* Re: [RFC] RCPI support in radiotap and in our wireless subsystems
[not found] ` <43e72e890803061238u50847f1fs587627c5fac028d6-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
@ 2008-03-06 20:55 ` Ivo van Doorn
2008-03-07 0:32 ` bruno randolf
1 sibling, 0 replies; 6+ messages in thread
From: Ivo van Doorn @ 2008-03-06 20:55 UTC (permalink / raw)
To: Luis R. Rodriguez
Cc: linux-wireless, radiotap-rN9S6JXhQ+WXmMXjJBpWqg, Ivan Seskar,
Haris Kremo, John W. Linville, Simon Barber, Dan Williams,
Luis Carlos Cobo, Javier Cardona, Sam Leffler, Jean Tourrilhes,
Stefano Brivio, Johannes Berg
Hi.
> ---
>
> For ipw2200:
>
> s8 antsignal = frame->rssi_dbm - IPW_RSSI_TO_DBM;
>
> and IPW_RSSI_TO_DBM is set to 112.
>
> Is antsignal above the "measure by the PHY sublayer of the received RF
> power in the channel measured over the entire received frame"?
For completeness, the rt2x00 & RSSI:
rt2400pci, rt2500pci, rt2500usb:
Same as ipw2200 only the IPW_RSSI_TO_DBM varies from 100 to 120 (as
hardcoded value in the register) to a unsigned char value read from
the EEPROM. The legacy drivers _suggest_ this is the rssi...
rt61pci, rt73usb:
The device reports an agc value, this is used as basis for a vague calculation
to determine the RSSI_TO_DBM offset based on LNA and current operating band.
Here too, the legacy driver suggests this is the rssi...
Ivo
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] RCPI support in radiotap and in our wireless subsystems
[not found] ` <43e72e890803061238u50847f1fs587627c5fac028d6-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2008-03-06 20:55 ` [RFC] RCPI support in radiotap and in our wireless subsystems Ivo van Doorn
@ 2008-03-07 0:32 ` bruno randolf
1 sibling, 0 replies; 6+ messages in thread
From: bruno randolf @ 2008-03-07 0:32 UTC (permalink / raw)
To: Luis R. Rodriguez
Cc: linux-wireless, radiotap-rN9S6JXhQ+WXmMXjJBpWqg, Ivan Seskar,
Haris Kremo, John W. Linville, Simon Barber, Dan Williams,
Luis Carlos Cobo, Javier Cardona, Sam Leffler, Jean Tourrilhes,
Stefano Brivio, Johannes Berg
On Friday 07 March 2008 05:38:45 Luis R. Rodriguez wrote:
> I've been reviewing use or RSSI value, signal strength and noise on
> several Linux drivers, namely MadWifi, ath5k, ipw2200 and b43, and how
> these are populated using radiotap headers. It quickly became clear we
> should probably abandon RSSI's use in radiotap and slowly move to
> using RCPI [1] for both radiotap and for later use on our wireless
> subsystems. Reasons for doing so is:
i think it's worth the effort to try to clean up this mess and get some
standardisation between the devices as far as possible but i'm afraid we are
at the mercy of the values the hardware gives us and the information we get
from hardware vendors about the meaning of these values.
> a. Currently Radiotap's definition and use of
> IEEE80211_RADIOTAP_DB_ANTSIGNAL and IEEE80211_RADIOTAP_DBM_ANTSIGNAL
> is not so clear
i think it's quite clear, except that it does not state when this signal is
supposed to be measured.
if all devices could use this in the same way that would already be great!
> For Atheros hardware:
>
> RSSI is defined to be equivalent to the Signal To Noise (SNR) [3] and
>
> SNR = Signal - Noise
>
> Now, this is great, however the next question is what Signal is and
> what Noise is. Is Signal or SNR here the "measure by the PHY sublayer
> of the received RF power in the channel measured over the entire
> received frame"?
no, according to the information we have from madwifi it is not:
/*
* rx_rssi is in units of dbm above the noise floor. This value
* is measured during the preamble and PLCP; i.e. with the initial
* 4us of detection.
