| dc.description.abstract |
The sensible utilization of radio spectrum has become an important challenge in
wireless communications. Frequency bands are closely and strictly managed by government
authorization and have nearly been used up with the quick increase in the number of
subscribers and wireless services recently. A question arises how to improve the efficiency of
using allocated bands to avoid wasting radio resource? The establishment of cognitive radio
network helped to solve the question partially. In cognitive radio network, the cognitive radio
users (CRs) can detect the available spectrum (white-space) of communication channels and
perform spectrum sensing by themselves (local spectrum sensing) or collaborating with each
other CRs (cooperative spectrum sensing). If the channel is in use, unlicensed user
(secondary users or cognitive radio users) is not allowed to access the channel in order to
avoid interference and then continue to sense another channels. There are some main
cognitive radio functions such as spectrum mobility, spectrum sharing, spectrum sensing.
In this thesis, we illustrate effects of collaborating spectrum sensing on the probability
of spectrum sensing detection through simulation and efficiency estimation of the detection
over Rayleigh fading channel and Log-normal shadowing channel in cognitive radio network.
We will prove that when the number of CRs reaches a certain value, the probability of
spectrum detection of collaborating spectrum sensing will get the best result without the
requirement of more CRs involved. Furthermore, we will study cooperative spectrum sensing
over correlated log-normal shadowing, when each CRs can impact to each other at a close
distance. |
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