Re: [Discuss-gnuradio] ofdm channel estimation

[Marcus Müller]

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Hi Xianda,

how should we possibly tell? You expect us to be able to guess what is
going wrong with your measurement, in an environment that is unknown
to us, using a receiving antenna, modified flowgraph and tx signal
that you did not really define.

As Martin said, if a detector outputs a 1, it might be a false alarm,
also known as bad luck.

With stochastic problems, you always have to make a trade off between
false alarm rate and type II errors. This is called receiver operating
characteristic. With most detectors, you can adjust their parameters
to accommodate your false alarm rate/detection rate needs.

Greetings,
Marcus



On 15.07.2014 12:56, xianda wrote:
> Oh,I guess that because i receive signal which at the frequency of
> 2.45e9.It is like the wifi.May be I receive the wifi signal?Am i
> right? Thank you.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> At 2014-07-15 05:17:35, "Martin Braun" <address@hidden>
> wrote:
>> On 07/15/2014 09:39 AM, xianda wrote:
>>> Hi Martin: Thank you for your kindly reply. Another question I
>>> want to ask. When I use the rx_ofdm,I add a UHD:USRP 
>>> Source.(Environment: USRP N210)I know when the block Schmidl
>>> &Cox OFDM synch. detect the signal,the port "detect" will
>>> output 1.And I test it.I use the rx_ofdm when I don't use the
>>> tx_ofdm.It means that no signal exist.But I find 1 in the port
>>> "detect".Why?When no signal exist,it should output 0.Why I see
>>> 1 from it?
>> 
>> ...bad luck? It's not impossible to generate false alarms. What
>> did you feed the block?
>> 
>> Martin
>> 
>> 
>> 
>>> Thank you so much. Best regards, xd
>>> 
>>> 
>>> 
>>> 
>>> At 2014-07-14 04:37:37, "Martin Braun" <address@hidden>
>>> wrote:
>>>> On 07/13/2014 01:06 PM, xianda wrote: >> Hi all: >> Have you
>>>> ever using
>>> the >> gnuradio/gr-digital/examples/ofdm/rx_ofdm.grc?And I
>>> change the >> rx_ofdm.py as follows: >> 
>>> self.connect((self.digital_ofdm_chanest_vcvc_0, 1), >> 
>>> blocks.file_sink(gr.sizeof_gr_complex * fft_len, 
>>> 'channel-estimate.dat')) >> And i use the matlab: > >Please
>>> read the fine manual:
>>>> http://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1ofdm__chanest__vcvc.html#details.
>>>>>
>>>> 
The channel estimate is on a tag. > >M >
>>>> _______________________________________________
>>>> >Discuss-gnuradio
>>> mailing list >address@hidden
>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradi
>>> 
>>> 
>> 
>> 
>> _______________________________________________ Discuss-gnuradio
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