On 09/18/2014 07:28 PM, Rick Stevens wrote:
On 09/18/2014 05:23 PM, jd1008 issued this missive:
# lspci | grep -i wifi
0c:00.0 Network controller: Intel Corporation WiFi Link 5100
dmesg | grep -i iwlwifi
[   10.019366] iwlwifi 0000:0c:00.0: Detected Intel(R) WiFi Link 5100
AGN, REV=0x54

dmesg also  shows
[  266.827254] wlan0: Limiting TX power to 36 (36 - 0) dBm as advertised
by 00:0d:67:6a:5a:19

iwconfig wlan0
$ iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:"attwifi"
           Mode:Managed  Frequency:2.462 GHz  Access Point:
00:0D:67:6A:5A:19
           Bit Rate=72.2 Mb/s   Tx-Power=15 dBm
           Retry short limit:7   RTS thr:off   Fragment thr:off
           Power Management:off
           Link Quality=35/70  Signal level=-50 dBm
           Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
           Tx excessive retries:0  Invalid misc:20   Missed beacon:0

So, reason I am asking is that I would like to increase Tx power to 30dBm
due to poor connectivity with the hotspot router.

I tried
# iwconfig wlan0 txpower 30dBm
{7917-jd@localhost}# echo $?
0
# iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:"attwifi"
           Mode:Managed  Frequency:2.462 GHz  Access Point:
00:0D:67:6A:5A:19
           Bit Rate=72.2 Mb/s   Tx-Power=15 dBm
           Retry short limit:7   RTS thr:off   Fragment thr:off
           Encryption key:off
           Power Management:off
           Link Quality=35/70  Signal level=-50 dBm
           Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
           Tx excessive retries:0  Invalid misc:20   Missed beacon:0

So, iwconfig is not setting Tx power. Not sure if this is a limitation
of the wifi card or a bug in the wifi driver or if a bug in iwconfig.

Uh, I don't think you can go above 15dBm. Try "iwconfig wlan0 txpower 10" and see if it dropped it to 10dBm. I bet it does (it does to me).
If it does, then iwconfig is doing its job. Bump it back up to 15 and
start playing with antenna locations on the access point. Your poor
connectivity is more likely due to bad incoming signal strength and in
that case boosting your transmission isn't going to help.

Well, then it is a physical limitation of the intel wifi card.

I do not have a physical access to the access point.
It is a public hotspot (at a restaurant). My laptop
has no antennas :)

I have had to send login info to gmail (via thunderbird) several times
and each time login timed out or failed. So I naturally assumed it is
the weak Tx power. But it could be a combination of both my Tx power
and the AP's Tx power, and whatever else is in between (walls ..etc).

I guess I will be searching for a 300N card that has higher Tx power and much
better Rx sensitivity.



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