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Doctorate thesis defense of Hanen LAJNEF BOUAOUAJA

Doctorate thesis defense on March 09th 2019 at 10H00 ,in Sup’Com Amphitheater Ibn Khaldoun.

Entitled :Investigation in the Compensation of Nonlinearities for Multi-Carrier Modulations Based Cognitive Radio Systems

Presented by :




Houria REZIG

Professor, ENIT, Tunis






Professor, Sup’Com, Tunis


Faouzi ZARAI

Professor, ENET'com, Sfax



Professor, ENISO, Sousse




Thesis Director :


Professor, Sup’Com, Tunis





Cognitive radio (CR) is the core technology of the next generation of wireless communication systems, which is taking increasing attention these last years. Indeed, it is seen as a promising solution to the problem of spectral congestion by introducing the notion of opportunistic spectrum use. Thanks to its advantages, it makes possible to intelligently change the communication parameters in response to the activity of other radio networks and user requests. In the context of CR, most efforts have been made on CR systems based on multi-carrier modulation (MCM). However, despite all the advantages offered by MCM systems, they suffer from two major problems. First, the large peak factor (PAPR) of MCM signals makes them very sensitive to non-linear distortion (NLD) caused by power amplifiers. Then, they are sensitive to synchronization errors whatever the multi-carrier modulations (OFDM/FBMC). In this dissertation, we present two types of contributions. The first concerns a practical spectrum detection study for nonlinear OFDM / FBMC systems. In this study, we propose adapted PAPR reduction techniques based on the nonlinear distortion cancellation (NDC) method. These techniques are tested and evaluated using several evaluation criteria such as PAPR reduction, complexity, bit error rate (BER) degradation, and bit rate. In addition, the impact of the overlap factor on the performance of the simulated techniques is also addressed. The second part of the contributions concerns a theoretical study of the performance of OFDM / FBMC systems in the presence of nonlinearities and synchronization errors. For this study, a theoretical analysis of interference has been developed. This analysis gave rise to analytic expressions of asynchronous interference. In the following part of the second part of the contributions, to solve asynchronous and non-linearity problems, a hybrid iterative method of compensation (NDC) and cancellation of parallel interference (PIC), was developed based on these two conditions. The studied scenario includes a reference mobile, a reference base station and several interfering base stations. For this scenario, we have developed analytical expressions of the signal to interference plus noise ratio (SINR) and bit error rate (BER) in the case of a frequency selective channel. The theoretical expressions obtained are validated by simulations and show the high sensitivity of the OFDM systems compared to the FBMC, the joint effect of synchronization errors and NLD.

Keywords :

Cognitive Radio, Multi-Carrier Modulation, OFDM, FBMC, PAPR, Asynchronous Interference, High Power Amplifiers, Nonlinear Distortions.