WiFi Tx power question

[jd1008]

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 at 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.