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Re: [Discuss-gnuradio] Bandwidth switching per symbol

From: Matthias Wilhelm
Subject: Re: [Discuss-gnuradio] Bandwidth switching per symbol
Date: Wed, 27 Jul 2011 14:47:42 +0200


i think this would be hard on the python level, you would need to notify the 
python code after each symbol to make adjustments, which will lead to latency 
between symbols ...

(As I understand you want to keep the chipping sequences, but change the 
sampling rate used for each symbol. You can have the same effect by changing 
the interpolation between samples, keeping the rate constant, and oversampling 
small bandwidths. )
For this, I would suggest that you add a "per packet schedule" that specifies 
the bandwidth of each symbol, and hack the C code to follow the schedule, 
changing the interpolation between chips for each symbol. 
Something like send_802_15_4_pkt (packet, "1,2,8,2,4,1"), meaning 1MChips/s for 
the first symbol, 2MChips/s (the default) for the second, then 8MChips/s, etc. 
The benefit is that you can go on working on the packet level in python.
On the C side, you would need to run the flow graph at 16MSamples (to get 2 
samples per chip @ 8MChips/s, basically fast enough to support the largest 
bandwidth you want), and decide for each symbol the necessary interpolation to 
generate the specified bandwidth (e.g., 16 samples/chip @1MChips/s). 


Am 27.07.2011 um 13:31 schrieb address@hidden:

> Hi,
> I'm currently using the UCLA ZigBee Phy implementation by Thomas Schmid and I 
> need to
> change the Bandwidth of the used wireless channel on a per symbol basis.
> I managed to change it on a per packet basis, which can be done on the python 
> level
> (tunnel.py, usrp_transmit_path.py etc.). Well now, I need to do the same 
> thing, but on a
> per symbol basis, which (up to my knowledge) is not possible from the python 
> level...
> Does anyone have an idea how I could do that? (Changing the Bitrate of the 
> USRP after
> each symbol (e.g. after sending 32 modulated bits (actually chips)))
> I would be very happy for any help or suggestions!
> Thanks a lot!
> best regards,
> Bjorn
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> Discuss-gnuradio mailing list
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