  Future space observatories achieve 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 pseudo-random noise 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 of the chip
modulation at frequencies within the measurement bandwidth as the main driver
for phase noise. This model, verified by numerical simulations, excludes binary
phase-shift keying modulations for missions requiring pico-meter noise levels
at the phase readout, while binary offset carrier modulation, where most of the
power has been shifted outside the measurement bandwidth, exhibits superior
phase measurement performance. Ranging analyses of the delay-locked loop 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 sub-meter ranging accuracy, irrespective of
the modulation type.
