  The Laser Interferometer Space Antenna (LISA) aims to observe gravitational
waves in the mHz regime over its 10-year mission time. LISA will operate laser
interferometers between three spacecrafts. Each spacecraft will utilize
independent clocks which determine the sampling times of onboard phasemeters to
extract the interferometric phases and, ultimately, gravitational wave signals.
To suppress limiting laser frequency noise, signals sampled by each phasemeter
need to be combined in postprocessing to synthesize virtual equal-arm
interferometers. The synthesis in turn requires a synchronization of the
independent clocks. This article reports on the experimental verification of a
clock synchronization scheme down to LISA performance levels using a hexagonal
optical bench. The development of the scheme includes data processing that is
expected to be applicable to the real LISA data with minor modifications.
Additionally, some noise coupling mechanisms are discussed.
