Muos Ka Downlink Performance Evaluation with Transmitter Distortion

Mobile user objective system (MUOS) employs a Ka-band feeder downlink from the satellite to the radio access facility (RAF). The feeder downlink transmits an octal phase shift keying (8-PSK) modulated signal. A high power amplifier (HPA) is used for the amplification of transmitted signals. The HPA produces distortions by creating AM/AM and AM/PM modulations in the transmitted signals. This non-linearity induces bandwidth expansion and nonlinear distortion in the in-band signals. 8-PSK is sensitive to HPA non-linear distortion. In this paper, we analyze the sensitivity of the MUOS feeder downlink bit error rate (BER) degradation to HPA output back-off (OBO). The analysis model consists of the non-linearity, additive white Gaussian noise (AWGN), and ideal carrier recovery and synchronization. Monte Carlo bit error rate (BER) simulations are performed with the analysis model to derive the distorted energy-per-bit to noise density ratio (E_b/N_o ) at the average BER. Finally, we derive reduction in E_b/N_o to achieve the target BER and characterize E _b/N_o degradation sensitivity to HPA OBO