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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
MODULE Direction of Communication
Direction Of Flow Simplex A B Half-duplex Full-duplex
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
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 Guard Band Channel 1 Frequency F1 Channel 2 Frequency F2 One physical medium (Coaxial cable).
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 Guard Bands 5 Mhz Channel 1 50 Mhz 10 Mhz Channel 2 150 Mhz 5 Mhz One cable with a bandwidth of 220 MHz.
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 Cable TV (carries multiple channels) TV 3 TV 1 TV 2 Tuned to Channel 77 at Frequency f77 Tuned to Channel 33 at Frequency f33 Tuned to Channel 65 at Frequency f65
An Example of Multiple Channel Communication in Space Channel 4 At freq.. F4 TV1 Regular TV Transmission TV2 Channel 11 At freq.. F11 Transmission Towers
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
MODULE Frequency Spectrum
Frequency Spectrum • Spectrum of frequencies available for communication • Ranges from voice to high speed optical communication