| Communications Toolbox | |
Digital Modulation Overview
Modulating a digital signal can be interpreted as a combination of two steps: mapping the digital signal to an analog signal and modulating the analog signal. These are depicted in the schematic below.
Two Steps of Digital Modulation
Except for FSK and MSK methods, when the receiver tries to recover a digital message from the analog signal that it receives, it performs two steps: demodulating the analog signal and demapping the demodulated analog signal to produce a digital message. These are depicted in the schematic below.
Two Steps of Digital Demodulation
For FSK and MSK methods, the demodulator uses correlation techniques instead of the two-stage process above.
The mapping process increases the sampling rate of the signal from Fd to Fs, whereas the demapping process decreases the sampling rate from Fs to Fd.
Functions in this toolbox can perform any of these steps, as summarized in the table below.
| Step |
Function |
| Mapping and modulation |
dmodce or dmod |
| Mapping only |
modmap |
| Modulation without mapping |
dmodce or dmod, with /nomap flag |
| Demodulation and demapping |
ddemodce or ddemod |
| Demodulation without demapping (ASK, PSK, or QASK) |
ddemodce or ddemod, with /nomap flag |
| Demapping only |
demodmap |
The functions are described in more detail in the sections that follow.
| | Filter Design Issues | Representing Digital Signals | |
