[ath9k-devel] linearity of ath9k CSI phase

[ath9k-devel] linearity of ath9k CSI phase

[Jeon]

Dear ath9k developers,

I am currently working with Atheros CSI Extraction Tool [1] to get a true
phase of each subcarrier.

- Background

[2], [3] and many other papers claim that phase information from extracted
CSI contains two components: true phase and unwanted phase offset due to
subcarrier and time delay.
i.e., measured_phase = true_phase + time_delay * subcarrier_index +
phase_offset_due_to_txrx_mismatch
This equation can be visualized as below:

http://i.imgur.com/rk9Hh1M.png

(Please note that this figure is based on CSI tool for Intel 5300 NIC.)

It contains unwanted linear phase offset and constant phase offset. Since
the true phase is relatively small, it seems that phase is monotonically
increasing or decreasing in macro view due to the unwanted phase offsets.
We cannot see a tiny true phase currently.

To remove phase offset due to subcarrier, the mentioned papers are
attempting to remove it with linear fitting ax + b,
where a = slope of the figure, b = average of measured phase, and x =
subcarrier index.

After removing unwanted phase offset components, the true phase is
estimated.
This estimated true phase seems steady and consistent across a time
duration shorter than < 100 - 1000 ms:

http://i.imgur.com/AO89vYV.png

Note that Y-axis scale is reduece from [-50, 10] to [5, -3]

- My question

I want to extract and manipulate CSI phase WITH ATH9K NIC.

After extracting CSI from my ath9k NIC (AR9580 @ 2.4 GHz) with Atheros CSI
extraction tool,
I've tried various fitting methods to eliminate unwanted components and
stacked results from nearly 100 packets:

http://i.imgur.com/5r9eYwO.png

[ath9k-devel] linearity of ath9k CSI phase

[Jeon]

Dear Joe Ayers,
Thank you for response.

I don't have a sort of RF anechoic chamber. So, I've captured CSI in a
quite realistic and practical environemnt with possible interference and
multipath components. There are other WLAN APs, Bluetooth devices. Also,
there exist desks, chairs and walls as reflectors.

Yet, I don't think it does matter to capture CSI and estimate true phase.
My attempts are based on a couple of papers which have done estimating true
phase and AoA of a signal with uniform linear antenna array (ULA) in a
realistic and practical living environment [1, 2, 3]. Which means, those
papers claim that they can identify directpath component and multipath
components with MUSIC algorithm [4].

One suspicious thing is, I think distance between antennas of ULA is
misconfigured. I placed them 6.5 cm apart from each other. With
calculation, a half of wavelength at 2.4 GHz band is less than 6.25 cm.
Does it matter a lot?

Regards,
Jeon.

[1]: K. Qian, C. Wu, Z. Yang, Y. Liu, and Z. Zhou, ?PADS: Passive detection
of moving targets with dynamic speed using PHY layer information,? in 2014
20th IEEE International Conference on Parallel and Distributed Systems
(ICPADS), 2014, pp. 1?8.
[2]: J. Xiong and K. Jamieson, ?ArrayTrack: A Fine-Grained Indoor Location
System,? in Presented as part of the 10th USENIX Symposium on Networked
Systems Design and Implementation (NSDI 13), Lombard, IL, 2013, pp. 71?84.
[3]: M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, ?SpotFi: Decimeter
Level Localization Using WiFi,? SIGCOMM Comput. Commun. Rev., vol. 45, no.
4, pp. 269?282, Aug. 2015.
[4]: R. Schmidt, ?Multiple emitter location and signal parameter
estimation,? IEEE Transactions on Antennas and Propagation, vol. 34, no. 3,
pp. 276?280, Mar. 1986.

2016-06-14 3:28 GMT+09:00 Joe Ayers <joe@ayerscasa.com>:

