Accurate detection of white spaces is crucial to protect primary user against interference
with secondary user. Multipath fading and correlation among diversity branches
represent essential challenges in Cognitive Radio Network Spectrum Sensing (CRNSS).
This dissertation investigates the problem of correlation among multiple diversity
receivers in wireless communications in the presence of multipath fading. The work
of this dissertation falls into two folds, analysis and solution. In the analysis fold,
this dissertation implements a unified approach of performance analysis for cognitive
spectrum sensing. It considers a more realistic sensing scenario where non-independent
multipath fading channels with diversity combining technique are assumed. Maximum
Ratio Combining (MRC), Equal Gain Combining (EGC), Selection Combining (SC)
and Selection and Stay Combining (SSC) techniques are employed. Arbitrarily,
constant and exponentially dual, triple and L number of Nakagami-m correlated
fading branches are investigated. We derive novel closed-form expressions for the
average detection probability for each sensing scenario with simpler and more general
alternative expressions. Our numerical analysis reveals the deterioration in detection
probability due to correlation especially in deep fading. Consequently, an increase in
the interference rate between the primary user and secondary user is observed by three
times its rate when independent fading branches is assumed. However, results also
show that this effect could be compensated for, through employing the appropriate
diversity technique and by increasing the diversity branches. Therefore, we say that
the correlation cannot be overlooked in deep fading, however in low fading can be
ignored so as to reduce complexity and computation. Furthermore, at low fading, low
false alarm probability and highly correlated environments, EGC which is simpler
scheme performs as good as MRC which is a more complex scheme. Similar result are
observed for SC and SSC. For the solution fold and towards combatting the correlation
impact on the wireless systems, a decorrelator implementation at the receiver will
be very beneficial. We propose such decorrelator scheme which would significantly
alleviate the correlation effect. We derive closed-form expressions for the decorrelator
receiver detection statistics including the Probability Density Function (PDF) from
fundamental principles, considering dual antenna SC receiver in Nakagami-m fading
channels. Numerical results show that the PDF of the bivariate difference could be
perfectly represented by a semi-standard normal distribution with zero mean and
constant variance depending on the bivariate's parameters. This observation would
significantly help simplifying the design of decorrelator receiver. The derived statistics
can be used in the problem of self-interference for multicarrier systems. Results also
show the outage probability has been improved by double, due to the decorrelator.
Closed-Form Expressions for Selection Combining System Statistics over Correlated Generalized-K Fading Channels in the Presence of Interference
