Wireless Technologies and WSA Overview Kevin Gifford, John Saiz April 13, 2005
Presentation Outline ! Wireless Technologies Overview ! WSA Overview
Wireless Technologies Overview ! Advantages of wireless networks ! Applicable wireless standards ! Wireless device classes/capabilities ! RF multipath and RF coexistence ! RF vs. Optical wireless systems
Wireless System Architecture (WSA) ! Goal ! High-level support for end-users ! Overview/Review/Progress in Phase I ! Future Work (Phase II) ! Summary
Topological considerations Habitat 1 Wired HAB network Primary Habitat 1 5 APP APP 2 4 3 NAG HAB Habitat 2 1 5 2 4 3 Wired HAB network 1 5 2 4 3
Advantages of wireless networks ! Flexibility: ! Communicate without restriction (outside of s/c as well) ! RF radio waves can penetrate walls ! Untethered mobility for users and devices ! Eliminate the need to run cabling ! Mass and volume reduction ! Harness complexity reduction/elimination ! Retro-fit existing infrastructure ! Ad-hoc networking ! Small form factor ! Robustness
Disadvantages of wireless networks ! Quality/reliability of service ! Cost ! Proprietary solutions, heterogenous devices (WSA to the rescue…) ! Transmission restrictions ! Security (more later)
Applicable wireless standards ! IEEE 802.11 (WiFi) ! IEEE 802.15.1 (Bluetooth) ! IEEE 802.15.4 LR-WPAN with Zigbee ! IEEE 802.15.3 HR-WPAN ! IEEE 1073 Medical devices ! IEEE 1451 Transducer (sensors) ! IrDA (Optical)
Important characteristics of IEEE wireless standards Wireless Bluetooth Zigbee WiFi 802.11b 802.11a 802.11g Standard (802.15.1) (802.15.4) Maximum 0.72 Mbps Up to 11 Mbps Up to 54 Mbps Up to 54 Mbps Up to 250 kbps data rate Radio 5.425 - 5.875 2.4 - 2.497 GHz 2.4 - 2.497 GHz 2.4 - 2.497 GHz 2.4 - 2.497 GHz frequencies GHz Modulation FHSS DSSS OFDM OFDM DSSS technique Typical TX power I mW 100 mW 100 mW 100 mW 0.1 – 10 mW Network Point-to- Point-to- Point-to- Ad hoc, star, Ad hoc piconets Topologies multipoint multipoint multipoint mesh System High High High High Low complexity Power required Medium High High High Very low Max through-put 0.72 Mbps 5.8 Mbps 12.4 Mbps 19.8 Mbps 250 kbps at 100 ft
Multipath fading considerations Wall Scattered Reflected waves Reflected are the source of multipath fading Diffracted Direct Wall RF transmission wave path classes
Multipath: random phase and amplitude fluctuations ! If signal fading depends upon position of receiver in room fading is a function of space ! When motion is involved fading is a function of time Peak Null ! If signal amplitude and phase changes is a function of frequency RF standing wave pattern from a reflecting wall
Multipath mitigation techniques ! Spatial diversity (multiple antennas) ! Temporal diversity ! Spectral diversity ! Alternative modulation techniques ! Feedback equalization ! Automatic Repeat Requests (ARQ) ! Forward Error Correction
RF interference/fading ! Fading is an “inward” type of interference ! Outward interference occurs when WLAN signals interfere with adjacent electronics ! In practice however, the use of spread spectrum signaling (DSSS and FHSS) eliminates this concern
RF Coexistence ! WiFi, Bluetooth, and 801.15.4 / Zigbee all transmit in the 2.4 GHz ISM band ! These transmissions all have the potential for collision with the result a dramatically reduced throughput ! Several mechanisms are available to minimize interference and maximize interoperability
RF Coexistence: signaling ! 802.11b, 802.15.4 are DSSS which operate over a wide amount of bandwidth ! Narrowband interference affects only part of the signal ! Wideband interference has disastrous effects on any type of radio transmission ! 802.15.1 is a FHSS transmission
RF co-existence
RF coesistence
RF Coexistence – mitigation mechanisms ! Engineer proper access point spacing ! TDMA ! CSMA ! DTPA: Dynamic TxPower Adjustment ! Implement collaborative mechanisms ! Engineer clear channel techniques ! Engineer frequency domain: s/w radios
IEEE 1451 Sensors ! Address heterogeneous naming and service identification issues ! 1451 uses a TEDS to specify naming and services ! No legacy installation bases ! Wireless devices have req’d CPU/EEPROM ! Desire for plug and play
RF vs Optical Visible light Microwaves Ultraviolet Gamma Rays Radio Waves Infrared X-Rays 10 11 10 12 10 13 10 14 10 17 10 18 10 19 10 8 10 9 10 16 10 21 10 6 10 7 10 20 10 15 10 5 10 10 Frequency, Hz IR (850 – 900 nm) uses diffuse light reflected at walls, furniture, etc., or a directed line of sight exists between the sender and the receiver
Advantages of Optical Simple and very cheap senders and receivers which are ! integrated into most mobile devices today. PDAs, laptops, notebooks, mobile phones, etc., have an infrared data association (IrDA) interface Version 1.0 of the IrDA standard implements data rates of up to ! 115 kbit/sec, while IrDA 1.1 defines higher data rates of 1.152 and 4 (maybe 16) Mbit/sec No licenses are needed for infrared transmission ! Shielding is very simple with IR devices – due to their limited ! range shielding is much less of an issue than with RF devices Electrical devices do not interfere with infrared transmission. !
