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Mobile Computing. Assistant Professor: Jenhui Chen Office number: 5990 Homepage: http://www.csie.cgu.edu.tw/jhchen. Textbooks and References. W. Stallings, Wireless Communications & Networks, Prentice Hall, August 2001.

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Mobile computing l.jpg

Mobile Computing

Assistant Professor: Jenhui Chen

Office number: 5990

Homepage: http://www.csie.cgu.edu.tw/jhchen

Dr. Jenhui Chen


Textbooks and references l.jpg
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

Dr. Jenhui Chen


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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%)

Dr. Jenhui Chen


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Selected Papers

  • 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

Dr. Jenhui Chen


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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)

Dr. Jenhui Chen


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Chapter 1

Introduction:

Why and who will be mobile?

Dr. Jenhui Chen


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Telecom Networks/Systems

  • 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

Dr. Jenhui Chen


Telecom statistics l.jpg

(1) Telephone (M)

(2) Mobile phone (K)

(3) Radio paging (K)

(4) Internet (K)

12.04

(4.7%)

11,541

(144.0%)

3,873

(-9.1%)

2,874

(72.6%)

9.17

(7.9%)

770

(31.8%)

2,083

(20.5%)

21

10.01

(9.2%)

970

(26.0%)

2,301

(10.5%)

165

(686.0%)

10.86

(8.5%)

1,492

(53.8%)

2,641

(14.8%)

429

(160%)

11.50

(5.9%)

4,727

(217.0%)

4,261

(61.3%)

1,665

(288%)

12.64

(5.0%)

17,743

(53.7%)

2,867

(-26.0%)

4,650

(61.8%)

Telecom Statistics

1995 1996 1997 1998 1999 2000

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%)

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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Mobile Computing Chart

Verticals

Horizontals

Applications

Operating systems

Mobile operation systems

Notebooks

Phones

Others

Devices

PDAs

WANs

LANs

Wireless networks

Dr. Jenhui Chen


Application layer l.jpg
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

Dr. Jenhui Chen


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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

Dr. Jenhui Chen


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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

Dr. Jenhui Chen


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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

Dr. Jenhui Chen



Field sales application l.jpg
Field Sales Application

  • Sales quotation

  • Inventory check

  • Order entry

  • Credit authorization

  • Invoicing

Dr. Jenhui Chen


Field service application l.jpg
Field Service Application

  • 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

Dr. Jenhui Chen


Transportation application l.jpg
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

Dr. Jenhui Chen


Personal communications application l.jpg
Personal Communications Application

  • Messaging

  • Calendaring

  • Directories

  • Info Systems

  • Fax

Dr. Jenhui Chen


Mobile office application l.jpg
Mobile Office Application

  • Fax

  • E-mail

  • LAN access

  • File transfer

  • Database access

Dr. Jenhui Chen


Vertical market examples l.jpg

Airlines

Police

Field sales

Emergency

Hospitals

Maintenance

Retail stores

Stock exchanges

Casinos

Hotel

Taxicabs

Rental car agencies

Transportation

Vertical Market Examples

Dr. Jenhui Chen


Challenges l.jpg

Security

User authentication

Data privacy

Privacy of user location

Bandwidth

Limited bandwidth (10K~10M)

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

Challenges

Dr. Jenhui Chen



Horizontal application examples l.jpg
Horizontal Application Examples

  • 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

Dr. Jenhui Chen


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Positioning of Wireless Networking

  • Comparison between wireless data & wired data capacities

  • Position of wireless networks relative to wired networks:

    • Not a replacement but an extension to wired networks

Dr. Jenhui Chen


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CDPD:Cellular Digital Packet Data

Daniel Grobe Sachs

Quji Guo

Dr. Jenhui Chen


What is cdpd l.jpg
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!

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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CDPD Market

  • 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)

Dr. Jenhui Chen


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Omnisky Coverage Map

Dr. Jenhui Chen

Source: Omnisky (http://www.omnisky.com)


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CDPD Infrastructure

Dr. Jenhui Chen

Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”


Cdpd layering l.jpg

Application

Transport

Network

Data link

Physical

CDPD - Layering

IP/CLNP

Connectionless Network Protocol

Subnetwork Dependant Convergence Protocol

Mobile Data Link Protocol

Media Access Control

Physical

SNDCP

MDLP

MAC

Physical

Network layer CDPD Layer

Dr. Jenhui Chen


Cdpd physical layer l.jpg
CDPD Physical Layer

  • 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 and decoder complexity.

  • 19.2kbps per channel.

IP/CLNP

SNDCP

MDLP

MAC

Dr. Jenhui Chen

Physical


Amps and cdpd l.jpg
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.

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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Channel Scanning

  • 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.

Dr. Jenhui Chen


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Handoff in CDPD

  • 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.

Dr. Jenhui Chen


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CDPD effects on AMPS

  • 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..

Dr. Jenhui Chen


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Data Transmission Format

  • 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

    • Shared multiple access for mobiles.

    • Reverse link activity indicated by BS.

IP/CLNP

SNDCP

MDLP

MAC

Dr. Jenhui Chen

Physical


Forward link structure l.jpg
Forward Link Structure

Dr. Jenhui Chen

Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”


Reverse link structure l.jpg
Reverse Link Structure

Dr. Jenhui Chen

Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”


Reverse link mac l.jpg
Reverse Link MAC

  • 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

Dr. Jenhui Chen

Physical


Reverse link mac45 l.jpg
Reverse Link MAC

Dr. Jenhui Chen

Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”


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Reverse Link MAC

  • 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.

Dr. Jenhui Chen


Mobile data link protocol l.jpg
Mobile Data Link Protocol

IP/CLNP

SNDCP

MDLP

MAC

Dr. Jenhui Chen

Physical

Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”


Cdpd mdlp l.jpg
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.

Dr. Jenhui Chen


Cdpd mdlp49 l.jpg
CDPD - MDLP

  • 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.

Dr. Jenhui Chen


Cdpd sndcp l.jpg
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?

      • Where and how to compress data?

IP/CLNP

SNDCP

MDLP

MAC

Dr. Jenhui Chen

Physical


Cdpd sndcp51 l.jpg
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.

Dr. Jenhui Chen


Cdpd sndcp52 l.jpg
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

Dr. Jenhui Chen


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CDPD - Registration

  • 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

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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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.

Dr. Jenhui Chen


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References

  • 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

Dr. Jenhui Chen


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