2 Data and Signals

Data

must be transformed to electromagnetic signals

Analog signals

which include speech, audio, and video, have an infinite number of values. These are represented as a sine wave

Digital signals

are predominantly binary in nature and thus are represented by two (2) values or bits: 0 and 1. These are represented as a square wave

Periodic signal

It completes a pattern within a measurable time frame, called a period, and repeats that pattern over subsequent identical periods. The completion of one (1) full pattern is called a cycle

Nonperiodic signal

It changes without exhibiting a pattern or cycle that repeats over time. Both analog and digital signals can be periodic or nonperiodic

Wavelength

is directly related to the frequency of a given waveform. Formula for Wavelength

Frequency

refers to the number of waves that pass a given point in each time period and is often expressed in terms of hertz (𝑯𝒛) or cycles per second

Amplitude

is a measure of how big the wave is, which is measured as follows:

crest

The height from the equilibrium point to the highest point of a

trough

The depth from the equilibrium point to the lowest point of a .

Modems

is a contraction of the words “modulator” and “demodulator.”

Modulation

is the process of converting data into radio waves by adding information to an electronic or optical carrier signal. A carrier signal is one with a steady waveform—constant height, or amplitude, and frequency

Amplitude modulation (AM)

It is the modulation technique in which carrier amplitude varies based on analog baseband information signal to be transmitted in a wireless medium

Frequency modulation (FM)

It is the modulation technique in which carrier frequency varies based on analog baseband information signal to be transmitted in a wireless medium

Phase modulation (PM)

It is the modulation technique in which the carrier phase varies based on analog baseband information signal to be transmitted in a wireless medium

Analog-to-Digital Conversion: From PAM to PCM

This method is used to convert an analog signal, such as voice and video, into a digital signal. Each time a sample is taken,

ADC (Analog-to-Digital Converter)

that converts the analog value to a digital (binary) equivalent.

Sampling

lays out of the analog signal in a graph.

pulse amplitude modulation (PAM).

converts analog amplitudes to discrete levels and is a type of modulation called

to quantize

the digital pulses, which means to approximate the amplitude value of a pulse to the nearest integer on a predefined set of permitted integers

Quantization

layers the discrete signal in the analog signal with less margin of error.

Encoding (pulse code modulation [PCM])

converts discrete signals into highs (1) and lows (0), making these the binary equivalent of a time-bound discrete signal. Line coding is the process of converting digital data into digital signals. It is the representation of the digital signal to be transmitted by a digital waveform.

Channel Impairments

As a signal propagates along a communication path from its source to its destination, it is subject to different types of impairments

Attenuation

The strength of a signal decreases as it travels along a transmission medium. The amount of attenuation depends on the medium, but in general, it increases with distance

Noise

It is usually defined as an unwanted signal that is superimposed on a desired signal.

Atmospheric noise

is the noise that is caused by such natural atmospheric phenomena as lightning discharge in thunderstorms and other electrical disturbances that occur in nature.

Man-made noise

is an electromagnetic (EM) noise that is caused by human activities, which are associated with the use of electrical equipment. High-voltage wires and fluorescent lamps also produce this type of noise

Extraterrestrial noise

is the noise that comes from outside the earth and includes solar noise and cosmic noise. Solar noise is the noise that originates from the sun, while cosmic noise is generated by distant stars

Thermal noise

occurs in electrical conductors and is caused by the thermal agitation of the charges in the material

Shot noise

arises from the time-dependent fluctuations in electrical current. This is caused by the discrete nature of electron charges. It is particularly noticeable in semiconductor devices

Distortion

It refers to the change or alteration of an object. Thus, in terms of data transmission, distortion means that the signal changes its form or shape

Delay distortion

is a phenomenon that is peculiar to guided transmission media

Signal-to-Noise Ratio

It is often useful to have a quantitative method for describing the quality of a signal in terms of its corruption by noise