Performance evaluation of non-ideal RF transmitter in LTE/LTE-Advanced systems

The long term evolution (LTE) and LTE-Advanced (LTE-A) standards are under development for the next generation mobile communication systems. High peak data rates and high spectral efficiency are some of the requirements of these standards, which should also include flexible spectrum usage (FSU) techniques for an efficient use of the limited available bandwidth (BW). Considering non-contiguous orthogonal frequency division multiplexing (NC-OFDM) as a possible FSU proposal for LTE/LTE-Advanced, in this paper an analysis of the effects of the RF imperfections -such as IQ imbalance, phase noise and non-linear power amplifier- on the downlink transmission in LTE/LTE-Advanced is presented. Two different aspects are pointed out. First, concerning NC-OFDM, it is shown that the RF transmitter causes an increase of the power spectral density (PSD) in the subchannels not used for transmission, which means interference with the other systems using those subchannels. Second, concerning the high data rates and high spectral efficiency, it turns out that the 64-QAM rate 3/4, used to reach these requirements, is deeply affected by the RF transmitter imperfections.