Nonlinear Analysis and Digital Pre-Distortion of the SC-FDMA Signals in LTE Uplink System

Single-carrier frequency division multiple access (SC-FDMA) has become a popular alternative to orthogonal frequency division multiple access (OFDM) in multi-user communication on LTE uplink systems. This is primarily due to the low peak-to-average power ratio (PAPR) of SC-FDMA compared to that of OFDM. Long-term evolution (LTE) uses SC-FDMA on the uplink to exploit this PAPR advantage to reduce transmit power amplifier (PA) back-off in mobile user terminals. However, the latest generation of communication systems requires high power efficiency and a large quantity of capacity in transmitting mobile data, bringing out some other critical problems: 1) the nonlinearity of Radio Frequency (RF) power amplifiers inevitably affects the power efficiency. Working beyond the saturation point is the main reason for power amplifiers having nonlinear properties; 2) In order to obtain adequate capacity, wide bandwidth is applied to the latest communication systems. Since in previous systems the pre-distorter would focus on memory-less distortion with relatively narrow bandwidth, this change makes memory distortion become a serious issue, degrading the transmission quality in the wireless communication systems.;The intent of this thesis is to present nonlinear analysis of the SC-FDMA Spectrum with the RF power amplifier. Relevant mathematical models were considered and applied to the RF power amplifier in terms of intermodulation products and the third-order intercept point. The equivalent mathematical model is applied for the first time to SC-FDMA signals and with the previous formulation of the PA model, the derivation of the expressions for spectrum regrowth of amplified SC-FDMA signals was first established and finally simulated with Matlab software. The digital pre-distortion (DPD) technology was also applied to SC-FDMA signals for the first time in this thesis. An inverse intermodulation and Autoregressive Moving-Average (IM-ARMA) model was introduced to linearize the PA distortion with memory in the LTE uplink system. The DPD was finally implemented by Matlab R2010b.;Conclusions are drawn that amplified power emission levels can be expressed by the form of third-order intercept point (IP3). The expressions for spectrum regrowth of amplified SC-FDMA signals have been verified for the first time with the comparison of simulation, measurement and calculation results. The effects of third order intermodulation have a greater impact than higher order components with respect to out-of-band emission power levels. Furthermore, the DPD algorithm reduced the spectrum regrowth of SC-FDMA signals by 12 dB. The proposed pre-distorter can effectively solve the distortion problem caused by the memory effect in RF power amplifier.