CHAPTER

Communication Direction, Bandwidth and Channels

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

ChapterFrequency Spectrum and Bandwidth

Chapter ObjectivesExplain the different types of directional flows in signal propagationDefine bandwidth and the use of the terminology in communicationsDiscuss communication channels and the splitting of bandwidth to accommodate multiple channelsDescribe 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 channelsDescribe baseband and broadband transmission and present practical examples in each case

Chapter Modules

Direction of communication Communication channelsBaseband and broadband channels

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

MODULEDirection of Communication

Direction Of FlowSimplexHalf-duplexFull-duplexAB

Direction Of Flow DetailsSimplexOne direction onlyRadio broadcastHalf-duplexOne direction at any one point in timeCB radioFull duplexBoth directions at the same timeTelephone lines

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

MODULEThe Concepts of Channels in Communication

A Definition of a Communication MediumOne that allows the propagation of information carried by either electromagnetic or optical signals

Types of MediaPhysical medium and the space or open mediumPhysical mediumAlso know as the guided mediumCoaxial cable, Optical fiber etc.Open Medium Denotes the space above the earthThe term space is galactic in scopeMultiple channels can be established in each of these media for communication

Presence of Multiple Channels in a Physical MediaChannel 1Channel 2One physical medium (Coaxial cable).Frequency F1Frequency F2Guard Band

Channel CharacteristicsA sub-bandwidth is assigned for each channel for communicationChannel differentiationEach channel transmits using a different frequencyThe transmission frequency chosen for a channel is usually near the middle of the assigned bandwidth for the channelGuard bands are present around each channel to minimize interference

Low and High-speed Channels in Medium Channel 1Channel 2One cable with a bandwidth of 220 MHz.50 Mhz150 Mhz5 Mhz5 Mhz10 MhzGuard Bands

Channel Characteristics of the ExampleChannel speeds within a medium need not be the sameChannel 2 in the previous example is faster than channel 1Channel 2 speed is Proportional to 150 HzChannel 1 speed is Proportional 50 HzTotal bandwidth of the medium is computed as follows:5 + 150 + 10 +50+5 =220 MHz

An Example of Multiple Channels in a Physical MediumTV 1TV 2TV 3Cable TV (carries multiple channels)Tuned toChannel 33 at Frequency f33Tuned toChannel 65 at Frequency f65Tuned toChannel 77 at Frequency f77

An Example of Multiple Channel Communication in Space TV1TV2Channel 4At freq.. F4Channel 11At freq.. F11Regular TVTransmissionTransmissionTowers

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

MODULEBaseband and Broadband Transmission

Baseband TransmissionSingle channel transmissionThe physical medium carries one and only one channelA good example is the LANEthernet LAN for instance uses baseband transmission

Broadband TransmissionThe presence of Multiple channels over a single physical medium One physical line is shared by multiple channelsCable TVInternet Due to packet switching, one is given the impression of the presence of multiple channels Virtual broadband communication

END OF MODULE

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

MODULEFrequency Spectrum

Frequency SpectrumSpectrum of frequencies available for communicationRanges from voice to high speed optical communication

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