Wireless, cellular and personal communications

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Wireless, cellular and personal communications

introduction

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Text books/references

Wireless communications, principles and practice 2nd edition by Theodore S. Rappaport

Wireless communication by R. Blake Wireless communication by William Stallin

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Grading policy

Sessional=20% Midterm=30% Final=50%

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Award of Sessional Marks

Quiz =5% Assignment=5% Presentation=5% Class participation=5%

(Can have positive as well as negative weightage)

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Historical Background

1864. Maxwell predicted the existence of electromagnetic wave (radio wave).

1887 Hertz demonstrated the existence of radio wave.

1901 Marconi realized first across Atlantic wireless transmission (England to Canada)

1906 First radio broadcast (AM radio)

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Historical Background

1946: AT&T introduced first mobile telephone service using line of sight analog FM radio transmission, 120 kHz per voice channel, limited to 50 miles from base, operator-assisted dialing

Mid-1960s: AT&T’s IMTS (Improved Mobile Telephone Service) uses 30 kHz voice channels, narrowband FM and direct dialing

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Historical Background (cont)

First generation analog cellular telephony late 1940s: AT&T develops cellular concept for

frequency reuse 1971: AT&T proposes High Capacity Mobile

Phone Service to FCC 1979: US standardizes it as AMPS (Advanced

Mobile Phone System)in 800-900 MHz range

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Historical Background (cont)

First generation analog cellular telephony 1983: AT&T launches AMPS in Chicago 1985:

Nordic Mobile Telephone (NMT 450) in Scandanavia, Total Access Communications System (TACS) in UK, C450 in W. Germany

Total six incompatible analog cellular systems in Europe

Motivated Europe to accelerate 2nd generation digital cellular

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Historical Background (cont) Second generation digital cellular

1989: Europe standardized Global System for Mobile Communications (GSM)

1992: GSM is launched 1990: Japan standardized Japanese Digital Cellular

(JDC) now called Personal Digital Cellular (PDC) 1990: Europe standardized Digital Cellular System

at 1800 MHz (DCS 1800, recently renamed GSM 1800)

1993: DCS 1800 launched

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History (cont)

1992: TIA / IS-54 TDMA (Digital AMPS) is deployed in US

1996: TIA/IS-95 CDMA in US 1995: Personal Handphone System (PHS) in Japan,

first widespread low-tier PCS, is hugely successful 1996: AT&T and Sprint offer PCS in major US

cities Smaller cell sites (0.25 km vs traditional 1-8 km),

smaller/lighter portable handsets, cheaper access points

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History (cont)

1998: ITU begins to study proposals for 3rd generation cellular

mid-2000s: UMTS, IMT-2000, W-CDMA, cdma2000, EDGE,...

2010-?: 4th generation? Self organizing, ad hoc?

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Multimedia Requirements

Voice VideoData

Delay

Packet Loss

BER

Data Rate

Traffic

<100ms - <100ms

<1% 0 <1%

10-3 10-6 10-6

8-32 Kbps 1-100 Mbps 1-20 Mbps

Continuous Bursty Continuous

One-size-fits-all protocols and design do not work well

Wired networks use this approach, with poor results

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Wireless Performance Gap

WIDE AREA CIRCUIT SWITCHING

User Bit-Rate (kbps)

14.4digitalcellular

28.8 modem

ISDN

ATM

9.6 modem

2.4 modem2.4 cellular

32 kbps PCS

9.6 cellular

wired- wireless bit-rate "gap"

1970 200019901980YEAR

LOCAL AREA PACKET SWITCHING

User Bit-Rate (kbps)

Ethernet

FDDI

ATM100 M Ethernet

Polling

Packet Radio

1st genWLAN

2nd genWLAN

wired- wirelessbit-rate "gap"

1970 200019901980.01

.1

1

10

100

1000

10,000

100,000

YEAR

.01

.1

1

10

100

1000

10,000

100,000

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Spectrum Radio Frequency (RF)

1MHz to 1GHz (general classification, not absolute) 100 MHz to 1GHz (more widely used definition) Applications: AM radio, FM radio, TV, some cellular telephone

systems, etc. Microwave

1 GHz to 300 GHz (general) 1 GHz to 100 GHz (more widely used) Most cellular telephone systems, wireless LAN, Satellite, etc.

