Re: [Discuss-gnuradio] ofdm channel estimation

[Martin Braun]

XD,

I'm having real trouble understanding what you're doing.

Try this: generate white noise and put it into the detector. Do you see
any 1s? I would guess no.

M

On 07/15/2014 03:11 PM, xianda wrote:
> Hi Marcus:
>                  Thank you.Sorry for that.
>                  I wrongly use the read_complex_binary to analyse the
> detect at the second time.As I said(But I test again and again,the
> rx_detect don't exist 1.And some little value approach 0 exists.).If I
> use the read_char_binary to analyse the detect.There is 1 under every
> test.I said the truth.It isn't stochastic problems maybe.And I attached
> my modified rx_ofdm.grc.You can run it when no tx signal exist.And you
> will see r_detect.dat will exist 1.(In matlab,use the
> read_char_binary.m).And a1.dat and a.dat isn't null.(In matlab,use the
> read_complex_binary.m).You can test it.Thank you.
>                  Maybe I am wrong,please correct me.Thank you.
> Best regards,
> xd
> 
> 
> 
> 
> 
> At 2014-07-15 08:48:15, "Marcus Müller" <address@hidden> wrote:
> 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 >
>>>>> _______________________________________________
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