Abstract
Radio frequency (RF) transmitter linearity has become a topic of intensive research worldwide in the wireless communication. With increasing demands for higher data rate and advanced modem techniques are being adopted by many wireless standards. However, to achieve this goal, the linearity of RF transmitter towards more and more critical. Instead of doing the analog power amplifier (PA) circuitry design, we propose several digital calibration techniques to cooperate with the analog RF PA and these digital compensation techniques help to correct for the PA nonlinerity which in turn improve the overall RF transmitter performance. In chapter 2 of this dissertation, we discuss the PA nonlinearity and exiting digital predistortion linearization schemes. Digital predistortion at baseband is an efficient and low-cost method for the linearization of a PA in a wireless system employing a non-constant-envelop modulation scheme, so as to reduce the adjacent channel interference. The look-up-table based digital adaptive predistortion (DAPD-LUT) approaches are low-cost and effective for PA linearization in wireless applications. However, most existing DAPD-LUT schemes are sub-optimum because they adopt uniformly-spaced LUTs regardless of the system state information (SSI), i.e., the PA characteristics and the input signal statistics. Other existing DAPD-LUT schemes assume either full or partial knowledge of the SSI to optimize and then to freeze the LUT spacing. Without prior knowledge of the SSI, in chapter 3 of this dissertation, we propose an SSI-learning low-complexity procedure to optimize the LUT spacing for a DAPD-LUT scheme. The proposed procedure is capable of online adapting the LUT spacing for PAs with various nonlinear characteristics, for input signals with various statistics, and for wireless environments with various time-varying properties. Orthogonal frequency division multiplexing system is sensitive to nonlinear distortion due to its large peak-to-average power ratio (PAPR) value. However, most existing PAPR reduction schemes are inflexible and sub-optimum because they adopt distortion or distortionless of PAPR reduction regardless of the PA characteristics. The nonlinear distortion caused by a PA is due to clipping distortion and compressive gain distortion. In chapter4, a separately optimized PAPR reduction and LUT-based predistortion scheme is proposed to efficiently mitigate both clipping distortion and compressive gain distortion. The proposed procedure is capable of online adapting the parameter of PAPR reduction scheme and the LUT spacing for PAs with various nonlinear characteristics, for various signal-to-distortion and noise ratio, and for wireless environments with various time-varying properties.