Re: [Discuss-gnuradio] Re channel state information on rx_ofdm.grc

[Marcus Müller]

Hi Avinash,

On 06/16/2016 03:29 PM, avinash kalyanaraman wrote:

i) These 64 complex values (a + ib) represent the 64 sub-carriers and I can get the amplitude and phase of each sub-carrier as sqrt( a^2 + b^2) and arctan(b/a) respectively ?

Yes.

ii) I see that the CSI calculation is per tag. I understand from your link that the tag represents additional information/metadata attached to a specific item. However, in this case, I am unsure what a tag denotes? In other words, could you please tell me what a “tag” is being attached to here, on which a channel estimate is calculated?

If I remember correctly:
To the first sample of the "chunk" of samples that were used for estimation, that is, on the first sample of the OFDM symbol.

I do think that if you're into channel estimation, reading the source code is very much worth your time, and you'll notice variable and method names were chosen sensibly to make understanding what's happening easier. Go for the get_chan_taps() method in ofdm_chanest_vcvc_impl.cc; you'll find it in your GNU Radio source tree; be sure to use a recent version of GNU Radio (3.7.7 or later).

iii) Please let me know what is the unit of rx_time ? Seconds?

  Offset: 76  Source: n/a     Key: rx_time   Value: {7 0.303}

  Offset: 77  Source: n/a     Key: rx_time   Value: {7 0.399}

http://gnuradio.org/doc/doxygen/page_uhd.html

look for "timestamp" on that page.

Best regards,
Marcus