1. Mobile Computing Assistant Professor: Jenhui Chen Office number: 5990
Homepage:
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Dr. Jenhui Chen

2. 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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3. Grading Midterm Report Oral presentation- over 15 pages (30%)
Final Project
Report 10 pages (40%)
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4. 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
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5. 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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Dr. Jenhui Chen

6. Introduction: Why and who will be mobile?
Chapter 1
Introduction:
Why and who will be mobile?
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Dr. Jenhui Chen

7. 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
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Dr. Jenhui Chen

8. Telecom Statistics 1995 1996 1997 1998 1999 2000 (1) Telephone (M)
(1) Telephone (M)
(2) Mobile phone (K)
(3) Radio paging (K)
(4) Internet (K)
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%)
12.04
(4.7%)
11,541
(144.0%)
3,873
(-9.1%)
2,874
(72.6%)
12.64
(5.0%)
17,743
(53.7%)
2,867
(-26.0%)
4,650
(61.8%)
Note: According to Jan 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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9. 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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10. 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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11. Mobile Computing Chart
Verticals
Horizontals
Applications
Operating systems
Mobile operation systems
Devices
Notebooks
PDAs
Phones
Others
WANs
LANs
Wireless networks
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12. 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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13. 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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Dr. Jenhui Chen

14. 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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15. 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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16. Applications Market by 2005
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17. Field Sales Application
Sales quotation
Inventory check
Order entry
Credit authorization
Invoicing
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18. 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
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19. 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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20. Personal Communications Application
Messaging
Calendaring
Directories
Info Systems
Fax
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21. Mobile Office Application
Fax
LAN access
File transfer
Database access
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22. Vertical Market Examples
Airlines
Police
Field sales
Emergency
Hospitals
Maintenance
Retail stores
Stock exchanges
Casinos
Hotel
Taxicabs
Rental car agencies
Transportation
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23. Challenges 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
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24. Application/Technology Matrix
Sector
Application
Technology
Cellular
Paging
Mobile Data
WLANs
Private
(corporate)
Service engineering ** *
Order entry
Vehicle routing
***
Incident control
Public
Network
Services
Facsimile
Text messaging
Info services
News
Market
Financial
Location tracking
Traffic alerts
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25. 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
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26. Positioning of Wireless Networking
Wireless Data
Today
Future
Mobile Data
10 Kbps
100 Kbps
Wireless LANs
1 Mbps
10 Mbps
Wired Data
Today
Future
100 Kbps
>1 Mbps
Wired LANs
10 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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27. CDPD: Cellular Digital Packet Data
Daniel Grobe Sachs
Quji Guo
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Dr. Jenhui Chen

28. 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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29. Design Goals Goals: Low speed, high latency data service
Primarily intended for paging and .
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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Dr. Jenhui Chen

30. 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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31. 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)
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32. Omnisky Coverage Map Source: Omnisky (http://www.omnisky.com)
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Source: Omnisky (

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

34. CDPD - Layering Application Transport Network Data link Physical
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
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Dr. Jenhui Chen

35. 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
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Physical

36. 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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Dr. Jenhui Chen

37. 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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38. 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.
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Dr. Jenhui Chen

39. 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.
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Dr. Jenhui Chen

40. 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..
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Dr. Jenhui Chen

41. 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
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Dr. Jenhui Chen
Physical

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

43. Reverse Link Structure
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Dr. Jenhui Chen
Source: A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach”

44. 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
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Dr. Jenhui Chen
Physical

45. Reverse Link MAC
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Dr. Jenhui Chen
Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”

46. 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.
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Dr. Jenhui Chen

47. Mobile Data Link Protocol
IP/CLNP
SNDCP
MDLP
MAC
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Dr. Jenhui Chen
Source: J. Agostsa et al., “CDPD: Cellular Data Packet Standards and Technoloy”
Physical

48. 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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Dr. Jenhui Chen

49. 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.
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Dr. Jenhui Chen

50. 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
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Dr. Jenhui Chen
Physical

51. 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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Dr. Jenhui Chen

52. 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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Dr. Jenhui Chen

53. 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
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Dr. Jenhui Chen

54. 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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Dr. Jenhui Chen

55. 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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56. 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
D. Saha and S. Kay, “Cellular Digital Packet Data Network,” IEEE Transactions on Vehicular Technology, August 1997, pp
A. Salkintzis, “Packet Data over Cellular Networks: The CDPD Approach,” IEEE Communication Magazine, June 1999, pp
A. Salkintzis, “Radio Resource Management in Cellular Digital Packet Data Networks,” IEEE Personal Communications, December 1999, pp
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