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Mobile Computing

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

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  1. Mobile Computing Assistant Professor: Jenhui Chen Office number: 5990 Homepage: http://www.csie.cgu.edu.tw/jhchen 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 Dr. Jenhui Chen

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

  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 Dr. Jenhui Chen

  5. 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

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

  8. (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

  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. Dr. Jenhui Chen

  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. Dr. Jenhui Chen

  11. Mobile Computing Chart Verticals Horizontals Applications Operating systems Mobile operation systems Notebooks Phones Others Devices PDAs WANs LANs Wireless networks Dr. Jenhui Chen

  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 Dr. Jenhui Chen

  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 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 Dr. Jenhui Chen

  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 Dr. Jenhui Chen

  16. Applications Market by 2005 Dr. Jenhui Chen

  17. Field Sales Application • Sales quotation • Inventory check • Order entry • Credit authorization • Invoicing Dr. Jenhui Chen

  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 Dr. Jenhui Chen

  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 Dr. Jenhui Chen

  20. Personal Communications Application • Messaging • Calendaring • Directories • Info Systems • Fax Dr. Jenhui Chen

  21. Mobile Office Application • Fax • E-mail • LAN access • File transfer • Database access Dr. Jenhui Chen

  22. Airlines Police Field sales Emergency Hospitals Maintenance Retail stores Stock exchanges Casinos Hotel Taxicabs Rental car agencies Transportation Vertical Market Examples Dr. Jenhui Chen

  23. 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

  24. Application/Technology Matrix Dr. Jenhui Chen

  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 Dr. Jenhui Chen

  26. 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

  27. CDPD:Cellular Digital Packet Data Daniel Grobe Sachs Quji Guo 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! Dr. Jenhui Chen

  29. 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

  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. Dr. Jenhui Chen

  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) Dr. Jenhui Chen

  32. Omnisky Coverage Map Dr. Jenhui Chen Source: Omnisky (http://www.omnisky.com)

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

  34. 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

  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 Dr. Jenhui Chen 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. 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. Dr. Jenhui Chen

  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. 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. 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.. 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 Dr. Jenhui Chen Physical

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

  43. Reverse Link Structure 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 Dr. Jenhui Chen Physical

  45. Reverse Link MAC 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. Dr. Jenhui Chen

  47. 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”

  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. 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. 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 Dr. Jenhui Chen Physical

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