CHAPTER Communication Direction, Bandwidth and Channels.

CHAPTERCHAPTER

Communication Communication Direction, Bandwidth Direction, Bandwidth

and Channels and Channels

© N. Ganesan, Ph.D. , All rights reserved.

Chapter

Frequency Spectrum and Bandwidth

Chapter Objectives• Explain the different types of directional

flows in signal propagation• Define bandwidth and the use of the

terminology in communications• Discuss communication channels and

the splitting of bandwidth to accommodate multiple channels

• Describe baseband and broadband transmission and present practical examples in each case

Chapter Objectives (continued)

• Discuss communication channels and the splitting of bandwidth to accommodate multiple channels

• Describe baseband and broadband transmission and present practical examples in each case

Chapter Modules

• Direction of communication • Communication channels• Baseband and broadband channels

© N. Ganesan, Ph.D. , All rights reserved.

MODULE

Direction of Communication

Direction Of Flow

Simplex

Half-duplex

Full-duplex

A B

Direction Of Flow Details

• Simplex– One direction only– Radio broadcast

• Half-duplex– One direction at any one point in time– CB radio

• Full duplex– Both directions at the same time– Telephone lines

END OF MODULE END OF MODULE

© N. Ganesan, Ph.D. , All rights reserved.

MODULE

The Concepts of Channels in Communication

A Definition of a Communication Medium

• One that allows the propagation of information carried by either electromagnetic or optical signals

Types of Media• Physical medium and the space or

open medium• Physical medium

– Also know as the guided medium– Coaxial cable, Optical fiber etc.

• Open Medium – Denotes the space above the earth– The term space is galactic in scope

• Multiple channels can be established in each of these media for communication

Presence of Multiple Channels in a Physical

Media

Channel 1

Channel 2

One physical medium (Coaxial cable).

Frequency F1

Frequency F2

Guard Band

Channel Characteristics

• A sub-bandwidth is assigned for each channel for communication

• Channel differentiation– Each channel transmits using a different

frequency– The transmission frequency chosen for a

channel is usually near the middle of the assigned bandwidth for the channel

• Guard bands are present around each channel to minimize interference

Low and High-speed Channels in Medium

Channel 1

Channel 2

One cable with a bandwidth of 220 MHz.

50 Mhz

150 Mhz

5 Mhz

5 Mhz

10 Mhz

Guard Bands

Channel Characteristics of the Example

• Channel speeds within a medium need not be the same

• Channel 2 in the previous example is faster than channel 1– Channel 2 speed is Proportional to 150 Hz– Channel 1 speed is Proportional 50 Hz

• Total bandwidth of the medium is computed as follows:– 5 + 150 + 10 +50+5 =220 MHz

An Example of Multiple Channels in a Physical

Medium

TV 1 TV 2 TV 3

Cable TV (carries multiple channels)

Tuned toChannel 33 at Frequency f33

Tuned toChannel 65 at Frequency f65

Tuned toChannel 77 at Frequency f77

An Example of Multiple Channel Communication in

Space

TV1

TV2

Channel 4At freq.. F4

Channel 11At freq.. F11

Regular TVTransmission

TransmissionTowers

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© N. Ganesan, Ph.D. , All rights reserved.

MODULE

Baseband and Broadband Transmission

Baseband Transmission

• Single channel transmission– The physical medium carries one and

only one channel

• A good example is the LAN– Ethernet LAN for instance uses

baseband transmission

Broadband Transmission

• The presence of Multiple channels over a single physical medium

• One physical line is shared by multiple channels

• Cable TV• Internet

– Due to packet switching, one is given the impression of the presence of multiple channels

– Virtual broadband communication

END OF MODULEEND OF MODULE

© N. Ganesan, Ph.D. , All rights reserved.

MODULE

Frequency Spectrum

Frequency Spectrum

• Spectrum of frequencies available for communication

• Ranges from voice to high speed optical communication

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END OF CHAPTER END OF CHAPTER