Re: [Discuss-gnuradio] Sounding signal output power and spectrum

[Qi Chen]

On Dec 1, 2008, at 2:24 PM, Johnathan Corgan wrote:

> On Sat, Nov 29, 2008 at 9:55 AM, Qi Chen <address@hidden> wrote:
>
> > 1. The gr-sounder default transmit amplitude is 4096, is there a  
> > particular
> > reason why this number is chosen? My guess is because a 12-bit DAC  
> > is used.
>
> You are correct.  This app uses a custom FPGA image for transmission,
> and unlike most GNU Radio applications, the amplitude here is directly
> converted to the DAC output values.  This is the maximum amplitude.

That makes sense. Do those measured output power values make sense?

> > 3. I did a indoor measurement with TX-RX separation of 50 meters  
> > (w/ LOS),
> > the received channel impulse response has 5 chunks of CIRs instead  
> > of one,
> > and the number of samples between each chunk is always 800 chips,  
> > I am sure
> > those CIRs are not multipath delays since in an indoor environment  
> > the
> > corresponding delays can't be 800-chips apart from each other(way  
> > too long).
> > Am I missing something here?
>
> You need to post your command line parameters for the transmitter  
> and receiver.
I am using the default parameters for both tx and rx.

My command lines are as follows:

Tx:  sudo ./usrp_sounder.py -t -f 2.44G -v -D
Rx: sudo ./usrp_sounder.py -t -f 2.44G -v -D -F output.dat

I use read_complex_binary.m to read the log file. The resulting  
channel impulse response looks like this:
Figure 1: http://www.ittc.ku.edu/~chenqi/cir1.jpg
Figure 2: http://www.ittc.ku.edu/~chenqi/cir2.jpg

Figure 1 is the first cycle of the recorded impulse response.
Figure 2 shows five chunks of CIRs the first and second group of CIRs  
are 800 chips apart.

Any clue on that?
> -Johnathan