| Summary: | The increased demand for a high data rate and spectral-efficient modulation techniques has led to the widespread adoption of orthogonal frequency division multiplexing (OFDM) systems in various communication standards, e.g. digital video broadcasting-satellite services to handhelds (DVB-SH). However, the performance of OFDM is susceptible to deteriorations due to impulsive noise distribution, high peak to average power ratio (PAPR) and frequency selectivity of the multipath fading channels. These shortcomings adversely affect the performance of the OFDM systems. In this thesis, several improved OFDM based systems are proposed to deal with these problems. Two schemes are proposed to reduce the impact of impulsive noise on the OFDM systems over frequency selective channels. However, the improvement in performance comes with the expense of high complexity which forms another challenge discussed in this thesis. Furthermore, a new low-complexity precoder that combines the processing computations of the Haar precoder and the inverse fast Fourier transform (IFFT) is proposed. The complexity of the new precoder, referred to as inverse D-precoder (IDP), is significantly lower than other state-of-the-art precoders found in literature. Based on the IDP, a new low- complexity OFDM system is proposed exhibiting low PAPR, and robustness against multipath fading channels in the presence of impulsive noise. Moreover, the thesis investigates the sensitivity of OFDM signals transmitted over frequency-selective fading channels. To combat the resulting intersymbol interference (ISI), a new low-complexity precoded OFDM based on the Haar precoder (H-OFDM) is introduced. The H-OFDM demonstrates improved Bit Error Rate performance compared to standard OFDM systems over multipath fading channels. The key merits of both the Haar precoder and the IDP are employed to introduce a low-complexity alternative to the conventional OFDM utilised in satellite systems. The performance analyses of these schemes are derived and verified by Monte Carlo simulations.
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