  In the past few years, the detection of gravitational waves from compact
binary coalescences with the Advanced LIGO and Advanced Virgo detectors has
become routine. Future observatories will detect even larger numbers of
gravitational-wave signals, which will also spend a longer time in the
detectors' sensitive band. This will eventually lead to overlapping signals,
especially in the case of Einstein Telescope (ET) and Cosmic Explorer (CE).
Using realistic distributions for the merger rate as a function of redshift as
well as for component masses in binary neutron star and binary black hole
coalescences, we map out how often signal overlaps of various types will occur
in an ET-CE network over the course of a year. We find that a binary neutron
star signal will typically have tens of overlapping binary black hole and
binary neutron star signals. Moreover, it will happen up to tens of thousands
of times per year that two signals will have their end times within seconds of
each other. In order to understand to what extent this would lead to
measurement biases with current parameter estimation methodology, we perform
injection studies with overlapping signals from binary black hole and/or binary
neutron star coalescences. Varying the signal-to-noise ratios, the durations of
overlap, and the kinds of overlapping signals, we find that in most scenarios
the intrinsic parameters can be recovered with negligible bias. However, biases
do occur for a short binary black hole or a quieter binary neutron star signal
overlapping with a long and louder binary neutron star event when the merger
times are sufficiently close. Hence our studies show where improvements are
required to ensure reliable estimation of source parameters for all detected
compact binary signals as we go from second-generation to third-generation
detectors.
