Communication channel

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

COMMUNICATION CHANNEL

BY.MD.FAIZAN AHMAD(M.Tech -2015-16)Reg no-15304013

PONDICHERRY UNIVERSITY

COMMUNICATION CHANNEL

It is physical medium that is used to send the signal from the Transmitter to the Receiver.

The communication channel provides the connection between the Transmitter and Receiver.

Wire line Channel.Fiber Optic Channel.Wireless–Electromagnetic Channel.Underwater Acoustic Channel.Storage Channel.

TYPES OF COMMUNICATION CHANNEL

The telephone network makes extensive use of wire lines for voice signal transmission as well as data and video transmission.

Twisted-pair wire line and coaxial cable are basically guided EM channel that provides relatively modest BW of KHz and for co-axial cable it has MHz range.

Signal Transmitted through such channel are distorted in both amplitude, phase and further corrupted by additive noise.

WIRELINE CHANNEL

A. Outer plastic sheathB. Woven copper shieldC. Inner dielectric insulatorD. Copper core

Co-axial cable

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.

Optical fiber offers the communication system designer a channel BW that is several order of magnitude larger than co-axial cable channels.

Transmitter or modulator in a fiber optic communication system is a light source, either a LED or a LESER.

FIBER-OPTIC CHANNEL

The structure of a typical single-mode fiber

1. Core: 8 µm diameter2. Cladding: 125 µm dia.3. Buffer: 250 µm dia.4. Jacket: 400 µm dia.

In wireless communication system EM energy is coupled to the propagation medium by an antenna which as the radiator.

The modes of the propagation of EM waves in the atmosphere and free space may be subdivided into three categories.

a) Ground Wave Propagation.b) Sky-wave Propagation.c) Line of sight(LOS) propagation.

Wireless EM Wave

Ground Wave propagation is a method of radio frequency propagation that uses the area between the surface of the earth and the ionosphere for transmission.

The ground wave can propagate a considerable distance over the earth's surface particularly in the low frequency and medium frequency portion of the radio spectrum. Ground wave radio propagation is used to provide relatively local radio communications coverage.

a) Ground Wave Propagation

Sky wave refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere.

Sky wave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands.

b) Sky wave propagation

Most long-distance shortwave (high frequency) radio communication—between 3 and 30 MHz—is a result of sky wave propagation.

Radio waves (black) reflecting off the ionosphere (red) during sky wave propagation.

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves.

Line-of-sight propagation is a characteristic of electromagnetic radiation. Electromagnetic transmission includes light emissions traveling in a straight line.

The rays or waves may be diffracted, refracted reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles.

c)Line of sight(LOS) propagation

Line of sight propagation to an antenna

Underwater acoustic communication is a technique of sending and receiving message below water.

Under water communication is difficult due to factors like multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation.

Underwater Acoustic Channel

The modulation methods developed for radio communications can be adapted for underwater acoustic communications (UAC).

Some of the modulation methods used for UAC are as follows:

Frequency Shift Keying (FSK) Phase Shift Keying (PSK) Frequency Hopped Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS) Frequency and Pulse Position Modulation

(FPPM and PPM) Multiple Frequency Shift Keying (MFSK)

 Underwater Acoustic Network 

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