well as the maximum number of possible pairwise communications of suchsimultaneously
with the primary. We proceed to propose algorithms for simultaneous
communication schemes to maximize the sum network capacity. These ap-
proaches allow cognitive radios to support and guarantee QoS when shar-
ing spectrum while limiting the interference to the incumbent user. In the
first approach, we employ a cognitive radio protocol where a virtual noise-
threshold is used as a proxy for the primary user to allow cognitive users to
profit from the primary user resources in an opportunistic manner, and at
the same time, to maintain a guarantee of service to the primary user when
cognitive communication is considered. The key idea is that the primary
user has a certain quality of service to fulfill. This gives the secondary user
a transmitting opportunity since the primary user will not, in any case, use
all its rate as long as it has its quality of service satisfied.
The previous approach relies on a virtual noise threshold assumption. The
approach is reminiscent of the interference temperature concept. However,
as a practical matter, the FCC abandoned the interference temperature ap-
proach due to the fact that it is not a workable concept and would result in
increased interference in the frequency bands where they were to be used.
Accordingly, to determine the spectrum band allocation that meets the QoS
requirements of different users, we propose, in the second approach, a dif-
ferent way to effciently protect primary systems from secondary system
interference, based on outage probability. We particularly propose a joint
distributed algorithm for power allocation and user selection that tends to
decrease control overhead in large cognitive radio networks.
In the end, we look at the problem of sensing in spectrum pooling scenar-
ios. The proposed approach is based on an information-theoretic sub-space
analysis for the detection of vacant sub-bands in a large spectrum context.
We also investigate empirical techniques and compare results to UMTS real-
world measurements as well as to other simulated signals in order to analyze
the robustness of the proposed approach in presence of increased levels of
The last ten years has seen an explosion in uses of wireless technologies.
This, in turn, has driven a demand for more spectrum to support these uses.
A recent spectrum license auction by the Federal Communications Commis-
sion (FCC), which regulates all civilian uses of wireless technologies in the
United States, found that the existing spectrum utilization can be improved
through opportunistic access to the licensed bands without interfering with
the existing users. Notably, it is suggested that Dynamic Spectrum Access
Networks as well as cognitive radio networks, will provide high bandwidth
to mobile users via heterogeneous wireless architectures and dynamic spec-
trum access techniques. Cognitive radio networks, however, impose several
research challenges due to the broad range of available spectrum as well as
diverse Quality-of-Service (QoS) requirements of applications. These het-
erogeneities must be captured and handled dynamically as mobile terminals
roam between wireless architectures and along the available spectrum pool.
In this dissertation, we study spectrum pooling strategies based on central-
ized and distributed resource allocation techniques. Throughout this work,
we consider different system models in which cognitive users compete for
a chance to transmit simultaneously or orthogonally with the primary sys-
tem. On the basis of these models, we define the specific resource allocation
problem addressed in this work in view of maximizing network capacity and
at the same time, insuring a QoS for the primary system. In particular, we
analyze the resource allocation problem and offer insights into user selection
strategies and spectrum sensing in a cognitive radio network environment.
We initially investigate the problem of orthogonal communication scenar-
ios between the primary system and cognitive users. For the first time,
our study attempts to quantify the asymptotic (with respect to the band)
achievable gain of using orthogonal spectrum pooling communications in
terms of spectral effciency. We then derive the total spectral effciency as
a spectrum pooling system.
Having looked at orthogonal communication scenario, we then extend the
cognitive protocol to allow the cognitive users to transmit