Introduction to Wireless Communication

Wireless and Mobile Communication Systems

Eengn5152

Chapter One

Overview of Wireless and Mobile Communications

By : Amare Kassaw

1

Goal of the Chapter

To give an overview on what and why wireless

communication

Assess impact of wireless communication in our daily life

Define basic terminologies, historic perspectives and

evolution of wireless communication

2

Lecture Outlines

Basic principles of wireless communication systems

History of wireless communication systems

Types and examples of wireless communication systems

Trends in cellular radio communication systemsTrends in cellular radio communication systems

3

Used Acronyms

ETSI: European telecommunication standard institute

IMT: International mobile telecommunication

DECT: Digital enhanced cordless telecommunication

HSCSD: High speed circuit switched data

GPRS: General packet radio service

FOMA : Freedom of mobile multimedia access

PDA Personal digital assistant

PDC: Personal digital cellular PDC: Personal digital cellular

GEO: Geosynchronous satellite

LEO: Low earth orbit satellite

UMTS: Universal mobile telecommunication systems

4

Basic Principles of Wireless Communications

Transfer of information (i.e., voice, data, and multimedia)

over a distance without the use of electrical wires

Distances involved may be

Short, e.g., remote control or

long, e.g., satellite communication

Information is transmitted using electromagnetic waves

Suitable frequencies are:

5

Is a broadcast medium

Multiple access methods are required

Transmissions are prone to interference

Wireless channel is unpredictable: e.g., mobility

System design is more challenging in wireless than in System design is more challenging in wireless than in

wired communication

Additional channel optimization technique is required.

Adaptive modulation and equalization

Coding and diversity 6

Wired Vs Wireless

7

No Mobility

Delay in New Connections

Security Hazards

Prone to Failures ( Line Disconnection,

etc )

Very less value added services

Merits of Wireless Communication

Freedom from wires

No cost of installing wires or rewiring

No bunches of wires running here and there

Instantaneous communication without the need for Instantaneous communication without the need for

physical connection setup (Bluetooth, Wi-Fi, WiMAX)

These reasons drive the market .

Various emerging standards.IEEE 802.11,.15,.16,.20

8

Global coverage

Communications can reach where wiring is infeasible or costly

rural areas, old buildings, battle fields, outer space, vehicular

communications, RFIDs

Wireless Ad-hoc Networks

Wireless Sensor Networks Wireless Sensor Networks

Stay connected

Roaming: allows flexibility to stay connected anywhere and

anytime

Rapidly growing market attests to public need for mobility and

uninterrupted access9

Flexibility :

Stay connected Any one, anywhere, anytime!

Services reach you wherever you go (mobility)

You dont have to go to the lab to check your mail

Connect to multiple devices simultaneously (no need for

physical connectivity)physical connectivity)

Increasing dependence on telecommunication services

for business and personal reasons

Consumers and businesses are willing to pay for it

10

Challenges of Wireless Communication

Bandwidth

Scares spectrum and dictates low data rates

Efficient use of finite radio spectrum

E.g., cellular frequency reuse, medium access control

protocols, MIMO systems instead of single TX/RX

antenna systems, ..

Reliability

Low data rate because of interference

Need interference minimizing or mitigating techniques11

Power Management

Mobility brings about battery operation

Need efficient hardware, e.g., low power transmitters,

receivers, and signal processing tools

Sleep mode

Security problem

Shared/broadcast medium => low security

Privacy and authentication needed

12

Consumer side challenges

Providing integrated services

Voice, data, multimedia over a single network

Service differentiation, priorities, resource scheduling

One size fits of all protocols and designs do not work well

13

Network supports user mobility

User location identification

Handover analysis

Impact of wireless channels: Fading & Doppler

Multipath leads to signal superposition at receiving antennas

High probability of data corruption: need for diversity

schemes

Quality of service (QoS)

Unreliable links

Traffic patterns and network conditions constantly change

14

Connectivity and coverage

Local networking

Internetworking

Regulatory issues

Spectral allocation/regulation heavily impacts the evolution

of wireless technologiesof wireless technologies

Worldwide spectrum controlled by ITU-R

ITU auctions spectral blocks for set of applications

Some spectrum set aside for universal use

Cost & efficiency, ..15

History of Wireless Communication Systems

Many people in history used light for communication

150 BC smoke signals for communication;

(Polybius, Greece)

Carrier Pigeons Carrier Pigeons

1794, optical telegraph, Claude Chappe

1895: G Marconi

First demonstration of wireless telegraphy (digital!)

