الفهرس 
Path LossOnly 14 pages are availabe for public view
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Abstract
Broadcast nature is one of the main characteristics of the wireless medium with
double-edged arm; the first is beneficial while the other is harmful. With respect to its
beneficial side; it allows applying what is called cooperative communications in
wireless system. Cooperative communication is a mechanism that aims to achieve
transmit diversity performance enhancements in terms of increased capacity and
improved transmission reliability in a new and interesting way. It enables many
wireless devices in multi-user environment which are limited by size or hardware
complexity to one antenna to share their antennas for forwarding their messages to the
destination together.
On the other side, the harmful side of the wireless medium broadcast nature lies in
its negative effect on the system security. Due to the broadcast nature of wireless
communication networks, the adversarial “eavesdroppers” nodes in their coverage
area can intercept transmissions and try to recover parts of the transmitted message.
Therefore, a resurgence of interest has been given recently for studying the security of
data transmission in wireless systems from physical layer point of view. The main
objective behind physical layer security is to enable the exchange of confidential
messages over a wireless medium in the presence of unauthorized eavesdroppers,
without relying on higher-layer encryption.
The work in this thesis can be divided into three main parts. The first part gives a
detailed overview about both cooperative communications and the physical layer
security; the two main topics which our thesis relies on them. Firstly, the different
cooperative protocols concerned with the processing of the signal received from the
source node at the relay node are discussed. Furthermore, different relay selection
metrics concerned with selecting the best relay among the available N relays with an
indication to the entity which evaluates these metrics and selects the relay are also
given. In addition to the foregoing, multiple cooperating approaches helping in
achieving secrecy at the physical layer of multiuser system through introducing the
cooperative jamming concept are discussed.
In the second part of this thesis, different relay and jammers selection schemes are
proposed in order to achieve security in one-way cooperative networks. Because of
two-way relay channel bandwidth efficiency and its potential application to cellular
networks and peer-to-peer networks, different relay and jammers selection schemes
are also proposed in the third part of this thesis to improve physical layer security in
two-way cooperative networks. It should be obvious that selecting the best relay is
necessary for applying cooperative communication idea through its assistance to the
source in forwarding its message to the corresponding destination besides its own
message. Moreover, selecting jammers is necessary for achieving physical layer
security through their intentional interference at the eavesdroppers’ nodes. The
selection schemes without jamming, the selection schemes with conventional
jamming, the selection schemes with controlled jamming and the hybrid switching
schemes are the four different proposed selection schemes presented through the
thesis.
The obtained results showed that, although the effectiveness of the proposed
jamming schemes in improving ergodic secrecy rate and secrecy outage probability
metrics of both one-way and two-way cooperative networks, they not always be the
efficient solutions for protecting the system security. Therefore, a hybrid scheme
which switches between both jamming and non-jamming selection schemes is
introduced as an efficient solution in such cases. Moreover, the obtained results
showed the ongoing effectiveness of different proposed selection schemes in
improving both cooperative networks performance metrics despite the presence of
multiple eavesdroppers. Finally, a comparison between relay and jammers selection
schemes in both one-way and two-way cooperative networks is given in terms of both
secrecy metrics to show the effectiveness of the two-way selection schemes over their
one-way counterparts.