1

Mobile ApplicationsMobile Applications

David TipperAssociate ProfessorAssociate Professor

Department of Information Science and Telecommunications

University of Pittsburghtipper@tipper@teletele..pittpitt..eduedu

http://www.http://www.teletele..pittpitt..eduedu/tipper.html/tipper.html

Telcom 2730 Fall 02

Course Outline Course Outline

•• Introduction Introduction – Review of mobile communication systems issues,

•• Engineering Economics?Engineering Economics?•• System Planning/Requirements?System Planning/Requirements?•• Case StudiesCase Studies

–– Group presentation of case studies and project milestonesGroup presentation of case studies and project milestones

•• Final Project Presentations and papers Final Project Presentations and papers •• Papers should be conference qualityPapers should be conference quality

Telcom 2730 Fall 02

MobileMobileCommunication SystemsCommunication Systems

• Mobile and Wireless are not interchangeable• Wireless vs. Mobile examples

stationary computer, pay phonecalling card, call forwardingwireless local loop cell phone, laptop with WLAN

• Mobile wireless communication systems focus– Communicate over the air via radio-waves– Support some form of user mobility

• Fundamentally different from wired networks

Telcom 2730 Fall 02

Wireless IssuesWireless Issues•• Wireless link implicationsWireless link implications

– communications channel is the air• poor quality: fading, shadowing, weather, etc.

– regulated by governments• frequency allocated, licensing, etc.

– limited bandwidth• low bit rate, frequency planning and reuse, interference

– power issues• power levels regulated, • mobile terminal battery life

– security issues• wireless channel is a broadcast medium!

2

Telcom 2730 Fall 02

Mobility IssuesMobility Issues• Mobility Types

– User mobility : user can access network while mobile • must handoff calls/connections in progress as user moves• track users as they move so they can receive info/calls

– Service mobility: user’s services follow them• Need to have authentication and services follow user

• Mobile devices –> portable device– Carry own power supply (limited power)– Limited memory and CPU power – Limited user interface

• Degree of Mobility – Geographic range + speed (e.g., cordless vs. car phone)

Telcom 2730 Fall 02

Mobile devices

performanceperformance

Pager• receive only• tiny displays• simple text messages

•two way pagers

Mobile phones• voice, data• simple text displays• simplified WWW

PDA• simple graphical displays• character recognition• simplified WWW

Palmtop• tiny keyboard• simple versions

of standard applications

Laptop• fully functional• standard applications

Sensors,embeddedcontrollers

Telcom 2730 Fall 02

Mobile Wireless SystemsMobile Wireless Systems•• Rapid growth in Rapid growth in somesome mobile systemsmobile systems

– cellular phones– wireless Local Area Networks (WLANs)– wide area data services (SMS, Paging, web access, etc.)– cordless phones and wireless PBXs– GPS and location services

• Some mobile wireless systems have failed.– satellite voice and data systems (Iridium, Globalstar, Teledesic)– LMDS

•• Why some systems so popular?Why some systems so popular?–– Users value: Users value: Mobility,Mobility, PortabilityPortability, , Convenience Convenience –– Focus on Services and Applications Focus on Services and Applications

Telcom 2730 Fall 02

Case Studies and ProjectsCase Studies and Projects•• Case Studies Case Studies

– 2G cellular technology choices– 2.5G RFP for service provider – WLAN vs LAN for Factory, etc.– Cellular data service for corporation

• Possible Projects – GPS based location services for Pitt bus– Power efficient software – algorithm or application– Mobile web site – location aware– Least loaded WLAN AP association– Design a CDMA based WLAN – technology and business case

3

Telcom 2730 Fall 02

•• Mobile phone systemsMobile phone systems– Support communication to mobile users via

wireless radio channel– Fastest growing technical device EVER!

• Nokia sold over 120 million phones last year!

