Improvement of power efficiency of HPA by the PAPR reduction and predistortion

In this paper, we propose the PAPR (peak to average power ratio) reduction methods of SLM (selected mapping), and PTS (partial transmit sequence) to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear HPA (high power amplifier) in the multi-code CDMA (code division multiple access) system. The phase rotation factors transmitted as side information in PTS and SLM methods play an important role in the BER performance. So, we newly derive the theoretical BER equation when the effects of side information are considered in the multi-code CDMA communication system. Simulation results show that the PTS reduces the PAPR by about 2 dB while SLM can reduce by about 3 dB, compared with the original MC-CDMA when QPSK is used for 32 branches. Also, we find the BER performance of multi-code CDMA system with and without predistorter in front of the HPA. When predistorter is used, 3 dB IBO (input backoff) is required in SLM method, and 5 dB IBO in PTS method to closely match with the linear amplifier. Without PAPR reduction method, more than 7 dB is required. Finally, we show that the simulation results are very close to the theoretical results.