Page 101 - DCAP406_DCAP_207_Computer Networks

Computer Networks/Networks

Notes The digital transmission requires a low pass channel with high bandwidth. The analog
transmission can be carried on band pass channels. The different methods that convert
binary data or a low pass analog signal into a band pass analog signal is called modulation.
The digital to analog conversion includes ASK (Amplitude Shift Keying), FSK (Frequency
Shift Keying), PSK (Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), QAM
(Quadrature Amplitude Modulation) and have been explained under the section Modem
Modulation Techniques.

Analog to analog signal conversion involves amplitude modulation, frequency
modulation and phase modulation techniques.

6.7 Keywords

Amplitude Modulation: It involves the modulation of the amplitude of the carrier as analog
sine wave.
Amplitude Shift Keying: ASK refers to technique how the carrier wave is multiplied by the
digital signal f(t) so that the strength of the carrier wave is varied to represent binary 0 and 1.
Baud Rate: It is the number of times per second the line condition can switch from “1” to “0”.
Binary Phase Shift Keying: BPSK involves two possible phases shift for the modulation.

Carrier Signal: It is the base signal generated by the sending device whose one of the
characteristics is altered in accordance with the digital signal to be modulated.
Differential Phase Shift Keying: In this method, the modem shifts the phase of each succeeding
signal in a certain number of degrees.
FDM: In frequency division multiplexing, multiple channels are combined together for
transmission over a single channel.

FDMA: This divides the frequency band into various channels based on the FDM techniques.
Each of these can carry a voice conversation or, with digital service, carry digital data.
Frequency Modulation: Frequency Modulation involves the modulation of the frequency of
the analog sine wave.
Frequency Shifted Keying: FSK describes the modulation of a carrier (or two carriers) by using
a different frequency for a 1 or 0.
Inter modulation: It involves two (or more) sinusoids effect one another to produce undesired
products, that is, unwanted frequencies (noise).
Modems: Refers to the modulator and demodulator that converts analog signal to digital
signal and vice versa.

Modulation: It is the act of translating some low-frequency (base band signal) such as voice,
data, etc. to a higher frequency.
Multiplexing: Refers to the process in which multiple channels are combined for transmission
over a common transmission path.
Phase Modulation: Phase Modulation (PM) is similar to frequency modulation. Instead of the
frequency of the carrier wave changing, the phase of the carrier wave changes.

Phase Shift Keying: In this modulation method a sine wave is transmitted and the phase of the
sine wave carries the digital data or the phase of sine wave is varied to represent binary 1 or 0
and both the amplitude and frequency of the analog waveform are kept constant.

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