Communications Systems

COMMUNICATION SYSTEMS

Elements of Communication Sytems!

The Source!

The Channels!

Types of Modulation!

Signal Bandwidth

OUTLINE

ELEMENTS OF

COMMUNICATION SYSTEM

SOURCE TRANSMITTER RECEIVER DESTINATION

CHANNEL

ELEMENTS OF

COMMUNICATION SYSTEM

SOURCE* TRANSMITTER RECEIVER DESTINATION

CHANNEL

• need to be in FORM to pass through CHANNEL

!• to employ

*SOURCE

TRANSMITTER and RECEIVER

ELEMENTS OF

COMMUNICATION SYSTEM

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SIGNAL MODULATED CARRIERS

about 300 Hz - 3 kHz

High-Fidelity Music

about 20 Hz - 20 kHzFrequency  (Hz)

!

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A N A L O G

about 4.2 Mhz

⇛SOURCEVoice

Video (TV)

ELEMENTS OF

COMMUNICATION SYSTEM

SOURCE

SIGNAL FREQUENCIES

Voice

Alphanumeric

ANY Bandwidth !!!DEPENDENT: !□ Transmission (bps) □ Method to convert binary 1’s & 0’s to electrical signal

Frequency  (Hz)!

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D I G I T A L

Video

⇛

ELEMENTS OF

COMMUNICATION SYSTEM

CHANNEL (a path for transmission of signal)

TYPES

Modulated Carriers !

• information signal • modulating signal • baseband

BASEBAND  Frequency  spectrum  of  information  signal

"⇛

Carrier  Signals

!

Analog

Digital

Carrier  Frequency  HIGHER  THAN  Information  Signal

CONDUCTOR PAIRS (DIRECT)

FIBER OPTICS

FREE SPACE

RADIO LINK !

• Not OK for DIRECT LINK • Needs HIGHER ANTENNA • INTERFERENCE • Needs CARRIER

• Process by which some characteristics of the carrier wave is varied in accordance with an information-bearing signal.$

• Done at Transmitter (TX)!• Demodulation (Detection) done at Receiver (Rx)$!

MODULATION

! Carrier is Sine Wave!

e(t) = Ec sin (wct + θ)!!

where e(t) = instantaneous voltage as a function of time$$ Ec = peak voltage (Amplitude)$$ wc = frequency in radians per second$$ t = time in seconds$$ θ = phase angle in radians$

SIGNAL BANDWIDTH

!I = ktB!

! where I = amount of information to be sent!! k = a constant dependent on modulation type (i.e. AM, FM, PCM etc.)!! t = time available!! B = channel bandwidth$

Hartley’s Law

FREQUENCY DIVISION MULTIPLEXING (FDM)

! Combining of two or more information signals.$

Multiplexing

! Process of dividing available frequency range among signals.$

Frequency Division Multiplexing (FDM)

TYPES OF MODULATION

SOURCE* TRANSMITTER RECEIVER DESTINATION

CHANNEL

• need to be in FORM to pass through CHANNEL

!• to employ

*SOURCE

TRANSMITTER and RECEIVER