Abstract:
The number of wireless systems and services has grown tremendously over the last two
decades. As a result, the availability of wireless spectrum has become extremely limited.
Cognitive radio is a new technique to overcome the issue of spectrum scarcity. In cognitive
radio networks, the licensed users of the spectrum are called primary users. Secondary
users equipped with cognitive radios can opportunistically transmit via so-called “spectrum
holes” which can be categorized as spatial or temporal spectrum holes.
In this dissertation, we propose a joint spatial-temporal spectrum sensing scheme for
cognitive radios. We show that our joint spatial-temporal spectrum sensing scheme outperforms
pure temporal sensing schemes. In addition, joint spatial-temporal sensing increases
the point-to-point transmission capacity of cognitive radio link compared to pure temporal
or spatial sensing. We also propose a temporal spectrum sensing scheme that exploits
multiuser diversity in wireless networks. In wireless networks with fading, multiuser diversity
exists because different users experience peak channel quality at different times.
By exploiting multiuser diversity, our spectrum sensing method can outperform the spectrum
sensing schemes that do not exploit multiuser diversity. We develop and analyze
a joint spatial-temporal sensing scheme that incorporates cooperative relaying to further
increase the capacity of a cognitive radio network. We consider both amplify-and-forward
and decode-and-forward cooperative transmission strategies. Finally, we study joint spatialtemporal
spectrum sensing in a multichannel cognitive radio scenario and present randomized
and maximized signal-to-noise ratio algorithms that improve performance in term of
symbol error probability.
