4,936 research outputs found
Outage Capacity and Optimal Transmission for Dying Channels
In wireless networks, communication links may be subject to random fatal
impacts: for example, sensor networks under sudden power losses or cognitive
radio networks with unpredictable primary user spectrum occupancy. Under such
circumstances, it is critical to quantify how fast and reliably the information
can be collected over attacked links. For a single point-to-point channel
subject to a random attack, named as a \emph{dying channel}, we model it as a
block-fading (BF) channel with a finite and random delay constraint. First, we
define the outage capacity as the performance measure, followed by studying the
optimal coding length such that the outage probability is minimized when
uniform power allocation is assumed. For a given rate target and a coding
length , we then minimize the outage probability over the power allocation
vector \mv{P}_{K}, and show that this optimization problem can be cast into a
convex optimization problem under some conditions. The optimal solutions for
several special cases are discussed.
Furthermore, we extend the single point-to-point dying channel result to the
parallel multi-channel case where each sub-channel is a dying channel, and
investigate the corresponding asymptotic behavior of the overall outage
probability with two different attack models: the independent-attack case and
the -dependent-attack case. It can be shown that the overall outage
probability diminishes to zero for both cases as the number of sub-channels
increases if the \emph{rate per unit cost} is less than a certain threshold.
The outage exponents are also studied to reveal how fast the outage probability
improves over the number of sub-channels.Comment: 31 pages, 9 figures, submitted to IEEE Transactions on Information
Theor
Multi-channel Hybrid Access Femtocells: A Stochastic Geometric Analysis
For two-tier networks consisting of macrocells and femtocells, the channel
access mechanism can be configured to be open access, closed access, or hybrid
access. Hybrid access arises as a compromise between open and closed access
mechanisms, in which a fraction of available spectrum resource is shared to
nonsubscribers while the remaining reserved for subscribers. This paper focuses
on a hybrid access mechanism for multi-channel femtocells which employ
orthogonal spectrum access schemes. Considering a randomized channel assignment
strategy, we analyze the performance in the downlink. Using stochastic geometry
as technical tools, we model the distribution of femtocells as Poisson point
process or Neyman-Scott cluster process and derive the distributions of
signal-to-interference-plus-noise ratios, and mean achievable rates, of both
nonsubscribers and subscribers. The established expressions are amenable to
numerical evaluation, and shed key insights into the performance tradeoff
between subscribers and nonsubscribers. The analytical results are corroborated
by numerical simulations.Comment: This is the final version, which was accepted in IEEE Transactions on
Communication
Precoded Integer-Forcing Universally Achieves the MIMO Capacity to Within a Constant Gap
An open-loop single-user multiple-input multiple-output communication scheme
is considered where a transmitter, equipped with multiple antennas, encodes the
data into independent streams all taken from the same linear code. The coded
streams are then linearly precoded using the encoding matrix of a perfect
linear dispersion space-time code. At the receiver side, integer-forcing
equalization is applied, followed by standard single-stream decoding. It is
shown that this communication architecture achieves the capacity of any
Gaussian multiple-input multiple-output channel up to a gap that depends only
on the number of transmit antennas.Comment: to appear in the IEEE Transactions on Information Theor
On the Utility of the Inverse Gamma Distribution in Modeling Composite Fading Channels
We introduce a general approach to characterize composite fading models based on inverse gamma (IG) shadowing. We first determine to what extent the IG distribution is an adequate choice for modeling shadow fading, by means of a comprehensive test with field measurements and other distributions conventionally used for this purpose. Then, we prove that the probability density function and cumulative density function of any IG-based composite fading model are directly expressed in terms of a Laplace-domain statistic of the underlying fast fading model, and in some relevant cases, as a mixture of well-known state-of-the-art distributions. We exemplify our approach by presenting a composite IG/two-wave with diffuse power fading model, for which its statistical characterization is directly attained in a simple form.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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