[ath9k-devel] varying RSSI values with ath9k_htc drivers for TL-WN721N USB wifi adapter.

[Harshal Vora <harshal@amideeptech.com>]

On Friday 26 April 2013 01:39 AM, Adrian Chadd wrote:
> Have you actually verified that the output power of those devices is
> actually constant?
>
>
>
> Adrian
>
> On 25 April 2013 07:08, Harshal Vora <harshal@amideeptech.com> wrote:
>> Hi,
>>
>> I are trying to achieve approximate location detection (room level
>> granularity) based on RSSI.
>> I am using TP-LINK TL-WN721N USB wifi adapter which require ath9k_htc
>> drivers.
>> Operating system: Ubuntu 12:04 LTS.
>>
>> The RSSI values recorded vary a lot, even when the transmitter (iPhone 5 and
>> sony xPeria and other phones) and the receiver are left untouched at the
>> same location.
>>
>> There is a difference of almost 15 to 20 dbm in the readings.
>> Sometimes it is in the range of -40 to -50dbm .. sometimes -50 to -60dbm
>>
>> Also sometimes the RSSI values are always between -75 to -85 dbm no matter
>> how short or long the distance is between the two devices.
>>
>> I am using airmon-ng to set the device in monitor mode and tshark to sniff.
>> I have tried with the drivers that come with ubuntu 12.04, with
>> compat-wireless 3.6.8-1 as well as compat-drivers 3.8.3-2
>>
>> The todo list on
>> http://wireless.kernel.org/en/users/Drivers/ath9k_htc#TODO
>> mentions
>> Low RSSI issue for UB91/94.
>>
>> Should this be a concern?
>>
>>
>> Regards,
>>
>> _______________________________________________
>> ath9k-devel mailing list
>> ath9k-devel at lists.ath9k.org
>> https://lists.ath9k.org/mailman/listinfo/ath9k-devel


Hi,

I have a MAC laptop which has inbuilt broadcom BCM 4331 chipset running 
on b43 drivers.

I put the iPhone in charging and it is always unlocked and on the wifi 
settings page which displays available networks.
 From what I understand, iPhone goes in power saver mode only when locked.
The readings on bcm4331 are much stable as compared to the wn721n usb 
adapter.
On broadcom, the dbm values differ mostly by 3-4 dbm and sometimes I see 
a spike with a difference of 7-8dbm.
On the other hand the dbm values using ath9k_htc drivers differ by 10-15dbm.

I have also tested with a locked iPhone to get similar results.

In another setup, I connected one wn721n chipset to hackberry and 
another to my laptop.
Again I took two sets of readings with transmitter as wn721n on 
hackberry and receiver as bcm4331 in the first run and receiver as 
wn721n on my mac in the second run.
Again similar observaions as the experiment with iPhone as transmitter.

How can I measure the output transmission power? I deployed the 
ath9k_htc drivers in debug mode with value 0xffffffff. But cannot get 
any relevant information from debugfs.
When I do ifconfig, it says power management off.
When I run sudo iwconfig "dev" txpower "value", it returns an error.

I have taken a lot of different sets of readings for ath9k_htc, and 
relatively the readings are correct. i.e. the dbm values will change as 
the distance between the transmitter and receiver changes. But sometimes 
the dbm values remain in a particular range say -75dbm to -85dbm no 
matter how near or far the transmitter is from the receiver.

Regards,