CPS196 - Fall 1999

Mobile Computing

Notes: By Michael Littman

Carla Ellis visits to talk with us about mobile computing.

Localization

GPS. Cruise missle: 50 feet off (satellite signal off).

Fix:

stationary base for correction: differential GPS.
inside a building: instrument the building
sensor fusion: trade off information from multiple sensors(dead reckoning, altitude, etc.).

Big questions in mobile computing: Where am I? What's nearby? How connect to the world arond me?

Battery management

uncertainty in what the power reserve is.

idle: actually saves power
bursty uses power more efficiently
slow down the processor, more efficient: when schedule, though?

Usually, designers set a threshold for when to switch to idle mode. Typically too long.

Can set this up as a ski rental problem (like when we discussed competitive analysis. Idea would be to wait to shut down until the power expended equals what it takes to restart after an idle (cost to power up).

Screen blanking is an interesting, since the computer can't directly tell when the user is looking at it. However, can take a mouse wiggle as a form of punishment.

However, system designers don't use competitive analysis. Why? Probably because the assumption of a malicious user is inaccurate. After all, it's my palm pilot. Operating system could detect ratio of use of different applications (book vs. address. vs. web browseer) and tailor accordingly.

Concurrency

Source of uncertainty, but it's inevitable with real-world devices. Very natural to use threads (otherwise you ed up writing your own scheduler).