EEE 307, Spring, 2015

Introduction to Communication Systems

Mariam B. Salim

Dept. of Electrical and Electronic Engineering

11/01/2015

Communication

Communication – transfer of information from one point to another

Tele (Far) + Communications – by converting the info into electrical signals

Early telecommunications smoke signals

Telegraph and telephone Telegraph (1837) – Wheatstone & Morse (separately) Telephone (1876) – Alexander Bell

Radio and television Telephony

Voice and Data

Process describing transfer of information, data, instructions between one or more systems through some media Examples

people, computers, cell phones, etc. Computer communication systems

Signals passing through the communication channel can be digital, or analog Analog signals: continuous electrical waves Digital signals: individual electrical pulses (bits)

Receivers and transmitters: phones (landline or mobile), desktop computers, laptops, etc.

Communication Systems

Communication Systems

A Communications Model

3 Main Components:

1. Transmitter (Tx)2. Channel3. Receiver (Rx)

The Transmitter

Converts the electrical signal to match the physical channel characteristics for transmission purposes.

a. Federal Communication Commission (FCC) specifies freq. range for each transmitting station. b. transmitter translates the information/message signal into an appropriate frequency range to match the frequency assigned to that specific transmitter… why? to insure multiple signals being transmitted don’t interfere with one another

Jobs of the Transmitter: 1. filter the message signal 2. modulate information/message signal 3. amplify the modulated signal

Analog Modulation – message signal is used to vary either the

amplitude, frequency, or phase of a sinusoidal carrier to match

the message signal to the channel characteristics. - allows transmission of multiple messages from many users over the same physical channel.

Types of Analog Modulation: a. Amplitude Modulation – transmitted message signal is

in the amplitude variations of the sinusoidal carrier.

i. Double Sideband-Suppressed Carrier AM

ii. Conventional Double Sideband AM

iii. Single Sideband AM b. Angle Modulation – transmitted message signal is contained in the

frequency or phase variations of the sinusoidal carrier. i. Frequency Modulation

ii. Phase Modulation

Modulation

tftmAtctmts cc 2cos)()()()(

tftmAtctmts cc 2cos)](1[)()()(

]2sin)(ˆ2cos)([)()()( tftmtftmAtctmts ccc

))(2cos()( ttfAts cc general form of angle modulation

The Receiver

Recovers the message signal contained in the

received signal. Carrier Demodulation - used to extract the message from the

sinusoidal carrier if the message signal is transmitted by carrier modulation.

a. usually demodulated message signal is degraded due to noise

and signal distortion present in the received signal.

Jobs of the Receiver: 1. Demodulation

2. Signal filtering

3. Noise Suppression, etc.

Communication Channels

A channel is a path between two communication devices

Channel capacity: How much data can be passed through the channel (bit/sec) Also called channel bandwidth The smaller the pipe the slower data transfer!

Consists of one or more transmission media Materials carrying the signal Two types:

Physical: wire cable Wireless: Air

destination network server

T1 lines

T1 lines

T1 lines

T3 lines

Physical Transmission Media A tangible media

Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc.

- Twisted-pair cable: One or more twisted wires bundled together Made of copper

- Coax-Cable: Consists of single copper wire surrounded by three layers of

insulating and metal materials Typically used for cable TV

- Fiber-optics: Strands of glass or plastic used to transmit light Very high capacity, low noise, small size, less suitable to natural

disturbances

Physical Transmission Media

plastic outer coating

woven or braided metal

insulating material

copper wire

twisted-pair cable twisted-pair wire

protective coating

glass cladding

optical fiber core

Coaxial cable Twisted-pair cable

Fiber Optics

Wireless Transmission Media Broadcast Radio

Distribute signals through the air over long distance Uses an antenna Typically for stationary locations Can be short range

Cellular Radio A form of broadcast radio used for mobile communication High frequency radio waves to transmit voice or data Utilizes frequency-reuse

Microwave Radio waves providing high speed transmission They are point-to-point (can’t be obstructed) Used for satellite communication

Infrared (IR) Wireless transmission media that sends signals using

infrared light- waves - Such as?

Wireless Transmission Media

Coaxial cable

Free Space Optical Communication

Satellite Communication

Broadcast or Mobile Communication

Frequency Range for Wired Channel

The frequency range for guided wire channel their wavelength distance.

Note: as frequency in Hz, the wavelength in meters

Electromagnetic Spectrum Chart

Signal Traveling through Channel

TX RX

Channelinput Output

(received signal)

distortion

n(t)

s(t) r(t) = s(t)+n(t)

Channel

: input [s(t)] does not match output [r(t)]

Additive noise channel