Bandlimited DPD Adapted APD for 5G Communication

Spectrally efficient techniques which help in achieving a high data rate in the communication system also generate signals with a high peak-to-average power ratio (PAPR), which drives the power amplifier (PA) in early saturation. This brief proposes a bandlimited digital predistortion (DPD) adapted analog predistortion (APD) method to linearize the PA. It uses the APD technique first to remove the out-of-band distortion, and then bandlimited DPD is used to remove the in-band distortion. Unlike the conventional DPD, the bandlimited DPD does not require a very high bandwidth feedback signal which is three-to-seven times the input signal bandwidth. The bandwidth of the feedback signal in the bandlimited DPD is the same as that of the input signal. This makes the proposed method more suitable for high bandwidth signals used in advanced communication standards like 5G. The experiments performed with 64-QAM OFDM signals of bandwidth 20 MHz and 100 MHz achieve a maximum normalized mean square error (NMSE) improvement of 21 dB and 18 dB over PA, respectively. The APD circuit used in the method is designed at a central frequency of 3.5 GHz, but the experiments are carried out in an extended frequency range of 2.5 to 4.5 GHz, and the results show that the proposed method delivers significant NMSE improvement in this frequency range.