Trends towards use of higher frequencies Maximum bandwidth » 10% of carrier frequency More users and higher data rate More difficult to design leading to more $$ of investment

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1st generation: analog voice Example: Advanced Mobile Phone Service (AMPS) 2nd generation: digital voice and narrowband

data Examples: GSM, D-AMPS (AT&T), IS-95 (Interim

Standard-95) (Sprint) 2.5 generation: GPRS

3rd generation: digital voice and broadband data Examples: WCDMA, cdma2000

STANDARDS: MOBILE TELEPHONE SYSTEMS

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STANDARDS: MOBILE TELEPHONE SYSTEMS contd…

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IS-95 (Narrowband CDMA) Code Division Multiple Access All users Tx simultaneously using the same frequency and

same time. Different codes are used to separate the signals from

different users. CDMA

Each user is assigned a unique code The code is known at both transmitter (Tx) and receiver

(Rx) All users Tx at the same frequency and time Receiver uses codes to pick up desired signals Also called spread sprectrum

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WCDMA (Wideband CDMA) Also called UMTS (Universal Mobile Telephone System) Proposed by Ericsson Will mainly be used in European countries

cdma2000 Proposed by Qualcomm Will mainly be used in North America

Both standards use CDMA Only some detailed technical differences

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Basic concepts

In most wireless communication systems, the wireless communication occurs between mobile station (MS) and base station (BS) MS: Cell phone, wireless laptop, wireless PDA, etc. BS: wireless access point, wireless router, etc.

Downlink Radio channel for transmission from BS to MS Also called forward link

Uplink Radio channel for transmission from MS to BS Also called reverse link

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Basic concepts contd…

Simplex Communication occurs only in one direction E.g.

paging system Half Duplex

Tx can occur in either direction, but only one way at a time E.g. Walki-Talki (police radio)

Full Duplex Tx can occur at both direction simultaneously E.g.

Telephone. Two simplex One Full Duplex

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Base station A fixed station a mobile radio system used for

radio communication with mobile stations. Base stations are located at the center or on the edge of a coverage region and consists of radio channels and transmitter and receiver antennas mounted on a tower.

Control channel Radio channel used for transmission of call setup,

call request, call initiation and other beacon or control purposes.

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Forward channel Radio channel used for transmission of information from

the base station to the mobile

Handoff The process of transferring a mobile station from one

channel or base station to another.

Mobile station A station in the cellular radio service intended to for use

while in motion at unspecified locations. Mobile station may be hand held personal unit or installed in vehicles.

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Mobile switching center Switching center which coordinates the routing of

calls in a large service area. In a cellular radio system, the MSC connects the cellular base stations and mobiles to the PSTN. An MSC is also called mobile telephone switching office.

Reverse channel Radio channel used for the transmission of

information from the mobile to base station.

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Roamer A mobile station which operates in a service area

other than that from which service has been subscribed.

Transceiver A device capable of simultaneously transmitting

and receiving radio signals.

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Transmission Fundamentals

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Electromagnetic Signal

Function of time Can also be expressed as a function of frequency

Signal consists of components of different frequencies

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Time-Domain Concepts

Analog signal - signal intensity varies in a smooth fashion over time No breaks or discontinuities in the signal

Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level

Periodic signal - analog or digital signal pattern that repeats over time s(t +T ) = s(t ) -¥< t < +¥

where T is the period of the signal

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Aperiodic signal - analog or digital signal pattern that doesn't repeat over time

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

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

signal repeats

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Period (T ) - amount of time it takes for one repetition of the signal T = 1/f

Phase () - measure of the relative position in time within a single period of a signal

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

two consecutive cycles

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Sine Wave Parameters

General sine wave s(t ) = A sin(2ft + )

Figure 2.3 shows the effect of varying each of the three parameters (a) A = 1, f = 1 Hz, = 0; thus T = 1s (b) Reduced peak amplitude; A=0.5 (c) Increased frequency; f = 2, thus T = ½ (d) Phase shift; = /4 radians (45 degrees)

note: 2 radians = 360° = 1 period

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Sine Wave Parameters

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Time vs. Distance

When the horizontal axis is time, as in Figure 2.3, graphs display the value of a signal at a given point in space as a function of time

With the horizontal axis in space, graphs display the value of a signal at a given point in time as a function of distance At a particular instant of time, the intensity of the signal varies as

a function of distance from the source

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Frequency-Domain Concepts

Fundamental frequency - when all frequency components of a signal are integer multiples of one frequency, it’s referred to as the fundamental frequency

Spectrum - range of frequencies that a signal contains Absolute bandwidth - width of the spectrum of a signal Effective bandwidth (or just bandwidth) - narrow band of

frequencies that most of the signal’s energy is contained in

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Frequency-Domain Concepts

Any electromagnetic signal can be shown to consist of a collection 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

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Relationship between Data Rate and Bandwidth

The greater the bandwidth, the higher the information-carrying capacity

Conclusions Any digital waveform will have infinite bandwidth BUT the transmission system will limit the bandwidth that can

be transmitted AND, for any given medium, the greater the bandwidth

transmitted, the greater the cost HOWEVER, limiting the bandwidth creates distortions

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Electromagnetic waves and energy

All electromagnetic systems send information from one point to another by transmitting electromagnetic energy from the sender to the intended receiver. This electromagnetic energy can travel in various modes: As a voltage or current through wires As radio emissions through air As light through optical fiber In all cases it follows following law

Wavelength( )=Velocity (c)

Frequency (f)

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Where “c” is the propagation velocity and it depends on the medium through which it is traveling. The fastest propagation velocity occurs in vacuum

and is symbolized by the letter “c” C=3*10^8 m/s

What is the wavelength in vacuum for a frequency of 1 million hertz?

