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dhalperi / linux-80211n-csitool-supplementary

802.11n CSI Tool based on iwlwifi and Linux-2.6
http://dhalperi.github.com/linux-80211n-csitool/
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unwraped phase is not linear #411

Open 764398256 opened 5 years ago

764398256 commented 5 years ago

_15414240011553 The unwraped phase should be linear，but not .why? hope your help

KeNopphon commented 5 years ago

Because of the multipath effect in the wireless channel and temporal phase offset/rotation from non-synchonization between two transceiver. If you manually connect tx and rx antennas with cable and measure the CSI, you should get a linear trend of CSI phase.

764398256 commented 5 years ago

@KeNopphon Thank you for your answer. Now，i want to get a more accurate CSI to verify the algorithm. If i manually connect tx and rx antennas with cable of different length and measure the CSI。Can the CSI accurately calculate the angle？

KeNopphon commented 5 years ago

Well, it depends on how much accuracy of CSI you need for your algorithm.

Even though you may avoid the multipath effect with cable connection, the measured CSI does not yet represent the channel. This is because the measured CSI still suffer from the temporal phase offset/rotation from non-synchonization which shift/rotate the CSI. Actually, there are many papers introducing phase offset mitigation algorithms such as phase sanitization, phase difference,. Our recent work also tested the possibility of recovering the CSI with cable connection in https://doi.org/10.3390/s18113795 .

Moreover, if the measurement is conducted with multiple tx antenna (MIMO/MISO), the measured CSI which is classified as the effective CSI (please read the thesis of the developer (Daniel) for the detail http://www.halper.in//) has not yet removed the Spatial matrix (SM) and Cyclic Shift Diversity (CSD). You may remove them first by using get_scaled_csi_sm.m

@KeNopphon Thank you for your answer. Now，i want to get a more accurate CSI to verify the algorithm. If i manually connect tx and rx antennas with cable of different length and measure the CSI。Can the CSI accurately calculate the angle？

764398256 commented 5 years ago

@KeNopphon thank you very much！

764398256 commented 5 years ago

In order to verify the correctness of the algorithm。If i connect 1 Tx and 3 Rx up through the power divider ，the received 3 signals should be the same。So the estimated angle is zero ideally。Is my idea correct?Thank you！ @KeNopphon

KeNopphon commented 5 years ago

Ideally, if there is no phase offset/rotation and considering the power divider is ideal(no reflection signal between ports and have the same gain) at all, you may receive the same signal. I am not sure what do u mean by the estimated angle but I assume it meant the phase difference of CSI between 2 ports which according to the previous sentence assumption could produce the zero CSI phase difference.

However, if you want to verify the correctness of the CSI phase, I think it is better to compare with the result from VNA, SDR instead