Master of Computer Science & IT (MCIT)

Fall Semester 2013

Elec1ve Course (CT-531) Wireless & Mobile Communica:on

Lecture 2

Dr. Muhammad Mubashir Khan mmkhan@neduet.edu.pk

Department of Computer Science & IT, NED University of Engineering & Technology, Karachi

September 2013

Background Topics Informa1on Signals Frequency and Frequency Bands Channel Capacity Mul1plexing Frequency Division Mul1ple Access (FDMA) Time Division Mul1ple Access (TDMA) Propaga1on Modes Ground wave, Sky wave, Line of sight transmission

Spread Spectrum Frequency Hopping Spread Spectrum (FHSS) Direct Sequence Spread Spectrum (DSSS) Code Division Mul1ple Access (CDMA)

Other points will be explained as needed

Electromagne1c signals Electromagne1c waves can be imagined as a self-propaga1ng transverse oscilla1ng wave of electric and magne1c fields.

Frequency and Wavelength The rela1ve wavelengths of the electromagne1c waves of three different colors of light (blue, green, and red) with a distance scale in micrometers along the x-axis.

Greater wavelength Smaller frequency

Smaller wavelength greater frequency

Frequency (f): Rate, in cycles per second, or Hertz (Hz) at which the signal repeats

Peak amplitude (A) - maximum value or strength of the signal over 1me; typically measured in volts

Wavelength () - distance occupied by a single cycle of the signal Or, the distance between two points of corresponding phase of two consecu1ve cycles

Phase () - measure of the rela1ve posi1on in 1me within a single period of a signal

Analog & Digital Signals Analog signal - signal intensity varies in a smooth fashion over 1me

No breaks or discon1nui1es in the signal Digital signal - signal intensity maintains a constant level for some period of 1me and then changes to another constant level

Periodic signal - analog or digital signal pa`ern that repeats over 1me s(t +T ) = s(t ) -< t < +

where T is the period of the signal

A digital signal waveform: (1) low level, (2) high level, (3) rising edge, and (4) falling edge.

William Stallings Book

Frequency, Spectrum, Bandwidth Fundamental frequency - when all frequency components of a signal are integer mul1ples of one frequency, its referred to as the fundamental frequency (the lowest frequency of a periodic waveform)

Spectrum - range of frequencies that a signal contains Absolute bandwidth - width of the spectrum of a signal Effec:ve bandwidth (or just bandwidth) - narrow band of frequencies that most of the signals energy is contained in

The greater the bandwidth, the higher the informa:on-carrying capacity

EM Spectrum

EM Spectrum = Gamma rays HX = Hard X-rays SX = Sok X-Rays EUV = Extreme-ultraviolet NUV = Near-ultraviolet Visible light (colored bands) NIR = Near-infrared MIR = Moderate-infrared FIR = Far-infrared EHF = Extremely high frequency (microwaves) SHF = Super-high frequency (microwaves) UHF = Ultrahigh frequency (radio waves) VHF = Very high frequency (radio) HF = High frequency (radio) MF = Medium frequency (radio) LF = Low frequency (radio) VLF = Very low frequency (radio) VF = Voice frequency ULF = Ultra-low frequency (radio) SLF = Super-low frequency (radio) ELF = Extremely low frequency (radio)

Fundamental Frequency Any electromagne1c signal can be shown to consist of a collec1on of periodic analog signals (sine waves) at different amplitudes, frequencies, and phases

The period of the total signal is equal to the period of the fundamental frequency

A`enua1on The gradual loss in intensity of any kind of signal (wave) through a medium. sunlight is a`enuated by dark glasses, X-rays are a`enuated by lead, and light and sound are a`enuated by water.

In electrical engineering and telecommunica1ons, a`enua1on affects the propaga1on of waves and signals in electrical circuits, in op1cal fibers, as well as in air (radio waves).

Rela1onship b/w Data Rate and Bandwidth The greater the bandwidth, the higher the informa1on-carrying capacity

Conclusions Any digital waveform will have infinite bandwidth

BUT the transmission system will limit the bandwidth that can be transmi`ed

AND, for any given medium, the greater the bandwidth transmi`ed, the greater the cost

HOWEVER, Limi1ng the bandwidth creates distor1ons making it difficult to interpret the received signal

The only way to get finest steep edge is by adding an infinite number of harmonics.

