4. EEE 307, Spring, 2015 Introduction to Communication Systems
Mariam B. Salim
Dept. of Electrical and Electronic Engineering
11/01/2015

5. 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

6. Communication Systems
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.

7. Communication Systems

8. A Communications Model
3 Main Components:
Transmitter (Tx)
Channel
Receiver (Rx)

9. The Transmitter Jobs of 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

10. Modulation
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
general form of angle modulation

11. 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.

12. 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
T3 lines

13. 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

14. Physical Transmission Media
Coaxial cable
Twisted-pair cable
plastic outer coating
woven or braided metal
insulating material
copper wire
twisted-pair cable
twisted-pair wire
protective coating
glass cladding
optical fiber core
Fiber Optics

15. 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?

16. Wireless Transmission Media
Coaxial cable
Satellite Communication
Free Space Optical Communication
Broadcast or Mobile Communication

17. Frequency Range for Wired Channel
The frequency range for guided wire channel their wavelength distance.
Note: as frequency in Hz, the
wavelength in meters

18. Electromagnetic Spectrum Chart

19. Signal Traveling through ChannelTX RX
Channel
input
Output
(received signal)
distortion
: input [s(t)] does not match
output [r(t)]
Channel
s(t)
r(t) = s(t)+n(t)
n(t)
Additive noise channel