– Variety of systems: • Analog : NMT, AMPS, TACS• Digital: GSM, USDC, IS-95 (cellular CDMA), PDC

– Scope of services and coverage areas growing• Short Message Service SMS, WebPhones, laptop data, etc.• Focus now on wireless data and location aware services

•

Review Review Mobile Phone SystemsMobile Phone Systems

Telcom 2730 Fall 02

• Penetration is defined as the percentage of the population who have a mobile/cellular phone (June, 2000 data)

8%

4%

8%

35%

46%

58%

60%

61%

63%

70%

World Total

China

Brazil

USA

Japan

Italy

Hong Kong

Sweden

Norway

Findland

Top 5

Mobile Phone PopularityMobile Phone Popularity

Telcom 2730 Fall 02

Cellular Network Architecture

• Cellular Systems: • provide wireless coverage to a geographic area with a set of slightly overlapping cells

• Cellular/PCS Network Components• Mobile Station (Terminal) – handset• Base Station (cell site)• Base Station Controller (BSC)• Mobile Switching Center (MSC)• HLR/VLR/AUC – databases to track, bill and authentic users

Telcom 2730 Fall 02

2G Cellular Network Architecture

4

Telcom 2730 Fall 02

• Worldwide market shares (April 2000 data)

Handsets

Nokia

Motorola

Erricsson

Samsung

Alcatel

Panasonic

Others

Mobile Terminal MarketMobile Terminal Market

•Stratification of market•Teenage•Business – low end•Business – high end•Families•Etc..

•Improvements in • microelectronics, • signal processing• display technology

•Smaller devices greater functionality => merger with other portable devices

Telcom 2730 Fall 02

Mobile Terminal MarketMobile Terminal Market

Telcom 2730 Fall 02

Base StationsBase Stations• Base Station (BS)

Provides radio channels between mobile units and network

Pico-cells : (indoor – 0-.5 Km) support 8-20 channels

micro-cells: (outdoor – 0-1 Km), macro-cells: (1-30 Km)

Telcom 2730 Fall 02

Base StationsBase Stations• Base Transceiver Station (BTS) - houses radio units

5

Telcom 2730 Fall 02

Base Station ControllerBase Station Controller

• Base Station Controller (BSC)Manages a cluster of BS, channel assignment, handoff, power control, some switching, etc

Telcom 2730 Fall 02

Mobile Switching CenterMobile Switching Center• Mobile Switching Center (MSC) (MTSO)

– Provides switching functions , coordinates location tracking, call delivery, handoff, interfaces to HLR,VLR, AUC, etc..

– Size of central office switch

Telcom 2730 Fall 02

HLR/VLRHLR/VLR• Home Location Register (HLR)

– Specialized database server contains billing info, service profile and general location of a mobile user

– Visitor Location Register (VLR) similar to HLR contains locationof users and their service profile of all users in a metro type area

Telcom 2730 Fall 02

Second Generation Cellular Second Generation Cellular Systems Systems

•• Motivation for 2G Digital Cellular: Motivation for 2G Digital Cellular: –– Increase System Capacity Increase System Capacity –– Add additional services/features (SMS, caller ID, etc..)Add additional services/features (SMS, caller ID, etc..)–– Reduce CostReduce Cost–– Improve Security Improve Security –– Interoperability among components/systems (GSM only)Interoperability among components/systems (GSM only)

•• Main 2G Systems Main 2G Systems North American TDMA (NANorth American TDMA (NA--TDMA)TDMA)Global System for Mobile (GSM)Global System for Mobile (GSM)

ISIS--95 (cellular CDMA)95 (cellular CDMA)

6

Telcom 2730 Fall 02

Cellular ConceptProposed by Bell Labs 1971 Service areas are divided into smaller “cells”Neighboring cells do not use same set of frequencies to prevent interference

Often approximate coveragearea of a cell by a idealizedhexagon

Increase system capacityby frequency reuse.

Telcom 2730 Fall 02

Cellular Concept• Why not a large radio tower and large service

area?– Number of simultaneous users would be very

limited (to total number of radio channels)– Mobile handset would have greater power

requirement• Cellular concept allows frequency reuse and

lower power handsets• Increases system capacity

Telcom 2730 Fall 02

Cellular Concepts (cont)• Let T = total number of duplex channels

K cells = size of cell cluster (typically 4, 7, or 12)T/K = number of channels per cell

• If clusters are replicated M times, then total number of channels – system capacity = M x T – Choice of K determines distance between co-

channel cells and depends on how much interference can be tolerated by mobile stations

