TX-Power limits for ath10k based card on Linux 3.18.24 (long term support)?

TX-Power limits for ath10k based card on Linux 3.18.24 (long term support)?

[Joerg Pommnitz]

Hello all,
I'm trying to use a COMPEX WLE600VX (see http://www.compex.com.sg:809/Datasheets/WLE600VX_Dsv1.0.2-141013-I.pdf) as an Access Point. According to the data sheet, the card should be able to transmit with about 20 dB (100mW). However, doing some measurements with a card on 2.4GHz channel 3 in 802.11g 54MBit coding I could only observe a TX power of about 7..9dB. During the measurement the card was under full load with iperf transmitting at 20..25 mbps. This is only a fraction of the stated TX power, so something strange must be going on. The measurements were done with a Marconi 6460 powermeter.


My hostapd.conf is very simple:
interface=ap
driver=nl80211
ssid2=<omitted>
channel=3
hw_mode=g
auth_algs=1
ignore_broadcast_ssid=0
eap_server=0
wpa=3
wpa_passphrase=<omitted>
wpa_key_mgmt=WPA-PSK WPA-PSK-SHA256 
wpa_pairwise=TKIP CCMP
ctrl_interface=/var/run/hostapd
macaddr_acl=0

The regdb (compiled directly into the kernel) shouldn't be a problem either:
global
country 00: DFS-UNSET
(2402 - 2472 @ 40), (N/A, 100), (N/A)
(2457 - 2482 @ 40), (N/A, 100), (N/A)
(2474 - 2494 @ 20), (N/A, 20), (N/A), NO-OFDM, PASSIVE-SCAN
(5170 - 5250 @ 80), (N/A, 20), (N/A), AUTO-BW, PASSIVE-SCAN
(5250 - 5330 @ 80), (N/A, 20), (0 ms), DFS, AUTO-BW, PASSIVE-SCAN
(5490 - 5730 @ 160), (N/A, 20), (0 ms), DFS, PASSIVE-SCAN
(5735 - 5835 @ 80), (N/A, 20), (N/A), PASSIVE-SCAN
(57240 - 63720 @ 2160), (N/A, 0), (N/A)

Does anybody have an idea, why the TX power seems to be so very low?


 -- Regards       Joerg

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Re: TX-Power limits for ath10k based card on Linux 3.18.24 (long term support)?

[Joerg Pommnitz]

Ben,
thanks for taking the time to answer. I followed your suggestion and repeated my tests
with your beta-15 firmware.
The results are interesting. At first I thought nothing had changed. The txpower was about 10dB, 

far short of the expected 20dB. Playing around with "iw dev ap set txpower fixed ... " did not result in significiant changes.

However, when I add an attenuator between the powermeter and the antenna, the measured txpower markedly increased. With 10dB attenuation I get 12dB, with 20dB attenuation the txpower increases to more than 15dB.

Question: Is this the expected behaviour? Can I force a fixed txpower instead of this dynamic adaptation?

 -- Regards       Joerg



> Ben Greear <greearb@candelatech.com> schrieb am 17:04 Dienstag, 17.November 2015:
> > You might try CT firmware...I fixed some issues with tx-power for single chain 
> rates.
> 
> http://www.candelatech.com/ath10k.php
> 
> I suggest version 'beta-15', it is about to be officile release-15.
> 
> I'm curious to know the results if you do test with it.
> 
> Thanks,
> Ben
> 
> 
> 
> On 11/17/2015 02:19 AM, Joerg Pommnitz wrote:
>>  Hello all,
>>  I'm trying to use a COMPEX WLE600VX (see 
> http://www.compex.com.sg:809/Datasheets/WLE600VX_Dsv1.0.2-141013-I.pdf) as an 
> Access Point. According to the data sheet, the card should be able to transmit 
> with about 20 dB (100mW). However, doing some measurements with a card on 2.4GHz 
> channel 3 in 802.11g 54MBit coding I could only observe a TX power of about 
> 7..9dB. During the measurement the card was under full load with iperf 
> transmitting at 20..25 mbps. This is only a fraction of the stated TX power, so 
> something strange must be going on. The measurements were done with a Marconi 
> 6460 powermeter.
>> 
>> 
>>  My hostapd.conf is very simple:
>>  interface=ap
>>  driver=nl80211
>>  ssid2=<omitted>
>>  channel=3
>>  hw_mode=g
>>  auth_algs=1
>>  ignore_broadcast_ssid=0
>>  eap_server=0
>>  wpa=3
>>  wpa_passphrase=<omitted>
>>  wpa_key_mgmt=WPA-PSK WPA-PSK-SHA256
>>  wpa_pairwise=TKIP CCMP
>>  ctrl_interface=/var/run/hostapd
>>  macaddr_acl=0
>> 
>>  The regdb (compiled directly into the kernel) shouldn't be a problem 
> either:
>>  global
>>  country 00: DFS-UNSET
>>  (2402 - 2472 @ 40), (N/A, 100), (N/A)
>>  (2457 - 2482 @ 40), (N/A, 100), (N/A)
>>  (2474 - 2494 @ 20), (N/A, 20), (N/A), NO-OFDM, PASSIVE-SCAN
>>  (5170 - 5250 @ 80), (N/A, 20), (N/A), AUTO-BW, PASSIVE-SCAN
>>  (5250 - 5330 @ 80), (N/A, 20), (0 ms), DFS, AUTO-BW, PASSIVE-SCAN
>>  (5490 - 5730 @ 160), (N/A, 20), (0 ms), DFS, PASSIVE-SCAN
>>  (5735 - 5835 @ 80), (N/A, 20), (N/A), PASSIVE-SCAN
>>  (57240 - 63720 @ 2160), (N/A, 0), (N/A)
>> 
>>  Does anybody have an idea, why the TX power seems to be so very low?
>> 
>> 
>>    -- Regards       Joerg
>> 
>>  _______________________________________________
>>  ath10k mailing list
>>  ath10k@lists.infradead.org
>>  http://lists.infradead.org/mailman/listinfo/ath10k
>> 
> 
> -- 
> Ben Greear <greearb@candelatech.com>
> Candela Technologies Inc  http://www.candelatech.com
> 

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Re: TX-Power limits for ath10k based card on Linux 3.18.24 (long term support)?

[Ben Greear]

On 11/17/2015 09:02 AM, Joerg Pommnitz wrote:
> Ben,
> thanks for taking the time to answer. I followed your suggestion and repeated my tests
> with your beta-15 firmware.
> The results are interesting. At first I thought nothing had changed. The txpower was about 10dB,
>
> far short of the expected 20dB. Playing around with "iw dev ap set txpower fixed ... " did not result in significiant changes.
>
> However, when I add an attenuator between the powermeter and the antenna, the measured txpower markedly increased. With 10dB attenuation I get 12dB, with 20dB attenuation the txpower increases to more than 15dB.
>
> Question: Is this the expected behaviour? Can I force a fixed txpower instead of this dynamic adaptation?

I'm not aware of any logic in the firmware that would adjust power automatically
based on attenuation on the antenna connectors.

Any chance the issue is how you are measuring things?

Maybe try the same test with an ath9k NIC and see how it performs?

Do you see similar results with other firmware when you add attenuation?

Are you connecting just to channel 0 on the NIC, or are you connecting to
all three antenna ports?  With 11g, you should only see signal on the
first channel I think.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


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