> Jeon,
>
> "only constant offset across subcarrier seems to be effective".    Could
> this be because there's not just one signal being received anymore, rather
> with microwaves, particularly with lots of nearby reflection surfaces,
> there's now ~10 signals bouncing in to the receive antenna at 10
> AoA's--some with 2x the distance-delay traveled--and resonance/nulls
> occurring?  How perfect is your test environment?
>
> Joe AE6XE
>
> On Mon, Jun 13, 2016 at 10:00 AM, Jeon <sjeon87+ath9k@gmail.com> wrote:
>
>> Dear ath9k developers,
>>
>> I am currently working with Atheros CSI Extraction Tool [1] to get a true
>> phase of each subcarrier.
>>
>> - Background
>>
>> [2], [3] and many other papers claim that phase information from
>> extracted CSI contains two components: true phase and unwanted phase offset
>> due to subcarrier and time delay.
>> i.e., measured_phase = true_phase + time_delay * subcarrier_index +
>> phase_offset_due_to_txrx_mismatch
>> This equation can be visualized as below:
>>
>> http://i.imgur.com/rk9Hh1M.png
>>
>> (Please note that this figure is based on CSI tool for Intel 5300 NIC.)
>>
>> It contains unwanted linear phase offset and constant phase offset. Since
>> the true phase is relatively small, it seems that phase is monotonically
>> increasing or decreasing in macro view due to the unwanted phase offsets.
>> We cannot see a tiny true phase currently.
>>
>> To remove phase offset due to subcarrier, the mentioned papers are
>> attempting to remove it with linear fitting ax + b,
>> where a = slope of the figure, b = average of measured phase, and x =
>> subcarrier index.
>>
>> After removing unwanted phase offset components, the true phase is
>> estimated.
>> This estimated true phase seems steady and consistent across a time
>> duration shorter than < 100 - 1000 ms:
>>
>> http://i.imgur.com/AO89vYV.png
>>
>> Note that Y-axis scale is reduece from [-50, 10] to [5, -3]
>>
>> - My question
>>
>> I want to extract and manipulate CSI phase WITH ATH9K NIC.
>>
>> After extracting CSI from my ath9k NIC (AR9580 @ 2.4 GHz) with Atheros
>> CSI extraction tool,
>> I've tried various fitting methods to eliminate unwanted components and
>> stacked results from nearly 100 packets:
>>
>> http://i.imgur.com/5r9eYwO.png
>>
>> From the result, in short, removing only constant offset across
>> subcarrier 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, ?PADS: Passive
>> detection of moving targets with dynamic speed using PHY layer
>> information,? in 2014 20th IEEE International Conference on Parallel and
>> Distributed Systems (ICPADS), 2014, pp. 1?8.
>> [3] M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, ?SpotFi: Decimeter
>> Level Localization Using WiFi,? SIGCOMM Comput. Commun. Rev., vol. 45, no.
>> 4, pp. 269?282, Aug. 2015.
>> [4] http://dhalperi.github.io/linux-80211n-csitool/ "Linux 802.11n CSI
>> Tool"
>>
>> _______________________________________________
>> ath9k-devel mailing list
>> ath9k-devel at lists.ath9k.org
>> https://lists.ath9k.org/mailman/listinfo/ath9k-devel
>>
>>
>
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[ath9k-devel] linearity of ath9k CSI phase

[Jeon]

Dear Joe Ayers

Thanks for your response again.
I started studying and investigating on antennas theories.

Regards,
Jeon.

2016-06-14 14:19 GMT+09:00 Joe Ayers <joe@ayerscasa.com>:

