[maemo-users] Power consumption and WLAN APs

From: Andrew Daviel advax at triumf.ca
Date: Mon Jul 21 12:14:53 EEST 2008
On Mon, 21 Jul 2008, Kalle Valo wrote:

>> I recently noticed that my tablet battery runs down faster at work than
>> at home, with the WiFi enabled but otherwise sitting idle (12%/hour vs
>> 1%/hour).
> What do you mean by 12%/hour? That the battery will run out in eight
> hours?

I guess. I was using the "battery-status" application which reports 
percentage of battery left, and measuring the slope.

> Yes, multicast and broadcast traffic will increase WLAN power
> consumption. But there has to be a lot of traffic going on to really
> notice it.

I tried doing a broadcast ping every 200ms at home (the tablet sees it if 
I run tcpdump) but it had no noticable effect on the battery consumption 

> If the AP is behaving correctly, the power consumption in PSM on a
> idle N800/N810 are mostly affected by these:
> o beacon interval (longer has smaller power consumption)
> o DTIM interval (same as above)
> o broadcast/multicast traffic

I'll have a look at the AP config tomorrow and see if I can find 
My linksys at home has beacon interval 100ms, DTIM=1 (i.e. default 
values). The Linksys docs 
suggest that DTIM data is only sent if there are broadcast packets 
waiting, so perhaps setting this larger would have little effect if I 
don't have much broadcast traffic. Besides, the problem is at work, not 

Andrew Daviel, TRIUMF, Canada

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