  The performance of pilot-aided joint-channel carrier-phase estimation (CPE)
in space-division multiplexed multicore fiber (MCF) transmission with
correlated phase noise is studied. To that end, a system model describing
uncoded MCF transmission where the phase noise comprises a common laser phase
noise, in addition to core- and polarization-specific phase drifts, is
introduced. It is then shown that the system model can be regarded as a special
case of a multidimensional random-walk phase-noise model. A pilot-aided CPE
algorithm developed for this model is used to evaluate two strategies, namely
joint-channel and per-channel CPE. To quantify the performance differences
between the two strategies, their respective phase-noise tolerances are
assessed through Monte Carlo simulations of uncoded transmission for different
modulation formats, pilot overheads, laser linewidths, numbers of spatial
channels, and degrees of phase-noise correlation across the channels. For 20
GBd transmission with 200 kHz combined laser linewidth and 1% pilot overhead,
joint-channel CPE yields up to 3.4 dB improvement in power efficiency or 25.5%
increased information rate. Moreover, through MCF transmission experiments, the
system model is validated and the strategies are compared in terms of
bit-error-rate performance versus transmission distance for uncoded
transmission of different modulation formats. Up to 21% increase in
transmission reach is observed for 1% pilot overhead through the use of
joint-channel CPE.
