WC Chapter 0 Introduction

8/13/2019 WC Chapter 0 Introduction

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Chapter 0Introduction to WirelessCommunications

Ha Hoang Kha, Ph.D

Ho Chi Minh City University of Technology

Email: [email protected]

Outline

1. Introduction to communication systems Block dia ram

2. Overview of wireless communication Generations of wireless communication Current wireless networks

.

4. Fundamental concepts

2 H. H. Kha, Ph.D.Introduction

Introduction

Introduction 3 H. H. Kha, Ph.D.

1. Introduction to communication system

The purpose of a communication system is to transportan information bearing signal from a source to a userdestination.

Analog communication systems: the information bearing signalis continuously varying in both amplitude and time.

The performance metric: SNR (Signal to Noise Ratio)

Digital communication system: the information bearing signalis re resented b a se uence of discrete messa es.

The performance metric: BER (Bit Error Rate)

.



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Block diagram of digital communication systems


Basic signal processing blocks

Transmitter: Source coding: eliminate or reduce redundancy so as to provide

an efficient representation of the source output. anne co ng: n ro uce re un ancy o prov e re a e

communication over a noisy channel. Modulation: to provide the efficient transmission of the signal

over the channel.

Channel: wired (telephone channels, coaxial cables, optical fibers)orwireless (microwave radio, satellite channels).

Receiver: demodulation, channel decoder, and source decoder.

Our ultimate goal is to communicate with any time of informationwith anyone at any time from anywhere. This is possible with aidofwireless technology.


2. Radio Communication

Radio or radio communicationmeans any transmission,emission, or reception of signs, signals, writing, images,sounds or intelligence of any nature by means ofelectromagnetic waves of frequencies lower than threethousand gigacycles per second (3000 GHz) propagated

in space without artificial guide.Examples of radio communication systems:

Radio broadcasting.

TV broadcasting.

Satellite communication.

Mobile Cellular Telephony.

Wireless LAN.

Multimedia communication & Mobile Internet


Classification of radio spectrum

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Frequency300-3000Hz

3-30kHz

30-300kHz

300-3000KHz

3-30MHz

30-300MHz

300-3000MHz

3-30GHz

30-300GHz

Wavelength1000

-100 km

100

-10 km

10

-1 km

1000

-100 m

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-10 m

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-1 m

100

-10 cm

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-1 mm

Term ELF VLF LF MF HF VHF UHF SHF EHF



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The Radio Spectrum

The frequency spectrum is a shared resource.Radio propagation does not recognize geopolitical

boundaries.

International cooperation and regulations are requiredfor an efficient use of the radio spectrum.

The International Telecommunication Union (ITU) isan agency, within the UN, that takes care of thisresource.

Frequency assignment. Standardization.

Coordination and planning of the internationaltelecommunication services.


History

1864: Maxwell describes radio wave mathematically1888: Hertz generates radio waves

1890: Detection of radio waves1896: Marconi makes the first radio transmission1915: Radio tubes are invented1948: Shannons law1948: Transistor1960: Communication Satellites

: e u ar tec no ogy


Evolution of Wireless Systems


Current Wireless Networks

Cellular Systems Satellite SystemsWireless broadband access (WiMax-compatible)

Wireless Wide Area Network (WWAN)

Paging Systems (one way, two way) Radio broadcast (analog/digital audio/video)

Cordless phone, personal handyphone systemWireless LANs BluetoothUltra-wideband radios

Networks MAN

Local Area Network LAN


g ee ra osInfrared wireless optical (IrDa)Remote control (toy, garage door)Special purpose: radar, sonar, missile guidance,,etc

Personal Area Networks PAN


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3. Mobile wireless technology


1G First generation wireless

Developed in 1980sAnalog transmission technology

ocus on vo ce

Data service almost non-existence

Incompatible standards:

Different frequencies and signalling

International roaming impossible


2G second generation wireless

2 G wireless

Its was invented and developed in 1990-91.

Increased quality of service

Possible f wireless data services2.5 G wireless

General packet radio service (GPRS)

Data rates: 56 kb/s to 115 kb/s

Services: WAP, MMS and SMS, Search and directory

2.75 G wireless

Maximum dara rate: 384 kbps.


3G third generation wireless

3 G wireless

Introduced in 2004-05

Applications: mobile TV, video on demand, video conferencing,location based serviced services.

3.5 G wireless

Known as HSDPA (high-speed downlink packet access)

Data transmission up to 8-10 Mbps (and 20 Mbps for somesystems)

. w re ess

Refereed to HSDPA (high-speed uplink packet access)

Speed: 1.4 Mbps-5 Mbps

Real-time person to person gaming



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4G Fourth generation wireless

A collection of technology creating fully packet-switched networks optimized for data.

