M.V. RAGHUNADHM.V. RAGHUNADHAssistant Professor, Dept. of ECEAssistant Professor, Dept. of ECE

NIT, Warangal – 506004.NIT, Warangal – 506004.

raghu@nitw.ac.inraghu@nitw.ac.in

INTRODUCTION TO

MOBILE & CELLULAR COMMUNICATIONS

Wireless system

What is a wireless system?

Provides communication without the use of wire

Computing and communication at anytime and anyplace

Small size, portable deviceUses radio wave, to send voice,

data, internet and video signalsGood energy managementAccess to resources

“ Mobile communications is not Cellular communications

but

Cellular communications is Mobile communications ” .

Mobile Com Ex :Public emergency services Police, Fire, Ambulance

Single frequency communications over entire area using one BS

and many mobile vehicular transceiver setsCellular Com

Public com services with frequency reuse over multiple cells in entire area using one BS and many

cellular phones in every cell.

“ Portable communicators are not

mobile but mobile communicators

are Portable ”

Communication devices exhibit followingCharacteristics

a. Fixed & Wired: Typical desktop PC, Telephone large, Data Loggers weight / high power

b. Mobile & Wired: Today’s laptop PCs mobile but connection to company via wired line of PSTN & Modem

c. Fixed & Wireless: WLL last mile in PSTN, in house wireless networks, local net in tradeshows.

d. Mobile & Wireless

Today’s Cell Phones, PDAs, Personal Communicators

Most interesting case, no cable restriction, full mobility, roaming between cities and even different networks

Ex: GSM , CDMA

> 900 million users worldwide

Applications:1.Vehicles:

Cars with

a) Digital Audio Broadcast (DAB) at 1.5 Mbps Music ,news, weather and GPS data

b) UMTS for Wireless Cell Telephony – voice & Data at 384 kbps

c) Adhoc Networks with emergency services Accidents, Maintenance Logistics.

d) Wireless Pico Nets PDA, Laptops, Mobile Phones ,Bluetooth / Wi-Fi.

e) Rail / Air Traffic

2.Emergencies

Ambulance high quality wireless adhoc nets – accidents, natural disasters.

3.Business Sales Database consistency,

wireless LAN hot spots at supermarkets, gas stations, laptop connections via LAN,DSL…

4.Infotainment Up-to-date info over wireless net

i. Travel guideii. Cash paymentiii. Adhoc gaming networks

5. Location Dependent Services

Mobile computing and WLANs applications need to

know the mobile unit location.

a. Follow on Services Call forwarding, e-mail, multimedia conferencing.

b. Location aware Services Printing service from a hotel control room.

c. Privacy Time dependent access/forwarding at the will & wish of user

d. Info. Services Travel guide

e. Support services Caching of data on mobile device via a wireless net access.

Wi-FiStands for “Wireless Fidelity”High-bandwidth category of wireless

communicationsShort range (300-1600ft)Used to connect laptops, PDAs, and

even workstations

Digital Cellular TelephonyCDMA, TDMA, GSMSmart phones and some PDAsLonger range than Wi-Fi

Mobile & Wireless Devices:

a. Sensors : Control state information sources

b. Embeded Controllers: Keyboards, mice, headset, washing machine, TV set,

…..

c. Pager : One or two line message service,

fast replaced by cell phone.

d. Mobile Phones : Vehicular Sets, Cell phones

e. PDA : Personal Communicators, Pocket/Palm Computers

f. Notebook / Laptop : Portable PCs

MOBILE, CELLULAR

&

PERSONAL COMMUNICATIONS

Mobility : Mobility of Talker ( Transmitter ) Mobility of Listener ( Receiver ) Mobility of Both ( TX & RX )

Definition : Communication facility between stationary and mobile or mobile and mobile users ( units )

UserTypes : Walking Pedestrians automobile computers car, bus, train, plane, ship.

What is Mobility?

A device that moves Between different geographical locations Between different networks

A person who moves Between different geographical locations Between different networks Between different communication

devices Between different applications

Device mobility Plug in laptop at home/work on Ethernet Wired network access only Network address changes May want access to information when no network

is available: hoard information locally Cell phone with access to cellular network Continuous connectivity Phone # remains the same (high-level network

address) Network performance may vary from place to

place Can we achieve best of both worlds? Continuous connectivity of wireless access Performance of better networks when available

Laptop moves between Ethernet, WaveLAN and Metricom networks Wired and wireless network access Potentially continuous connectivity Network address changes Radically different network performance on

different networks

Phone available at home or at work Multiple phone numbers to reach me Breaks in my reachability when I’m not in

Cell phone Only one number to reach me Continuously reachable Sometimes poor quality and expensive

connectivity Cell phone, networked PDA, etc. Multiple numbers/addresses for best quality

connection Continuous reachability Best choice of address may depend on

sender’s device or message content

People mobility

Mobility means changesHow does it affect the following? Hardware Lighter More robust

Lower power Wireless communication Can’t tune for stationary access

Network protocols Name changes ; Delay changes ;

Error rate changes Fidelity High fidelity may not be possible

Data consistency Strong consistency no longer

possible Location/transparency awareness Transparency not always desirable

Names/addresses Names of endpoints may change

Security Lighter-weight algorithms Endpoint authentication harder Devices more vulnerable

Example changes Addresses Phone numbers, IP addresses

Network performance Bandwidth, delay, bit error rates, cost,

connectivity Network interfaces PPP, eth0, strip

Between applications Different interfaces over phone & laptop

Within applications Loss of bandwidth triggers change from color

to B&W Available resources Files, printers, displays, power, even routing

Enabling Technologies Software Defined Radios Advanced media access technology to connect

different cores to different access technologies Variable spreading factor ( VSP ) All-IP networks and protocols Ad-Hoc Networking algorithms Ultra Wideband , variable power Hardware

Radio Network-layer mobility protocols Smart antennae MIMO (Multi Input Multi Output) devices Open platform architectures Smart mediation devices for Handsets Smart mediation devices for overlay network

Goal of emerging mobile & PCS systems To enable communication with any person, at any time, at any place (Home office in public in Transit), in any form / device ( Home /normal telephone, cellular/mobile phone , PC phone, PDA, fax, Multimedia terminal).

On the basis of On the basis of ““any time, any where, any one, any any time, any where, any one, any

service”service”

Information Services: Voice, Video, Text, Fax ,Image, Data, Files

Technological Trends

• All Digital Optical Fiber or Satellite media , • Hyper media content• Intelligent Networks• Universal Reachability & Accessibility• User specific & Interactive service • Global Roaming & Interoperability• Mobile ATM and Mobile Internet• Mobile data and computing• Guaranteed Quality of Service (QOS)• Standardized Universal ID Numbers/

Addresses• Personalization

The Electromagnetic Spectrum

ExtremelyLow

VeryLow

Low Medium High VeryHigh

UltraHigh

SuperHigh

Infrared VisibleLight

Ultra-violet

X-Rays

AM BroadcastShort Wave Radio FM Broadcast

Television Infrared wireless LAN

GSM:US ISM: 902-928 MHz

5 GHz802.11a (54 Mbps)

2.4 – 2.4835 GHz802.11b (11 Mbps)802.11g (54 Mbps)

CellularMicrowave

Wireless Network Area Definitions

WAN

WAN-MAN

MAN

Pico-Cell

MAN-LAN MAN-LAN

PAN

LAN-PAN

0km~50km ~2km ~10m

Courtesy of IEEE 802.15 Press Kit. Jan. 2001

BluetoothIEEE802.11HyperLan

GSMGPRSCDMA

Global layer

National layer

Local area layerWireless LANs

DAB and DVB-T

2G, 3G Cellular

Personal network layer

Hierarchical Layers for 4G Hierarchical Layers for 4G

Satellite

Regional layer

Wireless PANs

Vertical Handover

Horizontal Handover

IP-based backbone

The Internet

IP backbone

BillingVHE

Signalling Gateway

WAP Accounting

UMTS

Broadcast Networks (DAB, DVB-T)

Satellite FES

GSM / GPRS

Context-aware informationCentre

IP-based micro-mobility Wireless

LANs

ISPSIP Proxy Server

Inter-WorkingInter-Working

ENABLING CONCEPTS

FOR

MOBILE & PERSONAL COMMUNICATIONS.

