الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In the last few decades, the spectrum of wireless communication systems has been subjected
to the scarcity problem. This is due to the exponential increasing demand of wireless resources
in order to fulfill the growth of multiple wireless communication applications which is
characterized by an orthogonal assignment policy. Cognitive Radio (CR) was proposed as one
of promising techniques to exploit the scarcity in the spectrum underutilization.
To improve the spectrum utilization, CR networks (CRNs) technology permit the
coexistence of licensed and unlicensed networks over the same spectrum. In an underlay
spectrum sharing CRNs, secondary users (SUs) (i.e., unlicensed users) transmit simultaneously
with the primary users (PUs) (i.e., licensed users) in the same resource block
(time/frequency/code) where the interference caused by the SU to the PU remains below an
acceptable level or limit.
However, besides the transmission power limitation, the secondary network is subject to
numerous restrictions. Some of those main problems are impairments of the communications’
channels such as fading channels and interference from the PUs’ transmissions. Furthermore,
due to the broadcasting nature of CR nodes, CRNs are vulnerable to threating or eavesdropping
challenges.
To increase the transmission reliability within CR nodes, we jointly study cooperative CR
and non-orthogonal multiple access (NOMA) techniques. Particularly, NOMA has been
recently proposed for 3GPP Long Term Evolution (LTE) and envisioned to be a promising
technique for the future 5th generation (5G) mobile networks. The key idea behind NOMA is
to serve multiple users by the same resource block (i.e., time/frequency/code) but with different
power levels. Thus, NOMA technique introduces superior spectral efficiency (SE) for future
networks. This thesis is divided into two parts:
The aims of first part of this thesis is to analyze the performance of a practical cooperative
relaying CRN model. Owing to their CR characteristics, the underlay CRN is considered
regarding the spectrum sharing and security constraints. Distinct relay selection (RS) and SU
transmit power policies are proposed by developing exact mathematical methods under various mutual inter-network interference constraints (i.e., the worst-case scenarios), secrecy outage
constraints and achievable rates for both delay-sensitive and delay-tolerant applications.
Furthermore, a new promising transmission framework based on enhancing the physical
layer security is introduced. Describing the interplay between the CRN nodes, new closed-form
expressions are derived for the achievable rate, outage probability, non-zero secrecy capacity,
secrecy outage probability and diversity order which reveal an insightful system design.
The aims of second part of this thesis is to apply the basic principles of NOMA technique in
CRNs by integrating NOMA with the CR nodes (i.e., the CR elements) in order to increase the
transmission reliability, achieve superior performance, enhance the spectral efficiency and
achieve better utilization of the resources.
This approach provides several advantages over the existing members of multiple access
techniques (i.e., conventional orthogonal multiple access (OMA)). Specifically, the
performance of the relay-sharing based NOMA system within CR nodes is investigated for both
directional and bi-directional communications. Secondly, cooperative multiuser selection
schemes inspired NOMA system are proposed to overcome the problem of deep-fading
environment and achieve higher reliability for CRNs.
Finally, the issue of joint user fairness and the best choice of power allocation is addressed
here which play an important role in boosting the system performance while simulation results
are conducted to emphasize the superior performance and verify the correctness of our analysis.