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Mobile ApplicationsMobile Applications
David TipperAssociate ProfessorAssociate Professor
Department of Information Science and Telecommunications
University of Pittsburghtipper@[email protected]
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!
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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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
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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
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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