These concepts enable us to provide Universal PCS with standardized systems & services at local, regional, national and international levels.

They are :

Terminal Mobility with wireless AccessPersonal Mobility with personal NumberService Portability with Intelligent Network

These are for location independent availability of customized telecom services.

TERMINAL MOBILITY • The terminal mobility systems can locate and identify a mobile terminal as it moves

• Allows a mobile terminal to access telecom services from any location – even in movements

• Uses wireless Access• User must carry wireless terminal and be within a radio coverage area

• Functional parts reside on portable IC / Smart card

• Terminal and User have STATIC Relationship• Terminal and Network have DYNAMIC Relation

• Call delivery and Billing are based on Terminal / Mobile Station Number.

PERSONAL MOBILITY

• Terminal and user have DYNAMIC Relationship. Call Delivery & Billing are based on Personal Identity / Personal Number assigned to the user.

• Locate and identify the end users as they move

• Allows end users to access subscribed telecom services on any terminal, any location

• More broader access whether fixed or wireless

SERVICE PORTABILITY

• Network is capable to provide subscribed services at a terminal or location designated by the user.

• Depends on terminal capabilities• Uses intelligent Network concepts• Maintains User profile in a Database• User can access, query, modify to manage & control subscribed services.

• Intelligent services – seamless international roaming

CELLULAR CONCEPT

&

INITIAL IMPLEMENTATION

Conventional Mobile Tele phone System

A Land mobile system in which available frequency spectrum is divided into mobile radio telephone channels using FDM without reuse facility, serving an area with large size..

A dedicated channel is allocated for each user, whether uses it or not.

Principle of operation is similar to cellular radio telephony

As a result, It has several limitations that are given below.

1. Limited service capability

• Larger coverage area zones• High Power Transmissions• Re-initiation of call in every zone (no auto handoff)• One frequency per channel• No. of active users is equal to No. of channels allocated to zone

2. Poor Service Performance:

• Higher blocking probabilities due the smaller number of radio channels.

3. Inefficient frequency spectrum Utilization

• Smaller Frequency Utilization factor Mo = max. no. of customers/channel at Busy Hour.

• Each channel can serve only one customer at a time in whole area.

SOLUTION

Cellular approach

• Reuse of frequencies

• Multiple Access

• Cell Splitting

• Smaller coverage area (cell)

Principle : Divide large area into cells with 2 to 50 km diameter, each cell allocated with a set of RF channels

Starting point :

AMPS by Bell Labs, 1983, USA

A high capacity land mobile system in which available spectrum is divided into discrete channels, which are assigned in groups to geographic cells covering an area and the frequencies are reused, thus low power transmissions.

Cellular System :

A cellular system: The tower represent base station (BS) which provide radio access between mobile users and the mobile switching center (MSC).

BS BS BSMS

Cellular Advantages:

• Lower Power Transmissions

• Frequency Reusability

• Multiple Access capability

• Lower Antenna Heights

• Unlimited capacity and range

coverage

• Cell splitting & Micro cells

• Automatic hand off transparency

• Multi Level roaming

• Efficient Power control

• Handsets – Light weight, compact, Pocket held

• Digital Communication transceivers

• Value added & intelligent information services

• Mobile Multimedia broadband communication

• Minimal Blocking

• More than one license operator, Competition

• Better propagation models.

CELLULAR SYSTEM

ARCHITECTURE

Basic Cellular system components : 1. Mobile Station / Unit / Site (MS)

2. Cell site / Base station (BS)

3. Mobile Telephone switching office/ Centre

4. Data Links

Mobile Station : (MS)

Mobile station/unit contains a Transceiver, control unit and an Antenna.

Cell Site : (MSC)

Cell site contains a fixed Base station that has a tower antenna, Transceivers (BS) for MS and Fixed links to MTSO

MTSO or MSC

• This is the mobile switching exchange

• The central coordinating system for all the cells

• Contains cellular switch, control computer, mobile management software, user location mobile management software, user location registers, Interfaces and links to BS & PSTN.

• MTSO is the central administrator & Manager

• Cellular switch is Analog or Digital and switches the calls to connect mobile – mobile or mobile – fixed

• Coverage area is partitioned into nearly hexagonal shaped areas called radio cells

• Each cell is served by one Base station for radio coverage of all mobile units in that cell.

• Radio Link carries the VOICE and SIGNALLING information (Channels) between the MS and BS in that cell only.

• Base stations are connected to MSC through fixed circuits (cables or fiber or microwave)

• MSC interacts with a database of subscriber data and location information, to provide dynamic terminal (MS) location to the switching computer.

• MSC is connected to PSTN because majority of calls originate from or terminate at fixed PSTN phones.

• Every cellular system has some number of radio channels for its use, depending on cellular standard and RF band.

• The available radio channels are partitioned into groups of channels, each group being allocated

to an individual cell.

• These individual group of channels can be reused in distant cells without causing interference.

Radio System Planning:

• Cell size design • Cell location identification/assignment • Allocation of group of channels to

each cell • Performance criteria• Handoff mechanism• Propagation modeling

• In each cell, one Radio Channel is set aside permanently assigned to carry signaling information between the cellular network (base station) and all the mobile stations in that cell.

MS BS Signaling Channel Location updating , call set up.Paging response , user data

BS MS Signaling Channel Operating parameters (identities)Paging call, location updating, and control.

Location UpdatingMS always monitors overhead information broadcast by network on the signaling channel

• MS updates the operating parameters as and when necessary

• MS Checks Location information (area identity) broadcast by new cell, if it is in new cell location.

• MS advices the network about its new location

• Then network updates its location registers.

• This location information is used to route / switch the incoming calls or determining paging broadcast area for MS.

Mobile station initialization:

• Whenever a user activates the receiver of Mobile unit, the receiver scans SETUP CHANNEL list designated.

• It selects a strongest one and locks to it

• Each site has one set up channel only. Thus strongest channel selection is the nearest BS (Cell site) selection.

• This process is called SELF LOCATION

• This is done in Idle State also, transparently to user.

• But, it can’t provide location information to BS. Thus BS must search for idle mobile unit by paging.

• In future, registration scheme will be used, in which, the vehicles (MS) must register/update location regularly, as shown above.

Mobile originated call set up:

• Exact procedure depends on particular cellular standard.

• More or less similar in principle

• User places/keys in the called telephoned number into an originating register and checks for correctness in LCD display.

• Then user pushes ‘SEND’ button.

• This call request is sent on the already set up channel on the uplink signaling channel

there is no dial tone at all.

• The BS receives this call request signal and sends a request to MTSO (MSC) via high speed data link.

• BS selects an appropriate voice channel for the call and sends a speech channel (number) allocation message to mobile unit.

• MS now locks on to this allocated radio channel

• Network MSC proceeds now to set up the connection to the called party.

NETWORK ORIGINATED CALL SETUP

(Mobile Terminated Call)• A Landline phone dials a mobile unit number • The PSTN exchange recognizes that the number is a Mobile number

• PSTN exchange forwards this request to MTSO (MSC)

• MTSO first establishes current location area for the called mobile through signaling between Home Location Register (HLR) and Visiting Location Register (VLR).

• This process allows the call to be routed to the current serving MTSO (MSC)

• The serving MTSO initiates a paging message over the downlink-signaling channel toward the cells contained in the paging area, through a cell search algorithm

• Each cell site further transmits this paging signal on its own set up channel.

• If mobile is in ON state, it receives paging message, recognizes its own identification number in it and locks to the strongest set up channel (nearest BS).

• Only the intended mobile now sends back a response to its nearest cell site (BS) on the signaling channel.

• Now the respective BS, sends a speech channel allocation message to the mobile and informs the network so that connection can be established.

• The mobile unit tunes to the assigned voice channel tend initiates user alert of an incoming call

Call Termination:

• When mobile user turns OFF the transmitter, a signaling tone is sent to the BS.

• Both the sides free up the voice channel.

• BS and MTSO recognize this and disconnect the connections and refresh the switch.

