Many different modulation schemes can implement high bit rates. For example, frequency-shift keying (FSK) typically uses two different frequencies in each symbol interval to represent binary 0 and 1.
Abstract: An experiment in transmitting speech by Pulse Code Modulation, or PCM, is described in this paper. Each sample amplitude of a pulse amplitude modulation or PAM signal is transmitted by a ...
I think you should be able to re-use the schematic from the FSK implementation application note even for FM modulation. You could try changing the passive component values to tweak the VCO frequency ...