Transcript PowerPoint 簡報

Mobile Computing
Assistant Professor: Jenhui Chen
Office number: 5990
Homepage: http://www.csie.cgu.edu.tw/jhchen
2015/7/17
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Textbooks and References
W. Stallings, Wireless Communications &
Networks, Prentice Hall, August 2001.
 D.J. Goodman, Wireless Personal
Communications Systems, Addison-Wesley,
1997.
 Selected journal articles and conference papers
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Grading
Midterm Report
 Oral presentation- over 15 pages (30%)
 Final Project
 Oral presentation- over 15 pages (30%)
 Report 10 pages (40%)
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Selected Papers
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Journals:
 IEEE Transactions on Mobile Computing
 IEEE Journal on Selected Areas in Communications
 IEEE Transactions on Vehicular Technology
 ACM Computing Surveys
Magazine
 IEEE Pervasive Computing
 IEEE Wireless (Personal) Communications
 IEEE Communications
 Communications of the ACM
Conferences:
 IEEE INFOCOM, IEEE GLOBECOM, IEEE ICC
 ACM SIGCOM, ACM MOBICOM
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Related Topics
Sensor Networks
 Pervasive Computing (Wireless LAN)
 Internet Computing
 Personal Communication System
 UMTS (Universal Mobile Telecommunications
System)
 GPRS (General Packet Radio Service)
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Chapter 1
Introduction:
Why and who will be mobile?
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Telecom Networks/Systems
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Wired Networks (Internet)
 Local Area Networks (LANs)
 Public Data Networks, i.e., WANs
Wireless Networks
 Wireless LANs
 Mobile Data Networks
Fixed Telephone Networks, i.e., Public Switched
Telephone Networks (PSTNs)
Mobile Phone Systems
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Telecom Statistics
1995
1996
1997
1998
1999
2000
(1) Telephone (M)
9.17
(7.9%)
10.01
(9.2%)
10.86
(8.5%)
11.50
(5.9%)
12.04
(4.7%)
12.64
(5.0%)
(2) Mobile phone (K)
770
970
(31.8%) (26.0%)
11,541 17,743
1,492
4,727
(53.8%) (217.0%) (144.0%) (53.7%)
(3) Radio paging (K)
2,083
2,301
(20.5%) (10.5%)
2,641
4,261
(14.8%) (61.3%)
(4) Internet (K)
21
165
429
1,665
(686.0%) (160%) (288%)
3,873
2,867
(-9.1%) (-26.0%)
2,874
(72.6%)
4,650
(61.8%)
Note: According to Jan. 2001 statistics, total mobile phone subscribers are
18.3M in which CHT: 4.7M(25.7%), and others: 13.61M(74.3%)
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Some Forecasts

In 3 years, Internet traffic will grow to 10,000
times its current level.

Global e-business revenue will grow 86% per
year to $ 1.4 Trillion in 2003.

Bandwidth consumption will grow by a factor of
100 to 200 over the next four years.
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What is Mobile Computing?
Mobile Computing is also known as “Ubiquitous
Computing” (anywhere, anytime and any device)
 The scope covered by Mobile Computing
roughly includes: Mobile Data, Wireless LANs
and Ad Hoc Networks, etc.

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Mobile Computing Chart
Applications
Operating systems
Devices
Wireless networks
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Verticals
Horizontals
Mobile operation systems
Notebooks
PDAs
WANs
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Phones
Others
LANs
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Application Layer
Vertical applications: those apply to a function
part of an industry such as field sales and field
service, or to specific market segment such as
banking or health care
 Horizontal applications: apply to many people
across most market segments
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Operation Systems Layer
This layer provides tools for application
programmers to access different mobile devices
and different wireless networks
 A key layer to rapid growth of wireless
networking and proliferation of applications
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Device Layer
All the mobile devices we carry with us:
 Notebooks (NBs)
 Personal Digital Assistants (PDAs)
 Cellular phones
 Personal communicators
 Combination devices
 Combination devices are now rapidly emerging
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Wireless Networks Layer