• MS resumes monitoring the pages through the strongest setup channel, i.e. expects a paging message from nearest / strongest BS (current cell)

Hand Off:

• During a call, serving BS monitors mobile signal strength

• If signal strength falls below a threshold, Network requests all the neighboring cell BS to measure signal strength from this mobile.

• If any nearest BS indicates better quality and strength than the current serving BS, the MSC commands the current BS to send a signaling message to the mobile, asking it to retune to a free channel in neighboring cell.

• The MS retunes to new channel and network MSC switches call to new BS

Data and Communications Convergence

MediaStreaming videoVideo on demandInteractive video services

TelecommunicationPSTN and cellular servicesVideo telephonyWideband data services

ComputerInternet accessElectronic mailMobile computing

Wireless

Internet

Broadband

Convergence of High Speed Internet & Mobility A major driver of future wireless The Wireless Industry has grown at enormous

pace over the past decade.

More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move.

With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure.

The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective.

First generation (1G): Analog voice systems No standardization

Second Generation (2G): Digital voice systems Currently deployed systems CDMA, GSM (Global System for Mobile

communication) PDC (Japan) D-AMPS (Digital Advanced Mobile Phone System)

PCS Systems Second Generation – advanced (2.5G): Combining voice and data communications Providing enhanced data rate Two basic technologies:

GSM-based (high baud rate) GPRS (General Packet Radio Service) Utilizes voice time slots to send packet traffic An overlay over the existing voice system

Should really be called 2.1G!! Any standards?

Wireless Network Evolution

Third Generation (3G) Two basic proposals to handle voice and data

Ericsson: Universal Mobile Telecommunications systems (UMTS) Compatible with European GSM Backed by ETSI and Japan

Qualcom: CDM2000 Not compatible with GSM Compatible for IS-95 (supported by U.S)

3G Standards 1999 UMTS took over and an agreement was made over setting

some standards Major competing technologies

Bluethood Wireless LAN (IEEE 802.x standards) – also known as WiFi

Short range wireless communications Highly utilized and very popular: offices, airports, coffee

shops, universities and schools Two basic modes of operations:

• Ad-hoc networking: computers send data to one another • Access point:: sending data to the base station

Supporting heterogeneous multitude of systems Includes multiple networks:

Digital video broadband Digital audio broadband Wireless LAB, Bluethood-based networks

Open communication network: infrastructure independent which can access to any services and applications

Complete compatibility between wireless and wired networks through gateways

Supports statistical multiplexing of heterogeneous data over-the-air Latency, noisy environment, unpredictable discontinuities and

loss, etc. High-speed wireless transmission over the air

High performance physical layer 20Mbps (2G: 28Kbps, 3G: 2Mbps)

Scarce bandwidth availability Efficient frequency spectrum utilization Efficient hand off Dynamic bandwidth allocation Advanced digital transmission technology (modulation, low

power devices, etc.)

Fourth Generation (4G)

 

G-points in Mobile Comms History

1G analog- voice only- inflexible- not optimised- very transparent

2G digital (analog)- voice (data)- inflexible- optimised- transparent

2.5G digital- voice + data- flexible- optimised- transparent

3G digital- data + voice- very flexible- ‘optimisable’- not transparent

3.5G digital- more data (IP)- very flexible- ‘optimisable’- not transparent

4G digital/analog?- even more data- very flexible- ‘optimisable’- transparent

GSM Global System for Mobile Communications Digital cellular system for voice, fax, data >200 million customers >320 networks 137 countries Annual growth rate of 100% - 200% 4 new customers every second

Greater “presence” than MacDonalds!

no GSM

with GSM

Countries with GSMCountries with GSM

Wireless Networks

Motivated by people-on-the-go- PCs availability, Internet usage,

Mobile life

Aimed is to establish wide-area voice data communications

Includes mobile systems (cellular telecommunication systems)

Wireless Network Area Definitions

WAN

WAN-MAN

MAN

Pico-Cell

MAN-LAN

PAN

LAN-PAN

0km~50km ~2km ~10m

Courtesy of IEEE 802.15 Press Kit. Jan. 2001

BluetoothIEEE802.11HyperLan

GSMGPRSCDMA

WLAN Network Architecture

PDA

Laptop

Wired Network

FixedWorkstation

DBMS

FixedWorkstation

FixedWorkstation

Printer

Workstation

MobileAgent

MobileAgent

MobileAgent

Accesspoint

Accesspoint

Accesspoint

Wide Area

Metropolitan Area

Local Area

Personal Area

LAN:collection of secure “hot

spot” connections, providing broadband access to the Internet

PAN:collection of secure

connections between devices in a

“very” local area

WAN:everywhere outside of the hotspots, where wireless Internet connection are

provided

Bluetooth;< 800 Kb/s – < 30 ft, 10 m

802.11b; 802.11a; 802.11g2M > 54Mb/s – > 300 ft, 100 m

GPRS, 3G – UMTS< 400 Kb/s – xx Mls, Kms

MAN:Building to Building

connectionMMDS; LMDS; 802.1610M > 155 Mb/s - Kms

Convergence

Convergence of Cellular Mobile Networks and WLANs

BenefitsFor cellular mobile operators Higher bandwidths. Lower cost of networks and equipment. The use of licence-exempt spectrum. Higher capacity and QoS enhancement. Higher revenue.

For users Access to broadband multimedia services with lower

cost and where mostly needed (e.g. in Central Business

Districts and Business Customer Premises). Inter-network roaming.

These future networks will have the following inherent characteristics :

1. Broadband Internet access.

2. High (guaranteed) QoS.

3. Seamless access – fixed and mobile.

4. Intelligence.

The Internet is the driver

Million 1999 2000 2001 2002 2003 2004

USA 97 118 135 145 148 152

Japan 23 32 38 43 47 50

Asia Pac 32 70 104 120 135 150

W.Europe 54 81 114 145 164 179

ROW 35 72 105 118 130 140

Total 241 373 496 571 624 671

World Internet users (1999 – 2004)

PAN

Mobile Broadband Network Categories

W-LAN

W-WAN

Personal Area Networks

Wireless Local Area Networks

Wireless Wide Area Networks

Wireless Networking StandardsOverview

Reliability,

Power, Cost

Cost,

Convenience

Speed,

Flexibility

Reach quality

Success Metrics

1 - 100+1 - 10+1 - 1001,000+Transmission

Range (meters)

20 - 25072011,000+64 - 128+Bandwidth

(KB/s)

255 / 65,0007321Network Size

100 - 1,000+1 - 7.5 - 51-7Battery Life(days)

4KB - 32KB250KB+1MB+16MB+System

Resources

Monitoring &

Control

Cable

Replacement

Web, Email,

Video

Wide Area

Voice & Data

Application

Focus

ZigBee

802.15.4

Bluetooth

802.15.1

Wi-Fi

802.11b

GPRS/GSM

1xRTT/CDMA

Market Name

StandardUWB

802.15.3a

?

IrDA

Cablereplacement

?

?

1

9.6-115

1-5

Future PAN TechnologiesTechnology Max

SpeedIntroduction AdvantagesDis-

advantagesBottomline

Bluetooth 723.2Kbps 2001 Low cost Interference, security

Replace cables

Infrared 115Kbps In use Very low cost

LOS Replaced by Bluetooth

802.15.1 723.2Kbps 2002 Low cost Interference, security

Formalized Bluetooth

802.15.3 High rate

>20Mbps 2003 High data rates

Expensive, not

backwards compatible

Case not proven yet

Time Modulated Ultra Wideband (UWB)

>20Mbps 2006 High data rates, no dedicated frequency

Not approved, expensive

Under hyped. Potentially

revolutionary technology.

