Left panel: the effective potential ﹩{M}_{p}^{2}V(\tau )﹩ in inflationary (blue line) and bounce (green line) cosmologies. Middle panel: propagation of primordial GWs with different structure of effective potential (one-peak structure in the upper panel and two-peak structure in the lower panel). Right panel: the energy density spectrum in inflationary (blue line) and bounce (green line) cosmologies. Conformal time τ is rescaled such that τ = −τ_*(τ = 0) represents the location of negative (positive) peak in bounce scenario. ﹩{f}_{{\rm{IM}}}﹩ is the frequency of GWs that cross the horizon at the end of inflationary epoch/contraction phase, respectively.