EEE 307 Spring 2015 Introduction to Communication Systems

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

Communication l Communication – transfer of information from one point to another l Tele (Far) + Communications – by converting the info into electrical signals l Early telecommunications l l Telegraph and telephone l l smoke signals Telegraph (1837) – Wheatstone & Morse (separately) Telephone (1876) – Alexander Bell Radio and television Telephony l Voice and Data

Communication Systems l Process describing transfer of information, data, instructions between one or more systems through some media l l Signals passing through the communication channel can be digital, or analog l l l Examples l people, computers, cell phones, etc. l Computer communication systems Analog signals: continuous electrical waves Digital signals: individual electrical pulses (bits) Receivers and transmitters: phones (landline or mobile), desktop computers, laptops, etc.

Communication Systems

A Communications Model 3 Main Components: 1. Transmitter (Tx) 2. Channel 3. Receiver (Rx)

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

Modulation l 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. l 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

The Receiver l Recovers the message signal contained in the received signal. l 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. l Jobs of the Receiver: 1. Demodulation 2. Signal filtering 3. Noise Suppression, etc.

Communication Channels l l A channel is a path between two communication devices Channel capacity: How much data can be passed through the channel (bit/sec) l l l Also called channel bandwidth The smaller the pipe the slower data transfer! Consists of one or more transmission media l l Materials carrying the signal Two types: l Physical: wire cable l Wireless: Air T 1 lines destination network server T 3 lines T 1 lines

Physical Transmission Media l A tangible media l Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc. - Twisted-pair cable: l One or more twisted wires bundled together l Made of copper - Coax-Cable: l Consists of single copper wire surrounded by three layers of insulating and metal materials l Typically used for cable TV - Fiber-optics: l Strands of glass or plastic used to transmit light l Very high capacity, low noise, small size, less suitable to natural disturbances

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

Wireless Transmission Media l l Broadcast Radio l Distribute signals through the air over long distance l Uses an antenna l Typically for stationary locations l Can be short range Cellular Radio l A form of broadcast radio used for mobile communication l High frequency radio waves to transmit voice or data l Utilizes frequency-reuse Microwave l Radio waves providing high speed transmission l They are point-to-point (can’t be obstructed) l Used for satellite communication Infrared (IR) l Wireless transmission media that sends signals using infrared light- waves - Such as?

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

Frequency Range for Wired Channel l 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 input TX RX Output (received signal) distortion : input [s(t)] does not match output [r(t)] Channel s(t) r(t) = s(t)+n(t) Additive noise channel