Source: Gartner (2001)

Analogue (1G)

W-WAN Categories• AMPS• N-AMPS

• TACS• NMT

3G

Digital (2G)

2.5G

4G

• GSM• CDPD• PDC

• CDMA/cdmaOne/IS-95A• TDMA / IS-136

• GPRS• HSCSD• EDGE Classic

• EDGE Compact• CDMA / IS-95B• cdma2000 1xMC

• PDC-P

• W-CDMA• cdma2000 3xMC• CDMA 1x EVDV

• CDMA 1 XTREME

• Undefined

Technology

Max Speed

Introduction

Advantages

Dis-advantages

Bottomline

GPRS 171.2Kbps

2001 Packet data for GSM world

Data rates may

disappoint

Will be most

successful technology

through 2005

HSCSD 115Kbps In use Dedicated channels

Low deploymen

t, expensive

Will not be mainstrea

m

EDGE Classic

384Kbps 2003 Higher data rates for

both packet & circuit

Expensive, little

terminal support

Will not be able to

compete with W-CDMA.

EDGE Compact

250Kbps 2002 Higher data rates for

both packet & circuit TDMA

networks

AT&T (main proponent)

has changed direction

Unlikely to be

successful

Transaction - Based

• Mobile Banking• Mobile Stock Trading• Travel Reservation & Payment (Rail, LRT, Bus, Flights, Taxi, Hotel, Insurance)• Entertainment Reservation & Payment (Cinema, Theater, Concerts)• Pre-Paid Voucher Recharge• Vending Machine Purchases• Electronic Cash Download• Payment of Utility Bills (Electricity, Water, Astro, etc)• Other Payments (Restaurant Bills, Takeaways, Parking)• Online Auctions• Online Shopping (eg. CDs, Books)• Music MP3 Downloads

Technology Enabler:

SIMCard

2nd

SmartCard

Dual – Slot Hand Phone

• Customisable with SIM Toolkit• Remote Upgrading

• Credit Card• Debit Card• eCash Card• Pre-Paid Card• Loyalty Card

Mobile Transactions

NEXT GENERATION MOBILE VISION & CONCEPT

Ubiquitous connectivity for slow and fast moving users, accessing high speed internet and related multiple services at affordable cost and reasonable QOS

Cooperation between content providers and Wireless access providers- Virtual operators

Multi-Media, Multi-Environment, Multi-Operator Environment

User Driven, User Controlled, Context Aware Applications

Convergence of services, aggregation and inter-working of existing and emerging technologies and networks

Vertical and Horizontal Seamless Handover

.

80’s 90’s 00’s 10’s

1G

2G

2G evolution

3G

3G evolution

4G

Digital Voice, data

Analog Voice

Packet Data, On

Multimedia messages, multiple services

Cost efficient, Higher Data

Higher Data, Superior Radio Resource Management, Seamless mobility, Aggregation of Generations

Evolution towards better Data rates

and higher mobility

0.1 1 10 100 1000 MB/S

V

P

S

4G Research

Targets

Mobility

CDMA2000, WCDMA 802.11a,g

W-LAN802.11b

1X EV-DV

1X EVDO

CD

MA

1X ,

ED

GE

EVOLUTION

E-Mail 4.2 sec in 2G to 0.002s in 4G

Movie Download 926 hours in 2G to 1minute in 4G

3G E

volv

ed

Syste

ms

Convergence of High Speed Internet & Mobility A major driver of future wireless The Wireless Industry has grown at enormous pace over the past decade.

More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move.

With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure.

The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective.

GENERAL REQUIREMENTS

Handling multimedia TrafficData, Video, Voice

Seamless Services on the moveUser friendly smart devices

Diversified wireless accessUnder One Umbrella, Seamless

access Advanced Mobility ManagementIndependent of the IP versionProactive, always-onIntelligent integrated control

WIRELESS TRANSMISSION

WIRELESS TRANSMISSION

Mobile Radio (Wireless) signals undergo many impairments during transmission / propagation through the radio channel (atmosphere / free space / any medium)

Frequencies • Radio signals are modulated signals with carrier frequency allotted in any of the frequency bonds.

• ITU Region

1. Europe, Middle East, Africa

2. Greenland, North & South America

3. Far East, Australia, New Zealand

• LAND / SATELLITE CELLULAR RADIO BANDS

SIGNALS: Mostly SINUSOIDAL(AM/FM) or its variants (ASK, PSK) spectrum has side bonds or frequencies.

Fundamental + Harmonics

SIGNALS: Mostly SINUSOIDAL(AM/FM) or its variants (ASK, PSK) spectrum has side bonds or frequencies.

Fundamental + Harmonics

f) Ф

Ф = m sinФ 90°Phase

Zero phase

I = m cosФ

xx

zz

yy

ANTENNAS:

Energy Translators /Couplers from TX to CH.

Hence Radiation pattern.

Ideal Isotropic: Equal power in all directions

ANTENNAS:

Energy Translators /Couplers from TX to CH.

Hence Radiation pattern.

Ideal Isotropic: Equal power in all directions

SMART ANTENNAS→ Use DSP

Real Directive: DIPOLE omni directional uniform radiation in one plane fig.of 8 in other two planes

DIRECTIONAL ANTENNA: Main lobe in only one direction

SECTORIZED ANTENNA: Several directed antennas combined on a single pole

Real Directive: DIPOLE omni directional uniform radiation in one plane fig.of 8 in other two planes

DIRECTIONAL ANTENNA: Main lobe in only one direction

SECTORIZED ANTENNA: Several directed antennas combined on a single pole

λ /2λ /2

z

x

xx

yy

z

yy

xx

zz

xx

3 sector3 sector

yy

zz

yy

x

zz

x

zz

8 sector8 sector

Only one direction of transmission unlike wired transmission

Fixed error limited transmission range

Fixed error limited detection range

Interference range

SIGNAL PROPAGATION

d

Free space Loss or Los loss

Squared law pr α 1/d2

- Due to equal distribution of energy Over the surface of energy sphere.

Path Loss : Signal attenuation due to rain,fog,dust,smog,air,snow

Signal penetration medium attenuation frequency

SIGNAL IMPAIRMENTS

- Mobile signal reflects from sky scrapers, Walls, Trucks,Mountains,Towers,Birds.

Reflected signal is not as strong as the original.

Reflection Signal strength

Reflection : When λ < size of obstacle

Blocking or Shadowing :

- due to large obstacles

Scattering : obstace size ≤ λ

Incoming signal is scattered in multiple directions and become weak signals, due to many objects in atmosphere or space .

Diffraction : Similar to scattering Radio waves get deflected at edges signals become weak

Multi Path Effects :

POWER

t

ISI Fading – Short term Long term

Delay Spread

MULTIPLE ACCESS OR MULTIPLEXING :

Means of combining several user signals onto a common channel

Multiple users access and share a common channel with no interference (Hope fully)

Simple ex :1. Athletic tracks / Swimming lanes 2. Many cars/Buses/Trucks share a multiple lane road due to separation of lanes

Space Division Multiplexing

However, needs a special identification and control mechanism for proper MUX & DEMUX.

For Wireless Communication,4 types of Multiplexing

SPACE DIVISION MULTIPLEXING :

Assignment of space to each communication channel i.e., actually a source signal, with minimum

interference and a maximum medium utilization

Assume 3D space represented as shown

k1 k2 k3 k4 k5 k6CH

time t t

frequency fs1 s2 s3f

cccode

Coverage Space is represented via circles

Channels K1, K2, K3 can be mapped into three spaces S1, S2, S3 with clear separation and no overlap

What about K4, K5, K6 ?

Analogous to road traffic separate lanes Analog fixed Telephone Network separate wire pair / local loop

For wireless, SDM implies , a separate sender for each channel with wide space separations.

ex: FM radio stations.

• Problems arise if two or more channels occupy the same space

FREQUENCY DIVISION MULTIPLEXING (FDM / FDMA)

• Subdivision of frequency dimension into several non-overlapping frequency bounds or slots.

• Each channel Ki is allotted its own (dedicated) band

• Sender uses this band continuously

• Guard spaces do exist for no interferences.

Ex:- Am radio stations

f

t

c

S1 S2 S3

• Receivers must TUNE into the specific senders.

• Draw backs : Tremendous wasted frequency as user may not transmit all the time (usually less than 1Hr per day).

TIME DIVISION MULTIPLEXING TDM(A)

• A channel Ki is given whole bandwidth, but only for a fixed period of time

• Time dimension is partitioned into several Time slots

• Each channel is allocated one Time slot.

S1

S2

S3...

t1

t2

t3

f

c

t

• Needs precise synchronization in timings for TX or Rx.

