarify the differences with the standard mechanism included in IEEE 802.16e. We also propose some special algorithms aimed at reducing the computational complexity of the analysis
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