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[<bogus@does.not.exist.com>]

seems to be effective. But I'm not sure.
And sometimes, some phase measurement show large dispalcement along y-axis
even they are captured within very short duration.

Hence the question is,
Is ath9k reports CSI with those unwanted linear phase offset removed?
If it is not, should I look into Atheros CSI tool? As I look into it, it
just captures CSI from the kernel and does not modify it.
Or, Is CSI of Atheros different form that of Intel? I don't think so...

The final goal of extracting true phase from CSI of ath9k is to determine
angle of arrival (AoA) of signal.

Regards,
Jeon.

[1]: http://pdcc.ntu.edu.sg/wands/Atheros/ "Atheros CSI Extraction Tool"
[2] K. Qian, C. Wu, Z. Yang, Y. Liu, and Z. Zhou, =E2=80=9CPADS: Passive de=
tection
of moving targets with dynamic speed using PHY layer information,=E2=80=9D =
in 2014
20th IEEE International Conference on Parallel and Distributed Systems
(ICPADS), 2014, pp. 1=E2=80=938.
[3] M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, =E2=80=9CSpotFi: Decime=
ter
Level Localization Using WiFi,=E2=80=9D SIGCOMM Comput. Commun. Rev., vol. =
45, no.
4, pp. 269=E2=80=93282, Aug. 2015.
[4] http://dhalperi.github.io/linux-80211n-csitool/ "Linux 802.11n CSI
Tool"

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<div dir=3D"ltr">Dear ath9k developers,<br><br>I am currently working with =
Atheros CSI Extraction Tool [1] to get a true phase of each subcarrier.<br>=
<br>- Background<br><br>[2], [3] and many other papers claim that phase inf=
ormation from extracted CSI contains two components: true phase and unwante=
d phase offset due to subcarrier and time delay.<br>i.e., measured_phase =
=3D true_phase + time_delay * subcarrier_index + phase_offset_due_to_txrx_m=
ismatch<br>This equation can be visualized as below:<br><br><a href=3D"http=
://i.imgur.com/rk9Hh1M.png">http://i.imgur.com/rk9Hh1M.png</a><br><br>(Plea=
se note that this figure is based on CSI tool for Intel 5300 NIC.)<br><br>I=
t contains unwanted linear phase offset and constant phase offset. Since th=
e true phase is relatively small, it seems that phase is monotonically incr=
easing or decreasing in macro view due to the unwanted phase offsets. We ca=
nnot see a tiny true phase currently.<div><div><br>To remove phase offset d=
ue to subcarrier, the mentioned papers are attempting to remove it with lin=
ear fitting ax + b,<br>where a =3D slope of the figure, b =3D average of me=
asured phase, and x =3D subcarrier index.<br><br>After removing unwanted ph=
ase offset components, the true phase is estimated.<br>This estimated true =
phase seems steady and consistent across a time duration shorter than &lt; =
100 - 1000 ms:<br><br><a href=3D"http://i.imgur.com/AO89vYV.png">http://i.i=
mgur.com/AO89vYV.png</a><br><br>Note that Y-axis scale is reduece from [-50=
, 10] to [5, -3]<br><br>- My question<br><br>I want to extract and manipula=
te CSI phase WITH ATH9K NIC.<br><br>After extracting CSI from my ath9k NIC =
(AR9580 @ 2.4 GHz) with Atheros CSI extraction tool,<br>I&#39;ve tried vari=
ous fitting methods to eliminate unwanted components and stacked results fr=
om nearly 100 packets:<br><br><a href=3D"http://i.imgur.com/5r9eYwO.png">ht=
tp://i.imgur.com/5r9eYwO.png</a><br><br>From the result, in short, removing=
 only constant offset across subcarrier seems to be effective. But I&#39;m =
not sure.</div><div>And sometimes, some phase measurement show large dispal=
cement along y-axis even they are captured within very short duration.<br><=
br>Hence the question is,</div><div>Is ath9k reports CSI with those unwante=
d linear phase offset removed?</div><div>If it is not, should I look into A=
theros CSI tool? As I look into it, it just captures CSI from the kernel an=
d does not modify it.</div><div>Or, Is CSI of Atheros different form that o=
f Intel? I don&#39;t think so...</div><div><br></div><div>The final goal of=
 extracting true phase from CSI of ath9k is to determine angle of arrival (=
AoA) of signal.<br><br>Regards,<br>Jeon.<br><br>[1]: <a href=3D"http://pdcc=
.ntu.edu.sg/wands/Atheros/">http://pdcc.ntu.edu.sg/wands/Atheros/</a> &quot=
;Atheros CSI Extraction Tool&quot;<br>[2] K. Qian, C. Wu, Z. Yang, Y. Liu, =
and Z. Zhou, =E2=80=9CPADS: Passive detection of moving targets with dynami=
c speed using PHY layer information,=E2=80=9D in 2014 20th IEEE Internation=
al Conference on Parallel and Distributed Systems (ICPADS), 2014, pp. 1=E2=
=80=938.<br>[3] M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, =E2=80=9CSp=
otFi: Decimeter Level Localization Using WiFi,=E2=80=9D SIGCOMM Comput. Com=
mun. Rev., vol. 45, no. 4, pp. 269=E2=80=93282, Aug. 2015.<br>[4] <a href=
=3D"http://dhalperi.github.io/linux-80211n-csitool/">http://dhalperi.github=
.io/linux-80211n-csitool/</a> &quot;Linux 802.11n CSI Tool&quot;
</div></div></div>

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