الفهرس 
Research MotivationOnly 14 pages are availabe for public view
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Abstract
With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. Existing spectrum allocation policies of the Federal Communications Commission (FCC) prohibits unlicensed access to licensed spectrum, which causes spectrum scarcity. However, it has been shown by several spectrum measurement campaigns that the current licensed spectrum usage across time and frequency is inefficient. Cognitive Radio (CR) is an efficient solution for solving the spectrum scarcity problem and offers versatile, powerful and portable wireless transceivers. Orthogonal Frequency Division Multiplexing (OFDM) is a promising candidate for CR systems. OFDM supports high data rates that are robust to channel impairments. In addition, some subcarriers can be deactivated which constitutes a Non-Contiguous OFDM (NC-OFDM) transmission. However, there are two main problems for OFDM transmission: The first is high peak-to-average power ratio (PAPR) phenomenon due to the superposition of independent equally spaced subcarriers at the output of the inverse fast Fourier transform (IFFT) in the Transmitter. This requires the components, such as power amplifier (PA), digital-to-analog (D/A) converters, and analog-to-digital (A/D) converters, to have large dynamic ranges in order to avoid any clipping or non-linear distortions of the signal. The second is high out-of-band (OOB) radiation, which is caused by Sinc-type function representing the symbols during one time constant. Thus, high sidelobe power may occur that will interfere with neighboring transmissions. There are some techniques that solve each problem alone as follow: Firstly: The techniques that reduce the PAPR in NC-OFDM are interleaver, Selective Mapping (SLM), Partial Transmit Sequence (PTS), adaptive mode technique, and finally Tone Reservation (TR). Secondly: The sidelobe reduction techniques are Guard Band (GB), Subcarrier Weighting (SW), Cancellation Carrier (CC), Constellation Expansion (CE), Extended Data Carrier (EDC), and, Multiple Choice Sequence (MCS). The main aim of this thesis is to reduce these two problems together as follow: There are conventional techniques that solve the two problems together such as, Selective Mapping with Multiple Choice Sequence (SLM-MCS), Advanced Constellation Expansion with Peak Reduction (ACEPR) technique, multi-stages of PTS, and NContinuous with Serial Peak Cancellation (NC-SPC). Other techniques are proposed such as:>1- Adding interleaver to SLM-MCS technique (I-SLM-MCS) and its modified technique (phase adjustment). This technique improves the performance of PAPR, sidelobe power, and BER but increase the complexity. 2- Advanced Cancellation Carrier with Signal Set Expansion (ACC-SSE) technique and its modified technique. The important advantage in this technique is that there is no side information to be transmitted. 3- Hybrid precoding technique which combines two similar techniques, Zadoff-Chu technique which reduces the PAPR and precoding technique which reduces the sidelobe suppression. The comparative study between these all techniques (the conventional and the proposed) are also presented which compare between them to find the optimum one.