750 research outputs found
Energy Efficiency in MIMO Underlay and Overlay Device-to-Device Communications and Cognitive Radio Systems
This paper addresses the problem of resource allocation for systems in which
a primary and a secondary link share the available spectrum by an underlay or
overlay approach. After observing that such a scenario models both cognitive
radio and D2D communications, we formulate the problem as the maximization of
the secondary energy efficiency subject to a minimum rate requirement for the
primary user. This leads to challenging non-convex, fractional problems. In the
underlay scenario, we obtain the global solution by means of a suitable
reformulation. In the overlay scenario, two algorithms are proposed. The first
one yields a resource allocation fulfilling the first-order optimality
conditions of the resource allocation problem, by solving a sequence of easier
fractional problems. The second one enjoys a weaker optimality claim, but an
even lower computational complexity. Numerical results demonstrate the merits
of the proposed algorithms both in terms of energy-efficient performance and
complexity, also showing that the two proposed algorithms for the overlay
scenario perform very similarly, despite the different complexity.Comment: to appear in IEEE Transactions on Signal Processin
Spectrum Sharing Opportunities of Full-Duplex Systems using Improper Gaussian Signaling
Sharing the licensed spectrum of full-duplex (FD) primary users (PU) brings
strict limitations on the underlay cognitive radio operation. Particularly, the
self interference may overwhelm the PU receiver and limit the opportunity of
secondary users (SU) to access the spectrum. Improper Gaussian signaling (IGS)
has demonstrated its superiority in improving the performance of interference
channel systems. Throughout this paper, we assume a FD PU pair that uses proper
Gaussian signaling (PGS), and a half-duplex SU pair that uses IGS. The
objective is to maximize the SU instantaneous achievable rate while meeting the
PU quality-of-service. To this end, we propose a simplified algorithm that
optimizes the SU signal parameters, i.e, the transmit power and the circularity
coefficient, which is a measure of the degree of impropriety of the SU signal,
to achieve the design objective. Numerical results show the merits of adopting
IGS compared with PGS for the SU especially with the existence of week PU
direct channels and/or strong SU interference channels
Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage
With the rapid growth of demand for ever-increasing data rate, spectrum
resources have become more and more scarce. As a promising technique to
increase the efficiency of the spectrum utilization, cognitive radio (CR)
technique has the great potential to meet such a requirement by allowing
un-licensed users to coexist in licensed bands. In conventional CR systems, the
spectrum sensing is performed at the beginning of each time slot before the
data transmission. This unfortunately results in two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. To tackle these problems, in this paper we present a
new design paradigm for future CR by exploring the full-duplex (FD) techniques
to achieve the simultaneous spectrum sensing and data transmission. With FD
radios equipped at the secondary users (SUs), SUs can simultaneously sense and
access the vacant spectrum, and thus, significantly improve sensing
performances and meanwhile increase data transmission efficiency. The aim of
this article is to transform the promising conceptual framework into the
practical wireless network design by addressing a diverse set of challenges
such as protocol design and theoretical analysis. Several application scenarios
with FD enabled CR are elaborated, and key open research directions and novel
algorithms in these systems are discussed
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