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العنوان
PERFORMANCE ENHANCEMENT of COGNITIVE RADIO NETWORKS /
المؤلف
Hasan, Elzahraa Abdel Hameed Abdel Moaty.
هيئة الاعداد
باحث / Elzahraa Abdel Hameed Abdel Moaty Hasan
مشرف / Abdel Halim Abdel Naby Zekry
مشرف / Salah Sayed Ibrahim El Agooz
مناقش / Talaat Abdel Latif Fl Garf
تاريخ النشر
2019.
عدد الصفحات
106 P. :
اللغة
الإنجليزية
الدرجة
الدكتوراه
التخصص
الهندسة الكهربائية والالكترونية
تاريخ الإجازة
1/1/2019
مكان الإجازة
جامعة عين شمس - كلية الهندسة - قسم هندسة الالكترونيات والاتصالات
الفهرس
Only 14 pages are availabe for public view

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from 106

Abstract

Cognitive radio (CR) has been proposed for spectral efficiency improvement while avoiding interference with licensed users. Multicarrier modulation has been suggested as a candidate for CR systems since it allows high data rate transmission over parallel sub-channels. The utilization of multicarrier modulation has already been emphasized in spectrum sensing context as represented in high spectral resolution, commonality of sensing and flexiblity of building decision statistics from basic observations within the sensing window.
In the realistic scenarios of CR systems, imperfect channel sensing may occur due to false alarms and miss-detections. Channel estimation between the secondary user transmitter and another secondary user receiver is another challenge in CR systems, especially for frequency-selective fading channels.
In the CR context, most past efforts have been spent on Orthogonal Frequency Division Multiplexing (OFDM) based CR systems. However, OFDM technique exhibits some shortcomings in application due to its significant spectrum leakage. Filter Bank based Multi-Carrier (FBMC) modulation is also a promising candidate for CR-based systems. Although it behaves better in many aspects than OFDM, the application of some techniques to FBMC becomes more challenging due to the imaginary interference, as in Multiple-Input Multiple-Output (MIMO) technique.
In this thesis, we aim to improve the CR system performance. This is represented in the following steps:
• The thesis presents a study of the effects of imperfect channel sensing and channel estimation on the performance of CR systems. In particular, different methods of channel estimation are analysed under channel sensing imperfections.
• Expectation Maximization (EM) algorithm is presented in order to learn the channel fading coefficients. We further compare the performance of the proposed EM estimation algorithm with those of different estimation algorithms.
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• The complexity of the EM algorithm is reduced by presenting a sub-optimal algorithm. The obtained results show that the proposed sub-optimal algorithm provides a Bit Error Rate (BER) performance comparable to that of the optimal one, yet with less computational complexity.
• We also propose a new MIMO-based FBMC transceiver structure for CR systems. The proposed structure is based on QAM transmission to handle the interference presented in conventional OQAM-FBMC systems.
• We introduce two different methods to satisfy the orthogonality conditions for the even and the odd sub-carriers and cancel the residual interference in QAM-FBMC systems. Both methods are based on Discrete Cosine Transform (DCT) to achieve a superior spectrum confinement and better spectral efficiency.
• The computational complexity of the proposed structure is then evaluated and compared with that of the conventional OFDM and OQAM-FBMC techniques.
• Finally, we propose a resource allocation algorithm for the proposed structure that takes the impact of Inter-Carrier Interference (ICI) resulting from timing offset into account for both conventional OFDM and OQAM-FBMC techniques.
Keywords: Cognitive Radio; Expectation Maximization; Spectrum sensing; FBMC; DCT; Resources allocation; MIMO