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UBC Theses and Dissertations

Analysis and design of OFDM systems : loading and nonlinear distortion mitigation Mohammadnia-Avval, Mohammad


In wireless communication systems, multiples copies of the transmitted signal arrive at the receiver. This phenomenon causes channel variations in the frequency domain over the transmission bandwidth. Conventional systems use equalizers to tackle this problem. Another approach is to use multicarrier communication systems based on orthogonal frequency division multiplexing (OFDM). In this technique, the entire bandwidth is divided into several subchannels, and, as a result, each subchannel experiences almost a flat fading channel. In this dissertation, we work on three different areas in OFDM systems: (1) We propose new analytical methods to evaluate the error rate of coded OFDM systems for a particular channel realization. (2) Assuming the instantaneous channel is known both at the transmitter and the receiver, we introduce adaptive transmission techniques to enhance the performance of these systems, and (3) we propose a new receiver-based technique to recover the distortion caused by the practical non-linear power amplifier. To address the first subject, a novel analytical method for bit error rate evaluation of coded OFDM systems for a specific channel realization is proposed. As this method might be too complex for some applications, we also propose a simpler formula. As for the second subject, we introduce new adaptive bit loading and interleaving techniques to minimize the bit error rate of the system. Also, we propose novel adaptive bit and power loading and code rate selection techniques to minimize bit error rate, to minimize the transmit power, or to maximize the throughput of the system. To address the third subject, we propose a new method to estimate the original nonclipped signal. The estimation is done at the receiver and makes use of the newly proposed compressed sensing estimation technique.

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