158 research outputs found
On the Estimation of Channel State Transitions for Cognitive Radio Systems
Coexistence by means of shared access is a cognitive radio application. The
secondary user models the slotted primary users channel access as a Markov
process. The model parameters, i.e, the state transition probabilities
(alpha,beta) help secondary user to determine the channel occupancy, thereby
enables secondary user to rank the primary user channels. These parameters are
unknown and need to be estimated by secondary users for each channel. To do so,
the secondary users have to sense all the primary user channels in every time
slot, which is unrealistic for a large and sparsely allocated primary user
spectrum. With no other choice left, the secondary user has to sense a channel
at random time intervals and estimate the parametric information for all the
channels using the observed slots.Comment: 6 page
Cooperative Relaying in a Poisson Field of Interferers: A Diversity Order Analysis
This work analyzes the gains of cooperative relaying in interference-limited
networks, in which outages can be due to interference and fading. A stochastic
model based on point process theory is used to capture the spatial randomness
present in contemporary wireless networks. Using a modification of the
diversity order metric, the reliability gain of selection decode-and-forward is
studied for several cases. The main results are as follows: the achievable
\emph{spatial-contention} diversity order (SC-DO) is equal to one irrespective
of the type of channel which is due to the ineffectiveness of the relay in the
MAC-phase (transmit diversity). In the BC-phase (receive diversity), the SC-DO
depends on the amount of fading and spatial interference correlation. In the
absence of fading, there is a hard transition between SC-DO of either one or
two, depending on the system parameters.Comment: 5 pages, 2 figures. To be presented at ISIT 201
On the Deployment of Cognitive Relay as Underlay Systems
The objective of this paper is to extend the idea of Cognitive Relay (CR).
CR, as a secondary user, follows an underlay paradigm to endorse secondary
usage of the spectrum to the indoor devices. To seek a spatial opportunity,
i.e., deciding its transmission over the primary user channels, CR models its
deployment scenario and the movements of the primary receivers and indoor
devices. Modeling is beneficial for theoretical analysis, however it is also
important to ensure the performance of CR in a real scenario. We consider
briefly, the challenges involved while deploying a hardware prototype of such a
system.Comment: 6 pages, 7 figures, 4 tables, accepted in Proceedings of CrownCom
2014, Oulu (Finland), June 2-4, 201
Interference in Poisson Networks with Isotropically Distributed Nodes
Practical wireless networks are finite, and hence non-stationary with nodes
typically non-homo-geneously deployed over the area. This leads to a
location-dependent performance and to boundary effects which are both often
neglected in network modeling. In this work, interference in networks with
nodes distributed according to an isotropic but not necessarily stationary
Poisson point process (PPP) are studied. The resulting link performance is
precisely characterized as a function of (i) an arbitrary receiver location and
of (ii) an arbitrary isotropic shape of the spatial distribution. Closed-form
expressions for the first moment and the Laplace transform of the interference
are derived for the path loss exponents and , and simple
bounds are derived for other cases. The developed model is applied to practical
problems in network analysis: for instance, the accuracy loss due to neglecting
border effects is shown to be undesirably high within transition regions of
certain deployment scenarios. Using a throughput metric not relying on the
stationarity of the spatial node distribution, the spatial throughput locally
around a given node is characterized.Comment: This work was presented in part at ISIT 201
Interference and Throughput in Aloha-based Ad Hoc Networks with Isotropic Node Distribution
We study the interference and outage statistics in a slotted Aloha ad hoc
network, where the spatial distribution of nodes is non-stationary and
isotropic. In such a network, outage probability and local throughput depend on
both the particular location in the network and the shape of the spatial
distribution. We derive in closed-form certain distributional properties of the
interference that are important for analyzing wireless networks as a function
of the location and the spatial shape. Our results focus on path loss exponents
2 and 4, the former case not being analyzable before due to the stationarity
assumption of the spatial node distribution. We propose two metrics for
measuring local throughput in non-stationary networks and discuss how our
findings can be applied to both analysis and optimization.Comment: 5 pages, 3 figures. To appear in International Symposium on
Information Theory (ISIT) 201
Outage Capacity of Bursty Amplify-and-Forward with Incremental Relaying
We derive the outage capacity of a bursty version of the amplify-and-forward
(BAF) protocol for small signal-to-noise ratios when incremental relaying is
used. We show that the ratio between the outage capacities of BAF and the
cut-set bound is independent of the relay position and that BAF is outage
optimal for certain conditions on the target rate R. This is in contrast to
decode-and-forward with incremental relaying, where the relay location strongly
determines the performance of the cooperative protocol. We further derive the
outage capacity for a network consisting of an arbitrary number of relay nodes.
In this case the relays transmit in subsequent partitions of the overall
transmission block and the destination accumulates signal-to-noise ratio until
it is able to decode.Comment: 5 pages, 3 figures, submitted to IEEE International Symposium on
Information Theory, Austin, TX, June 13-18, 201
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