865 research outputs found
Listen-and-Talk: Full-duplex Cognitive Radio Networks
In traditional cognitive radio networks, secondary users (SUs) typically
access the spectrum of primary users (PUs) by a two-stage "listen-before-talk"
(LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before
transmit in the second stage. In this paper, we propose a novel
"listen-and-talk" (LAT) protocol with the help of the full-duplex (FD)
technique that allows SUs to simultaneously sense and access the vacant
spectrum. Analysis of sensing performance and SU's throughput are given for the
proposed LAT protocol. And we find that due to self-interference caused by FD,
increasing transmitting power of SUs does not always benefit to SU's
throughput, which implies the existence of a power-throughput tradeoff.
Besides, though the LAT protocol suffers from self-interference, it allows
longer transmission time, while the performance of the traditional LBT protocol
is limited by channel spatial correction and relatively shorter transmission
period. To this end, we also present an adaptive scheme to improve SUs'
throughput by switching between the LAT and LBT protocols. Numerical results
are provided to verify the proposed methods and the theoretical results.Comment: in proceeding of IEEE Globecom 201
Distributed Cooperative Sensing in Cognitive Radio Networks: An Overlapping Coalition Formation Approach
Cooperative spectrum sensing has been shown to yield a significant
performance improvement in cognitive radio networks. In this paper, we consider
distributed cooperative sensing (DCS) in which secondary users (SUs) exchange
data with one another instead of reporting to a common fusion center. In most
existing DCS algorithms, the SUs are grouped into disjoint cooperative groups
or coalitions, and within each coalition the local sensing data is exchanged.
However, these schemes do not account for the possibility that an SU can be
involved in multiple cooperative coalitions thus forming overlapping
coalitions. Here, we address this problem using novel techniques from a class
of cooperative games, known as overlapping coalition formation games, and based
on the game model, we propose a distributed DCS algorithm in which the SUs
self-organize into a desirable network structure with overlapping coalitions.
Simulation results show that the proposed overlapping algorithm yields
significant performance improvements, decreasing the total error probability up
to 25% in the Q_m+Q_f criterion, the missed detection probability up to 20% in
the Q_m/Q_f criterion, the overhead up to 80%, and the total report number up
to 10%, compared with the state-of-the-art non-overlapping algorithm
Social Data Offloading in D2D-Enhanced Cellular Networks by Network Formation Games
Recently, cellular networks are severely overloaded by social-based services,
such as YouTube, Facebook and Twitter, in which thousands of clients subscribe
a common content provider (e.g., a popular singer) and download his/her content
updates all the time. Offloading such traffic through complementary networks,
such as a delay tolerant network formed by device-to-device (D2D)
communications between mobile subscribers, is a promising solution to reduce
the cellular burdens. In the existing solutions, mobile users are assumed to be
volunteers who selfishlessly deliver the content to every other user in
proximity while moving. However, practical users are selfish and they will
evaluate their individual payoffs in the D2D sharing process, which may highly
influence the network performance compared to the case of selfishless users. In
this paper, we take user selfishness into consideration and propose a network
formation game to capture the dynamic characteristics of selfish behaviors. In
the proposed game, we provide the utility function of each user and specify the
conditions under which the subscribers are guaranteed to converge to a stable
network. Then, we propose a practical network formation algorithm in which the
users can decide their D2D sharing strategies based on their historical
records. Simulation results show that user selfishness can highly degrade the
efficiency of data offloading, compared with ideal volunteer users. Also, the
decrease caused by user selfishness can be highly affected by the cost ratio
between the cellular transmission and D2D transmission, the access delays, and
mobility patterns
Listen-and-Talk: Protocol Design and Analysis for Full-duplex Cognitive Radio Networks
In traditional cognitive radio networks, secondary users (SUs) typically
access the spectrum of primary users (PUs) by a two-stage "listen-before-talk"
(LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before
transmitting in the second. However, there exist two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. In this paper, we propose a "listen-and-talk" (LAT)
protocol with the help of full-duplex (FD) technique that allows SUs to
simultaneously sense and access the vacant spectrum. Spectrum utilization
performance is carefully analyzed, with the closed-form spectrum waste ratio
and collision ratio with the PU provided. Also, regarding the secondary
throughput, we report the existence of a tradeoff between the secondary
transmit power and throughput. Based on the power-throughput tradeoff, we
derive the analytical local optimal transmit power for SUs to achieve both high
throughput and satisfying sensing accuracy. Numerical results are given to
verify the proposed protocol and the theoretical results
On the maximum likelihood estimation for progressively censored lifetimes from constant-stress and step-stress accelerated tests
In order to gather the information about the lifetime distribution of a product, a standard life testing method at normal operating conditions is not practical when the product has an extremely long lifespan. Accelerated life testing solves this difficult issue by subjecting the test units at higher stress levels than normal for quicker and more failure data. The lifetime at the design stress is then estimated through extrapolation using an appropriate regression model. Estimation of the regression parameters based on exponentially distributed lifetimes from accelerated life tests has been considered by a number of authors using numerical methods but without systematic or analytical validation. In this article, we propose an alternative approach based on a simple and easy-to-apply graphical method, which also establishes the existence and uniqueness of the maximum likelihood estimates for constant-stress and step-stress accelerated life tests under progressive censorings
A Study on the Translation Strategies of “Chinese Keywords” in International Publicity Texts From the Perspective of Eco-Translatology
This article focuses on the translation effect of Keywords to understand China in international publicity texts, with attention paid to the different translation versions of these keywords. From the perspective of “three-dimensional” (communicative, cultural, and linguistic) adaptative selection and transformation in eco-translatology, the translation effect of “Chinese keywords” is mainly analyzed, and translations from different periods are compared to explore the experience and inspiration of successful international publicity translations
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