ath5k: AP throughput and signal strength problem

ath5k: AP throughput and signal strength problem

[Dennis Borgmann]

Hello linux-wireless!
Hello hostapd-users!

I observe some remarkable behavior of the ath5k-driver/nl80211/hostapd -
I don't know, which one makes me sad. Maybe, it's even me being the
problem, so I would have a problem configuring or a problem with cfg80211.

All the following bases on antennas used with 5dBi gain.

I have an AP using ath5k in version 0.6.0 running on kernel 2.6.33.7, iw
in version 0.9.21 and using hostapd 0.7.3. The wireless card is a
AWPC085 from AlfaNetwork with an AR5414 chip. There are two things, I
observe:

1. Thoughput measurements:
I have tried several setups with wireless interfaces. My reference was a
LinksysWRT54GL(http://www.linksysbycisco.com/DE/de/products/WRT54GL)
with DD-WRT(http://www.dd-wrt.com) being installed. I ran "iperf" on two
laptops associated wireless with the Linksys-AP, one laptop running the
old madwifi-driver, one running ath5k. Both reached around 27Mbit/s with
iperf and the Linksys-AP, while the iperf-server was on another machine
for not blasting the AP with CPU-load due to iperf.
Then - same setup with an AP based on an ALIX-board from
PC-Engines(http://pcengines.ch/alix3d2.htm). Data rates with iperf only
up to 6Mbit/s. The AP shows:

# iw dev wlan0 station
dump


Station xx:xx:xx:xx:xx:xx (on
wlan0)


        inactive time:  23559
ms


        rx bytes:
15480534


        rx packets:
10217


        tx bytes:
20534


        tx packets:
112


        signal:         -33
dBm


        tx bitrate:     11.0 MBit/s

So the bitrate is far too low to gain higher values, but the AP is
placed 3m line-of-sight next to the laptop and still the value for tx
bitrate is this bad. I would suggest it being higher. How come? And why
is the Linksys so much faster with the same laptops associated?

2. Signal strength measurements:
In addition, the signal levels are in general about 10dBm lower than the
ones of the Linksys if I start moving around. I made no adjustments at
the tx power rates - neither at the Linksys nor at the Atheros-device.
And still, I observe this:

I am using a program called airview from Ubiquity to analyze the traffic
and strength of signals in the air: http://www.ubnt.com/airview

What I can observe is, that as long as the Atheros-AP only transmits
beacons, its output power is around 5dBm below the power measured once
there is traffic on the interface (I am doing a simple "ping <IP> -f").
The client is situated far away from both the AP and the measuring
Laptop with "airview" in order not to disturb the measurement.

The problem I would suggest from this measurement is, that I a client
standing quite far away from the AP not finding the AP as long as it
only transmits beacons - although the signal would still be good enough
since the output power would be higher, if there was traffic.

And in fact - I can observe this problem. If I move far away from the
AP, at a certain point I can still receive beacons from the
Linksys-machine, but no more beacons from the Atheros-AP with ath5k. So
the client won't associate with the Atheros ath5k-AP, but with the
Linksys. If I associate with the Atheros-AP before, there will still be
a connection with data throughput possible.

Am I wrong? How to put up the output power while transmitting beacons?
In general, the Linksys is according to my tests more powerful than the
Atheros-AP. At least with my current setup. I'd like to turn this around
and make the Atheros-AP become stronger ;-)

Thanks for any hint,
Dennis Borgmann

Re: ath5k: AP throughput and signal strength problem

[Dennis Borgmann]

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Hello hostapd and linux-wireless list!

Problem solved. I had to activate ieee80211d in hostapd.conf. Now the
device works fine. Seems like it worked in 802.11b mode before. Signal
strength and throughput are ok now. Sorry for bothering!

For those being interested, check attached picture, which shows power
levels of Linksys(channel 1) and Atheros(channel 6) measured 3m away
from each AP.

One last point - the performance is a lot lower with the Atheros-APin
border areas of receiving wireless signals than with the Linksys. I have
tested the two APs with several walls in between the AP and the station
used for testing, here are the results:

Setup: Linux client running kernel 2.6.37, iw 0.9.22 and a wireless card
from Atheros with AR5414 chip associates with a
LinksysWRT54GL("Linksys") and for comparison with a linux client
configured as AP with hostapd running linux kernel 2.6.37 and hostapd
0.7.3 with a wireless card from Atheros with AR5414 chip("Atheros").

