CS294-01 Mobile Computing

Notes from Sept. 7, 2000
scribe: Chris Wells

Projects

• start thinking about them now
• teams of 2 to 3 people (3 if the class remains large)
• project topic must be related to the course
  • ideas will be posted on the web page
  • lots of related projects are possible in ICEBERG, Ninja, OceanStore, Telegraph, SmartDust, etc.
• should be detailed
  • lots of related work
  • analysis of the status quo
  • analysis of simulation / implementation of a new idea

Hardware Changes

• Base stations are smaller and cheaper
  • Today's are composed of commodity PC components
• Cell management (where to place antennas) is still difficult
• 802.11 standard: one device interacts with several wireless networks
  • This is post-1994
• Faster CPUs
  • 1 GHz P3 is here, but has high power consumption
  • Low power alternatives
    • StrongArm (undeployed because of compatibility issues)
    • Motorolla chip in the Palm Pilot
• Battery improvements
  • Battery power grows ~2X / 5 years
  • CPU power use grows ~2X / 18 months
  • DRAM uses lots of power (8MB in PDAs, 256 MB in laptops)
  • Fixed storage (disks) use lots of power while spinning
  • Displays use more power than any component other than CPUs

Software Changes

• New Mobile IP Standard
  • Triangle routing problem (indirect communication through possibly distant home node)
• Proxy computing like TranSend
• Changes in user interface
  • PDA's small size precules use of keyboard
  • Speech recognition is perhaps inappropriate for PDA use
  • Graffiti

"The Challenges of Mobile Computing"

George H. Forman and John Zahorjan

• Disconnections are inherent in wireless communications
  • Goal: decouple communication time from the time a program produces / consumes data
  • Coda File System uses hoarding and emulation to achieve this goal
• Low bandwidth issues
  • Wireless networks will always deliver lower bandwidth than wired networks
  • Software solutions
    • Data compression
    • Caching
    • Prefetching
    • Migrating computation from wireless devices to wired base stations
  • Hardware solutions
    • Add more cells to communication by overlapping cells on different frequencies
    • Shorten range of cells
• Heterogeneous Networks
  • Vertical handoff (mobile device should be able to select among different service providers to get best service)
• Mobility
  • Address migration mechanisms
    • Broadcast
    • Central services
    • Homebase
    • Forwarding pointers
  • Location dependent information is required
  • Privacy issues arise from distributing location information
• Security Risks
  • Information transmitted in the air is easy to intercept
  • Need strong encryption
  • Strong encryption is CPU expensive (can PDAs handle it?)
• Power Consumption
  • Software Power management
  • Hardware solutions
    • Reduce capacitance
    • Reduce voltage
    • Reduce clock frequency
• Portability
  • Laptop data is "fragile" (laptops can be dropped, etc.)
    • Can rely on unportable backing store
    • Increases Quality of Service requirements
    • Server overload can be reduced by sending deltas rather than data
  • Small user interfaces exist on PDAs
    • Pen-based interface
    • Voice recognition
  • Limited storage capacity (tradeoff between weight and availability)
• Discussion
  • Why did Palm Pilot succeed, while Apple Newton failed? The Pilot...
    • ...is Smaller
    • ...is more extensible
    • ...does a smaller number of things better
    • ...adapts computing to people, rather than vice versa

"The Computer for the 21st Century"

Mark Weiser

• People want computers to be ubiquitous (invisible and omnipresent)
• Created three kinds of devices: tabs, pads, and boards
• Requirements
  • Low cost
  • Low power
  • Mass producible
  • Pervasive network
  • Software support is the main issue
• Challenges and Technologies
  • Cheap computers and displays (here)
  • Large displayes (almost here)
  • Fast CPUs (here)
  • Large storage (here)
  • OS for ubiquitous devices (almost here)
  • User interfaces (not here)
  • Networking for ubiquitous devices (almost here)
• Social Issues
  • Privacy and security
• Discussion
  • What do you do with networked PDAs?
    • Email
    • Instant messaging
    • Networked videograms

"Wireless Personal Communications: What is it?"

Donald C. Cox

• Classifies current wireless technologies into six groups
  • Cellular mobile radio
  • Paging / messaging
  • Cordless phone
  • Wide are wireless data
  • High speed wireless local data
  • Satellite
• Evolution: these six will evolve into three groups
  • High-tier PCS
    • Satellite
    • Cellular
    • Paging / messaging
  • High-speed wireless LAN
  • Low-tier PCS
    • Cordless telephones
• High-tier versus low-tier PCS
  • High-tier has higher quality of service
  • Low-tier has higher capacity
  • These two technologies can be used together in composite services
• Wireless LANs
  • 900MHz ISM band had litle sucess
  • 2GHz band is better
  • Bluetooth (will it deliver?)
• Discussion
  • Standards
    • In North America, there are lots of standards
      • AMPS, FDMA, TDMA, CDMA, GSM
      • Presumably, more standards creates more market competiong
    • In Europe, there is one standard: GSM
    • GSM is good for voice, but has a high latency for data
  • What kind of end device is desirable?
    • Nokia Communicator
      • A cell phone and a PDA in one
      • Large, bulky, and unsuccessful.
    • People want to accessorize (lots of little, simple devices)