  String cosmology models predict a relic background of gravitational wave
produced during the dilaton-driven inflation. It's spectrum is most likely to
be detected by ground gravitational wave laser interferometers (IFOs), like
LIGO, Virgo, GEO, as the energy density grows rapidly with frequency. We show
the certain ranges of the parameters that underlying string cosmology model
using two approaches, associated with 5% false alarm and 95% detection rate.
The result presents that the approach of combining multiple pairs of IFOs is
better than the approach of directly combining the outputs of multiple IFOs for
LIGOH, LIGOL, Virgo and GEO.
