First stage of LISA data processing: Clock synchronization and   arm-length determination via a hybrid-extended Kalman filter
  In this paper, we describe a hybrid-extended Kalman filter algorithm to synchronize the clocks and to precisely determine the inter-spacecraft distances for space-based gravitational wave detectors, such as (e)LISA. According to the simulation, the algorithm has significantly improved the ranging accuracy and synchronized the clocks, making the phase-meter raw measurements qualified for time- delay interferometry algorithms. 
Yan Wang, Gerhard Heinzel, and Karsten Danzmann
gr-qc astro-ph.IM