HYBRID-FTDMA:• A channel Ki use a certain frequency band fi for only a

certain amount of time ti

• More robust against frequency selective interference / jamming.

• Better protection against Tapping / Intruder.

• But needs coordination between senders.

t

c

f

All channels use same frequency at the same

time.

Separation through coding each channel with its own code.

Guard space is the distance in code space

CODE DIVISION MULTIPLEXING : CDM(A)

t

c

f

Ex:- ORTHOGONAL CODES

Due to VITERBI.

Ex:- Different telephone calls use same band width but different languages (Codes), at same

time.If language is same, then SDM is needed.

Thus secret codes (Languages) provide security

Code space is huge. Hence better protection against interference and tapping .

However, the intended receiver must know the code and also must synchronize with Tx for correct decoding .

MODULATIONANALOG

DIGITAL

AM

FM

BINARY

M - ary

ASK, PSK, FSK

MSK, QAM, GMSK,

QPSK, DQPSK

Analog

Modulation

Digital

Modulation

Analog Base band

signalDigital Data

101101001

Radio Carrier

SPREAD SPECTRUM MODULATION

Developed for secured communication

Means of transmitting a data sequence that occupies larger bandwidth than the original base

hand

Spreading of bandwidth is through the use of a code that is independent of data

Chief Advantages: 1. Resistance to narrow band interference or

jamming

2. Multiple Access Communication.

Purposeful bandwidth spread to make the signal to possess noise like appearance so as to blend into the back ground noise.

f

Power P

i )

f

P

ii )

f

P

iii )

f

P

iv )

f

P

v )

BPF

STEP i) Narrow band user input data

ii) Tx Spreads the signal into a wide band signal. But energy is same as original.

iii) A Wide band interference and Narrowband interference get added

to wide band signal during transmission

iv) Receiver dispreads the signal into narrowband. Thus narrow band interference gets spread and wide band interference gets left as it is.

v) Receiver uses a BPF to band limit the user signal to original bandwidth and yield high SNR

MOBILE RADIO SIGNAL PROPAGATION & ENVIRONMENT

Mobile radio signals propagating through a communication medium are subjected to many changes or modifications.

Propagation path loss :-

- Due to beam Divergence (Free space Loss) - Proportional to 1/d2

Terrestrial Losses :-

Terrain Dependent (Path Loss)

- Texture, roughness of terrain tends to dissipate propagated energy.

• Scattering and Multipath effects :

- Signal gets scattered at ≤ λ obstacle points and travel in multipaths.

- Result is different delay spreads of signal.

- Thus severe FADING of the received signal (sum total of multipath signals).

- Because of low mobile antenna height and near ground communication.

MS Stationary

MS moving

S(t)

r(t)

m(t)

Local mean

avg Pr

Time or distance

• Instantaneous Signal Strength :

• Depends on whether Mobile station (MS) is in movement or stationary.

• Fading is always present due to multipath effects due to multiple scattering points, reflection points, dissipations.

• Delay spread is the smearing of received signal due to lengthening of time period as a result of different multipath signals arriving with

different phases.

• Short term fading is obtained by

m(t) - r(t) (t)r0 In db

Received Long term fading

• Signal fades about 40 dB

• Nulls around

• Rate of fading α vehicle speed.

m(t) (t)r r(t) 0 Model

2 / λ

(t)r0

- multipath fading

- Rayleigh fading - due to multiple reflections from buildings, structures.

m(t)- Local mean long

term fading due to terrain contour

PROPAGATION PATH LOSS:

• Due to the presence of radio wave scatterers along the path.

• No. of scatterers depend on the contour variations, terrain roughness

▼

▲

▼

)(θ θФ

T BS antenna

Snell’s law

MS antenna

• Therefore changes in the propagation as a result of specular Reflection, Diffuse Reflection and Diffraction.T

Specular Reflection from smooth flat and slopy terrains : • Occurs when radio waves encounter a smooth

interface between two dissimilar media and linear dimension of interface is larger than λ

Ex: Mirror reflection defined by Snell's law.

▼

h1

Elevation

Distance

• Reflected wave at point θ due to reflection of incident wave from BS antenna T can be thought of as originated from a fictitious image antenna TI and passed through the surface without refraction.

h1

Diffuse Reflection: • Occurs when radio waves encounter a rough

textured surface with roughness of order of λ

• Unlike specular reflection, this scatters energy and focus a divergent radio path.

▼

€

d2d1

LOS

LOS

LOSh1

)d1

d1

(λ2

1h

21

p

h2

BS

MS

• Hygen’s principle explains this.

• In tensing of signals is smaller than that of specular reflected wave

• Both these reflections correspond to LOS propagation of reflected signals.

€

▼

l

hp

BS

h2

h1

Elevation

Distance

Diffraction:

• Attenuation depends on whether obstruction extends through the path or protrudes into LOS path.

• Knife edge diffraction modals are used.

• Occurs when the propagation path is obstructed by the features of an intervening terrain between two antennas.

•Thus out of sight propagation.

Path Loss : Propagation frequency distance Path Loss

►

►(Ә2

Ә1(

►

100m

> 2 km

▼3m

Ә1

Ә2

- incident angle / elevation angle

- reflected angle

Propagation path loss is 40 dB / decade or 10 km.

Received carrier powered is inversely proportional to R4.

- For Mobile Radio Channel.

- For Free space Radio Channel.

- For Real Mobile radio model 2 < γ < 5

FADING:

• Antenna height of Mobile unit is less than its surroundings.

• Carrier signal wavelength is smaller than sizes of surrounding structures.

4-R α C

γ- Rα

2- R α

Result : Multipath Fading due to net sum of multiple path arriving signals with different phase.

Fading fluctuation range about 40 dB. (10 dB above, 30 dB below avg / mean). 

• Nulls of fluctuation at the base band at about every in space, but not with same levels. 

• Rate of fluctuation α vehicle speed. 

2

λ

Multi path fading occurs in Three situations :

1.Mobile unit and surrounding scatterers are still / stationary

2.Static Multipath Mobile unit standing still scatterers moving

3.Mobile unit and scatterers moving.

Static Multipath Signal :

Envelope

} i

)-t(f 2 i { 0

0e ) -t ( x s(t)

ai → attenuation factor of ith path.

N signal paths,

N

1i0 i )(ts as(t) i

i f 2 j-i0

0e aax(t)

→ additional relative delay on ith path.

i → Propagation time

i

Case 2 : MS still scatterers

moving cars

i , ai are uniquely different along ith path at any instant.

js}-{Ra e A(t) 0(t) jψ-

t f 2 j-j

00 e e x(t)s(t)

(t) fj2-i i00 e (t)a a x(t)

220 SRa A(t)

RS Tan ψ(t) 1-

Case 3 : MS Moving – a) Scatters are absent b) only one scatterer present c) Many scatterers present near MS. v▼

(t)s0

θ

] ) cosθ vt βφ tω ( j [ Expa s(t) 0 0 0

λ

2π β

X(t)

Voltage

Doppler effect contributes additional frequency due to movement of Mobile

cosθλ

v cosθ f f mdoppler

travel of direction on depending

Thus concept of standing waves is applied to radio signals to understand the multipath effects. 

A resultant signal due to an incident signal and a perfect scatterer reflected signal, reaching a mobile of speed V is

The envelope of S(t) looks like a standing wave pattern.

)2

ω - vt (β sin 4a (t) x

0 2 20

2

Fading Frequency → 2V/λ

] ) ω - vt β φ t ω ( j [0

vt] β - φ t ω [ j0

00000 e a - e a s(t)

▼v

Scatterers (Houses)As a mobile unit proceeds in a street, it is passing through an avenue of scatterers as shown. 

Highest Doppler Frequency fd is

df

W(f)

λ

v2

)cosθλ

v (max )f (max f dm

λ

v

Why 800 MHz Band? 

ITU - T and FCC chose 800 MHz initially because. 

- Severe spectral limitations at lower frequency Bands

 - Maritime (ship) mobile service at 160 MHz

 - Fixed station services from 30 to 100 MHz

 - FM and VHF/UHF TV Bands from 80-600 MHz

 - No Mobile radio transmission beyond 10 GHz due to propagation path loss, multipath fading and rain loss.

