[ath9k-devel] linearity of ath9k CSI phase

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 <[email protected]>:

> 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 <[email protected]> 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 <[email protected]>:
>>
>>> 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 <[email protected]> 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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