Long wave transmission, high transmission power

necessary (> 200kw)

16

1907: Commercial transatlantic connections

huge base stations (30 antennas, each 100m high)

1915:Wireless voice transmission New York -San Francisco

1920: Discovery of short waves by Marconi

reflection at the ionosphere reflection at the ionosphere

smaller sender and receiver, possible due to the

invention of the vacuum tube (1906, Lee DeForest and

Robert von Lieben)

17

1933: Frequency modulation (FM) introduced by E. H.

Armstrong

FM has been the primary modulation technique for

mobile communication systems until late 80

1979 : NMT at 450MHz (Scandinavian countries)

1982: Start of GSM-specification

Goal: pan-European digital mobile phone system with

roaming

18

1983 : Start of the American AMPS (Advanced Mobile

Phone System, analog)

1984 : CT-1 standard (Europe) for cordless telephones

1991 : Specification of DECT

Digital European Cordless Telephone (today: Digital

Enhanced Cordless Telecommunications)

1880-1900MHz, ~100-500m range, 120 duplex channels,

1.2Mbit/s data transmission, voice encryption,

authentication, up to several 10000 user/km2, used in

more than 50 countries.19

1992 : Start of GSM

In D as D1 and D2, fully digital, 900MHz, 124 channels

Automatic location, hand-over, cellular

Roaming in Europe - now worldwide in more than 170 countries

Services: data with 9.6kbit/s, FAX, voice, ...

1996 : HiperLAN (High Performance Radio Local Area Network)

ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s

Recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz)

as wireless ATM-networks (up to 155Mbit/s)

20

1997: Wireless LAN - IEEE802.11

IEEE standard, 2.4 - 2.5GHz and infrared, 2Mbit/s

Already many (proprietary) products available in the beginning

1998: Specification of GSM successors

For UMTS (Universal Mobile Telecommunication System) as

European proposals for IMT-2000European proposals for IMT-2000

1998 : Iridium

66 satellites (+6 spare), 1.6GHz to the mobile phone

1999: Standardization of additional wireless LANs

IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s

Bluetooth for piconets, 2.4Ghz,

1999: Decision about IMT-2000

Several members of the family: UMTS, cdma2000, DECT

1999: Start of WAP (Wireless Application Protocol) and i-mode

First step towards a unified Internet/mobile communication system

Access to many services via the mobile phone

2000 : GSM with higher data rates

HSCSD offers up to 57.6kbit/s

First GPRS trials with up to 50 kbit/s (packet oriented!)

22

2000: UMTS auctions/beauty contests

Hype followed by disillusionment (approx. 50 B$ payed in

Germany for 6 UMTS licences)

2001: Start of 3G systems

Cdma2000 in Korea, UMTS in Europe, Foma (almost

UMTS) in Japan

2005: Broadband wireless

First public WiMAX/IEEE 802.16 last mile experiments

23

Types and examples of wireless communication

Types of Wireless Communication

Radio Transmission

Easily generated, Omni-directionally travel long

distances

Easily penetrate buildingsEasily penetrate buildings

Problems

Frequency dependent

Relatively low-bandwidth for data communication

Tightly licensed by governments

24

Microwave Transmission

Widely used for long distance communications

Give a high SNR ratio

Relatively inexpensive

Problems Problems

Dont pass through building well: LOS Communication

Weather and frequency-dependent

25

Infrared and Millimetre Wave Transmission

Widely used for millimetre waves : above 30 GHz

Unable to pass through solid objects

Used for indoor Wireless LANs, not for outdoors: 10m range

May need a production of new devices May need a production of new devices

26

Light Wave Transmission

Unguided optical signal, such as laser

Connect two LANs in two buildings via laser mounted on

the roofs

Unidirectional, easy to install, dont require license

Problems

Unable to penetrate rain or thick fog

Laser beam can be easily diverted by turbulent air

27

Examples of Wireless Networking

1. Cellular systems : Architecture

29

Geographic region divided into cells

Frequency/timeslots/codes are reused at spatially separated locations

Co-channel interference between same frequency using cells

Shrinking cell size increases capacity as well as networking burden

Edges are determined based on

Link budget: total power emitted and received Link budget: total power emitted and received

Number of users

Interference: dictates re-use factor

There is an overlap of cells at the boundary

Handoff takes place during roaming

30

Cellular system :Basic terminology

Mobile station (MS)

A station in the cellular radio service intended for use while in

motion at unspecified locations

They can be either hand-held personal units (portables) or

installed on vehicles (mobiles)

Base Station (BS)

