Title:  Nonlinear Distortion Mitigation in Dynamic-range-limited Optical Wireless Communication System

Committee: 

Dr. Zhou, Baxley, Advisor     

Dr. Ma, Chair

Dr. G.K. Chang

Dr.

Abstract: The objective of the proposed research is to mitigate the nonlinear distortion in dynamic-range-limited optical wireless communication (OWC) systems. The light emitting diode (LED) is the major source of nonlinearities since the electrical-to-optical conversion in the LED is nonlinear. Moreover, to drive the LED, the input electric signal must be positive and exceed the turn-on voltage of the device. On the other hand, the signal is also limited by the saturation point or maximum permissible value of the LED. As a result, the nonlinearity in an OWC system can be treated as a family of dynamic-range-limited nonlinearities. To overcome nonlinearities, we can deal with either the signal or the system. One straightforward approach is to choose or modify input signals such that they are insensitive to the nonlinear distortions. Another approach is to compensate for the nonlinearities by predistortion or postdistortion. In the preliminary research, we will analyze how to maximize the signal-to-noise-plus-distortion ratio (SNDR) of the nonlinearities in optical wireless communication (OWC) systems. The result herein can serve as a guideline to design predistortion linearization of nonlinear devices like LEDs. Additionally, we will study the constrained clipping method which can mitigate the distortions so that the clipping levels can be more aggressive than the simple clipping to further reduce the peak-to-average power ratio (PAPR) for orthogonal frequency division multiplexing (OFDM) signals. In the proposed research, we will extend our work to multiple-input multiple-output (MIMO) OWC systems and bit-loaded OFDM systems. In MIMO OWC system, we will study the design of MIMO transceiver under the OWC-specific constraints such as the dynamic-range constraint. In bit-loaded OFDM system, we will consider constellation-wise distortion constraints into the design of PAPR reduction techniques.