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Re: [Discuss-gnuradio] Help : Where is the demodulation blocks implement

From: ton ph
Subject: Re: [Discuss-gnuradio] Help : Where is the demodulation blocks implemented in gnuradio [ GMSK,PSK etc].
Date: Fri, 8 Apr 2011 12:35:40 +0530

Thanks Marcus for your valuable information .
Now as per you have said that the usrp/gnuradio doesnt do any default demodulation , that means if i apply a demodulation technique to the captured file from usrp_rx_cfile.py , i will get the required output.For example if i apply GMSK demodulation to the captured file i ll get the properly formatted output as per the GSM protocol ... right.

On Thu, Apr 7, 2011 at 10:02 PM, Marcus D. Leech <address@hidden> wrote:
On 07/04/2011 10:34 AM, ton ph wrote:
Hi guys ,
 I Just want to confirm a thing regarding the demodulation of the digital dat in the gnuradio as the signals are received from the usrp. The doubt are,
 1. Where is the demodulation is implemented in the gnuradio .
 2. What demodulation is implemented by default in the urp_rx_cfile ...
please do help me someone in clearing my doubts .

Gnu Radio is a generic digital-signal-processing framework. Which includes *many* pre-built processing blocks, including demodulators
 and modulators, correlators, detectors, etc, etc.

There is no *default* demodulation scheme anywhere in the basic architecture, and usrp_rx_cfile is used to simply copy samples as they
 come off the USRP hardware into a file.

The USRP hardware doesn't do any demodulation--the signal you see delivered to the host PC is just filtered/decimated baseband
 samples as they come off the ADC, appropriately scaled for use inside Gnu Radio.  The USRP hardware doesn't know anything
 about modulation or demodulation, per se.  All of that is the responsibility of the host software.  Correspondingly, the transmit
 side of the USRP hardware doesn't *know* anything about modulation, either.  It is entirely up to the host software to provide
 appropriately-modulated samples for the hardware to dutifully turn into analog signals and then (usually) up-convert to the
 desired RF band of interest.  Generally, the host interface operates in "baseband" mode--the (complex) samples are centered at DC.


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