Digital modulation is encoding a data signal onto a carrier wave for transmission. There are several different methodologies for digital modultion.
Modulation is the process of impressing a transmission signal (called a carrier) with information to be transmitted. Digital Modulation is the process where a data stream of binary signals is impressed upon a carrier for transmission. The carrier may be either analog or digital. In analog transmission (such as the PSTN or public switched telephone network) The carrier will have a well defined bandpass that determines the timing requirements for the modulation and demodulation of digital transmission to the carrier. ( In the PSTN example analog signals are 300hz to 3.3khz) Digital modulation of a digital carrier is usually a matter of multiplexing the carrier into a higher frequency transmission line on a time multiplexed basis. An example of this is a single subscriber line telephone circuit may be digitized as a 64kilobit/second signal. Several of these may be multiplexed together into a T1 line that is clocked at a higher data rate of 1.5 Mbits/second. Common digital modulation schemes are ASK Amplitude shift Keying APSK Amplitude/Phase shift keying CPM Continuous Phase Modulation FSK Frequency shift Keying MFSK Multiple Frequency shift keying MSK Minimum Shift Keying OOK On off Keying PPM Pulse Position Modulation PSK Phase Shift Keying QAM Quadrature Amplitude Modulation SC-FDE Single Carrier Frequency Division Encoding TCM Trellis Modulation CSS Chirp Spread Spectrum DSSS Direct Sequence Spread Spectrum FHSS Frequency Hopping Spread Spectrum THSS Time Hopping Spread Spectrum