A fixed station in a mobile radio system used for radio A fixed station in a mobile radio system used for radio

communication with the mobile stations

Base stations are located at the centre or edge of a coverage

region, consists of transmitter and receiver antennas, and are

mounted on top of towers

Provides gateway functionality between wireless and wire-line

links

Base stations coordinate handoff and control functions31

Mobile Switching Center (MSC)

Switching center which coordinates the routing of calls in a

large service area

In a cellular radio system, the MSC connects the BS and MS to

the PSTN (telephone network)

o Mobile Telephone Switching Office (MTSO)

Subscriber

A user who pays subscription charges for using a mobile A user who pays subscription charges for using a mobile

communication system

Transceiver

A device capable of simultaneously transmitting and receiving

radio signals

32

Handoff/ Handover

The process of transferring a mobile station from one channel or

base station to another

Roamer

A mobile station which operates in a service area (market)

other than that from which service has been subscribed

Page

A brief message which is broadcast over the entire service

area, usually in simulcast fashion by many base stations at the

same time

33

Channel types

Control channel

Radio channel used for transmission of call setup, call

request, call initiation and other beacon and control

purposes

Downlink (forward) channel

Radio channel used for transmission of information from

the base station to the mobile

Uplink (reverse) channel

Radio channel used for transmission of information from

mobile to base station34

Duplexing and Multiplexing Techniques

The information from sender to receiver is carried over a well-

defined frequency band

This is called a channel

Each channel has a fixed frequency bandwidth and capacity

(bit-rate)

Different frequency bands (channels) can be used to transmit

information in parallel and independently

Duplexing and multiplexing techniques are required

35

Duplexing

Given a single pair of communicating peers, duplexing

describes rules when each peer is allowed to send to the

other one

Using the resources like : FDD, TDD

Multiplexing

Given several pairs, multiplexing describes when which

pair, using which resources (eg. TDMA, FDMA), is

allowed to communicate

Main resources: Time, frequency, (+ some others)

36

Duplexing Types for Cellular Systems

Simplex, half- and full-duplex: Variants of duplexing

Simplex:

Is a one way communication, i.e., one source transmits

and the other only receives

Example: remote control, radio broadcast

To enable two-way communication, we can use

Frequency as in FDD or

Time as in TDD

37

Half duplex systems

Communication systems which allow two-way communication by

using the same radio channel for both transmission and reception

At any given time, the user can either transmit or receive

information

Use one frequency band but peers transmit one after the other, Use one frequency band but peers transmit one after the other,

called TDD

38

Full Duplex Systems

Communication systems which allow simultaneous two-way

communication

Transmission and reception is typically on two different

channels (FDD)

Downlink and uplink channels use different frequency bands.

Providing two simultaneous but separate channels to both the

users by using FDD or TDD

39

Frequency Division Duplexing (FDD):

Supports two way communication with two distinct radio channels.

One channel is transmitted downstream from the BS to the MS.

The second is used in the upstream direction and supports

transmission from the MS to the BS.

Hence simultaneous transmission in both directions is possible. Hence simultaneous transmission in both directions is possible.

To mitigate self-interference between upstream and downstream

transmissions, a minimum amount of frequency separation must be

maintained between the frequency pair.

40

Time Division Duplexing (TDD):

TDD uses a single frequency band to transmit signals in both

the downstream and upstream directions.

TDD operates by toggling transmission directions over a time

interval.

This toggling takes place very rapidly and is imperceptible to

the user.

41

Multiplexing

Used for sharing radio resources

Multiplexing: Gives a means to

regulate access to a resource

that is shared by multiple users

The switching element that serves as a The switching element that serves as a

controller

Main resources to be shared

Time, frequency, (+some others)

Techniques

TDMA, FDMA, SDMA, CDMA 43

2. Paging Systems

Broad coverage for short , low rate, one way messaging

Message broadcast from base stations to highly mobile users.

Simple terminals

Low complexity, very low powered

pagers (receiver) devicespagers (receiver) devices

Optimized for one way transmission

Answer-back hard

Overtaken by cellular

44

3. Personal Area Networks ( PANs)

Network of devices carried by an individual person

Music player, cell phone, laptops ....

Networks that connect devices within a small range

Typically on the order of 10-100 meters

Application areas

Data and voice access points Data and voice access points

Real-time voice and data transmissions

Cable replacement

Eliminates need for numerous cable attachments

Ad-hoc networking

Device with PAN radio can establish connection with

another when in range 45

Wireless Personal Area Networks(PANs)

Cable replacement RF technology (low cost)

Short range (10m, extendable to 100m)

Operates in the unlicensed 2.4 GHz ISM band

Widely supported by telecommunications, PC, and consumer

electronics companieselectronics companies

Provides an ad-hoc approach to enable various devices to

communicate.

