Depends on modulation method and boundary conditions like noise, see the Shannon–Hartley theorem. The simplest context is given by the Nyquist rate limiting equation: fp ≦ 2B , where fp is the pulse frequency (in pulses per second) and B is the bandwidth (in Hz) - quoted from the a.m. Wiki explanation page.
I.e. the bandwidth must be greater than - or at least equal to - half the data rate.