Analog & Digital Communication

Definition: Companding is a technique of achieving non-uniform quantization. It is a word formed by the combination of words compression and expanding. Companding is done in order to improve SNR of weak signals. We know if the characteristics of the quantizer is non-linear then it causes the step size to be variable despite being constant then it is known as non-uniform quantization. As we know in non-uniform quantization, the step size varies according to the signal level.If the signal … [Read more...] about Companding

Definition: WDM is a short form used for Wavelength Division Multiplexing. It is a technique in which signals of different wavelength are multiplexed together in order to get transmitted over an optical link. The concept of WDM was arrived in 1970. It is an analog multiplexing technique used in fiber optic communication. Here, optical signals of multiple wavelengths are transmitted using a fiber link. Basically, the technique acts in a way that signals get combined using a multiplexer … [Read more...] about Wavelength Division Multiplexing (WDM)

Definition: Phase modulation is another type of angle modulation in which the phase of the carrier wave is changed according to the amplitude (magnitude) of the message (modulating) signal. In phase modulation of an analog signal, the phase change is a continuous back and forth movement. While in case of digital signal there exist an abrupt change in the phase of the carrier signal. The phase modulation of the digital signal is generally known as phase shift keying. The process of phase … [Read more...] about Phase Modulation (PM)

Definition: A category of angle modulation in which the frequency of the carrier wave is changed according to the amplitude of the message signal is known as frequency modulation. It is abbreviated as FM and is a widely used analog modulation technique. One can modulate a signal by varying the amplitude of the carrier signal according to the message signal, which we commonly knew as amplitude modulation (AM). The implementation of AM is simple. However, it possesses various … [Read more...] about Frequency Modulation (FM)

Definition: Amplitude Modulation is a technique by which the amplitude of the carrier wave is changed according to the signal wave or modulating signal. Among various modulation schemes, amplitude modulation is the simplest and oldest modulation technique. Basically, the information that is carried by the low frequency modulating signal is superimposed on the carrier wave of high frequency by varying the amplitude of the carrier. Thus it is termed as amplitude modulation. Theory of Amplitude … [Read more...] about Amplitude Modulation

Definition: A modulation technique that allows variation in the position of the pulses according to the amplitude of the sampled modulating signal is known as Pulse Position Modulation (PPM). It is another type of PTM, where the amplitude and width of the pulses are kept constant and only the position of the pulses is varied. Simply put, the pulse displacement is directly proportional to the sampled value of the message signal. To understand the generation of the PPM signal, it is … [Read more...] about Pulse Position Modulation (PPM)

Definition: A modulation technique that converts or encodes message signal into a binary bit stream is known as Delta Modulation. Here only 1 bit is used to encode 1 voltage level thus, the technique allows transmission of only 1 bit per sample. As PCM has the property of converting message signal directly into a sequence of a binary coded pulse, this resultantly increases the bandwidth requirement of the system. So, in order to remove the drawbacks of PCM, delta modulation is … [Read more...] about Delta Modulation (DM)

Definition: A modulation technique where the width of the pulses of the pulsed carrier wave is changed according to the modulating signal is known as Pulse Width Modulation (PWM). It is also known as Pulse duration modulation (PDM). Basics of Pulse Width Modulation It is a type of Pulse Time Modulation (PTM) technique where the timing of the carrier pulse is varied according to the modulating signal. In pulse duration modulation (PDM), the amplitude of the pulse is kept constant and only … [Read more...] about Pulse Width Modulation (PWM)

Definition: A modulation technique in which the amplitude of the pulsed carrier signal is changed according to the amplitude of the message signal is known as Pulse Amplitude Modulation (PAM). Simply put, the transmission of data takes place by the variation of the amplitude of pulse according to the modulating signal. Basics of PAM The technique does not show much variation in comparison to continuous wave modulation. The only difference is that the carrier in the pulse modulation … [Read more...] about Pulse Amplitude Modulation (PAM)

Definition: A technique by which analog signal gets converted into digital form in order to have signal transmission through a digital network is known as Pulse Code Modulation. It is abbreviated as PCM. PCM systems are basically signal coders also known as waveform coders. PCM allows the representation of the continuous time message signal as a sequence of binary coded pulses. The binary form permits only 2 probable states i.e., 0 and 1. The major steps involved in PCM is sampling, … [Read more...] about Pulse Code Modulation (PCM)