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 <j...@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+at...@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 <j...@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+at...@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@lists.ath9k.org >>>> https://lists.ath9k.org/mailman/listinfo/ath9k-devel >>>> >>>> >>> >> >> _______________________________________________ >> ath9k-devel mailing list >> ath9k-devel@lists.ath9k.org >> https://lists.ath9k.org/mailman/listinfo/ath9k-devel >> >> >
_______________________________________________ ath9k-devel mailing list ath9k-devel@lists.ath9k.org https://lists.ath9k.org/mailman/listinfo/ath9k-devel