46

Wireless Local Area Networks (WLANs)

Network between devices in close physical proximity (offices,

homes, ), usually stationary or moving at low speed, provide

access to fixed infrastructure

Good options for coffee shops, airports, libraries, etc.. . to provide

internet connection (connect local computers in 100m range)internet connection (connect local computers in 100m range)

The term Wi-Fi is widely used

47

Channel access is shared (random access)

WLANs provides license-free, low-power short-range data

communication

48

WLAN Standards

802.11b

Standard for 2.4GHz ISM band

Direct sequence spread spectrum (DSSS)

Speeds of 5.5 - 11 Mbps, approx. 100 m Speeds of 5.5 - 11 Mbps, approx. 100 m

802.11a/g

Standard for 5GHz band /also 2.4GHz

OFDM in 20 MHz with adaptive rate/codes

Speeds of 54 Mbps, approx 100 m range

49

802.11n (recently approved)

Standard in 2.4 GHz and 5 GHz bands

Adaptive OFDM/MIMO in 20/40 MHz (2-4 antennas)

Speeds up to 600Mbps, approx. 100 m range

Other advances in packetization , antenna use, etc. Other advances in packetization , antenna use, etc.

50

Wireless Metropolitan Area Networks (WMANs)

Network covering a city, metropolitan areas

Last mile application, usually at best low mobility

Technologies

Various IEEE 802.11 derivates

Integration of fixed and mobile systems

WiMAX: Worldwide Interoperability for Microwave Access

WiMAX/IEEE 802.16 competes with DSL WiMAX/IEEE 802.16 competes with DSL

IEEE 802.20 (???)

51

Wide Area Networks( WAN) : Comparison

Network covering country/continent/earth

Anytime, anywhere connectivity

Good for even highly mobile users

Technologies

Cellular systems (GSM, UMTS, HSDPA)

Broadcast systems (DVB)

Satellites

52

4. Satellite Communication Systems

Cover very large areas

Very useful in sparsely populated areas, rural areas, sea,

mountain areas

Limited-quality voice/data transmission

Has different orbit heights

GEOs (36000 Km) versus LEOs (2000 Km) GEOs (36000 Km) versus LEOs (2000 Km)

Optimized for one-way transmission

Radio and movie broadcasts

Expensive Base stations (satellite)

Moving base stations unlike the cellular system

53

Iridium, Globalstar, Teledesic, Inmarsat

Examples of LEO satellite constellation for satellite

phone and data communications

54

5. Emerging Wireless Networks

Ad-hoc Wireless systems

Sensor Networks

Ultra Wideband (UWB) systems

56

Mobile Ad-Hoc Networks( MANETs )

Peer-to-peer communications with no backbone infrastructure

Topology is dynamic

One challenge: Routing which can be multihope

Fully connected with different links SINRs

Example scenarios for MANETs Example scenarios for MANETs

Meetings

Emergency or disaster relief situations

Military communications

Wearable computers

Sensor networks57

Ad-hoc networks provide a flexible network infrastructure for

many emerging applications

Transmission, access, and routing strategies for these networks

are generally ad hoc

Cross layer design is critical and very challenging

Energy constraints impose interesting design tradeoffs for

communication and networking

58

Ad-Hoc network representation

59

Wireless Sensor Networks

Nodes powered by non-rechargeable batteries

Data flows to centralized location, called sink

Low per-node rates but up to 100,000 nodes

Data highly correlated in time and space

Nodes can cooperate in transmission, reception,

compression, and signal processing

61

Ultra Wide Band (UWB) Systems

An emerging wireless communication technology that can

transmit data around 100 Mb/s (up to 1000 Mb/s)

UWB transmits ultra-low power radio signals with very

narrow pulses (nanoseconds)

Because of its low power requirements, UWB is very

difficult to detect (hence secure)

62

Why UWB?

Exceptional multi-path immunity

Low power consumption

Large bandwidth

Secure communications

Low interference

No need for license to operate

64

Trends in Cellular Radio Communication Systems

66

First Generation (1G)

Analog systems, mostly FM

E.g., NMT, AMPS

Voice traffic

FDMA/FDD multiple access

Second Generation (2G)

Digital systems

Digital modulation

Voice traffic

TDMA/FDD and CDMA/FDD multiple access70

2.5G

Digital systems

Voice + Low-rate data service

Third Generation (3G)

Digital

Voice + high-rate data service

Also multimedia transmission

71

Documents

Introduction to Wireless Communication