Bo Han wrote:
> Hi,
>
> When I do iwlist scan using my BCM 4318 cards, the reported noise
> level is very high, around -57 dBm. I don't expect the card to
> measure the background noise accurately. But this value looks
> unreasonable and it is higher than the signal strength of most of the
> data packets. I noticed that in the driver code,
> b43_rssi_postprocess(...) is called for signal strength, but not for
> noise level. Are they both using dBm? How to interpret the noise
> level?
Yes, both are in dBm after the rssi_postprocess routine is called.
>
> PS, I also tried another card in the same room, whose reported noise
> level is around -70 dBm.
On my system:
lspci
06:00.0 Network controller: Broadcom Corporation BCM4318 [AirForce One
54g] 802.11g Wireless LAN Controller (rev 02)
iwlist wlan0 scan
Cell 01 - Address: 00:1A:70:46:BA:B1
Channel:1
Frequency:2.412 GHz (Channel 1)
Quality=49/70 Signal level=-61 dBm
Encryption key:on
ESSID:"lwfdjf_rad"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=000000515a64a93f
Extra: Last beacon: 516ms ago
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
Cell 02 - Address: 00:14:BF:0C:7E:14
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=30/70 Signal level=-80 dBm
Encryption key:on
ESSID:"linksys"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=000000d993312192
Extra: Last beacon: 380ms ago
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
Where is the noise level in the scan? It doesn't show up on my system.
When I do the iwconfig command, wlan0 reports a signal of -43 dBm and
a noise of -72 dBm when connected to the AP with ESSID "lwfdjf_rad".
Yes that noise level is higher than the signal from the AP with ESSID
of "linksys". You must remember that channel 1 is occupied by an AP
about 2 m from the computer, whereas the AP on channel 6 is a lot
further away and the noise is lower.
00:00.0 Host bridge: ALi Corporation M1541 (rev 04)
00:01.0 PCI bridge: ALi Corporation M1541 PCI to AGP Controller (rev 04)
00:03.0 CardBus bridge: O2 Micro, Inc. OZ6832/6833 CardBus Controller (rev 34)
00:03.1 CardBus bridge: O2 Micro, Inc. OZ6832/6833 CardBus Controller (rev 34)
00:04.0 Communication controller: Rockwell International HSF 56k
Data/Fax/Voice/Spkp (w/Handset) Modem (rev 01)
00:07.0 ISA bridge: ALi Corporation M1533/M1535/M1543 PCI to ISA Bridge
[Aladdin IV/V/V+] (rev 0a)
00:0e.0 Multimedia audio controller: ESS Technology ES1969 Solo-1 Audiodrive
(rev 02)
00:0f.0 IDE interface: ALi Corporation M5229 IDE (rev 20)
00:11.0 Bridge: ALi Corporation M7101 Power Management Controller [PMU] (rev 09)
00:13.0 USB Controller: ALi Corporation USB 1.1 Controller (rev 03)
01:00.0 VGA compatible controller: Silicon Motion, Inc. SM710 LynxEM (rev a3)
06:00.0 Network controller: Broadcom Corporation BCM4318 [AirForce One 54g]
802.11g Wireless LAN Controller (rev 02)
eth1 Scan completed :
Cell 01 - Address: 00:1A:70:46:BA:B1
Channel:1
Frequency:2.412 GHz (Channel 1)
Quality=49/70 Signal level=-61 dBm
Encryption key:on
ESSID:"lwfdjf_rad"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=000000515a64a93f
Extra: Last beacon: 516ms ago
IE: Unknown: 000A6C7766646A665F726164
IE: Unknown: 010882848B9624B0486C
IE: Unknown: 030101
IE: Unknown: 2A0100
IE: Unknown: 2F0100
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
IE: Unknown: 32048C129860
IE: Unknown: DD06001018020004
Cell 02 - Address: 00:14:BF:0C:7E:14
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=30/70 Signal level=-80 dBm
Encryption key:on
ESSID:"linksys"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=000000d993312192
Extra: Last beacon: 380ms ago
IE: Unknown: 00076C696E6B737973
IE: Unknown: 010882848B962430486C
IE: Unknown: 030106
IE: Unknown: 2A0104
IE: Unknown: 2F0104
IE: Unknown: 32040C121860
IE: Unknown: DD06001018020004
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
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