FREQUENCY CHANNEL ENCODING

Pulse Modulation (PAM, PPM, and PFM):

In digital communication the bit steam associated with the data stream derived from the message source may also be encoded in modulated carrier formats -- viz.
 
 
Analog Encoding
Digital Encoding
Amplitude modulation (AM)
 
Pulse amplitude modulation (PAM) 
or 
Amplitude shift keying (ASK)
 
Phase modulation (PM) 
 
Pulse phase modulation (PPM) 
or 
Phase shift keying (PSK)
 
Frequency modulation (AM)

 
Pulse frequency modulation (PFM) 
or 
Frequency shift keying (FSK)
 

TEMPORAL REPRESENTATIONS OF ASK AND FSK SIGNALS

ASK encoding of a given bit stream                       FSK encoding of the same bit stream