*/
(this is copied from a comment in hal/ah_desc.h)
> So I propose IEEE80211_RADIOTAP_RCPI, defined as above, and hopefully
> we can start figuring out what exactly RSSI values are in the
> different cards we support to compute this. Comments?
it's good to extend radiotap to include this possibility, but at least for
atheros hardware we know we can't supply this value (unless newer devices
allow us to get a RCPI value somehow, but we probably would need atheros
support to know that).
it would already be an important step to better define the variables inside
mac80211, so drivers can report what they support (and mac80211 can make the
translations to the weird values iwconfig uses).
right now the variable names inside mac80211 are really ambigous and not very
well defined. in struct ieee80211_rx_status we have:
* @ssi: signal strength when receiving this frame
* @signal: used as 'qual' in statistics reporting
* @noise: PHY noise when receiving this frame
it could be changed to something like:
* @signal: signal strength in dBm above noise or RCPI according to flag
* @noise: PHY noise in dBm when receiving this frame
(remove ssi)
bruno
^ permalink raw reply [flat|nested] 6+ messages in thread
[parent not found: <200803070932.51396.bruno@thinktube.com>]
* [RFC] RCPI support in radiotap and in our wireless subsystems
@ 2008-03-06 20:38 Luis R. Rodriguez
0 siblings, 0 replies; 6+ messages in thread
From: Luis R. Rodriguez @ 2008-03-06 20:38 UTC (permalink / raw)
To: linux-wireless, radiotap-rN9S6JXhQ+WXmMXjJBpWqg
Cc: Ivan Seskar, Haris Kremo, John W. Linville, Simon Barber,
Dan Williams, Luis Carlos Cobo, Javier Cardona, Sam Leffler,
Jean Tourrilhes, Stefano Brivio, Johannes Berg
I've been reviewing use or RSSI value, signal strength and noise on
several Linux drivers, namely MadWifi, ath5k, ipw2200 and b43, and how
these are populated using radiotap headers. It quickly became clear we
should probably abandon RSSI's use in radiotap and slowly move to
using RCPI [1] for both radiotap and for later use on our wireless
subsystems. Reasons for doing so is:
a. Currently Radiotap's definition and use of
IEEE80211_RADIOTAP_DB_ANTSIGNAL and IEEE80211_RADIOTAP_DBM_ANTSIGNAL
is not so clear and it seems different drivers set it to different
values. MadWifi uses DB_ANTSIGNAL for RSSI, ath5k uses DB_ANTSIGNAL as
RSSI + noise, ipw2200 doesn't set it despite it having a value which
can be used for it. The b43 driver, although like ath5k is a mac80211
driver, uses DB_ANTSIGNAL as:
status.ssi = b43_rssi_postprocess(dev, jssi,
(phystat0 & B43_RX_PHYST0_OFDM),
(phystat0 & B43_RX_PHYST0_GAINCTL),
(phystat3 & B43_RX_PHYST3_TRSTATE));
We have no clue what jssi is, nor what this yields, yet we use it.
b. For roaming purposes we need to standardize on a value so that the
upper layers can reliably count on for signal strength and I believe
RCPI was defined for just that purpose
c. For strong subsystem rate control algorithms we need to count on
reliable signal strength values. Right now mac80211's PID rate control
algorithm [2] doesn't make use of signal strength, it just uses
non-acked frames and re-transmission counters. I would think using
signal strength here might help somehow.
However, to support RCPI it seems you need to rely on a way to
accurately compute signal strength, but more accurately "received RF
power in the selected channel for a received frame. This parameter
shall be a measure by the PHY sublayer of the received RF power in the
channel measured over the entire received frame or by other equivalent
means which meet the specified accuracy". I've tried reviewing RSSI
value for a few hardware out there to see if we can easily start
adding support for this in our drivers but I am not confident in the
exact value that RSSI represents as it varies on hardware and there is
an obvious the lack of documentation in that area.