The Wireless Wide Area Network (WAN) is also called
“Mobile Data” including:
 Packet networks: RAM/Mobitex, ARDIS/Modacom
 Paging networks
 Data over cellular: CDPD (over AMPS), GPRS (over
GSM)
 Data over satellite
Wireless LANs: with much higher rate but smaller
coverage than Mobile Data networks
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Applications Market by 2005
16%
Transportation
8%
45%
5%
Field service
Field sales
Personal communications
Mobile office
26%
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Field Sales Application
Sales quotation
 Inventory check
 Order entry
 Credit authorization
 Invoicing
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Field Service Application
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Obtaining a maintenance history of the item requiring
service
Performing complex diagnostics that require access to
databases and applications at other locations
Checking parts inventory if required
Updating the maintenance database after the service is
done
Invoicing for the job
Real-time dispatching of the field engineer
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Transportation Application
The oldest application
 Including:
 Automatically locating the vehicle
 Dispatching the vehicle to the next job
 Routing the vehicle if required
 Capturing data from the vehicle
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Personal Communications Application
Messaging
 Calendaring
 Directories
 Info Systems
 Fax
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Mobile Office Application
Fax
 E-mail
 LAN access
 File transfer
 Database access
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Vertical Market Examples
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Airlines
Police
Field sales
Emergency
Hospitals
Maintenance
Retail stores
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Stock exchanges
Casinos
Hotel
Taxicabs
Rental car agencies
Transportation
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Challenges
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Security
 User authentication
 Data privacy
 Privacy of user
location
Bandwidth
 Limited bandwidth
(10K~10M)
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Software
 Still in its infancy
 The main/ biggest reason
for late data
implementations
Safety
 Radiation is harmful to
human beings
 Trends: low power, thus
less radiation
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Application/Technology Matrix
Sector
Private
(corporate)
Public
Network
Services
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Technology
Application
Cellular
Paging
Mobile Data
WLANs
Service engineering
**
*
**
*
Order entry
**
0
**
*
Vehicle routing
**
0
**
***
Incident control
**
0
**
***
Facsimile
***
0
*
0
Text messaging
**
***
***
***
News
*
**
*
0
Market
*
**
*
0
Financial
*
**
*
0
Location tracking
*
0
0
0
Traffic alerts
*
***
**
0
Info services
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Horizontal Application Examples

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Near term horizontal applications (LAN app.)
 Dynamic work environment
 Trade show
 conference
 Difficult to wire areas
 New employees who need immediate service
Broad-based horizontal applications (WAN app.)
 Wireless meeting
 Wireless traveler
 Interactive TV
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Positioning of Wireless Networking
Wireless
Data
Mobile
Data
Wireless
LANs
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Today Future
10
Kbps
1
Mbps
100
Kbps
10
Mbps
Wired
Data
Wired
Data
Wired
LANs
Today Future
100
Kbps
10
Mbps
>1
Mbps
>100
Mbps
Comparison between wireless data & wired data capacities
Position of wireless networks relative to wired networks:
 Not a replacement but an extension to wired networks
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CDPD:
Cellular Digital Packet Data
Daniel Grobe Sachs
Quji Guo
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What is CDPD?

Motivation: Packet data over AMPS
 AMPS is unsuited for packet data
 Long call setup times
 Modem handshaking required
 Analog providers have AMPS allocation.
 Use AMPS channels to provide data service.
 “Cellular digital packet data”
 Can’t interfere with existing analog service.
 CDPD is cheap: no new spectrum license needed!
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Design Goals

Goals:
 Low speed, high latency data service
 Primarily intended for paging and email.
 Provide broadcast and multiple-access service.
 Dynamically shared media, always online.
 Share channels with AMPS allocation
 Transparency to existing AMPS service.
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CDPD History
Standard released Jan, 1995 (v1.1)
 Initially used by police (~1996)
 Wide service availability around 2000
 Omnisky, Verizon Wireless, others.
 Covers most US population centers
 Champaign-Urbana now covered.
 Rural area coverage poor.
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CDPD Market

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CDPD is used primarily for
 Law enforcement
 Handheld/laptop IP access
 Main competition: “Wireless Web” phones.
CDPD costs:
 Wireless modems: ~$300 (Omnisky Palm V)
 Service: $30-$40 per month (handheld)

$40-$80 per month (laptop)
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Omnisky Coverage Map
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Source: Omnisky (http://www.omnisky.com)
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CDPD Infrastructure
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Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”
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CDPD - Layering
Application
Transport
Network
Data link
Physical
Network layer
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IP/CLNP Connectionless Network Protocol
SNDCP Subnetwork Dependant Convergence Protocol
MDLP
Mobile Data Link Protocol
MAC
Media Access Control
Physical Physical
CDPD Layer
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CDPD Physical Layer
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30KHz BW channels, shared with AMPS
Separate forward and reverse channels
 Forward channel is continuous
 Reverse channel is multiple access.
Gaussian Minimum-Shift Keying-GMSK
 GMSK compromises between channel bandwidth
IP/CLNP
and decoder complexity.
SNDCP
19.2kbps per channel.
MDLP
MAC
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Physical
AMPS and CDPD
CDPD runs alongside AMPS
 AMPS system is unaware of CDPD system
 CDPD system watches AMPS behavior
 AMPS generally has unused channels.
 Blocked calls when all channels are allocated.
 1% block probability => all channels used
only 1% of the time.
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CDPD Channel Usage
CDPD uses unused AMPS channels.
 Usually are several available.
 Each 30KHz channel = 19.2kbps up and down
 CDPD channel hopping.
 Forced: AMPS must be vacated within 40ms
of allocation for voice use.
 Planned: Regular hops prevent AMPS system
from identifying channel as unusable.
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Channel Scanning
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1. Check signal levels from nearby cells.
 Use a list of reference channels distributed by the
CDPD infrastructure to find levels.
2. Select cell with best signal.
 If non-critical and no cell is significantly better than
current, no handoff is done (hysteresis)
3. Scan RF channels in cell for CDPD.
 Stop when an acceptable channel is found.
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Handoff in CDPD
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Critical handoffs: Must choose new channel
 High error rate is observed or BS signal lost.
 Received signal strength below a threshold.
 Base station does not receive data from mobile.
Noncritical handoffs
 Channel rescan interval expires.
 Signal strength changes significantly.
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CDPD effects on AMPS