Telcom 2730 Fall 02

Cell Design - Reuse Pattern (cont)• Example: Cell cluster size = 7, frequency

reuse factor = 1/7, assume S = 490 total channels, k = 70 channels per cell

B

A

E

C

D

G

F

B

A

E

C

D

G

F

B

A

E

C

D

G

F

Assume S = 490 total channels,k = 70 channels/cell

Clusters are replicated M=3 times

C = 3x490 = 1470 total channels

7

Telcom 2730 Fall 02

Cell Design - Traffic Engineering

• Required grade of service?– Usually 2% blocking probability during busy hour– Busy hour may be (1) busy hour at busiest cell (2)

system busy hour (3) system average over all hours

• Estimated traffic distribution?– Traffic intensity is measured in erlangs

(mathematician AK Erlang)– One erlang = completely occupied channel, eg, a

radio channel occupied for 30 min. per hour carries 0.5 erlangs

Telcom 2730 Fall 02

Fix Channel Assignment SchemeMarket Study Demographics

AssumeCalls/subs during

Peak one hour withAverage holding time

Number of SubscribersPer cell

Erlangs/cell

Assume GOS(telephone quality

< 5 %)

Apply:Erlang BErlang C

Number of Channels per cells andNumber of channels per system

Telcom 2730 Fall 02

Cell Design - Traffic Engineering (cont)

– Traffic intensity A = average call request rate λ x average holding time H

• Given C = number of channels, and traffic intensity A, probability of blocking is given by Erlang B formula:

Pr(blocking) = AC /C!

Ak / k!k=0

C

∑

Telcom 2730 Fall 02

Cell Design - Traffic Engineering (cont)

– Often consult a table or graph

[Rappaport Fig 2.6] Erlang B blocking probabilities

8

Telcom 2730 Fall 02

Cell Design - Traffic Engineering (cont)

• Not totally accurate but practical– Erlang B formula assumes:

• Calls originate as Poisson process (number of calls in any time interval is random sample from Poisson probability distribution)

• Holding times are random samples from exponential probability distribution

• Blocked calls are cleared (lost without waiting)– Holding times change because of handoffs – Mobility causes changes in estimated traffic

distributions

Telcom 2730 Fall 02

Cellular Concepts (cont)• Due to hexagonal geometry, choices of N

must satisfy N = i2 + ij + j2 where i and j are non-negative integers– To find nearest co-channel neighbor of a cell,

move i cells along any chain of hexagons, turn 60 degrees counterclockwise, and move j cells (example: i=3, j=2, N=19)

[Rappaport Fig 2.2]Locating co-channel cells

Telcom 2730 Fall 02

Frequency Reuse

A

B

B

A

B

A

B

AA

B

A

B

A

B

K = 19

Telcom 2730 Fall 02

Frequency ReuseSITE A SITE B

RSSI, dBm

C/I

Distance

R dINTERFdINTERF

D = R + dINTERF

-60

-90

-120

9

Telcom 2730 Fall 02

Cluster Size

132

43 1

42

12

34

1

31

42

6 75

1

1

11

1

1K = 4

K = 72

98

6

71

3

1011

124

5

65

8

6

7

98

124

5

3

1011

124

910

11 K = 12

Telcom 2730 Fall 02

Sectoring

43

52

1

67

55

5

55

5

12

32

1

3

120 sectoring

Telcom 2730 Fall 02

Multiple Access

• Common techniques:– FDMA (frequency division multiple access :

separate signals into non-overlapping frequency bands

– TDMA (time division multiple access): use non-overlapping time slots in round robin

– CDMA (code division multiple access): use signals with little cross-correlation

• Each signal can be extracted by correlators

Telcom 2730 Fall 02

Multiple Access (cont)

time

freq

uenc

y

user 1

user 2

user 3

guard band

guard band

FDMA

time

freq

uenc

y

user

1gu

ard

time

TDMA

time

freq

uenc

y

3

2

CDMA

user

2

user

3gu

ard

time

1

31,2,3

10

Telcom 2730 Fall 02

Cell Planning RevisitedCell Planning Revisited•• Link BudgetLink Budget

– Used to plan useful radio coverage of cells• Relates transmit power, path losses, margins,

interference, etc. • Used to find max allowable path loss ib each link• frequency allocated, licensing, etc.

– Typical Factors in Link Budget• Transmit Power, • Antenna Gain, Diversity Gain, • Receiver Sensitivity• Shadow Margin, Interference Margin, Vehicle

Penetration, Body Loss, Building Penetration, etc..– Gains are added, Losses are subtracted

Telcom 2730 Fall 02

Link BudgetLink Up Down

TX Power 30dbm 30dbm

Antenna Gain 3 5

Antenna Diversity Gain 5 X

Shadow Margin 10 10

Body Anttenuation 2 2

Vehicle Penetration 5 5

Receiver Sensitivity -105 -90

Path Loss Budget 126 db 108 db

Typical Cellular System Downlink Limited!

