This document discusses different types of communication channels. It describes wireline channels like twisted pair and coaxial cable. It covers fiber optic channels and their advantages over coaxial cables. It also explains wireless electromagnetic channels, including ground wave propagation, skywave propagation, and line of sight propagation. Additionally, it discusses underwater acoustic channels and their challenges. Finally, it lists some common modulation methods used for underwater acoustic communications.

1. DEPARTMENT OF ELECTRONICS AND
COMMUNICATION ENGINEERING
COMMUNICATION CHANNEL
BY.
MD.FAIZAN AHMAD
(M.Tech -2015-16)
Reg no-15304013

2.  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.

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

4.  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.

5. A. Outer plastic sheath
B. Woven copper shield
C. Inner dielectric insulator
D. Copper core

6.  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.

8.  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.

9.  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.

10.  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.

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

14.  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.

16.  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.

17.  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)

19. THANK YOU