1,066 research outputs found
Optimal time sharing in underlay cognitive radio systems with RF energy harvesting
Due to the fundamental tradeoffs, achieving spectrum efficiency and energy
efficiency are two contending design challenges for the future wireless
networks. However, applying radio-frequency (RF) energy harvesting (EH) in a
cognitive radio system could potentially circumvent this tradeoff, resulting in
a secondary system with limitless power supply and meaningful achievable
information rates. This paper proposes an online solution for the optimal time
allocation (time sharing) between the EH phase and the information transmission
(IT) phase in an underlay cognitive radio system, which harvests the RF energy
originating from the primary system. The proposed online solution maximizes the
average achievable rate of the cognitive radio system, subject to the
-percentile protection criteria for the primary system. The
optimal time sharing achieves significant gains compared to equal time
allocation between the EH and IT phases.Comment: Proceedings of the 2015 IEEE International Conference on
Communications (IEEE ICC 2015), 8-12 June 2015, London, U
Difference Antenna Selection and Power Allocation for Wireless Cognitive Systems
In this paper, we propose an antenna selection method in a wireless cognitive
radio (CR) system, namely difference selection, whereby a single transmit
antenna is selected at the secondary transmitter out of possible antennas
such that the weighted difference between the channel gains of the data link
and the interference link is maximized. We analyze mutual information and
outage probability of the secondary transmission in a CR system with difference
antenna selection, and propose a method of optimizing these performance metrics
of the secondary data link subject to practical constraints on the peak
secondary transmit power and the average interference power as seen by the
primary receiver. The optimization is performed over two parameters: the peak
secondary transmit power and the difference selection weight . We show that, difference selection using the optimized parameters
determined by the proposed method can be, in many cases of interest, superior
to a so called ratio selection method disclosed in the literature, although
ratio selection has been shown to be optimal, when impractically, the secondary
transmission power constraint is not applied. We address the effects that the
constraints have on mutual information and outage probability, and discuss the
practical implications of the results.Comment: 29 pages, 9 figures, to be submitted to IEEE Transactions on
Communication
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Effective Capacity in Cognitive Radio Broadcast Channels
In this paper, we investigate effective capacity by modeling a cognitive
radio broadcast channel with one secondary transmitter (ST) and two secondary
receivers (SRs) under quality-of-service constraints and interference power
limitations. We initially describe three different cooperative channel sensing
strategies with different hard-decision combining algorithms at the ST, namely
OR, Majority, and AND rules. Since the channel sensing occurs with possible
errors, we consider a combined interference power constraint by which the
transmission power of the secondary users (SUs) is bounded when the channel is
sensed as both busy and idle. Furthermore, regarding the channel sensing
decision and its correctness, there exist possibly four different transmission
scenarios. We provide the instantaneous ergodic capacities of the channel
between the ST and each SR in all of these scenarios. Granting that
transmission outage arises when the instantaneous transmission rate is greater
than the instantaneous ergodic capacity, we establish two different
transmission rate policies for the SUs when the channel is sensed as idle. One
of these policies features a greedy approach disregarding a possible
transmission outage, and the other favors a precautious manner to prevent this
outage. Subsequently, we determine the effective capacity region of this
channel model, and we attain the power allocation policies that maximize this
region. Finally, we present the numerical results. We first show the
superiority of Majority rule when the channel sensing results are good. Then,
we illustrate that a greedy transmission rate approach is more beneficial for
the SUs under strict interference power constraints, whereas sending with lower
rates will be more advantageous under loose interference constraints.Comment: Submitted and Accepted to IEEE Globecom 201
Band Allocation for Cognitive Radios with Buffered Primary and Secondary Users
In this paper, we study band allocation of buffered secondary
users (SUs) to orthogonal primary licensed bands, where each
primary band is assigned to one primary user (PU). Each SU is assigned to one
of the available primary bands with a certain probability designed to satisfy
some specified quality of service (QoS) requirements for the SUs. In the
proposed system, only one SU is assigned to a particular band. The optimization
problem used to obtain the stability region's envelope (closure) is shown to be
a linear program. We compare the stability region of the proposed system with
that of a system where each SU chooses a band randomly with some assignment
probability. We also compare with a fixed (deterministic) assignment system,
where only one SU is assigned to one of the primary bands all the time. We
prove the advantage of the proposed system over the other systems.Comment: Accepted in WCNC 201
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