Performance Analysis of Sequential Carrier- and Code-Tracking Receivers in the Context of High-Precision Spaceborne Metrology Systems

Future space observatories achieve the detection of gravitational waves by interferometric measurements of a carrier phase, allowing to determine relative distance changes, in combination with an absolute distance measurement based on the transmission of pseudorandom noise (PRN) chip sequences. In addition, usage of direct-sequence spread spectrum modulation enables data transmission. Hereafter, we report on the findings of a novel performance evaluation of planned receiver architectures, performing phase and distance readout sequentially, addressing the interplay between both measurements. An analytical model is presented identifying the power spectral density (PSD) of the chip modulation at frequencies within the measurement bandwidth (BW) as the main driver for phase noise. This model, verified by numerical simulations, excludes binary phase shift keying (BPSK) modulations for missions requiring picometer noise levels at the phase readout, while binary offset carrier (BOC) modulation, where most of the power has been shifted outside the measurement BW, exhibits superior phase measurement performance. Ranging analyses of the delay-locked loop (DLL) reveal strong distortion of the pulse shape due to the preceding phase tracking introducing ranging bias variations. Numerical simulations show that these variations, however, which originate from data transitions, are compensated by the delay tracking loop, enabling submeter ranging accuracy, irrespective of the modulation type.