3,426 research outputs found
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
RF-Powered Cognitive Radio Networks: Technical Challenges and Limitations
The increasing demand for spectral and energy efficient communication
networks has spurred a great interest in energy harvesting (EH) cognitive radio
networks (CRNs). Such a revolutionary technology represents a paradigm shift in
the development of wireless networks, as it can simultaneously enable the
efficient use of the available spectrum and the exploitation of radio frequency
(RF) energy in order to reduce the reliance on traditional energy sources. This
is mainly triggered by the recent advancements in microelectronics that puts
forward RF energy harvesting as a plausible technique in the near future. On
the other hand, it is suggested that the operation of a network relying on
harvested energy needs to be redesigned to allow the network to reliably
function in the long term. To this end, the aim of this survey paper is to
provide a comprehensive overview of the recent development and the challenges
regarding the operation of CRNs powered by RF energy. In addition, the
potential open issues that might be considered for the future research are also
discussed in this paper.Comment: 8 pages, 2 figures, 1 table, Accepted in IEEE Communications Magazin
Sensing-Throughput Tradeoff for Interweave Cognitive Radio System: A Deployment-Centric Viewpoint
Secondary access to the licensed spectrum is viable only if interference is
avoided at the primary system. In this regard, different paradigms have been
conceptualized in the existing literature. Of these, Interweave Systems (ISs)
that employ spectrum sensing have been widely investigated. Baseline models
investigated in the literature characterize the performance of IS in terms of a
sensing-throughput tradeoff, however, this characterization assumes the
knowledge of the involved channels at the secondary transmitter, which is
unavailable in practice. Motivated by this fact, we establish a novel approach
that incorporates channel estimation in the system model, and consequently
investigate the impact of imperfect channel estimation on the performance of
the IS. More particularly, the variation induced in the detection probability
affects the detector's performance at the secondary transmitter, which may
result in severe interference at the primary users. In this view, we propose to
employ average and outage constraints on the detection probability, in order to
capture the performance of the IS. Our analysis reveals that with an
appropriate choice of the estimation time determined by the proposed model, the
degradation in performance of the IS can be effectively controlled, and
subsequently the achievable secondary throughput can be significantly enhanced.Comment: 13 pages, 10 figures, Accepted to be published in IEEE Transactions
on Wireless Communication
Cooperation and Underlay Mode Selection in Cognitive Radio Network
In this research, we proposes a new method for cooperation and underlay mode
selection in cognitive radio networks. We characterize the maximum achievable
throughput of our proposed method of hybrid spectrum sharing. Hybrid spectrum
sharing is assumed where the Secondary User (SU) can access the Primary User
(PU) channel in two modes, underlay mode or cooperative mode with admission
control. In addition to access the channel in the overlay mode, secondary user
is allowed to occupy the channel currently occupied by the primary user but
with small transmission power. Adding the underlay access modes attains more
opportunities to the secondary user to transmit data. It is proposed that the
secondary user can only exploits the underlay access when the channel of the
primary user direct link is good or predicted to be in non-outage state.
Therefore, the secondary user could switch between underlay spectrum sharing
and cooperation with the primary user. Hybrid access is regulated through
monitoring the state of the primary link. By observing the simulation results,
the proposed model attains noticeable improvement in the system performance in
terms of maximum secondary user throughput than the conventional cooperation
and non-cooperation schemes
Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors
We address the design of opportunistic spectrum access (OSA) strategies that
allow secondary users to independently search for and exploit instantaneous
spectrum availability. Integrated in the joint design are three basic
components: a spectrum sensor that identifies spectrum opportunities, a sensing
strategy that determines which channels in the spectrum to sense, and an access
strategy that decides whether to access based on imperfect sensing outcomes.
We formulate the joint PHY-MAC design of OSA as a constrained partially
observable Markov decision process (POMDP). Constrained POMDPs generally
require randomized policies to achieve optimality, which are often intractable.
By exploiting the rich structure of the underlying problem, we establish a
separation principle for the joint design of OSA. This separation principle
reveals the optimality of myopic policies for the design of the spectrum sensor
and the access strategy, leading to closed-form optimal solutions. Furthermore,
decoupling the design of the sensing strategy from that of the spectrum sensor
and the access strategy, the separation principle reduces the constrained POMDP
to an unconstrained one, which admits deterministic optimal policies. Numerical
examples are provided to study the design tradeoffs, the interaction between
the spectrum sensor and the sensing and access strategies, and the robustness
of the ensuing design to model mismatch.Comment: 43 pages, 10 figures, submitted to IEEE Transactions on Information
Theory in Feb. 200
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