الفهرس 
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Abstract
As a solution for the spectrum scarcity problem, cognitive radio (CR) proposes an opportunistic spectrum usage approach, in which frequency bands that are not being used by their primary (licensed) users are utilized by cognitive radios. CR employs smart wireless devices with awareness, sensing, learning, and adaptation capabilities to achieve a very efficient spectrum utilization.On the other hand, UWB is a promising technology for future short and medium range wireless communication networks with various throughput options including very high data rates. It has many tempting features such as low power consumption and significantly low complexity transceivers. UWB systems occupy a very wide spectrum range from 3.1 to 10.6 GHz that overlaps with the spectra of several narrowband systems without requiring a license,and may cause interference to existing users of the same and nearby bands. Even though narrowband signals interfere with a small portion only of the UWB spectrum, due to their relatively high power with respect to the UWB signal, the performance and capacity of UWB systems can be obviously affected.By combining UWB with CR technology, coexistence with licensed communication.systems can be achieved by employing interference avoidance and cancelation methods, and adapting the transmission parameters such as power, pulse shape and data rate. The coexistence of UWB with high power interferers can be in achieved in two ways, either the UWB system design considers avoiding the transmission of the UWB signal over frequencies of strong narrowband interferers or to provide narrowband interference (NBI) suppression techniques at the UWB receivers to cancel the NBI and consequently improving the performance of UWB systems.The thesis aims at proposing several CR techniques to mitigate the interferences between UWB systems and the existing systems. The proposed techniques dramatically suppress the interferences without the need of lowering UWB pulse PSD over the whole frequency band. This gives a chance to increase the range of UWB systems.Chirp-Based Cognitive Ultra-wideband Radio is first presented as a method for NBI mitigation. Delayed Pulse Detection Technique for Interference Rejection is taken as an example for NBI suppression using Linear Chirp Signals. Non-linear chirp waveforms are then used as a method to suppress narrow-band interference sources as they have more interference rejection capabilities than linear chirp signals. MATLAB simulations have been performed to test the interference rejection capabilities of the nonlinear chirp UWB signals. Several pulse design methods of UWB Impulse Radio (IR) Signals have been proposed to for NBI Mitigation. However, most of these pulses do not achieve optimal spectral utilization.To satisfy the bandwidth constraints without sacrificing data rate or system capacity, we have the challenge of designing new pulses that are strictly limited in time to reduce interference while, at the same time, contain their power distribution within a frequency band from 3.1 to 10.6 GHz specified by FCC. The goal of UWB pulse shape design is to find a waveform that has high spectral utilization efficiency, while at the same time complying with the FCC spectral mask. A number of Pulse Design Methods for NBI Mitigation such as Parks-McClellan (PM) Algorithm, Eigen Decomposition Approach (EVD), and Pulse Design Method Based on Semidefinite Programming (SDP) are then presented. These methods give a chance of increasing the UWB transmitted power and enlarging the application range of UWB systems, while meeting the FCC spectral mask. The methods are discussed in details followed by their extension to suppress single and double NBI suppression. MATLAB simulation is used study the performance of these signals. In particular, the BER performance of the IEEE 802.15.4a UWB system is evaluated for both the Parks-McClellan Algorithm and the Eigen Decomposition Approach in case of single and double NBI. Results showed that the Single Notch adaptive PM Pulse outperforms the Eigen-Value pulse. In case of double NBI, results show that the performance of the Double Notch Eigen Pulse is nearly the same as that of Double Notch adaptive PM Pulse; BER is nearly the same at any SNR value. A new Interference Aware Cognitive Radio (IA-CR) UWB) system based on a Modified Eigen-Method have superior performance over non-cognitive ultra wide band systems. With the proposed UWB cognitive radio capability, the UWB system performs spectrum sensing to pick the most suitable transmit and receive filters that minimizes its error rate performance. The application of the proposed to the IEEE 802.15.4a UWB system shows its enhanced performance over non adaptive pulse transmission.