Ways of altering the carrier
electromagnetic wave in order to transmit a signal efficiently. Examples are amplitude
modulation AM (data contained in amplitude of carrier), phase modulation PM (data contained in changes of phase),
frequency modulation FM (data contained in changes of frequency), Frequency shift keyed FSK (data contained in changes between two frequencies of carrier), pulse duration PDM (data contained in the duration of pulses), pulse position PPM (data contained in the position of the pulses relative to a reference point), continuous wave CW (data contained in a carrier which is switched on and off). In some cases, it is best to use a different modulation technique to and from a
tag.