Root spectral density of GW strain as a function of GW frequency. Black symbols represent the GW signal of sdB+NS systems from the CE ejection channel, where ~D = 10 kpc, T = 4 yr are assumed. The dashed and dotted lines plot the sensitivity curves of LISA with an S/N = 1 and S/N = 5, respectively (Klein et al. 2016), and the solid line shows the full sensitivity curve combining the instrument noise and Galactic confusion noise (Cornish & Robson 2018).