Data, Signal, Transmission Data - en11es that convey meaning, or informa1on Signals - electric or electromagne1c representa1ons of data

Transmission - communica1on of data by the propaga1on and processing of signals

Analog data Video Audio

Digital data Text Integers

Analog Signals A con1nuously varying electromagne1c wave that may be propagated over a variety of media, depending on frequency

Examples of media: Copper wire media (twisted pair and coaxial cable) Fiber op1c cable Atmosphere or space propaga1on

Analog signals can propagate analog and digital data

Digital Signals A sequence of voltage pulses that may be transmi`ed over a copper wire medium

Generally cheaper than analog signaling Less suscep1ble to noise interference Suffer more from a`enua1on Digital signals can propagate analog and digital data

Different combina1ons are possible Digital data, digital signal Equipment for encoding is less expensive than digital-to-analog equipment

Analog data, digital signal Conversion permits use of modern digital transmission and switching equipment

Digital data, analog signal Some transmission media will only propagate analog signals

Examples include op1cal fiber and satellite Analog data, analog signal Analog data easily converted to analog signal

Analog and Digital transmission Transmit analog signals without regard to content A`enua1on limits length of transmission link Cascaded amplifiers boost signals energy for longer distances but cause distor1on Analog data can tolerate distor1on Introduces errors in digital data

Digital Signal Repeaters achieve greater distance Repeaters recover the signal and retransmit

Analog signal carrying digital data Retransmission device recovers the digital data from analog signal

Generates new, clean analog signal

Channel Capacity Channel (A specific radio frequency, pair or band of

frequencies) Impairments, such as noise, limit data rate that can be

achieved For digital data, to what extent do impairments limit data

rate? Channel Capacity the maximum rate at which data can be

transmi`ed over a given communica1on path, or channel, under given condi1ons

Related concepts Data rate - rate at which data can be communicated (bps) Bandwidth - the bandwidth of the transmi`ed signal as constrained by the transmi`er and the nature of the transmission medium (Hertz)

Noise - average level of noise over the communica1ons path Error rate - rate at which errors occur Error = transmit 1 and receive 0; transmit 0 and receive 1

Signal to Noise Ra1o Ra1o of the power in a signal to the power contained in the noise thats present at a par1cular point in the transmission

Typically measured at a receiver Signal-to-noise ra1o (SNR, or S/N)

A high SNR means a high-quality signal, low number of required intermediate repeaters

SNR sets upper bound on achievable data rate

Shannon's Capacity Formula Equa1on:

Represents theore1cal maximum that can be achieved

Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB

Using Shannons formula

Transmission Media Transmission Medium Physical path between transmi`er and receiver

Guided Media Waves are guided along a solid medium E.g., copper twisted pair, copper coaxial cable, op1cal fiber

Unguided Media Provides means of transmission but does not guide electromagne1c signals

Usually referred to as wireless transmission E.g., atmosphere, outer space Transmission and recep1on are achieved by means of an antenna

Configura1ons for wireless transmission Direc1onal Omni-direc1onal

General Frequency Ranges Microwave frequency range 1 GHz to 40 GHz Direc1onal beams possible Suitable for point-to-point transmission Used for satellite communica1ons

Radio frequency range 30 MHz to 1 GHz Suitable for omnidirec1onal applica1ons

Infrared frequency range Roughly, 3x1011 to 2x1014 Hz Useful in local point-to-point mul1point applica1ons within confined areas

Terrestrial Microwave Descrip1on of common microwave antenna Parabolic "dish", 3 m in diameter Fixed rigidly and focuses a narrow beam Achieves line-of-sight transmission to receiving antenna Located at substan1al heights above ground level

Applica1ons Long haul telecommunica1ons service Short point-to-point links between buildings

Satellite Microware Descrip1on of communica1on satellite Microwave relay sta1on Used to link two or more ground-based microwave transmi`er/receivers

Receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)

Applica1ons Television distribu1on Long-distance telephone transmission Private business networks

Broadcast Radio Descrip1on of broadcast radio antennas Omnidirec1onal Antennas not required to be dish-shaped Antennas need not be rigidly mounted to a precise alignment

Applica1ons Broadcast radio VHF and part of the UHF band; 30 MHZ to 1GHz Covers FM radio and UHF and VHF television

Mul1plexing Capacity of transmission medium usually exceeds capacity required for transmission of a single signal

Mul1plexing - carrying mul1ple signals on a single medium More efficient use of transmission medium

Why Mul1plexing? Cost per kbps of transmission facility declines with an increase in the data rate

Cost of transmission and receiving equipment declines with increased data rate

Most individual data communica1ng devices require rela1vely modest data rate support

Basic Mul1plexing Techniques Frequency-division mul1plexing (FDM) Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal

Time-division mul1plexing (TDM) Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal

FDM

TDM

Get in touch

Course homepage h`ps://sites.google.com/site/WirelessMobileCommunica1on/

Best way to contact me is to email: mmkhan@neduet.edu.pk