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On a Wistron CM9-GP Mini PCI card I did some Sensitivity measurements =
using a calibrated Rohde & Schwarz RF-test system.
I tested three different configurations:
a) Host: IBM R40 ThinkPad, Windows XP, Driver 4.12.38 (1/04/2005)
b) madwifi 0.9.3 svn r2100 with Linux 2.4.20
c) madwifi 0.9.3.2
Results:
a) On the windows xp system the card shows an excellent receiver =
sensitivity which is far better than -90dBm on the low rates in both, =
11b and 11g modes.
b) Running svn r2100 the sensitivity in 11b-Mode is also excellent. I =
have measured down to -98dBm at PER 8% using 1Mbit/s.
But the behaviour in all 11g OFDM-rates is really strange:=20
It seems that the receiver refuses operation at signal levels below =
-77dBm.
Characteristical for all WLAN-receivers is that the Packet Error Rate =
rises when the RF-level is about 3dB to 5 dB higher then the sensitivity =
limit.
The typical limit is better than -90dBm for the lowest 11g OFDM-Rate =
6Mbit/s.
Interesting thing is that in this configuration the receiver suddenly =
looses about 70% of all packets at -77dBm RF-Level without having =
CRC-errors in RX-packets, so while really having a PER =3D0%, on all =
11g-rates.
(54Mbit/s excepted from this observation, cause it reaches its =
sensitivity limit typical at about -75dBm +- 2dB anyway)
And there is a Hysteresis in the dependance on the RF-Level:
Once the receiver is in the mode of loosing >70% of all packets, it =
won't stop loosing packets until the level is increased for at least =
10dB (to -67dBm) for at least one second.
The receiver starts to work properly again.
Then the level can be slowly decreased again to -76dBm and nothing =
changes, all packets are received.
When -77dBm are reached, the receiver looses >70% of all packets again - =
this procedure can be repeated as often you want.
That means that this limit is not reached because of physical reception =
problems, the receiver has not reached his limit by far!
It seems to be a configuration problem of the driver initialising the =
card.
And it is obviously only dependant on the RSSI-Level and not on the =
quality of the radio reception...
c) We tried the 0.9.3.2 and the result was the same as seen in b) with =
one significant difference:
The hysteresis behaviour was gone. There was one hard threshold: below =
-77dBm RF-level still >70% of packets were lost at 0% PER.
But increasing the RF-Level of about 1..2dB, all packets were received =
again.
For low 11g-Rates, the user will see a reduction of the expected =
coverage range down to about 1/10 of what is known as usual with this =
technology.
Any idea how we can get better receive sensitivity ?
Regards,
Roman=20
=20
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<DIV><FONT size=3D2>On a Wistron CM9-GP Mini PCI card I did some =
Sensitivity=20
measurements using a calibrated Rohde & Schwarz RF-test =
system.</FONT></DIV>
<DIV>
<P><FONT size=3D2>I tested three different configurations:</FONT></P>
<P><FONT size=3D2>a) Host: IBM R40 ThinkPad, Windows XP, Driver 4.12.38=20
(1/04/2005)</FONT></P>
<P><FONT size=3D2>b) <SPAN class=3D247194509-21092007>madwifi 0.9.3 =
</SPAN><FONT color=3D#ff0000><FONT color=3D#000000>svn r2100</FONT><SPAN =
class=3D247194509-21092007><FONT color=3D#000000> with</FONT> <FONT=20
color=3D#000000>Linux 2.4.20</FONT></SPAN></FONT></FONT></P><FONT =
size=3D2>
<P>c) <SPAN class=3D247194509-21092007>madwifi </SPAN></FONT><FONT =
color=3D#ff0000=20
size=3D2><FONT color=3D#000000>0.9.3.2</FONT></P></FONT><FONT size=3D2>
<P>Results:<BR>a) On the windows xp system the card shows an excellent =
receiver=20
sensitivity which is far better than -90dBm on the low rates in both, =
11b and=20
11g modes.</P>
<P>b) Running </FONT><FONT size=3D2>svn r2100</FONT><FONT size=3D2> the =
sensitivity=20
in 11b-Mode is also excellent. I have measured down to -98dBm at PER 8% =
using=20
1Mbit/s.<BR>But the behaviour in all 11g OFDM-rates is really strange: =
<BR>It=20
seems that the receiver refuses operation at signal levels below=20
-77dBm.<BR>Characteristical for all WLAN-receivers is that the Packet =
Error Rate=20
rises when the RF-level is about 3dB to 5 dB higher then the sensitivity =
limit.<BR>The typical limit is better than -90dBm for the lowest 11g =
OFDM-Rate=20
6Mbit/s.<BR>Interesting thing is that in this configuration the receiver =
suddenly looses about 70% of all packets at -77dBm RF-Level without =
having=20
CRC-errors in RX-packets, so while really having a PER =3D0%, on all=20
11g-rates.<BR>(54Mbit/s excepted from this observation, cause it reaches =
its=20
sensitivity limit typical at about -75dBm +- 2dB anyway)<BR>And there is =
a=20
Hysteresis in the dependance on the RF-Level:<BR>Once the receiver is in =
the=20
mode of loosing >70% of all packets, it won't stop loosing packets =
until the=20
level is increased for at least 10dB (to -67dBm) for at least one =
second.<BR>The=20
receiver starts to work properly again.<BR>Then the level can be slowly=20
decreased again to -76dBm and nothing changes, all packets are =
received.<BR>When=20
-77dBm are reached, the receiver looses >70% of all packets again - =
this=20
procedure can be repeated as often you want.<BR>That means that this =
limit is=20
not reached because of physical reception problems, the receiver has not =
reached=20
his limit by far!<BR>It seems to be a configuration problem of the =
driver=20
initialising the card.<BR>And it is obviously only dependant on the =
RSSI-Level=20
and not on the quality of the radio reception...</FONT></P>
<P><FONT size=3D2>c) We tried the </FONT><FONT color=3D#ff0000 =
size=3D2><FONT=20
color=3D#000000>0.9.3.2</FONT> </FONT><FONT size=3D2>and the result was =
the same as=20
seen in b) with one significant difference:<BR>The hysteresis behaviour =
was=20
gone. There was one hard threshold: below -77dBm RF-level still >70% =
of=20
packets were lost at 0% PER.<BR>But increasing the RF-Level of about =
1..2dB, all=20
packets were received again.<BR>For low 11g-Rates, the user will see a =
reduction=20
of the expected coverage range down to about 1/10 of what is known as =
usual with=20
this technology.</FONT></P>
<P><FONT size=3D2><SPAN class=3D247194509-21092007><FONT size=3D2>Any =
idea how we can=20
get better receive sensitivity ?</FONT></SPAN></FONT></P>
<P><FONT size=3D2><SPAN class=3D247194509-21092007>Regards,<BR> =
Roman=20
</SPAN></FONT></P>
<P><FONT size=3D2><SPAN class=3D247194509-21092007><FONT=20
face=3DArial></FONT></SPAN> </P></FONT></DIV></BODY></HTML>
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