Data communication systems

Modulation and transmission

Information rides on a high-frequency carrier. In AM the carrier's amplitude follows the signal; bandwidth $=2f_m$. In FM its frequency varies; bandwidth $\approx2(\Delta f+f_m)$, wider but much less affected by noise. Signals travel through copper wire, optical fibre or free space (radio, microwaves); time-division multiplexing sends many channels down one link by interleaving samples.