Editing Wifi power saving mode
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The tablets support what is called Wifi Power Saving Mode (PSM). PSM allows the tablet to switch its wifi radio on and off several times a second to save battery. While this does greatly improve battery life (6-8 hours idle on Wifi without PSM, 3-4 days with), there are still many routers on the market which do not support PSM or have a buggy implementation and this can cause problems for the tablets. | The tablets support what is called Wifi Power Saving Mode (PSM). PSM allows the tablet to switch its wifi radio on and off several times a second to save battery. While this does greatly improve battery life (6-8 hours idle on Wifi without PSM, 3-4 days with), there are still many routers on the market which do not support PSM or have a buggy implementation and this can cause problems for the tablets. | ||
- | Because using PSM introduces extra latency for incoming packets, the tablets try to optimize performance by remaining in Constant Active Mode (CAM) if there is constant traffic. On the other hand, CAM consumes a lot of power, so the timeout should be as short as possible. For more detailed description, see [http://lists.maemo.org/pipermail/maemo-users/2008-July/ | + | Because using PSM introduces extra latency for incoming packets, the tablets try to optimize performance by remaining in Constant Active Mode (CAM) if there is constant traffic. On the other hand, CAM consumes a lot of power, so the timeout should be as short as possible. For more detailed description, see [http://lists.maemo.org/pipermail/maemo-users/2008-July/034755.html this posting on the subject]. |
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== Issues == | == Issues == | ||
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PSM can be configured on a per-connection basis in the Connectivity control panel (Application menu -> Settings -> Control panel -> Connectivity). Under the Other tab of Advanced settings when editing a saved connection. There are 3 options available: On (Maximum), On (Intermediate), and Off (note, the WLAN transmission power setting will not significantly impact battery life—though it will impact Wifi roaming distance—and is simply there for legislative reasons). Maximum and Intermediate change the timeout period (200ms and 1000ms, respectively), and Off turns off PSM entirely. | PSM can be configured on a per-connection basis in the Connectivity control panel (Application menu -> Settings -> Control panel -> Connectivity). Under the Other tab of Advanced settings when editing a saved connection. There are 3 options available: On (Maximum), On (Intermediate), and Off (note, the WLAN transmission power setting will not significantly impact battery life—though it will impact Wifi roaming distance—and is simply there for legislative reasons). Maximum and Intermediate change the timeout period (200ms and 1000ms, respectively), and Off turns off PSM entirely. | ||
- | == Ad-hoc prevents PSM | + | == <s>Ad-hoc prevents PSM</s> == |
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- | http:// | + | <s>Ad-hoc mode cannot use power-saving modes other than reduce transmit power - since there's no master or slave where the slave can spend a lot of time "asleep", it prevents power saving modes.</s> (This is false and needs fixed. The stations trade off acting as "master". [http://books.google.com/books?id=9rHnRzzMHLIC&pg=PA193&lpg=PA193&dq=ibss+power+management&source=bl&ots=3wzOD62aBr&sig=lUehrHBabk4WX8NT6_XEyIjxy5Y&hl=en&ei=9zVNTOjWD4z4sAPg2PhI&sa=X&oi=book_result&ct=result&resnum=7&ved=0CC0Q6AEwBg#v=onepage&q=ibss%20power%20management&f=false 802.11 ibss psm]) || Anyway any master would need to send beacons every few fractions of a second, something that largely defeats the purpose of powersaving. Otherwise the time sync between the two peers gets lost rather quickly which basically means the connection gets lost or huge delay gets introduced. |
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== Routers known to be incompatible with PSM mode == | == Routers known to be incompatible with PSM mode == |
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