Impact of baseband filtering on the SGLS waveform

This paper investigates the effects of the baseband filtering on the data performance of the Space-Ground Link Subsystem (SGLS) uplink. The uplink SGLS waveform investigated in this paper includes data, command, and ranging signals. The performance of the data channel will be evaluated analytically for ideal conditions, namely, perfect carrier/sub-carrier tracking, frequency synchronization, timing recovery, and filtering. For imperfect conditions, a computer simulation model has been developed to examine the impacts of baseband filtering on the power spectral density (PSD) of the uplink signal and bit error rate (BER) performance of the data channel. It was found that (1) the baseband filter improves the out-of-band attenuation by about 35 dB, and (2) the additional bit signal-to-noise (SNR) degradation due to baseband filtering is about 0.5 dB. In addition, to optimize BER performance when inserting the baseband filter, it is necessary to adjust the effective modulation indices.