What is the frequency when the measured wavelength is 6 m?

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The propagation velocity is less in any medium other than vacuum.

In air the propagation velocity of electromagnetic energy is about 95 to 98% of the value in vacuum.

In wire it is anywhere from 60 to 85% of c, depending on wire type, construction and insulation.

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Data Communication Terms

Data - entities that convey meaning, or information

Signals - electric or electromagnetic representations of data

Transmission - communication of data by the propagation and processing of signals

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Analog Signals

A continuously varying electromagnetic 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 optic cable Atmosphere or space propagation

Analog signals can propagate analog and digital data

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Digital Signals

A sequence of voltage pulses that may be transmitted over a copper wire medium

Generally cheaper than analog signaling Less susceptible to noise interference Suffer more from attenuation Digital signals can propagate analog and digital

data

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Analog Signaling

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Digital Signaling

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Reasons for Choosing Data and Signal Combinations

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 optical fiber and satellite

Analog data, analog signal Analog data easily converted to analog signal

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Analog Transmission

Transmit analog signals without regard to content Attenuation limits length of transmission link Cascaded amplifiers boost signal’s energy for

longer distances but cause distortion Analog data can tolerate distortion Introduces errors in digital data

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Digital Transmission

Concerned with the content of the signal Attenuation endangers integrity of 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

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About Channel Capacity

Impairments, such as noise, limit data rate that can be achieved

Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions

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Concepts Related to Channel Capacity

Data rate - rate at which data can be communicated (bps) Bandwidth - the bandwidth of the transmitted signal as

constrained by the transmitter and the nature of the transmission medium (Hertz)

Noise - average level of noise over the communications path

Error rate - rate at which errors occur Error = transmit 1 and receive 0; transmit 0 and receive 1

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Nyquist Bandwidth

For binary signals (two voltage levels) C = 2B

With multilevel signaling C = 2B log2 M

M = number of discrete signal or voltage levels

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Signal-to-Noise Ratio

Ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission

Typically measured at a receiver Signal-to-noise ratio (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

power noise

power signallog10)( 10dB SNR

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Shannon Capacity Formula

Equation:

Represents theoretical maximum that can be achieved In practice, only much lower rates achieved

Formula assumes white noise (thermal noise) Impulse noise is not accounted for Attenuation distortion or delay distortion not accounted for

SNR1log2 BC

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Example of Nyquist and Shannon Formulations

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

Using Shannon’s formula

251SNR

SNRlog10dB 24SNR

MHz 1MHz 3MHz 4

10dB

B

Mbps88102511log10 62

6 C

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Example of Nyquist and Shannon Formulations

How many signaling levels are required?

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log4

log102108

log2

2

266

2

M

M

M

MBC

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Classifications of Transmission Media

Transmission Medium Physical path between transmitter and receiver

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

Unguided Media Provides means of transmission but does not guide

electromagnetic signals Usually referred to as wireless transmission E.g., atmosphere, outer space

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Unguided Media

Transmission and reception are achieved by means of an antenna

Configurations for wireless transmission Directional Omnidirectional

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General Frequency Ranges Microwave frequency range

1 GHz to 40 GHz Directional beams possible Suitable for point-to-point transmission Used for satellite communications

Radio frequency range 30 MHz to 1 GHz Suitable for omnidirectional applications

Infrared frequency range Roughly, 3x1011 to 2x1014 Hz Useful in local point-to-point multipoint applications within

confined areas

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Terrestrial Microwave

Description 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 substantial heights above ground level

Applications Long haul telecommunications service Short point-to-point links between buildings

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Satellite Microwave

Description of communication satellite Microwave relay station Used to link two or more ground-based microwave

transmitter/receivers Receives transmissions on one frequency band (uplink),

amplifies or repeats the signal, and transmits it on another frequency (downlink)

Applications Television distribution Long-distance telephone transmission Private business networks

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Broadcast Radio

Description of broadcast radio antennas Omnidirectional Antennas not required to be dish-shaped Antennas need not be rigidly mounted to a precise alignment

Applications Broadcast radio

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

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Multiplexing

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

Multiplexing - carrying multiple signals on a single medium More efficient use of transmission medium

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Multiplexing

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Reasons for Widespread Use of Multiplexing

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 communicating devices require relatively modest data rate support

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Multiplexing Techniques

Frequency-division multiplexing (FDM) Takes advantage of the fact that the useful bandwidth

of the medium exceeds the required bandwidth of a given signal

Time-division multiplexing (TDM) Takes advantage of the fact that the achievable bit rate

of the medium exceeds the required data rate of a digital signal

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Frequency-division Multiplexing

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Time-division Multiplexing

Wireless, cellular and personal communications

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