Many digital modulation methods such as COFDM use the electromagnetic spectrum very efficiently, allowing for a very tight spectral mask.
12.
In practice this upper bound can only be approached for line coding schemes and for so-called vestigal sideband digital modulation.
13.
By switching the sound field on and off very rapidly the deflected beam appears and disappears in response ( digital modulation ).
14.
It is for this reason that, in the context of digital modulations, digitally modulated signals are usually referred to as carriers.
15.
Thus the analogue modulations can be viewed as extreme cases of higher-order digital modulations for which the order is equal to infinity.
16.
Digital modulation schemes are possible because the transmitter-receiver pair have prior knowledge of how data is encoded and represented in the communications system.
17.
The bit stream is split into several parallel data streams, each transferred over its own sub-carrier using some conventional digital modulation scheme.
18.
Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion.
19.
Most textbooks would consider digital modulation schemes as a form of digital transmission, synonymous to data transmission; very few would consider it as analog transmission.
20.
You can't talk about it in terms of " bit rate " ( as you could with digital modulation schemes like PSK and OFDM ).
