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In the context of the Laser Interferometer Space Antenna (LISA), the lasersubsystems exhibit frequency fluctuations that introduce significant levels ofnoise into the measurements, surpassing the gravitational wave signal byseveral orders of magnitude. Mitigation is achieved via time-shiftingindividual measurements in a data processing step known as time-delayinterferometry (TDI). The suppression performance of TDI relies on accurateknowledge and consideration of the delays experienced by the interferinglasers. While considerable efforts have been dedicated to the accuratedetermination of inter-spacecraft ranging delays, the sources for onboarddelays have been either neglected or assumed to be known. Contrary to theseassumptions, analog delays of the phasemeter front end and the laser modulatorare not only large but also prone to change with temperature and heterodynefrequency. This motivates our proposal for a novel method enabling acalibration of these delays on-ground and in-space, based on minimal functionaladditions to the receiver architecture. Specifically, we establish a set ofcalibration measurements and elucidate how these measurements are utilized indata processing, leading to the mitigation of the delays in the TDI Michelsonvariables. Following a performance analysis of the calibration measurements,proposed calibration scheme is assessed through numerical simulations. We findthat in the absence of the calibration scheme, the assumed drifts of the analogdelays increase residual laser noise at high frequencies of the LISAmeasurement band. A single, on-ground calibration of the analog delays leads toan improvement by roughly one order of magnitude, while re-calibration in spacemay improve performance by yet another order of magnitude. Towards lowerfrequencies, ranging error is always found to be the limiting factor for whichcountermeasures are discussed.

Compensation of front-end and modulation delays in phase and ranging measurements for time-delay interferometry