On the power spectral density of SGLS and USB waveforms

Most of the DoD satellites utilize the Space-to-Ground Link Subsystem (SGLS) for tracking, telemetry, and command (TT and C) controls. The standard SGLS waveform uses a phase modulation (PM) scheme on the combined PCM/FSK/AM signal and pseudo-random noise (PRN) square wave signal for command and ranging, respectively. The SGLS uplink operates in the 1755-1850 MHz (L-band), while the downlink operates in the 2200-2290 MHz (S-band). On the other hand, the non-DoD satellites for other various governmental agencies primarily use Unified S-Band (USB) for their TT and C links. Two waveforms, PCM/PSK/PM and PCM/PM/Bi-Phase, are mainly used in the USE for command along with either PRN squarewave or sinusoidal tone for ranging. Due to a high demand of utilizing the L-band for the mobile satellite services, the government has been thinking of migrating its SGLS uplink from L-band to USB to avoid the increasing radio frequency interference (RFI) from/to other mobile satellite systems. Such a migration raises a concern with respect to interference between the immigrated and existing links. To study the RFI impact, the power spectrum density (PSD) of both SGLS and USE waveforms and their respective bandwidth efficiency need to be studied. This paper derives the PSD for the SGLS and USB waveforms and compares their respective occupied bandwidths.