.

Provide wireless alternative for broadband access toresidential and business customers.

5 G Wireless (coming?)Data rate: ~10 Gbps


Comparison between 1G-4G


3G and 4G capabilities and features


Mobile broadband landscape

Cellular wireless law of speed vs decade

time



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Satellite Systems

Cover very large areasDifferent orbit heights s m versus s m

Optimized for one-way transmission Radio (XM, Sirius) and

movie (SatTV, DVB/S) broadcasts

Most two-way systems struggling or bankrupt

Satellite signals used to pinpoint location

Popular in cell phones, PDAs, and navigation devices


Wireless Local Area Networks (WLANs)

01011011

Internet

Access

0101 1011

Wireless LAN Standards

WLANs connect local computers (100m range)

Breaks data into ackets

Point

Channel access is shared (random access)

Backbone Internet provides best-effort service

Poor performance in some apps (e.g. video)


Wireless LAN Standards

802.11b (Old 1990s) Standard for 2.4GHz ISM band (80 MHz) Direct sequence spread spectrum (DSSS) pee s o ps, approx. range

802.11a/g (Middle Age mid-late 1990s) Standard for 5GHz NII band (300 MHz) OFDM in 20 MHz with adaptive rate/codes Speeds of 54 Mbps, approx. 100-200 ft range

Many WLAN

cards have

all 3 (a/b/g)

802.11n (Hot stuff, standard close to finalization) Standard in 2.4 GHz and 5 GHz band Adaptive OFDM /MIMO in 20/40 MHz (2-4 antennas) Speeds up to 600Mbps, approx. 200 ft range Other advances in packetization, antenna use, etc.


WiMAX (Worldwide Interoperability for Microwave Access)

(802.16)

Wide area wireless network standard

System architecture similar to cellular

OFDM/MIMO is core link technology

Operates in 2.5 and 3.5 MHz bands

Different for different countries, 5.8 also used.

Bandwidth is 3.5-10 MHz

Fixed (802.16d) vs. Mobile (802.16e) WiMAX

Fixed: 75 Mbps max, up to 50 mile cell radius

Mobile: 15 Mbps max, up to 1-2 mile cell radius



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Bluetooth

Bluetooth is a wireless technology standard for exchanging dataover short distances (using short-wavelength radio transmissions

in the ISM band from 24002480 MHz) from fixed and mobile

devices, creating personal area networks (PANs) with high levels

of security

Short range (10m, extendable to 100m)

1 Data (700 Kbps) and 3 voice channels, up to 3 Mbps

Widely supported by telecommunications, PC, and consumer


electronics companies

Few applications beyond cable replacement

Ultrawideband Radio (UWB)

UWB is an impulse radio: sends pulses of tens ofpicoseconds(10 -12) to nanoseconds (10-9) Duty cycle of only a fraction of a percent

A carrier is not necessarily needed Uses a lot of bandwidth (GHz) High data rates, up to 500 Mbps 7.5 GHz of free spectrum in the U.S. (underlay) Multipath highly resolvable: good and bad

New UWB proposals (802.15.3): OFDM-based orCDMA-based Limited commercial success to date


IEEE 802.15.4 / ZigBee Radios

Wireless personal area networks built from small, low-power digital

radios.

ZigBee operates in the industrial, scientific and medical (ISM) radio

bands; 868 MHz in Europe, 915 MHz in the USA and Australia and

2.4 GHz in most jurisdictions worldwide.

Data rates of 20, 40, 250 Kbps

The low cost allows the technology to be widely deployed in

wireless control and monitoring applications

Very low power consumption

Focus is primarily on low power sensor networks


Tradeoffs

3G

Rate

802.11n

802.11b

802.11g/a

UWB

Power

ZigBee

Bluetooth

Range



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Backbone infrastructures: PSTN, Internet,and HFC


3. Requirements and Design Challenges

Voice VideoData

Delay


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Radio Communication

Three main problems: The path loss

o se

Sharing the radio spectrum


Crosslayer Design

Application

Network

Access

Link

Hardware

Rate Constraints

Energy Constraints

Adapt across design layers

Reduce uncertainty through scheduling

Provide robustness via diversity


Crosslayer Techniques

Adaptive techniques Link, MAC, network, and application adaptation

Resource management and allocation (power control)

Diversity techniques Link diversity (antennas, channels, etc.)

