648 research outputs found
Secrecy Outage and Diversity Analysis of Cognitive Radio Systems
In this paper, we investigate the physical-layer security of a multi-user
multi-eavesdropper cognitive radio system, which is composed of multiple
cognitive users (CUs) transmitting to a common cognitive base station (CBS),
while multiple eavesdroppers may collaborate with each other or perform
independently in intercepting the CUs-CBS transmissions, which are called the
coordinated and uncoordinated eavesdroppers, respectively. Considering multiple
CUs available, we propose the round-robin scheduling as well as the optimal and
suboptimal user scheduling schemes for improving the security of CUs-CBS
transmissions against eavesdropping attacks. Specifically, the optimal user
scheduling is designed by assuming that the channel state information (CSI) of
all links from CUs to CBS, to primary user (PU) and to eavesdroppers are
available. By contrast, the suboptimal user scheduling only requires the CSI of
CUs-CBS links without the PU's and eavesdroppers' CSI. We derive closed-form
expressions of the secrecy outage probability of these three scheduling schemes
in the presence of the coordinated and uncoordinated eavesdroppers. We also
carry out the secrecy diversity analysis and show that the round-robin
scheduling achieves the diversity order of only one, whereas the optimal and
suboptimal scheduling schemes obtain the full secrecy diversity, no matter
whether the eavesdroppers collaborate or not. In addition, numerical secrecy
outage results demonstrate that for both the coordinated and uncoordinated
eavesdroppers, the optimal user scheduling achieves the best security
performance and the round-robin scheduling performs the worst. Finally, upon
increasing the number of CUs, the secrecy outage probabilities of the optimal
and suboptimal user scheduling schemes both improve significantly.Comment: 16 pages, 5 figures, accepted to appear, IEEE Journal on Selected
Areas in Communications, 201
Adaptive OFDM Index Modulation for Two-Hop Relay-Assisted Networks
In this paper, we propose an adaptive orthogonal frequency-division
multiplexing (OFDM) index modulation (IM) scheme for two-hop relay networks. In
contrast to the traditional OFDM IM scheme with a deterministic and fixed
mapping scheme, in this proposed adaptive OFDM IM scheme, the mapping schemes
between a bit stream and indices of active subcarriers for the first and second
hops are adaptively selected by a certain criterion. As a result, the active
subcarriers for the same bit stream in the first and second hops can be varied
in order to combat slow frequency-selective fading. In this way, the system
reliability can be enhanced. Additionally, considering the fact that a relay
device is normally a simple node, which may not always be able to perform
mapping scheme selection due to limited processing capability, we also propose
an alternative adaptive methodology in which the mapping scheme selection is
only performed at the source and the relay will simply utilize the selected
mapping scheme without changing it. The analyses of average outage probability,
network capacity and symbol error rate (SER) are given in closed form for
decode-and-forward (DF) relaying networks and are substantiated by numerical
results generated by Monte Carlo simulations.Comment: 30 page
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