3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Carrier frequency offset synchronization and phase noise compensation in coherent optical OFDM systems(2018) Balogun, Muyiwa BlessingThe deployment of optical networks has become inevitably paramount due to the phenomenal advancement in the communications industry and the associated extraordinary demand for high data throughput. Optical networks provide the needed solution and reliability especially in this era where bandwidth-hungry devices are in high demand. The current technical trend seeks to increase the optical networks capacity, flexibility and reconfigurability, in order to effectively support long haul data transportation. The orthogonal frequency division multiplexing (OFDM) technique has been proposed as a viable scheme that can be incorporated so as to greatly enhance the overall output of the existing optical transport networks. The OFDM technique has become a popular scheme in telecommunications due to its support for high data-rate transmission, robustness and spectral efficiency. The scheme is particularly of great interest and very attractive for use in optical transport system due to its tolerance to chromatic dispersion. However, with the introduction of the OFDM scheme comes the attendant challenges of carrier frequency offsets (CFO) and phase noise, which must be adequately addressed in order to ensure optimum performance of the coherent optical OFDM communication system. This research work therefore, seeks to address the impact of phase noise and carrier frequency offset on a non-simplistic, complex and an all-encompassing optical OFDM system model which considers the influence of polarization mode dispersion, group velocity dispersions, attenuation and other polarization-dependent losses in the optical link. The effectiveness of the algorithms, utilized to combat phase noise and carrier frequency offset based on the simplistic optical OFDM models in the literature, is verified using the non-simplistic comprehensive system model. Also, a closed-form maximum likelihood (ML) method is developed and utilized for phase noise and CFO estimation. First, a closed-form ML estimator is derived and implemented for CFO estimation in coherent optical OFDM (CO-OFDM) system. Thereafter, this is then extended so that the phase noise and the CFO are jointly acquired using the derived closed-form ML method.Item Channel estimation techniques for filter bank multicarrier based transceivers for next generation of wireless networks(2017) Ijiga, Owoicho EmmanuelThe fourth generation (4G) of wireless communication system is designed based on the principles of cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) where the cyclic prefix (CP) is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) in order to achieve higher data rates in comparison to the previous generations of wireless networks. Various filter bank multicarrier systems have been considered as potential waveforms for the fast emerging next generation (xG) of wireless networks (especially the fifth generation (5G) networks). Some examples of the considered waveforms are orthogonal frequency division multiplexing with offset quadrature amplitude modulation based filter bank, universal filtered multicarrier (UFMC), bi-orthogonal frequency division multiplexing (BFDM) and generalized frequency division multiplexing (GFDM). In perfect reconstruction (PR) or near perfect reconstruction (NPR) filter bank designs, these aforementioned FBMC waveforms adopt the use of well-designed prototype filters (which are used for designing the synthesis and analysis filter banks) so as to either replace or minimize the CP usage of the 4G networks in order to provide higher spectral efficiencies for the overall increment in data rates. The accurate designing of the FIR low-pass prototype filter in NPR filter banks results in minimal signal distortions thus, making the analysis filter bank a time-reversed version of the corresponding synthesis filter bank. However, in non-perfect reconstruction (Non-PR) the analysis filter bank is not directly a time-reversed version of the corresponding synthesis filter bank as the prototype filter impulse response for this system is formulated (in this dissertation) by the introduction of randomly generated errors. Hence, aliasing and amplitude distortions are more prominent for Non-PR. Channel estimation (CE) is used to predict the behaviour of the frequency selective channel and is usually adopted to ensure excellent reconstruction of the transmitted symbols. These techniques can be broadly classified as pilot based, semi-blind and blind channel estimation schemes. In this dissertation, two linear pilot based CE techniques namely the least square (LS) and linear minimum mean square error (LMMSE), and three adaptive channel estimation schemes namely least mean square (LMS), normalized least mean square (NLMS) and recursive least square (RLS) are presented, analyzed and documented. These are implemented while exploiting the near orthogonality properties of offset quadrature amplitude modulation (OQAM) to mitigate the effects of interference for two filter bank waveforms (i.e. OFDM/OQAM and GFDM/OQAM) for the next generation of wireless networks assuming conditions of both NPR and Non-PR in slow and fast frequency selective Rayleigh fading channel. Results obtained from the computer simulations carried out showed that the channel estimation schemes performed better in an NPR filter bank system as compared with Non-PR filter banks. The low performance of Non-PR system is due to the amplitude distortion and aliasing introduced from the random errors generated in the system that is used to design its prototype filters. It can be concluded that RLS, NLMS, LMS, LMMSE and LS channel estimation schemes offered the best normalized mean square error (NMSE) and bit error rate (BER) performances (in decreasing order) for both waveforms assuming both NPR and Non-PR filter banks. Keywords: Channel estimation, Filter bank, OFDM/OQAM, GFDM/OQAM, NPR, Non-PR, 5G, Frequency selective channel.