397 research outputs found
Performance Analysis of Arbitrarily-Shaped Underlay Cognitive Networks: Effects of Secondary User Activity Protocols
This paper analyzes the performance of the primary and secondary users (SUs)
in an arbitrarily-shaped underlay cognitive network. In order to meet the
interference threshold requirement for a primary receiver (PU-Rx) at an
arbitrary location, we consider different SU activity protocols which limit the
number of active SUs. We propose a framework, based on the moment generating
function (MGF) of the interference due to a random SU, to analytically compute
the outage probability in the primary network, as well as the average number of
active SUs in the secondary network. We also propose a cooperation-based SU
activity protocol in the underlay cognitive network which includes the existing
threshold-based protocol as a special case. We study the average number of
active SUs for the different SU activity protocols, subject to a given outage
probability constraint at the PU and we employ it as an analytical approach to
compare the effect of different SU activity protocols on the performance of the
primary and secondary networks.Comment: submitted to possible IEEE Transactions publicatio
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
State of the Art, Taxonomy, and Open Issues on Cognitive Radio Networks with NOMA
The explosive growth of mobile devices and the rapid increase of wideband
wireless services call for advanced communication techniques that can achieve
high spectral efficiency and meet the massive connectivity requirement.
Cognitive radio (CR) and non-orthogonal multiple access (NOMA) are envisioned
to be important solutions for the fifth generation wireless networks.
Integrating NOMA techniques into CR networks (CRNs) has the tremendous
potential to improve spectral efficiency and increase the system capacity.
However, there are many technical challenges due to the severe interference
caused by using NOMA. Many efforts have been made to facilitate the application
of NOMA into CRNs and to investigate the performance of CRNs with NOMA. This
article aims to survey the latest research results along this direction. A
taxonomy is devised to categorize the literature based on operation paradigms,
enabling techniques, design objectives and optimization characteristics.
Moreover, the key challenges are outlined to provide guidelines for the domain
researchers and designers to realize CRNs with NOMA. Finally, the open issues
are discussed.Comment: This paper has been accepted by IEEE Wireless Communications
Magazine. Pages 16, Figures
The Achievable Rate of Interweave Cognitive Radio in the Face of Sensing Errors
Cognitive radio (CR) systems are potentially capable of mitigating the spectrum shortage of contemporary wireless systems. In this paper, we provide a brief overview of CR systems and the important research milestones of their evolution, along with their standardization activities, as a result of their research. This is followed by the detailed analysis of the interweave policy-based CR network (CRN) and by a detailed comparison with the family of underlay-based CRNs. In the interweave-based CRN, sensing of the primary user's (PU) spectrum by the secondary user's (SU) has remained a challenge, because the sensing errors prevent us from fulfilling the significant throughput gains that the concept of CR promises. Since missed detection and false alarm errors in real-time spectrum sensing cannot be avoided, based on a new approach, we quantify the achievable rates of the interweave CR by explicitly incorporating the effect of sensing errors. The link between the PU transmitter and the SU transmitter is assumed to be fast fading. Explicitly, the achievable rate degradation imposed by the sensing errors is analyzed for two spectrum sensing techniques, namely, for energy detection and for magnitude squared coherence-based detection. It is demonstrated that when the channel is sparsely occupied by the PU, the reusing techniques that are capable of simultaneously providing low missed detection and false alarm probabilities cause only a minor degradation to the achievable rates. Furthermore, based on the achievable rates derived for underlay CRNs, we compare the interweave CR and the underlay CR paradigms from the perspective of their resilience against spectrum sensing errors. Interestingly, in many practical regimes, the interweave CR paradigm outperforms the underlay CR paradigm in the presence of sensing errors, especially when the SNR at the SU is below 10 dB and when the SNR at the PU is in the range of 10-40 dB. Furthermore, we also provide rules of thumb that identify regimes, where the interweave CR outperforms the underlay CR
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