  Third-generation gravitational wave detectors, such as Einstein Telescope and
Cosmic Explorer, will detect a bunch of gravitational wave (GW) signals
originated from the coalescence of neutron star and black hole binary systems
out to the higher redshifts, $z\sim 5-10$. There is a potential concern that
some of the GW signals detected at a high statistical significance eventually
overlap with each other, and the parameter estimation of such an overlapping
system can differ from the one expected from the single event. Also, there is
certainly the overlapping systems in which one of overlapping events has low
signal-to-noise ratio unable to clearly detect. Those system will be
potentially misidentified with a single GW event, and the estimated parameters
of binary GWs can be biased. In this paper, we estimate the occurrence rate of
those overlapping events, and study their statistical impacts on the parameter
estimation based on the Fisher matrix analysis. Our finding is that the
overlapping signals produce neither large statistical errors nor serious
systematic biases on the parameters of binary systems, unless the coalescence
time and the redshifted chirp masses of the two overlapping GWs are very close
to each other. The occurrence rate of such a closely overlapping event is shown
to be very small with the third-generation detectors.
