MODEM in digital communications
MODEM
MODEM is cobination of modulator and demodulator. Computer data is binary in nature and consists of sequence of 1s and 0s. Telephone lines are analog in nature and can carry only analog electrical signals. So devices called MODEMs are needed to transmit data over telephone lines.
| MODEM = MODulator + DEModulator |
- A computer without MODEM is like a dog without bones
- A computer without MODEM is like a car without petrol
- Two computers nearby can be connected directly. This connection is called NULL modem.
Modem consists of two sub-units called modulator and demodulator
Modulator converts digital signal into analog signal.
Demodulator converts analog signal back to digital signal. Remember that computer can understand only digital signal.
NOTE: Modulation is the process of adding carrier to modulating signal. Demodulation is the process of removing carrier from modulated signal. (Refer my video lecture on Modulation in Electronic Communication System).
DIGITAL MODULATION TECHNIQUES
Various digital modulation techniques used for conversion of analog to digital and vice-versa are:
- ASK (Amplitude Shift Keying)
- FSK (Frequency Shift Keying)
- PSK (Phase Shift Keying)
- QPSK (Quadrature Phase Shift Keying)
- QAM (Quadrature Amplitude Modulation)
- MSK (Minimum Shift Keying)
- GMSK (Gaussian MSK)