Value for numbers: Mbit/s, measured with iperf using UDP

No walls
Linksys - 28
Atheros - 27

One wall
Linksys - 27
Atheros - 27

Five walls
Linksys - 24
Atheros - 26

Six walls - roundabout 20m away from the AP
Linksys - 9
Atheros - 5

Seven walls - roundabout 25m away from the AP
Linksys - 10
Atheros - 1

Client shows -76dBm at "Seven walls" for Linksys-AP and -83dBm for
Atheros-AP. Any idea on how to improve this furthermore?

Kind regards,
Dennis Borgmann


Dennis Borgmann schrieb:
> Hello linux-wireless!
> Hello hostapd-users!
>
> I observe some remarkable behavior of the ath5k-driver/nl80211/hostapd -
> I don't know, which one makes me sad. Maybe, it's even me being the
> problem, so I would have a problem configuring or a problem with cfg80211.
>
> All the following bases on antennas used with 5dBi gain.
>
> I have an AP using ath5k in version 0.6.0 running on kernel 2.6.33.7, iw
> in version 0.9.21 and using hostapd 0.7.3. The wireless card is a
> AWPC085 from AlfaNetwork with an AR5414 chip. There are two things, I
> observe:
>
> 1. Thoughput measurements:
> I have tried several setups with wireless interfaces. My reference was a
> LinksysWRT54GL(http://www.linksysbycisco.com/DE/de/products/WRT54GL)
> with DD-WRT(http://www.dd-wrt.com) being installed. I ran "iperf" on two
> laptops associated wireless with the Linksys-AP, one laptop running the
> old madwifi-driver, one running ath5k. Both reached around 27Mbit/s with
> iperf and the Linksys-AP, while the iperf-server was on another machine
> for not blasting the AP with CPU-load due to iperf.
> Then - same setup with an AP based on an ALIX-board from
> PC-Engines(http://pcengines.ch/alix3d2.htm). Data rates with iperf only
> up to 6Mbit/s. The AP shows:
>
> # iw dev wlan0 station
> dump
>
>
> Station xx:xx:xx:xx:xx:xx (on
> wlan0)
>
>
>         inactive time:  23559
> ms
>
>
>         rx bytes:
> 15480534
>
>
>         rx packets:
> 10217
>
>
>         tx bytes:
> 20534
>
>
>         tx packets:
> 112
>
>
>         signal:         -33
> dBm
>
>
>         tx bitrate:     11.0 MBit/s
>
> So the bitrate is far too low to gain higher values, but the AP is
> placed 3m line-of-sight next to the laptop and still the value for tx
> bitrate is this bad. I would suggest it being higher. How come? And why
> is the Linksys so much faster with the same laptops associated?
>
> 2. Signal strength measurements:
> In addition, the signal levels are in general about 10dBm lower than the
> ones of the Linksys if I start moving around. I made no adjustments at
> the tx power rates - neither at the Linksys nor at the Atheros-device.
> And still, I observe this:
>
> I am using a program called airview from Ubiquity to analyze the traffic
> and strength of signals in the air: http://www.ubnt.com/airview
>
> What I can observe is, that as long as the Atheros-AP only transmits
> beacons, its output power is around 5dBm below the power measured once
> there is traffic on the interface (I am doing a simple "ping <IP> -f").
> The client is situated far away from both the AP and the measuring
> Laptop with "airview" in order not to disturb the measurement.
>
> The problem I would suggest from this measurement is, that I a client
> standing quite far away from the AP not finding the AP as long as it
> only transmits beacons - although the signal would still be good enough
> since the output power would be higher, if there was traffic.
>
> And in fact - I can observe this problem. If I move far away from the
> AP, at a certain point I can still receive beacons from the
> Linksys-machine, but no more beacons from the Atheros-AP with ath5k. So
> the client won't associate with the Atheros ath5k-AP, but with the
> Linksys. If I associate with the Atheros-AP before, there will still be
> a connection with data throughput possible.
>
> Am I wrong? How to put up the output power while transmitting beacons?
> In general, the Linksys is according to my tests more powerful than the
> Atheros-AP. At least with my current setup. I'd like to turn this around
> and make the Atheros-AP become stronger ;-)
>
> Thanks for any hint,
> Dennis Borgmann
>   


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