> This increased spacing looks to impact the detection angle before aliasing
> occurs with grating lobes.   Google around, but looks like 1/2 wave length
> spacing gives full +/-90 deg.  Going up to 1 wave length spacing reduces
> the detection angle to +/-30 deg before aliasing.
>
>
>
> On Mon, Jun 13, 2016 at 8:39 PM, Jeon <sjeon87+ath9k@gmail.com> wrote:
>
>> Dear Joe Ayers,
>> Thank you for response.
>>
>> I don't have a sort of RF anechoic chamber. So, I've captured CSI in a
>> quite realistic and practical environemnt with possible interference and
>> multipath components. There are other WLAN APs, Bluetooth devices. Also,
>> there exist desks, chairs and walls as reflectors.
>>
>> Yet, I don't think it does matter to capture CSI and estimate true phase.
>> My attempts are based on a couple of papers which have done estimating true
>> phase and AoA of a signal with uniform linear antenna array (ULA) in a
>> realistic and practical living environment [1, 2, 3]. Which means, those
>> papers claim that they can identify directpath component and multipath
>> components with MUSIC algorithm [4].
>>
>> One suspicious thing is, I think distance between antennas of ULA is
>> misconfigured. I placed them 6.5 cm apart from each other. With
>> calculation, a half of wavelength at 2.4 GHz band is less than 6.25 cm.
>> Does it matter a lot?
>>
>> Regards,
>> Jeon.
>>
>> [1]: K. Qian, C. Wu, Z. Yang, Y. Liu, and Z. Zhou, ?PADS: Passive
>> detection of moving targets with dynamic speed using PHY layer
>> information,? in 2014 20th IEEE International Conference on Parallel and
>> Distributed Systems (ICPADS), 2014, pp. 1?8.
>> [2]: J. Xiong and K. Jamieson, ?ArrayTrack: A Fine-Grained Indoor
>> Location System,? in Presented as part of the 10th USENIX Symposium on
>> Networked Systems Design and Implementation (NSDI 13), Lombard, IL, 2013,
>> pp. 71?84.
>> [3]: M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, ?SpotFi: Decimeter
>> Level Localization Using WiFi,? SIGCOMM Comput. Commun. Rev., vol. 45, no.
>> 4, pp. 269?282, Aug. 2015.
>> [4]: R. Schmidt, ?Multiple emitter location and signal parameter
>> estimation,? IEEE Transactions on Antennas and Propagation, vol. 34, no. 3,
>> pp. 276?280, Mar. 1986.
>>
>> 2016-06-14 3:28 GMT+09:00 Joe Ayers <joe@ayerscasa.com>:
>>
>>> Jeon,
>>>
>>> "only constant offset across subcarrier seems to be effective".    Could
>>> this be because there's not just one signal being received anymore, rather
>>> with microwaves, particularly with lots of nearby reflection surfaces,
>>> there's now ~10 signals bouncing in to the receive antenna at 10
>>> AoA's--some with 2x the distance-delay traveled--and resonance/nulls
>>> occurring?  How perfect is your test environment?
>>>
>>> Joe AE6XE
>>>
>>> On Mon, Jun 13, 2016 at 10:00 AM, Jeon <sjeon87+ath9k@gmail.com> wrote:
>>>
>>>> Dear ath9k developers,
>>>>
>>>> I am currently working with Atheros CSI Extraction Tool [1] to get a
>>>> true phase of each subcarrier.
>>>>
>>>> - Background
>>>>
>>>> [2], [3] and many other papers claim that phase information from
>>>> extracted CSI contains two components: true phase and unwanted phase offset
>>>> due to subcarrier and time delay.
>>>> i.e., measured_phase = true_phase + time_delay * subcarrier_index +
>>>> phase_offset_due_to_txrx_mismatch
>>>> This equation can be visualized as below:
>>>>
>>>> http://i.imgur.com/rk9Hh1M.png
>>>>
>>>> (Please note that this figure is based on CSI tool for Intel 5300 NIC.)
>>>>
>>>> It contains unwanted linear phase offset and constant phase offset.
>>>> Since the true phase is relatively small, it seems that phase is
>>>> monotonically increasing or decreasing in macro view due to the unwanted
>>>> phase offsets. We cannot see a tiny true phase currently.
>>>>
>>>> To remove phase offset due to subcarrier, the mentioned papers are
>>>> attempting to remove it with linear fitting ax + b,
>>>> where a = slope of the figure, b = average of measured phase, and x =
>>>> subcarrier index.
>>>>
>>>> After removing unwanted phase offset components, the true phase is
>>>> estimated.
>>>> This estimated true phase seems steady and consistent across a time
>>>> duration shorter than < 100 - 1000 ms:
>>>>
>>>> http://i.imgur.com/AO89vYV.png
>>>>
>>>> Note that Y-axis scale is reduece from [-50, 10] to [5, -3]
>>>>
>>>> - My question
>>>>
>>>> I want to extract and manipulate CSI phase WITH ATH9K NIC.
>>>>
>>>> After extracting CSI from my ath9k NIC (AR9580 @ 2.4 GHz) with Atheros
>>>> CSI extraction tool,
>>>> I've tried various fitting methods to eliminate unwanted components and
>>>> stacked results from nearly 100 packets:
>>>>
>>>> http://i.imgur.com/5r9eYwO.png
>>>>
>>>> From the result, in short, removing only constant offset across
>>>> subcarrier 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, ?PADS: Passive
>>>> detection of moving targets with dynamic speed using PHY layer
>>>> information,? in 2014 20th IEEE International Conference on Parallel and
>>>> Distributed Systems (ICPADS), 2014, pp. 1?8.
>>>> [3] M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, ?SpotFi: Decimeter
>>>> Level Localization Using WiFi,? SIGCOMM Comput. Commun. Rev., vol. 45, no.
>>>> 4, pp. 269?282, Aug. 2015.
>>>> [4] http://dhalperi.github.io/linux-80211n-csitool/ "Linux 802.11n CSI
>>>> Tool"
>>>>
>>>> _______________________________________________
>>>> ath9k-devel mailing list
>>>> ath9k-devel at lists.ath9k.org
>>>> https://lists.ath9k.org/mailman/listinfo/ath9k-devel
>>>>
>>>>
>>>
>>
>> _______________________________________________
>> ath9k-devel mailing list
>> ath9k-devel at lists.ath9k.org
>> https://lists.ath9k.org/mailman/listinfo/ath9k-devel
>>
>>
>
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