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Chapter 4

Chapter 4. Wireless Communications & Pervasive Technology. Introduction. 1990's -- mobile computing age Mobile "everything" GPS Many companies Wireless LAN "How did we survive before wireless?" Mobile Ubiquitous Computing aka Pervasive Computing. Pervasive Computing.

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Chapter 4

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  1. Chapter 4 Wireless Communications & Pervasive Technology

  2. Introduction • 1990's -- mobile computing age • Mobile "everything" • GPS • Many companies • Wireless LAN • "How did we survive before wireless?" • Mobile Ubiquitous Computing • aka Pervasive Computing

  3. Pervasive Computing • Environment is saturated with hidden computer & communication capabilities • Help us in daily life without major behavior change • "Everything" connected to network • What are some less obvious items? • Wireless is a MUST!! • Building block for smart environments • What was emphasis of Chapter 3?

  4. WLAN Standards • 802.11 currently not adequate for environments • Need • Smaller, cheaper, lighter, lower power • 802.15.4 -- PAN (Personal Area Network) • Currently most promising for short-range, low data rate PAN • WLAN for industrial & home control, inventory management, wireless sensor networks

  5. Ambient Intelligence • Long term vision -- beyond 2010 • "World around us is organized as a pervasive network of intelligent devices that cooperatively gather, process, and transport information." • Avatars, cymans (our synthetic self)

  6. Chapter 4 -- Overview • State of wireless computing • Evolution of wireless computing • Existing & emerging technologies • Standards • What next?

  7. Categories of Area Networks (AN) • Figure 4.1 (pg. 65) • BAN (body) -- 1 meter • PAN (personal) -- 10 meters • LAN (local) -- 500 meters • MAN (metropolitan) -- 7500 meters • WAN (wide) – 1million meters (600 miles)

  8. Smart Space • Well defined, small area • Room, courtyard • Use BAN, PAN, LAN • User environment • MAN & WAN • For public use • Not really for smart environments • Wireless sensor network also not for small areas

  9. Wireless LAN, PAN, BAN • WLAN needs same capabilities as wired LAN • New problem • Security • Mobility • Power consumption • Bandwidth limitations • WLAN is too much PAN • PAN -- less range & power consumption

  10. Wireless LAN, PAN, BAN • BAN -- not always able to carry device • Problems -- bulky • T. G. Zimmerman(footnote 3, pg. 66) • Use skin & transmit data thru handshake

  11. Challenges: Wired to Wireless • No environment boundaries - absolute or easily observable • Channel unprotected – interference • Less reliable • Channel propagation varies by time & has asymmetric properties

  12. Challenges: Wired to Wireless • Transmission resources are limited - scarce & expensive • Weak security: open to all; attacks easier

  13. Carrier Sensing Problems • Some rely on carrier sensing random access protocol (802.11) • Hidden station (terminal) • 2 or more stations cannot detect each others transmissions due to being outside, each others transmission ranges, but transmission ranges are not disjoint

  14. Carrier Sensing Problems • Exposed station (terminal) • Permission transmission from mobile station to another is delayed due to irrelevant transmission activity between 2 other mobile stations within sender's range

  15. Wireless Standards Necessary for development at competitive prices 1980's -- IEEE 802 committees specified connectivity standards for distributed environments • Physical (PHY) and • Medium Access Control (MAC) • For wired & wireless LANs & MANs

  16. Standards - Wireless/Pervasive More recent 802 committee standards 802.11 for WLAN • Support wireless activity in home, office & other pre-specified areas 802.15 for WPAN • Short-range communication among computers, peripherals & (wearable) consumer electronics • Also suitable for WBAN 802.16 FOR Broadband WMAN • Fixed broadband wireless access systems aka last-mile access networks

  17. Chapter 4 -- Focus on Standards 802.11 -- more mature - more discussion 802.15 – less developed 802.16 -- beyond scope Two Approaches to WLAN Infrastructure based Infrastructure less aka peer-to-peer or ad hoc

  18. Infrastructure based Network • Centralized Controller for each cell • Called Access Point (AP) or Base Station • Controls all communications within its transmission range (i.e. Service Area) • All mobile devices communicate thru AP • AP often connected to wired network • Used for WiFi hotspots • Currently most common for mobile devices

  19. Infrastructure based Network • Disadvantage: cost & time to purchase and install infrastructure

  20. Infrastructure-less Network • Sometime infrastructure not possible or cost effective; dynamic environments • Ad hoc or peer-to-peer • A set of stations within range of each other that dynamically configure to set up a temporary network • No AP is required

  21. Infrastructure-less Network • ad hoc or peer-to-peer (cont’d) • Basis for MANET (Mobile Ad hoc Network) • Pure ad hoc - Users devices are the network • Requires high-density of devices • Also used for first-mile problem in hot-spots

  22. 802.11 Standards • WLAN standards; first adopted in 1997 • Extended since 1997 (a, b, c, …) • a, b, g Wireless Fidelity (WiFi) • Other extensions for different bands • Some backwards compatibility • Groups still active • h: European regulations

  23. 802.11i - Wired EquivalentPrivacy (WEP) • Form of encryption to provide same security as a wired network • Support data encryption & integrity • 40-bit secret key • Manually installed; no exchange • WEP has many flaws & weaknesses • 802.11i task group is addressing these issues • Will apply to a, b & g also • Work being based on IETF Extensible Authentication Protocol (EAP)