- 800 MHz allocated to educational TV Channels was heavily under utilized.

Even though not an ideal frequency for mobile radio, the 800 MHz band demonstrated the feasibility.

History of 800 MHz spectrum:  

1958 -Bell lab proposal for 75 MHz system at 800 MHz.

1974 -FCC allocated 40 MHz spectrum for one cellular operator licensed per market area.

1980 -FCC revised its policy and introduced competition with two licensed carriers per service area of course this resulted in trunk efficiency degradation

Ban Mobile Base System 

A 824-835,845-846.5 869-880, 890-891.5 non wire line.

B 835-845, 846.5-849 880-890, 891.5-894 Wire line

1986 – FCC added 5 MHz to each band. 

old 333 + new 83 = 416 channels per band with 30 KHz per channel.

FCC assigned frequencies in 20 MHz groups, as

TRUNKING EFFICIENCY: 

No. of calls per hour per cell =

Φ = Offered traffic load / average calling time

Trunking efficiency degradation factor

η = {φOne carrier – φ Multi carrier} / φOne carrier

Blocking probability %

30

10

20

0 1 52 10 30

5 career/market

2 career/market

η%

UNIQUENESS OF MOBILE RADIO ENVIRONMENT

Propagation path loss increases with

        - Frequency

- distance θ1 elevation angle θ2 incident angle

▼

d

h

Direct pathReflected path

(2θ

1θ (

2 km

30 – 100 m

▼

Cell antenna height: 30 -100 m

Mobile antenna height: 3 m 4-R C Received carrier Power

Difference in Powers

2

1 12

R

R log 40 dB in C - C C

4-

1

2

2

1 )( R

R

C

C

General Rule

=>40 dB/dec path loss

Δc = - 40dB

Free Space- c α R-2

Mobile radio CH- c α R-4

dB/dec 20 R

R log 20 C

2

1

dB/dec 40 R

R log 40 C

2

1

Received signal fading levels:

10 dB above and 30 dB below mean. 2R-e R P(R)CDF

lcr R η2π

βν )(RLevel crossing rate

Average fading duration R

-t

βν

2π (R)

-t afd

η

PATH LOSS MODELPATH LOSS MODEL

• Different, often complicated, models are used for different environments.

• A simple model for path loss, L, is

The path loss exponent = 2 in free space;

2 4 in typical environments.

where Pr is the local mean received signal powerPt is the transmitted powerd is the transmitter-receiver distancef is frequency,

K is a transmission constant.

Pr 1

Pt f2d

= KL =

PATH LOSS LIMITATIONS

• Given the performance requirement SNR SNRo, the path loss imposes limits on the bit rate and the signal coverage.

• The received signal-to-noise power ratio, SNR, is

SNR = = •Pr KPt 1

Pn d NoB

( )B or d

KPt

dNoSNRo

KPt

NoBSNRo

1/

where No is the one-sided noise power spectral density B is the signal bandwidth.

SHADOW FADING• The received signal is shadowed by obstructions such as hills and buildings. • This results in variations in the local mean received signal power,

• Implications – nonuniform coverage – increases the required transmit power

Pr (dB) = Pr (dB) + Gs

where Gs ~ N(0, s ), 4 s 10 dB.2

First order statistics of Fading => Average power CDF, BER

Second order statistics of Fading =>lcr, afd,

word Error Rate

independent of time

time/velocity dependent

Rayleigh Fading :

_LLe1L)P(y

22_AA-e1- A)P(x CDF

NOISE LEVEL IN CELLULAR BANDS:

THERMAL NOISE -129 dBm at B = 30 KHz, T=290K

IGNITION NOISE -124 to –104 dBm at B=30 KHz, T=290K

AMPLIFIER NOISE KTB

G)N(NNF

ai

DELAY SPREAD

• Base station sends an impulse signal to the mobile station.

a0

▼

1 2 3 4 t

4

31

▼

BS Antenna

t

2

4 scatter case Delay spread N=4

s(t)a(t)s 00 error

• Because of multipath scattering, the impulse gets reflected many times and thus many impulses (echo's) arrive at mobile unit at different times.

a0

N>>4

t

N-scatter case delay spread

• Received impulse signal is

t ω j e E(t)

t ω j j 0 e )-δ(taas(t)

• As number of scatterers (N) increases, the received impulse sequence becomes a continuous signal pulse, with a pulse length Δ (called DELAY SPREAD).

Delay envelopes contain multiple peaks.

 Shortest path signal need not necessarily produce highest peak as the scatterer could be absorb in nature.

 Mean delay time d is the first moment or average.

0

dt E(t) t d

Standard deviation or delay spread Δ is

2

0

22d - E(t)dt t

t=0 → Leading edge of envelope E(t).

DELAY SPREADFREQUENCY DOMAIN INTERPRETATION

Bs = signal bandwidth 1/TH(f)

Bs

12

f

• small flat fadingT

• large frequency-selective fadingT

 Parameter Open Urban Suburban Area Area Area 

Mean Delay Time d, μs 0.2-0.5 1.5-2.5 0.1-2.0

Path Length, km 20–300 450-750 30-600

Max. Delay Time 0.5-2 5-12 0.3-7 (-30dB)

Path Length, Km 0.5-1 1.5-3.6 0.9-2.1

Range of delay spread 0.1-2.0 1-3 0.2-2 Δi, μs

Mean Delay Spread <0.2 3 0.5

Delay spread is assumed independent of frequency.

DOPPLER SPREADDOPPLER SPREAD

• A measure of the spectral broadening caused by the channel time variation.

• Implications – signal amplitude and phase decorrelates after a time period ~ 1/fD

Example: 900 MHz, 60 mph, fD = 80 Hz5 GHz, 5 mph, fD = 37 Hz

8C32810.87-Cimini-7/98

fD v

COHERENCE BANDWIDTH:

Bandwidth in which either the amplitudes or the phases of two received signals have high degree of similarity or correlated.

• Different delays in two fading signals that are closely spaced in frequency can cause the two signals to become correlated.

• The frequency spacing that allows this condition depends on the delay spread Δ .

• This frequency interval is called coherence or correlation Bandwidth Bc.

Scattered component

Channel input response model

d

E(t)

t

Specular component

Δdt

Coherence bandwidth

Correlation function

f

C(f)

Scattered component

• A typical definition of Bc → ΔΠ 2

1 Bc

AM

or

Δ8

1 Bc

ΔΠ 4

1 PM

FM

NOISE IN MOBILE RADIO CHANNEL:

THERMAL NOISE

WHITE NOISE

WIDEBRAND

GAUSSIAN WHITE NOISE

NARROWBAND

(t)jn(t)nn(t) sc

URBAN

HUMAN MADE NOISE

SUBURBAN

GALACTICSOLAR

EXTERNAL NOISE

ATMOSPHERIC

-10 8642 10 100 1000 105 109

0SOLAR

RURAL QUITE

GALACTIC

RURAL

SUBURBAN

URBAN

INTERNAL RECEIVER

f

NFatmospheric

Mean Noise Figure Fa : 28 db / decade slopes for all.  

Automotive Traffic Noise Power increases with traffic density decreases with frequency

ELEMENTS OF CELLULAR MOBILE RADIO SYSTEM DESIGN

GENERAL DESCRIPTION OF PROBLEM:

CONCEPT efficient Spectrum Utilization

Major Elements of System Design  

1. Frequency Reuse Channels

2. Co channel Interference Reduction Factor

3. Carrier-Interference Ratio

4. Handoff Mechanism

5. Cell Splitting

Limitation / constraint In system design Frequency Resource

Challenge / goal greatest no. of customers with a specified system quality.

Ex :- Max. no. of calls/hour/cell Q Max. No. of frequency Channels /cell - N

Q depends on

- cell size

- traffic conditions

Ex :- A BUSY Traffic area of 12 Km radius is divided into seven 2 Km cells. Assume a traffic situation with the busiest traffic cell cover 4 freeways and 10 heavy traffic streets, with a total length of

• 64 Km of TWO 8 lane roads

• 48 Km of Two 6 lane freeways

• 588 Km of forty three 4 lane roads

average spacing of cars is 10m during busy periods. One half cars have phones and eight tenths of them make a call (ηc= 0.8) during the busy hour. 