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CDPD logically transparent to AMPS
Can reduce AMPS service quality
 More channel usage => increased interference.
 If AMPS system is close to SIR margin, CDPD can
push it below.
 Full CDPD usage can push SIR down ~2dB
 19 channels/cell, Pblock = 0.02, 12.3 Erlangs
 Limiting channels used reduces SIR cost..
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Data Transmission Format
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All links are base to mobile.
 Mobile to mobile goes through base station.
 Full-duplex; separate forward and reverse links.
Forward link
 Continuous transmission by BS
Reverse link
IP/CLNP
 Shared multiple access for mobiles.
SNDCP
MDLP
 Reverse link activity indicated by BS.
MAC
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Physical
Forward Link Structure
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Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”
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Reverse Link Structure
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Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”
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Reverse Link MAC
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Near/Far problem
 Mobile may not detect a faraway transmitter.
 Base station must report busy status.
Protocol:
 Digital Sense Multiple Access
 Nonpersistant: Checks once for busy state.
 Slotted: Can only start when BS reports state.
Similar to Ethernet MAC.
IP/CLNP
SNDCP
MDLP
MAC
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Physical
Reverse Link MAC
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Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”
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Reverse Link MAC

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Reverse link idle => can transmit.
 Busy status checked before transmission starts..
 Continue burst unless error is indicated.
 If BS indicates error, assume collision; exponential
backoff is used.
Reverse link busy:
 Delay for a random number of slots.
 Check busy status again.
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Mobile Data Link Protocol
IP/CLNP
SNDCP
MDLP
MAC
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Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”
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Physical
CDPD - MDLP

Mobile Data Link Layer Protocol (MDLP)
 High-level data link control (HDLC)
 Similar to ISDN HDLC.
 Mobile (M-ES) to Infrastructure (MD-IS)
 In this layer, air link and BS become transparent
 Connection oriented
 MDLP Frame (message structure)
 Address, control field, information field
 No checksum; MAC discards incorrect packets.
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CDPD - MDLP
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Temporary equipment identifier (TEI)
 Identifies destination mobile - virtual address.
 Assigned by infrastructure.
Packet types
 Unacknowledged information
 Sequenced information
 Sequence number, ack, timeout
 Sliding window
 Selective rejection supported.
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CDPD - SNDCP

Subnetwork-Dependent Convergence Protocol (SNDCP)
 Between IP or CLNP and MDLP
 In both mobile and infrastructure (MD-IS)
 Segmentation, compression, encryption
 Questions:
 Where and how to segment data?
IP/CLNP
 Where and how to compress data?
SNDCP
MDLP
MAC
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Physical
CDPD - SNDCP
Segmentation
 Goal: to fit the size of underlying frames
 Two type of headers
 Sequenced headers:
• For compressed, encrypted, and segmented
user data.
 Unnumbered headers: Control information.
 Efficiency consideration (similar to X.25)
 Which layer should segment/assemble messages?
 Use “More” indicator to avoid IP fragmentation.
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
CDPD - SNDCP

Compression
 Header compression
 To send the “Delta” information
 Data compression
 V.42bis – a dictionary-based compression
 Which layer should compress data?
 Source-dependent compression – higher layer
 Source-independent compression – lower layer
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CDPD - Registration
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Low-level protocols ignore authentication.
Registration and Authentication
 M-ES, serving MD-IS, home MD-IS
 Base station (MDBS) has no network function.
 Network Equipment identifier (IP, etc.)
 Forwarding database in home MD-IS
Deregistration
 Table maintenance timer
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Problems with CDPD
Limited bandwidth
 19.2kbps shared per channel
 Modern applications demand more bandwidth.
 Security:
 “Man in the middle” identity theft attack
 IP network attacks
 Denial of Service attacks easy.
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Potential Improvements
Multichannel / multicarrier transmission
 Would allow faster rates with AMPS
compatibility.
 Security Improvements
 Secure against “man-in-the-middle” attacks.
 Switch to CDMA/GSM.
 Digital cellular services are more able to
accommodate data services.

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References
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J. Agosta and T. Russell, CDPD: Cellular Packet Data Standards and
Technology, McGraw Hill, 1996.
Y. Frankel et al., “Security Issues in a CDPD Wireless Network,” IEEE
Personal Communications, August 1995, pp. 16-26.
D. Saha and S. Kay, “Cellular Digital Packet Data Network,” IEEE
Transactions on Vehicular Technology, August 1997, pp. 697-706.
A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach,”
IEEE Communication Magazine, June 1999, pp. 152-159.
A. Salkintzis, “Radio Resource Management in Cellular Digital Packet Data
Networks,” IEEE Personal Communications, December 1999, pp. 28-36
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