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Transmitter

Transmitter. The transmitter modifies the message signal into a form suitable for transmission over the channel, which involves varying some parameter of a carrier wave in accordance with the message signal. This process is called modulation. Two Types of Modulation Process:.

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Transmitter

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  1. Transmitter The transmitter modifies the message signal into a form suitable for transmission over the channel, which involves varying some parameter of a carrier wave in accordance with the message signal. This process is called modulation. Two Types of Modulation Process: 1. CW (Continuous-Wave) Modulation: a sinusoidal wave is used as the carrier Analog Communication • AM (Amplitude Modulation) • Angle Modulation • FM (Frequency Modulation) • PM (Phase Modulation) Analog or Digital Communication 2. Pulse Modulation: the carrier consists of a periodic sequence of rectangular pulses -can itself be of an analog or digital type. Note: Multiplexing, results from the use of modulation. Multiplexing is the process of combining several message signals for their simultaneous transmission over the same channel. Three commonly used methods of multiplexing are: • Frequency-division multiplexing (FDM), makes use of CW modulation • Time-division multiplexing (TDM), makes use of pulse modulation • Code-division multiplexing (CDM)

  2. Analog Pulse Modulation The amplitude, duration, or position of a pulse is varied in accordance with sample values of the message signal: PAM, Pulse-Amplitude Modulation PDM, Pulse-Duration Modulation PPM, Pulse-Position Modulation Digital Pulse Modulation Pulse-Code Modulation, PCM starts out essentially as PAM, but with an important modification: the amplitude of each modulated pulse (i.e., sample of the original message signal) is quantized or rounded off to the nearest value in a prescribed set of discrete amplitude levels and then coded into a corresponding sequence of binary symbols. The binary symbols 0 and 1 are themselves represented by pulse signals that are suitably shaped for transmission over the channel. As a result of the quantization process, some information is always lost and the original message signal cannot therefore be reconstructed exactly. Pulse Modulation

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