Telcom 2730 Fall 02

3G Driving Factors3G Driving Factors• Forecast 1 billion wireless subscribers by 2004,

– more than number of wired access lines!

•• Predicted explosion in Predicted explosion in wireless Internet serviceswireless Internet services– more users than the wired Internet 2002 –2004– high-speed data/multimedia services from

anywhere/any time – mobile INTERNET– email, web, m-commerce, location aware service, etc.– data revenue > voice revenue in parts of Europe

• Converge different regional/national 2G systems

Telcom 2730 Fall 02

Wireless Web Access

Source: IEEE Communications Magazine, Dec 2000, pp.136

11

Telcom 2730 Fall 02

Data ARPU Forecast

$10$14 $17

0

5

10

15

20

$ pe

r mon

th

1999 2004 2010

ARPU (per Data User) in W. Europe ARPU trendimpacted by:-

- downward pressure due to changing user mix (more consumers)

- increase due to availability of new applications

55% datapenetration

75% datapenetration

Telcom 2730 Fall 02

Evolutionary Pathsfor 3G systems

Circuit Sw. Data (28k)

Improved VoiceGPRS based

43.2 kbps

IMT-2000384 k EDGE

Telcom 2730 Fall 02

2.5 G Systems• 2G Systems provide slow speed data service

– 9.6 Kbps – 14.4 Kbps• 2.5G

– Attempt to improve data services from 2G and build customer base for wireless data service

– GPRS, HSCSD, cdma 2000 1x– Mislabeled as 3G– Basically overlay network of data service on 2G

networks– Max data rate 57 Kbps – 150 Kbps– Typical data rates 33-56 Kbps – similar to dialup

modem service

Telcom 2730 Fall 02

Current status of 3G• Two partnership projects to harmonize and

standardize ETSI, ARIB, ANSI etc.– 3GPP that deals with European WCDMA proposal

• Chip rates of 3.84 Mcps• FDD and TDD mode

– 3GPP2 that deals with the US cdma2000 proposal• Multicarrier CDMA• Chip rates of 3.686 Mcps

– Deployments occuring ??• Service providers strapped for cash• Almost all carriers going with 2.5 G first

12

Telcom 2730 Fall 02

Trends• 2.5G

– More data services and usage than ever before– GPRS, HSCSD, EDGE, cdma 2000 1x

• High speed WLANs– 802.11

• 3G– (UMTS) WCDMA, CDMA 2000 1xEV-DV– IP in the backbone, All IP?– Higher data rates

• B3G/4G– Hybrid wireless data networks, cellular +WLAN

Telcom 2730 Fall 02

B3G Hybrid Network

Laptops

Handheld PCs Switch & mobility and

radio resource management

Public Switched Telephone or Public

Data Network

Base Station

Multimedia terminal

WLAN

Switch

Access Point

Horizontal or Intra-tech Handoff

Vertical or Inter-tech Handoff Router

LAN Segment

Cell

LEGEND

Telcom 2730 Fall 02

Wireless LANsWireless LANs

•• Wireless Local Area Networks Wireless Local Area Networks – Support communication to mobile data users via

wireless channel– IEEE 802.11 a, b standard (wireless Ethernet)

• 1Mbps, 2Mbps, 11Mbps, 54 Mbps rates• Infrastructure based and Ad-Hoc based networks

• Wireless LAN market– Medical– Education– Manufacturing– Retail– Public Access (Hotels, airports, Starbucks)

Telcom 2730 Fall 02

Infrastructure based Architecture

Access Point (AP)

Basic Service Area (BSA)a.k.a cell

Basic Service Set (BSS)Members of the cell covered by one AP

Ad hoc

IBSS

13

Telcom 2730 Fall 02

Infrastructure-based Architecture

AP1

Extended Service Area (ESA): Disjoint or connected

Extended Service Set (ESS)

AP2AP3

Distribution System

Portal

Telcom 2730 Fall 02

Ad-hoc networks

Ad-hoc networks: IEEE 802.11, Bluetooth, HiperLAN

No fixed infrastructure: tradeshow, conference center, meeting

7.4.1