Thanks Marcus.
Following up on the rx_time format, I notice from the link that the
timestamp format is the same as uhd::time_spec_t . Therefore the timestamp
printed out on a tag is of the form: full_seconds and a fractional_seconds.
For e.g., I see: Offset: 667 Source: n/a Key: rx_time Value: {2317
0.394114}
2317 is the full second and 0.39 is the fraction of that 2317th second ?
Could you please tell me what these seconds calculated are with respect to
- i.e. 2317 seconds since when ?
When does the fraction of second roll over?
For example, I see:
Offset: 1034 Source: n/a Key: rx_time Value: {2317 1.39162}
Offset: 1035 Source: n/a Key: rx_time Value: {2318 0.393495}
What does it mean to have a fraction of 1.39 of a second ?
Thanks!
On Fri, Jun 17, 2016 at 1:12 PM, Marcus Müller <[email protected]>
wrote:
> Hi Avinash,
>
> that's pretty much a basic OFDM question:
>
> You take the DFT of the input signal. Hence, the bins of the DFT are
> f_nyquist/l_fft spaced.
>
> Best regards,
>
> Marcus
> On 17.06.2016 17:57, avinash kalyanaraman wrote:
>
> Thanks Marcus - that helps.
>
> Could you please let me know what's the bandwidth of each sub-carrier? How
> can I calculate that and reconfigure the same?
>
>
> On Sat, Jun 18, 2016 at 12:50 AM, Marcus Müller <[email protected]>
> wrote:
>
>> 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
>>
>
>
>
> --
> Avinash
>
>
>
--
Avinash
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