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

[Bruhtesfa Ebrahim]

Johnathan Corgan wrote:

> 
> The custom FPGA code performs the correlation in the USRP.  The
> algorithm is a sequential correlator that processes an entire PN code
> sequence per impulse reponse lag time.  So the data rate coming out of
> the USRP is 64 Msps (ADC rate) divided by 8190 samples per PN sequence
> (default degree of 12), or about 7.8 ksps.  Since each record is 4095
> samples long, this outputs a full impulse response record about twice
> a second.
> 
> The impulse response record still represents the original 32 Mchip/sec
> correlation, so in your received data, each sample represents a lag of
> about 31.25 ns.
> 
> -Johnathan



Thank you for the replies Johnathan!!!

But, i still get some problems when i experiment with it.

My objective is to measure impulse response of a room and extract 
information on the movement of people inside the room.

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?

2. As, expected there is frequency offset on the received impulse 
response.  what can i do to synchronize transmitter and receiver 
daughter boards?     Thanks!

Bruhtesfa



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