Disadvantages of Optical ! Low bandwidth compared to other LAN technologies ! Infrared is quite easily shielded. Infrared transmission cannot penetrate walls or other obstacles, and for good transmission quality and high data rates typically a direct line-of- sight is required ! Much less flexibility for mobility as compared to RF
Advantages of RF ! Long term experiences made with radio transmission for wide area networks (e.g., microwave links) and mobile cellular telephones ! Radio transmission can cover larger areas and can penetrate (thinner) walls, furniture, plants, etc ! RF does not require direct line of sight for reliable communication transmission ! Current RF-based products offer higher transmission rates (e.g., 10 Mbit/sec) than infrared.
Disadvantages of RF ! Long term experiences made with radio transmission for wide area networks (e.g., microwave links) and mobile cellular telephones ! Radio transmission can cover larger areas and can penetrate (thinner) walls, furniture, plants, etc ! RF does not require direct line of sight for reliable communication transmission ! Current RF-based products offer higher transmission rates (e.g., 10 Mbit/sec) than infrared ! Most WLAN technologies rely on RF instead of optical
Wireless System Architecture (WSA) ! Goal ! High-level support for end-users ! Overview/Review/Progress in Phase I ! Future Work (Phase II) ! Summary
WSA Goal ! To provide the required architectural infrastructure to support heterogeneous wireless devices in a single unified system ! System evolution ! Ground system ! ISS as a testbed ! Support Exploration effort
WSA Objectives ! Hide complexity of implementation ! Easy to integrate disparate devices ! Easy to compose data manipulation applications ! Support applicable standards ! IEEE 802.11, 802.15.1, 802.15.4 ! IEEE 1451, 1073, and IrDA
WSA Middleware emphasis Presentation and Application Application layers Transport Middleware: session IP Layer and presentation Data Link Network /Transport Physical Data Link / Physical Wireless distributed system WWW network emphasis emphasis
Middleware services ! Integrate heterogeneous devices ! Wireless device network management ! Time synchronization ! Device and Service discovery ! Security ! Grouping ! Database management
HAB – NAG specifics WSA-standard application interface Application Power Event RT Data Device Custom Data to the nag Monitor Monitor Display Command Apps Visualize Layer Network Aggregator (nag) WSA-standard Middleware hab-nag interface T W M Hardware L M T E I e E T O a I Abstractors S S d m e C n n T - I b l A t y (habs) H C c e o T I o A O a r s E s s B 2 l Device specific WSN - interface Transport / UWB Custom Bluetooth (in kernel) TCP/IP tdma/csma Network Net Layer Net Layer Net Layer or Zigbee WSN - Data Link / Eth Eth UWB Custom Bluetooth (hardware) custom or PHYS LAN WLAN PHYS PHYS 802.15.1 802.15.4
Deployment Scenario Habitat 1 Wired HAB network Primary Habitat 1 5 APP APP 2 4 NAG 3 HAB Habitat 2 1 5 2 4 3 Wired HAB network 1 5 2 4 3
Naming Host 0 Host 0 nag Wired network Mantis Mantis hab hab “Destiny” “Russian” Mantis node ID 0 Mantis node ID 0
HAB Development Kit WSA-standard application interface App to the nag Network Aggregator (nag) Develoment WSA-standard Kit for HAB hab-nag interface with published Hardware APIs. Abstractors (habs) Device specific interface (in kernel) (hardware)
Example Application: Bedrest Study ! Issue: Subjects may move excessively on the bed, or they could leave the bed and fall ! Goal: Record the subject’s activity over the duration of the study to ensure study protocol compliance and to account for possible deviations between subjects. To ensure a subject’s safety the nursing staff will be alerted when the bedridden subject is standing or walking
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