  24. Architecture - 802.11MAC Layer Basic Service Set (BSS) - infrastructure based • Periodically sends beacon frame (e.g. clock synchronization) used by mobile devices to join network Independent Basic Service Set (IBSS) - ad hoc • Allows two 802.11 stations to communicate without centralized AP • Synchronization to common clock sufficient • Beacon process distributed * BSS off-shelf more common due to IBSS problems

  25. IEEE 802.11 Specifications Layers for WLAN MAC (Medium Access Control) Layer PHY (Physical) Layers -- 3 • All but DSSS PHY layer are abandoned in 802.11 enhanced versions • Direct sequence spread spectrum

  26. 802.11 - DSSS PHY Layer • Operates in 2.4 -- 2.4835 GHz domain • 14 overlapping channels • Each country's regulations specify bands used

  27. 802.11 -- MAC Layer • Provides both contention-based & contention-free access • Protocol DCF – • Distributed Coordination Function • Contention-based CSMA/CA

  28. Contention-based • Station listens (carrier senses) - if idle for appropriate time, starts transmission; otherwise defer & CA is applied • Collision -- 2 stations start transmission • Don't "detect" • If ACK not received, retransmit • "Times" are well-defined & named • Pg. 72-73

  29. Contention-free • PCF (Point Coordination Function) uses DCF (Distributed CF) • Uses polling system with a Point Coordinator (PC) - infrastructure based • Guarantees contention-free frame transmission using beacons • Can have poor QoS (802.11e), due to • Unpredictable delays • Unknown duration of transmission time of each polled station

  30. Power Consumption/Saving • Most wireless nodes use batteries • One of biggest constraints in wireless • Power saving techniques can increase by an order of magnitude *See Table 4.2 - pg. 75

  31. Power Consumption/Saving • Cannot transmit from sleep, must be idle • On = transmit/receive • State changed requires time & energy • Sleep on: 1 ms • Off idle: 100 ms • Sleep mostly - wake-up occasionally & check for transmissions

  32. Power Management Infrastructure WLAN • AP buffers data frames & delivers upon request - efficient • Nodes can sleep for "long" periods of time • AP sends beacons (every 100 ms) • Nodes sleep for several beacon periods • Nodes wake, if traffic is waiting, ask AP for messages

  33. Power Management Infrastructure-less WLAN • Fully distributed process – each manages own • Beacon interval is defined • At interval, nodes wake & contend to transmit synchronization signal • Stay awake for AITM window • Ad hoc traffic indication message • If no message @ end of ATIM, sleep • else, remain awake to send/receive

  34. Power Management Infrastructure-less WLAN (cont) • Power saved depends on intervals, load • Also consider delays, throughput • Few studies so far, but results are moderate & highly variable

  35. 802.11b • Introduces higher speed PHY in the ISM band • Guarantees compatibility with 802.11 cards • Lower transmission rate (more power per symbol) increases transmission distance • 3 components of interest – results vary • Transmission range (TX_range) • Physical carrier sensing range (PCS_range) • Interference range (IF_range)

  36. 802.11a & 802.11g High Speed WLANS • a & g define standards to provide maximum data rate of 54 Mbps • Meets bandwidth needs of 802.11b 802.11e - QoS • Not complete (?) • Will address QoS requirements for various applications • Details pg. 82-84

  37. 802.15 - WBAN & WPAN • Short distances; little or no infrastructure • Standards for wireless networks for portable & mobile devices; • e.g. PC, PDA, peripherals, cell phone, pager, consumer electronics

  38. 802.15 - WBAN & WPAN Ongoing, with 4 Task Groups (TG) • TG1 - WPAN based on Bluetooth • TG2 - guarantee coexistence between 802.11 & 802.15 (ongoing) • TG3 – high-rate WPAN (draft); also imagining & multimedia (ongoing) • TG4 - low data rate, low cost, low power solutions for WPAN (ongoing)

  39. Really Brief Overview of Some Major Points Bluetooth - 802.15.1 • Define low-cost, short-range radio links among mobile PC's, phones & other devices • Based on Piconet: 8 active stations (1 master, 7 slaves) – sync., same channel • Scatternet: connectivity of piconets, a shared slave • Exists when a unit exists in 2+ piconets • Ad hoc network • Uses Encryption

  40. Brief Overview - 802.15.3 • For high-rate WPAN's - applications performing audio & video distribution • Multimedia (home theater, gaming, MP3, photo …) • Also based on piconet • Several levels of security can be defined • Encryption

  41. 802.15.3a • New subgroup because 802.15.3 data rate is not sufficient for many multimedia applications • UWB - Ultrawideband radio – FCC app. • Most promising technology to date • Spreads signal over exceptionally large bandwidth (beyond CDMA) • Low power eliminates it's interference to other devices • New version uses multiple bands; offers many advantages

  42. 802.15.4 - Low-Rate WPAN(LR-WPAN) • Goals • Long battery life (months/years one AAA) • Low cost • Suitable for moderate data throughput & relaxed QoS requirements • Good potential for smart environments • Better than Bluetooth due to power consumption & cost

  43. 802.15.4 - Low-Rate WPAN(LR-WPAN) • Wireless communication among very simple devices • FFD - Full Function Device - requires 1 to control network • RFD - Reduced Function Device - mostly sleep, wake-up occasionally to send/receive messages • Centralized or peer-to-peer

  44. Chapter 4 Summary • Pervasive computing • Wireless solutions • Radio signals on unlicensed band preferred • Many issues • Heterogeneous devices • Distances • Security

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