---
For Atheros hardware:
RSSI is defined to be equivalent to the Signal To Noise (SNR) [3] and
SNR = Signal - Noise
Now, this is great, however the next question is what Signal is and
what Noise is. Is Signal or SNR here the "measure by the PHY sublayer
of the received RF power in the channel measured over the entire
received frame"? Noise is computed upon noise calibration time, and I
think its computed during SIFS time, but I haven't yet finished
reading the patent that describes this stuff yet [4] so not too sure.
I guess its not important as long as we can rely on the value.
---
For ipw2200:
s8 antsignal = frame->rssi_dbm - IPW_RSSI_TO_DBM;
and IPW_RSSI_TO_DBM is set to 112.
Is antsignal above the "measure by the PHY sublayer of the received RF
power in the channel measured over the entire received frame"?
----
For Broadcom:
We have something called jssi and then get what we think is an RSSI
value. We don't know what either of them are.
status.ssi = b43_rssi_postprocess(dev, jssi,
(phystat0 & B43_RX_PHYST0_OFDM),
(phystat0 & B43_RX_PHYST0_GAINCTL),
(phystat3 & B43_RX_PHYST3_TRSTATE));
---
At least RCPI seems to be well defined, and I think we can add it to
radiotap for those drivers that can reliably compute this value.
Quoting from Simon's post:
"The allowed values for the Received Channel Power Indicator (RCPI) parameter
shall be an 8 bit value in the range from 0 through 220, with indicated
values rounded to the nearest 0.5 dB as follows:
0: Power < -110 dBm
1: Power = -109.5 dBm
2: Power = -109.0 dBm
and so on where
RCPI = int{(Power in dBm +110)*2} for 0dbm > Power > -110dBm
220: Power > -0 dBm
221-254: reserved
255: Measurement not available
RCPI shall equal the received RF power within an accuracy of +/-5 dB
(95% confidence interval) within the specified dynamic range of the
receiver. The received RF power shall be determined assuming a receiver
noise equivalent bandwidth equal to the channel bandwidth multiplied by
1.1."
So I propose IEEE80211_RADIOTAP_RCPI, defined as above, and hopefully
we can start figuring out what exactly RSSI values are in the
different cards we support to compute this. Comments?
Luis
[1] http://www.mail-archive.com/netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg19487.html
[2] http://linuxwireless.org/en/developers/Documentation/mac80211/RateControl/PID
[3] http://madwifi.org/wiki/UserDocs/RSSI
[4] http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=7245893.PN.&OS=PN/7
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2008-03-07 15:41 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <43e72e890803061238u50847f1fs587627c5fac028d6@mail.gmail.com>
[not found] ` <43e72e890803061238u50847f1fs587627c5fac028d6-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2008-03-06 20:55 ` [RFC] RCPI support in radiotap and in our wireless subsystems Ivo van Doorn
2008-03-07 0:32 ` bruno randolf
[not found] ` <200803070932.51396.bruno@thinktube.com>
[not found] ` <200803070932.51396.bruno-L9ZBdB2wSWtl57MIdRCFDg@public.gmane.org>
2008-03-07 3:04 ` Luis R. Rodriguez
[not found] ` <43e72e890803061904h742df37fuaa12977c45e457a@mail.gmail.com>
[not found] ` <43e72e890803061904h742df37fuaa12977c45e457a-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2008-03-07 8:57 ` bruno randolf
[not found] ` <200803071757.19302.bruno@thinktube.com>
[not found] ` <200803071757.19302.bruno-L9ZBdB2wSWtl57MIdRCFDg@public.gmane.org>
2008-03-07 15:41 ` Luis R. Rodriguez
2008-03-06 20:38 Luis R. Rodriguez
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).