[Discuss-gnuradio] Re: Re: Re: what is the rate(sampling) of the impulse response using usrp_sounder.py ?

[Bruhtesfa Ebrahim]

Johnathan Corgan wrote:
> On Tue, Dec 16, 2008 at 8:26 AM, Bruhtesfa Ebrahim 
> <address@hidden> wrote:


>> 1. I tried to monitor the impulse response of the room for 5 sec. So,
>> according to the discussion above(i.e since the FPGA computes impulse
>> response of length 4095,32MHZ in 0.5sec), I will have 10 impulse
>> response vectors in 5sec. But when i set { samples = 10 *
>> self._length**2 in usrp_sounder_rx.py } and run the code, it takes about
>> 160 seconds to complete. So, I am confused. Does the recorded impulse
>> response correspond to 5sec or 160sec?
> 
> I don't understand how you've modified the script to collect 5 seconds 
> of data.

 In the python code usrp_sounder_rx.py the number of impulse response 
vectors is set to 100 by default. I have seen that from the statement ( 
samples = 100 * self._length**2) in class usrp_sounder_rx(gr.top_block). 
I have also experiment with it.Then,I see by reading the file in matlab 
that it really records 100 impulse response vectors or 100*4095 sampled 
values.

 In my case, I want to use PN code of degree 12 and 32MHZ chip rate.And 
this takes 4095*4095/32MHZ=0.5sec to record a single impulse response 
vector (according to our previous discussion). Now, If I want to monitor 
the room for 5sec, I need 5sec/0.5sec=10 impulse response vectors.

  So, I modified the PN code degree, chip rate and number of impulse 
response vectors in usrp_sounder_rx.py. To change the number of impulse 
response vectors to 10, I just used (samples = 10 * self._length**2) 
instead of the default (samples = 100 * self._length**2)in the code.

But, When I run the code, it takes about 160sec to complete instead of 
the expected 5sec.

So, I get confused? Is there a mistake I made ?
or, is there any factor that can delays the computation and recording of 
a single impulse response vector slower than 4095*4095/32MHZ?



>> 2. As, expected there is frequency offset on the received impulse
>> response.  what can i do to synchronize transmitter and receiver
>> daughter boards?     Thanks!
> 
> You will need to use a stable time reference like a GPSDO on both the
> transmitter and receiver.

Is there any method of synchronization by just wiring the transmit and 
receive daughter boards together?

Thanks for your help!
Bruhtesfa



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