Performance analysis and enhancement of OFDM-based WLAN systems in the presence of nonlinear HPAs and narrowband interference for single and multiple transmit antennas

OF THE DISSERTATION Performance Analysis and Enhancement of OFDM-based WLAN Systems in the Presence of Nonlinear HPAs and Narrowband Interference for Single and Multiple Transmit Antennas by David Wei-Ting Chi Doctor of Philosophy in Electrical Engineering (Communication Theory and Systems) University of California San Diego, 2008 Professor Pankaj Das, Chair Professor Rene L. Cruz, Co-Chair This dissertation addresses the performance issue of Orthogonal Frequency Division Multiplexing (OFDM) based WLANs operating in the presence of nonlinear high power amplifiers (HPAs), narrowband interference (NBI) or jammer and channel estimation error in Rayleigh fading channels for Single Input Single Output (SISO) and Multiple Input Multiple Output (MIMO) antennas configurations. Furthermore, to loosen the design criteria of practical HPAs, a novel PAPR reduction algorithm and receiver structure are proposed in the dissertation to improve the system performance. In the first part of the thesis, we analyze the performance of a M-ary Quadrature Amplitude Modulation (M-QAM) SISO-OFDM system that is impaired by nonlinear HPAs, jammer and channel estimation error. We also present a more practical jammer model in this part of analysis. Next, we will consider a M-QAM SISO-OFDM system that is subject to nonlinear HPAs and channel estimation error in fading channels. In this case, we utilize the channel estimation error model1 to significantly reduce the complexity of the bit error rate (BER) expression. For the third part of thesis, we extend the work presented in part one to include the scenario where the system has multiple transmit antennas while it is still impaired by nonlinear HPAs, NBI and channel estimation error. Finally, we propose a new algorithm to minimize the nonlinear distortion introduced by nonlinear HPAs and a new receiver structure that offers superior performance in fading channels. The performance of a SISO-OFDM system which is impaired by nonlinear HPAs, NBI and channel The model was proposed by M. Al-Gharabally in his work, M. Al-Gharabally and P. Das, ”On the Performance of OFDM Systems in Time Varying Channels with Channel Estimation Error”, IEEE ICC, 2006, pp. 5180-5185