28,0000.82

70,000hourbusy in calls No.of

7000010m

700km cars of number Total

700km5884864 roads of length Total

MAX. No. of Frequency Channels per cell (N)

• depends on average calling time T

• depends on maximum calls per hour per cell Qi

• Determined from a plot or Table that shows N,B and A

• OFFERED TRAFFIC LOAD =

Erlangs60

TQA

I

Problems in wireless communicationProblems in wireless communication

• Available unlicensed spectrum allocation

(government regulation)

• Only low transmission power levels allowed

(No brute force possible: strong signal in

narrow band)

• Multi-path propagation echoes

• Interference

• Noise

RADIO ENVIRONMENTRADIO ENVIRONMENT

• Path Loss • Shadow Fading • Multipath • Interference • Infrared Versus Radio

• Path Loss • Shadow Fading • Multipath

Limit the Bit Rate and/or Coverage

BASE STATION

• Frequencies (or time slots or codes) are reused at spatially-separated locations.• Introduces interference system capacity is interference-limited.• Mainly designed for circuit-switched communications• Base stations perform centralized control functions. (call setup, handoff, routing, etc.)

FREQUENCY REUSEFREQUENCY REUSE

• Reuse Distance (D)

– distance between cells using the same frequency, time slot, or code– smaller reuse distance packs more users into a given area, but also increases their co-channel interference

• Cell Radius

– decreasing the cell size increases system capacity, but complicates the network functions of handoff and routing

DESIGN CONSIDERATIONS

History of Mobile Radio &Cellular Communication SystemsHistory of Mobile Radio &Cellular Communication Systems

FCC allots 40 MHz bandwidth in 800-900 MHz band

First cellular system by NTT in Japan First US cellular land mobile phone service in 800-900 MHz band with 40 MHz bandwidth

1974 1979 1981

FCC – 152 MHz duplex radio telephony 1964 Simplex radio telephony system-450 MHz 1956

FCC permitted 4 channels in 30-40 MHz 1933

Police car radio at 2 MHz in Detroit 1921

First radio transmission by Marconi 1897

Initial radio demo by Hertz 1880

Telecom EventTelecom Event YearYear

1984 AMPS cellular system introduced by AT&T in US

1986 FCC added 5 MHz extended band; two operators per market

1988 TDMA digital cellular standard in North America (NA)

1992 GSM operable in Germany D2 cellular system

1993 CDMA chosen as digital cellular standard in NA

1994 American TDMA started in Seattle; PDC in Tokyo, Japan

1995 CDMA in Hong Kong

1996 Six PCS licensed bands at 120 MHz given in US

1997 Broadband CDMA chosen as 3G Technology for UMTS

1999 ITU decides nextG standards- W-CDMA, CDMA2000, TD-SCDMA

2001 First commercial W-CDMA service in Japan

2002 FCC approves additional band for UWB

It is widely believed that the fixed landline telecom network (Telephone, fax, etc) are the largest and most complete integrated systems at present in the world.

The cellular radio has rapidly evolved and had already crossed the size of the fixed land telephone network.

Let us consider the important differences between the conventional landline telephone network and the cellular radio telephone network.

Let us recall the basic features of the plain old land telephone network (Public switched telephone network – PSTN).

Plain old telephone:

DTMF Keypad for number dialing:

i) Telephone Number is registered solely in the local exchange.

ii) Numbers are dialed from DTMF keypad as shown above.

iii)Central Battery supplies power to telephone handset.

iv)Subscriber loop is a 2 wire half duplex circuit.

v) Trunk circuits employ 4 wire circuits with Hybrid coil doing 2/4 wire conversion.

vi)ON/OFF HOOK state of cradle switch is an indication to the exchange about call REQ/ Disconnect signaling information.

vii) subscriber can start dialing (entering telephone no.) only after receiving the dial tone from the exchange.

viii) User must go to instrument to make a land phone call.

Features of land phone:Features of land phone:

Features of mobile/cellular phone:

i) There is no dial tone and cradle switch (i.e. on/off Hookon/off Hook)

ii) User types in/ calls from memory and presses ‘SEND’ button to transmit telephone number of called party

iii)Power comes from the local Battery (LB), not from CB

iv)Local exchange is replaced by a base station (BS) and a mobile switching centre (MSC)

v) Local 2 wire loop is replaced by 2 way HDX radio channel

vi)Cellular user talks on Reverse channel (MS to BS radio link) and listens on forward channel (BS to MS radio link)

vii) signaling information is exchanged via separate set up or control channels in each direction, user transparently

Fundamental principles of cellular Fundamental principles of cellular communications:communications:

Cellular technology had evolved from the mobile radio telephone technology.

Mobile radio telephone (R/T):Mobile radio telephone (R/T):

It is basically a transceiver handset with a 2 way duplex link connecting to a base station and switching centre.

Mobile unit carries its own telephone number in a SIM / smart card, which allows roaming using same number.

BS and MS always keep in touch by handshaking protocols via control channels, transparent to the user.

The following figure depicts the components of a R/T.

Cellular radio phone and its components:

There are many ways of providing wireless and mobile communications

For ex:- cordless phones used at homes employ wireless technology, with a low power transmitter and hence has small coverage area(<100 m)

Such phones used in adjacent homes do not experience any interference, even by operating at same frequency exactly

This is a perfect example for frequency reuse

The same principle of frequency interference avoidance is used in cellular systems also, even with much more transmission powers

Radio Cell Shape:

All users in a cell are served by central BS -gateway of cell !

Ideally all the cells are circular in shape for omnidirectional coverage, with BS located at its centre as shown below.

Cell area and periphery are decided by minimum signal strength, height of BS antenna, presence of hills, tall trees/buildings and atmospheric conditions.

Thus actual shape of cell and coverage area is an irregular zigzag circle, but modeled by a hexagonal building blocks.

Ex:- Bee hives are 3D hexagons

Multiple accessing is employed in cellular systems to allow multiple cellular subscribers to access the same BS in a cell

They are FDMA, TDMA and CDMA

The limited bandwidth allocated to operator is divided into number of radio channels, which are further grouped into subsets, to assign one group of channels to a particular cell

This is the principle of FDMA employed in first generation cellular systems.

Because of unique frequency sets allocated for each cell, it is possible to use the same frequency set in a distant cell, as long as the two transmissions do not interfere with each other.

This is the principle of frequency reuse, a central theme of cellular communications

Radio coverage in a single cell:Radio coverage in a single cell:The fundamental radio cell and parameters that dictate the radio coverage are shown below

Different cellular ranges for mobile radio communications are indicated. The reverse path (MS to BS) limits the radio range, due to limited TX. Power of mobile unit.

The no. of subscribers covered by a single cell depends on the radius or area of the cell, as given in the table.

Cell radius km

Coverage area km2

Number of subscribers

covered 1 3.14 100

3 28.3 900

10 314 10,000

25 1960 60,000

Cell area and number of subscribers coveredCell area and number of subscribers covered

Typical cellular system layout and signal power distribution are shown below. One can see the extensive signal processing required to meet this.

MULTIPLE CEL LAYOUT:MULTIPLE CEL LAYOUT:

The intracellular communication is duplex radio communication between cell site (BS) and mobile unit (MS).

It needs a block allocation of frequencies for the control and voice radio channels

Adjacent cells are not assigned the same frequency sets to avoid the cochannel and adjacent channel interferences.

A handoff mechanism is required to automatically handover an ongoing mobile call from one group to another frequency group used in the next cell, as and when mobile unit is crossing cell boundaries.

That means the cellular phone circuits must be frequency agile to retune to a new frequency without call disconnects.

Basic cellular system architecture:Basic cellular system architecture:

Cellular technology replaced a large coverage area mobile radio system with many smaller cells, with a single BS covering one particular cell only, as depicted in the following figure.

The mobile and wireless devices used by subscribers are cell phones, PDAs, palmtop/laptop PCs, web phones, etc.

