25-08-2017, 09:32 PM
Efficient Code-based Relay Algorithm for Reliable Cognitive Radio Systems
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Abstract
Cooperative spectrum sensing taking into account the
error effect on the sensing information reporting and increase in
efficiency is studied. Employing the relay, a novel cooperative
spectrum sensing algorithm based on network coding is proposed
by correcting the received sensing information. In this paper we
study the performance of network coding in presence of
opportunistic relay selection. We conjecture that relay selection
schemes should be aware of, and account for, the network coding
operation in case of its presence. The efficiency of the algorithm
and the method of relay selection are given. Based on system level
simulation results, it is demonstrated that such an awareness
provides considerable capacity gains as compared to its
traditional opportunistic counterparts, in addition to increased
fairness among the encoded sources.
INTRODUCTION
Wireless networks are characterized by a fixed spectrum
assignment policy in most countries. However, the allocated
spectrums are vastly underutilized sporadically and
geographically with a high variance in time [1]. There are
increasing interests in increasing the spectrum efficiency.
Cognitive radio (CR) enables much higher spectrum efficiency
by dynamic spectrum access [2]. Therefore, it is a potential
technique for future wireless communications to mitigate the
spectrum scarcity issue.
In cognitive radio systems, cognitive users need to have
cognitive radio capabilities, such as sensing the spectrum
reliably to check whether it is being used by a primary user. A
number of different methods are proposed for identifying the
presence of signal transmission and improve in efficiency,
such as matched filter detection, energy detection, feature
detection techniques and wavelet approach [3]. However, due
to the fading and the shadowing effects, the sensing
performance for one cognitive user will be degraded. To
enhance the sensing performance, cooperative spectrum
sensing has been discussed [4].
NC-AWARE RELAY SELECTION
With the area of cooperative communications gaining more
interest, the topic of relay selection is being the subject of
tremendous research. In particular, the studied relay selection
algorithms can be generically divided into two categories[14]:
• opportunistic relay selection
• multiple relay selection.
One of the most critical issues in relaying systems is relay
selection. The use of relays can adversely affect the
performance as opposed to not using any relays in the case
where the relay selection is done randomly or inappropriately.
Intuitively stated, this can be likened to the case when a user
is connected to the wrong base station. When applying relay
selection in conjunction with NC, the problem gets even more
challenging.
CONCLUSION
In this work, we have modeled and analyzed the streaming
transmission problem over downlinks in a single part of
cognitive radio system. We have characterized the optimal
throughput with reliability for the coded against uncoded cases
with hard deadline constraints, and shown that the capacity
region of network coded transmission is strictly larger than
uncoded cases.
We have proposed and analyzed a novel network coding
(NC) scheme, which achieves the asymptotic capacity without
the knowledge about the packet delivery probability. In
addition, our simulation shows that the NC scheme achieves
strictly higher throughput than the best uncoded cooperative
scheme even for very small file size N. A Lyapunov analysis
of the index advancement has been developed, which sheds
further insight into the NC scheme for both the file-streaming
and livestreaming applications.