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

From: Qi Chen
Subject: Re: [Discuss-gnuradio] Sounding signal output power and spectrum
Date: Mon, 1 Dec 2008 16:04:33 -0600

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?

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