All devices are referred to as Mobile Stations/Units (MS)

An MS can communicate only with its nearest BS of a cell in which it is located ( i.e., belongs to).

Hence a BS (with a base transceiver) acts as a gateway switch/router to the rest of the world, to any MS.

Every BS is controlled by one base station controller (BSC), which in turn is connected to a mobile switching centre (MSC) as shown in the following figure.

Several MSCs are interconnected to PSTN and ATM backbone networks.

Cellular system architecture:

Home location register (HLR) and visitor location register (VLR) are two database pointers that support mobility and enable the use of same telephone number worldwide in cellular communications.

HLR is located at the home MSC where MS is registered

VLR stores all the visiting mobiles in that particular area

Authentication centre (AUC) provides authentication for an user attempting to make a cellular call.

This uses a 15 digit unique IMEI number programmed into the MS at registration time and also stored in Equipment identity register (EIR).

Network management and operations control are the functions of the centers NMC and OMC.

BS and MS signaling and voice communication:BS and MS signaling and voice communication:

In any cellular system, four simplex radio channels are needed to exchange synchronization and data between BS and MS, as shown below.

The control channels are used to exchange control messages like, authentication, subscriber identity, call parameter negotiation, power control, etc.

Traffic (information) channels are used to transfer actual data (voice/digital data)

Forward CH/ Downlink BS to MS transmissions

Reverse CH/ Uplink MS to BS transmissions

Control information shall be exchanged before the actual data transfer can take place.

This necessitates the use of handshaking protocols for cellular call setup, maintenance and disconnection.

Handshaking protocols in cellular call setup:Handshaking protocols in cellular call setup:

Simplified handshaking steps for a cellular call setup are illustrated in following figure.

BSBS MSMS

1. Need to establish path1. Need to establish path

2. Frequency/time slot/code assigned2. Frequency/time slot/code assigned

3. Control information acknowledgement3. Control information acknowledgement

4. Start communication 4. Start communication

fig. steps for a call set up from MS to BSfig. steps for a call set up from MS to BS

MSMS BSBS

1. Call for MS # pending1. Call for MS # pending

2. Ready to establish a path2. Ready to establish a path

3. Use of frequency/timeslot/code3. Use of frequency/timeslot/code

4. Ready for communication 4. Ready for communication

steps for a call set up from MS to BS:steps for a call set up from MS to BS:

5. Start communication 5. Start communication

Wireless LANs and PANs:Wireless LANs and PANs:

Mobile wireless networks find extensive use in different facets of human life.

Already we are accustomed to line orientd to Local Area Networks (LAN) and Wide Area Networks (WAN).

Ex:- Internet access, a value added service offered by landline telephone network PSTN

Wireless LANs (WLAN) are being developed to provide mobile access to data users.

Personal access Networks (PAN) cover very small areas referred to as Pico cells using low powers in ISM band.

WLANs and PANs are becoming popular choice and influence the wholesome home and office automation.

It is predicted that the percentage of nonvoice multimedia data traffic is increasing heavily.

Also the digital voice technology is permitting the integration of voice and nonvoice traffic into unified data stream.

Thus convergence of voice and nonvoice networks into a single unified network supporting multimedia communications is the order of the day.

Standards like IEEE 802.11, Bluetooth, HomeRF, HiperLAN etc., are being developed and deployed worldwide.

Adhoc networks are being devised for commercial and military applications.

MOBILE ADHOC NETWORKS (MANNET):MOBILE ADHOC NETWORKS (MANNET):Adhoc networks are basically peer to peer multihop mobile networks for freely moving mobile users and hosts interconnected by nodes (mobile transceivers).

Information packets are transmitted using a store andforward protocol as shown in the fig.

Nodes are very small transceivers with antennas and can be located inside airplanes, ships, trains, trucks, cars, homes, offices, etc.

This adhoc network topology (multihop graph) may change with time as the nodes move or adjust their transmission or reception parameters.

Typical adhoc network is shown below.

Wireless Sensor Networks:Wireless Sensor Networks:

Sensor networks are the newest members of a special class of wireless networks.

A large no. of tiny immobile sensors are planted on the adhoc basis to sense and transmit some physical characteristics of the environment.

An associated BS collects the information reported by the sensors on a data centric basis.

Ex:- Battlefield surveillance of enemy territory/war front by sensors dropped from a low flying aircraft.

Potential commercial uses include machinery prognosis, biosensing and environment monitoring.

Typical wireless sensor network:

WLAN and PAN characteristics and features Type of network

Range of node

Primary function Deployed locations

IEEE IEEE 802.11802.11

30 m30 m Standard for Standard for wireless nodeswireless nodes

Any peer-peer Any peer-peer connectionconnection

Hiper-Hiper-

LANLAN

30 m30 m High speed indoor High speed indoor connectivityconnectivity

Airports, Airports, warehouseswarehouses

Adhoc Adhoc NetworksNetworks

≥ ≥ 500m 500m mobiles, wireless, mobiles, wireless, similar to wired similar to wired connectivityconnectivity

Battlefields, Battlefields, disaster networksdisaster networks

Sensor Sensor NetworksNetworks

2 m2 m Monitor Monitor inaccessible, inaccessible, inhospitable terraininhospitable terrain

Nuclear, Nuclear, chemical plants, chemical plants, oceansoceans

Home RFHome RF 30 m30 m Resource sharing, Resource sharing, device connectionsdevice connections

HomesHomes

BluetoothBluetooth 10 m10 m Avoid wire clutter, Avoid wire clutter, low mobility low mobility provisionprovision

offices, buildingsoffices, buildings

indoorsindoors

HANDOFFHandoff is defined as a process used to allow a call/data transfer to continue uninterrupted as the mobile terminal moves between cells

Hard handoff vs. Soft handoffHard handoff- break before makeSoft handoff – Make before break

Vertical Handoff vs. Horizontal HandoffVertical Handoff- Between Different NetworksHorizontal Handoff- Between Same Networks

Decision to handoff is based on the receivedsignal strength or S/I ratio.

CHANNEL ASSIGNMENTCHANNEL ASSIGNMENT

• Fixed Channel Assignment (FCA) – each cell is assigned a fixed number of channels

– channels used for both handoff and new calls

• Reservation Channels with FCA – each cell reserves some channels for hand off calls

• Channel Borrowing – a cell may borrow free channels from

neighboring cells

• Dynamic Channel Assignment

• Interference Averaging (CDMA)

• Interference Reduction(power adaptation, sectorization)

• Interference Cancellation(smart antennas, multi user detection)

• Interference Avoidance(dynamic resource allocation)

METHODS TO IMPROVESPECTRUM UTILIZATION

PHYSICAL LAYER ISSUES

• Link Performance Measures

• Modulation Tradeoffs

• Flat Fading Countermeasures

• Delay Spread Countermeasures

LINK PERFORMANCE MEASURESPROBABILITY OF BIT ERROR

• The probability of bit error, Pb, in a radio environment is a random variable.

• Typically only one of these measures is useful, depending on the Doppler frequency and the bit rate.

– average Pb, Pb

– Pr [Pb > Pbtarget] outage, Pout=

HOW DO WE OVERCOME THELIMITATIONS IMPOSED BY THE

RADIO CHANNEL?

• Flat Fading Countermeasures – Fade Margin

– Diversity

– Coding and Interleaving

– Adaptive Techniques

• Delay Spread Countermeasures – Equalization

– Multicarrier

– Spread Spectrum

– Antenna Solutions

DIVERSITY

• Independent signal paths have a low probability of experiencing deep fades simultaneously.

• The basic concept is to send the same information over independently fading radio

• Independent fading paths can be achieved by separating the signal in time, frequency, space, polarization, etc.

The chance that two deep fades occur simultaneously is rare.

0

0-20-40-60-80

-1004 8 12 16 dRec

eive

d S

ign

al

Po

wer

(dB

m)

DIVERSITY COMBINING TECHNIQUES

• Selection Combining: picks the branch with the highest SNR.

• Equal-Gain Combining: all branches are coherently combined with equal weights.

• Maximal-Ratio Combining: all branches are coherently combined with weights which depend on the branch SNR.

Combiner Output

1 2 3 M

• • •

THANK THANK YOUYOU