الفهرس 
Chapter 1 : IntroductionOnly 14 pages are availabe for public view
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Abstract
Recent wireless communication system faces a growing demands for broadband and
multimedia services and also will be the future wireless system. According to a statistical
estimation from Cisco, globe mobile data traffic grew about 2.5-fold every year during 2008 to
2011, and the number of mobile-connected devices, including smartphone, laptop, etc., was
estimated to be over 7.1 billion in 2015, which is approximately equal to the world’s population.
In order to support the rapid demand growth, numerous research efforts had been done in this
active field. With the scarcity of the radio resources such as Bandwidth and Power, etc. Researcher
had proposed an intelligent communication system named Cognitive Radio Networks CRNs for
efficient optimization of the available radio resources. Exploiting the empty frequency bands of
the licensed system improve the spectrum utilization and enable more wireless services and
networks to communicate concurrently.
The problem of resource allocation, is to intelligently allocate limited power and
bandwidth resources among users according to each user requirements in an intelligent and
efficient manner which can be achieved through CRNs. It has been discussed heavily from the
point of view of power and bit allocation. Through formulating it as an objective problem
depending on different criteria and approaches such as spectral efficiency, interference power,
fairness, throughput and etc. Aiming to maximize it through optimization methods like
evolutionary algorithms, Game theory, heuristics…etc.
One of the main basic principles in any wireless communication paradigm is throughput
improvement. Many researchers aiming to reaches to this goal through different mechanism like
modulation techniques, deploying MIMO antenna System and the power allocation strategies
based on different optimization algorithms
In this thesis, the problem of maximizing the secondary throughput in downlink CRNs based
on power optimization strategies, Multicarrier Modulation (MCM) techniques and MIMO antenna
system in CRNs was considered. This maximization problem will occurred under some constraints
Abstract _
III
like maximum transmit power for secondary network and interference power level at each PU
receiver.
As the first topic of this research, we aim to maximize the secondary system throughput for
downlink Orthogonal Frequency Division Multiplexing (OFDM)-based in Sensing-Based
Spectrum Sharing CRNs. Using a heuristic algorithm named Simulated Annealing (SA) for
enhancing the transmission power of secondary system in order to improve its performance.
Taking into account the constraints of total transmitted power and the aggregated interference
introduced on the licensed network.
Secondly, an optimal power allocation scheme was proposed using an optimization techniques
called Particle Swarm optimization aiming to maximize the minimal throughput among overall
secondary users and also the total system throughput in downlink MIMO-based CRNs. While
keeping the SUs’ interference on each PU below a given threshold to assure the QoS of PUs, also
considering QoS of SUs. Further, the comparison between different optimization techniques based
on the complexity, process time and system throughput was discussed.
The third topic discussed the deploying of a different Multi-carrier Modulation technique
named Generalized Frequency Division Multiplexing (GFDM) for CRNs to solve some of OFDM
related problems such as PAPR, Out-Of-Band Radiation and large overhead. In addition, a study
for different system parameter was done to evaluate the performance of the new modulation
technique. Also, a power loading algorithm was proposed to efficiently improve the system
throughput under a predefined power and interference constraints.