EEE 307, Spring, 2015 Introduction to Communication Systems Mariam B. Salim Dept. of Electrical and Electronic Engineering 11/01/2015
Jan 20, 2016
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