Access diversity

Route diversity

Application diversity

Content location/server diversity

Scheduling Application scheduling/data prioritization

Resource reservation

Access scheduling


4. Fundamental concepts

Simplex

Half-duplex

-

The 2 channels can be separated in frequency

Frequency Division Duplex (FDD) The 2 channels can be separated in time to share a

single physical channel Time Division Duplex(TDD)



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FDD vs TDD


Multiple Access


Multiple Access

Multiple access

FDMA (Frequency Division Multiple Access)

me v s on u t p e ccess

SDMA (Space Division Multiple Access)

SSMA (Spread Spectrum Multiple Access)

FHMA (Frequency Hopped Multiple Access)

CDMA (Code Division Multiple Access)


Multiple Access



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Multiple Access


The Cellular Concept


Before Cellular Systems


One call per channel



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Why cellular? Radio spectrum is a finite resource.

ow to accommo ate a arge num er o users overa large geographic area within a limited radiospectrum?

The solution is the use of cellular structure whichallows frequency reuse.





The large geographic area is divided into smallerareas cells.

Each cell has its own base station rovidincoverage only for that cell.

Each base station is allocated a portion of the total

number of channels available to the entire system.Neighboring base stations are assigned different

groups of channels to minimize interference.The same rou of channels can be reused b

another base station located sufficiently far away tokeep co-channel interference levels within tolerable limits.





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Frequency reuse


Cells


Cellular Systems: Reuse channels to maximize capacity

Geographic region divided into cells Frequency/timeslots/codes/ reused at spatially-separated

locations. Co-channel interference between same color cells.

Base stations/M SOs coordinate handoff and control functions Shrinking cell size increases capacity, as well as networking burden

BASE

STATION

MTSO



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Cellular Phone Networks

San Francisco

BSBS

MTSOPSTN

MTSO

New YorkInternet

BS


3G: ITU-developed,

UMTS/IMT-2000

Satellite

Global

Macrocell Microcell

UrbanIn-Building

Picocell

Suburban


Basic Terminal

PDA Terminal

Audi o/Visual Terminal

Spectrum Regulation

Spectral Allocation in US controlled by FCC(commercial) or OSM (defense)

FCC auctions spectral blocks for set applications.

Some spectrum set aside for universal use

Worldwide spectrum controlled by ITU-R

Regulation is a necessary evil.

Innovations in regulation being considered worldwide,including underlays, overlays, and cognitive radios


US Spectrum allocation today



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Coexistence Challenge:Many devices use the same radio band

Technical Solutions: Interference Cancellation

Smart/Cognitive Radios


Standards

Interacting systems require standardization

Companies want their systems adopted as standard

Alternatively try for de-facto standards

Standards determined by TIA/CTIA in US

IEEE standards often adopted

Process fraught with inefficiencies and conflicts

Worldwide standards determined by ITU-T In Europe, ETSI is equivalent of IEEE


Emerging Systems

4th generation cellular (4G)

OFDMA will be PHY la er like Wimax

Other new features and bandwidth still in flux

Ad hoc/mesh wireless networks

Cognitive radios

Sensor networks

Distributed control networks


Cognitive Radio Paradigms

Co nitive radio of aspectrum hole andopportunisticspectrum sharing



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Cognitive Radio Networks


Key Techniques

Adaptive Techniques Link, MAC, network, and application adaptation Resource mana ement and allocation ower control

Diversity techniques

Link diversity (space, time, frequency)

Access diversity

Route diversity

Multi lexin

Spatial multiplexing (MIMO, beamforming)

Frequency multiplexing (OFDM, multi-carrier)


Subject contents

Chapter 1: Channel modelsChapter 2: Channel Capacity

Chapter 4: Equalizer

Chapter 5: OFDMChapter 6: MIMOChapter 7: Cooperative wireless networks: Cognitive

radio/relay networks


Grading

- Group projects: 20% (2 persons/group)

Final exam: 50%



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Projects

1) Channel simulation: Flat/frequency selective fading,time-varying channels, small/large fading

2) OFDM: spectrum, BER, ICI cancellation

3) MIMO: space-time code, multiplexing, beamforming.

4) Cognitive Radio: underlay, overlay

5) Wireless Relay Networks: AF, DF relay,single/multiple hops


References

Textbook: . , , ,

2005

References:[2] T.S. Rappaport ,Wireless Communications, Prentice Hall PTR, 1996[3] J. G. Proakis , M. Salehi , G. Bauch Contemporary CommunicationSystems Using MATLAB, Cengage Learning, 2012.

DSPlog Signal Processing for Communicationhttp://www.dsplog.com/


WC Chapter 0 Introduction

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